1.

Fish have gills to carry out gaseous exchange.
a) How are the gills of a fish adapted to carry out gas exchange efficiently?
b) Explain why countercurrent flow is important for a fish to absorb oxygen.

2.

A group of students carry out an experiment on the rate of transpiration in a plant.
a) Complete the table below with a cross in the right column to show how the rate of transpiration would be affected by each factor.

b) What role does transpiration play in transporting water from the roots to the leaves?

3.

The circulatory system is composed of blood vessels.

a) Name two structural differences between veins and arteries.

i. __________________________________________
ii. __________________________________________

b) Explain the role of the capillaries within the lymph system.

c) Name two functions of the circulatory system.

i. __________________________________________

ii. __________________________________________

ANSWERS

1.

a) Answers include:
i. The lamellae give them a large surface area which increases the rate of diffusion
ii. They’re composed of a thin epithelium do the distance of diffusion is short
iii. The water and the fish’s blood flow in opposite directions (countercurrent) which ensures a concentration gradient is maintained
iv. Their blood circulation increases that blood saturated with oxygen is continuously replaced
b)
i. If the blood and water flowed in the same direction then the first blood to come into contact with the water would take up the oxygen quickly as the concentration gradient would be high. However, as the water moved along the lamellae the concentration would decrease because the blood flowing with the water would take up more and more oxygen until there was no concentration gradient left for the oxygen to move across. The blood, however, would only be able to be 50% saturated.With countercurrent flow the blood can reach at least 80% saturation: the blood is able to move through the lamellae and continue to absorb oxygen as it does because a concentration gradient it maintained.

2.
a)

b) Transpiration is the process by which water leaves the leaves via the stomata. As the water escapes the hydrostatic pressure at the top of the plant drops and the pressure difference between the top and bottom of the plant sucks the water up.

3.
a) Answers include:
i. Arteries consists of thick walls made of elastic fibres while veins have thinner walls with less elastic fibres
ii. Veins contain valves
iii. Arteries have a smaller lumen than veins
b) Capillaries play an important function in regards to tissue fluid. Tissue fluid is the substance formed when water along with a few white blood cells and other dissolved substance diffuse through the capillaries. Some of the tissue fluid flows back into the capillaries and end up in the lymphatic vessels where it becomes lymph.
c) Answers include:
i. transport
ii. defence
iii. homeostasis
iv. lymph and tissue fluid production