transport and immunity

Question 1

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Answer 1

The fluid mosaic model of the cell surface membrane is know as this because a) the individual phospholipid molecules can move relative to each other making the membrane fluid and b) the proteins embedded in the membrane are varied in shape and size, creating a mosaic.

Question 2

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Answer 2

Diffusion is the net movement of molecules from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.

Question 3

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Answer 3

Facilitated diffusion is a passive process that involve molecules moving down a concentration gradient through protein channel or carrier proteins.

Question 4

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Answer 4

Protein channels allow facilitate diffusion of ions whereas carrier proteins transport molecules such as glucose. in both cases the protein changes shape but this does not require ATP.

Question 5

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Answer 5

Water will move by osmosis from a region of higher (less negative) water potential to a region of lower (more negative) water potential.

Question 6

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Answer 6

Addition of a diluted to pure water lowers the water potential.

Question 7

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Answer 7

In co-transport, sodium ions are actively transported out of the epithelial cells of the ileum so that there is a higher concentration of sodium ions in the lumen than the epithelial cells.

Question 8

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Answer 8

In co-transport, sodium ions diffuse from the linen into the epithelial cells of the ileum through co-transport proteins and carry either amino acids or glucose molecules with them.

Question 9

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Answer 9

When a phagocyte engulfs a pathogen it forms a vesicle around the pathogen known as a phagosome.

Question 10

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Answer 10

lysosomes fuse with the phagosome and release lysozymes which hydrolyse the pathogen.

Question 11

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Answer 11

After phagocytosis the phagocyte presents the pathogen antigen on its cell surface membrane.

Question 12

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Answer 12

Activated T-helper cells have four roles 1) Develop into memory cells 2) Stimulate phagocytosis 3) Stimulate B cells to divide and secrete antibodies 4) Activate Cytotoxic T cells.

Question 13

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Answer 13

Cytotoxic T-cells cause infected body cells to die by secreting a protein called perforin which makes holes in the cell surface membrane.

Question 14

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Answer 14

Antibodies are made of four polypeptide chains; two heavy chains and two light chains.

Question 15

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Answer 15

Antibodies have a constant region, a variable region and an antigen binding site.

Question 16

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Answer 16

Home pregnancy tests use monoclonal antibodies that bind to the hCG protein in pregnant women’s urine.

Question 17

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Answer 17

Some people have ethical concerns over the use of monoclonal antibodies as their production involves inducing cancer in mice.

Question 18

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Answer 18

Some pathogens such as the common cold show high levels of antigenic variability and so we do not become immune to them.

Question 19

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Answer 19

The HIV virus is a retrovirus and the enzymes reverse transcriptase converts its RNA into DNA before inserting this into the hosts DNA for transcription and translation.

Question 20

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Answer 20

HIV can be tested for using the ELISA test which involves antibodies attaching to the HIV antigens, these antibodies then attach to further enzyme carrying antibodies; the enzyme turns a colourless substrate coloured.