Describe The Process of Excretion in Plants | Plants Excretion

Excrition in Plants: 

    The removal of all harmful substances produced in the metabolic processes, from the body of plant is called excrition. 

    In plants the rate of catabolic processes is slow and waste products are produced in less amount. These products are not accumulated in plant body, they are used again in their anabolic processes.

      In plants the nitrogenous waste products are also used in the chemical processes, they are not removed from the body.

Mostly carbohydrates are used in metabolic processes, so CO2 and water are produced. These products are not very harmful.

The substances which are produced in excess amount are:

• Water
• Co2 and O2
• Ions

(A) Removal of Water 

        Extra amount of water is removed from the body of plant by two methods:

(i) Transpiration: 

       When extra amount of water is removed from the body of plant in the form of vapours is called transpiration. Mostly transpiration takes place through stomata of leaves.

(ii) Guttation: 

         When water is removed from plant body in the forms of small drops, the process is called guttation. Guttation occurs by special openings, called hydathodes. These are openings without guard cells present on the tip or margin of leaves. 

         Guttation takes places in those plants which grow in tropical rain forests, where rate of absorption is high because there is high rain fall and due to humidity in air, the rate of transpiration is low.

(B)  Release of Oxygen (O2) and Carbondioxide (Co2)

       In the presence of sunlight the plants use CO2 for photosynthesis and release O2 but in the absence of light there is no photosynthesis and during respiration the plants use O2 and release CO2.

(C) Ions: 

        In the body of plants the excess amont of ions are combined with organic compounds, then they are deposited in dead cells of the body such as heartwood and bard or sometimes in order cells of the body.

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Describe Halophytes & their Characters | Halophytes

The plants which grow in marshy soil or salty are known as halophytes. In such conditions soil is completely filled with water and the oxygen disappears as well as amount of salts is excess. The characters of halophytes are as follows:

• Due to the absense of oxygen, these are known as respiratory roots.
• The amount of minerals in the soil is high, so exomosis may take place but in these plants mechanism of active transport occurs, So water doesn't move from inside to outside and roots absorb water from the soil.
• In the leaves of plants salt glands are present which help in the removal of salt and water from the body.
• Some halophytes absorb humidity by leaves due to the concentration of salts in the leaves.

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Describe Mesophytes & their Characters | Mesophytes

Mesophytes  are the plants which grow in such soil which contain sufficient amount of water. The water is not in huge amount and soil is also not dry. These are the land plants with temperate regions. The characters of mesophytes are as follows:

• Their roots are well developed.
• Their body is covered by a layer known as Cuticle. It prevents transpiration.
• They contain stomata for evaporation of extra amount of water e.g. Mango rose etc.
• Some mesophytes of rainy regions contain hydathodes (opening without guard cells). Through these hydathodes water is excreted out in the form of drops, this process is called guttation.

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Describe Hydrophytes & their Characters | Hydrophytes

Hydrophytes: are plants which grow in water, they are found in ponds, lacks or steams. Their complete body is found in water or in some plants lower part remains in water and upper parts, such as leaves are above water. Their characters are as follows:

• They have soft body without cuticle.
• Roots are either absent or poorly developed. The whole body may perform the function of absorption of water.
• The leaves which are above water contain stomata in the upper surface which take part in transpiration.
• The hydropytes which are in water contain hydathodes (openings without guard cells) for the excretion of water e.g. Hydilla, Lotus, Lily plants.

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Water relations of cell: 

                 Water  is life of a living body. It acts as a biological solvent. It takes part in metabolic activities of cell. Its movements in and outside the cell is called osmosis. Osmosis is a process in which solvent moves from higher concentration to the lower concentration through the cell membrane.

Balance of Water and Solutions in the body: 

                 Water is used in most of the metabolic processes in the body of plants. The water moves and comes out of the cells by Osmosis. In osmosis the solvent moves from the region of higher concentration to the region of lower concentration through the plasma membrane.

                  When a plant cell is placed in pure water or hypotonic solution (solution contains more water than cell sap), then endosmosis takes place, due to which water enters the plant cell. As a result of this process the cell becomes turgid. By the continue movement of water inside the cell, it does not burst, because cell wall causes internal hydrostatic pressure or pressure potential, which does not allow further movement of water inside the cell.

                 When plant cell is placed in a hypertonic solution (more concentrated solution than cell sap), exosmosis occurs, the water moves from inside to outside, so the cytoplasm of cell shrinks from the cell wall, it is called plasmolysis.

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Describe The Negative & Positive Feed Back | Defination of Negative and Positive

Negative Feed Back: 

        When there is an opposite  reaction due to any change in the internal body fluid, It is called Negative feed back. For example, when more sweet is taken in the food, the amount of glucose becomes high in blood. Due to this change a system becomes active and takes part to decrease the amount of glucose, after that its amount is regulated. It is the negative feed back.

Positive Feed Back:  

         When there is a change in the internal body system and it is further increased by the process, it is called positive feed back. For example in warm blooded animals when internal body temperature is increased due to heat-stroke, the body temperature is further increased. It is the positive feed back. It may be useful in some conditions but may be harmful in other conditions.

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