[3 marks Question Answer]

Question 13 Marks

Name any three minerals whose deficiency causes diseases in plants. Give the symptoms of each deficiency.

Answer

The nutrient elements i.e. minerals are essential for the plants to grow well and complete their life$-$cycle properly. The minerals are divided into two main categories:
$(i)$ Macro$-$Nutrients : They are required in larger concentrations and they are obtained from soil.
The three macro-nutrients $($minerals$)$ whose deficiency causes diseases in plants are:
$1.$ Nitrogen $(N) –$ Yellowing of leaves,wrinkling of cereal grains.
$2.$ Phosphorus $(P) –$ Purple and red spots on leaves, delay in seed germination.
$3.$ Potassium $(K) –$ Poor Growth
$(ii)$ Micro$-$Nutrients : They are required in small amounts and they are also obtained from soil.
The three micro$-$nutrients $($minerals$)$ whose deficiency causes diseases in plants are:
$1.$ Iron $(Fe) –$ Yellowing of Leaves.
$2.$ Manganese $(Mn) –$ Yellowing of leaves, with grey spots.
$3.$ Zinc $(Zn)$ Desphaped leaves, yellowing of leaves, stunted plant growth.

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Question 23 Marks

Name the factors which affect the rate of transpiration? State their role in each case.

Answer

The following are the main factors that affect the rate of transpiration:
$1.$ Sunlight: During daytime, the rate of transpiration is faster. This is because the stomata remain open to allow the inward diffusion ofcarbondioxide for photosynthesis.
During dark, the stomata are closed, and hence transpiration hardly occurs at night.
$2.$ Temperature:Transpiration is faster on hot summer days as compared to cold winter.
Wind:Transpiration is more when the wind is blowing faster as water evaporates faster from the leaves.
$3.$ Humidity:Transpiration is reduced if the air is humid. Air cannot hold any water molecules when it is already laden with moisture $($humidity$)$.
$4.$ Low atmospheric pressure:The rate of transpiration increases when the pressure is low.

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Question 33 Marks

How does transpiration help the roots absorb water and minerals from the soil?

Answer

Transpiration process in plants creates a suction pressure which pulls up water from xylem of the roots to the stem and then to the leaves.
Xylem tissues are in the form of capillary tubes $($tracheids and fibres$)$ where narrower the diameter, greater will be the force. Whenever the xylem vessels lay empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force.
Due to transpirational pull more and more water molecules are pulled up due to their tendency of remaining joined $($cohesion$)$. Such pulling force created by the leaves is very important in the case of tall trees where an upward conduction of water takes place.

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Question 43 Marks

Draw a magnified view of the root$-$hair, and describe, how it helps in the absorption of water from the soil.

Answer

Give above is a magnified view of a root$-$hair. It is a long protuberance of a cell. This cell contains a fluid called cell sap which is more concentrated than the surrounding soil water.
The root hair is covered by a very thin ceil membrane that allows water molecules to pass through, but prevents the larger molecules. So the water from the soil passes into the root hairs by osmosis.

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BIOLOGY [3 marks Question Answer]

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