NUTRITION IN PLANTS
WHY DO WE NEED FOOD?
How do you feel if you do not have food for a day or two? You may feel exhausted and weak. But if you do not get food for a few days, will you survive and grow? You will probably say‘No’. All living things need food.
Plant nutrition is an important aspect in the growth of plants.
Plant nutrition is the study of the chemical elements and compounds necessary for plant growth, plant metabolism and their external supply.
PHOTOSYNTHESIS
(Photo :light; synthesis : make)
Photosynthesis is ‘a biochemical process by which green plants manufacture their own food using carbon dioxide and water as raw materials in the presence of sunlight and chlorophyll’.
Oxygen is released as a by-product in this process.
The overall equation of photosynthesis is given here.
Plants produce their own food through photosynthesis and hence, they are called autotrophs.
Photosynthesis is the only process by which solar (sun’s) energy is converted into chemical energy.
6CO2 + 12H2O ⎯⎯→ C6H12O6 + 6H2O + 6O2 ↑
Essential raw materials for photosynthesis
Chlorophyll
Photosynthesis takes place only in chloroplast. In chloroplast, green pigment present in the each cells of leaves.
Sunlight
Sunlight is absorbed by chlorophyll as solar energy.
Carbon dioxide and water
Carbon dioxide and water are combined in the chloroplast with the help of a number of enzymes to yield sugar which is converted into starch. Oxygen will be formed during photosynthesis through the stomata.
Significance of Photosynthesis
1.Photosynthesis is responsible for providing food to all living beings.
Oxygen released during photosynthesis is used for respiration by living beings.
TRANSPORTATION IN PLANTS
Transport of Materials in Plants
(i) Transport of water
- Roots of plants take up water and minerals from the soil.
- Tracheids and vessels, which are non-living cells of xylem, transport water picked up by root hairs from soil to the leaves.
- The upward movement of water and minerals from soil termed ‘ascent of sap’ isagainst gravity and is due to transpiration pull.
- The process in which a lot of water evaporates (as water vapour) from stomata is called transpiration. There will be evaporation of water from the stoma and pulls water upwards through xylem. This is known as transpiration pull.
(ii) Transport of food material
- Sugars and other food molecules synthesized in the leaves are transported to other parts of the plant through phloem.
- Sieve tubes are living cells of the phloem, which transport food for all parts.
- The food material is transported and send to all parts of the plant is known as translocation.
RESPIRATION
Respiration in Plants
- Plants do not have any special respiratory organs.
- Roots take up oxygen from air trapped in the soil by means of root hairs.
- Root hairs are embedded in the soil.
- Oxygen in the air surrounding them diffuses into the root hair and from there into the roots.
- Carbon dioxide given out, similarly, diffuses out through roots.
- Stomata in leaves opens to let in oxygen and release carbon dioxide.
- In the older parts of roots or bark of woody plants, tiny openings called lenticels are present.
- It is through these lenticels that oxygen reaches the inner living tissues and
- carbon dioxide moves out.
- Guard cells help in the opening and closing of stomata.
- When guard cells get filled up with water, they swell and become turgid.
- The two guard cells curve away from each other opening the stomata.
- When guard cells become flaccid, stoma closes.
- Minerals also play a role in making guard cells turgid or flaccid
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