Comparison of coordination between animals and plants

Comparison of coordination between animals and plants:

1. The general behavior of animals and plants: Plants are more passive compared to animals. But they are complex dynamic organisms. They grow, change, react to external/internal stimuli, and show response. It can be said that plants also behave but their behavior is fundamentally different from that of animals. The difference is due to two ways of life. Plants are sessile. While the animals are motile. Much of the behavior of plants depends on variations in growth rates, or changes in the turgidity of cells. The most obvious difference is that the plants show a slow response.

2. Nature of the control system in animals and plants:

movements. Plants and animals use different ways to show respond. So they have evolved different control systems. The control system of plants is composed of hormones. Theses hormones show a slow response. While the animals have a variety of hormones and nervous control. So they show the response with greater speed to specific stimuli.

3. Hormonal control in animals and plants:

Hormonal control in plants is relatively a slow process. Even after hormone is transported, there is a delay between the release, its arrival at the target cells, and its action in the body. So, response to the stimulus is usually not immediate.

Keeping in view the slowness of the mechanisms of plant movement, the delay involved in hormonal, control is insignificant. All the activities of plants from growth to fruit production and ripening are under the control of plant hormones.

Plants, therefore, respond to the stimuli by:

➤ Regulating their growth and development in inappropriate ways.

➤ Controlling their body functions through plant hormones or growth hormones.

PLANT MOVEMENTS

Many plants do not show locomotion (movement of the whole organism).

However, the movements of plant organs are possible. These movements are modified according to the nature and intensity of external stimuli. There are two kinds of plant movements: turgor movements and growth movements.

Responses to environmental stresses in Plants

All plants need water, light, carbon dioxide, and a variety of nutrients from their environment. These chemicals are used for optimal development and growth. The absence or shortage of any of these factors in the environment may exert environmental stresses on plants. This environmental stress can destroy the health and survival of the plant. Examples:

1. If plants are grown without light, they become extremely long and fail to form chlorophyll. The plants without chlorophylls are called etiolated.

2. Many plants become yellow when they fail to form sufficient chlorophyll. This condition is known as chlorosis. It usually arises from short supplies of mineral nutrients in the soil.

PLANT HORMONES

The special substances produced by the plants which influence the growth and plant responses are called plant hormones. There are the following plant hormones.

(a) Auxins:

Auxins are chemically Indole acetic acid (IAA) or their variants. Auxins play the following role in plants.

1. It promotes cell enlargement in the region behind apex in the stem. It also promotes cell division in the cambium.

2. In the root, it promotes growth at very low concentrations. But it inhibits. growth at higher concentrations, e. g. geotropism.

3. Promote the growth of roots from cuttings and calluses.

4. Promote bud initiation in shoots. But sometimes it is antagonistic to cytokinins and is inhibitory.

5. Promote apical dominance and fruit growth. It can sometimes induce parthenocarpy.

6. Cause delay in leaf senescence (aging) in a few species.

7. Inhibits abscission.

Commercial applications:

The chemists have synthesized many synthetic auxins after the discovery of IAA. The synthetic auxins are economical than IAA to produce. The plant generally does not have necessary enzymes to break down these synthetic auxins So these are often more active than the natural auxins.

(b) Gibberellins:

Gibberellins are produced commercially from fungal cultures. It performs the following functions in plants

1. It promotes cell enlargement in the presence of auxins. It also promotes cell division in apical meristem and cambium.

2. It promotes the 'bolting' of some rosette plants.

3. It promotes bud initiation in shoots of chrysanthemum callus.

4. It promotes leaf growth and fruit growth. It may induce parthenocarpy.

5. It enhances the action of auxins in apical dominance.

6. It breaks bud and seed dormancy.

7. Sometimes, it may be a substitute for the red light. Therefore, it promotes flowering in long-day plants. But it inhibits flowering in short-day plants.

8. It causes a delay in leaf senescence in a few species.

Commercial applications of gibberellins:

Some of their commercial applications are as under.

1. GA promotes fruit setting e. g. in tangerines and pears. So it is used for growing seedless grapes, (parthenocarpy). It also increases berry size.

2. GA₃ is used in the brewing industry. It stimulates a-amylase enzyme production in barley. A-amylase promotes malting.

3. It delays the ripening of bananas. So it improves the storage life of bananas and grapefruits.

(c) Cytokinins:

It performs the following functions in plants:

1. It promotes stem growth by cell division in apical meristem and cambium.

2. It inhibits primary root growth.

3. It promotes lateral root growth.

4. It promotes bud initiation and leaf growth.

5. It promotes fruit growth. But it can rarely induce parthenocarpy.

6. It promotes lateral bud growth. It also breaks bud dormancy.

7. It causes a delay in leaf senescence.

8. It promotes stomatal opening.

Commercial application:

1. Cytokinins delay the aging of fresh leaf crops, such as cabbage and lettuce (delay of senescence).

2. They keep the flowers fresh.

3. They can also be used to break the dormancy of some seeds.

(d) Abscisic acid:

1. It inhibits stem and root growth, especially during physiological stress, e. g. drought, waterlogging.

2. It promotes bud and seed dormancy.

3. It promotes flowering in short-day plants, and in the long-day plants. So it is antagonistic to gibberellins.

4. Sometimes, it promotes leaf senescence.

5. It promotes abscission.

6. It promotes the closing of stomata under conditions of water stress (wilting).

Commercial application:

Abscisic acid can be sprayed on tree crops. It regulates fruit drop at the end of the season. This removes the problems of picking fruits in a large time- span.

(e) Ethene:

1. It inhibits stem growth, especially during physiological stress.

2. It inhibits root growth.

3. It breaks the dormancy of bud.

4. It promotes flowering in pineapple.

5. It promotes fruit ripening.

Commercial application:

1. Ethene induces flowering in pineapple.

2. It stimulates the ripening of tomatoes and citrus fruit.

3. The commercial compound ethephon breaks down and releases ethene in plants. It is applied on rubber plants. It stimulates the flow of latex in a rubber plant.

4. It causes nervous coordination and chemical coordination in higher animals.