Ch 1 Cell Structure And Organisation 6i3c5n

Cell Structure and Organisation Characteristics of all living things All living organisms have certain common characteristics 1. Movement: This is more obvious in animals; in plants movements take place mainly inside cells. 2. Feeding: Food is needed for growth and carrying out daily activities; animals feed in quite different ways from plants. 3. Respiration: It is the giving out of energy from food; the energy is used for movement, growth, reproduction, etc. 4. Excretion: This is the process by which poisonous waste substances are removed from the body of animals. Plants, however, change waste substances into something harmless. 5. Growth: Increase in size, weight and development all contribute to the growth of an organism. 6. Reproduction: It is the production of a new generation of offspring. 7. Irritability: This is the sensitivity to any changes in the environment (light, sound, touch, temperature, etc) Cells Cells are units of living substance which can only be seen under high magnification and they consist of jelly-like substance called protoplasm. The basic features of cells are: a) Nucleus: A round or oval body which contains a number of threadlike chromosomes. These chromosomes contain materials inherited from the parents. Nuclei are important in cell division and in controlling the cells’ life processes.

b) Cytoplasm: Greylish jelly-like living substance which contains the nucleus and many specialized structures called organelles. Numerous chemical reactions take place in the cytoplasm. The following structures are important organelles found within the cytoplasm. i.

Mitochondria

These are small rod-shaped structures that control the release of energy within the cell. ii.

Ribosomes

They are tiny structures concerned with the manufacture of proteins and are found along a network of tubules called endoplasmic reticulum. iii.

Centrioles

They are a pair of tiny structures found near the nucleus. These play a part in cell division but are absent in higher plants. iv.

Golgi apparatus

It consists of stacks of flattened membranous sacs and vesticles involved in secretions. c) Cell or plasma membrane: A thin, delicate and protective structure surrounding the cell. It is selectively permeable. It controls the age of substances into and out of the cell.

1) Cell Wall

2) Chlorophyll 3) Vacuoles

4) Centrioles 5) Food storage

6) Method of feeding

7) Movements

8) Scheme of growth

9) Sensitivity

Typical animal Absent in animal cell.

Typical plant A rigid cell wall often composed of cellulose that surrounds the cell and s the plant. Absent in animal cell. Green pigments found in the green parts of plants Usually absent, but if present, Usually large and few in are small and numerous. number. Contain watery fluid called cell sap. Present in animal cells Absent in cells of higher plants. Excess glucose is stored as Excess glucose is stored as glycogen granules in the body starch, or sometimes as oil or cells, particularly in the liver. complex sugar, in the Fat is stored beneath the skin cytoplasm or the cells of roots, (also keeps body warm) and stems or leaves. around internal organs. Heterotrophic – feeding on Autotrophic – making its own ready-made organic food. organic food by utilizing the sun’s radiant energy to build complex organic substances from carbon dioxide and water by photosynthesis. Most animals possess organs Plants do not possess any of locomotion organ of locomotion. The only visible movements are growth movements, eg. Shoots growing towards light, etc. Usually stops growing at a Usually continue to grow certain age, but repair and throughout life. renewal of cells continue throughout life. Usually has well-developed Any response made to any sense organs and nervous external stimuli is usually a system to react immediately to growth response. any stimuli, eg. Light, smell, etc.