In Agricultural practice plants are classified according to their uses as follows :
- Cereal Plant :These are plants rich in carbohydrate they contain low level of protein. Their fruits are one seed small low level of protein. Their fruits are one seed and small. They are known as grains examples are maize, rice, wheat, barley, oath, rye and millet.
- Legumes or Pulses : Plants whose seeds are rich in protein, seed are contained fruits called pod. Fruits are many seeded, examples are bean, ground nut, cow pea, pigeon pea, soya bean, sword bean, Lima bean etc.
- Oil Crops : These are crops that store fats in their seeds is fruits that can yield oil if processed. The oil can be eaten or used in soap making or as fuel or lubricant in industries. Examples are oil palm tree, coconut, melon, ground nut, castor oil etc.
- Root and Tuber Plant : Plants without roots are modified as storage organs, store a lot of carbohydrates food. Root and tuber are underground storage organs of plants. Root crop is cassava. Tuber crops include : yam, potatoes only tubers can be use to propagate the crop.
- Fibre Crops : These crops are grown for their fires. Fires are enough elongated tapering cells which can be use for making ropes, mats and nets. Examples are urena labota, sissal hemp ( Agave ) etc.
- Sugar Crops : These are crops that store their carbohydrate reserves in the form of complex sugar ( Sucrose ). Examples are sugar cane and beet.
- Stimulants and Beverage Crops : These plants produce seeds that processed into beverages which are used as stimulants examples are cocoa, coffee, tea, tobacco etc.
- Latex Crops : These are plants that have milky exudate in their bark and leaves . The latex is tapped, coagulated and used for making rubber examples rubber trees, Allamader,Thevetia, Peruvians, jatropha, cactus. etc.
- Ornamental Plants : The plants have brightly coloured leaves or flowers or produced sweet smelling nectar. They are grown to beautify the dwelling place example Croton, Hibiscus , Allamander, Acalypha etc.
Classification based on Life Span
Flowering plants can be classified into three (3) groups on the basis of their life span. The group are annuals, biennials and perennial. We shall explain them according to their format which they appear.
- ANNUALS: These are crops which complete their life span in one year. Within the one year they grow and develop their vegetative bodies and carry out reproduction and die off. Examples include the maize, yam, ground nut, okro etc.
- BIENNIALS: These are crops that complete their life span in two years of growth. In the first year they developed their vegetative structure and in the second year they develop flowers and carry out reproduction, after which they die. Examples are carrot, cocoyam.
- PERENNIAL: The plants in this group complete their life span in more than two years. They live for many years and they reproduce from year to year until they become old and die. Examples are Oil palm tree, Mango, orange etc.
One of the facts of cell theory states that no new cell are made, additional cells are made from the already existing one through cell division. The already existing one cell divides into two, the two divide into four and the four into eight and so on.
Thus is how the unicellular ones achieve growth and increase in size. Two types of cell division are known. They are mitosis and meiosis. Both divisions occur in four phase of prophase, metaphase, anaphase and telophase. However these four phases are repeated a second time in meiosis. The first division us reduction division in which the chromosome number (2n) is reduced to two haploid cells so that four haploid cells are formed from one diploid cell. In all cell division the nucleus or nuclear materials divide first ( karyokinesis) followed by the division of the cytoplasm ( cytokinesis ).