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Transport in Animals
Large multicellular organisms cannot rely on diffusion to move substances
around. They need a transport system. Key reasons:
Size = cells inside large organisms are far from its surface; diffusion
pathway is increased. Diffusion is too slow to supply all requirements.
Outer layer uses supplies, so less reaches inner cells.
SA:V ratio = smaller animals have larger SA:V ratio. They have enough
body area for exchange to occur.
Metabolic rate = larger organisms have higher metabolic rates. They
require more substances and produce lots of waste. Diffusion alone won’t
be sufficient.
Metabolism = all chemical reactions that happen within a cell.
Features of a good transport system:
A fluid or medium to carry nutrients, oxygen and waste around the body
(blood)
A pump to create pressure that pushes fluid (heart)
Exchange surfaces that enable substances to enter/leave the blood
(capillaries)
Circulatory systems
Closed circulatory systems can be single or double. Complex organisms tend to
have double.
Single = blood travels from heart to organs and back to heart in 1 circuit
Double = blood travels from heart to exchange surface, back to heart and then
to organs
Single circulatory system, e.g. a fish
Blood pressure reduces as blood flows through gill capillaries – slows down
flow to rest of body. Limits rate of delivery of oxygen and nutrients, and
removal of waste.
Efficient for fish activity, but not mammals. Fish don’t need to maintain body
temperature – they respire less than mammals.
Advantages:
Less energy used (some organisms don’t maintain body temperature)
Disadvantages:
Low blood pressure limits substance delivery and removal
, Double circulatory system, e.g. mammals
More efficient than single. Heart composed of 2 pumps. Right pumps to lungs
and left pumps to body at high pressure.
This is necessary due to the higher level of activity (energy) and to maintain
body temperature.
Also need to deliver and remove materials from cells rapidly – high blood
pressure.
Advantages:
More efficient, especially for organisms with faster metabolism
Higher blood pressure maintains steep concentration gradients (faster
diffusion)
Blood must be lower pressure at lungs to avoid damage – pumped to
body after
Disadvantages:
More energy used so must respire more
Open circulatory systems, e.g. insects
Insect blood is called haemolymph. Flows freely through body cavity and makes
direct contact with organs and tissues. Does NOT carry oxygen.
Few little pumps (hearts) push the haemolymph through the single blood
vessel that runs along the back side, in one direction, to the haemocoel.
When heart relaxes, haemolymph blood is sucked back via pores called ostia.
Haemolymph moves around the haemocoel due to movement of the organism.
Advantages:
Less energy used for distribution
Suitable for smaller, less active organisms
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