8) Define and explain plasmolysis.
PLASMOLYSIS :
The shrinkage of protoplasm due to the loss of water is called plasmolysis.
EXPLANATION :
Wilting in plants occurs as a result of plasmolysis or loss of turgidity.Artificially this process takes place when the cell is placed in concentrated solution.As a result the water of the cell sap diffuses out.The shrinkage condition is known as plasmolysis or flaccidity and the cell in which the shrinkage is taken place is called plasmolysed cell or flaccid cell.
9) Define and explain turgidity.
TURGIDITY :
When a cell absorbs water,it swells and becomes turgid.This phenomenon is called turgidity.
EXPLANATION :
When all the cells in the leaf of a plant are turgid,the whole structure is firm and hard.
In plants it is the turgor of their cells which keeps the stem upright.The water in side the cell at the time of turgidity increases the pressure inside.It is known as TURGOR PRESSURE.
If the cell loses water faster than they can take in,the pressure in the vacoule falls and the cells lose their turgor gradually.The leaf becomes limp and the plant is said to be willed.
10) Define and explain wilting with examples.
WILTING :
It is defined as the drooping of leaves and the great tender stems of a plant as a result of excessive evaporation as compared to the uptake of water by roots.
EXPLANATION :
It usually occurs in hot weather,when the rate of transpiration exceeds water absorption.The plants also wilt there is no water in the soil.During wilting the plants,especially the leaves lose their turgidity,which leads to wilting.
11) Write a note on the transport of water and salts in unicellular and simple multicellular plants.
TRANSPORT OF SALTS AND WATER IN UNICELLULAR AND SIMPLE MULTICELLULAR PLANTS :
In unicellular or simple multicellular plants,the exchange of substances with the enviroment occurs by diffusion,osmosis or active transport through their general surface.
12) Write a note on ascent of sap in flowering plants.
ASCENT OF SAP :
The rising of soil water from the bottom to the top of a plant through xylem is called ascent of sap.
EXPLANATION :
The flowering plants on the other hand are multicellular and complex.All of their cells are not exposed to the external enviroment.For this purpose flowering plants need a special transport system called vascular system.
Flowering plants absorb water and salts from the soil by their roots through osmosisand active transport collectively.The path of transport from the soil to roots is root hairs,cortex,endodermis and finally xylem of the root.From the xylem it rises up to the top of the plant.
13) Write a note on transport of food and its storage.
TRANSPORT OF FOOD :
The food manufactured in the leaves of the green plant is transported in the phloem to various parts of a plant body for use or storage.The process of transport of food in the plant body is the opposite of water transport.In the transpiration stream,water and dissolved salts move from the roots to the leaves whereas the food materials travel down from the leaves towards the stem and roots.under certain conditions,the food can travel in opposite direction i.e from the root to the stem and leaves.In such situation the stored food in the roots is carried upwards for distributin to other parts of the body.
STORAGE OF FOOD :
A portion of the carbohydrates made by the leaves during photosynthesis is used for growth and development of leaves.The remainder sugar and starch not used in the leaf are carried to other parts of a plant through the phloem.The underground structures,which store food,are root tubers of carrot and stem tubers of potatoes.In addition to sugar and starch,some minerals are also transported to the underground parts for storage.During spring,when the buds are sprouting,starch stored in the underground parts is again converted into sugars.The sugars and amino acids travel up the stem to supply energy and raw materials for growth of buds and shoots.These food materials are also supplied to developing seeds and fruits.
Plants store mostly carbohydrates in their roots,stem and leaves in the form of starch.the fruits and seeds are sites for storing proteins,fats and minerals in addition to carbohydrates.During germination of the seed,the stored carbohydrates and proteins are used till the seedling starts manufacturing its own food.
14) Define transpiration.Describe the factors effecting transpiration.
TRANSPIRATION :
It is defined ass "the evaporation of water from the aerial parts of the plant mainly through stomata."
FACTORS EFFECTING TRANSPIRATION :
There are several factors which effect the rate of transpiration.
a) LIGHT :
Light has a direct effect on transpiration.Primarily it opens the stomata and secondly it increases the temperature.Both these factors increase the rate of transpiration.The stomata normally opens in light and closes in dark.
b) TEMPERATURE :
The rate of transpiration increases with the increase in temperature.The rate of transpiration becomes approximately double for every 10 degree centigrade rise in temperature.It means that the rate of transpiration is directly proportional to the temperature upto certain limits.
c) HUMIDITY :
The rate of transpiration increases with decrease in humidity of the air.It means that the rate of transpiration is inversely proportional to the atmospheric humidity.Dry and less humid air increases the rate of transpiration.
d) WIND :
Moving air is called wind,which increases the rate of transpiration.Wind replaces moist air from the surroundings of leaves with dry air,which favours transpiration.
e) SOIL MOISTURE :
Transpiration depends on the availibility of water in the soil and its absorption by the roots.If transpiration is not accompanied by sufficient moisture available from the soil,then the plants start wilting.under such conditions the stomata get closed and the rate of transpiration decreases.
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