Viruses and Major Groups of Living Things

Tree and rock stones covered by mosses plant a topic studied by biology form one students

There are many species of living organisms in the world. These organisms are placed in groups based on their common or shared characteristics. Each group has its own features that make it distinct from others.

Viruses

A virus is an extremely small fragment of nucleic acid (DNA or RNA) surrounded by a protein coat.

It is smaller than a living cell.

A virus is not a cell.

Different types of viruses

(a) Tobacco mosaic virus

(b) Bacteriophage virus

Characteristics of viruses

(a) They do not have a nucleus, cytoplasm, or cell organelle.

(b) They have a simple structure consisting of a small piece of nucleic acid (DNA or RNA) surrounded by a protein coat called a capsid.

Some viruses have viral envelopes. These are membranes enclosing capsids. The envelopes are made up of proteins from the host cell.

(c) They cannot reproduce on their own. They must attack a host cell and use the materials in the cell to reproduce. This is called obligate parasitism.

Obligate parasitism is the ability of a virus to reproduce inside the cell and crystallize in the absence of a living host places them between living and non-living things.

Viral reproduction

(a) Virus attaches itself to a host cell and injects DNA into the cell.

(b) The virus DNA undergoes replication inside the host cell and forms viral components.

(d) The host bursts to release new viruses.

(d) When outside a host cell, they show no symptoms of life (do not grow, feed, excrete, or respire). They exist in a dormant state.

(e) They are host-specific. This means a certain type of virus attacks only a specific host.

For example, the rabies virus affects only mammals and HIV attacks only certain types of white blood cells in human beings.

(f) Most viruses are infectious. This means they can cause diseases to their hosts.

The structure of viruses

Viruses are composed of strands of genetic material (DNA or RNA) which forms the core.

The core is enclosed by a protein coat called capsid as in bacteriophage.

DNA or RNA are of various shapes and sizes according to the type of the virus.

Advantages of viruses

(a) Viruses are important in the study of cell and molecular Biology. They are used by scientists to manipulate and investigate the functions of cells.

(b) Some viruses are used to make vaccines. For example, the first vaccine against smallpox was a small dose of the virus that causes cowpox, which is a mild infection. On recovering from cowpox, the body developed antibodies that could resist both cowpox and smallpox.

(d) Some viruses are used in biological control to eradicate pests, such as insects. This is due to their characteristics of being host specific and infectious.

Disadvantages of viruses

(a) Most viruses are pathogenic. They cause infections and diseases such as tobacco mosaic disease, tomato spotted wilt disease, cassava mosaic disease, rabies, chickenpox, COVID-19, polio, and AIDS.

Pathogenic viruses can reproduce very fast, leading to large-scale epidemics.

(b) Its difficult to cure viral infections. This is because virus can alter themselves. For example, there are many different types of viruses that can cause common cold and influenza.

Exercise

Why are viruses regarded as non-living things?

Explain why some viruses are used in agriculture to fight against pests and disease vectors.

Viruses can be regarded as a threat to human health. Explain.

Kingdom Monera

Kingdom Monera consists of bacteria and blue-green algae.

The scientific study of bacteria is called Bacteriology.

Characteristics of bacteria

(a) They are prokaryotic as their cells lack a well-defined nucleus. Their nucleus has no nuclear membrane. They also lack other membrane-bound organelles.

(b) They are small unicellular organisms. Some bacteria stick together to form chains or clusters called colonies.

Free-living bacteria exist on their own.

Parasitic bacteria depend on other organisms known as hosts for their needs. Examples include hosts such as human beings and other animals.

Saprophytic bacteria get their food from dead organic matter by external digestion.

(d) Free-living bacteria and some parasitic bacteria have flagella for movement.

(e) Bacteria have a slimy outer layer. This layer helps to protect them from parasites like viruses and predators such as protozoa.

(f) They reproduce asexually by binary fission or through spores.

(g) They occur in various shapes. There are five known shapes of bacteria. These are spherical.

Shaped bacteria or cocci (singular is coccus),

rod-shaped or bacilli (singular is bacillus),

spiral-shaped bacteria or spirilla (singular is spirillum),

and comma-shaped bacteria or vibrio (singular is vibrion).

The following table shows various shapes of bacteria.

Activity: Observing features of bacteria

Materials

Microscope

Prepared microscope slides of bacteria

Charts showing structure of bacteria

ICT tools

Notebook and pen or pencil

Procedure

Observe the charts that show the structure of bacteria or prepared slides of bacteria using the microscope.

Search from reliable internet sources the videos that show structures and shapes of bacteria.

Describe the shapes and structural features of the bacteria you observed.

Structure of bacteria

Bacteria have circular DNA suspended in the cytoplasm without being enclosed by the nuclear membrane. The cell wall encloses the cell membrane.

Slime capsule: Outer protective layer.

Circular DNA: Genetic material not enclosed in a nucleus.

Cell wall: Provides structural support.

Cell membrane: Controls movement of substances in and out.

Cytoplasm: Jelly-like substance where reactions occur.

Flagella: Tail-like structures used for movement.

Fimbriae or pili

Fimbriae are hair-like structures on the surface of some bacteria. For example, Escherichia coli have fimbriae that attach themselves to the lining of the urinary tract or the intestines.

Flagella

These are long tail-like structures that help some pathogenic bacteria to move.

Classification of Bacteria

Bacteria can be classified as pathogenic or non-pathogenic.

1. Pathogenic Bacteria

These are bacteria that can cause infections and diseases.

In plants: Diseases include fire blight and crown gall.

In animals: Diseases include tuberculosis, tetanus, cholera, and gonorrhoea.

Features: Pathogenic bacteria often have fimbriae (for attachment) and flagella (for movement) to help spread infection.

Toxins

Some bacteria produce toxic compounds that harm their hosts. The human body may react by inducing vomiting or diarrhoea to remove these toxins.

For instance, toxins released by Clostridium sp. can lead to severe diarrhoea.

2. Non-pathogenic Bacteria

These bacteria are harmless even when inside a plant or animal body.

Example: Rhizobium sp. found in the root nodules of leguminous plants help convert atmospheric nitrogen into nitrates in the soil.

Human Gut: Bacteria like Escherichia coli synthesize vitamins K and B12.

Advantages of Bacteria

(a) Some bacteria are used to remover harmful substances like petroleum waste, dyes, and pesticides.

(b) They help in digestion: Bacteria in the stomachs of goats and cattle secrete the cellulase enzyme, which helps digest cellulose.

(c) They convert nitrogen: Nitrogen-fixing bacteria convert nitrogen from the air into nitrates that plants use to make proteins.

(d) They recycle essential elements through decomposition: Bacteria break down dead bodies of plants and animals, recycling essential elements like nitrogen, carbon, and phosphorus.

(e) Food Production: Bacteria produce lactic acid through fermentation, which is essential for making cheese, yoghurt, vinegar, and alcohol.

(f) Medicine: Certain bacteria are used to produce antibiotics to treat infections.

(g) Bacteria are used to produce hormones such as insulin and human growth hormone.

(h) they produce vitamins: Bacteria in the human gut synthesize vitamins K and B12.

Disadvantages of Bacteria

(a) Animal Disease: Causes infections like typhoid fever (Salmonella typhi), Tuberculosis (Mycobacterium tuberculosis), and gonorrhoea (Neisseria gonorrhoeae).

(b) Crop Disease: Causes diseases like fire blight on pea and apple, and leaf spot in cotton.

(d) Material Damage: Sulphur bacteria produce sulphuric acid, which can damage buried metal pipes.

(e) Denitrifying bacteria convert soil nitrates into atmospheric nitrogen; therefore, they reduce soil fertility.

Exercise

1. Your friend has disposed a fruit waste in a dump site. Explain what may happen to a fruit overtime and provide reasons why the process is important for environmental conservation.

2. Students are advised to wash their hands after handling samples of bacteria. What is the reason for this advice?

3. Describe a generalised structure of a bacterium.

Kingdom Protoctista

Members of this kingdom include Amoeba sp., Euglena sp., Plasmodium sp., Paramecium sp., and Trypanosoma sp.

Task

From the library and available internet sources, search information about protoctists (characteristics, advantages, and disadvantages).

Characteristics of protoctists

(a) They are eukaryotic as they have a nucleus and other membrane bound organelles.

(b) Most of them are unicellular organisms.

(d) Some protoctists are autotrophs (manufacture their own food) while others are heterotrophs (obtain nutrients from other organisms).

(e) Some protoctists reproduce sexually and others asexually while others reproduce both sexually and asexually.

(f) Many protoctists have locomotory structures, such as cilia, flagella or pseudopodia.

Phyla of kingdom Protoctista

Protoctista is subdivided into several phyla. Only five phyla of this kingdom will be described in this section.

These phyla are: Rhizopoda, Apicomplexa, Euglenophyta, Ciliophora, and Zoomastigina.

Phylum Rhizopoda

Organisms included in phylum Rhizopoda move and feed using structures known as pseudopodia (singular is pseudopodium).

An example of organisms found in this phylum is Amoeba sp. Parasitic amoeba includes Entamoeba histolytica, which feeds on cells of the human colon and cause amoebic dysentery.

Free living amoeba are found in sea water, freshwater, and in the soil. They can also be found in muddy ponds and slow flowing streams containing decaying organic matter.

(a) Amoeba have two layers of cytoplasm; a viscous outer layer called ectoplasm and a more fluid internal layer called endoplasm.

(b) Most of them are free living, feeding on plant and animal matter. Others are parasitic in animals, including human beings.

(d) They have contractile vacuoles which regulate the amount of water in the freshwater amoeba.

(e) They form temporary food vacuoles to hold and digest food particles.

(f) In amoeba, waste products, such as urea and ammonia are excreted by simple diffusion.

Diffusion is the movement of substances from a region of high concentration to a region of low concentration.

Diffusion in Amoeba

Diffusion is the movement of substances from a region of high concentration to a region of low concentration.

When there is a high concentration of urea or ammonia in the amoeba, these substances flow out of the amoeba into the surrounding water.

(g) In amoeba, oxygen and carbon dioxide gases are exchanged by diffusion.

(h) They are unicellular organisms.

(i) They reproduce asexually by binary fission

Advantages of amoeba

(a) Amoeba are commonly used in laboratories to study cell structure and function.

(b) Amoeba are important decomposers in aquatic environments, feeding on organic particles in the water.

Disadvantage of amoeba

Some species of Amoeba cause diseases. For example, Entamoeba histolytica causes amoebic dysentery in humans and Entamoeba gingivalis causes teeth and gum diseases.

Exercise

1. Imagine you are a scientist studying micro-organisms in a pond ecosystem. While examining a water sample under a microscope, you come across a single-celled organism with unique appearance. Describe the characteristics you would look for to determine whether this organism is a protoctist.

2. You are a medical researcher investigating an outbreak of amoebic dysentery in a community. You have collected samples from patients and identified the causative organism using a microscope. Describe the key characteristics of this organism that would help you confirm that the organism is the one responsible for causing amoebic dysentery.

3. Explain the advantages of amoeba.

Phylum Euglenophyta

This phylum consists of unicellular aquatic organisms most of which live in freshwater and possess flagella. Euglena sp. is an example of organisms found in this phylum.

Characteristics of Euglena sp.

(a) They are unicellular.

(b) They have chloroplasts which contain chlorophyll for photosynthesis.

(c) Most of them are found in freshwater; only a few are found in salt water. They are protected by a pellicle which surrounds the cytoplasm. The pellicle allows the euglena to change shape.

(d) They have flagella for movement.

(e) They have an eye spot for detection of light intensity.

(f) They are eukaryotic cells.

(g) They possess both plant and animal characteristics. The plant characteristic is the possession of chloroplasts which contain chlorophyll for photosynthesis. The animal characteristic is the ability to move using a flagellum, presence of an eyespot for detection of light intensity, and presence of a gullet for ingesting food.

Advantages of Euglena sp.

(a) They are used for sewage treatment due to their heterotrophic mode of nutrition.

(b) Euglena sp. is an important source of food to aquatic organisms such as fish.

(c) During photosynthesis, Euglena sp. produces oxygen gas. This oxygen is useful to aquatic organisms. It also helps to balance oxygen gas levels in sewage treatment plants.

Disadvantages of Euglena sp.

Euglena sp. blooms can be harmful to fish. The toxins produced by some Euglena species can kill fish and other aquatic organisms.

Phylum Apicomplexa

Organisms found in this phylum are unicellular and parasitic.

Plasmodium sp. which cause malaria in humans is an example of members of phylum Apicomplexa.

Characteristics of Plasmodium sp.

(a) They are unicellular.

(b) They are eukaryotes.

(d) They reproduce sexually in the human host and asexually by multiple fission in the mosquito vector and human host.

(e) When a plasmodium enters the human body, it attacks the red blood cells and liver cells.

Advantage of Plasmodium sp.

Plasmodium sp. is used in medical and other researches.

Disadvantage of Plasmodium sp.

Plasmodium parasites cause malaria. Malaria can cause inflammation and rupture of the spleen, and miscarriages. It can also cause anaemia due to the destruction of red blood cells. Severe malaria can cause death.

Phylum Ciliophora

Organisms found in this phylum are unicellular and are found in aquatic habitats.

Paramecium sp. is an example of members of phylum Ciliophora.

Characteristics of Paramecium sp.

(a) They are unicellular and slipper-shaped.

(b) They are eukaryotes.

(d) They live in freshwater.

(e) The body is covered with short hairy structures called cilia.

(f) They use cilia to move and to create a feeding current.

(g) The body of the Paramecium cell is enclosed by a stiff but elastic membrane, called the pellicle.

(h) Food enters the organism through an opening called the oral groove.

(i) They have food vacuoles which are formed to hold and digest food particles.

(j) They have anal pores which are used for elimination of undigested food.

(k) Paramecium can reproduce either asexually or sexually, depending on their environmental conditions. Asexual reproduction takes place when nutrients are available, while sexual reproduction takes place under conditions of starvation.

(l) Contractile vacuoles regulate the amount of water in the cytoplasm.

Advantages of Paramecium sp.

Paramecium sp. play important ecological role in the environment as they help to clean up small particles of debris in the water as well as feeding on small animals.

Disadvantages of Paramecium sp.

(a) Some species of Paramecium invade and destroy the lining of the intestine, causing a disease called balantidiasis.

(b) Paramecium sp. feed on bacteria which decompose sewage. This may delay decomposition of sewage.

Phylum Zoomastigina

Organisms found in this phylum are unicellular flagellate protoctists. Generally, they are found in the intestine, but can also be found in blood stream or in the heart.

Trypanosoma sp. is an example of members of phylum Zoomastigina.

Characteristics of Trypanosoma sp.

(a) They are unicellular, slender, elongated, and dorsally and ventrally flattened in shape.

(b) They are parasites in wild animals, domesticated animals, and human beings.

(d) The body is covered with a thin, elastic, and firm pellicle.

(e) Most of them reproduce asexually by binary fission while inside the host body.

(f) Some have an undulating membrane for locomotion.

Advantages of Trypanosoma sp.

Trypanosoma brucei has been extensively studied by scientists, as it is a model organism for understanding the biology of parasites and the diseases they cause.

Research on Trypanosoma brucei has led to the development of new drugs and treatments for sleeping sickness and related diseases.

Disadvantages of Trypanosoma sp.

(a) Trypanosoma brucei is the causative agent of the disease called human African trypanosomiasis or sleeping sickness.

The disease affects mostly African countries. It can be transmitted through bites of a vector called tsetse fly or through blood contact from an infected individual.

(b) Trypanosoma sp. also cause animal trypanosomiasis or Nagana to cattle, buffalos and other large herbivores.

Exercise

1. Imagine you are on the field trip to a stagnant water body for your Biology class. Your teacher asks you to collect water samples for microscopic investigation from two different locations in the pond, one near the surface and the other from the bottom. During microscopic examination, you observed presence of Euglena sp. from the surface sample and Paramecium sp. from the bottom sample. Describe the characteristics of the micro-organisms observed from the samples.

2. You are given a microscope and a slide with a sample of Trypanosoma sp. to observe in your Biology class. While looking at the slide under the microscope, your teacher asks you to describe the key characteristics of Trypanosoma sp. that you can observe. What features would you look for to explain the characteristics of the sample?

Activity: Investigating different protoctists

Materials

Specimen bottles, microscope, microscope slides and coverslips, pond water, a notebook, and a pencil.

Procedure

Go to a pond or any other place with stagnant water.

Caution:

Care must be taken when collecting water samples from the pond.

Fetch water from the pond using specimen bottles.

In the Biology laboratory, put a drop of the pond water on a microscope slide, add stain and cover it with a coverslip.

Observe the slide under the microscope. Do you identify any organisms? If Yes, name them.

Kingdom Fungi

Task

Read from reliable internet sources, library and other biology books information about fungi.

The kingdom Fungi contains a variety of eukaryotic organisms that consist of bounded cell organelles, such as mitochondria and nucleus. Most of them are multicellular (made up of many cells) and some are unicellular (made up of a single cell).

Example of unicellular fungi is yeast (Saccharomyces sp.).

Examples of multicellular fungi include bread mould (Rhizopus sp.), pin mould (Mucor sp.), and mushroom (Agaricus sp.).

General characteristics of Fungi

Members of the kingdom Fungi have the following general characteristics:

(a) They are found in various places including air, water, soil, food, and in the bodies of animals and plants.

(b) They are eukaryotic organisms with true nucleus which is enclosed in a nuclear membrane.

(d) Their body is made up of a mycelium consisting of a network of fine, tube-like filaments called hyphae (except yeast).

(e) They feed saprophytically, for example mushroom, but some of them are parasitic for example Candida albicans.

(f) Some fungi form symbiotic associations with other species.

(g) They reproduce both sexually by spores and asexually by budding.

(h) They store carbohydrates in the form of glycogen.

Distinctive features of Fungi

(a) They have cell walls made up of chitin, which is a substance containing protein and complex sugars.

(b) Their bodies are made up of a mycelium consisting of a network of fine, tube-like filaments called hyphae (except yeast).

Phyla of the kingdom Fungi

The members of kingdom Fungi are classified into different phyla.

There are three main phyla in kingdom Fungi:

- Ascomycota,

- Zygomycota,

- Basidiomycota.

Phylum Ascomycota

Members of this phylum are commonly called ascomycetes or sac fungi. This is because their sexual spores are enclosed in sac-like structures known as asci (singular is ascus). Some ascomycetes such as yeast are single-celled (unicellular) organisms.

Characteristics of ascomycetes

(a) Some ascomycetes such as yeast are unicellular and others such as Penicillium sp. are multicellular.

(b) Most ascomycetes have a saprophytic mode of feeding and can grow on surfaces of dead organic materials such as rotting fruit and other foods.

(d) They reproduce sexually through spores known as ascospores, and asexually through fission, fragmentation, or budding..

Activity: Investigating the structure of yeast cells

Materials

Dry yeast, water, methylene blue reagent, microscope, coverslips, microscope slides, dropper, pencil, and notebook.

Procedure

Dissolve some dry yeast cells in water.

Using a dropper, place a drop of the yeast solution on a microscope slide and cover it with a coverslip.

Examine the specimen using the low-power objective lens of the microscope.

Identify some yeast cells.

Describe the structures you have observed in yeast cells when using the high-power objective lens of the microscope.

Phylum Zygomycota

The members of this group are known as zygomycetes because they have sexual spores known as zygospores.

Zygospores are produced in the structures called zygosporangia. They also have asexual spores known as sporangiospores, which are produced in the structures called sporangia.

Zygomycetes grow as a mass of white or dark tiny threads and feed on rotting or decaying food materials like bread, cassava, pawpaw, and tomato.

Examples of organisms in this group include mucor and black bread mould.

(a) black bread mould by mucor

(b) (Labels: Sporangium, Sporangiophore, Stolon, Rhizoids, Mycelium)

Characteristics of zygomycetes

(a) They are saprophytic, growing on decaying organic materials.

(b) They reproduce sexually through zygospores or asexually through sporangiospores.

Activity: Investigating the structure of bread mould

Materials

A piece of bread, petri dish or watch glass, hand lens, forceps, microscope, microscope slides, pencil, and notebook.

Procedure

Take a slice of bread, put it on a petri dish and moisten it.

Leave the bread on the moist place for 2–3 days until a greyish or dark spots appear on it.

Observe the changes that might have occurred on the surface of the bread.

(a) Use a hand lens and observe the dark spots that might have developed on the surface of the bread.

(b) Take a small sample of dark spots using forceps and place it on a microscope slide, add a drop of water, and cover with a coverslip.

(d) Based on your observations of the structures on the bread using the microscope, describe the features you observe.

Phylum Basidiomycota

Members of the phylum Basidiomycota are called basidiomycetes. They have structures called basidia (singular is basidium) that produce sexual spores.

The basidia are usually club-shaped structures. Hence, members of this group are also known as club fungi because they all possess basidia.

Their sexual spores are called basidiospores. The common examples of basidiomycetes are mushrooms and toadstools, such as Agaricus bisporus (edible mushroom).

Other examples of basidiomycetes include brackets, puffballs, and rust fungi. They are well recognizable in various habitats, especially in areas rich in nutrients.

Characteristics of basidiomycetes

(a) They are multicellular organisms.

(b) They are saprophytic, growing on decaying organic matter.

Activity: Investigating the structure of a mushroom

Materials

Mushroom, hand lens, scalpel, petri dish, scissors or sharp knife, pencil, and notebook.

Procedure

Use a hand lens to examine the mushroom structure.

Describe the key features and structures you observe when you:

(a) view from the side

(b) view from the lower surface of the cap

Use a scalpel or knife to cut the mushroom vertically into two equal parts.

Caution:

Care should be taken when using sharp objects, such as knives.

Describe the features and structures you see in:

(a) the whole mushroom, as seen from the side

(b) the cut surface of the mushroom

Advantages of fungi

(a) Most strains of mushrooms and toadstools, such as Agaricus sp., are edible. They are used as sources of food and they have a high content of proteins and vitamins.

(b) Fungi, such as yeast (Saccharomyces sp.), are used in food manufacturing industries, such as in bakeries (they make dough to rise). Yeast is also used in brewing beer by fermenting sugars to produce alcohol.

(d) Some fungi such as Penicillium sp. are important in the production of drugs such as penicillin.

(e) Most species of fungi are used in genetic engineering and biological researches.

(f) Saprophytic fungi are very important in the decomposition of dead organisms and waste materials. Through decomposition by fungi, important nutrients are released into the soil. The nutrients are then absorbed and used by plants.

(g) Some types of ascomycetes and basidiomycetes develop symbiotic relationship with roots of higher plants.

Disadvantages of fungi

1. Some fungi cause diseases to human beings and other organisms. Some of the diseases caused by fungi in humans include athlete’s foot, ringworms, meningitis, and skin infections. In some people, the fungal spores can cause allergic reactions.

2. In plants, some fungi, such as ascomycetes, cause various diseases like potato blight, maize rust, rice blast, and powdery mildew in beans and other legumes. Some fungi attack timber used in building houses and making furniture.

3. Some fungi, such as Candida albicans, live in the bodies of human beings. They grow naturally in the human body, particularly in the mouth, throat, gut, and female reproductive tracts without causing any harm. These fungi can cause infection if they grow in excess and enter other parts of the body organs and systems, such as in the bloodstream, kidney, heart or brain.

4. Some parasitic fungi, such as certain types of ascomycetes, produce poisonous substances called mycotoxins. The most common mycotoxin is known as aflatoxin, which is commonly found in harvested maize and groundnuts that have been left in moist places. Aflatoxin is carcinogenic (causing cancer).

5. Some mushrooms, such as Amanita, are poisonous to humans when eaten.

6. Some fungi, such as moulds and other parasitic fungi, cause food spoilage.

Exercise

1. Suppose you are in a class and your Biology teacher brings an unknown specimen. Which characteristics will you look for to confirm that it belongs to the kingdom Fungi?

2. Name the phylum to which each of the following organisms belongs.

(a) Bread mould

(b) Mushroom

3. Due to the occurrence of ringworms caused by fungi, many people view fungi as a threat. How would you educate them on the beneficial aspects of fungi in our daily lives?

Kingdom Plantae

Kingdom Plantae is composed of a wide variety of plants. Members of this kingdom vary greatly in size, forms, habitat, means of reproduction, and morphology. Kingdom Plantae includes; mosses, ferns, cone bearing plants, and flowering plants. Plants are found in various habitats, such as on land, in oceans, and in freshwater.

Activity: Investigating plant parts

Materials: A variety of plants, hand lens, notebook and pen or pencil

Procedure:

Collect a variety of plants from the school or home environment.

Caution

Care must be taken when collecting plants, since some plants such as milkweed and oleander are poisonous.

Examine each of the plant parts using a hand lens. The parts to be examined include roots, stems, leaves, flowers, and fruits. Do all plants have these parts?

Group the plants according to their similarities and differences.

General characteristics of members of the kingdom Plantae

(a) They are multicellular and eukaryotic organisms.

(b) They have cell organelles called chloroplasts that contain chlorophyll.

(c) Green plants are photoautotrophs. This means that they manufacture their own food using sunlight through the process of photosynthesis.

(d) Some plants reproduce sexually through flowers or cones while others reproduce asexually by means of spores or vegetative propagation.

(e) Their cells are organised into tissues, organs, and organ systems.

(f) They show limited movement, for example opening and closing of flower petals and growth movements towards stimuli such as light and water.

Distinctive features of members of the kingdom Plantae

(a) They have a cell wall made up of cellulose.

(b) Higher plants have vascular tissues for conduction of water, mineral salts, and manufactured food.

Divisions of kingdom Plantae

The kingdom Plantae is divided into four main divisions. These are:

division Bryophyta;

division Filicinophyta or Pteridophyta;

division Coniferophyta;

and division Angiospermophyta.

Division Bryophyta

Members of the division Bryophyta are called bryophytes, which are the most primitive plants. They are found in wet and shaded environments, such as on forest floors, rock surfaces, bare soil, cracks of paved surfaces, bricks, as well as on trunks and branches of trees.

The sexual reproduction process in bryophytes depends on availability of water; that is why their distribution is restricted to shady and moist places.

Examples of bryophytes are mosses and hornworts.

Activity: Investigating the structure of bryophytes

Materials: Mosses, hand lens, notebook, and pen or pencil

Procedure:

Collect moss plants from the school or home environment.

Use a hand lens to observe the structure of a moss plant.

Describe the observed external features of the moss plant.

Questions

What is the significance of bryophytes in ecosystems?

General characteristics of bryophytes

(a) Bryophytes live in moist, damp, and shaded areas.

(b) They do not produce flowers, fruits, or seeds.

(d) They reproduce sexually and asexually by spores.

Distinctive features of bryophytes

(a) They are simple plants which lack true roots, stems, and leaves

(b) They have an erect plant body, which is leafy in nature.

(d) They usually depend on water for sexual reproduction.

Advantages of mosses

(a) They help to decompose dead logs and enhance nutrient circulation.

(b) They are early colonisers of open woodland; hence they help in creating a favourable environment for the development of higher plants.

(d) They play a great role in preventing soil erosion by holding the soil particles together.

(e) They contribute in the production of oxygen to the atmosphere, which is used by animals and other organisms.

Disadvantages of mosses

(a) Moss plants are common weeds in gardens and can be difficult to eliminate.

(b) Sometimes, they grow on the surface and walls of buildings, making them look old and unattractive.

Division Filicinophyta (Pteridophyta)

Activity: Investigating the structure of a fern plant

Materials: Fern plants, petri dish, hand lens, notebook, and pen or pencil

Procedure:

Collect some fern plants from the school or home environment.

Caution

Care must be taken when collecting fern plants. Get only what is required instead of destroying the whole plant.

Use a hand lens to examine different types of ferns.

Describe the external features.

Examine the underside of one of the fronds. Describe the structure you have observed.

Question

What is the significance of filicinophytes in ecosystems?

Members of division Filicinophyta are called filicinophytes or pteridophytes. Examples of filicinophytes are ferns, club mosses, and horsetails.

Filicinophytes are much more advanced than bryophytes because they have true roots, stems and leaves.

Leaves of filicinophytes are called fronds.

Fronds are usually composed of a leafy blade and petiole (leaf stalk).

General characteristics of filicinophytes

(a) They live in moist, damp and shady areas.

(b) They are less dependent on water for survival and reproduction than bryophytes.

(d) They have vascular tissues.

(e) They reproduce by means of spores.

(f) They do not produce flowers and seeds.

Distinctive features of ferns

(a) Their leaves bear spore-producing structures called sori (singular is sorus). A sorus is a cluster of spore-producing structures called sporangia (singular sporangium).

(b) Their leaves are arranged in a clump and are called fronds.

Advantages of ferns

(a) They constitute ground-cover in moist areas.

(b) They produce food for themselves and for heterotrophic organisms in ecosystems.

(d) They are the major components of coal, a fossil fuel which is made up of the remains of primitive plants.

(e) Ferns, such as Azolla sp. are used as biological organic fertiliser. They are able to fix nitrogen from the air into compounds that can be absorbed by plants.

(f) Some ferns, such as Dryopteris sp. have medicinal value.

Disadvantage of ferns

Ferns are regarded as weeds in many places.

For example, the giant fern plants are the worst aquatic weeds that threaten the life of other aquatic organisms.

In terrestrial environment, some species of fern plants, such as Pteridium sp. are considered weeds.

Division Coniferophyta

Activity: Investigating the distinctive features of conifers

Materials:

A variety of conifers, such as a whole plant or branches of pine, cedar, cypress, fresh or preserved cones, notebook, and pen or pencil.

Procedure

Collect the branches of pine, cypress, and cedar plants from the school or home environment.

Caution

Care must be taken when collecting a variety of conifer branches or cones. Get only what is required instead of destroying the whole plant.

Observe the structural features that are possessed by these plants which are different from those of other plants.

Note down the distinctive features of conifers.

Questions

What features have you observed?

What features distinguish conifers from other plants?

Coniferophyta is one of the divisions of the kingdom Plantae.

Plants under the division Coniferophyta are sometimes called coniferous trees or simply conifers.

These conifers bear cones and they are referred to as coniferophytes.

The conifers are non-flowering plants whose seeds are not enclosed in ovaries, but are arranged spirally giving the shape of the cone.

Examples of conifers include casuarinas, spruces, cedars, pines, and cypress plants.

General characteristics of conifers

Conifers possess the following features:

(a) They are non-flowering seed-bearing plants.

(b) They produce naked seeds.

(c) They have reproductive structures called cones. There are male and female cones. The male cones are smaller and usually occur in clusters. The female cones are the most conspicuous and produce seeds.

(d) They form soft wood.

(e) They have needle-like or scaled leaves with thick cuticle for protection and reduced water loss.

(f) Conifers are widely distributed but commonly found in areas with cold climate where they form evergreen forests.

Distinctive features of conifers

(a) They bear cones.

(b) The pollen grain develops air bladder-like structure which facilitate their movement. Hence, they are wind pollinated plants.

(d) The mature seeds are typically winged. This is an adaptation for seed dispersal by wind.

Advantages of conifers

(a) Conifers are evergreen plants, which are grown in large forests and produce useful timber called softwood.

(b) Conifer forests are home to many birds and other animals.

(d) Turpentine which is used as cleaning agent for painting as well as production of disinfectants and insecticides is also a product of conifers.

(e) Conifer trees are used as firewood; hence they are a source of heat.

(f) They are a source of food to organisms, such as insects and squirrel.

(g) Many species of Pinus are used as ornaments when planted in parks and gardens. Cypress also is commercially grown and harvested for decoration during festivals, such as Christmas.

(h) Conifers remove carbon dioxide from the atmosphere through photosynthesis.

Disadvantages of conifers

(a) Coniferous forest completely shades the ground and prevents the growth of other plants.

(b) Wood products from conifers are soft and can be easily attacked by termites if not treated.

Division Angiospermophyta

Activity: Investigating the structure of flowering plants

Materials: Hibiscus flower, common bean plant, maize plant, elephant grass plant, hand lens, notebook, and pen or pencil.

Procedure

Collect hibiscus plant, common bean plants, maize plants and elephant grass plants from the school or home environment. Make sure that you carefully uproot the entire plant in order to display their root system clearly, except for hibiscus.

Caution

(a) Get only what is required instead of destroying the whole plant.

(b) Do not collect dangerous plants, such as thorny plants, itching and poisonous plants.

Using a hand lens, observe carefully the leaves, flower arrangement and roots of the collected plants and state the classes to which each plant belongs.

Question

Summarize the morphological differences between the classes of the collected plants in tabular form, including the characteristics, such as leaf shape, flower arrangement, and root structure.

Angiospermophyta is the division in kingdom Plantae which comprises plants commonly known as flowering plants or angiosperms.

Angiosperm are the most diverse and successful group of all the plants. They are found in most habitats, such as aquatic and terrestrial habitat including deserts.

They range in size from small plants, such as herbs and grasses to big trees like baobab.

General characteristics of angiosperms

The following are the general features of angiosperms.

(a) Angiosperms are found in terrestrial, freshwater and marine habitats.

(b) Angiosperms have well-developed root system, stem and leaves.

(d) They produce seed bearing fruits.

(e) They have well developed conducting tissues which contain xylem and phloem.

Classes of the division Angiospermophyta

The division Angiospermophyta is divided into two classes. These classes are:

- Monocotyledoneae

- Dicotyledoneae

The word “Mono” means one and “Di” means two. Monocots have been named from having one cotyledon and dicots from having two cotyledons. Cotyledon is the part of seed that develops into the leaves after germination.

Class Monocotyledoneae

This class contains plants with one cotyledon. Examples of plants in this class include maize, sugarcane, wheat, millet, sisal, coconuts and banana plants.

Distinctive features of the class Monocotyledoneae

(a) Flower parts normally occur in three or multiples of three.

(b) They have parallel leaf venation

(d) Monocot leaves are composed of an open or closed sheath which encloses the stem.

(e) Their vascular bundles in stems are scattered.

(f) They have fibrous root system.

(g) They have long and thin leaves.

Based on the image provided, here is the transcribed text organized by section for easy reading:

Class Dicotyledoneae

This class contains plants with two cotyledons. Examples are beans, mangoes, coffee, groundnuts and sunflower plants.

Distinctive features of the class Dicotyledoneae

(b) Dicot leaves have net-like venation.

(d) They have a tap root system.

(e) Their seed embryo has two cotyledons.

(f) Dicot plants have petioles that support the leaf.

(g) They have short and broad leaves.

Advantages of Angiosperms

(a) They provide food: Angiosperms are important for the survival of humans and other animals. For humans, angiosperms provide foods, such as beans, rice, maize, sugarcane, and oranges. Some members of the grass family are used as food for livestock.

(b) They are habitat to many insects, birds and other animals.

(d) They provide fibres, Some angiosperms, such as cotton, flax, and hemp provide fibres that are raw materials in textile industries.

(e) They prevent soil erosion. Angiosperms form ground cover which prevents soil erosion.

(f) They make environment attractive. Some plants such as roses, lilies, and hibiscus make the environment attractive.

(g) They provide varieties of wood for furniture, paper, and building materials.

Disadvantages of Angiosperms

(a) Others are poisonous. Some angiosperms such as thorn apple, oleander, and milkweed are poisonous. When eaten by humans and other animals as they may cause death.

(b) Source of addictive drugs. Drugs derived from some angiosperms can be dangerous. For example, tobacco and caffeine can be addictive.

(c) They reduce crop yield. Some angiosperms, such as star grass are weed plants, which compete with food crops leading to reduction of crop yield. Others are parasites to other plant species. For example, parasitic weeds in crops, such as mango, orange and cashew nut trees, and they cause serious loss of crop yield.

(d) They can affect the ecosystem. Some aquatic angiosperms, such as water hyacinth can colonise water bodies and affect the ecosystem as well as hindering fishing activities.

Kingdom Animalia

Kingdom Animalia comprises wide varieties of animals. Animals vary greatly in their structure, morphology and the way their bodies function.

Kingdom Animalia includes worms, insects, and higher animals. They are found in various habitats, such as on land, in oceans, and in freshwater.

General characteristics of animals

(a) They are eukaryotes; therefore, they possess a clearly defined nucleus and their cells have membrane bound organelles.

(b) They are multicellular, that means they are made up of more than one cell.

(d) Most animals are mobile and hence they can move from one place to another searching for shelter, food, mates, and safety.

(e) Most of the animals have bilateral symmetrical bodies. This means that their bodies can be divided longitudinally into two equal parts.

(f) Most of the animals have high level of tissue differentiation and specialised body organs.

(g) Most of the animals have a developed nervous system.

(h) Most of the animals have anterior and posterior ends, with oral and anal openings.

(i) The majority of the animals digest food internally in the gut and store carbohydrates in the form of glycogen.

Distinctive features of animals

(a) They depend on other organisms as source of food.

(b) Most animals digest food internally in the gut.

(c) Most animals are capable of locomotion; hence they can move from one place to another. Few animals, such as oysters are sessile. They are found attached on rocks and other hard surfaces and they are not capable of self-locomotion.

(d) Most animals have a well-developed nervous system that helps them in detecting changes in their surroundings. This allows them to be aware of the changes occurring in their environment.

Activity: Differentiating animals from other organisms

Materials: A variety of plants and animals, charts showing a variety of plants and animals, notebook, and pen or pencil.

Procedure

Walk around the school compound and observe a variety of plants, insects, and other animals or observe charts that show a variety of plants and animals.

Observe the organisms and note as many observable features as possible.

Group the observed organisms according to their similarities and differences.

Outline the similarities and differences among the grouped organisms.

Question

Give reasons why animals and plants are placed in different kingdoms.

Phyla of the Kingdom Animalia

Kingdom Animalia comprises several phyla. However, only five phyla will be covered in this section. These are:

(a) Phylum Platyhelminthes includes pork tapeworm (Taenia solium), beef tapeworm (Taenia saginata), liver flukes (Fasciola species), blood flukes (Schistosoma species) and planaria.

(b) Phylum Nematoda, formerly known as Aschelminthes, includes ascaris, hookworms and filarial worms.

(d) Phylum Arthropoda includes prawns, crabs, ticks, spiders, butterflies and cockroaches.

(e) Phylum Chordata includes advanced organisms, such as human beings, cattle, fish, chicken, frogs, birds and snakes.

Phylum Platyhelminthes

Members of the phylum Platyhelminthes are the flatworms and they are commonly called platyhelminths. They can be free living or parasites.

Activity: Observing the external features of the flatworms

Materials: Preserved specimens of tapeworm, liver fluke, petri dishes, forceps, hand lens, notebook and pencil.

Procedure

Using forceps pick a liver fluke, and tapeworm from preserving containers and put each in different petri dishes.

Using a hand lens, carefully observe and identify the following external structures (if any): the mouth, suckers, body shape and the posterior region of the organism.

Describe each specimen.

Questions

1. How does the body structure of a tapeworm differ from that of a liver fluke?

2. What is the function of suckers in platyhelminths?

General characteristics of platyhelminths

(a) They have dorso-ventrally flattened bodies. This is the reason why they are called flatworms.

(b) Most flatworms have only one opening that is the mouth. However, tapeworms lack both mouth and anus.

(d) Some members have hooks and suckers for attachment to the host. Such members include tapeworms and the liver fluke.

(e) Some flatworms, such as planaria have hair-like structure called cilia on their outer body surface for locomotion.

(f) Few members, such as planaria are free living and inhabit freshwater, marine water and land. Most of its members, such as liver flukes and tapeworms are parasitic.

(g) they have flame cells. This cells are specialised for excretion and osmoregulation.

(h) They lack respiratory and circulatory systems. Transportation of oxygen for respiration and other materials takes place by simple diffusion.

(i) Their bodies are bilaterally symmetrical. This means their bodies can be divided longitudinally into two equal parts.

(j) They are hermaphrodites, meaning that they have both male and female reproductive organs. Hence, their reproduction can either be through self-fertilisation or cross-fertilisation.

(k) They are heterotrophic, meaning that they get food from other organisms. Flatworms may be parasites, predators or scavengers.

Distinctive features of platyhelminths

(a) They are dorso-ventrally flattened with ribbon or leaf-like body.

(b) If present, their digestive system is incomplete. The digestive tract has only a single opening which is the mouth.

(d) They have suckers, hooks, or both for attachment to the host.

Advantages of platyhelminths

(a) Some flatworms, such as planaria are scavengers, feeding on organic particles from dead bodies of other organisms.

(b) Some are used as biological specimens in the field of education and medicine. Examples of such flatworms include tapeworms and liver flukes.

Disadvantages of platyhelminths

Task

Search from reliable internet sources the videos or images showing beef or pork infected with tapeworms. Note down what you have observed.

(a) Many species are parasites that cause diseases to humans, livestock and wild animals. For example:

(i) Tapeworm causes taeniasis, which is an intestinal tapeworm infection transmitted through consuming raw or undercooked beef or pork infected with tapeworms. The infected caused by larval stages of tapeworms can lead to heart attack or epilepsy. If the infection is located in the heart muscles it can cause heart attack and if it is located in the brain, it can cause epilepsy.

(ii) Liver fluke causes fascioliasis. This disease causes liver rot in sheep, cattle and humans.

(iii) Some species of blood flukes, such as Schistosoma spp. cause bilharzia (schistosomiasis). If untreated it may cause urinary bladder cancer or intestinal cancer.

(b) Parasitic flatworms can cause reduction in quality and amount of meat and milk produced by livestock due to infections. They can also cause untold growth and even death in young animals.

(c) They cause general body weakness and frequent hunger in the hosts as they feed on digested nutrients from the hosts. Working animals, such as oxen cannot perform work to their full capacity if infected with a large number of parasitic flatworms.

(d) Parasitic flatworms can also cause loss of income due to costs incurred for treatment of diseases.

Exercise

1. Describe the distinctive features of members of phylum Platyhelminthes.

2. Imagine you are conducting a laboratory investigation. In one of your experiments, you come across a specimen of a tapeworm. What features will enable you to tell whether the specimen is a tapeworm?

3. Why is it not advisable to eat raw or undercooked beef?

Phylum Nematoda

Task

Search from reliable internet sources the videos or images that show round worms.

Phylum Nematoda comprises round worms which are among the most numerous multicellular animals on the earth.

Round worms inhabit a wide range of environments, including soil, marine and freshwater.

Examples of nematodes include the animal parasites, such as ascaris and plant parasites, such as eelworms.

General characteristics of nematodes

(a) They have round, cylindrical, elongated and unsegmented bodies with pointed ends.

(b) They depend on other organisms as source of food.

(c) They have no blood circulatory system; therefore, transport is by simple diffusion through the thin moist cuticle or through the fluid-filled body cavity.

(d) Many species of nematodes are parasites of both animals and plants, but there are also many free-living species found in marine and freshwater sediments and in the soil.

(e) they have separate sexes. They are dioecious. Males are usually smaller than females.

Distinctive features of nematodes

The following features differentiate nematodes from other animals.

(a) They have a cylindrical, elongated and unsegmented body with pointed ends.

(b) They have special sensory structures known as amphids and phasmids.

Activity: Observing external features of roundworms

Materials:

Preserved specimen of ascaris (female and male), hand lens, forceps, notebook, pen and two petri dishes

Procedure

Use forceps to pick up male and female specimens of ascaris from a preserving container and put them into separate petri dishes.

Carefully observe the male and female ascaris specimens with a hand lens.

Describe their external features.

Compare the observed features with those depicted in Figure 5.29.

Question

What features distinguish roundworms from flatworms?

Figure: External structure of ascaris (a) male (b) female

Advantages of nematodes

(a) Nematodes have been used in various biological studies. For example, some discoveries in the field of genetics involved the use of nematodes.

(b) Some nematodes are used as biological control agents to control pests, such as locusts and vectors, such as mosquitoes. Parasitic roundworms attack and eat varieties of caterpillars.

Disadvantages of nematodes

Search from reliable internet sources the videos or images that show elephantiasis. Note down what you have observed.

(a) They cause diseases in human, such as elephantiasis or bancroftian filariasis which affects the human lymphatic system. This results in accumulation of the lymph in legs, hands, mammary glands or scrotal sacs.

They also cause ascariasis in humans and pigs. This may lead to obstruction of the gut and may also cause anaemia.

(b) they cause diseses in plants: some species of roundworms cause root knot galls in plants, hence drains photosynthetic products.

Phylum Annelida

The word Annelid is derived from a latin word “annelus” which means little ring.

Thus, members of this phylum are known as ringed or segmented worms. Annelida is a large phylum comprising ragworms, peacock worms, leeches, and earthworms.

General characteristics of annelids

(a) They have elongated, cylindrical bodies that are divided into distinct segments.

(b) They have bilateral symmetrical bodies.

(d) They have a moist outer covering called cuticle.

(e) They have closed circulatory system whereby the blood flows within the blood vessels.

(f) They have a lip-like extension on the first segment above the mouth called prostomium.

(g) They are commonly found in soil, freshwater, and marine environment while some species are parasitic.

Distinctive features of annelids

(a) Most annelids have hair-like structures called chaetae made up of chitin. These are used for locomotion.

(b) They have a segmented body.

Activity: Observing external features of the earthworm

Materials:

Preserved or live specimen of earthworm, hand lens, petri dish, notebook, pencil, and forceps.

Procedure

Using forceps, pick an earthworm from a preserving container and put it in a petri dish.

Using a hand lens, observe the specimen carefully to identify its external features.

Identify its external features, including its mouth, anus, clitellum, and chaeta.

Questions

(a) How are the earthworms adapted to their environment?

(b) Explain two features that distinguish earthworms from round worms.

Advantages of annelids

(a) Some annelids improve soil aeration through burrowing and mixing up of soil layers. Earthworms play important role in improving soil aeration, hence maintaining soil fertility.

(b) They are used for commercial production of compost manure in the process known as vermicomposting.

(c) Some annelids are used as bait in the fishing industry. Examples of annelids used as bait include earthworms and lugworms.

(d) They are used as source of nutritious food for some fish and birds. They are rich in proteins and vitamins.

(e) Some annelids are ecological decomposers, hence, they contribute to nutrient circulation in the ecosystems.

(f) They remove pollutants from the soil and clean the environment by transforming organic wastes during feeding.

(g) Faeces and urine of some annelids have considerable value as manure and they increase soil fertility.

(h) They are used as specimens in biological studies.

(i) The excretory waste of some annelids which are in the form of cast increases sticking together of soil particles. This in turn increases water holding capacity of the soil.

Disadvantages of annelids

(a) Some annelids damage young roots of the growing plants.

(b) Leeches are harmful to mammals, reptiles and fishes, because they suck blood from them.

Exercise

1. What morphological features differentiate earthworms from tapeworms?

2. What is the function of chaeta found in most annelids?

3. Imagine you are walking around school farm and you come across someone who is killing earthworms. Educate that person on the importance of earthworms.

Phylum Arthropoda

The term Arthropoda originates from two Greek words, “arthron” meaning joint and “podos” meaning foot.

Literally, arthropods are organisms with jointed appendages.

Arthropods are the most successful animals on the earth. They are found almost in every habitat, including marine, freshwater, and terrestrial habitats.

They vary widely in their habitats and feeding habits.

Examples of arthropods include prawn, scorpion, tick, beetle, butterfly, crab, spider, centipede, millipede and grasshopper.

General characteristics of arthropods

(a) They have exoskeleton made up mostly of chitin. The exoskeleton serves different purposes, such as muscles attachment, support and protection against physical damage.

(b) Some arthropods grow by periodically shedding off their exoskeleton in a process called moulting or ecdysis.

(c) They have segmented bodies. In most arthropods, the body is organised into three major regions. These regions are the head, thorax and abdomen. In some arthropods, such as arachnids and crustaceans, the thorax and head are fused together to form the cephalothorax. Therefore, these arthropods have two major body parts, namely cephalothorax and abdomen.

(d) They have jointed and paired appendages that may be modified in various ways to form structures, such as antennae, mouthparts, legs and reproductive organs. The modified appendages are used for various functions, such as feeding, gaseous exchange, locomotion and sensation.

(e) Their body plan is bilaterally symmetrical. This means, their bodies can be divided longitudinally into two equal parts through a central axis.

(f) They have compound or simple eyes.

(g) They have open circulatory system where blood is not confined to the blood vessels and heart only. Blood flows into the body cavity to reach various tissues and organs.

Distinctive features of arthropods

(a) They have jointed appendages, which serve different purposes, such as feeding, locomotion and sensation.

(b) They have segmented bodies organised into regions called tagmata.

Classes of phylum Arthropoda

Based on the presence of antennae, position and numbers of appendages, habitats, life histories and habits, arthropods are classified into five classes.

These are:

class Crustacea which includes crabs and lobsters;

class Arachnida which includes spiders and scorpions;

class Chilopoda which includes centipedes;

class Diplopoda which includes millipedes;

and class Insecta which includes cockroaches, termites, and grasshoppers.

Activity: Observing the external structure of crab, spider, grasshopper, and millipede

Materials

Preserved specimens or pictures of crab, spider, grasshopper, and millipede, notebook, pen and hand lens.

Procedure

Using forceps, pick specimens from a preserving container and put them in a petri dish.

Using a hand lens, observe the specimens carefully to identify their external features.

Questions

(a) List down two observable features which show that these specimens are arthropods.

(b) What two external features that distinguish a spider from a grasshopper?

Advantage of arthropods

(a) They are used as food for human beings and other animals. They are rich in protein and calcium minerals. Example of edible arthropods are lobsters, prawns, shrimps, edible grasshopper, and larvae of beetles and butterflies.

(b) They are used for production of various substances. For example, honey bees produce honey wax and bee venom; silk worms produce silk that can be used for commercial purpose; and silk from spiders is used to produce threads.

(c) They are used in biological control of pests. Some arthropods have been used effectively as predators to kill or control pests. For example, lady beetles are used to kill aphids. Aphids are the insect pests that transmit viruses to plants.

(d) Insects, such as bees and butterflies act as pollinators. Many plants depend on insects for pollination.

(e) They are used in scientific researches particularly in the fields of physiology, genetics and evolution. Fruit flies (Drosophila melanogaster) are among the insects used for this purpose.

(f) Some insects are used in production of medicine. Such insects include blister beetles that produce cantharidin which is used for treatment of urinogenital diseases.

(g) Some arthropods are scavengers and feed on rotten or decayed materials, hence helping in reducing wastes and ensuring nutrient circulation in the ecosystem. Examples of such arthropods are millipede and cockroaches.

(h) Some arthropods improve soil aeration and soil fertility. For example, termites break down plant tissues and diplopods feed on decaying plant and animals, thus improving soil fertility.

(i) Some crustaceans are used for decoration purpose especially crabs and crayfish.

Disadvantages of arthropods

(a) Chilopods, such as centipedes have venomous claws. They can bite humans and other animals.

(b) Some arthropods, such as scorpion, wasps and bees can cause painful bites and stings. Stinging insects that live in colonies can cause a significant injury and even death.

(c) Some insects are vectors of animal and plant diseases. For example, mosquitoes carry Plasmodium spp. which cause malaria and tsetse flies carry Trypanosoma which cause sleeping sickness to human beings. In addition, white flies carry tomato yellow leaf curl virus which causes chlorosis in plants.

(e) Some arthropods are parasites to mammals and other vertebrates. For examples, ticks and bedbugs.

Phylum Chordata

This phylum comprises animals with a high degree of body organisation.

The majority of animals under this phylum have a supporting column of bones known as backbone or vertebral column.

Activity : Observing the external features of fish, chicken, frog, lizard and rat or mouse

Materials:

Preserved or fresh specimens of fish, frog, chicken, catfish, lizard, rat, charts showing pictures or drawing of fish, frog, chicken, lizard, rat, hand lens, scalpels, notebook, pen and a tray.

Procedure

Place each specimen on a tray.

Observe each specimen carefully.

Describe the external features you observed, including the arrangement of scales, presence of gills, type of fins, and the external shape of each specimen.

Question

What features distinguish a fish from a frog?

General characteristics of chordates

(a) They occupy both terrestrial and aquatic habitats.

(b) Most chordates have a complete digestive system with two openings, the mouth and anus.

(d) Most chordates have a closed circulatory system.

(e) Most have endoskeletons made up of bones and cartilages.

(f) Some chordates have central nervous system made up of the well-developed brain and a spinal cord.

Distinctive features of chordates

Chordates have unique features that differentiate them from other animals. Chordates have the following features at some stages of embryological development.

(a) A supporting skeletal structure called notochord. In many vertebrates, the notochord is replaced by the vertebral column during development.

(b) A dorsal hollow tubular nervous tissue known as nerve cord that is found inside vertebral column.

(c) Gill slits at least during early developmental stages and may later develop into various structures, such as gills in fish or component of the ear and throat in mammals.

(d) Post anal tail. In humans it is only present during embryonic stages.

Advantages of chordates

(a) Chordates, such as fish, chicken, goats, sheep, cattle and buffalo are used as source of food to human beings and other animals.

(b) Their excreta in the form of faeces or dung are used as organic manure which adds nutrients to the soil, thus improving soil fertility.

(d) Chordate derived products such as fish oil and shark collagen are used to treat diseases in human beings and livestock. Snake skin, tortoise shell and shark fins are used in traditional medicine.

Disadvantages of chordates

(a) Some chordates are dangerous because they can attack humans, causing injury or death. Examples of such chordates include crocodiles, sharks, lions, leopards, buffalo, elephants and hyenas.

(b) Some chordates are vectors of diseases. For example, birds can transmit viruses that cause bird flu. Cats and rats can spread fleas which transmit bacteria and other pathogens that cause diseases, such as plague. Infected dogs can also transmit rabies, which is a viral disease of dogs and can also infect humans.

(d) Some snakes, frogs, toads and newts produce toxins which cause skin irritation and even death to human beings.

Revision Exercise

Choose the correct answer in questions 1–7.

1. The following are diseases caused by fungi in plants and animals EXCEPT ______.

(a) wheat rust and maize rust

(b) candidiasis

(d) powdery mildew

2. Which of the following is the advantage of bryophytes?

(a) They cause fungal diseases in human beings

(b) They help to retain water in the soil

(d) They are good sources of timber

3. One of the following plants is an example of conifers.

(a) Mango tree

(b) Orange tree

(d) Pine tree

4. Which of the following groups of organisms belong to the same Phylum?

(a) Liver fluke, hook worm, earthworm, and spider

(b) Tapeworm, earth worm, grasshopper and rat

(d) Crabs, grasshopper, spider, and centipede

5. Which of the following is among the distinctive features of annelids?

(a) Their bodies have similar body segments

(b) They have a cylindrical, elongated and unsegmented body

(d) They have suckers, hooks or both

6. Which of the following is not a distinctive feature of animals?

(a) They depend on other organisms as source of food

(b) Most of animals are capable of locomotion

(d) They have exoskeleton

7. Which of the following is correctly matched?

(a) Platyhelminthes - segmented worms

(b) Nematoda - round worms

(d) Arthropoda – flatworms

Write TRUE for a correct statement and FALSE for an incorrect statement in the spaces provided.

A virus is an extremely small organism. ______

Kingdom Monera includes Amoeba sp. ______

Plasmodium sp. is a parasite that causes sleeping sickness. ______

Rhizoids are found in moulds and mosses. ______

Coniferophyta is one of the divisions of the Kingdom Plantae. ______

13. Explain the effects of the following organisms to humans.

(a) Entamoeba sp.

(b) Plasmodium sp.

14. List characteristics of phylum to which Euglena sp. belongs.

15. A bread was put in a mist cupboard. After a few days black thread-like structures which ended up in club-like structure appeared on the bread.

(a) Write the common name of the organism that grew on the bread surface.

(b) Name the kingdom to which the observed organism belongs.

(d) Outline the advantages of the members of the kingdom you mentioned in (b) above.

16. What features make cockroach and human being to belong in the same kingdom?

17. Classify each of the following organisms to phylum level;

(a) tape worm

(b) housefly and (c) monkey.

18. Mtakuja villagers believe that all insects are dangerous. They decided to kill them by spraying insecticide. As a biologist, convince them that insects are beneficial to their lives.