Key Unit CompetenceApply the basic knowledge of classification to group living organisms into the three domains.
Learning objectives
–– Describe the classification of species into the taxonomic hierarchy of domain, kingdom, phylum, class, order, family, genus and species.
–– Outline the characteristic features of the three domains Archaea, Bacteria and Eukarya.
–– Draw and label the structure of a typical bacterial cell.
–– Identify common bacterial diseases in plants and animals.
–– Outline the characteristic features of the kingdoms Protoctista, Fungi, Plantae and Animalia.
–– Explain why viruses are not included in the three domain classification.
–– Outline how viruses are classified limited to type of nucleic acid and their host.
–– Describe the role of bacteria in the production of dairy products.
–– Describe methods of preventing common bacterial diseases.
–– Construct a dichotomous key for a group of organisms.
–– Recognize that microorganisms can survive in hot springs
Introductory activity
Collect different fruits such as oranges, lemons, avocado, green paper, red paper, bananas, mangoes and tomatoes.
1. Observe each of the above fruits and group them based on their external features.
2. Based on groups made, which fruits are most closely related?
For more than 3.5 billion years, life on earth has been constantly changing. Natural selection and other processes have led to a staggering diversity of organisms. A tropical rain forest, for example, may support thousands of species per meter square.
Recall that a species is a population of organisms that share similar characteristics and breed with another to produce fertile offspring. Biologists have identified and named about 1.5 million species so far, and they estimate that between 2 and 100 million additional species have yet to be discovered.
2.1 Taxonomic hierarchy
Activity 2.1
You are provided with cards written on a list of words such as continent, district,
country, cell, province, sector, village and family.
1. Arrange the above words in increasing size
2. What is your opinion about the people of the same family and those in the
whole country?
3. Compare your arrangement above with 8 groups of the biological
taxonomic hierarchy.
Taxonomy is the study and practice of classification, which involves placing organisms in a series of taxonomic units, or taxa (singular: taxon). In biological classification, these taxa form a hierarchy. Each kind of organism is assigned to its own species, and similar species are grouped into a genus (plural: genera). Similar genera are grouped into a family, families into an order, orders into a class, classes into a phylum (plural: phyla) and phyla into a kingdom. The domain is at the top of this hierarchical system.
The hierarchy classification starts from the largest group, the domain. The eight levels of classification are known as taxa (taxon in singular), these include: Domain, Kingdom, phylum, class, order, family, genus and species. As one moves down the taxonomic hierarchy, it follows that the number of individuals decreases but the number of common features increases. For example, there are numerous individuals in the domain Eukarya, with very few features in common.
Binomial nomenclature
When precision is not required one generally reverts to common names. The trouble is that an organism may be known by different common names, and sometimes the same name may be given to two quite different organisms because common names are not internationally recognized and they change from one region to another one, or from one country to another one. To solve this problem, the binomial system also known as scientific name was introduced and it was pioneered by the Swedish naturalist Carl Linnaeus (1707-1778).
In this system, each organism is given two Latin names: a generic name beginning with a capital letter and a specific name beginning with a lowercase letter based on the physical characteristics of studied species. The scientific name is in italic when printed otherwise it is underlined, when hand written.
For example, many cats belong to the genus Felis but there are many species of cats:
A wild cat is Felis sylvestris while a domestic cat is Felis domesticus. These names are in
italic because this book was written by the use of computer. Hierarchy taxonomy of human, earthworm and hibiscus plant are given in the table 2.1.
Table 2.1 Taxonomic classification of human being, earthworm and hibiscus
Scientific names present more advantages than common names.
–– They are necessary whenever precise identification is required, and they enable scientists to communicate accurately with each other.
–– They are used worldwide and have the merit that every biologist knows exactly which organism is being referred to.
Currently, with DNA technology, it is possible to investigate relationships based on genes or DNA structure. As this new technology comes to greater use, it is possible to find that some species had to be reclassified into different taxa.
Self-assessment 2.1
1. An African bush elephant belongs to order Proboscidae and family Elephantae. Its scientific name is Loxodonta africana.
a. Make a table indicating the hierarchy classification of African bush elephant
b. Use the examples from table 2.1 to define the term “taxon”
2. Classify each of the following organisms under the following kingdom, phylum and class taxa: honey bee, cockroach, maize, and spider.
3. Describe the system of naming species that Linnaeus developed.
2.2 Three domains: Archaea, Bacteria and Eukarya.
Activity 2.2.
Using text books and other sources identify the characteristics of each of the three biological domains
Three domains are used by biologists to divide organisms into three large groups based on their cell structure. The domain is the highest taxon in the hierarchy. The prokaryotes are divided between the domains Bacteria and Archaea, while all the eukaryotes are placed into the domain Eukarya.
a. Domain Bacteria
Domain bacteria include prokaryotic organisms as their cells have no true nucleus. They are all microscopic that vary in size between 0.2 to 10 micrometres. The characteristic features of bacteria are:
–– Cells with no true nucleus
–– DNA exists in circular chromosome and does not have histone proteins associated with it
–– No membrane-bound organelles (mitochondria, endoplasmic reticulum, Golgi body, chloroplasts)
–– Contain mesosomes as infolding of membrane and acts as sites for respiration.
–– Ribosomes (70 S) are smaller than in eukaryotic cells
–– Cell wall is always present and contains peptidoglycans in place of cellulose
–– Cells divide by binary fission
–– Usually exist as single cells or colonies
b. Domain Archaea
This contains bacteria that live in extreme environments where few other organisms can survive. They are classified according to the environments they live in;
–– Methanogenic bacteria that live in habitats deprived of oxygen and give off methane as a product of metabolism for example those that live in the guts of ruminant animals
–– Halophilic bacteria live only in salty conditions
–– Thermoacidophilic bacteria tolerate extreme acid and temperature that exceed boiling point of water and a pH below 2.
c. Domain Eukarya
All the organisms classified into this domain have cells with nuclei and membrane bound
organelles. Their characteristic features are:
–– Cells with a nucleus and membrane-bound organelles
–– linear DNA associated with histones arranged within a chromosome in the nucleus
–– Ribosomes (80S) in the cytosol are larger than in prokaryotes, while chloroplasts and mitochondria have 70S ribosomes, like those in prokaryotes.
–– Chloroplast and mitochondrial DNA is circular as in prokaryotes suggesting an evolutionary relationship between prokaryotes and eukaryotes
–– A great diversity of forms: unicellular, colonial and multicellular organisms
–– Cell division is by mitosis
–– Many different ways of reproduction including asexually and sexually.
Self-assessment 2.2
1. What are the three domains of living things?
2. Describe the ways in which a domain differs from a kingdom?
3. It is confirmed that: “Some bacteria can survive in extreme temperatures such
as hot springs”. Justify this statement.
4. How is the information about evolutionary or phylogenetic relationships useful in classification of the living things?
2.3 Five kingdoms of organisms
Activity 2.3.
Collect organisms from a habitat near your school including a housefly, spider, frog, gecko, bean/maize plant, moulds/mushroom, spirogyra (algae) and a hen. If there are small rapidly moving land animals such as insects, anaesthetise them by placing them in an ether/ethanol bottle for few seconds. Preserve the collected specimens for future use
1. Examine each organism, using a hand lens.
2. Make a table of the features observed and identify the kingdom to which each organism belongs.
There are different ways of classifying the living world into kingdoms but the most common and recommended is the five kingdom classification. According to Kent (2000) the kingdoms are:
–– Kingdom Monera or prokaryote
–– Kingdom Protoctista
–– Kingdom Fungi or kingdom mycota
–– Kingdom Plantae
–– Kingdom Animalia
2.3.1 Kingdom Protoctista
This kingdom is made up of a very diverse range of eukaryotic organisms, which
includes those that are often called protozoans and algae. Any eukaryote that is not
a fungus, plant or animal is classified as a protoctist. The characteristic features of
protoctists are listed according to the different phyla due to their diverse range:
–– Rhizopods that have pseudopodia for locomotion. Example, amoeba
–– Flagellates which are hereorophic organisms with at least one flagellum for locomotion. Example, trypanosoma.
–– Sporozoans which are mainly parasitic organisms that reproduces by multiple fission. Example plasmodium.
–– Ciliates which are organisms with cilia. Example paramecium
–– Euglenoid flagellates which are organisms with flagella but with a biochemistry quite distinct from that of flagellates. Example Euglena
–– Oomocytes which are similar to fungi except that they have cell wall with cellulose. Example Phytopthora infestans; potato blight
–– Green algae which are photsynthetic organisms with chlorophyll pigments similar to the ones of plants. Example chlorella
–– Red aglae which are photosynthetic organisms with organelles with red pigment as well as chlorophyll. Example, chondrus
–– Brown algae which are photsynthetic organisms with organelles which contain brown pigments as well as chlorophy. Example Fucus, sea weed Living things such as paramecium (a), amoeba (b), euglena (c) and plasmodia belong to the kingdom Protoctista.
2.3.2 Kingdom Fungi
Fungi have some similarities with plants, but none of them is able to photosynthesise. They are all heterotrophic, obtaining energy and carbon from dead and decaying matter or by feeding as parasites on living organisms. There is a vast range in size from the microscopic yeasts to what may be the world’s largest organisms. Other characteristic features of fungi are:
–– Heterotrophic nutrition – they use organic compounds made by other organisms as their source of energy and source of molecules for metabolism
–– Reproduce asexually by means of spores and sexually by conjugation
–– Simple body form, which may be unicellular or made up of long threads called hyphae (with or without cross walls).
–– Large fungi such as mushrooms produce large compacted masses of hyphae known as fruiting bodies to release spores
–– Cells have cell walls made of chitin or other substances
2.3.3 Kingdom Plantae
Plants are all multicellular photosynthetic organisms. They have complex bodies that are often highly branched both above and below the ground. Characteristic features of plants are:
–– Multicellular eukaryotes with cells that are differentiated to form tissues and organs.
–– Few specialized cells
–– Cells have large and often permanent vacuoles for support with cell walls made of cellulose
–– Most plants store carbohydrates as starch or sucrose
2.3.4 Kingdom Animalia
Animals (Fig 2.3) are multicellular organisms that are all heterotrophic with different methods of obtaining their food. Organisms in this kingdom have other additional features.
–– Different types of specialized cells
–– Cells do not have chloroplasts and cannot photosynthesize (although some,
such as coral polyps have photosynthetic protoctists living within their tissues)
–– Cell vacuoles are small and temporary (for example lysosomes and food vacuoles)
–– Cells do not have cell walls
–– Communication is by the nervous system
Activity 2.3
Which feature do all animals (except sponges) have that distinguishes them from plants and fungi?
2.3.5. Kingdom Monera
Organisms in this kingdom have single cells that do not have a nucleus. They are prokaryotic. They are the smallest and simplest organisms. Examples are bacteria which form a diverse group with members that range widely in size and shape. Some of them stick together to form chains or clusters while others are single cells. The figure below (Figure 2.4) shows a typical structure of a bacterial cell which contains all the main features of prokaryotes
Self-assessment 2.4
1. The kingdom protoctista contains groups which do not appear to show an evolutionary relationship. On this basis, is the five kingdom classification a natural or artificial classification?
2. What are the three methods that protists use to obtain food?
3. Identify three characteristics of protists
4. The following is a list of organisms belonging to various kingdoms: housefly (Musca domestica), maize (Zea mays), Frog (Rana spp), Bat and Eagle.
a. Classify these organisms into their kingdoms
b. Name any two organisms that are not closely related and give a reason.
5. How are fungi different from members of kingdom plantae?
2.4 Economic importance of bacteria
Activity 2.4
“Bacteria are both useful and harmful to humans”. Discuss the validity of the statement.
Bacteria are economically important because they are essential in many beneficial biological and industrial processes. There exist some examples of bacteria that are pathogens as they cause disease and spoilage of food..
2.4.1 Useful bacteria
a. Biotechnology
Bacteria are used in biotechnology and industry. They are used to manufacture products such as ethanol, acetone, organic acid, enzymes, and perfumes. In the chemical industry, bacteria are most important in the production of pharmaceuticals. For example, E. coli is used for commercial preparation of riboflavin and vitamin K.
b. Genetic engineering
Bacteria are used in genetic engineering through the manipulation of genes, also called recombinant DNA technology. In this case, bacterial cells are transformed and used in production of commercially important products for example, production of human insulin used in treatment of diabetes.
c. Decomposition
In addition, bacteria are important in decomposition of dead organisms and animal wastes such as feces to form organic matter. This process improves soil fertility and plays an important role in mineral recycling in an ecosystem.
d. Fibre retting
Some bacteria including Clostridium butyricum are used to separate fibres in a process called retting. In this process, fibres are formed to make ropes and sacks.
e. Nitrogen fixation
Some other bacteria are used to fix nitrogen in form of nitrates into the soil. For example, Rhizobium bacteria which live in root nodules of leguminous plants. Such bacteria help in improvement of soil fertility.
f. Digestion
Some bacteria living in the gut of ruminant animals such as cattle, horses and other herbivores secrete cellulase, an enzyme that helps in the digestion of cellulose of plant cell walls. Another example is Escherichia coli that live in the human large intestine which synthesizes vitamin B and releases it for human use.
g. Biological control
Some bacteria are used as biological agents in biological pest control such as Bacillus thuringiensis (also called BT) instead of pesticides. Because of their specificity to the
host, these bacteria are regarded as environmentally friendly, with little effect on humans, wildlife, pollinators, or other beneficial insects.
2.5 Common bacterial diseases in plants and animals
Activity 2.5
Suppose there is cholera outbreak in your village and the executive secretary invited you to sensitize people about preventive measures against cholera. Prepare a brief presentation for this purpose.
The bacteria that cause diseases are harmful to humans and other animals and are referred to as pathogenic bacteria. The body is a home to many millions of bacteria both useful and harmful to humans.
A bacterial disease is caused by entry of bacteria into a host where theycan grow, flourish then causing harm to the host. Bacteria e diseases include cholera, tuberculosis (TB), typhoid fever, pneumonia, tetanus, and diphtheria, and bacterial meningitis, tooth decay in humans and anthrax in cattle.
Table 2.2. Common bacterial diseases in humans
2.5.1 Common Bacterial Diseases in Plants
The table 2.3 common bacterial diseases in plants
Self-assessment 2.5
Mr. Green lives in one of the slums in a certain city. He prepares and sells chapattis on street. He is usually very clean, but one morning, he is late for work so he does not bother to wash his hands after visiting the toilet. That day he prepares 400 chapattis all of which are sold. Few hours later, his customer Sandra suffered from a disease with the following signs and symptoms: severe diarrhea, excessive loss of water leading to dehydration, and vomiting. Five dayslater, all his customers were rushed and admitted in hospital due to the same problem.
1. Suggest the disease that Mr. Green’s customers were suffering from and what caused the disease
2. Name three ways this disease might be spread around city.
3. After reading this scenario, what message do you have for people who are like Mr. Green?
4. Suppose you were the health officer for the area in town with such a
problem. What steps would you take to prevent the disease from spreading further?
5. House flies are described as vectors. Describe how houseflies transmit diseases to humans.
2.6 Structure and classification of Viruses
Activity 2.6
Discuss the reasons why viruses are not classified in any of the five kingdoms of
living organisms.
Viruses are microorganisms whose structure is only visible with electron microscopes. Viruses are acellular and lack cellular structure. Viruses have none of the features that we traditionally use for classification. They are particles made of proteins and nucleic
acids that are found in all cellular organisms, but show metabolism only once inside the host cell.
When they infect cells, they use biochemical machinery and proteins of the host cell to copy their nucleic acids and to make proteins coats often leading to destruction of the host cells. The energy for these processes is provided by the ATP from the host cell.
2.6.1. Structure of a virus
A typical virus consists of DNA or RNA within a protective protein coat called capsid. The shape of the capsid may vary from one type of virus to another, as shown in Figure 2.5 below.
Some viruses have an envelope of phospholipids and proteins. The envelope is made
from portions of the host’s cell membrane. It surrounds the capsid and helps protect the virus from the host’s immune system. The envelope may also have receptor molecules that can bind with host cells and facilitate the virus to infect the cells.
2.6.2. Characteristics of viruses
An individual virus is called a virion. It is a tiny particle much smaller than a prokaryotic cell. Because viruses do not consist of cells, they also lack cell membranes, cytoplasm, ribosomes, and other cell organelles. Without these structures, they are unable to make proteins or even reproduce on their own.
Instead, they must depend on a host cell to synthesize their proteins and to make copies of themselves. Viruses infect and live inside the cells of living organisms. They are also regarded as parasites since they depend entirely on living cells for their survival. Although viruses are not classified as living things, they share two important traits with living things: They have genetic material, and they can evolve.
2.6.3. Classification of viruses
Viruses can be classified according to:
–– Type of nucleic acid molecules of DNA or RNA, forming the core of the capsid:
Most animal viruses contain RNA while plant viruses contain DNA
–– Type of host cell: plant or animal viruses as they are specific to their hosts
–– Presence or absence of the envelope: Plant viruses’ bacteriophage are nonenveloped
while animal viruses like HIV and influenza virus are enveloped.
2.6.4. Viruses and human disease
When viruses infect cells of their host, they cause disease. Examples of diseases caused by viruses include HIV/AIDS, influenza (flu), chicken pox, and the common cold. The human immunodeficiency viruses that causes AIDS is a retrovirus. Other viral diseases include rabies, measles, diarrheal diseases, hepatitis A, B and C, polio, and cold sores. One-way virus cause disease is by causing host cells to burst open and die. Viruses may also cause disease without killing host cells. They may cause illness by disrupting homeostasis in host cells.
Some viruses live in a dormant state inside the body. The virus that causes chicken pox may infect a young child and causes the short-term disease chicken pox. Then the virus may remain latent in nerve cells within the body for decades. The virus may re-emerge later in life as the disease called shingles, where the virus causes painful skin rashes with blisters. Some viruses can cause cancer. Examples include the human papillomavirus (HPV) causing cancer of the cervix in females. Hepatitis B virus causes cancer of the liver. A viral cancer is likely to develop only after a person has been infected with a virus for many years.
Self-assessment 2.6
1. What is meant by the term virus?
2. State the main components of a virus.
3. Describe the two ways how viruses cause an infection.
4. Differentiate between a bacteriophage and a retrovirus?
5. Do you think viruses should be considered as a form of life? Give reasons for your answer.
2.7 Dichotomous key of identification of organism
Activity 2.7
The figure below represents different types of plant leaves. Make a classification of these plants based on the external structure of the leaves.
The dichotomous key is also referred to as biological identification key. It is made up of a series of contrasting statements called leads indicated by the numbers 1, 2, 3… where each lead deals with a particular observable characteristic. The characteristics used in keys should be readily observable morphological features which may be either qualitative, such as shape of abdomen, nature of legs, or quantitative, such as number of antennae, number of pairs of legs and length of the antennae in case of arthropods. It is essential to note that size and color are often less considered as both can be influenced by the environment, the season, the age or state of the organism at the time of identification.
2.7.1. Guidelines used in construction of a dichotomous key:
The following guidelines must be considered while constructing a dichotomous key.
–– Use morphological characteristics which are observable as much as possible such as leaf venation, nature of margin, apex, lamina and nature or length of the petiole (leaf stalk).
–– Start with a major characteristic that divide the organism or the specimen into two large groups such as the type of a leaf.
–– Select a single characteristic at a time and identify it using a number for
example: simple leaf………go to 2, compound leaf………go to 5. This means that in 2 you will deal with only simple leaves and 5 only compound leaves.
–– Use similar forms of words for two contrasting statements for example at 2:
leaf with parallel venation …………go to G and leaf with network venation ………go to 3.
–– The first statement should always be positive.
–– Avoid generalizations or overlapping variations, be specific and precise to the point.
Example
–– Collect leaves from the following plants: cassava, avocado, jacaranda, cassia, hibiscus bean, maize or paspalum grass,
–– Label different leaves collected as, A, B, C, D, E, F and G
–– Observe and familiarize with the specimens before starting the experiment to minimize errors during the identification process
–– Make a table summarising the specimens and steps followed to identify each
of them.
–– Construct a dichotomous key based on the observable features (characteristics) and table of steps followed.
Solution: The dichotomous key of specimens A, B, C, D, E, F and G.
1. a. Simple leaves ---------------------------------------------------------------------go to 2
b. Compound leaves ---------------------------------------------------------------go to 5
2. a. Parallel venation ------------------------------------------------------------------------G
b. Network venation --------------------------------------------------------------go to 3
3. a.Simple digitate ---------------------------------------------------------------------------A
b. Non simple digitate -------------------------------------------------------------go to 4
4. a. Leaf with serrated margin -------------------------------------------------------------E
b. Leaf with smooth margin -------------------------------------------------------------B
5. a.Leaf with three leaflets (compound trifoliate)-------------------------------------F
b. Leaves with more than three leaflets --------------------------------------go to 6
6. a. Pinnate leaf ------------------------------------------------------------------------------ D
b. Bipinnate leaf --------------------------------------------------------------------------- C
2.7.2. Common features used for identification of animals
Animals are classified based on the following features:
–– Locomotory structures such as legs, wings and fins
–– Antennae (presence, nature and number)
–– Presence or absence of eye and eye type
–– Number of body parts for example insects have three body parts
–– Body segments (nature and number)
–– Body surface structures such as fur, hair, feathers and scales
–– Feeding structures such as mouth parts in arthropods for example in insects
–– Type of skeleton present such as endoskeleton, exoskeleton and hydrostatic
2.7.3. Common features used for identification of plants
Plants can be classified basing on the following features:
–– The leaf structure such as nature of apex, margin, venation, lamina and petiole
–– The flower structure including inflorescence type, flower shape and number of floral parts
–– The type of stem (woody, fleshy and herbaceous), shape (rectangular,
cylindrical) and texture of the stem (smooth, spiny and thorny) …
–– The type of root system, tap root, storage root, fibrous roots… Precaution
–– Care must be taken while collecting and handling some organisms because
some are poisonous, have thorns and others are able to sting
–– Collection of specimen should be done a day or few days before the experiment
depending on nature of the experiment
–– Avoid and try to minimize where possible, uprooting, cutting down or plucking
and pruning of plants as this may threaten the biodiversity as well as result
into environmental degradation
Activity 2.8
Construct and interpret a dichotomous key of arthropods listed below.
–– Collect the following litter arthropods: honey bee, spider, millipede, butterfly,
sugar ant, centipede and mosquito and label each specimen as A, B, C, D, E, F and G respectively
–– Observe and familiarize yourself with the specimens before starting the experiment.
–– Use sharply contrasting external features of collected specimens /diagrams to construct a dichotomous key.
Self-assessment 2.7
Read and interpret the dichotomous tree below and use it to answer the following questions.
1. Specify the phylum of kingdom animalia represented by the above dichotomous tree?
Give one observable reason to support your answer.
2. According to this dichotomous tree, which characteristic feature was used to classify different insects?
3. Which observable characteristic feature distinguishes between a spider and a mosquito?
4. How does a millipede differ from a centipede?
5. To which classes do a millipede and a centipede belong?
6. Which class of arthropods is not represented on the dichotomous tree?
d. Phylum
3. Which one of the following is not a kingdom of living organisms?
a. Monera
b. Animalia
c. Annelida
d. Protoctista
4. Which one of the following is a characteristic feature common to fish, reptiles and birds but absent in mammals?
a. Possession of scales
b. Has no limbs
c. Possession of feathers
d. Undergo internal fertilization
5. Which one of the following statements about fish is not correct?
a. Fish live both in water and on land and undergo external fertilization.
b. Most fish have bones while others are cartilaginous
c. Most fish have streamlined body, lateral line and swim bladder.
d. Gills are organs for gaseous exchange in fish
6 Which one of the following is not a characteristic of all insects?
a. They have three body parts namely head, thorax and abdomen.
b. They have three pairs of jointed legs attached on segment of the thorax.
c. They have four pairs of jointed legs
d. They have a pair of antennae attached on the head.
7. The following are characteristics of all mammals except;
a. They have mammary glands to secrete milk feed their young ones.
b. Their skin is covered with hair.
c. Undergo internal fertilization and internal development of the embryo.
d. They have a pair of wings made up feathers.
8. The point where the leaf joins the stem is called;
a. Apex
b. Margin
c. Leaf base
d. Lamina
e. Length of petiole.
9. Which of the following is less considered while identifying feature to construct
a dichotomous key of leaves?
End of unit assessment 2
1. Which one of the following living organisms belongs to domain bacteria?
a. Euglena
b. Vibrio cholerae
c. Paramecium
d. moulds
2. The group of classification where organisms resemble one another and are
capable of interbreeding together to produce viable offspring is known as:
a. Species
b. kingdom
c. Genus
a. Nature of margin
b. Nature of apex
c. Size and color of leaf
10. The following are characteristics of arachnids except;
a. Four pairs of jointed legs
b. Two body parts
c. Three body parts
d. Do not have wings
11. Match the structures with the organisms which possess them.
12. A group of S4 students drew a Venn diagram below to summarize the five kingdoms into which organisms are classified. Study the diagram and answer the questions that follow:
a. Which kingdoms are represented by the letters x and y?
b. State one characteristic that organisms of x may share with:
i. Prokaryotes
ii. Fungi
iii. Plantae
13. Complete the table to summarize the characteristics of each class of phylum Arthropoda.
14. What is the significance of classification of living organisms?
15. The binomial system of naming a blue monkey, Cercopithecus mitis, is provided below;
Complete the table by filling the missing words.
Scientific names present more advantages than common names.
Activity 2.3
Some viruses have an envelope of phospholipids and proteins. The envelope is made
The dichotomous key is also referred to as biological identification key. It is made up of a series of contrasting statements called leads indicated by the numbers 1, 2, 3… where each lead deals with a particular observable characteristic. The characteristics used in keys should be readily observable morphological features which may be either qualitative, such as shape of abdomen, nature of legs, or quantitative, such as number of antennae, number of pairs of legs and length of the antennae in case of arthropods. It is essential to note that size and color are often less considered as both can be influenced by the environment, the season, the age or state of the organism at the time of identification.2.7.1. Guidelines used in construction of a dichotomous key:
1. Specify the phylum of kingdom animalia represented by the above dichotomous tree?
12. A group of S4 students drew a Venn diagram below to summarize the five kingdoms into which organisms are classified. Study the diagram and answer the questions that follow:
a. Which kingdoms are represented by the letters x and y?
14. What is the significance of classification of living organisms?