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

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

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

To show Geotropism in Seedlings Investigation 17.1 To show Geotropism in Seedlings

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.

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.

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.

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.

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)

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

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.

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 …

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.

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.

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

To show Phototropism in Shoots Investigation 17.3 To show Phototropism in Shoots

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...

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.

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.

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.

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

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

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

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

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

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

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

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

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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