Summary questions

Question 1

Describe the function of a circulatory system (3 marks)

Answer 1

1 Transports metabolic waste from cells into excretory organs
1 transports material made in one place to another where it’s needed
1 Transports products for metabolism e.g. oxygen, food molecules to cells

Question 2

Explain why circulatory systems are found in multicellular organisms but not unicellular organisms (2 marks)

Answer 2

2 Unicellular organisms have large SA : V ratio so diffusion distance is small and metabolic demands are
low so diffusion can supply and remove substances quickly and efficiently enough

2 Multicellular organisms have small SA : V ratio, so long diffusion distances. Metabolic demands are high – diffusion alone can no longer supply all needs quickly and efficiently enough

Question 3

Compare open and closed circulatory systems (6 marks)

Answer 3

Similarities:
1 liquid transport medium
1 vessels to transport the medium
1 pumping mechanism to move transport fluid around system

Differences:
1 open has few vessels; closed has transport medium (blood) enclosed in vessels
1 in open transport medium is pumped into body cavity (haemocoel) under low pressure; in closed
heart pumps blood around body under pressure

Comparisons
1 In open, transport medium is in direct contact
with body cells; in closed transport medium has no direct contact with body cells
1 In open, transport medium returns to heart through open ended vessel; in closed blood flows relatively fast and returns to heart all within vessels

Question 4

Land predators such as foxes have double closed circulatory systems. Aquatic predators such as pike are effective with single closed circulatory systems. Explain why these 2 predators have different circulatory systems. (6 marks)

Answer 4

Land predators
top land predators hunt so need ability to move in fast bursts (1); they grow large
and maintain own body temperature (1); need to support body against gravity (1); they may be
pregnant and so have to support needs of growing fetus as well as own body needs (1) (max 3
marks) high metabolic rate (1); they need a very efficient circulatory system supply. Double circulatory
system supplies blood to lungs to be oxygenated and then returns it to heart to be pumped around
body (1); so tissues receive a high level of oxygen and high levels of carbon dioxide
can be removed. (1).

Aquatic predators
such as pike need to hunt so also need efficient circulatory system (1); their single
system less efficient than a double system (1); but bony fish have operculum so continuous flow of
water over gills to oxygenate blood (1); countercurrent flow allows efficient oxygen uptake (1); they do
not maintain their own body temperature and are supported by water (1); so demands of tissues much
lower than those of an animal like a fox (1); so single circulation is adequate to supply their needs.