Living World Of Plants - Plant Physiology

Shoots are positively phototropic so they bend towards light whereas roots grow towards earth’s gravity i.e. they are positively geotropic. So roots are in contact with soil and branches grow straight.

The growth movement of plants in response to touch stimulus is called thigmotropism. Vines when get any support they coil around the support and grows and this type of tropic movement is called thigmotropism.

Water gets oxidised to form oxygen. Water splits by absorbing light energy to form oxygen. This is known as photolysis of water. Carbon dioxide is reduced to form glucose in dark phase of photosynthesis reaction by help of some enzymes.

Transpiration is the loss of water in form of water vapours from the aerial parts of the plant like leaves, stem etc. There are minute openings called stomata on leaves surface and lenticels on surface of old, woody stem through which water is lost.

Heliotropism

It is the motion of flower in response to the direction of sun. Sunflower follows the path of sun from east to west from dawn to dusk. Then it moves from west to east during night.

Positive Geotropism

The movement of plant parts in response to gravity of earth is called geotropism. If the plant parts like root moves towards earth’s gravity it is called positive geotropism.

Thigmonastic and photonastic movements.

When we touch the leaves of Touch-me-not they droop down, this response to touch stimulus is called thigmonastic movement. Dandelion flowers open their petals in bright light during day time and close their petals at night which is an example of photonastic movements.

Non-directional

In case of tropic movements movement of plant parts are directional i.e. either towards or away from the stimulus. But in case of nastic movements they are non-directional i.e. their movement is neither towards the stimulus nor away from the stimulus.

Carbon dioxide and water

Carbon dioxide and water are the raw materials required for photosynthesis which in presence of chlorophyll and sunlight energy gets converted into glucose and oxygen. This process mainly occurs in leaves.

Starch

When iodine solution is added to the leaf the portion of leaf which contains starch turns blue-black colour whereas those portion which does not contain any starch turns brown colour.

Starch

Glucose is synthesized in leaves by photosynthesis process some of glucose is utilized by the plants whereas the remaining glucose is stored in form of starch in the leaves.

Oxygen

Oxygen is required for living because it oxidises glucose to release energy in form of ATP that is required to carry out various metabolic activities.

1%

Only about 1% of absorbed water by roots is utilized for photosynthesis and other activities remaining 99% is lost in form of vapours from the plants.

Stomata

Through stomata exchange of gases occurs. Oxygen is taken in and carbon dioxide is given out during respiration but in photosynthesis carbon dioxide is taken in and oxygen is given out.

True

When we touch the leaves of Mimosapudica plant the leaves gets folded up because due to loss of turgor pressure and this non-directional movement in response to touch stimulus is called thigmonasty.

False

The petals of moon flower open up in night and closes in the morning which is an example of photonasty.

This non-directional movement of flower to the stimulus light is called photonastic movement.

False

Photosynthesis produces glucose and oxygen.

During photosynthesis process carbon dioxide and water in presence of chlorophyll and sunlight produces glucose and oxygen.

True

In photosynthesis process carbon dioxide is taken in and oxygen is given out and oxygen is the life supporter which is required by every living organisms for respiration process. It also supports combustion. Hence oxygen is used up rapidly so plants release this gas by photosynthesis process to maintain the balance in the environment.

False

Plants lose water when the stomata on leaves are open.

When stomata are open during day time water is lost through these openings by the plants.

1. Moon flower closes at day time but opens during night time. This non-directional movement in response to stimulus light is called photonasty.

2. Mimosapudica closes its leaves when slightly touched and this non-directional movement in response to stimulus touch is called thigmonasty.

3. Tulipasp. responds to temperature and this movement is called thermonasty.

a. Tropic movements

Tropic movements are growth dependent movements occurring in response to external stimuli like light, temperature, water, earth’s gravity etc.

b. Nastic movements

Nastic movements are growth independent movements which occur in flowers and leaves of the plants mainly in response to stimuli like touch, light, temperature etc.

Shoot grows towards the stimulus light whereas away from gravity of earth. Similarly root grows away from light and bends towards gravity of earth.

Nastic movement is seen in pneumatophores of Avicennia.

Thigmonasty is also called seismonasty.

The non-directional movements which occurs in response to touch is called thigmonasty or seismonasty.

Moon flower closes its petals during day time and open at night time which is opposite to that of Dandelion.

Shoot grows away from water is an example for negative hydrotropism.

6CO₂ + 6H₂O _→C6H₁₂O₆ + 6O_2↑

Glucose and oxygen are the products of photosynthesis process.

Oxygen gas is evolved during photosynthesis.

Water gets splits by absorbing photons from sunlight energy which release oxygen gas.

Chlorophyll is a green pigment present in chloroplast of leaves which traps sunlight energy for photosynthesis process.

Micronutrients are required in very minute quantities by plants. Examples are iron, manganese, boron, molybdenum, copper etc.

Root shows positive geotropism because root bends towards earth’s gravity and the movement of plant parts towards a stimulus is called positive tropism.

When we touch the leaves of Mimosapudica plant the leaves droop down due to loss of turgor pressure. This phenomenon is known as thigmonasty or seismonasty.

i.

a. During day time dandelion flower opens its petals.

b. During night time it closes its petals.

ii. This phenomenon is known as photonasty i.e. non-directional movements of flowers in response to stimulus of light.

Sunflower moves from east to west during day time in direction of sun and this movement is called heliotropism i.e. movement of flower in response to stimulus sunlight. Again in evening time it moves from west to east direction. The leaves of Mimosapudica droops down when touched and this is an example of thigmonasty i.e. movement of leaves in response to stimulus touch.

Photo means light and synthesis means to build. It is the process by which cells containing chlorophyll by using carbon dioxide and water in presence of sunlight will synthesise glucose and oxygen gas is evolved as by-product.

The process of transpiration can be demonstrated by tying a polythene bag around the rose plant and keeping the plant in sunlight for one or two hours. Droplets of water would be seen on the inner sides of polythene bag due to transpiration.

Stomata are minute openings present on surface of leaves whose opening and closing are guarded by guard cells. Guard cells have thick inner walls and thin outer walls. They have chloroplasts within them. Stomata open during day time when guard cells turn turgid. The cells surrounding the guard cells are called epidermal cells.

(a) Fig. ii shows correct position. Because roots are positively geotropic so they bends towards earth’s gravity downwards. Shoots are positively phototropic so they bend towards light i.e. move upwards.

(b) Shoot bends towards light so they exhibit positive phototropism. The movement of plant parts in response to stimulus light is called phototropism and as the shoot bends towards light so it is positive phototropism.

The directional movement of plant parts in response to stimulus light is called phototropism. The directional movement of plant parts in response to stimulus earth’s gravity is called geotropism. The directional movement of plant parts in response to water is called hydrotropism. Roots bend away from light so they are negatively phototropic. Roots bend towards water and earth’s gravity so they are positively hydrotropic and geotropic respectively. Shoot bends towards light but bends away from earth’s gravity so it is positively phototropic but negatively geotropic. It shows no response to water.

As tips of shoot are covered with tin foil cap the shoot does not show any bending towards light. Because light cannot penetrate through tin foil cap to reach shoot tip to break down auxin. Auxin are responsible for bending of shoot tip towards light.

When the portion of leaf covered with black paper is tested for starch it will show brown colouration i.e. indication of absence of starch as that portion of leaf does not receive sunlight so photosynthesis cannot occur.

A- water, B- carbon dioxide, C- oxygen, D- glucose

Chlorophyll containing cells in leaves trap sunlight energy and by using raw materials carbon dioxide and water synthesize glucose and release oxygen gas into atmosphere. This process is called photosynthesis.

Thigmonastic or seismonastic movement- where when we touch the leaves of Mimosapudica plant its leaves droop down and this movement is immediate, quick and easily noticed. This is non-directional movement in response to stimulus touch.

Roots bend towards gravity and water but bends away from light. Shoots bend towards light but away from gravity. It shows no response to water.

Guard cells surround the stoma. They are bean or kidney shaped. They have thick inner walls but thin outer walls. When they become turgid the stomata opens during day time. But at night time the guard cells turn flaccid closing the stomata.

Assertion is correct. When the plant part moves in the direction of gravity i.e. root it is called positive geotropism. When the plant part shows its movement towards the stimulus it is called positive tropism.

But reason is incorrect because stem moves away from the earth’s gravity so it is called negative geotropism.

Assertion is correct. The loss of excess water from aerial parts of the plant in the form of water vapour is known as transpiration.

Reason is also correct. Stomata are minute openings found on the surface of leaves through which water is lost in form of vapours. So transpiration process occurs through stomata.

a. The flowers show nastic movements i.e. photonasty. These are non-directional movement caused by stimulus light.

b. Dandelion flower [ Taraxacumofficinale ] opens up in the morning in bright light while closes its petal in dark or night time. Moon flower [ Ipomoeaalba ] opens its petals at night and closes during day time.

c. The leaves of plant C exhibit seismonasty or thigmonasty. These are non-directional movements which occur in response to touch and these are very quick.

d. Mimosapudica [touch-me-not] plant, leaves droop down immediately when slightly touched due to change in turgor pressure.

a. Stimulus A is water as roots bend towards it but shoot bends away from it. Roots are positively hydrotropic whereas shoot is negatively hydrotropic.

b. Stimulus B is gravity of earth. Roots bend towards earth gravity so it is positively geotropic whereas shoot bends away from it so it is negatively geotropic.

c. Stimulus C is light as shoot bends towards light showing positively phototropism but roots bend away from light showing negatively phototropism.

a. Organism A is green plant which cannot move from one place to another. It prepares simple food B which is glucose. Complex food H is starch i.e. excess glucose is stored in form of starch in the plants.

b. C and D are carbon dioxide and water respectively which are important raw materials required for preparation of glucose by the green plants.

c. Green pigment E is chlorophyll which is found in cell organelle chloroplast. Chloroplast has disc like structures called thylakoids and in their walls chlorophyll pigment is present.

d. Process G is photosynthesis where chlorophyll containing cells in presence of light energy using raw materials carbon dioxide and water synthesize glucose and oxygen is released as by-product.

a. Sunlight is required for photosynthesis. This experiment shows that sunlight is an important factor that is required for photosynthesis. Because in absence of sunlight glucose cannot be synthesized by the leaves of the plant.

b. The plant was kept in dark for 24-48 hours to destarch the plant so that whole stored starch would be used up by the plant and it will not interfere on the experiments of photosynthesis.

c. First the leaf is placed in boiling water followed by boiling the leaf in methylated spirit which removes chlorophyll. Then iodine solution is poured over leaf. The blue-black colour will indicate the presence of starch whereas brown colour will indicate absence of starch.

d. Carbon dioxide, water and chlorophyll are required for photosynthesis.

False

The response of a plant part to the chemical stimulus is called chemotropism.

The growth of pollen tube down the style to reach ovary in response to the sugars secreted by style is an example of chemotropism.

True

Shoot is positively phototropic i.e. it bends towards light so it is a positive response towards the stimulus light. Shoot bends away from gravity of earth so it is negatively geotropic i.e. negative response towards the stimulus earth’s gravity.

False

Scientific term used to represent the bending of roots towards water is called hydrotropism.

The bending of roots towards water is an example of hydrotropism.

False

Jan Baptist van Helmont devised an experiment to find out that water alone was the cause of the increase in the weight of the plant.

He weighed the dry soil, then he weighed the small sapling and placed in the pot allowing only air and light and he regularly watered the plant. When sapling grows into a small tree again he weighed the plant. He found in increase of weight of the plant. He dried the soil in the pot in which sapling grew and took the weight of dried soil. He found very less difference in the weight of the soil before planting the sapling and after sapling grew into a small plant. So he came into conclusion that water was the cause of increase in weight of the plant.

False

When weather is hot, water evaporates faster due to opening of stomata.

During day time it is hotter due to heat rays of sun and stomata are open at that time so more water is lost through these openings.

Light

Shoot grows towards light so it moves upwards in response to stimulus light and this response towards stimulus light is called phototropism.

Root

Roots show its growth towards earth’s gravity as well as water so it is positively geotropic as well as positively hydrotropic.

Chlorophyll

Chlorophyll a green pigment is present in the mesophyll cells of leaves which traps sunlight energy that is required for photosynthesis process.

Macronutrient

The minerals like nitrogen, potassium and phosphorus are required in more quantities by plants and hence are known as macronutrients. Other examples of macronutrients include carbon, hydrogen, oxygen, calcium, magnesium etc.

Positive tropism

The directional movement of plant parts towards a stimulus is positive tropism.

Response towards light

The directional movement of plant parts in response to stimulus light is called phototropism.

Chloroplast

Chloroplast contains green pigment chlorophyll which traps sunlight energy to perform photosynthesis.

Dance of Desmodiumgyrans i.e. Indian telegraph plant leaf shows a mesmerizing movement.

It is also called dancing plant as the leaflets move up, back and then down finally back to its original position showing rhythmic movement. This plant was first used by Indian Scientist J.C. Bose for his experiment.

a. Positive geotropism

Roots grow towards gravity of earth so it is positively geotropic.

b. Hydrotropism

Roots bend towards water showing positively hydrotropic movements.

(a) The plant in the above figure is Mimosapudica. When we touch the leaves of this plant the leaves fold up and droop down and this type of movement is known as seismonasty or thigmonasty.

(b) This plant shows nastic movement i.e. it is not a directional movement of the plant part with response to the stimulus. Whatever the direction of stimulus may be it affects all parts of plant equally. When we touch the leaves of this plant due to loss of turgor pressure its leaves droop down.

The end product of photosynthesis are glucose, oxygen, water. Glucose is utilized by plants or it is stored in form of starch. Oxygen is released into environment through stomata. Water is reutilized for photosynthesis process.

Stomata are minute openings found on the lower surface of the leaf through which exchange of gases occurs and water is also lost in form of vapours.

The movement of plant part in response to an external stimulus in which the direction of response is not determined by the direction of stimulus is known as nastic movement. Nastic movement may or may not be growth movement. Examples- Drooping down of leaves of Touch-me-not plant when slightly touched.

a. Root bends towards gravity of earth i.e. it is positively geotropic but it bend away from light so it is negatively phototropic.

b. Shoot bends towards light i.e. positively phototropic but bends away from gravity of earth so negatively geotropic.

a. X is light energy and Y is chemical energy.

The sunlight energy is trapped by chlorophyll and is used in photosynthesis process. By using raw materials carbon dioxide and water in presence of light energy, glucose and oxygen are produced. The whole process occurs in chloroplasts. Glucose is a chemical compound so light energy is converted into chemical energy.

b. Plants can prepare their own food, they do not depend upon others for food. They have chlorophyll pigment which can trap sunlight energy and by using carbon dioxide and water they produce glucose. So they are autotrophic in nature.

Transpiration is the process of loss of water in form of water vapour from aerial parts of the plant.

There are three types of transpiration i.e. cuticular- where water is lost from cuticle of leaves, stomatal transpiration- where water is lost from stomata, lenticular transpiration- where water is lost from lenticels.

The orientation of plant part in response to water is called hydrotropism.

Activity to demonstrate hydrotropism:

Two glass troughs A and B were taken. Both the troughs were filled with soil upto two-third level. A tiny seedling was placed in both the troughs. A small clay pot with soil was placed in trough B. In trough A water was added uniformly to the soil but in trough B water was put only in small clay pot.

Observations: After few days it was noticed that in trough A roots of the seedlings had grown straight as water is added uniformly to the soil. But in trough B roots of seedling had grown in the direction towards the clay pot because water is contained in the clay pot. This shows that roots of plant shows its growth in the direction of water.

Hydrotropism is the directional movement or orientation of plant part in response to stimulus water. Bending of roots of the plants towards water is an example of positive hydrotropism.

Phototropism is the directional movement or orientation of plant part in response to stimulus light. As the top part of seedling i.e. plumule bends towards light so it shows positive phototropism.

Root of plant bends towards earth’s gravity so it is positively geotropic but it bends away from light so it is negatively phototropic. Roots of plants bend towards water so it is positively hydrotropic.

Stem bends away from earth’s gravity so it exhibits negative geotropism.

The non-directional movement of plant part in response to temperature is called thermonasty. The position of flowers and leaves of plants changes in response to temperature of surroundings which are called thermonastic movements.

The position of plant part changes in response to the stimulus light but these are non-directional movements and do not involve growth which is known as photonastic movement. Dandelion flower open their petals in bright light during day time and closes their petals during night time.

Oxygen is given as a by-product from the plants by photosynthesis process. They take in carbon dioxide and release oxygen during preparation of glucose by the cells containing chlorophyll mainly in leaves.

Chlorophyll pigment is present within chloroplasts which traps sunlight energy and by using raw materials carbon dioxide and water, the leaves prepare glucose and release oxygen into the environment. This process is called photosynthesis.

When a plant is kept in dark it cannot perform photosynthesis process so it will used up the stored starch. Hence when a plant is kept in dark for more than 24 hours the stored starch will be used up by the plant, which will not interfere with the photosynthesis experiments.

Stomata are the minute openings found on the surface of leaves through which water is lost in form of vapours to the atmosphere. This process is called transpiration.