1. Homework: Study for homeostasis test on Thursday
Title: Plants and tropisms 13th March 2014
Learning question: How do plants use hormones to respond to stimuli?
Homework: Study for homeostasis test on Thursday
Starter:
Key words…
Tropism
Positive phototropism
Negative phototropism
Geotropism
Auxins
gibberellins

2. Tropisms Plants do not move actively from place to place
They do not possess muscle or a nervous system, but they do respond to:
Light (phototropism)
Gravity (geotropism)
Changes in temperature
Contact
These tend to initiate very small changes in growth or direction of growth. This is called tropisms.

3. Responses of different parts of the plant

7. Tropisms A 'tropism' is a growth in response to a stimulus.
Plants grow towards sources of water and light, which they need to survive and grow.
Auxin is a plant hormone produced in the stem tips and roots, which controls the direction of growth.

8. Auxins and phototropism
Auxins are produced at the shoot tips .
They make the cells here elongate.
Causes plants to grow towards a light source

9. Auxins and gravitropism
Auxins in root tips have the opposite effect to those in shoot tips – they stop elongation of cells.
Encourages positive geotropism
Helps roots to anchor the plant in place

10. Seed structure Provides a source of energy for the growing plant
Part of the seed that grows into a new plant
Protects the seed before germination takes place

11. Seed Germination
Germination is the development of the embryo root and shoots into a young plant.
During germination, the food reserves in the seed are used up to provide the energy for the growth of the root and the shoot.

12. Gibberellins
Another plant hormone called gibberellins causes starch stored in seeds to ne broken down into sugars.
Sugar is then used for respiration so that the root and shoots can grow
Gibberellins also stimulate flower and fruit production in some plants

13. Task
Complete questions 1 – 6 on pages in your class book

14. Using plant hormones – Higher tier
Weedkillers
Selective weedkillers kill some plants but not others.
This can be useful for getting rid of dandelions in a lawn without killing the grass
The selective weedkiller contains growth hormone that causes the weeds to grow too quickly.
The weedkiller is absorbed in larger quantities by the weeds than the beneficial plants.

15. Rooting powder
Rooting powder makes stem cuttings quickly develop roots.
Rooting powder contains growth hormones.

16. Controlling fruit ripening
Some hormones slow the ripening of fruits and others speed it up.
These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops.

17. Seedless fruit Some seedless fruit are produced using plant hormones.
The flowers are sprayed with plant hormones that cause fruits to develop but not their seeds
Other plants, like some varieties of grape, have naturally seedless but small fruits. The fruits are sprayed with gibberellins to increase their size

18. Dormancy
Dormancy stops seeds germinating until conditions are ideal for growth.
Hormones can be used to remove the dormancy of a seed so it can germinate at all times of year.
Buds and flowers can also be naturally dormant.
Hormones can also be used to make plants grow bushier, make them flower or control the growth of hedge plants.

19. Task
Complete questions 1 – 6 on pages in your class book