SS1 BIOLOGY THIRD TERM

MICRO-ORGANISMS AROUND US

CONCEPT OF CULTURING

MICRO-ORGANISMS IN ACTION

SEXUALLY TRANSMITTED INFECTIONS (STIS)

TOWARDS BETTER HEALTH

POPULATION

FUNCTIONING ECOSYSTEM

ENERGY TRANSFORMATION IN NATURE

Week: 1

Topic: Micro-Organisms Around Us

Introduction

Micro-organisms make up a large part of the planet’s living material and play a major role in maintaining the Earth’s ecosystem.

Micro-organisms or microbes are microscopic organisms that exist as unicellular, multicellular, or cell clusters. Micro-organisms are widespread in nature and are beneficial to life, but some can cause serious harm.

Micro-organisms found in Air and Water

Air: The air harbour micro-organisms like fungi (Rhizopus, Yeast, Mucor, Aspergillus and Penicillium spores); bacteria like Mycobaterium spp, micrococci, sarcina and finally viruses like Rhino virus (which causes common cold), pox virus, measle virus, etc.

Water: Bacteria like Salmonela, Mycobacteria, Escherichia Proteus, Pseudomonas are known to live in water. Others are phytoplanktons, blue-green algae, fungi like Aspergillus, Rhizopus, moulds, oscillatoria, spirogyra and ulothrix. The protozoa include Amoeba and Paramecium

Microorganisms are divided into five types: bacteria, protozoa, algae, fungi, and viruses. Each type has a characteristic cellular composition, morphology, mean of locomotion, and reproduction.

Microorganisms are beneficial in producing oxygen, decomposing organic material, providing nutrients for plants, and maintaining human health, but some can be pathogenic and cause diseases in plants and humans.

Bacteria         

All bacteria are unicellular prokaryotes, meaning they do not have a defined cellular nucleus. Their genetic information is in their nucleoid, – single, circular tightly- packed DNA molecule.

According to their shape, all bacteria are divided into four groups:

• spirilla (with a spiral body shape);
• cocci (with a spherical body shape);
• bacillus ( with a rod (stick) shaped body)
• vibrio (curved shape).

Some types of bacteria live on their own and others form colonies. Some bacteria are quite mobile and others ‘stay put’ for their whole life. Bacteria move using their cytoplasmic tail – flagella, or by secreting slimy substances that allow them to slide along surfaces.

The cell walls of most bacteria contain a polysaccharide called peptidoglycan. Differences in their cell wall structure is a major feature used in classifying these organisms. The staining abilities of bacteria are also based on their cell wall structure. According to the way they stain, bacteria can be classified as either Gram – positive or Gram – negative.

Based on their response to gaseous oxygen, all bacteria can be divided into the following groups:

• Aerobic – living in the presence of oxygen;
• Anaerobic – living without oxygen;
• Facultative anaerobes – can live in both environments.

According to the way they obtain energy, bacteria are classified as heterotrophs or autotrophs. Autotrophs make their own food by using the energy of sunlight or chemical reactions, in which case they are called chemoautotrophs. Heterotrophs obtain their energy by consuming other organisms. Bacteria that use decaying life forms as a source of energy are called saprophytes.

Protozoa

Protozoa is a subkingdom of unicellular, mostly aerobic, eukaryotic organisms. Sometimes they are also called protists. They are neither plants nor animals. They make up the largest group of organisms in the world in terms of numbers and biomass. Protozoa have been traditionally divided based on their mode of locomotion:

• Flagellates produce their own food and use their whip-like structure to propel forward, e.g. Euglena
• Ciliates have tiny hair that beat to produce movement, e.g. Paramecium
• Amoeboids have false feet or pseudopodia used for feeding and locomotion, e.g. Amoeba
• Sporozoans are non-motile e.g. Plasmodium

They also have different means of nutrition, which groups them as autotrophs or heterotrophs.

Some protozoans, like Euglena, have chloroplasts like plants and make their own food, which makes them autotrophs. Others, like amoeba, are heterotrophs. Protozoans can be free-living or parasitic, unicellular or colonial. Some parasitic protozoans can cause diseases in humans.

Because heterotrophic protozans consume bacteria, they play a very important role in controlling biomass. Biomass is the total weight of living organimsms in a given area.

Fungi

Fungi are saprophytic (feed on decaying organic matter) and parasitic organisms. Fungi include moulds, rusts, mildews, smuts, mushrooms and yeast. By breaking down dead organic material, they continue the cycle of nutrients through ecosystems. Some plants have a symbiotic relationship with fungi. Symbiosis is a mutually beneficial co-existence of dissimilar organisms. For example, there are mushrooms that live near tree roots and supply them with essential nutrients.

All fungi are made of eukaryotic cells. Fungi can be unicellular (single-celled) or multicellular (with cells arranged in filaments called hyphae) and their cell wall is composed of chitin. Yeasts are unicellular fungi. Masses of hyphae are called mycelia. Mycelia can be well structured, as in a mushroom, or tangled and unstructured, as in moulds. Some fungi can exist in the form of yeast and hyphae. These types of fungi are called dimorphic.

All fungi are heterotrophic, meaning that they obtain their energy and carbon compounds from organic nutrients. None of the fungi are photosynthetic. Some fungi are parasites and can cause diseases in humans, animals and plants. . Fungi reproduce by releasing spores. Some fungi are used in the food industry and pharmaceutics (antibiotic production).

Viruses

Although viruses are not considered living organisms, they are sometimes classified as microorganisms. Viruses are much smaller than common microbes. They are made of a DNA molecule covered with a protein shell called a capsid. Retroviruses are made of an RNA molecule covered with a capsid. Capsids can take many shapes. Viruses cannot reproduce outside the host cell, but they cannot be called parasites either. Scientists still argue today about whether viruses are true living forms because they are not cells and they cannot metabolise on their own.

Viruses can infest prokaryotic and eukaryotic cells, often causing diseases in organisms. A virus that infects bacteria is known as a bacteriophage.

Algae

Algae, also called cyanobacteria or blue-green algae, are unicellular or multicellular eukaryotes that obtain nourishment by photosynthesis. They live in water, damp soil, and rocks and produce oxygen and carbohydrates used by other organisms. It is believed that cyanobacteria are the origins of green land plants.

Test Questions

1. Microorganisms are divided into _____ types
   a) 2
   b) 5
   c) 3
   d) 4
2. They are made of a DNA molecule covered with a protein shell called a _____
   a) capsid
   b) capsule
   c) cocci
   d) spirilla
3. Fungi are ______ and parasitic organisms
   a) saprophytic
   b) symbiotic
   c) holophytic
   d) holozoic
4. All these are examples of protozoa except ____
   a) Flagellates 
   b) Ciliates have tiny hair that beat to produce movement, e.g. Paramecium
   c) Amoeboids 
   d) Virus
5. All bacteria are ______ prokaryotes
   a) multicellular
   b) bicellular
   c) unicellular
   d) a & c
6. One of the following is not a group of bacteria
   a) Aerobic 
   b) Propylactic
   c) Anaerobic 
   d) Facultative anaerobes 
7. One of the following is not a shape category of bacteria 
   a) spirilla 
   b) cocci 
   c) vibralto
   d) bacillus 
8. All fungi are heterotrophic. True or False
9. All fungi are photosynthetic. True or False
10. Protozoans can be free-living or parasitic, unicellular or ______
    a) colonial
    b) colony
    c) free
    d) grouped

Week: 2

Topic: Concept Of Culturing 

Culturing simply involves the techniques of growing micro-organisms in special media in the laboratory. It involves the making of sterile medium, inoculating, incubating and examining micro-organisms. By this means, micro-organism characteristics such as colour, pattern of growth and appearance can be seen. Culture of micro-organisms can be grown from water, air, animals, plants and various parts of human body.

Preparation of Culture Solution

• The culture solution called Agar is prepared under sterile conditions
• Then boil and pour it into sterile petri-dish
• Allow it to cool and set in the petri-dish
• A heat sterilizer may be used to kill micro-organisms in the petri-dish
• The material is then introduced into the agar medium and covered immediately
• Place the petri-dish in warm but dark compartment or an incubator
• Observe and record what you have seen for 2-3 days

Instruments Required for the Preparation of Culture Solution

Major instruments required for the preparation of culture solution are:

• Slides
• Cover slips
• Inoculating needles or loops
• Inoculating chamber if available

Precautions to be Taken During Preparation of Culture Solution

1. Wash hands with soap before and after the preparation of agar solution
2. Open petri-dish only slightly and cover at once
3. Close petri-dish firmly with adhesive tape
4. Sick person should not be permitted to take part in culturing experiments
5. Avoid talking, coughing, sneezing and touching of infected jelly
6. Unused agar should be sterilized by washing with antiseptic soap and disinfectant, e.g. 40% folmadehyde. Heat can also be used to sterilize
7. All instruments should also be sterilized before the beginning of culture solution preparation.

Identification of Micro-organisms

Micro-organisms can be identified in the air, pond water, river and stream by preparing a culture medium. The following procedures should be followed:

1. Five petri-dishes with culture medium labelled K, L, M, N and O respectively
2. Expose petri-dish K to air for about 10-15 minutes and then cover it.
3. Put in petri-dish L a few drops of pond water and cover it
4. Put in petri-dish M a few drops of river water and cover it
5. Put in petri-dish N a few drops of stream water and cover it
6. Allow petri-dish O to serve as control, i.e. do not introduce anything into it
7. Leave all the petri-dishes in the laboratory for 3-4 days
8. Observe all the petri-dishes for any development and note any difference in each of the petri-dishes
9. Record the characteristics (colour, pattern of growth, appearance) of colonies of micro-organisms in each petri-dish

Practice Questions

1. All these instruments are used for culturing except _____
   a) slides
   b) cover slips
   c) needles
   d) innoculating chamber
2. ______ simply involves the techniques of growing micro-organisms in special media in the laboratory.
   a) Culturing
   b) Culture
   c) Innocluation
   d) Separation
3. One of the following is not part of a culturing method
   a)  sterile medium
   b) inoculation
   c) incubation
   d) ejaculation
4. ______ is the name of the white transparent plate used to culture medium
   a) Petri dish
   b) Metric dish
   c) White dish
   d) Experimental dish
5. Micro-organisms can be identified in the air, pond water, river and stream by preparing a _____ medium
   a) cultural
   b) innoculating
   c) culture
   d) sterile

Week 3

Topic: Micro-Organisms in Action

Introduction

Growth of micro-organisms, like all living things, do increase in size and multiply in number of cells using either the culture medium provided or any suitable surface such as moist bread as source of food. Micro-organisms can also increase in mass. Such an increase in size, mass or number of cells is regarded as growth in micro-organisms.

If environmental conditions of growth such as food, adequate temperature and humidity are favourable, such an increase in mass, size and number of cells of the colony is an index of growth of micro-organisms.

Ways of Measuring Growth in Micro-organisms

There are two major ways of measuring growth in micro-organisms. These are:

First method: A bacterial sample is inoculated into a nutrient agar (a clear liquid culture medium). As the bacterial population increases, the clear liquid medium becomes cloudy and turbid. Progressive increase in turbidity indicates a related increase in the number of bacterial cells. This property is used to measure bacterial growth.

In the laboratory, turbidity can be measured with a spectrophotometer. This instrument measures the amount of light that can pass through a liquid medium.

Second method: In this method, small samples of bacteria are taken from the nutrient agar at regular interval of time. Each sample is diluted several times. Each diluted sample is innoculated on to a nutrient agar medium in a petri-dish and incubated. The number of colonies formed in each petri-dish is counted. As each colony is formed by the multiplication of a single bacterium, the number of colonies indicate the number of living bacterial cells in the diluted sample. From this, the actual number of bacteria in the original sample can be calculated.

Beneficial Effects of Micro-Organisms

Some micro-organisms especially bacteria and fungi are beneficial to man in three major ways: in nature, medicine and in industries

In Nature

1. Compost formation: Micro-organisms especially bacteria aid compost formation through the decay of dead organisms and humus
2. Nitrogen fixation: Certain bacteria (Rhizobium leguminosarium) aid nitrogen fixation into plants through the root nodules of leguminous plants.
3. Maintenance of soil fertility: Most saprophytic bacteria, due to their decomposition activities, release nutrients into the soil which aid its fertility through nitrogen cycle
4. Digestion of cellulose: Some bacteria living in the rumen of ruminant animals like cattle, sheep and goat help such animals to digest cellulose in the rumen
5. Decomposition: Micro-organisms, especially saprophytic bacteria also aid the decomposition of dead of dead plants and animals thereby releasing nutrients to the soil
6. Silage making: Some bacteria are also useful in silage making which involves the preservation of pasture crops for future use.
7. Sewage treatment: Bacteria are also involved in the decomposition of sewage into harmless substance

In Medicine

1. Manufacturing of drugs/ vaccines: Micro-organisms are used in medicine for the manufacturing of drugs, vaccines and antibiotic which help in curing many human diseases, e.g. penicillin (an antibiotic) is obtained from Penicilium notatun (a fungus) and streptomycin, another antibiotic, is obtained from a bacterium called Streptomyces griseus
2. Sources of vitamin B: Yeast and certain bacteria are rich sources of vitamin B complex.
3. Sources of enzymes: Certain yeast and bacteria are also rich sources of enzymes like amylase and invertase

In Industries

1. For baking: Yeast (fungus) is useful in baking industries as it causes dough to rise in bread and other allied food processing
2. Preparation of alcoholic drinks: Yeast is also useful in brewing industries as it is used for the fermentation of sugar to produce alcohol
3. Making of cheese / yoghurt: Certain bacteria are used in food processing such as cheese, vinegar and yoghurt
4. Retting of jute: Certain bacterial action are used in the retting of jute to obtain sack fibres from flax plants
5. Curing of tobacco: Bacteria are useful in the curing or ripening of tobacco leaves
6. Tanning of hides and skins: The action of bacteria is useful in the conversion of hides and skin to leather during the tanning process

Harmful Effects of Some Micro-Organisms

1. Cause of disease: Micro-organisms are responsible for various diseases in plants and animals
2. Spoilage of food: micro-organisms are generally known to cause food spoilage
3. Deterioration of materials: Micro-organisms are also responsible for the deterioration of materials like wood, cotton, paper, leather, etc.
4. Causes of death: Micro-organisms can also cause the death of plants and animals

Types of Disease-Causing Micro-organisms

Organisms that cause disease are called pathogens. They are also parasites, living off their host, which does not benefit as a result.
There are 4 types of microbes (micro-organisms) that cause disease;

• Viruses
• Bacteria
• Fungi
• Protozoa (also known as protoctista).

Virus: Viruses are inactive when outside of a living cell, but once their nucleic acid is inside they take over the cell’s activities. Usually they make many copies of themselves inside the cell, then break out of the cell and infect others. Viruses cannot be killed by antibiotics such as penicillin.
Examples of diseases caused by viruses: flu (influenza), common cold, measles, mumps, german measles (Rubella), smallpox, cowpox, chicken pox, HIV (can lead to AIDS), rabies

Bacteria: Not all bacteria cause disease; some are very useful “in nature”. When bacteria infect the body, they can reproduce quite fast. Often they produce chemicals called toxins which have the actual effect which causes an illness. Bacteria can usually be killed by antibiotics such as penicillin.
Examples of diseases caused by bacteria: cholera, tuberculosis (TB), septicaemia (“blood poisoning”), anthrax.

Fungi: Not all fungi cause disease; some are very useful “in nature”.
Examples of diseases caused by fungi: Athlete’s foot (not only caught by athletes, or confined to the foot!), ringworm (not a worm), thrush (not a bird)

Protozoa: Are generally single celled organisms with true nuclei and a cell membrane, so they are quite like our body cells.
Examples of diseases caused by protozoa/protoctista: Malaria, sleeping sickness, dysentery

Spread of Disease-Causing Micro-organisms

Micro-organisms can spread or transmit diseases through the following ways:

• Air, i.e. air-borne pathogens
• Water, I.e. water-borne pathogens
• Food, i.e. food-borne pathogens
• Animal vectors or carriers
• Personal or direct skin contact

Certain diseases known as contagious diseases can be controlled by direct contact with an infected person, e.g. leprosy, measles, tuberculosis and sexually transmitted disease (STD) such as gonorrhea, syphilis and AIDS.

Names of some diseases, causative micro-organisms, mode of transmission, host and major symptoms are stated in the table below

Food and Water-Borne Diseases

Diseases	Causative organisms	Mode of transmission	Host	Major symptoms
Infective	Virus hepatitis	Water	Man (female and male of all ages)	Swollen liver, fever, headache and jaundice
Typhoid	Bacteria (Salmonella typhi)	Food and water	Man (female and men of all ages	High temperature with diarrhoea, or constipation
Cholera	Bacterium (Vibro cholera)	Drinking water	Man (female and male of all ages)	Serious diarrhea with vomiting, high temperature and abdominal pain
Polio myelitis (infant paralysis)	Virus	Water	Children	High fever, headache, stiffness of limbs due to nervous disorder that result from attack on muscle nerves
Amoebic dysentery	Protozoan (Entamoeba histolytica)	Food and water	Man	Abdominal pain, heavy vomiting and diarrhoea
Bacillic dysentery	Bacterium (shigella dysenteriae)	Water and food	Man	Fever, abdominal pain and diarrhoea
Food poisoning	Bacteria (Salmonella spp.)	Infected food	Man	Headache, restlessless, abdominal pain and vomiting
Para-typhoid	Bacterium (Salmonella para-typhi)	Water and food	Man	High fever, constipation or diarrhea

Air-Borne Diseases

Diseases	Causative organism	Mode of transmission	Host	Major symptoms
Tuberculosis	Bacterium (Mycobacterium tuberculosis)	Airborne and food	Man and cow	Persistent dry cough and profuse sweating at night, high temperature, loss of weight and blood in sputum
Measles	Virus contact	Air and body	Man and children	High fever, skin rashes, headache, cold, cough and body pain
Pneumonia	Bacteria	Air	Man, pig, birds and cows	High fever, difficult breathing and cough
Meningitis (cerebrospinal fever)	Bacteria (Meningococcus)	Airborne	Children and young adults	High fever, headache, vomiting and stiffness of the neck
Small pox	Virus	Airborne	Man	High fever, skin rashes and small blister
Common cold	Virus	Airborne	Man	High fever, headache and runny nose
Influenza	Virus	Airborne	Man	High fever, headache, body pain and shivering
German measles	Virus	Airborne	Man	Rashes on the face and swollen glands on the neck
Whooping cough	Bacteria	Airborne	Man of all ages	Cold, high fever, cough and vomiting
Chicken pox	Virus	Airborne	Man of all age	Itchy skin rash

Diseases Spread by Vectors

A vector is an animal which transmits a disease-causing organism (pathogen) from the person suffering from the disease to another person. The table below shows the vectors, micro-organisms, and the diseases they transmit.

Disease	Causative organism	Vector/ mode of transmission	Host	Main symptoms
Malaria	Plasmodium spp (protozoan)	Female anopheles mosquito bite	Man	High fever associated with shivering and sweating
Sleeping sickness (Trypanosomiasis)	Trypanosomes (protozoan)	Tse-tse fly bite	Man	Regular and uncontrollable sleepiness, fever and headache, sluggishness and drownsiness
Plague	Rat flea	Bacterium	Man	Shivering, fever, cough and difficult breathing
Typhus fever	Rickettsia	Body louse	Man	High fever, severe pains in the muscle
Dengue fever	Virus	Female Aedes mosquito bite	Man and monkey	High fever, severe pains in the joints, back and head, nausea and vomiting
Yellow fever	Virus	Aedes mosquito bite	Man	High fever, headache and backache, temperature falls and virus enter the liver and kidneys, jaundice develops
River blindness (Onchocerciasis)	Protozoan	Blackfly	Man	Severe headache, high fever and gradual blindnesss

Diseases Spread Through Sexual Contact

Diseases which are transmitted by sexual contact are known as venereal diseases (VD) or sexually transmitted diseases (STD).

Some sexually transmitted diseases, causative organisms, mode of transmission, their hosts and symptoms are outlined in the table below:

Diseases	Causative organism	Mode of transmission	Host	Major symptoms
Gonorrhea	Bacterium (Neisseria gonorrhea)	Sexual intercourse	Man	Inflamed urethra, burning sensation during urination, and a thick, yellowish discharge in male. In female, redness around the urinary opening, vaginal discharge or swelling of the vulva. It may cause blindness to babies during pregnancy
Syphilis	Bacterium (Treponema pallidum)	Sexual intercourse	Man	A small painless sore or chancre appears on the penis or vulva. A mild fever, skin rashes, mouth ulcers and aching pains in the lymph node regions. It may lead to abortions, attack the brain and cause blindness, insanity or loss of control of movement
AIDS	Virus (Human Immuno virus (HIV))	Sexual intercourse, blood transfusion, injection needle	Infected person	High fever, loss of weight, chronic diarrhoea, skin rashes, wasting away of muscles and finally death
Staphylococcus	Bacterium	Sexual intercourse	Man	Itching around private parts, burning sensations around waist in male. In females, there are itching around private parts, burning sensation in waist and stomach, vaginal discharge, irregular menstruation and inability to get pregnant

Practice Questions

1. Staphylococcus can be transmitted by one of the following ways _______
   a) blood transfusion
   b) sexual intercourse
   c) mating
   d) injection
2. Microorganisms are harmful but they are also beneficial to man. True or False
3. The causative organism for syphilis is _______ 
   a) bacterium
   b) virus
   c) fungi
   d) animal
4. Diseases which are transmitted by sexual contact are known as _____ diseases
   a) sexual 
   b) venereal
   c) blood 
   d) a & b
5. What is the meaning of AIDS?
   a) Acquired Immune Deficient Syndrome
   b) Acquire Immunization Deficiencey Syndrome
   c) Acquired Immune Deficiency Symptom
   d) Acquired Immune Deficiency Syndrome
6. A _______ is an animal which transmits a disease-causing organism  from the person suffering from the disease to another person
   a) Scalar
   b) Predator
   c) Vector
   d) Pathogen
7. ________ is the name of the vector that transmitts Malaria
   a) Plasmodium spp
   b) Male Aedes Mosquito
   c) Female anopheles mosquito
   d) Protozoan
8. Micro-organisms can spread or transmit diseases through the following ways except
   a) air
   b) water
   c) direct contact 
   d) body louse
9. All these are airborne diseases except _____
   a) measles
   b) sleeping sickness
   c) tuberculosis
   d) pneumonia
10. All these diseases are  transmitted by vectors except _____
    a) Syphilis
    b) Yellow fever
    c) Malaria
    d) River blindness

Week 4

Topic: Sexually Transmitted Infections (STIs)

Introduction

Sexually transmitted infections (STIs) are infections that are spread primarily through person-to-person sexual contact. There are more than 30 different sexually transmissible bacteria, viruses and parasites.

The most common conditions they cause are gonorrhoea, chlamydial infection, syphilis, trichomoniasis, chancroid, genital herpes, genital warts, human immunodeficiency virus (HIV) infection and hepatitis B infection.

Several, in particular HIV and syphilis, can also be transmitted from mother to child during pregnancy and childbirth, and through blood products and tissue transfer.

What is a sexually transmitted infection (STI)?

It is an infection passed from person to person through intimate sexual contact. STIs are also called sexually transmitted diseases, or STDs.

Major Sources of STI Transmissions

You can get an STI by having intimate sexual contact with someone who already has the infection. You can’t tell if a person is infected because many STIs have no symptoms. But STIs can still be passed from person to person even if there are no symptoms. STIs are spread during vaginal, anal, or oral sex or during genital touching. So it’s possible to get some STIs without having intercourse. Not all STIs are spread the same way.

Signs and Symptoms of STI

Many STIs have only mild or no symptoms at all. When symptoms do develop, they often are mistaken for something else, such as urinary tract infection or yeast infection. This is why screening for STIs is so important. The STIs listed here are among the most common or harmful to women.

Symptoms of sexually transmitted infections

STI	Symptoms
Bacterial vaginosis (BV)	Most women have no symptoms. Women with symptoms may have: Vaginal itching Pain when urinating Discharge with a fishy odour
Chlamydia	Most women have no symptoms. Women with symptoms may have: Abnormal vaginal discharge Burning when urinating Bleeding between periods Infections that are not treated, even if there are no symptoms, can lead to: Lower abdominal pain Low back pain Nausea Fever Pain during sex
Genital herpes	Some people may have no symptoms. During an “outbreak,” the symptoms are clear: Small red bumps, blisters, or open sores where the virus entered the body, such as on the penis, vagina, or mouth Vaginal discharge Fever Headache Muscle aches Pain when urinating Itching, burning, or swollen glands in genital area Pain in legs, buttocks, or genital area Symptoms may go away and then come back. Sores heal after 2 to 4 weeks.
Gonorrhea	Symptoms are often mild, but most women have no symptoms. If symptoms are present, they most often appear within 10 days of becoming infected. Symptoms are: Pain or burning when urinating Yellowish and sometimes bloody vaginal discharge Bleeding between periods Pain during sex Heavy bleeding during periods Infection that occurs in the throat, eye, or anus also might have symptoms in these parts of the body.
Hepatitis B	Some women have no symptoms. Women with symptoms may have: Low-grade fever Headache and muscle aches Tiredness Loss of appetite Upset stomach or vomiting Diarrhea Dark-colored urine and pale bowel movements Stomach pain Skin and whites of eyes turning yellow
HIV/AIDS	Some women may have no symptoms for 10 years or more. About half of people with HIV get flu-like symptoms about 3 to 6 weeks after becoming infected. Symptoms people can have for months or even years before the onset of AIDS include: Fevers and night sweats Feeling very tired Quick weight loss Headache Enlarged lymph nodes Diarrhea, vomiting, and upset stomach Mouth, genital, or anal sores Dry cough Rash or flaky skin Short-term memory loss Women also might have these signs of HIV: Vaginal yeast infections and other vaginal infections, including STIs Pelvic inflammatory disease (PID) that does not get better with treatment Menstrual cycle changes
Human papillomavirus (HPV)	Some women have no symptoms. Women with symptoms may have: Visible warts in the genital area, including the thighs. Warts can be raised or flat, alone or in groups, small or large, and sometimes they are cauliflower-shaped. Growths on the cervix and vagina that are often invisible.
Pubic lice (sometimes called “crabs”)	Symptoms include: Itching in the genital area Finding lice or lice eggs
Syphilis	Syphilis progresses in stages. Symptoms of the primary stage are: A single, painless sore appearing 10 to 90 days after infection. It can appear in the genital area, mouth, or other parts of the body. The sore goes away on its own. If the infection is not treated, it moves to the secondary stage. This stage starts 3 to 6 weeks after the sore appears. Symptoms of the secondary stage are: Skin rash with rough, red or reddish-brown spots on the hands and feet that usually does not itch and clears on its own Fever Sore throat and swollen glands Patchy hair loss Headaches and muscle aches Weight loss Tiredness In the latent stage, symptoms go away, but can come back. Without treatment, the infection may or may not move to the late stage. In the late stage, symptoms are related to damage to internal organs, such as the brain, nerves, eyes, heart, blood vessels, liver, bones, and joints. Some people may die.
Trichomoniasis (sometimes called “trich”)	Many women do not have symptoms. Symptoms usually appear 5 to 28 days after exposure and can include: Yellow, green, or gray vaginal discharge (often foamy) with a strong odor Discomfort during sex and when urinating Itching or discomfort in the genital area Lower abdominal pain (rarely)

Testing for STIs

There is no one test for all STIs. Ask your doctor about getting tested for STIs. She or he can tell you what test(s) you might need and how it is done. Testing for STIs is also called STI screening. Testing (or screening) for STIs can involve:

• Pelvic and physical exam — Your doctor can look for signs of infection, such as warts, rashes, discharge.
• Blood sample
• Urine sample
• Fluid or tissue sample —  A swab is used to collect a sample that can be looked at under a microscope or sent to a lab for testing.

Treatment of STIs

The treatment depends on the type of STI. For some STIs, treatment may involve taking medicine or getting a shot. For other STIs that can’t be cured, like herpes, treatment can help to relieve the symptoms.

Prevention and control of STI

You can lower your risk of getting an STI with the following steps. The steps work best when used together. No single strategy can protect you from every single type of STI.

• Don’t have sex: The surest way to keep from getting any STI is to practice abstinence. This means not having vaginal, oral, or anal sex. Keep in mind that some STIs, like genital herpes, can be spread without having intercourse.
• Be faithful: Having a sexual relationship with one partner who has been tested for STIs and is not infected is another way to lower your risk of getting infected. Be faithful to each other. This means you only have sex with each other and no one else.
• Use condoms correctly every time you have sex: Use condoms for all types of sexual contact, even if intercourse does not take place. Use condoms from the very start to the very end of each sex act, and with every sex partner. A male latex condom offers the best protection.
• Know that some methods of birth control, like birth control pills, shots, implants, or diaphragms, will not protect you from STIs. If you use one of these methods, be sure to also use a condom correctly every time you have sex.
• Talk with your sex partner(s) about STIs and using condoms before having sex: It’s up to you to set the ground rules and to make sure you are protected.
• Talk frankly with your doctor and your sex partner(s) about any STIs you or your partner has or has had. Talk about symptoms, such as sores or discharge. Try not to be embarrassed. Your doctor is there to help you with any and all health problems. Also, being open with your doctor and partner will help you protect your health and the health of others.
• Have a yearly pelvic exam. Ask your doctor if you should be tested for STIs and how often you should be retested. Testing for many STIs is simple and often can be done during your checkup. The sooner an STI is found, the easier it is to treat.
• Avoid using drugs or drinking too much alcohol. These activities may lead to risky sexual behavior, such as not wearing a condom.

HIV and AIDS

The Human Immunodeficiency Virus (HIV) is a retrovirus that infects cells of the immune system, destroying or impairing their function. In other words, HIV is a virus that weakens the body’s immune system, which is the body’s defense system. As the infection progresses, the immune system becomes weaker, and the person becomes more susceptible to infections.

The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS). It can take 10-15 years for an HIV-infected person to develop AIDS; however, antiretroviral drugs can slow down the process even further.

HIV is transmitted through unprotected sexual intercourse (anal or vaginal), transfusion of contaminated blood, sharing of contaminated needles, and between a mother and her infant during pregnancy, childbirth and breastfeeding.

Modes of HIV Transmissions

HIV is spread through some of the body’s fluids. HIV is in:
• Blood
• Semen
• Vaginal fluids
• Breast milk
• Some body fluids that may be handled by health care workers (fluids surrounding the brain and spinal cord, bone joints, and around an unborn baby)

HIV may be passed from one person to another by:
1. More common

• Having sex (vaginal, anal, or oral) with a person who has HIV
• Sharing needles with someone who has HIV, such as when using drugs
• Pregnancy, labour, birth, or breastfeeding if a mother has HIV

2. Less common

• Blood transfusion from an HIV positive blood donor, which is very unlikely today because blood banks test donated blood for HIV
• Eating food that has been pre-chewed by an HIV-infected person. The blood in a caregiver’s mouth can mix with food while chewing. This is rare and has only been noted among infants whose HIV positive caregiver gave them pre-chewed food.
• Using a dirty tattooing needle (if it was used before on someone with HIV). Make sure the needle is new.
• Sharing a toothbrush or razor with someone who has HIV

HIV is not spread through:

• Kissing (there is a small chance of getting HIV from open-mouthed or “French” kissing except there’s contact with blood)
• Touching, hugging, or handshakes
• Sharing food or drinks
• Sharing food utensils, towels and bedding, telephones, or toilet seats
• Donating blood
• Working with or being around someone with HIV
• Biting insects, such as mosquitoes
• Swimming pools or drinking fountains
• Playing sports

The Science behind HIV

HIV attacks and destroys the immune system’s infection-fighting cells, called CD4 cells. They also are called CD4 positive T cells. HIV gets into these cells, makes copies of itself, and kills the healthy cells. As a person loses CD4 cells, the immune system weakens, making it harder for the body to fight infections and cancer. There are many different strains (types) of HIV. Most people have the HIV-1 strain. But, a person can be infected with more than one strain at a time.

HIV turns to AIDS when the immune system gets very weak. One way to know if a person has AIDS is if her CD4 cell count (the number of CD4 cells in a sample of blood) is very low (less than 200). Another way is if she has certain infections or cancers. Moving from HIV to AIDS is different for everyone. Some people live for 10 years or more with HIV without developing AIDS. Others get AIDS faster.

Signs and Symptoms of HIV/AIDS

Many people have no symptoms when they first get HIV. Some have no symptoms for years. It varies from person to person. But some people get a flu-like illness within a month or two after first getting HIV. It’s important to remember that HIV is active inside your body, even when you don’t have symptoms. As HIV spreads in your body, you’ll start to feel sick. For many people, the first symptom they notice is large lymph nodes (swollen glands) that last for more than three months. Symptoms of HIV include:
• Being very tired (fatigue)
• Quick weight loss
• Fevers and night sweats
• Headache
• Diarrhea, vomiting, and nausea
• Mouth, genital, or anal sores
• Dry cough
• Rash or flaky skin
• Short-term memory loss

Test for HIV

You cannot rely on symptoms to know whether you have HIV. If you have symptoms, they may be caused by something else. And many people infected with HIV have no symptoms for many years. The only way to know whether you have HIV is to get a test.

Prevention of Transmission of HIV

HIV prevention refers to practices done to prevent the spread of HIV/AIDS. HIV prevention practices may be done by individuals to protect their own health and the health of those in their community, or may be instituted by governments or other organizations as public health policies.

Anybody can get HIV, but you can take steps to protect yourself from HIV infection.

• Don’t have sex: Abstinence (not having sex of any kind) is the surest way to avoid HIV infection through sexual contact.
• If you must have sex, get tested and know your partner’s HIV status: Talk to your partner about HIV testing and get tested before you have sex.
• Be faithful to your partner: If you and your partner are both HIV negative and have sex only with each other, you are not at risk of HIV infection through sexual contact.
• Use condoms: Use a condom every time you have vaginal, anal, or oral sex.
• Limit your number of sexual partners: If you have more than one sexual partner, get tested for HIV regularly. Get tested and treated for sexually transmitted infections (STIs), and insist that your partners do, too. Having an STI can increase your risk of becoming infected with HIV.
• Don’t inject drugs: But if you do, use only clean needles and equipment and don’t share your equipment with others.

Some HIV medicines used to prevent HIV infection

In some situations HIV medicines are used to reduce the risk of HIV infection

Pre-exposure prophylaxis (PrEP) – PrEP is an HIV prevention method that involves taking an HIV medicine every day. PrEP is intended for people who don’t have HIV but who are at high risk of sexually transmitted HIV infection. PrEP should always be combined with other prevention methods, including condom use.

Post-exposure prophylaxis (PEP) – PEP involves taking HIV medicines as soon as possible after exposure to HIV to reduce the risk of HIV infection. For example, a health care worker exposed to HIV in the workplace may require PEP.

Prevention of mother-to-child transmission of HIV – HIV-infected women take HIV medicines during pregnancy and childbirth to reduce the risk of mother-to-child transmission of HIV. To further reduce the risk, their newborn babies also receive HIV medicine for six weeks after birth. In the United States, women with HIV are counseled not to breastfeed their babies to prevent mother-to-child transmission of HIV in breast milk.

Management of HIV (Use of Anti-Retro Viral Drugs)

Once HIV infection is diagnosed, a person has a life-long condition which will go through several stages and has many consequences. The disease needs to be managed by people with HIV themselves as well as their healthcare providers.

An overview of the needs of a person with HIV infection (not necessarily in order of priority) is as follows:
1. Education / information – learning how to best take care of yourself, staying informed about new treatments or approaches
2. Maintaining general health – self care, nutrition
3. Financial planning – medical aid, future provision for self and dependents
4. Monitoring HIV disease – regular medical check-ups, monitoring tests
5. Preventing opportunistic disease – avoiding exposure, alertness to early signs of disease, prophylactic medication
6. Psychological health – informing others, dealing with stigma, spiritual support, managing anxiety and depression
7. Sexual and reproductive – safer sex for partners and self, whether to have a baby, avoiding infection of the baby
8. Antiretroviral treatment: Standard antiretroviral therapy (ART) consists of the combination of at least three antiretroviral (ARV) drugs to maximally suppress the HIV virus and stop the progression of HIV disease. Huge reductions have been seen in rates of death and suffering when use is made of a potent ARV regimen, particularly in early stages of the disease.
9. Terminal care – care and treatment during the final stages of the disease.

Agencies/Organisation for HIV/AIDS Control

The non-governmental organisations listed below help in the control of HIV/AIDS around the world.

1. IAS (International AIDS Society)

2. UNAIDS (Joint United Nations Programme on HIV/AIDS)

3. WHO (World Health Organization)

Others include:

4. National Agency for the Control of AIDS (NACA)
5. Society for Family Health (SFH)

Myths about HIV/AIDS

1. I can get HIV by being around people who are HIV-positive: The evidence shows that HIV is not spread through touch, tears, sweat, or saliva.

You cannot catch HIV by:
• Breathing the same air as someone who is HIV-positive
• Touching a toilet seat or doorknob handle after an HIV-positive person
• Drinking from a water fountain
• Hugging, kissing, or shaking hands with someone who is HIV-positive
• Sharing eating utensils with an HIV-positive person
• Using exercise equipment at a gym

2. I don’t need to worry about becoming HIV positive, new drugs will keep me well: Yes, antiretroviral drugs are improving and extending the lives of many people who are HIV-positive. However, many of these drugs have serious side effects. None yet provides a cure. Also, drug-resistant strains of HIV make treatment an increasing challenge.

3. I can get HIV from mosquitoes: Because HIV is spread through blood, people have worried that biting or bloodsucking insects might spread HIV. Several studies, however, show no evidence to support this even in areas with lots of mosquitoes and cases of HIV. When insects bite, they do not inject the blood of the person or animal they have last bitten. Also, HIV lives for only a short time inside an insect.

4. I’m HIV-positive, my life is over: In the early years of the disease epidemic, the death rate from AIDS was extremely high. But today, antiretroviral drugs allow HIV-positive people — and even those with AIDS — to live much longer, normal, and productive lives.

5. I’m straight and don’t use HIV drugs, I won’t become HIV-positive: Most men do become HIV-positive through sexual contact with other men or through injection drug use. However, about 16% of men and 78% of women become HIV-positive through heterosexual contact.

6. If I’m receiving treatment, I can’t spread the HIV virus: When HIV treatments work well, they can reduce the amount of virus in your blood to a level so low that it doesn’t show up in blood tests. Research shows, however, that the virus is still “hiding” in other areas of the body. It is still essential to practice safe sex so you won’t make someone else become HIV-positive.

       ASSESSMENT.

1. What is a Sexually Transmitted Infection?
2. List the examples of STI you know.
3. What are the major sources of STI?
4. What are the signs and symptoms of STI?

Week 5

Topic: Towards Better Health

Introduction

Pathogenic or harmful micro-organisms have the ability to wipe out the whole of humanity directly or indirectly. They therefore must be controlled through some measures in order to stay healthy.

Control of Harmful Micro-Organisms

1. The use of drugs like antibodies performs key role in checking the spread of microorganisms
2. Dehydration tends to inactivate the micro-organisms since most of them require water for metabolism
3. The use of high salinity or salt especially in preservation of food
4. Application of high temperature destroys pathogens. This is used in sterilization of materials e.g. in hospitals
5. Antiseptic application involves the use of low concentration of chemicals like phenol (carbonic acid). They prevent or inhibit the growth of micro-organisms. At times they kill them
6. Disinfectants are high concentration of phenol (carbolic acid). They kill micro-organisms outright.
7. The use of low temperature (freezing) also kills or inactivates some micro-organisms
8. The use of irradiation controls the growth of micro-organisms
9. Immunization: Vaccination or inoculation of anti-disease sera protects the individual from contacting the disease. This is because antibodies or anti-toxins are produced by the body

VECTORS

A vector is an organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another.

Species of mosquito, for example, serve as vectors for the deadly disease Malaria.

Note:

• A pathogen is a micro-organism that has the potential to cause disease.
• An infection is the invasion and multiplication of pathogenic microbes in an individual or population.
• Disease is when the infection causes damage to the individual’s vital functions or systems.

Common Vectors and Diseases They Transmit

Vector	Organisms responsible	Disease
Female anopheles mosquito	Plasmodium parasites	Malaria
Housefly	Vibro cholerae	Cholera
Tsetse fly (Glossina spp)	Trypanosome spp	Sleeping sickness (Trypanosomiasis)
Aedes mosquitoes	Virus (arbovirus)	Yellow fever
Black fly (Simulium damnosum)	Round worm (Onchocera)	River blindness (Onchocerciasis)
Water snail	Flatworm (Schistosoma)	Bilharziasis or Schistosomiasis

WAYS OF CONTROLLING VECTORS

Housefly

1. Adults are killed using insecticides
2. Preventing breeding grounds
3. Covering our foods from flies
4. The surrounding pit-toilet must be covered and kept clean
5. Continuous spraying of insecticides even after the initial spray
6. The general environment must be kept clean

Mosquitoes

1. Breeding grounds must be destroyed
2. Surrounding bushes must be cut
3. Physical destruction of mosquitoes with brooms
4. Chemical destruction using insecticides e.g. dieldrin
5. Spraying of oil on water to frustrate their ability to breed due to lack of oxygen
6. Destroying or burying empty cans and bottles
7. The use of insect repellant on the body
8. The use of biological controls such as introducing tadpoles, bacilli bacteria, which are known to feed on the larvae
9. Making provision for nets in our doors and windows

Blackflies

1. The vectors are very difficult to fight. The only way possible is the destruction of the breeding sites
2. Other methods include the use of drugs such as suramin and diethyl carbamazine (with serious side effects)

Water snails

1. The use of molluscicides affects breeding of infective larvae
2. Good hygiene and sanitation in order to maintain clean environment
3. Outright treatment of infected people to stop the spread
4. Disrupting the food chain by killing some water weeds eaten by snails

Maintenance of Good Health

Introduction

For a person to remain healthy, he must maintain cleanliness around his environment. He must eat good food, drink clean and pure water, wear clean clothes and keep his environment tidy. This method will help a lot in preventing disease outbreak. However, keeping the environment clean is not the sole responsibility of single individuals. It involves the combined effort of the household, communities, nations and the world as a whole.

Ways of Maintaining Good health in a Community 

Effective public health administration in a community can be achieved through the following ways:

Refuse disposal: Refuse are solid waste materials discharged through human activities from homes and industries into the environment. Reckless refuse dump around dwelling places creates bad odour, provides breeding grounds for insects and rodents that spread diseases

Refuse disposal can be done through the following ways:

1. Provision of dust bins in strategic locations
2. Burning refuse in incinerators
3. Dumping them in isolated areas far from human habitation
4. Burying refuse in a sanitary landfill

Sewage disposal: Sewage are waste water materials discharged from laundries, kitchens, toilets, bathrooms, e.g. urines and faeces

Sewage disposal can be done through:

1. The use of pit toilets where faeces and urine are passed into deep pits
2. The use of septic tanks where water is used to flush faeces and urine into a big tank dug in the ground
3. Community treatment process where sewage from various homes are collected and treated before being discharged into oceans or rivers

Protection of Water: In view of numerous diseases which man can contact because of drinking unclean water, water should be protected through the following ways:

1. Addition of alum to water
2. Boiling of water before drinking it
3. Filteration of water on cooling
4. Addition of chlorine to kill microscopic germs
5. Storage of water in clean containers

Note: All these should be done before water is passed through pipes into houses and other places where it is required.

Protection of food: It is true that diseases can be contracted through food. Therefore, both raw and cooked food should be properly protected. The following methods of food protection are recommended:

1. Keep food in refrigerators or deep freezers
2. Boil or cook raw food properly before eating
3. There should be inspection of food meant for public consumption
4. Washing of hands before and after eating of food
5. Food can also be preserved through canning
6. Keep the environment where the food is prepared clean
7. Avoid exposure of food to flies and other micro-organisms

Control of diseases: Individuals can control diseases by living in clean environment. Therefore, they can prevent diseases through the following ways:

1. Daily sweeping of the surroundings
2. Eating of good food and balanced diet
3. Taking of bath regularly
4. Wearing of clean and neat dresses
5. Living in well-ventilated houses
6. Cleaning of latrines and urinals with disinfectants regularly
7. Cleaning of teeth regularly with toothbrush and paste
8. Doing exercises regularly
9. Treatment of any injury immediately or reporting same to the nearest hospital for treatment
10. Taking children through the various immunisations as prescribed by doctors
11. Taking no drugs except those prescribed by doctors

HEALTH ORGANIZATIONS

Health organizations are corporate (local and international) bodies concerned with the maintenance of good health of the people. International health organizations include:

• World Health Organisation (WHO)
• United Nations Children’s Education Fund (UNICEF)
• International Red Cross Society

The major local health organisation in Nigeria is the Nigerian Medical Association (NMA)

Roles of Health Organizations

World Health Organization (WHO)

This is a specialised division of the United Nation Organisation (UNO) established in 1948 with headquarters in Geneva, Switzerland. Its major aim is to improve the health of the people in all the countries of the world.

The main functions of the organisation are:

1. It promotes measures for the control of the world’s major diseases through vaccination programmes and use of antibiotics
2. It co-ordinates research programmes in all fields of health and makes the results known to all member-nations
3. It provides advice and help on health matters to member-nations on request, e.g. provision of medical experts, setting up health centres, etc.
4. It publishes medical journals
5. It helps to set up international quarantine regulations
6. It helps to provide drugs and vaccines in case of emergency
7. It provides warning signals in the event of an outbreak of epidemic diseases
8. It assists national health organisations in the control of diseases and vectors of diseases
9. It helps in maternal and child health care
10. It helps to set and recommend safe standard for drugs

United Nations Children’s Education Fund (UNICEF)

The UNICEF, another special agency of the United Nations Organisation was set up to improve the health and welfare of the children all over the world. Specific functions of UNICEF are:

1. To provide for the emergency needs of children in devastated areas
2. To improve the nutrition of under-nourished children
3. To feed destitute children
4. To supply vaccines or equipment to prevent or control diseases that specifically affect children such as whooping cough, diphtheria, poliomyelitis and tuberculosis
5. To provide children’s clothings and other needs
6. To assist in the improvement of the mothers and their children by providing training programmes and necessary equipment, e.g. provision of Oral Rehydration Therapy (ORT) to control diarrhoea in children

International Red Cross Society

The international Red Cross Society plays important roles in two major ways:

In time of war

1. They take proper care of the injured
2. They provided emergency and to those in distress
3. They are involved in the negotiation of the exchange of prisoners of wars between countries
4. They provide transport for the evacuation of refugees
5. They also provide welfare for the prisoners of war

In time of peace

1. They provide the general first-aid to patient
2. They assist in preventing accidents
3. They assist in the training of nursing aides
4. Red cross society maintains maternal and child welfare clinics
5. They provide help to victims of natural disasters such as earthquakes, floods, fire, etc.

Nigerian Medical Association (NMA)

The Nigerian Medical Association (NMA) is a national body concerned with the maintenance of good health within Nigeria. The main functions of NMA include:

1. Advising the government on how to improve the health status of the people
2. Alerting the nation where there is an outbreak of a disease
3. Carrying out research into ways of preventing and controlling diseases
4. Monitoring the recruitment of well trained doctors in hospitals
5. Assisting in the training of medical and paramedical staff needed in health care delivery.

Test Questions

1. A _____ is an organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another.
   a) Pathogen
   b) Vector
   c) Parasite
   d) Predator
2. Diseases can be controlled in the following ways except
   a) By treating injuries late
   b) By cleaning latrines and urinals with disinfectants
   c)  By wearing of clean and neat dresses
   d)  By living in well-ventilated houses
3. Female anopheles is to Malaria: Tsetse fly is to ____
   a) Sleeping sickness
   b) Night Blindness
   c) Cholera
   d) River Blindness
4. _______ is a way of maintaining good health
   a) Littering the street with dirts
   b) Improper sewage disposal
   c) Protection of food
   d) Pollution of water
5. Vibro cholerae is responsible for one of the following diseases
   a) Typhoid
   b) Malaria
   c) Bilharzia
   d) Cholera
6. ________ is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine.
   a) Innoculation
   b) Immunization
   c) Protection
   d) Vaccinate
7. ______ is not a way of cleaning or purifiying water
   a) Filteration of water
   b) Addition of Chlorine
   c) Addition of Acid
   d) Addition of Alum
8. List 4 ways with which food can be protected.

Week: 6

Topic: Population Studies

Introduction

Population is defined as the total number of organisms of the same species living together in a given area at a particular time. In an ecosystem, the community is made up of many populations of different species.

In population studies of a habitat, the following are usually studied:

• Types of organisms: This involves the listing of the various types of populations that are found in the particular habitat. It helps to determine the relationships that exist between the various organisms (plants and animals) in a habitat.
• Dominance: Dominance refers to those species that exert a greater influence or a major controlling effect on the other members of the community. The relative importance of a species in the community is expressed by dominance.

Dominance could be expressed in terms of:

o   Their number

o   Occupation of largest portion of space

o   Possession of the highest biomass and

o   The largest contribution to the energy flow in the habit. For a species to be dominant in a habitat, it should possess some of these attributes over other species.

Population Characteristics

These characteristics include:

• Population size: This refers to the total number of the species of the same kind in a given area or habitat. A large population stands a better chance of surviving dangerous and unfavourable conditions such as fire, diseases etc while a small population can easily be wiped out.
• Population density: Population density is defined as the number of individual organisms per unit area or volume of the habitat.

Mathematically, Population density = total population or population size / Area of habitat

Population density can be used to estimate the total number of individuals of a population or population size. Mathematically, population size = population density x area of habitat.

• Population frequency: This refers to the number of times an organism occurs within a given area a habitat.
• Percentage cover: This refers to the area or space covered or occupied by a given species in its habitat and it is expressed in percentage.
• Population growth rate: This refers to the net result of the influence of natality (birth rate) and mortality (death rate) of organisms in a giver habitat.

Factors Affecting Population

Factors which may affect the population of organisms in a given habitat include:

1. Natality (birth rate): This refers to the rate of given birth to new organisms. This generally (be it plants or animals) leads to increase in population.
2. Mortality (death rate): This refers to the rates at which organisms die in a habitat. Mortality generally leads to a decrease in population.
3. Immigration (dispersal): This is the movement of organisms from different habitats into a new habitat. This tends to increase the population of this new area.
4. Emigration: This is the movement of organisms out of a habitat due to either scarcity of food or unfavourable conditions or for breeding purposes. This, however, reduces the population of a habitat.
5. Availability of food: The availability of food in a given habitat tends to increase the population of that habitat through rapid rate of reproduction and other organisms coming into feed.
6. Seasonal Climatic Changes: Unfavourable climatic changes may result in the decrease of population since most organisms may die or migrate out of the habitat while the reverse is the case when the conditions are favourable.
7. Breeding periods: Most organisms move out of a habitat during the breeding period or season, thereby reducing the population decreases during the breeding season in fish, toad, termite etc.
8. Natural Disasters: Natural disasters like fire, drought, floods, earthquakes etc may lead to a decrease in population as many organisms may die or move out of that habitat to a new area.

Method of Population Study

1. Population Studies by Sampling Method

Population studies can easily be carried out in a habitat especially in terrestrial habitat by sampling method, making use of an instrument called the quadrat. A quadrat is made of a square or rectangular wire, plastic, wooden or metal frame with predetermined area. For example, the area of a quadrat may be 1.5m².

How to Conduct Population Studies

The population size or total population and population density of a particular species in a terrestrial habitat can be estimated by the following procedure:

1. Choose and locate the sample plot
2. Then identify the species in the plot
3. Measure the area with a measuring tape to know the area of the habitat
4. Throw or toss the quadrat randomly at intervals for up to 10 or above times
5. After each throw or toss, the number of species within the area of quadrat is recorded
6. The density of species is calculated by dividing the average number of times the species occurs within the quadrat by the area of the quadrat.

The calculation can be worked out this way:

Frequency of species = X

Number of toss = Y/10

Average number of species per quadrat = X = Z

Example: Estimate the population density and population size of specific grasses using the quadrat.

Solution:

Total area of habitat = 1.5m²

Frequency of the organisms (grasses), that is, the total number of times an organisms occurs in all the quadrats thrown in the habitat. Assume 400 times.

Number of tosses = 50

Average number of organisms per quadrat tossed = 400/50 = 8

Area of quadrat = 1.6m²

Density of organisms = 8 / 1.6 = 5 grasses per m²

Population size = Density x Area of habitat = 5/m² x 16m² = 80

The population size of grasses in the habitat = 80 grass plants.

Estimation of Population using the transect Method: The tape should stretch with marking at intervals. The plants within the various intervals are recorded. This procedure is repeated a number of times until an accurate estimate of the number and types of plants in the habitat are obtained.

Capture mark recapture method

Censuring wild animal population is fraught with many difficulties of sampling errors and statistical bias. Occasionally, direct counts are possible, as in aerial birds or sea bird colonies, but for most animals this is impossible and various kinds of sampling methods must be employed. Most animals are not readily visible because of their behavior and habitat, or because they exist in such abundance or scarcity that they cannot be readily counted. It therefore becomes necessary to estimate numbers through programmes of capture-mark recapture.

The ratio of marked to unmarked animals in subsequent trapping runs provides a population estimate known as the Lincoln index. This is mathematically expresses as follows:

P / M₁  = T₂ / M₂

Where:

P = Unknown population

M₁ = Total number of individuals marked in the first capture period

T₂ = Total number of individuals captured in the second period

M₂ = Total number of those in the second capture period, which were previously marked.

However, the validity of this method involves the assumption that the:

1.     Marked animals mix randomly in the population
2.     Probability of recapture is the same as for each individual

iii.     The system must be a closed one, i.e., there is no immigration or emigration, death or birth of the animal under investigation between the periods of sampling.

Ecological Factors

Ecological factors are those factors in the environment which can influence living organisms or cause changes in any habitat, be it aquatic or terrestrial habitat.

Ecological factors are grouped into two categories Biotic and Abiotic factors.

Biotic Factors

The biotic factors are made up of the effects of other plants and animals on a given organisms.

Examples of biotic factor are:

1. Competitions:Competition involves the interactions among two organisms of the same species or different species in which one neither outgrows the other nor survives while the other cannot grow nor survive.
2. Parasitism: This is a close association between two organisms in which one called the parasite lives in or on, and feeds at the expense of the other organisms called the host. The parasitic benefits from the association while the host usually suffers harm or even die.
3. Commensalism: Commensalism neither is an association between two organisms living together in which only one (the commensal) benefitted nor is harmed.
4. Predation: Predation is a type of association between two organisms in which the predator kills the other called the prey and feeds directly on it.
5. Pathogens: These are micro‐organisms which can cause diseases in plants and animals leading to their reduction through death.
6.  Mortality: Mortality is the death rate of organisms (plants or animals) in an environment. Mortality generally reduces the population of organisms in any habitat.
7. Migration: This is the movement of organisms either into a new habitat (immigration) or out of a habitat (emigration). These movements usually have effects on the other organisms inhibiting that habitat.
8.  Dispersal: Dispersal is the spreading of new individuals from their parents to new habitat so as to start a new life in the new environment. Such spreading habits may affect the lives of other organisms in the new area.
9. Natality: This is the rate of giving birth to new offspring. Natality is generally known to increase the population of the habitat which will subsequently lead to certain problems among the organisms in that habitat
10. Food: Availability of food in a habitat generally leads to increase in population while lack of food leads to starvation and dearth
11.  Diseases: Diseases are known to reduce the population of organisms (both plants and animals) in any habitat.
12. Pest: Pests are also known to affect the performance of plants in terms of yield and growth, in severe cases, the plants may even die.

Abiotic Factors

The abiotic factors comprise the following;

1. Climatic factors: These are temperature, rainfall, wind, pressure, sunlight or sunshine, humidity etc.
2. Chemical factors: These are made up of oxygen carbon dioxide, mineral salts, water and nitrogen.
3. Edaphic factors: These consist of soil, its water, chemical and physical composition, its pH, its nutrient, profile, structure and texture
4. Topographic factors: These are caused as a result of the shape of the earth’s surface, e/g. effects of rivers, hills, mountains and valleys.

Ecological Factors common to all Habitat.

Factors affecting or common to all habitats (both aquatic and terrestrial habitats) include:

• Temperature
• Rainfall
• Light
• Wind
• Pressure
• Hydrogen ion concentration (pH).

Of these factors, temperature and rainfall determine the major biomes of the world.

Temperature

1. Temperature determines the vegetation of an area
2. It is necessary for the germination of seeds
3. It affects the distribution of plants and animals
4. It regulates the activities of majority of the living things.
5. High temperature affects evapo‐transpiration and reduces the performance of animals.
6. It affects the wilting of field crops, ripening and maturity of crops.
7. It leads to loss of soil nutrients through volatilization
8. Unfavourable temperature may result in seed dormancy.

Rainfall

1. Rainfall determines seasons in some places e.g. Nigeria where we have rainy and dry seasons.
2. It determines the type of vegetation in an area.
3. It determines the distribution of plant and animal
4. Rainfall provides a dwelling place or habitat for some organisms, e.g. fish, crab, shrimps, sea weeds.etc.
5. Rainfall is necessary for seed germination
6. It helps to dissolve nutrient in the soil thereby making them available to plants
7. It is the main source of water in rivers, ponds, lakes, oceans etc.
8. Plants use water for photosynthesis.

Wind

1. Wind determines seasons in Nigeria, for instance, the South‐West wind is responsible for rainy season while the North‐East wind brings harmattan or dry season.
2. It helps in the distribution of rainfall
3. It can aid the spread of diseases
4. It aids the pollination of flowers
5. It also aids the disposal of seeds and fruit
6.  High velocity wind may cause wind erosion
7. Wind is responsible for water currents and waves.

Light

1.  Sunlight is necessary for photosynthesis to take place in green plant.
2. It affects evapo‐transpiration.
3. It affects the productivity of crops due to length of day, i.e., photosynthesis
4. Light affects flowering and fruiting in plant
5.  Light is the ultimate source of energy for all organisms.
6. It affects the activities of animals, e.g. some animals are active during the day while others are active at night.

Pressure

1.  Atmospheric pressure decreases as one goes up from the sea level
2.  In aquatic environment, pressure increases as one move down the water.
3. Plants and animals have special adaptations of a particular level of pressure to enable them survive.
4. Too high or too low pressure will affect the lives and activities of plants and animals
5. Pressure is responsible for the movement of winds.

Hydrogen Ion Concentration (pH)

1. pH values range from 1 to 14, with pH 1 being very acidic, pH 7 neutral and pH 14 very alkaline.
2.  Living organisms are highly sensitive to pH changes.
3. Too high or two low pH will affect the lives and activities of plants and animals
4. Plants and animals are adapted to special pH values. E.g. pH of fresh water is low while marine pH is high.
5. Most plants thrive well in neutral or slightly alkaline soil while acidic soils support little vegetation.

Ecological Factors Common to Aquatic Habitats

Factors affecting or common to aquatic habitats are:

• Temperature
• Rainfall
• Wind
• Light
• Pressure
• Hydrogen ion concentration (pH)

These factors have been explained above. Other factors not explained are:

• Salinity: Salinity is defined as the degree of saltiness or concentration of salt solution in water. Salinity is low in fresh water, high in sea water and moderate in brackish water. Aquatic organisms need to maintain the osmotic balance between their body fluids and their aquatic surroundings to survive. For example, organisms living in fresh water will require some adaptive features to enable them get rid of excess water that enters their bodies while those in sea water equally have adaptations to enable them cope with excess water in their bodies.
• Turbidity/Transparency: Turbidity is caused as a result of suspended materials in water. Clear water has low turbidity is also influenced by season. It is higher during the rainy season than in dry season. Turbidity reduces light penetration into the water, resulting in the inability of aquatic green plants to carry out photosynthesis, and it causes pollution.
• Dissolved Gases: Dissolved gases in this case refer to oxygen and carbon dioxide. The oxygen concentration of water decreases with depth. Oxygen is required by most aquatic organisms for respiration. It is also required for the decaying of organic substance. Carbon dioxide is required as raw materials for photosynthesis.
• Density: Density of water varies with the types of aquatic habitats. While the density of pure fresh water is 1.00, that of sea water is 1.028 at atmospheric pressure and 0⁰C. Organisms like fish, have streamlined bodies which enable them to move easily through water while other organisms which float on the water surface are sensitive to changes is density.
• Current: Water currents increase aeration and the turbidity of the water. It also affects the distribution of aquatic organisms. The type of organisms found in an aquatic habitat is affected by the speed of water current. For example, animals living in fast moving waters usually have structures for attaching themselves to rock surfaces so that they cannot be swept away.
• Total movement and waves: Tidal movements and waves affect the organisms in certain level of the water attach themselves to substances or may even live in burrows. Some may possess hard body cover to prevent evaporation of water from their bodies. In the open sea, wave cause the aeration of the surface waters, enabling aquatic organisms to have sufficient supply of dissolved gases for their respiration.

Ecological factors common to terrestrial habitats

Factors affecting terrestrial habitats are:

• Temperature
• Rainfall
• Wind
• Light
• Pressure
• Hydrogen ion concentration pH

These factors have been discussed under factors common to all habitats. Other factors not discussed are:

• Relative humidity: Relative humidity is the amount of water vapour in the air. It results in the formation of rain. Relative humidity affects the performance of plants and animals, and also determines their distribution. Low humidity causes aridity or dryness of a place. It also wheat is grown in northern Nigeria during harmattan.
• Edaphic or soil factors: These include:

1. Soil type:  The type of soil determines the fertility of the soil. It also determines the type of vegetation found in an area. Soil types determine the type of crops to be grown. They equally determine the porosity and water retaining capacity, e.g. while sandy soil is porous and cannot retain water; clay soil is not porous and can retain water.
2. Soil texture: Soil texture refers to the degree of coarseness or fineness of soil particles. It determines the type of soil in an area, the level of soil fertility and the type of crops to be grown. Soil texture affects the level of leaching and erosion.
3. Soil structure: Soil structure refers to the arrangement of the various soil particles in the soil. It determines the fertility of the soil, and its water retaining capacity. It also affects the level of soil organisms as well as the level of soil aeration and percolation.
4. Moisture content: Moisture content is the amount of water available in the soil. It affects the type of vegetation of an area, the distribution of plants and animals. It also determines the fertility of the soils as well as the growth of plants in the habitat.

Topographic factors or land surface: Topographic factors or land surfaces include:

1. Elevation: Elevation refers to the height of the land above the sea level. Elevation affects the growth of plants and the level of erosion in an area. It also determines the distribution of plants and animals.
2. Type of drainage: Drainage is the removal of excess water from the soil. It affects the availability of water in the soil and determines the growth of plants in the area. Excessive drainage leads to soil erosion and poor growth of plants.
3. Degree of Exposure: The degree of exposure of the land is affected by rainfall and vegetation cover. Low degree of exposures ensures the availability of nutrients to plants and the distribution of plants and animals. It also has effects on erosion and evaporation.

Measurement of Ecological Factors

Ecological factors that require measurement are: rainfall, temperature, wind, relative humidity, pressure, light, pH, turbidity, depth of water, slop etc. These ecological factors and the instruments used in measuring them are outlined below:

Instrument Functions/uses

1. Rain gauge – Measuring the amount of rainfall
2. Minimum and maximum mercury on glass thermometer – Measurement the lowest and highest temperature of the day
3. Anemometer – Measuring the speed of wind
4. Wind vane—Indicate the direction of wind
5. Hygrometer – Measures relative humidity
6. Barometer – Measures pressure
7. Photometer or light meter – Measures light intensity on land
8. Hydrophotometer – Measures light intensity in water
9. Colorimeter or pH indicator – Measures acidity or alkalinity of soil or solution.

Test Questions

1. ______  is defined as the total number of organisms of the same species living together in a given area at a particular time.
   a) Crowding
   b) Overpopulation
   c) Population
   d) Survival
2. _____ is used to measure acidity or alkalinity of soil or solution.
   a) Colorimeter
   b) Hydrometer
   c) pH vane
   d) Wind vane
3. _______  is caused as a result of suspended materials in water
   a) Turgidity
   b) Turbidity
   c) Salinity
   d) Moving waters
4. ________ is defined as the degree of saltiness or concentration of salt solution in water
   a) Salinity
   b) Salt Level
   c) Turbulence
   d) Turbidity
5. _______ refers to the total number of the species of the same kind in a given area or habitat
   a) Population density
   b) Population characteristics
   c) Population
   d) Population size
6. One of this is not an ecological factor affecting terrestial habitats.
   a) Temperature
   b) Rainfall
   c) Wind
   d) Porosity
7. Sunlight is not necessary for photosynthesis to take place in green plant. True or False
8. _______ is used to measure pressure
   a) Barometer
   b) Colorimeter
   c) Wind vane
   d) Speedometer
9. ______ refers to the number of times an organism occurs within a given area a habitat
   a) Population density
   b) Population size
   c) Population frequency
   d) Population Growth
10. _______is the movement of organisms either into a new habitat or out of a habitat.
    a) Immigration
    b) Migration
    c) Emgration
    d) Movement

Week 7

Topic: Functioning Ecosystem

Introduction

An ecosystem is a basic functioning unit in nature. It is made up of living organisms (plants and animals) and their non-living environment. The biotic or living components such as the producers and consumers interact in their environment resulting in the ecosystem being a functional unit.

Autotrophs, Heterotrophs and Decomposers

Autotrophs

Autotroph is an organism that serves as a primary producer in a food chain. Autotrophs obtain energy and nutrients by harnessing sunlight through photosynthesis (photoautotrophs) or, more rarely, obtain chemical energy through oxidation (chemoautotrophs) to make organic substances from inorganic ones. Autotrophs do not consume other organisms; they are, however, consumed by heterotrophs.

Energy Production

Autotrophs produce their own energy by one of the following two methods:

• Photosynthesis – Photoautotrophs use energy from sun to convert water from the soil and carbon dioxide from the air into glucose. Glucose provides energy to plants and is used to make cellulose which is used to build cell walls. E.g. Plants, algae, phytoplankton and some bacteria. Carnivorous plants like pitcher plant use photosynthesis for energy production but depend on other organisms for other nutrients like nitrogen, potassium and phosphorous. Hence, these plants are basically autotrophs.
• Chemosynthesis – Chemoautotrophs use energy from chemical reactions to make food. The chemical reactions are usually between hydrogen sulfide/methane with oxygen. Carbon dioxide is the main source of carbon for Chemoautotrophs. E.g. Bacteria found inside active volcano.

Heterotrophs

Heterotrophs are organisms that survive by feeding on organic matter produced by or available in other organisms. It is an organism that consumes other organisms in a food chain, hence, they are called consumers.  In contrast to autotrophs, heterotrophs are unable to produce organic substances from inorganic ones. They must rely on an organic source of carbon that has originated as part of another living organism. Heterotrophs depend either directly or indirectly on autotrophs for nutrients and food energy.

Decomposers

Decomposers are organisms that feed on dead organisms and other decaying organic materials. Fungi and bacteria are decomposers in energy transformation in an ecosystem. They are responsible for breaking down the complex organic compounds into simple nutrients. There are different types of decomposer organisms, which are responsible for returning simpler nutrients to the soil to be used by plants — and so the energy transformation cycle continues.

Food Chain and Food Web

Every organism needs to obtain energy in order to live. For example, plants get energy from the sun, some animals eat plants, and some animals eat other animals.

food web (in an aquatic habitat)

Food Chain

A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. In other words, food chain is defined as a feeding relationship involving the transfer of energy through food from producers to consumers. A food chain starts with the primary energy source, usually the sun. The next link in the chain is an organism that makes its own food from the primary energy source — an example is photosynthetic plants that make their own food from sunlight (using a process called photosynthesis) and chemosynthetic bacteria that make their food energy from chemicals in hydrothermal vents. These are called autotrophs or primary producers.

Some eat the autotrophs; these organisms are called herbivores or primary consumers — an example is a grasshopper that eats grass.

The next link in the chain is animals that eat herbivores – these are called secondary consumers — an example is a rat that eat grasshopper.

The next link in the chain is animals that eat the secondary consumers – these are called tertiary consumers – an example is a snake the eat rat

In turn, these animals are eaten by larger predators — an example is an owl that eats snakes.

The tertiary consumers are eaten by quaternary consumers — an example is a hawk that eats owls. Each food chain ends with a top predator and animal with no natural enemies (like an alligator, hawk, or polar bear).

The arrows in a food chain show the flow of energy, from the sun or hydrothermal vent to a top predator. As the energy flows from organism to organism, energy is lost at each step.

Trophic Levels

The trophic level of an organism is the position it holds in a food chain.

Primary producers (organisms that make their own food from sunlight and/or chemical energy from deep sea vents) are the base of every food chain – these organisms are called autotrophs.

Primary consumers are animals that eat primary producers; they are also called herbivores (plant-eaters).

Secondary consumers eat primary consumers. They are carnivores (meat-eaters) and omnivores (animals that eat both animals and plants).

Tertiary consumers eat secondary consumers.

Quaternary consumers eat tertiary consumers.

Food chains “end” with top predators, animals that have little or no natural enemies.

When any organism dies, it is eventually eaten by detrivores (like vultures, worms and crabs) and broken down by decomposers (mostly bacteria and fungi), and the exchange of energy continues.

Some organisms’ position in the food chain can vary as their diet differs. For example, when a bear eats berries, the bear is functioning as a primary consumer. When a bear eats a plant-eating rodent, the bear is functioning as a secondary consumer. When the bear eats salmon, the bear is functioning as a tertiary consumer (this is because salmon is a secondary consumer, since salmon eat herring that eat zooplankton that eat phytoplankton, that make their own energy from sunlight).

A network of many food chains is called a food web. Food web is defined as a complex feeding relationship among organisms in the same environment with two or more inter-related food chains.

Numbers of Organisms:

In any food web, energy is lost each time one organism eats another. Because of this, there have to be many more plants than there are plant-eaters. There are more autotrophs than heterotrophs, and more plant-eaters than meat-eaters. Although there is intense competition between animals, there is also interdependence. When one species goes extinct, it can affect an entire chain of other species and have unpredictable consequences.

Equilibrium

As the number of carnivores in a community increases; they eat more and more of the herbivores, decreasing the herbivore population. It then becomes harder and harder for the carnivores to find herbivores to eat, and the population of carnivores decreases. In this way, the carnivores and herbivores stay in a relatively stable equilibrium, each limiting the other’s population. A similar equilibrium exists between plants and plant-eaters.

The number of organisms in a food chain can be represented graphically in a pyramid. Each bar represents the number of individuals at each trophic level (feeding level) in the food chain.

In this example a large number of caterpillars living in a single oak tree provide food for several blue tits, which in turn are consumed by a sparrowhawk.

The pyramid of numbers usually shows that the number of organisms at each trophic level gets smaller towards the top. This particular case is an exception – one tree provides food for many caterpillars.

Pyramid of Biomass

A pyramid of biomass is a more accurate indication of how much energy is passed on at each trophic level.

Biomass is the mass of living material in each organism multiplied by the total number of organisms in that trophic level. This makes it easier to compare the food value of a small number of large organisms with a large number of small organisms. Pyramids of biomass usually are a true pyramid shape.

The biomass in each trophic level is always less than the trophic level below. This is because biomass is a measure of the amount of food available. When animals eat, only a small proportion of their food is converted into new tissue, which is the food for the next trophic level. Most of the biomass that animals eat is either not digested, or used to provide the energy needed for staying alive.

Processes of Ecosystems

The diagram with the plants, zebra, lion, and so forth illustrates the two main ideas about how ecosystems function: ecosystems have energy flows and ecosystems cycle materials. These two processes are linked, but they are not quite the same.

Energy Flows and Material Cycles

Energy enters the biological system as light energy, or photons, is transformed into chemical energy in organic molecules by cellular processes including photosynthesis and respiration, and ultimately is converted to heat energy. This energy is dissipated, meaning it is lost to the system as heat; once it is lost it cannot be recycled.  Without the continued input of solar energy, biological systems would quickly shut down. Thus the earth is an open system with respect to energy.

Elements such as carbon, nitrogen, or phosphorus enter living organisms in a variety of ways. Plants obtain elements from the surrounding atmosphere, water, or soils. Animals may also obtain elements directly from the physical environment, but usually they obtain these mainly as a consequence of consuming other organisms. These materials are transformed biochemically within the bodies of organisms, but sooner or later, due to excretion or decomposition, they are returned to an inorganic state. Often bacteria complete this process, through the process called decomposition or mineralization.

During decomposition these materials are not destroyed or lost, so the earth is a closed system with respect to elements. The elements are cycled endlessly between their biotic and abiotic states within ecosystems.

ASSESSMENT.

1. Define the term “Ecosystem”.
2. Explain the following terms; Autotrophs, Heterotrophs and Decomposers.
3. What is a “Food chain”?
4. Draw an illustration of a food chain.

Week 8

Topic:  Energy Transformation In Nature 

Introduction 

The transformations of energy in an ecosystem begin first with the input of energy from the sun. Energy from the sun is captured by the process of photosynthesis. Carbon dioxide is combined with hydrogen (derived from the splitting of water molecules) to produce carbohydrates (CHO). Energy is stored in the high energy bonds of adenosine triphosphate, or ATP.

Energy Loss in the Ecosystem

The solar radiation is used by plants during photosynthesis. Some are lost to the earth’s surface while some are stored in plants’ parts stems, leaves, etc. and are not used up.

LAWS OF THERMODYNAMICS 

First Law of Thermodynamics

The law states that energy can neither be lost nor created especially as it is converted from one form to another.

Second Law of Thermodynamics

The law states that no energy transformation is 100% efficient, since some are lost in form of heat.

Decomposition in Nature

Decomposers are organisms, mainly bacteria and saprophytes responsible for the breaking down of dead organic materials which could be of plants or animals origin. These decomposers are grouped into two classes:

1. Micro-decomposers: These are small or microscopic organisms that can cause decay, e.g. certain bacteria and fungi.
2. Macro-decomposers: These are bigger organisms that can cause decay of dead organic materials, e.g. earthworms, termites, snails, mushroom, toad stools, etc.

Process of Decomposition

The decomposers secrete enzymes onto their food source such as decaying plant. These enzymes break down complex organic compounds (food) like carbohydrates and proteins into simple soluble inorganic compounds.

Roles of Decomposers in Ecosystem

1. Decomposers play major roles in the ecosystem in the following ways:
2. They enrich the soil with nutrients required for plant growth
3. They contribute to environmental pollution
4. Decomposition is useful in the making of cheese and yogurt
5. They also prevent an unsightly accumulation of remains and wastes of living organisms on earth surface.

Test Questions

1. What law of thermodynamics is this? “The law states that no energy transformation is 100% efficient, since some are lost in form of heat.” 
   a) First Law
   b) Second Law
   c) Third Law
2. There are two types of decomposers namely ______
3. Energy from the sun is captured by the process of ________
4. Energy is stored in the high energy bonds of ________
5. ______ are organisms, mainly bacteria and saprophytes responsible for the breaking down of dead organic materials which could be of plants or animals origin.

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