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- What are autotrophs?
Ans. Living organisms that are capable of making their own food from inorganic substances (i.e.carbon dioxide and water) using Sun's light energy, are called autotrophs. E.g. all green plants and some kind of bacteria.
- What are heterotrophs?
Ans. Living organisms like animals and human beings that depend on other organisms for their food are called heterotrophs.
- What is autotrophic nutrition?
Ans. The mode of nutrition by which some living organisms like green plants make their food from inorganic substances by trapping light energy from the Sun, is called autotrophic nutrition.
- What is heterotrophic nutrition?
Ans. The mode of nutrition by which living organisms obtain their food from other living organisms, is called heterotrophic nutrition.
- Define photosynthesis.
Ans.The process by which green plants take in organic substances (carbon dioxide and water) from the outside surroundings and convert these into carbohydrates in the presence of sunlight and chlorophyll is called photosynthesis.
- List the steps involved in photosynthesis. OR List the events that occur during photosynthesis.
Ans.Steps involved in photosynthesis:
- Light energy is absorbed by chlorophyll and is converted into chemical energy.
- Water molecules split into hydrogen and oxygen.
- Carbon dioxide is reduced (converted) to carbohydrate.
- What is chloroplast?
Ans.The cell organelle present in the green leaves of green plants that contain chlorophyll is called chloroplast.
- Write an activity to show that chlorophyll is essential for photosynthesis.
- Take a potted plant with variegated leaves and keep it in a dark room for three continuous days.
- After three days, take the potted plant from the dark room and keep it in sunlight for six hours.
- After six hours, pluck a leaf from the plant and mark the green areas in the leaf and trace these on a sheet.
- Keep the leaf in boiling water for few minutes and then immerse it in a beaker containing alcohol.
- Carefully place the beaker in a water bath and heat till alcohol begins to boil.
- The leaf decolourises on boiling in alcohol.
- Place the decolourized leaf in a petri dish and add few drops of iodine solution to it.
- Take out the leaf and rinse off the iodine solution.
- Observe the color of the leaf and compare it with the tracing of the leaf that was taken before boiling it in alcohol.
- It is observed that the part of the leaf that was green turns blue black which indicates the presence of starch. While the non-green parts of the leaf turn yellow.
- The above activity proves that only the cells containing chlorophyll synthesized starch. Thus it is concluded that chlorophyll is essential for photosynthesis.
Note for the students:
- A leaf that has both green part containing chlorophyll and non-green part that do not contain chlorophyll is known as a variegated leaf.
- Starch turns blue black when iodine is added to it.
- Answer the following questions based on the above activity:
- Why the potted plant is kept in the dark room for three days?
Ans.The potted plant is kept in the dark room for three days so that all the starch in the green parts of the leaves gets used up.
- Why the leaf is boiled in alcohol?
Ans.The leaf is boiled in alcohol to decolorize it.
- Why some parts of the leaf turned blue black on adding iodine solution?
Ans. Some parts of the leaf turned blue black on adding iodine solution as these parts contained starch. Starch turns blue black when iodine is added to it.
- Explain the closing and opening of stomatal pores.
Ans. The opening and closing of stomatal pores are controlled by the guard cells. These cells swell when water flows into them causing the stomatal pore to open. The guard cells shrink when water flows out of these cells causing the stomata to close.
- What is meant by parasitic mode of nutrition?
Ans. The mode of nutrition by which some organisms like leeches, hookworm, tapeworm, ticks, cuscuta etc derive their nutrition from plants or animals without killing them, is known as parasitic mode of nutrition.
- What are parasites?
Ans. Living organisms that get their nutrition from plants or animals without killing them are called parasites. E.g. cuscuta, lice, leeches, hookworm etc.
- Explain briefly the nutrition in amoeba.
Ans. Amoeba is a unicellular organism. When it comes in contact with food, the cell surface temporarily changes into finger-like projections called pseudopodia which fuse over the food particle forming a food vacuole.
The complex substances inside the food vacuole are broken down into simpler ones which then diffuse into the cytoplasm of amoeba. The remaining undigested material moves to the body surface and is thrown out of the body.
- List (Name) the organs of human alimentary canal
Ans. The human alimentary canal is a long tube extending from mouth to anus with different organs in various regions specialized to perform specified functions. The organs of alimentary canal are:
- Oesophagus (food pipe)
- Gall Bladder
- Bile duct
- Small intestine
- Large intestine