Plant Biology Revision Notes

1. What is the difference between the response brought about in plants by growth regulators versus the nervous system in humans?

1. The response brought about by chemicals is slower whilst the nervous system response is faster
2. The response brought about by chemicals is long acting whilst in the nervous system it is short-lived.

2. What are the similarities between type of response brought about by auxins and hormonal responses in humans?

The response is slow, long-lasting and chemical in nature

3. What are the two roles of water in the process of germination?

1. Activate enzymes
2. Soften testa

4. What are two possible food stores in seeds?

1. Cotyledon
2. Endosperm

5. What are the uses of growth regulators in horticulture/agriculture?

1. Herbicide
2. Rooting powder
3. Fruit ripening
4. Tissue culturing (micropropagation)
5. Seedless / larger fruit.

6. What is a seed?

A fertilised ovule

7. What are mechanisms by which plants protect themselves from adverse external environments?

1. Thorns (prevent the plant from being eaten)
2. Thick cuticles in their leaves (prevent water loss)
3. Poisons (produced at the edge of leaf to kill anything that tries to eat the leaf.)

8. What are the chemical ways plants protect themselves?

Plants produce heat shock proteins, which form at temperatures around 40°C and surround enzymes to protect them from heat damage.

9. Why is there more transpiration from the lower epidermis of a leaf than the upper?

There is more stomata on the lower surface

10. Why is the rate of transpiration lower at night?

1. Stomata are closed in the absence of light, reducing gas exchange and limiting water loss. (Less $CO₂$ uptake for photosynthesis.)
2. Lower temperatures result in reduced evaporation, and the plant does not need to lose water to cool down.

11. Under what conditions do cells become turgid?

Cells become turgid when placed in a hypotonic solution, where water enters the cell by osmosis, causing it to swell and become firm.

12. What is a possible reason for plants wilting?

More water is being lost through transpiration than is being replaced.

13. Can animal cells become turgid?

No. Animal cells lack a cell wall, so they cannot become turgid. If excess water enters by osmosis, the plasma membrane stretches and may eventually burst

14. What is the function of airspace in a leaf?

Greater surface area for gaseous exchange.

15. Why is support from turgor pressure not required by animals?

Animals have a skeleton.

16. How do plants control the rate of transpiration?

1. Waxy cuticle – Reduces water loss by creating a waterproof barrier on the leaf surface.
2. Action of stomata – Stomata open and close to control water loss and gas exchange.
3. Location of stomata – Stomata are often found on the lower leaf surface, where they are less exposed to direct sunlight, reducing water loss.