BIOLOGY O LEVEL(FORM ONE) NOTES – CLASSIFICATION OF LIVING THINGS

CLASSIFICATION OF LIVING THINGS

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Classification is a grouping of organisms based on their similarities and differences. Organisms that are similar are placed in one group. These similarities could be in terms of ancestry, structure, or the way they carry out life processes such as feeding and reproduction.

Classification is a branch of biology that deals with the grouping of living organisms according to their structure, way of life, and origin.

TAXONOMY

It is a branch of biology that deals with classifying organisms.

TAXONOMIST

A person (biologist) who studies classification.

TAXON

Any named established group in the ranks of classification.

IMPORTANCE OF CLASSIFYING LIVING THINGS

1. There are millions of living things in the world; grouping them makes it easy to study and identify them.
2. Scientific names enable scientists to identify organisms easily, no matter which part of the world they are in.
3. It is easier to study organisms in a group because the members of a group have many things in common.
4. Classification enables scientists to make predictions.
5. It provides an organized system in which newly identified similar organisms can be fitted in the future.
6. It helps man arrange information about living organisms in an orderly manner to avoid confusion.

CLASSIFICATION SYSTEM

There are two main types of biological classification, namely:

1. Artificial classification
2. Natural classification

ARTIFICIAL CLASSIFICATION

Artificial classification system is grouping of organisms according to observable features. For example, presence of legs or wings: bees, birds, and bats would be grouped together because they have wings. Snakes, earthworms, and snails would also be grouped together because they do not have legs.

Artificial classification also involves classifying organisms according to their size, how they move, where they live, or what they eat.

Advantages of artificial classification

• It is straightforward and easy to use.
• It can be done very fast.
• Artificial classification is less costly than natural classification.

Disadvantages of artificial classification

• Some organisms that are dissimilar in their internal makeup are grouped together because of the resemblance of their external features.
• Some similar organisms are put in different groups because they do not have a lot of physical resemblance.
• It is less accurate because it uses only a few observable characteristics.
• Artificial classification depends a lot on what the scientist is interested in; therefore, it varies from person to person.

NATURAL CLASSIFICATION

In this system, classification is based on evolutionary relationships and the presence of a large number of common and similar characteristic features that show homologous and analogous structures.

Homologous structures: Structures having the same origin but performing different functions. For example, forelimbs of a whale and forelimbs of a man.

Analogous structures: Structures having different origins but performing the same function. For example, wings of birds and wings of insects.

Advantages of natural classification

1. It gives a lot of information about living things.
2. It is most accurate.
3. It is universal.
4. It avoids confusion.

Disadvantages of natural classification

1. It requires a lot of time.
2. It needs high skills.
3. It is difficult to classify.
4. It is expensive.
5. It is not stable.

Difference between artificial and natural classification

1. Artificial classification is not accurate, while natural classification is most accurate.
2. Artificial classification is cheap, while natural classification is expensive.
3. Artificial classification classifies living organisms according to external features, while natural classification classifies living organisms according to internal features.
4. Artificial classification does not require scientific skills, while natural classification requires scientific skills and knowledge.

MAJOR GROUPS OF LIVING ORGANISMS

There are five major groups of living organisms:

1. Kingdom Animalia e.g., cow, cockroach
2. Kingdom Plantae e.g., maize, tree, peas
3. Kingdom Monera e.g., bacteria
4. Kingdom Protoctista e.g., amoeba
5. Kingdom Fungi e.g., yeast

RANKS OF CLASSIFICATION

1. Kingdom
2. Phylum or Division
3. Class
4. Order
5. Family
6. Genus

– Kingdom has the greatest variety of organisms.

– At kingdom level, organisms show few features in common. As you move down the ranks, each unit has fewer organisms, and the members of each unit have more features in common.

At the species level, organisms are least varied but share more features. Members of the same species can interbreed and produce viable offspring that can reproduce. Organisms from different species do not usually interbreed because of differences in genetic makeup, physical features, size, and geographical location. However, there are a few exceptions to this rule. Dogs and wolves can interbreed to produce viable offspring.

In the table below, some common organisms have been classified from kingdom to species level. This should guide you in classifying other organisms.

CLASSIFICATION OF SOME COMMON ORGANISMS

KINGDOM

For example, human being and donkey.

Kingdom Animalia is subdivided into phyla (phylum in singular).

Kingdom Plantae is subdivided into divisions. The phyla or divisions are further subdivided into classes; each class is subdivided into orders; every order is subdivided into families; and families are subdivided into genera (genus in singular).

A genus is subdivided into species. Kingdom, phylum, divisions, classes, orders, families, genera, and species are ranks of classification and are called units or taxa.

The following flow chart shows how Kingdom Plantae and Kingdom Animalia are subdivided.

BINOMIAL NOMENCLATURE

Nomenclature is a system of naming organisms whereby every name is made up of two Latin words.

This system is divided into two parts:

The first part of the name represents the genus; it is also called the generic name.

The second part of the name represents the species; it is also called the specific name.

For example: The scientific name of human being is Homo sapiens. Homo is the generic name and sapiens is the specific name. The following rules are observed when writing scientific names:

1. The generic name is written before the specific name.
2. The generic name must start with a capital letter.
3. The specific name is written in small letters.
4. In published documents such as books, scientific names are written in italics, e.g., Zea mays and Homo sapiens. When handwritten or typed, the names should be underlined.

SCIENTIFIC NAMES OF SOME COMMON ORGANISMS

VIRUSES

A virus is an extremely small microorganism.

It is smaller than a living cell. A virus is not a cell.

The study of viruses is called virology.

Different types of viruses:

STRUCTURE OF VIRUSES

A virus has a very simple structure consisting of genetic material with a protein shell. The protein shell is called a capsid. Viruses do not have a nucleus or complex membrane cell organelles. Some viruses have viral envelopes.

There are membranes enclosing the host cell.

Viruses cannot reproduce on their own. They must attack a host cell and use the material in that cell to reproduce.

This is called obligate parasitism.

CHARACTERISTICS OF VIRUSES

• Viruses do not grow, feed, excrete, or respire. Viruses exist in a dormant state when outside a host cell.

They show no signs of life; they can stay that way for months or even years.

• A virus particle outside a host cell is called a virion. The virion attacks and causes diseases.
• Viruses are host-specific, meaning that a certain type of virus only attacks a certain host. For example, some viruses affect only certain types of white blood cells in humans.

Advantages of viruses

– Viruses are important in the study of cellular and molecular biology. They are used by scientists to manipulate and investigate the function of cells.

– 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 milder infection. On recovering from cowpox, the body had antibodies that could resist both cowpox and smallpox.

– Bacteriophages are viruses that attack bacteria; they help in treating bacterial infections and diseases.

Disadvantages of viruses

1. Viruses are pathogens; they cause diseases and infections such as rabies, measles, chickenpox, and polio. They also destroy living cells.
2. They can reproduce very fast, leading to large-scale epidemics.
3. Viruses can mutate often, making them difficult to destroy. For example, there are many different types of viruses that cause the common cold and influenza. This makes it difficult to develop vaccines or cures for these infections.

KINGDOM MONERA

This kingdom consists of bacteria and blue-green bacteria. The scientific study of bacteria is called bacteriology.

CHARACTERISTICS OF BACTERIA

1. They are prokaryotic.
2. They are unicellular; some bacteria stick together to form chains or clusters called colonies.
3. Some are free-living while others are parasites or saprophytes. Free-living bacteria exist on their own, for example in sewage or soil. Parasitic bacteria live on other organisms and get their food from them, for example in humans and animals.

Saprophytic bacteria grow and get their food from dead organic matter.

4. Free-living bacteria have flagella for movement.
5. Bacteria have a slimy outer layer. This layer helps to protect the bacteria.
6. They reproduce either asexually by binary fission or through spores, or sexually through conjugation.
7. Bacteria occur in various shapes.

A bacterium consists of nucleic materials suspended in the cytoplasm (no nucleus).

The cytoplasm is enclosed by a folded cell membrane; a cell wall and slimy layer enclose the cell membrane.

Pathogenic bacteria

These are bacteria that can cause disease. Some of the diseases caused by bacteria are fire blight, ring rot, and tobacco mosaic in plants, and TB, typhoid, tetanus, cholera, syphilis, and gonorrhea in animals.

Fimbriae or pili

These are hair-like structures found on the surface of bacteria. The hairs attach themselves to the host so that they cannot be removed easily. For example, Escherichia coli produce 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 to a site where they can survive.

TOXINS

Some bacteria produce toxin (poisonous) compounds that harm hosts. In humans, these toxins cause effects such as vomiting, diarrhea, fever, and muscle cramps. For instance, toxins released by Salmonella bacteria can cause severe diarrhea.

Invasion and colonization

Some bacteria attack themselves and become resistant to modes of treatment. For example, the bacterium that causes tuberculosis has become resistant to many antibiotics by transforming itself.

RESISTANCE

Some types of bacteria release a substance known as biofilm that protects them from harmful substances such as drugs.

NON-PATHOGENIC BACTERIA

These are bacteria that are harmless even when they are on a plant or animal body.

CHARACTERISTICS OF NON-PATHOGENIC BACTERIA

1. Some non-pathogenic bacteria feed on substances that are harmful to the environment and in the process neutralize them. For example, they neutralize petroleum waste from petroleum industries, disease, and pesticides, thereby making the environment safe.
2. Bacteria such as Rhizobium that are found in the root nodules of leguminous plants, Clostridium, and Azotobacter help to convert atmospheric nitrogen to nitrates. Plants need nitrates for their growth.
3. Bacteria in the stomach of ruminant animals such as goats and cows secrete enzymes that help in the digestion of cellulose, which forms a large part of the diet of ruminants.
4. Bacteria in the animal gut manufacture vitamins K and B.
5. Lactic acid bacteria produce lactic acid as a result of fermentation of carbohydrates. This is important in the production of fermented food and alcoholic drinks.
6. Autotrophic bacteria carry out photosynthesis.

ADVANTAGES OF KINGDOM MONERA

1. Bacteria that neutralize harmful substances help clean the environment.
2. Bacteria found in the gut help animals to digest food and break it down into a form that can be absorbed into the body.
3. Vitamins produced by bacteria are important for the health of animals including humans.
4. Fermentation is used in the production of yoghurt, vinegar, and alcohol.
5. Controlled fermentation is used in curing tea and tobacco and retting of flax, helping to treat and preserve these products.
6. Retting of flax is important in the production of fiber.
7. Some bacteria are used to produce antibiotics which are used to treat bacterial infections.
8. During photosynthesis, autotrophic bacteria release oxygen into the atmosphere. Oxygen is vital for respiration in all living things.

DISADVANTAGES OF KINGDOM MONERA

1. Bacteria cause infections and diseases in animals; some of these are fatal.
2. Bacterial diseases in crops cause decreased production and losses to farmers.
3. Bacteria cause food to decay and spoil.
4. Denitrifying bacteria in the soil convert nitrates to nitrogen. This reduces the nutrients available for plants.

CHARACTERISTICS OF KINGDOM PROTOCTISTA

1. They are eukaryotic.
2. Most are unicellular organisms. Only a few are multicellular.
3. Most live in or near water or in moist places.
4. Some are autotrophic (produce their own food) while others are heterotrophic (obtain nutrients from other organisms).
5. Some are mobile while others are stationary.
6. Some reproduce sexually and others asexually.
7. Many of them have locomotory structures such as cilia and flagella.

PHYLA OF THE KINGDOM PROTOCTISTA

The following table shows some of the phyla of kingdom protoctista.

AMOEBA

Amoeba is a free-living, unicellular organism found at the bottom of ponds and in lichen.

CHARACTERISTICS OF AMOEBA

1. Amoeba has two layers of cytoplasm: the outer layer called ectoplasm and the inner layer called endoplasm.
2. Endoplasm is more fluid and contains granules and vacuoles.
3. Amoeba is aquatic and can be found in fresh water.
4. They use pseudopodia (cell extensions) for locomotion and to engulf food particles.
5. Contractile vacuoles regulate the amount of water in the freshwater amoeba.
6. A temporary food vacuole is formed to hold and digest food particles.
7. Waste products such as urea and ammonia are excreted by simple diffusion.
8. Oxygen and carbon dioxide are exchanged by simple diffusion.
9. Amoeba reproduce by binary fission.

Advantage of Amoeba

Amoeba is commonly used in laboratories to study cell structure and function.

Disadvantage of Amoeba

Amoeba can cause diseases. For example, Entamoeba histolytica causes amoebic dysentery in humans.

PLASMODIUM

Plasmodium is the parasite that causes malaria in humans.

Plasmodium is transmitted by Anopheles mosquitoes and sand flies (vectors), and mammals, birds, and reptiles are hosts.

CHARACTERISTICS OF PLASMODIUM

1. They are unicellular.
2. They are parasitic, with very complex life cycles involving the host and the vector.
3. They reproduce sexually in the vector and asexually when Plasmodium enters the human body. It attacks the red blood cells and the liver.

Effect of Plasmodium

Plasmodium parasites cause malaria, which can lead to inflammation of the spleen, miscarriage, and anemia due to the destruction of red blood cells. Severe malaria can cause death.

EUGLENA

Euglena is characterized by the green scum that appears on stagnant water.

CHARACTERISTICS OF EUGLENA

1. They are unicellular.
2. They are found in both fresh water and salt water.
3. Euglena moves using flagella.
4. Some have chloroplasts for photosynthesis while others are heterotrophs.
5. They reproduce asexually.
6. Some Euglena have a pellicle, a flexible layer within the cell membrane. The pellicle helps Euglena to change shape.

ADVANTAGE OF EUGLENA

Euglena is used to treat sewage because of their unique capacity to change from being autotrophic (when Euglena photosynthesizes and produces oxygen) to heterotrophic (when they use oxygen). This helps to keep oxygen levels balanced in sewage treatment plants.

Euglena, called phytoplankton, are an important source of food for many types of aquatic microorganisms.

Phytoplankton produce large quantities of oxygen during photosynthesis.

DISADVANTAGE OF EUGLENA

Euglena blooms can be harmful to fish; these are sudden increases in the number of microorganisms in the water.

PARAMECIUM

Characteristics of Paramecium

1. They are unicellular and slipper-shaped.
2. Paramecia are heterotrophic.
3. They live in water.
4. They use cilia to move.
5. Their bodies are covered with a pellicle.
6. Food enters the organism through an opening called the oral groove.
7. Paramecia feed on bacteria and microorganisms.
8. They reproduce either sexually or asexually.
9. Contractile vacuoles regulate the amount of water in the cytoplasm.

Advantage of Paramecia

Paramecia are eaten by small water animals.

Disadvantage of Paramecia

Balantidium coli is a type of paramecium that causes disease.

It invades and destroys the living things’ intestines, causing a disease called balantidiasis.