HOMEOSTASIS (BOTANY PART)

the important aspect of internal environment that must be kept constant are :

Osmoregulation

it is the control of the gain and loss of water and dissolved solute

Excretion

removal of excess and unwanted products from cell

Thermoregulation

it is the maintenance of internal temperature within range that allows cell to function efficiently

Feed back system

There are number of of physiological proceses functioning in the body to maintain the homeostasis . Homeostasis require check and balance . The check and balance mechanism is called feed back system . Usually hormones control this feed back system but it is ultimately controlled by nervous system . When any change in the internal environment takes place , it is detected by receptors and immediately reported to control center (Brain) which decides about appropriate response and sends its instructions to effector , which plays its role and brings the substance back to normal . The feed back mechanism may be negative or positive .

negative feed back

Negative feed back refers to opposite effect produced in relation to any change in body fluids . For example when we take sugar, the level of glucose is raised in blood . It triggers the mechanism , which decreases the level of glucose back to normal level.

positive feed back

Positive feed back refers to similar effects produced which leads to the enhancement of change. For example once child birth process begins, then each succeeding event makes it more likely that the process will continue until completion.

osmoregulation

The metabolic reactions on which life depends require a precise balance of water and dissolved salts. Among the salts whose concentration must be regulated are amino acids, protein and dissolved ions such as Sodium, Potassium, Calcium and bicarbonate . Each cell must adapt to definite quantity of water in relation to salts in it, to perform its function. Homeostatic mechanism maintains this concentration by osmoregulation.

balance of water and salts

Osmosis occurs when two solutions of different concentrations are separated by cell membrane. There is net movement of water from hypotonic solution to hypertonic solution until the solute concentration are equal on both sides of cell. When the concentration of water is greater outside the cell (High water potential) the water moves from outside to inside the cell and the cell becomes turgid . The cell swells and may burst. But if there is loss of water from cell , the cell shrinks and dries. To prevent these conditions cell osmoregulate themselves to keep water and salt balance.

OSMOREGULATION IN PLANTS

Efficient functioning of plant cell and the whole plant depends upon maintaining the water content at a steady state. According to the availability of water plants are divided into four groups 1. Hydrophytes 2. Mesophytes 3. Xerophytes 4. Halophytes

1.Hydrophytes

Hydrophytes are those plants which are found in fresh water. The plants may be partly or totally submerged in water. They do not have any difficulty in obtaining water. To remove excessive water, they have following adaptations

Adaptations to remove extra water

Their leaves are large so surface area is large for removal of excessive water by transpiration .

they have large number of stomata at upper surface of leaves.

Stems and leaves are without cuticle.

The stomata remain open.

Root is absent , if present root hairs are absent.

2.Mesophytes

These are those plants which are found in moderate supply of water , majority of angiosperm are mesophytes . These are land plants and can easily maintain their water balance .

Adaptations

When there is sufficient supply of water , the stomata are kept open but when there is restricted supply , the stomata are closed .

To prevent excessive loss

Shape of leaf is variable which also helps in regulating water. Leaf fall also help in regulating water.

3. Xerophytes

These are the plants , which are found at dry places such as desert , steep hills . Under such conditions , the water potential is very low . They have the following adaptations to prevent the water loss .

Adaptations

Root is deep vertical to absorb more water from soil and it also spread horizontally.

Leaves in most cases are absent or shed during dry season , in such cases stem become green and perform the function of photosynthesis .

Leaves become small or modified into spines to reduce to rate of transpiration .

The leaves are covered with cuticle ( thick waxy layer ) or by hairs .

Number of stomata are reduced with sunken type .

In rainy season stem, root and leaves store water in their parenchymatous cells such parts are called succulents .

Leaves fold themselves to reduce the rate of transpiration .

Germination of seed occurs during rainy season .

4. Halophytes

The plants growing in salt marshes close to sea are called halophytes. They have to absorb water, which has high salt concentration in their root cells i.e. with lower water potential.

Adaptations

Such plants actively absorb salt by their roots and as the salt concentration in their root cells become high, they absorb water by osmosis .

Excess of salt absorbed by roots, stored in the cells is excreted out from salt glands in leaves.

The salt thus secreted by some species help them to trap water vapours from air , which is being absorbed in liquid form by leave surface .

EXCRETION

Survival in any environment requires an accurate balance between excretion and animal's need of water and salts . The excretory system plays a central role in homeostasis by forming and excreting urine while regulating the amount of salt and water in body fluids .

Excretion in plants

Among plants Oxygen , Water, Carbon dioxide and some mineral crystals could be looked as waste .

1. Oxygen

It is a by product of of photosynthesis and is eliminated through stomata .

2 Carbon dioxide

it is a by product of respiration which is eliminated through stomata .

2. Water

Extra amount of water is excreted by transpiration or in some land plants it is exuded from hydathodes found at the margin of and tips of the leaves which is called Guttation

3. Crystal formation

Plants produce some organic and inorganic salts which are stored in the leaves , the leaves die and fall off and thus plant get rid off these salts .

Falling of yellow leaves in autumn season is a mean to get rid of such poisonous substances

4. Storage of wastes in wood

Ions present in excessive amount combines with organic compounds and are deposited on dead cells of plants such as heart wood , bark or in the cell which are at the point of their death .

5. Metabolic waste

In plants metabolic waste accumulates more slowly however the catabolic products , the nitrogenous products are used by green plants in their anabolic processes .

ADAPTATIONS OF PLANTS TO LOW AND HIGH TEMPERATURE

Low temperature

In plants low temperature effects the fluid nature of plasma membrane and lipids of the membrane become locked into crystalline structure by which transport of solution is affected . The protein structure of membrane is also affected , which ultimately effects the transport of solute .

Under such conditions , the proportion of fatty acids is increased which prevents crystal formation.

Freezing temperature causes ice crystal formation . This formation crystals around cell wall does not affect as badly and plant survive . But the formation of ice crystal within protoplasm perforates the cell membrane and organelles and cell dies .

Plants native to cold regions such as Oaks , Maples and Roses have adapted to bring changes in solute compostiion of cell which causes cytosol (cytoplasm) ti super cool without ice formation , although ice crystals may form in cell wall .

High temperature

High temperature is more harmful than ow temperature because it de natures the enzymes and damages the metabolism and therefore kills or harms the cells . The plants the cool down themselves with the help of transpiration . But as transpiration becomes high , the stomata are closed and plats suffers. The plants growing in hot areas are well adapted and when temperature reaches to 40 centigrade or above , the plant synthesize special shock protein that protects the enzymes and other proteins .

In addition to these mechanisms , plants may have shiny cuticle , small leaves , which prevents them from over heating.

-PRACTICAL CENTRE NOTES