CE Biology-A Summary

Part 4-Development of Organism & Continuity of Life 

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Section 4  Development of organisms and continuity of life

Reproduction

Asexual reproduction is the production of offspring without gamete formation and fusion. Only one parent is involved.

1.      Binary fission-an organism divides in to two equal halves, e.g. amoeba.

2.      Budding-a small outgrowth (bud) of a cell is separated to form another cell, e.g. yeast.

3.      Spore formation-a spore is a nucleus surrounded by a small piece of cytoplasm. Lower plants, e.g. bread moulds, usually use this method.

4.      Vegetable propagation-it is the production of offspring from the vegetative parts of an angiosperm, i.e. roots stems and leaves, e.g. rhizomes, corm, bulb and tuber.

The use of artificial propagation

Many plants have the ability to regenerate from damaged parts. This is employed in the production of new plants by artificial methods such as:

1.      Stem cutting, e.g. Coleus

2.      Leaf cutting, e.g. African Violet

Sexual reproduction involves the formation and fusion of gametes of two different sexes.

In flowering plants

Pollination

1.      Transfer of male gametes in plant is achieved by pollination, which is the transfer of pollen grains (a carrier of male gamete) to stigma.

2.      Transfer of pollens by wind is called wind pollination.

3.      Transfer of pollens by insects is called insect pollination.

Fertilization is the fusion of gametes of different sexes. In flowering plants, the following steps are involved:

1.      Formation of pollen tube by pollens in the sugary solution on the stigma;

2.      Male gametes are carried inside the pollen tube through the style towards the ovules inside the ovary;

3.      The male gamete enters the ovules to fuse with the female gamete to form a zygote.

Seeds and fruits

After fertilization

Fruits ¡V protect and disperse the seeds

Seeds ¡V provide food and protection for the embryo; help in dispersal of the plant

Adaptation of fruits (seed)

Importance of seed and fruit dispersal to survival of plants

1)      It reduces overcrowdings and competition for limited resources.

2)      It increases the chance for the seed to land a suitable place for germination, hence enable plants to colonize new area.

Water, oxygen and suitable temperature are required for germination.

Growth and development

Growth is the permanent increase in size of an organism. It is a process involving cell division and cell enlargement.

Cell division in plant: it occurs in the region where meristems are present, e.g. tip of root and shoots.

Activities occur in cells in:

1)      The region of cell division - the cells divide mitotically to produce new cells.

2)      The region of cell elongation - the cells enlarge by taking in water.

3)      The region of differentiation - the cells become specialized for performing different function.

Cell division in animal: it occurs in all parts of the body of animal

#In humans, the zygote grows by repeated mitotic division to from the embryo and then the foetus. Tissues, organs and system are gradually developed before birth.

Growth of an organism can be detected by

Development results from differentiation of cells into differentiation in to different cell types forming tissues, organs and system.

The process of forming specialized cells to perform different functions is called differentiation.