BY2 Jan 2013

Question 1

What term is used to describe a common structure but different functions?

Answer 1

Homologous

Question 2

What term is used to describe common functions but different structures?

Answer 2

Analogous

Question 3

Describe 3 properties that all respiratory surfaces must posses and explain why they must have them.

Answer 3

Thin-small diffusion distance
Large surface area-large contact with air for gas exchange
Moist-allow gases to dissolve

Question 4

Give two reasons why gills do not function effectively on land.

Answer 4

Unable able to remain moist.

They collapse.

Question 5

Define counter-current flow and explain why it makes gas exchange more efficient.

Answer 5

Blood flows across gill in opposite direction to water.
Diffusion gradient maintained across whole surface/equilibrium is never reached.
A greater concentration of O2 in the blood is achieved.

Question 6

Name the tissue strengthened with lignin.

Answer 6

Xylem

Question 7

Name the tissue which has sieve tubes.

Answer 7

Phloem

Question 8

State the function of sieve tube cells.

Answer 8

Translocation of products of photosynthesis e.g. sucrose

Question 9

State the function of companion cells.

Answer 9

Carry out respiration to supply sieve cells with ATP for active transport.

Question 10

Name and describe the 3 pathways by which water moves across the root cortex.

Answer 10

Vacuolar pathway-from vacuole to vacuole of adjacent cells.
Apoplast pathway-via cell walls.
Symplast pathway-via cytoplasm.

Question 11

How does the Casparian strip affect the route water takes into the stele?

Answer 11

Makes water pass through the symplast pathway, preventing it going through the apoplast pathway.

Question 12

State why having an exoskeleton is a problem for growth and explain how it is overcome.

Answer 12

Exoskeleton is rigid/doesn’t grow.
They shed the exoskeleton.
Then grow a new one, vulnerable whilst hardening.

Question 13

Describe two features of an amniote egg.

Answer 13

Protective hard shell.

Embryo within yolk sac.

Question 14

Give 3 advantages of internal development I embryos over external development.

Answer 14

The young are retained for a longer time in the mother’s womb.
The embryo is nourished there from the placenta.
Protection from predators.
Young are born in a relatively advanced state of development.

Question 15

Explain the advantage of the position of the curve for human foetal haemoglobin.

Answer 15

Foetal haemoglobin has greater affinity for oxygen than adult.
Reaches saturation at lower pp.
This ensures oxygen moves from mother’s blood to foetus.

Question 16

What would happen to the curve for adult haemoglobin if the pp of CO2 increased and name this effect.

Answer 16

The curve would move right.

Name of effect is Bohr shift.

Question 17

Explain the mechanism (Bohr shift) and the significance of this during exercise.

Answer 17

Muscles give off more CO2 in exercise.
CO2 dissolves to make carbonic acid, lowering the pH.
Reduces affinity of haemoglobin for O2, O2 dissociates more readily.
More O2 is released as added demand when muscles need it.

Question 18

Define the term parasite.

Answer 18

Organisms that live on or in another organism (the host) obtaining nourishment at the expense of the host, causing harm to the host.

Question 19

Identify and explain two structures that allow the tapeworm survive in the gut of a human.

Answer 19

Hooks and suckers-attach the worm to the wall of the gut, worm doesn’t get moved along, resisting peristalsis, preventing worm being egested.

Question 20

State why the adult tape worm doesn’t need a digestive system and explain how it’s tape like structure enables it to feed without a mouth or gut.

Answer 20

It lives surrounded by food that has been broken down by host’s digestive system.
It is very long-gives a large surface area to absorb digested food.
It is thin- short distance for diffusion.

Question 21

Describe how the tapeworm’s reproductive strategy helps to ensure it’s survival.

Answer 21

It lays large number of eggs.
Eggs can resist adverse conditions.
Hermaphroditism-tapeworm has both male and female reproductive systems, no need for mate to reproduce.

Question 22

Describe how the sequence of events that takes place during the cardiac cycle is initiated and controlled.

Answer 22

Heart muscle is myogenic, it can contract without any nerve stimulation.
The stimulus to contract originates from the sinoatrial node(SAN).
SAN acts as pacemaker.
It is situated in the wall of the RA.
Electrical impulse from SAN causes the two atria to contract.
Thin layer of connective tissue prevents the stimulus spreading to ventricles.
At bottom of wall separating the two atria is the atrioventricular node(AVN).
This delays impulse before passing on.
Impulse spreads down Bundle of His.
Conveyed upwards along Purkinje.
Causing a wave of ventricular contraction starting from bottom up.
SAN stimulated by various factors to change its pacing.
E.g. hormones (adrenalin)

Question 23

Define the term species.

Answer 23

A group of organisms that can interbreed to produce fertile offspring