Plant Physiology Online Test 9th Science Lesson 19 Questions in English

Explanation 

Animals move in search of food, shelter and for reproduction. Have you observed the leaves of Mimosa pudica (touch-me-not plant) closes on touching, whereas Helianthus annuus (sunflower) follows the path of the sun from dawn to dusk, (from east to west). These movements are triggered by an external stimulus.

Explanation 

Unlike animals, plants do not move on their own from one place to another, but can move their body parts for getting sunlight, water and nutrients. They are sensitive to external factors like light, gravity, temperature, etc.

Explanation 

Tropism is a unidirectional movement of a whole or part of a plant towards the direction of stimuli. Based on the nature of stimuli, tropism can be classified into some types. 

Explanation 

Tropism is generally termed positive if growth is towards the signal and negative if it is away from the signal. Shoot of a plant moves towards the light, the roots move away. Thus, the shoots are positively phototropic.

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Usually shoot system of a plant is positively phototropic and negatively geotropic and root system is negatively phototropic and positively geotropic.

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Some halophytes produce negatively geotropic roots (e.g. Rhizophora). These roots turn 180° upright for respiration.

Explanation

Nastic movements are non-directional response of a plant or part of a plant to stimulus. Based on the nature of stimuli, nastic movements are classified.

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Movement of a part of a plant in response to light is called Photonasty. e.g. Taraxacum officinale, blooms in morning and closes in the evening.

Explanation 

Ipomea alba (Moon flower), opens in the night and closes during the day. Movement of a part of a plant in response to light is called Photonasty.

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Movement of a part of plant in response to touch is called Thigmonasty. It is also known as Seismonasty.

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Movement of a part of plant in response to touch. e.g. Mimosa pudica, folds leaves and droops when touched.

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The Venus Flytrap (Dionaea muscipula) presents a spectacular example of thigmonasty. It exhibits one of the fastest known nastic movement.

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Movement of part of a plant is associated with change in temperature. e.g. Tulip flowers bloom as the temperature increases.

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‘Photo’ means ‘light’ and ‘synthesis’ means ‘to build’. Thus, photosynthesis literally means ‘building up with the help of light’.

Explanation 

Green plants are autotrophic in their mode of nutrition because they prepare their food materials through a process called photosynthesis. During this process, the light energy is converted into chemical energy.

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Tel Aviv University Scientists have found out that Vespa orientalis (Oriental Hornets) have capabilities to trap solar energy.

Explanation 

Vespa orientalis (Oriental Hornets) have a yellow patch on its abdomen and an unusual cuticle structure which is a stack of 30 layers thick. The cuticle does not contain chlorophyll but it contains the yellow light sensitive pigment called xanthopterin. This works as a light harvesting molecule transforming light energy into electrical energy.

Explanation 

The end product of photosynthesis is glucose which will be converted into starch and stored in the plant body. Plants take in carbon dioxide for photosynthesis; but for its living, plants also need oxygen to carry on cellular respiration.

Explanation 

Certain things are necessary for photosynthesis. They are: 

1. Chlorophyll – Green pigment in leaves 
2. Water 
3. Carbon dioxide (from air) 
4. Sun light

Explanation 

The loss of water in the form of water vapour from the aerial parts of the plant body is called as transpiration. The leaves have tiny, microscopic pores called stomata.

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Stomatal transpiration is the loss of water from plants through stomata. It accounts for 90- 95% of the water transpired from leaves.

Explanation 

In Lenticular transpiration, Loss of water from plants as vapour through the lenticels. The lenticels are tiny openings that protrude from the barks in woody stems and twigs as well as in other plant organs.

Explanation 

Transpiration is necessary for the following reasons:

1. It creates a pull in leaf and stem. 
2. It creates an absorption force in roots. 
3. It is necessary for continuous supply of minerals. 
4. It regulates the temperature of the plant.

Explanation 

The leaves have minute pores called stomata through which the exchange of air takes place. These minute pores can be seen through a microscope.

Explanation 

Air exchange takes place continuously through the stomata. Plants exchange gases (CO2 to O2) continuously through these stomata. You will study more about these physiological process in your higher classes.

Explanation

Phototropism is the movement of a plant part towards light. e.g. shoot of a plant. Geotropism is the movement of a plant in response to gravity. e.g. root of a plant.

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Movement of a part of plant in response to chemicals is called as Chemotropism. e.g. growth of a pollen tube in response to sugar present on the stigma.

Explanation 

Thigmotropism is the movement of a plant part due to touch. e.g. climbing vines. Hydrotropism is the movement of a plant or part of a plant towards water. e.g. root of a plant.