2. Tropism (Tropic Movement)
A directional growth movement made by a part of a stationary plant response to unilateral stimulus

3. Types of Tropism stimulus tropism response water gravity
unilateral light
geotropism
phototropism
hydrotropism
negative
no response
shoot
positive
root
positive
negative
positive

4. Importance of Geotropism
provide firm anchorage for roots
ensure the plant can get adequate supply of water & mineral salts

5. To show Geotropism in Seedlings
Investigation 17.1
To show Geotropism in Seedlings

6. What has happened to the radicles and plumules ?
in complete darkness P Q R
plumule
radicle
after 2 days
(a) Beginning of experiment
(b) End of experiment
What has happened to the radicles and plumules ?
Ans: The radicles grow downwards, while the plumules grow upwards.

7. Why is it necessary to leave the apparatus in darkness ?
in complete darkness
in complete darkness
plumule
radicle
after 2 days P P Q Q R R
(a) Beginning of experiment
(b) End of experiment
Why is it necessary to leave the apparatus in darkness ?
Ans: To avoid any stimulus from light.

8. Do the radicles show positive geotropism or negative geotropism ?
in complete darkness
in complete darkness
plumule
radicle
after 2 days P P Q Q R R
(a) Beginning of experiment
(b) End of experiment
Do the radicles show positive geotropism or negative geotropism ?
Ans: Positive geotropism.

9. What advantage do the seedlings have by showing such geotropism ?
in complete darkness
in complete darkness
plumule
radicle
after 2 days P P Q Q R R
(a) Beginning of experiment
(b) End of experiment
What advantage do the seedlings have by showing such geotropism ?
Ans: Roots grow downwards deep into the soil to provide a firm anchorage underground and absorb water and mineral salts in the soil.

10. Clinostat for control experiments
contains a cork disc which can be set to rotate in a vertical or horizontal plane by a motor
to make factors uniform (evenly distributed)

11. To show the effect of Gravity by using a Clinostat
Investigation 17.2
To show the effect of Gravity by using a Clinostat

12. What is the purpose of marking the radicles at equal intervals ?
plastic cover lined with moist blotting paper X Y
in complete darkness
seedling in X
seedling in Y
What is the purpose of marking the radicles at equal intervals ?
Ans: To find out which region of the radicle grows faster.

13. plastic cover lined with moist blotting paper
seedling in X X
in complete darkness
seedling in Y Y
Does the direction of growth of the seedlings in clinostats X and Y change ?
Ans: The radicle of the seedlings in clinostat X bends downwards in response to the pull of gravity …

14. plastic cover lined with moist blotting paper
seedling in X X
in complete darkness
seedling in Y Y
Does the direction of growth of the seedlings in clinostats X and Y change ?
Ans: since every side of the radicle of the seedling in clinostat Y is acted on by gravity, the radicle will grow straight horizontally.

15. What is the purpose of setting up clinostat Y ?
plastic cover lined with moist blotting paper
seedling in X X
in complete darkness
seedling in Y Y
What is the purpose of setting up clinostat Y ?
Ans: Serve as a control for comparison.

16. Importance of Phototropism
enables leaves to be in a position to receive as much sunlight as possible for photosynthesis

17. To show Phototropism in Shoots
Investigation 17.3
To show Phototropism in Shoots

18. What has happened to the shoots of plants A, B and C ?
unilateral light
in complete darkness A B C
light-proof box
clinostat
What has happened to the shoots of plants A, B and C ?
Ans: The shoots in pot A respond by growing towards the light source. The shoot in pot B do not show any curvature but grow vertically upwards...

19. What has happened to the shoots of plants A, B and C ?
unilateral light
in complete darkness A B C
light-proof box
clinostat
What has happened to the shoots of plants A, B and C ?
Ans: the shoots in pot C grow vertically upwards with slender and longer nodes, and carries smaller leaves which are yellow in colour.

20. What is the effect of the clinostat on the shoot of plant B ?
unilateral light
in complete darkness A B C
light-proof box
clinostat
What is the effect of the clinostat on the shoot of plant B ?
Ans: The revolving clinostat cancel out the effect of unilateral light on the shoot of plant B.

21. What is the significance of phototropism to plants ?
unilateral light
in complete darkness A B C
light-proof box
clinostat
What is the significance of phototropism to plants ?
Ans: This tropism ensures that a plant gets enough light energy for photosynthesis.

22. Importance of Hydrotropism
ensures that a plant gets enough water as a raw material for photosynthesis & enough mineral salts to maintain normal growth

23. Experiments on Oat Coleoptiles
cut & replaced tip
dark box
decapitated
few days later
no growth
grows
Conclusions :
The tip is responsible for growth

24. Experiments on Oat Coleoptiles
unilateral
light
black covers
few days later
Conclusion :
the tip is the place responsible for bending

25. Experiments on Oat Coleoptiles
dark box
agar plate
few days later
Conclusions :
the head must have produced a diffusible chemical substance which stimulates growth

26. Experiments on Oat Coleoptiles
bending directions
bending directions
mica
plate
Can the explanation still work ?
the tip is put aside
Explanation of results :
The side with the tip has a higher concentration of that particular chemical, the growth rate is faster than the other side

27. Auxins commonest plant hormones
regulate growth & other physiological processes in plants
produced by root tip / shoot tip
they affect the elongation region of the tip

28. Effect on Plant Parts shoot positive growth root Growth of plant low
conc.
auxin
concentration
high
conc.
negative
growth
auxin concentration
plant growth
high conc.
low conc.
shoot
root
positive
no effect
negative
positive

29. Phototropism in Shoot
The shoot tip produces auxins which diffuse downward
The auxins diffuse to the shaded side due to the presence of unilateral light
High auxin concentration stimulates growth in shoot
The shaded side grows faster than the lighted side
The shoot bends towards the light

30. Geotropism in Root
The root tip produces auxins which diffuse to the elongation region
The auxins diffuse to the lower side due to gravity
High auxin concentration inhibits growth in root
The lower side grows slower than the upper side
The root bends downward

31. ~ END ~