1.1 Circulation Flashcards
1.1 Understand why many animals have a heart and circulation (mass transport to overcome limitations of diffusion in meeting the requirements of organisms).
1
Q
Why do we have a heart and circulatory system?
A
- to move substances around the body
- large organisms have a small SA:vol ratio so cannot rely on diffusion
- this is because the diffusion distance is too great, and so diffusion would be too slow (diffusion is not efficient enough to meet all the requirements of all cells)
- therefore we rely on mass transport systems that move substances efficently by mass flow
2
Q
Why can single celled organisms rely on diffusion?
A
- the SA:vol ratio is big
- the diffusion distance is short, so the rate of diffusion is quick
- therefore diffusion is efficient enough to meet all the needs of the cell
3
Q
What needs to be delivered to cells?
A
glucose and oxygen for aerobic respiration, which releases energy
4
Q
What is mass transport?
A
- the bulk movement of gases or liquids in one direction, usually via a system of vessels and tubes
- there is movement in one direction only because of the difference in pressure in the blood vessels
5
Q
What are mass transport systems used for?
A
- to carry substances from specialised exchange organs to the body cells
- to remove metabolic waste
6
Q
What are open circulatory systems? How do they work?
A
- blood circulates in large open spaces
- the heart pumps blood into the cavities around organs and diffusion of substances occurs
- blood is drawn back into the heart as it relaxes
7
Q
What are closed circulatory systems? How do they work?
A
- blood is enclosed in tubes
- blood leaves the heart at high pressures
- blood travels along the arteries, then the arterioles, then the capillaries
- diffusion occurs
- blood travels along the venules, then the veins back to the heart
- blood returns to heart at low pressures
8
Q
What are single and double circulatory systems?
A
- single: blood flows through the heart once for each complete circuit
- double: blood flows through the heart twice for each complete circuit
9
Q
What are the advantages of double circulatory systems?
A
- the heart gives the blood returning to the lungs an extra boost
- so it takes less time to circulate around the body
- this increases the rate of gas exchange in cells, to meet the demands of organisms with a high metabolic rate (e.g. mammals and birds)
