Transport in Animals Notes
Edexcel GCSE Biology: Revision notes
Key facts
- Organisms transport oxygen, carbon dioxide, water, dissolved food, mineral ions and urea.
- As organisms grow, their surface area to volume ratio falls.
- Blood contains red blood cells, phagocytes, lymphocytes, plasma and platelets.
- Arteries are thick and muscular; veins have valves; capillaries are one cell thick.
- 1
Arteries
away from the heart
- 2
Capillaries
exchange with tissues
- 3
Veins
back to the heart
Why organisms need transport
Cells need materials delivered and wastes removed.
Organisms must transport oxygen for aerobic respiration, carbon dioxide, water, dissolved food, mineral ions and urea.
Delivered to cells
- Oxygen
- Water
- Dissolved food
- Mineral ions
Removed from cells
- Carbon dioxide
- Urea
Name a waste substance transported from cells for excretion.
Surface area to volume ratio
As an organism grows its surface area to volume ratio falls, so diffusion alone is too slow.
As organisms grow, their surface area to volume ratio decreases. Diffusion alone becomes too slow, so they need exchange surfaces and a transport system.
Worked example
Compare the surface area to volume ratio of a 2 cm cube and a 4 cm cube.
- 1
2 cm cube: surface area = cm², volume = cm³, ratio = .
- 2
4 cm cube: surface area = cm², volume = cm³, ratio = .
As an organism gets larger, what happens to its surface area to volume ratio?
The blood
Blood carries oxygen, defends against infection and clots, in plasma that carries dissolved substances.
Red blood cells carry oxygen with haemoglobin, have no nucleus and are biconcave. Phagocytes engulf pathogens. Lymphocytes produce antibodies. Plasma transports dissolved substances and heat, and platelets help blood clot.
Red blood cells
- Carry oxygen
- Haemoglobin, no nucleus, biconcave
Phagocytes
- Engulf pathogens
Lymphocytes
- Produce antibodies
Plasma and platelets
- Plasma transports dissolved substances and heat
- Platelets help clotting
Which blood component produces antibodies?
Blood vessels
Arteries, veins and capillaries each have a structure suited to their function.
Arteries carry blood away from the heart at high pressure. Veins carry it back at low pressure and have valves. Capillaries are one cell thick for exchange with tissues.
Artery
- Thick, muscular wall
- Narrow lumen
- High pressure, away from heart
Vein
- Thin wall, wide lumen
- Valves
- Low pressure, to heart
Capillary
- One cell thick
- Exchange with tissues
Why do veins have valves?
Try an exam question
A 2 cm cube has a surface area to volume ratio of 3:1 and a 4 cm cube has 1.5:1. Explain why a large organism needs a transport system.
[3 marks]
- [1]Larger organisms have a smaller surface area to volume ratio.
- [1]Diffusion alone is too slow to supply all the cells.
- [1]So they need exchange surfaces and a transport system.
That's the notes covered.
Carry on to the next subtopic.