- When an animal cell Eg: red blood cell, is placed in water which is less concentrated than the solution within the red blood cell, water enters the cell by osmosis. This causes the cell to swell and burst because there is no animal cell to prevent the outside pressure.
- Crenation: When a red blood cell is placed in a solution which is stronger ( Eg: salt solution) than that inside the cell, the cell looses water by osmosis. It shrinks and wrinkles and looks spiky. This is called Crenation.
- ACTIVE TRANSPORT
Active transport is:
- The selective movement of substances across a living membrane
- It is usually from a region of lower concentration to a region of higher concentration.
- It involves the use of energy in form of ATP provided by respiration in the mitochondria.
- Cells that carry out active transport usually have lot of mitochondria, hence a high concentration of ATP.
- Active transport helps liver cells to accumulate glucose molecules from blood plasma.
DIFFERENCES BETWEEN ACTIVE TRANSPORT AND DIFFUSION
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DIFFUSION
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ACTIVE TRANSPORT
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Not selective
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Selective (cell absorbs only what is needed)
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Substances move only from a region of high concentration o that of low concentration
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Substances move in even from a region of low concentration to that of high concentration
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Living membrane is not needed
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Living membrane is needed
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Energy is not used
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Energy is used
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- FACILITATED TRANSPORT OR FACILITATED DIFFUSION
- It is the transport of molecules and ions across a membrane by specific carriers in the direction of lower concentration of those molecules.
- It is a passive process and it saturates if all carriers are in use.
CEREALS
Cereals belong to the family Garminae and are monocots. They are produce grains. Eg: Wheat, corn, rice, maize, millet, barley.
Storage and Prevention
Corn cob or maize is usually store in dry places. Dry grains prevent the development of pests. Eg: weevils. Large quantity storage needs chemicals. Eg: Atelic acid. Common diseases of corn include: corn smut and rust.
Corn smut is caused by a fungus; it attacks the leaves, stem and cob. Most of these diseases can be prevented by practicing crop rotation, destroying the infected crops and by using fungicides.
Economic Importance of Cereals
- Cereals are used as food for man and other animals.
- Dry cereals can be milled to prepare pap and flour for puff ball.
- They serve as a source of income.
- Cereals cultivation is a source of employment.
