Topic 2 Cell membrane past paper questions

Question 1

State what is meant by osmosis

Answer 1

• diffusion of water molecules down a water potential gradient through a
  partially permeable membrane

Question 2

Compare and contrast exocytosis and endocytosis (4)

Answer 2

both used to transport large particles
both involve phospholipid membrane vesicles.
Exocytosis is export and endocytosis is import of material

Question 3

Explain how oxygen molecules can pass directly through the cell membrane

Answer 3

oxygen is small
oxygen is non-polar it can therefore pass between gaps in cell membrane

Question 4

State what is meant by gene

Answer 4

sequence of bases of DNA that code for a polypeptide.

Question 5

Describe how the two strands of DNA forming the double helix in a gene are held together.

Answer 5

complementary bases it enables the formation of two hydrogen bonds between adenine and thymine

Question 6

Explain why each codon for the DNA genetic code must contain at least three bases.

Answer 6

enough codons needed for 20 different amino
acids
four bases are used in the genetic code
triplet code provides enough

Question 7

Explain how human lungs are adapted for rapid gas exchange. (4)

Answer 7

many small alveoli to provide a large surface area to increase the rate of diffusion
thin epithelium to increase rate of diffusion.
good supply to maintain diffusion gradient.

Question 8

State what is meant by the term allele. (1)

Answer 8

a version of a gene

Question 9

Explain how this mutation results in a non-functioning CFTR protein. (4)

Answer 9

there will be different sequence of R groups
therefore the CFTR protein has a different tertiary structure.
because of different types of bonds between the R groups.
therefore the movement of chloride ions through the cell membrane is affected.

Question 10

Explain why people with cystic fibrosis may develop lung infections. (4)

Answer 10

produces very thick sticky mucus because of reduced water transport from cells.
cilia lining airways are unable to move mucus therefore micro-organism get trapped in the mucus.

Question 11

Describe the roles of RNA in the synthesis of collagen (5)

Answer 11

• an mRNA molecule codes for each of the polypeptide chains in collagen.
• mRNA carries a copy of the genetic code for collagen out of the nucleus to ribosome.
• each tRNA carries its own specific amino acid to the ribosome.
• anticodon on tRNA binds to codons on the mRNA.
• tRNA holds the amino acid in place while peptide bonds form.

Question 12

Explain how the primary structure of collagen determines its properties. (4)

Answer 12

• insoluble because there are hundreds of amino acids
• insoluble because there are many hydrophobic R groups
• strong because of the triple helix
• therefore there are many repeating amino acid sequences

Question 13

Explain why only five amino acids are coded by this sequence of bases (2)

Answer 13

because three bases form one code for one amino acids.
because there is no stop codon in this sequence.

Question 14

Explain why some amino acids such as alanine, have more than one genetic code. (3)

Answer 14

• because it’s a degenerate code which means they are more codes than needed.
• arranging the four bases in triplets gives 64 possible
  combinations and there are 20 amino acids to code for and stop codons.
  minimises the effect on mutations.

Question 15

Explain the role of the other three genetic codes. (2)

Answer 15

• remaining codes are stop codons on RNA.
• therefore no more amino acids can be added to the
  polypeptide chain.

Question 16

State what is meant by the term semi-conservative replication? (2)

Answer 16

• an increase in the number of DNA molecules
• each new molecule consists of one parent strand and one new strand.

Question 17

Name one enzyme involved in semi-conservative replication. (1)

Answer 17

DNA polymerase

Question 18

Explain the importance of semi-conservative replication in the production of new cells. (1)

Answer 18

because it results in genetically identical daughter cells. They will have the same structure as the parent cell.

Question 19

Compare and contrast the structure of messenger RNA (mRNA) with the structure of transfer RNA (tRNA).

Answer 19

both contain RNA nucleotides
both are single stranded
mRNA is a straight chain and tRNA is folded
size of mRNA is variable and the size of tRNA is constant.

Question 20

Describe the effects of cholesterol and temperature on membrane permeability, as shown in the graph

Answer 20

As the cholesterol increases the membrane permeability decreases
As temperature increases the membrane permeability increases.
cholesterol has a greater effect on membrane permeability at high temperatures.

Question 21

Describe the effects of cholesterol and temperature on membrane permeability, as shown in the graph

Answer 21

As the cholesterol increases the membrane permeability decreases
As temperature increases the membrane permeability increases.
cholesterol has a greater effect on membrane permeability at high temperatures.

Question 22

Explain why cholesterol and temperature affect membrane permeability

Answer 22

because an increase in temperature increases the movement of phospholipids
because the cholesterol decreases the fluidity of the membrane

Question 23

Explain which of the four bases P, Q, R or S is adenine?

Answer 23

R because it forms hydrogen bonds
R because it has a large base.

Question 24

Suggest two reasons why prenatal testing for brittle bone disease is not offered to all pregnant women.

Answer 24

1. they may not be a family history to this condition
2. cost being high.

Question 25

Explain what is meant by the term gene mutation.

Answer 25

a change in base sequence of DNA coding for a particular polypeptide.

Question 26

Compare endocytosis with exocytosis. (2)

Answer 26

both involve the formation of a vesicle.
endocytosis takes substances into the cell and exocytosis removes substances from the cell.
both need energy.

Question 27

Suggest two reasons why a change in one amino acid in prothrombin may have no effect on the blood clotting process. (2)

Answer 27

Prothrombin has different primary sequence of amino acids.
change in tertiary structure of prothrombin.

Question 28

Describe the role of RNA molecule in the synthesis of a protein using this section of DNA as a template.

Answer 28

complementary mRNA strand is formed.
mRNA moves into the cytoplasm.
mRNA associates with ribosomes.

Question 29

Describe the process of DNA replication.

Answer 29

DNA molecule unwinds
DNA mononucleotides line up alongside both DNA strands by complementary base pairing.
Hydrogen bonds forming between DNA bases.
Formation of phosphodiester bonds between adjacent DNA mononucleotides.

Question 30

Explain the roles of RNA in translation.

Answer 30

mRNA is a copy of the genetic code

mRNA carries a genetic information to the ribosomes.

tRNA carries a specific amino acid.

tRNA holds the amino acids in place while the peptide bond form.

Question 31

State what is meant by the term enzyme

Answer 31

biological catalysts

Question 32

Explain why it is necessary to measure the initial rate of reaction when investigating the effect of substrate concentration on enzyme activity

Answer 32

as the reaction proceeeds the substrate is used up.
therefore substrate limits the rate of the reaction and substrate becomes the limiting factor.