Gaseous Exchange in plants

Gaseous Exchange in plants:

Plants have no organs or systems for the exchange of gases with the environment. Every cell of the plant body exchanges gases with the environment by its own.

The leaves and young stems have stomata in their epidermis. The gaseous exchange occurs through these stomata. The inner cells of leaves (mesophyll) and stems also have air spaces among them, which in the exchange of gases

Leaf cells face two situations. During the daytime when the mesophyll cells of leaves are carrying out photosynthesis and respiration side by side, the oxygen produced in photosynthesis is utilized in cellular respiration. Similarly the carbon dioxide produced during cellular respiration is utilized in photosynthesis. However, during night when there is no photosynthesis occurring, the leaf cells get oxygen from the environment and release carbon dioxide through stomata.

In woody stems and mature roots, the entire surface is covered by bark which is impervious to gases or water. However, there are certain pores in the layer of bark. These are called the lenticels.

The lenticels allow air to pass through them.

Gases diffuse in and out of the general surface of the young roots. The gases are found in the soil surrounding the roots.

The aquatic plants get the oxygen dissolved in water and release carbon dioxide in the water.

Osmotic adjustments in Plants:

Osmotic adjustments in Plants:

On the basis of the available amount of water and salts, plants are divided into three groups.

Hydrophytes:

Hydrophytes are the plants which live completely or partially submerged in freshwater. Such plants do not face the problem of water shortage. They have developed mechanisms for the removal of extra water from their cells. Hydrophytes have broad leaves with a large number of stomata on their upper surfaces. This characteristic helps them to remove the extra amount of water......

Xerophytes:

Xerophytes live in dry environments. They possess thick, waxy cuticle over their epidermis to reduce water loss from internal tissues. They have less number of stomata to reduce the rate of transpiration. Such plants have deep roots to absorb maximum water from soil.

Succulent Oxygen:

Some xerophytes have special parenchyma cells in stems or roots in which they store large quantities of water. This makes their stems or roots wet and juicy, called Succulent Organs.

Halophytes:

Halophytes live in sea waters and are adapted to salty environments. Salts enter in the bodies of such plants due to their higher concentration in sea water.

Homeostasis in Plants:

Homeostasis in Plants:

How Homeostasis occurs in Plants? Explain the various modes of Homeostasis.

Plants respond to environmental changes and keep their internal conditions constant i.e. Homeostasis. They apply different mechanisms for the homeostasis of water and other chemicals (oxygen, carbon dioxide, nitrogenous materials etc)......

Removal of Extra Carbon dioxide and Oxygen:

In Daytime, the carbon dioxide produced during cellular respiration is utilized in photosynthesis and hence it is not a waste product.

At Night, It is surplus because there is no utilization of carbon dioxide.

It is removed from the tissue cells by diffusion. In leaves and young stems, carbon dioxide escapes out through tomatoes. In young roots, carbon dioxide diffuses through the general root surface, especially through root hairs.

Role of Mesophyll

Oxygen is produced in mesophyll cells only during daytime, as a by-product of photosynthesis. After its utilization in cellular respiration, the mesophyll cells remove the extra amount of oxygen through stomata.

Removal of Extra Water:

The plants obtain water from soil and it is also produced in the body during cellular respiration. Plants store large amount of water in their cells for turgidity.

Extra water is removed from plant bogy by transpiration. At night, transpiration usually does not occur because most plants have their stomata closed. If there is a high water content in soil, water enters the roots and is accumulated in xylem vessels.

Gutation

Some plants such as grasses force this water through special pores, present at tips or edges, and from drops. The appearance of drops of water on the tips or edges of leaves is called Guttation.

Removal of other Metabolic Wastes:

Plants deposit many metabolic wastes in their bodies as harmless insoluble materials.

Shedding of Leaves:

In trees which shed their leaves yearly, the excretory products are removed from body during leaf fall. Other waste materials that are removed by some plants are resins by coniferous trees, gums by keekar, latex by rubber plant and mucilage by carnivorous plants and ladyfinger etc.

Resign drops from a cut tree latest being extracted from a tree mucilage drops on by carnivorous plants.