Absorption of Water
Short Questions and Answers
One mark questions and answers
- Attraction of water molecules to polar surface is known as
- In root hair water enters due to
Answer: Osmotic pressure
- The soil water easily available to the root system is
Answer: Capillary water
- Who introduced the concept of apoplast and symplast?
Answer: E. Munch
- Apoplastic movement of water and minerals in the root is stopped at
- Field capacity is
Answer: The amount of water in the soil after drainage takes place.
- In waterlogged field crops usually show signs of wilting because
Answer: The amount of CO2 increases in the soil.
- In roots, root hair occur in the zone of
Answer: Cell maturation
- When the absorption of soil solutes is low the absorption of water increases or decreases
- In comparison to clay the water holding capacity of sand is more or less
- Absorption of water through roots can be increased by
Answer: increased transpiration
- Name the form of water available to the plants.
Answer: Capillary water
Two marks questions and answers
1. Name the forms of soil water not available to plants.
Answer: Runoff water, gravitational water, hygroscopic water and combined water.
2. Name the specific part of the root which is concerned with the absorption of water.
Answer: Zone of elongation, zone of maturation and root hair cell.
3. The passage cells do not contain casparian strips. Explain its importance.
Answer: Passage cells help the movement of water due to absence of casparian strips directly from protoxylem.
4. What is the effect of auxin on water absorption?
Answer: Like other metabolic activity, absorption also increases in the presence of auxins.
5. What are the factors affecting the absorption of water?
Answer: The soil temperature, the concentration of soil solution, aeration of soil and availability of soil water are the various factors which affect the absorption of water.
6. Explain why the waterlogged soil is said to be physiological dry.
Answer: In waterlogged soils all the pore spaces of soil get filled with water and air is driven out. There is unavailability of oxygen. Hence the water absorption is checked.
7. Many transplanted seedlings fail to survive. Explain.
Answer: Root hairs play an important role in absorption of water and minerals. If root hairs are damaged during transplantation absorption of water and minerals cannot take place. Hence, transplanted seedling may not survive.
8. What is the non osmotic theory of active absorption of water?
Answer: The non osmotic theory was given by Thimann (1951) and kramer (1959). According to this theory water is absorbed against concentration gradient and it requires some energy. This energy is released from the metabolic activity of the roots.
Three marks questions and answers
1. What is the importance of water for plants?
Answer: It is a solvent in which various minerals, organic compounds and gases are dissolved. These substances are distributed throughout the plant body in the form of solutes. Water is a raw material in the synthesis of organic compounds. Besides it is an essential medium for the activity of enzymes. It provides turgidity to the cells which is necessary for growth and maintenance of shape.
2. Differentiate between symplast and apoplast.
Answer: Symplast refers to the continuous arrangement of protoplasts of a plant, which are interconnected by plasmodesmata whereas, apoplast refers to the non-protoplasmic components of a plant, including the cell wall and the intercellular spaces. In symplast water movement occurs by osmosis whereas in apoplast, the movement of water occurs by passive diffusion. In symplast the movement of water is slower whereas, in apoplast the movement of water is rapid.
3. How active absorption of water is different from passive absorption?
Answer: Active water absorption cannot take place in the absence of roots where as passive water absorption can occur even in the absence of roots. Active water absorption is not influenced by transpiration whereas passive water absorption is dependent upon transpiration. Active water absorption uses metabolic energy where as passive water absorption uses radiation energy.
4. Plants die if they remain flooded with water for long. Explain why?
Answer: A well aerated soil supplies required quantity of oxygen to the cortex and therefore roots respire normally. In poorly aerated soil or waterlogged soils the external supply of oxygen is insufficient for the root respiration. Hence absorption by roots is inhibited in such soils and plants shows signs of wilting.
5. Water absorption is generally rapid on a bright sunny day. Explain.
Answer: It is because the rate of transpiration is high on a bright sunny day. Water is lost from the guard cells which lead to decrease in water potential of the guard cell as compared to the surrounding cell. In this condition, water rushes from the neighbouring cells which creates a pull in the xylem vessels allowing water up to the guard cells.
Fill in the blanks
1 In waterlogged soil all ……… are filled with water, hence the roots are unable to absorb water.
2 ……. water is available to the plant in maximum amount.
3. Sand has low water holding capacity because of large ……….
4. The pathway in which water travels through the living cells is known as ………… movement.
5. In passive absorption what are the factors responsible for absorption develop at the ………..
6. Presence of auxins ………. the rate of water absorption.
7. ……. pressure is responsible for ……. absorption of water.
8. Apoplastic movement of water occurs through ……… and ……..
- air spaces
- pore spaces
- transpiring surface
- intercellular spaces/ cell walls
True and false statement
- Water is absorbed by the roots and aerial parts of the plant.
- Capillary water is available to the plant in maximum amount.
- The principal source of soil water is rain.
- All forms of water present in the soil are collectively known as combined water.
- A ball of soil is always kept around the root of a seedling to protect root hair when it is transplanted.
- Tonoplast is a selectively permeable membrane.
- Symplastic and apoplastic movement of water occurs simultaneously.
- The absorption is maximum in a well aerated soil.
- False (water is absorbed by roots)
- False (combined water is the chemical constituent of soil particles)