AQA A Level Bio 2.4 Immune System Part III

U. marinum cells ingest bacteria and digest them in the cytoplasm. Describe the role of one named organelle in digesting these bacteria. (3)

Lysosomes (1)
fuse with vesicle/phagosome (1)

(Releases) Hydrolytic enzymes/lysozymes (1)

Read the following passage.

Kidney cells produce a glycoprotein hormone called erythropoietin (EPO). An EPO molecule contains 165 amino acids and approximately 50% of its mass is carbohydrate.

EPO is transported in the blood and stimulates the bone marrow to produce red blood cells. In this way, enough red blood cells are produced to maintain the blood’s oxygen-carrying capacity.

Some athletes choose to increase their blood EPO concentration by injecting synthetic EPO. This practice is called blood boosting and is banned in sport as

a form of drug abuse. Athletics’ authorities use a programme of drug testing to detect athletes who have injected EPO. In this programme, an ELISA test is performed on urine samples to measure the concentration of EPO in the athlete.

Two types of monoclonal antibody are used in this ELISA test:

• anti-human EPO antibody, prepared by injecting human EPO into mice

• anti-mouse antibody, prepared by injecting anti-human EPO antibody into

goats. An enzyme is attached to the anti-mouse antibody.

Use the information in the passage and your own knowledge to answer the following

questions. Describe the roles of anti-human EPO antibody and anti-mouse antibody with enzyme attached (lines 14−16) in producing a positive result for EPO in the ELISA test. (3)

(Anti-human EPO antibody) attaches/binds to EPO/antigen (in plastic well) (1)

(Anti-mouse antibody) attaches/binds to anti-human antibody (1)

Substrate is added, enzyme causes colour change/product (is positive result) (1)

The protein ZO-1 is found on the surface of ileum cells. A scientist used an anti-ZO-1 monoclonal antibody to identify ileum cells in a sample of intestine observed using an optical microscope. Suggest how the monoclonal antibody helped the scientist to identify ileum cells in the sample of intestine. (3)

Antibody is complementary (to ZO-1) (1)

(so) binds/attaches to the ZO-1/protein (1)

(cells identified with) dye/stain/fluorescent marker linked to antibody (1)

A student investigated the effect of two antimicrobial substances, J and K, on the growth of E. coli bacteria. She transferred E. coli cells using a sterilised pipette to make three identical cultures, 1, 2, and 3. She then added:

• no antimicrobial substance to culture 1

• antimicrobial substance J to culture 2

• antimicrobial substance K to culture 3.

She incubated the cultures for 24 hours, after which she determined the number of cells per mm³ in each culture.

After 24 hours, the student compared the number of cells per mm3 in cultures 1, 2 and 3. She found:

• substance J killed 80% of the cells

• substance J killed twice as many cells as substance K. Using the axes shown in Figure 9, sketch a bar chart showing the results the student obtained from cultures 1, 2 and 3. Do not draw a grid on the chart. Do not include figures for the number of cells per mm³ (3)

(3)