1. Exchange in plants
Text p.228

2. Homework
White book p103,104 gas and solute exchange, 108 water flow through plants

3. Objectives Stomata and gas exchange in a leaf Root hairs and function
Transpiration
Factors affecting transpiration

4. There are small openings called stomata in the leaves of a plant.
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5. Stomata
These open to allow gases in and out for photosynthesis and respiration. But at the same time water is lost by evaporation.
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6. Stomata
Label a diagram of a stoma Time allowed… Could show stomata video in lesson folder

7. Lower epidermis
cell
Guard cell
Pore for
gas diffusion
Uneven celulose
cell wall
nucleus
chloroplast
vacuole

8. How do guard cells work?
When the cell is turgid the uneven cellulose cell wall causes it to become curved so it opens the pore
When the cell is flaccid the cell is not curved and the pore closes

9. Stomata are the pores in leaves Function
Open during the day to allow CO2 to enter for photosynthesis
This is not ideal as the plant loses water vapour so they close at night. There is enough oxygen in the air spaces for the plant to respire through the night
Other ways a plant has to minimise water loss are:
waxy cuticle on upper surface of leaves
Wilting (less contact with solar heat so less evaporation)

10. Gas exchange in a leaf
The flattened shape of a leaf, and internal air spaces increase the surface area of the leaves.
Large area for diffusion of carbon dioxide in and oxygen out
For photosynthesis

11. Why are stomata on the underside of leaves?
Less solar radiation
Less wind
Therefore less water loss
Not clogged by dust
Less chance of infection by airborne microbes

12. that most of the water and mineral ions are absorbed by root hair cells

13. Root hairs Label the diagram Ans q2 p229 Cellulose cell wall nucleus
Cell membrane
Label the diagram
Ans q2 p229
cytoplasm
vacuole
Root hair extension to increase
surface area

14. Q2 p229
thin, large surface area, root hairs, short diffusion distance, mitochondria and protein pumps for active transport in their membranes
Large surface area, moist, small distances for diffusion, plants are not as effective in maintaining their concentration gradients, but have plenty of active transport systems to help them out

15. Summary Extension – what is transpiration?
Why can it be described as a necessary evil?

16. Plants take in water through their roots in the soil…
Transpiration
Plants take in water through their roots in the soil…

17. …it moves up through the plant…
Transpiration
…it moves up through the plant…
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18. …..and is lost through the leaves in the transpiration stream.
Corel 178(NT)
…..and is lost through the leaves in the transpiration stream.
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19. Transpiration
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20. Rate of transpiration
When it is hot and dry, photosynthesis and respiration take place quickly. As a result, plants also very quickly lose water.
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21. Graph of bubble movement against time.
Transpiration rate
Graph of bubble movement against time.
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22. The steeper the graph, the faster the transpiration rate!
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23. Which potometer experiment was run in drier air?
Transpiration rate
Which potometer experiment was run in drier air?
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24. The drier the air, the faster the transpiration rate!
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25. Factors affecting transpiration stream write how and why each affects it
Light
Humidity
Wind speed
Temperature

26. Transpiration (sounds like…)
Perspiration (=sweating)
The evaporation of water from the leaves
As water evaporates more is pulled up through the xylem vessels
A plant has to open its stomata to gain carbon dioxide for photosynthesis, but also loses water through transpiration through them
Stomata close at night to prevent water loss by transpiration
When it is hot and dry, photosynthesis and respiration take place quickly. As a result, plants also very quickly lose water.

27. Extension - Adaptations for plants growing in a dry environment
Curled leaves.
Stomata on the curled side only.
Moist air trapped inside the curl.
Thick waxy cuticle.
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28. Adaptations for plants growing in a dry environment
Corel 46(NT)
Marram grass leaves will even uncurl slightly in the wet and curl up more in the dry.
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