Classification is defined as the arrangement of living things into groups based on structural, genetic, and cellular organization.  This is called TAXONOMY. The system of classification of living things used today is based on that introduced by the Swedish naturalist Carl Von Linne(1707-1778). His name was better known in Latin as Carolus Linnaeus. He published the classification of plants in 1753 and that of animals in 1758.

Living things are first separated into a large group called a KINGDOM. The division of the kingdom smaller group called PHYLA (PHYLUM). The term division rather than phylum is usually used for plants. Phyla are divided into smaller groups called CLASSES. Each class is further divided into ORDER. Orders are further divided into smaller units called FAMILIES. Families are again divided into GENERA (genius). A genius is broken into SPECIES. A species is a population of related organisms that can interbreed within themselves to produce fertile offspring. Genius is a group of closely related species. A family is a group of genera. An Order is a group of related families. A class is a group of related objects. A phylum is a group of related classes. A kingdom is a group of related phyla.

Living things, according to the modern classification system, which is based on physiology, biochemistry, and embryology, are classified into five kingdoms: MONERA, PROTOCTISTA, FUNGI, PLANTAE, AND ANIMALIA.

MONERA (Characteristics.    They lack organized DNA, i.e., the Deoxyribonucleic acid (DNA) is scattered in the cytoplasm and not in the nucleus; hence, they are called prokaryotes.

• They have no mitochondria in their cytoplasm
• Their cell walls lack cellulose; their cell wall is made up of protein and fatty materials
• They are microscopic, single-celled organisms
• Some are motile while some are non-motile
• They feed both autotrophically and heterotrophically. Blue-green bacterium & blue-green algae
• vii. They reproduce only by asexual means.

KINGDOM PROTOCYSTA (Characteristics)

• They have well-organized DNA in the nucleus bounded by the nuclear membrane; hence, they are called eukaryotes
• They are single-celled organisms or unicellular organisms
• Some are motile while some are non-motile
• They live in water, damp soil, leaf litter, and other terrestrial habitats that have sufficient moisture.
• All protists use mitochondria for cellular respiration
• They form cysts to survive adverse conditions
• They all reproduce both sexually and asexually. Examples are Amoeba, Euglena, Chlamydomonas, and Plasmodium.
• Examples of Monera are:  bacteria and photosynthetic blue-green bacteria, also known as blue-green algae.

KINGDOM FUNGI (Characteristics)

1. They all feed heterotrophically because they lack chlorophyll and therefore cannot photosynthesize.
2. They are simple multicellular organisms that grow like plants but are not plants because they are not green in colour.
3. Their bodies are not divided into true roots, stems, and leaves
4. They are mostly non-motile organisms composed of thread-like multinucleate hyphae collectively known as mycelium
5. They reproduce using spores. Spores are unicellular microscopic structures that are capable of germinating to a new organism.
6. The fungi store carbohydrate as glycogen, just like animals, not as starch as done by plants
7. Their cell wall is made up of chitin and not cellulose like plants
8. Examples are Mucor, Rhizopus, Mushroom and Slime mould.

KINGDOM PLANTAE (Characteristic)

1. They are multicellular and non-motile organisms
2. Their cells are bounded by rigid cellulose cell walls external to the cell membrane
3. They contain chlorophyll that enables them to manufacture their food by photosynthesis
4. Most plants store carbohydrates as starch or sucrose.

Classification Of Kingdom Plantae Based On Botanical Classification

The kingdom Plantae is divided into four main phyla or divisions

(i)  Thallophyta (algae)

–  They are simple microscopic plants

– They have no true root, stem, or leaves

– They are found in an aquatic habitat

-They are autotrophic plants, i.e., they can synthesize their food

– They reproduce both by asexual means and sexual means

– They have a cellulose cell wall

 Many of them are pigmented, such as red, blue, and brown in addition to chlorophyll.

– Some are filamentous (algae), and the cells are not differentiated into tissue

(ii)  Bryophyte (Moss and liverwort)

– They are non-vascular multicellular plants

– They have chlorophyll as the only photosynthetic pigment

– They are terrestrial but grow in a moist environment

– Their body is differentiated into stem-like and leaf-like structure, but no true root, stem, and leaves

– They have no vascular tissue; therefore, they are unable to transport food and material around the body

– They reproduce asexually using spores, while sexual reproduction by gametes and it takes place in water

– They exhibit what is called alternation of generations.

iii Division Pteridophyta (ferns)

– Their body is divided into the true root, stem, and leaves

– They have well-developed vascular bundles comprising of xylem and phloem

– The underground stem is rhizome

– They reproduce by means of spores

– They need water of sexual reproduction which is by gametes formation

– The plants are mostly terrestrial while few are aquatic

– They exhibit alternation of generations

– They  have an asexual reproductive organ called sori, while the sexual reproductive organ is heart-shaped, called prothallus

iv) SPERMATOPHYTA

– They are seed-bearing plants

– They have well-developed vascular bundles

– They are well-adapted to terrestrial habitats and they are the most successful land plants

The Spermatophyta are divided into two:

(a)         Division Gymnospermatophyta or Coniferophyta

– They are large plants with well-developed vascular bundles with true roots, stems, and leaves

– Their leaves are green in colour, small, and needle-like

–  Their naked seeds are born in a cone because there is no ovary and no fruit

(b)        Division Angiospermatophyta

– They possess true flowers for sexual reproduction

– They have well-developed true root, stem and leaves

– They have well-developed vascular bundles

– Seeds and fruits are produced after fertilization, and the seed are enclosed within the ovary

– They are terrestrial, but some are aquatic

            The Angiospermatophyta is divided into two classes

1. Monocotylenoneae (Monocot)
2. Dicotyledoneae (Dicot)

Classification Of Plants Based On Agriculture

Agricultural classification is the grouping of plants according to the product for which they are cultivated or grown

1. CEREALS OR GRAIN CROPS: These are crops which are cultivated for their grain. They have high starch content. Examples are maize, guinea corn, millet, wheat, ryes, barley and oats.
2. LEGIUMOUS PLANT OR POD: These are important plants which contain high protein content. They are source of nitrate in the soil. Examples are groundnut, beans, melon, flamboyant, crotalaria e.t.c.

iii.        ROOT CROPS: These are plant which are tuberous and are specialized for food storage. They are good source of carbohydrate. Examples are sweet potatoes, irish potatoes, yam, cassava and carrot  iv. VEGETABLE CROPS: These are herbaceous plant which are important constituents of a diet. They serve as source of vitamins and mineral salts. Examples are tomatoes, pepper, onions, cabbage, lettuce, okra and vegetables.

1. FRUITS: These are plants that are grown for production of fruits\. Fruits are rich sources of vitamin A, C and minerals. They are usually eaten in their natural form (raw). They include mangoes, pawpaw, guava, bananas, and pineapple e.t.c.
2. CASH CROP (ECONOMIC CROP): These are crops grown mainly for the purpose of money making. They include oil producing plant e.g. oil palm, latex crop e.g. rubber, fibre crop e.g. cotton, beverage and drug plants e.g. cocoa and spices.

vii.       OIL PLANTS: These are plants that produce oil as food reserve and store it in their fruit or seeds. Example are palm oil fruit and kernel, seed of melon, cotton seed, groundnut, coconut and shea butter.

viii.      FIBRE CROPS: These are crops that \are grown for their fibres that are used for making clotting, ropes, sacks e.t.c.

1. BEVERAGES AND DRUG PLANT: These are crops that produce non-alcoholic beverages e.g. cocoa, coffee.
2. QUININE: is a drug that is obtained from the bark of cinchona spp. It is an anti-malaria drug extracted from plant.
3. SPICES: These are vegetables plants that are used to add flavour and taste to modern dishes. Examples are ginger, cloves, pepper, vanilla, nutmeg.

            Classification of Plant based on life cycle

1. ANNUAL: These are plants that have one growing season. They produce seeds during the first year of growing and then die off. Examples are maize, Guinea corn, wheat, groundnut, bean e.t.c
2. BIENNIALS: These are plants that grow for two seasons. The first year constitutes the vegetable stage during which the store of food material is built up and seeds are produced in the second year e.g. cabbage, carrot, cocoyam, cassava e.t.c.
3. PERENNIALS: These are plants that grow for three or more seasons or years e.g. shrub and three.

Relevance of Biology to Agriculture

Agriculture is defined as an act of growing crops and rearing farm animals to provide man’s basic need for (i)         Food       (ii) Shelter       (iii) Clothing        (iv) Materials for industrial purposes