1. Adaptations for Gas Exchange
To Start: A RECAP OF GCSE

2. Today:

3. The Need for an Exchange Surface
All animals must:
Maintain a supply of materials that they need for respiration and growth:
nutrients
oxygen
Remove the waste products of metabolism:
carbon dioxide
ammonium
urea

4. Diffusion as an Exchange Mechanism
The net movement of molecules from an area of high concentration to an area of low concentration.

5. The Need for an Exchange Surface
In small organisms, diffusion across their body surface is sufficient:
distances are short (less than 0.5 mm)
surface area is relatively large.
The body/cell surface acts as the exchange surface.

6. How does size affect diffusion?

7. Surface area sphere = 4πr2
Imagine an animal composed of a ball of cells What is the relationship between size, surface area, volume and SA:V? 2 4 6
Diameter
/ mm  8
Surface area / mm2
Volume
/ mm3
SA:V 10
Surface area sphere = 4πr2
Volume of sphere = 4/3πr3

8. Surface area sphere = 4πr2 Volume of sphere = 4/3πr36
Diameter
/ mm  8
Surface area / mm2
Volume
/ mm3
SA:V 10
12.6
50.3
113.1
201.1
314.2
4.2
33.5
113.1
268.1
523.6
3:1
1.5:1
1:1
0.75:1
0.60:1

10. Write a few sentences to describe the results in your table.
Grade C: Qualitative statement
The bigger/smaller the…. the bigger/the smaller the …...
Grade B: Qualitative statement supported by quantitative data or a description of the correlation.
The bigger/smaller the…. the bigger/the smaller the …, as can be seen with an object with a diameter of ….. having a SA:V of….. compared with…..
Grade A: Qualitative statement supported by a description of the correlation and quantitative data.
The bigger/smaller the…. the bigger/the smaller the …, as can be seen with an object with a diameter of ….. having a SA:V of….. compared with…… This is illustrated by the …………… correlation between ……. and ……….

11. What effect does an increase in size have on the need for a specialist exchange surface in larger animals?
As size increases, volume increases disproportionately compared to surface area.
Demands of cells for nutrients and waste removal also increased disproportionately:
the surface does not increase sufficiently to accommodate these extra demands
must be met by a specialist exchange surface with enhanced surface area.

12. The Need for an Exchange Surface
Large active organisms cannot rely upon their body surface:
surface area relative to volume is insufficient for exchange
distances are too great.

13. Meeting the Demand Thus there is a need for the following:
Specialised exchange surface to meet the demands of high activity levels in multi-cellular organisms
Efficient transport system to deliver materials to and from the exchange surface

14. Examples of adaptations for gas exchange
Calculate the SA:V of: A cube 10x10x10mm A cuboid 1x1x1000mm What do you notice?

15. Examples of adaptations for gas exchange

16. Examples of adaptations for gas exchange

17. General Features of Exchange Surfaces
A large SA:V ratio to increase the rate of exchange to suit the needs of the individual organism (according to its metabolism and size).
Very thin so that diffusion distance is short and materials can cross rapidly.
Partially permeable to allow relevant substances to diffuse through quickly.
Environmental medium is constantly flowing (to maintain a concentration gradient).
Internal medium is constantly flowing (to maintain a concentration gradient).
Often internally located to avoid being damaged (due to being thin and fragile).

18. Comprehension Activity
Read the information on the sheets and answer all of the questions. Finish for homework and bring your answers to the lesson on Wednesday.

19. A GCSE start, A GCSE finish.
Why is it important for the body to maintain blood flow around the body? (2 marks) To maintain a concentration gradient at the lungs and at the cells for oxygen and carbon dioxide. To deliver oxygen to cells for respiration and remove waste for exhalation and excretion.