2013 Unit 2

Question 1

Describe the role of centromere in mitosis

Answer 1

• Holds chromatids together
• Attaches chromatids to spindle
• Allows chromatids to be separated/ move to opposite poles/centromere divides/splits at metaphase/anaphase

Question 2

Homologous chromosomes carry the same genes but they are not genetically identical.
Explain why

Answer 2

• Homologous chromosomes carry

different alleles

Question 3

Other than independent segregation, give one way in which meiosis allows the
production of genetically different cells.

Answer 3

• Crossing over
• Alleles exchanged between chromatids or chromosomes
• Genetic recombination

Question 4

What is a species?

Answer 4

• Groups of similar organisms/organisms with similar features/organisms with the same genes/chromosomes
• That reproduce/produce fertile offspring

Question 5

The forest was cleared to make more land available for agriculture.
After the forest was cleared the species diversity of insects in the area decreased.
Explain why.

Answer 5

• Decrease in a variety of plants/ fewer plant species
• Fewer habitats/niches
• Decrease in variety of food/fewer food sources

Question 6

Explain what is meant by hierarchy.

Answer 6

• Groups within groups

* No overlap between groups

Question 7

Explain what is meant by a phylogenetic group.

Answer 7

• Grouped according to evolutionary links

Question 8

DNA helicase is important in DNA replication. Explain why.

Answer 8

• Separates/unwinds/unzips strands/helix/ breaks hydrogen bonds
• So nucleotides can attach/ strands can act as template

Question 9

Give one way in which antibiotics can prevent the growth of bacteria.

Answer 9

• Prevent cell wall formation/cause cell lysis/inhibit ribosomes/inhibit protein synthesis/prevent DNA replication/affect function of cell membrane

Question 10

Describe how bacteria can become resistant to antibiotics by vertical gene transmission.

Answer 10

• Plasmid/ genes transmitted through cell division/replication/reproduction
• Binary fission

Question 11

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

Answer 11

• Higher affinity/ loads more oxygen
• At low/same/high partial pressure
• Oxygen moves from mother/ to foetus

Question 12

After birth, fetal haemoglobin is replaced with adult haemoglobin. Use the graph to suggest the advantage of this to the baby.

Answer 12

• Low affinity/ oxygen dissociates

* Oxygen to respiring tissue/muscles/cells

Question 13

Suggest how a mutation can lead to the production of a protein that has one amino acid missing.

Answer 13

• Loss of 3 bases/triplet

Question 14

Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome.

Answer 14

• Change in tertiary structure/ active site;

* (So) faulty/non-functional protein /enzyme

Question 15

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves.

Answer 15

• Casparian strip only allows symplast pathway
• Active transport by endodermis
• (Of) ions/salts into xylem
• Lower water potential in xylem / water enters xylem by osmosis
• Evaporation / transpiration (from leaves);
• (Creates) cohesion/ H-bonding between water molecules
• Water molecules bind to xylem;
• (Creates continuous) water column;

Question 16

Abdominal pumping increases the efficiency of gas exchange between the tracheoles
and muscle tissue of the insect. Explain why.

Answer 16

• More air/oxygen enters / air/oxygen enters quickly/quicker;
• (So) maintains/greater diffusion or concentration gradient;

Question 17

Explain how their small size enables gas exchange to be efficient without the need for abdominal pumping.

Answer 17

• Large(r) SA:VOL / short(er) diffusion distance (to tissues);

Question 18

The insect opens its spiracles at a lower frequency in very dry conditions.
Suggest one advantage of this.

Answer 18

• Less/no water lost / (more) water retained;

Question 19

Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles
and muscle tissue. Suggest one reason why.

Answer 19

• Greater surface area exposed to air
• Gases move/diffuse faster in air than through water
• Increases volume/amount of air