1. The principles of
exchange
and
transport

2. diffusion and surface area
Understand the relationship between an organism’s size and its surface area to volume ratio
activity
diffusion and surface area
Froggy page 52

3. and it affects the rate of exchange of materials at exchange surfaces
surface area
is the total number of cells in direct contact with the surrounding environment
and it affects the rate of exchange of materials at exchange surfaces

4. and it influences the demand for metabolites.
volume
is the total three-dimensional space occupied by metabolically active tissues
and it influences the demand for metabolites.

5. surface area influences of metabolites to tissues
the rate of supply
of metabolites to tissues
As an organism’s size increases its surface area increases less than its volume as many cells are not in direct contact with the surrounding environment.

6. have a small surface area to volume ratio
large animals
have a small surface area to volume ratio
small animals
have a large surface area to volume ratio

7. exchange surfaces are adpated by passive and active methods
to maximise exchange
by passive and active methods
This includes having
methods of increasing surface area
thin separating surface
concentration gradients

8. Look at the following examples and discuss how each is adapted for exchange.

9. Root hair cell
Leaf
Alveoli
Erythrocytes
Capillaries

10. leaf mesophyll root hairs capillaries erythrocytes alveoli
Explain how the following exchange surfaces are adapted to maximise exchange.
Include:
Function
Adaptation
Diagram
leaf mesophyll
root hairs
capillaries
erythrocytes
alveoli

11. Main site of photosynthesis
Mesophyll
Main site of photosynthesis
Palisade mesophyll
tall & thin
arranged end on
less cell wall for light to cross
large volume to contain chloroplasts
Spongy mesophyll
Lots air spaces
Allow diffusion CO2 to palisade cells
As cell PS they use CO2, maintaining a high concentration gradient for CO2 uptake

12. Root hair cell Uptake water by osmosis
Uptake mineral ions by active transport
Long thin cytoplasmic extension creates large surface area to volume ratio

13. Capillaries Site of gas and nutrient exchange with all cells in body
Walls one cell thick, reduces diffusion distance
Cells flattened (squamous / pavement epithelium)

14. Erythrocytes Biconcave shape maximises SA:Vol for exchange oxygen
No nucleus to maximise volume to carry haemoglobin

16. Alveoli Site of gas exchange in lungs
Walls one cell thick, reduces diffusion distance
Squamous epithelial cells
Breathing movements maintain concentration gradients
Carbon dioxide conc always higher in blood
Oxygen conc always higher in alveolus

17. The principle of mass flow
ANIMALS
Animals need a constant supply of oxygen and nutrients.
And they need to get rid of waste products such as carbon dioxide.
Simple animals, such as sea anemones, flatworms and nematodes can do this by diffusion across their moist body surfaces, because they have a really large SA:VOL ratio.

18. But in larger animals diffusion is too slow to supply all the body cells efficiently.
They need a transport system to carry oxygen, nutrient, carbon dioxide, waste products and hormones to and from the special exchange surfaces.
Our respiratory system carries oxygen rich air to the exchange surfaces in the lungs and removes carbon dioxide laden air from the body.
Our own circulatory system transports large volumes of fluid to all parts of our bodies.
This is an example of a mass flow system.

19. PLANTS
Carbon dioxide is able to diffuse into the leaves from the atmosphere through the stomata.
Water and mineral nutrients have to reach the leaves from the roots and photosynthetic products, such as sugars and amino acids, need to be transported away from the leaves to maintain concentration gradients.
In simple organisms, such as algae, these processes take place by diffusion.

20. But in complex, multicellular plants, a mass flow system is needed.
There are two such systems:-
Xylem tissue – which transports water and mineral salts up the xylem from the roots to the leaves.
Phloem tissue – transports the materials made in photosynthesis to all other parts of the plants.