cells exam-style qs

Question 1

explain why it is not possible to determine the identity of the structures labelled X using an optical microscope [2]

Answer 1

• resolution is too low
• because wavelength of light it too long

Question 2

describe the role of one named organelle in digesting (these) bacteria [3]

Answer 2

• lysosomes
• fuse with vesicle
• to release hydrolytic enzymes

Question 3

describe how a sample of chloroplasts could be isolated from leaves [4]

Answer 3

• break open cells and filter
• in ice cold isotonic buffer solution
• centrifuge to remove nuclei
• centrifuge at higher speed so nuclei settle out

Question 4

outline the role of organelles in the production, transport and release of proteins from eukaryotic cells [4]

Answer 4

• DNA in the nucleus is code for protein
• ribosomes / rough endoplasmic reticulum produce protein
• mitochondria produce ATP for protein synthesis
• golgi apparatus packages and modifies
• vesicles transport
• vesicles fuse with cell-surface membrane

Question 5

explain how the body responds to a cold and suggest why you can get a cold again [5]

Answer 5

• you will complete the primary immune response after first exposure to cold virus
• producing specific memory T/B lymphocytes
• secondary immune response is only possible if re-exposed to same strain with same virus
• there are multiple strains of cold virus
• these strains all have different antigens
• more likely to encounter strain with different antigen, requiring new primary immune response

Question 6

2 changes to the structure of the cell-surface membrane that would increase the rate at which glucose is transported into the cell

Answer 6

1. increase SA with microvilli
2. more proteins with pores that span the PLB

Question 7

explain why glucose does not easily pass through the PLB [2]

Answer 7

• only lipid-soluble substances diffuse across the PLB easily
• water-soluble substances (like glucose) diffuse only very slowly

Question 8

explain why reabsorption of glucose into the blood in the kidneys occurs by active transport rather than by diffusion [2]

Answer 8

• diffusion, at best, can only reabsorb 50% of the glucose lost from the blood
  > the other 50% will be lost from the body
• active transport can absorb all of the glucose, leaving none to be lost from the body

Question 9

how can rate of movement across membranes be increased? [3]

Answer 9

• increase SA
• increase concentration gradient
• increase density of protein channels

Question 10

why does the body’s immune system take a number of days to control the pathogen after it has entered? [1]

Answer 10

lymphocytes that will finally control the pathogen need to build up their numbers and this takes time

Question 11

why would it be inaccurate to say that the body takes days to ‘respond’ to the pathogen? [1]

Answer 11

the body ‘responds’ to the pathogen immediately; the delay is in building up the numbers of lymphocytes and therefore controlling the pathogen

Question 12

suggest why lysozymes are also found in tears [3]

Answer 12

• the protective covering of the eye, especially the tear ducts, are potential entry points for pathogens
• the eyes are vulnerable to infection because the coverings are thin to allow light through
• lysozymes will break down the cell walls of any bacterial pathogens and so destroy them before they can cause harm

Question 13

suggest why antibodies made of proteins, rather than carbohydrates or fats, are more likely to be effective against a wider range of diseases [2]

Answer 13

• there must be a massive variety of antibodies as each responds to a different antigen, of which there are millions
• only proteins have the diversity of molecular structure to produce millions of different types