Cell Function & Inheritance

Cell membranes, cellular response and viruses.

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1. The plasma surrounding a cell is composed of protein and phospholipid molecules. The are thought to be arranged in a fluid model.
2. The bilayer of molecules provides the cell with a stable boundary. The molecules vary in function. Some give support, some contain to allow passive transport of small molecules, others act as and actively transport molecules into or out of the cell.
3. The membranes surrounding cell have the same basic structure as the plasma membrane.
4. A constant environment is maintained within a cell by the membrane acting as a barrier and regulating the entry and of materials.
5. Small molecules may enter or leave the cell by moving passively by (or osmosis) along a concentration from high to low concentration.
6. Molecules or ions enter or leave a cell by being transported across the membrane a concentration gradient from low to high concentration. This requires .
7. Endocytosis is the process by which the cell membrane relatively large particles in a vesicle. is the process by which a vesicle formed in the cell fuses with the membrane and expels its contents to the exterior.
8. Immunity to disease-causing organisms can be innate or acquired. immunity is inborn; immunity is gained during the person's lifetime.
9. is a type of innate immunity by which cells such as engulf bacteria and destroy them using enzymes in .
10. Antibody production is a type of acquired immunity. It is the response made by cells called to the presence in the body of alien molecules called . An possesses receptor sites which bind to one particular type of antigen and render it harmless.
11. B-lymphocytes produce free () antibodies to deal with antigens; T-lymphocytes employ direct contact ( response) to destroy cells infected with antigens.
12. Natural is acquired by a person who suffers and survives a disease by producing appropriate antibodies. Some B- and T-lymphocytes remain as cells. immunity is gained by a person receiving antibodies made by another person or animal.
13. Active immunity is gained by a person's system responding to an antigen and producing its own antibodies; immunity is gained by a person receiving antibodies made by another person or animal.
14. An over-reaction to a harmless substance by the immune system is called an reaction.
15. Each person's cells have an antigen which is recognised by the immune system as 'self'. This normally guarantees the cell's safety. However under exceptional circumstances, occurs and the immune system attacks 'self' cells.
16. Viruses are very tiny micro-organisms which are unusual in that is the only true characteristic of living things that they exhibit.
17. A virus consists of DNA or surrounded by a coat of protein. It depends on the host cell for energy and building materials.
18. Once inside the host cell, a virus alters the cell's biochemistry, enabling mass of viral nucleic acid to occur. Many copies of the virus are produced and released by of the host cell.
19. Some viral diseases can be prevented using vaccines containing virus to induce immunity.
20. Human Immunodeficiency Virus disrupts the immune system by slowly destroying T cells. Attempts to produce a vaccine have so far failed.