THE TYPES OF MOVEMENT OBSERVED IN PLANTS NEXT

TROPISM (TROPIC MOVEMENT) A directional growth movement made by a part of a stationary plant response to unilateral stimulus. The dictionary defines tropism as an orientation of an organism to an external stimuli. There are numerous types of tropisms : Hydrotropism Phototropism Geotropism Chemotropism Thigmotropism Heliotropism Thermotropism And many more……….. (These are the 3 main types of tropism and these would broadly discussed accordingly.) NEXT

TYPES OF TROPISM Stimulus Tropism Response Water Gravity Unilateral light Geotropism Phototropism Hydrotropism Negative No response Shoot Positive Root Positive Negative Positive NEXT

It is the growth of an organism away from the centre of the earth. GEOTROPISM Geotropism is the growth of a living organism in response to gravity. There are two types of geotropisms. They are: Positive geotropism Negative geotropism Negative Geotropism Positive Geotropism It is the growth of an organism (i.e. plants) towards the centre of the earth. Negative Geotropism It is the growth of an organism away from the centre of the earth. Positive Geotropism An example of geotropism is given in the picture. NEXT

IMPORTANCE OF GEOTROPISM Provides firm anchorage for roots. Ensure the plant can get adequate supply of water & mineral salts. NEXT

PHOTOTROPISM The growth response of a living organism on response to light direction is called phototropism. Like geotropism even phototropism is of 2 types: 1. Positive 2. Negative Positive Phototropism In positive phototropism living organism grow towards the light. For example- Stems are positively phototrophic. Negative Phototropism In negative phototropism living organisms grow away from the light. For example- Roots are negatively phototrophic. NEXT

IMPORTANCE OF PHOTOTROPISM Phototropism enables leaves to be in a position to receive as much sunlight as possible for photosynthesis. NEXT

HYDROTROPISM Hydrotropism is the growth of a living organism in response to water. Hydrotropism is the directed growth of the root in relation to the gradient in moisture. It begins in the root cap with the sensing of moisture. Growing away from water (Negative Hydrotropism) Both positive and negative hydrotropism exist in living organisms and its direction of growth depends upon a stimulus or gradient in water concentration. Growing towards water (Positive Hydrotropism) NEXT

IMPORTANCE OF HYDROTROPISM Ensures that a plant gets enough water as a raw material for photosynthesis & enough mineral salts to maintain normal growth NEXT

Let’s start the experiment Experiment Number 1 To show Geotropism in Seedlings Let’s start the experiment

Why is it necessary to leave the apparatus in darkness ? In complete darkness In complete darkness Plumule Radicle After 2 days P P Q R Q R (a) Beginning of experiment (b) End of experiment Why is it necessary to leave the apparatus in darkness ? Answer: To avoid any stimulus from light.

In complete darkness In complete darkness Plumule Radicle After 2 days P P Q R Q R (a) Beginning of experiment (b) End of experiment Do the radicles show positive geotropism or negative geotropism? Answer: 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 R Q R (a) Beginning of experiment (b) End of experiment What advantage do the seedlings have by showing such geotropism ? Answer: Roots grow downwards deep into the soil to provide a firm anchorage underground and absorb water and mineral salts in the soil.

To show the effect of Gravity by using a Clinostat Want to know what a clinostat is ? CLICK HERE EXPERIMENT NUMBER 2 To show the effect of Gravity by using a Clinostat

Clinostat Used for controlling experiments Let’s go back to the experiment. Clinostat Used for controlling experiments Contains a cork disc which can be set to rotate in a vertical or horizontal plane by a motor Used to make factors uniform (evenly distributed).

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 ? Answer: 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 Does the direction of growth of the seedlings in clinostats X and Y change ? Answer: The radicle of the seedlings in clinostat X bends downwards in response to the pull of gravity 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 X Y in complete darkness seedling in X seedling in Y What is the purpose of setting up clinostat Y ? Ans: Serve as a control for comparison.

To show Phototropism in Shoots EXPERIMENT NUMBER 3 To show Phototropism in Shoots Let’s start the experiment

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 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 ? Answer: 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 ? Answer: This tropism ensures that a plant gets enough light energy for photosynthesis.

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

SOME OTHER TYPES OF TROPISM NEXT

THIGMOTROPISM Thigmotropism is the growth of a living organism in response to a touch/contact. As in all tropisms there exist positive and negative thigmotropism. Positive thigmotropism is where a living organism grows and clings to a wall or a fence. Negative thigmotropism is the opposite. It is where a living organism grows away from a touching object. NEXT

HELIOTROPISM Heliotropism is quite similar to phototropism. Now, as we know that phototropism is the response of a living organism in response to light but heliotropism is the diurnal motion of the plant flowers or leaves in response to the direction of the sun. The most famous examples of heliotropism is the sunflower. Heliotropism was first described by Leonardo Da Vinci. NEXT

THERMOTROPISM Thermotropism is the tendency of plants or other organisms to bend toward or away from heat. s the movement of a plant or plant part in response to changes in temperature. A common example is the curling of Rhododendron leaves in response to cold temperatures. Thermotropism is often called thermotropic movement . NEXT

Chemotropism Chemotropism is movement caused by chemical stimulus in organisms such as bacteria and plants. An example of chemotropic movement can be seen during the growth of the pollen tube. This growth of the pollen tube is always towards the ovules. NEXT

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