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A directional growth movement made by a part of a stationary plant response to unilateral stimulus.

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Presentation on theme: "A directional growth movement made by a part of a stationary plant response to unilateral stimulus."— Presentation transcript:

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3 A directional growth movement made by a part of a stationary plant response to unilateral stimulus

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

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

6 To show Geotropism in Seedlings

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

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

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

10 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. in complete darkness P Q R P Q R plumule radicle after 2 days (a) Beginning of experiment (b) End of experiment

11 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)

12 To show the effect of Gravity by using a Clinostat

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

14 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 … plastic cover lined with moist blotting paper X Y in complete darkness seedling in X seedling in Y

15 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. plastic cover lined with moist blotting paper X Y in complete darkness seedling in X seedling in Y

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

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

18 To show Phototropism in Shoots

19 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... unilateral light in complete darkness ABC light-proof box clinostat

20 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. unilateral light in complete darkness ABC light-proof box clinostat

21 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. unilateral light in complete darkness ABC light-proof box clinostat

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

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

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

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

26 few days later dark box agar plate Conclusions : the head must have produced a diffusible chemical substance which stimulates growth

27 Experiments on Oat Coleoptiles bending directions 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 the tip is put aside bending directions mica plate Can the explanation still work ?

28 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

29 Effect on Plant Parts positive growth negative growth root shoot auxin concentration Growth of plant high conc.low conc. auxin concentration plant growth shoot root positiveno effect negativepositive high conc. low conc.

30 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

31 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

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