Biology
Explain the mechanism of the closing and opening of the stomata.
Roots Absorption
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Answer
The closing and opening of the stomata depends on the turgidity of the guard cells. Each guard cell has a thicker wall on the side facing the stoma and a thin wall on the opposite side. Guard cells contain chloroplasts. As a result of the synthesis of glucose during photosynthesis and some other chemical changes, the osmotic pressure of the contents of the guard cells increases and they absorb more water from the neighbouring cells, thus becoming turgid. Due to turgor, the guard cells become more arched outwards and the aperture between them widens, thereby opening the stoma. At night or when there is shortage of water in the leaf, the guard cells turn flaccid and their inner rigid walls become straight, thus closing the stomatal aperture.
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Related Questions
Three cylinders of potato were carefully dried on a blotting paper and weighed. Each piece weighed 3 grams. Each one was placed in the beaker as shown below:

Answer the following questions:
(a) After 48 hours, which potato cylinder would be the heaviest?
(b) The movement of which substance is mainly responsible for the weight change in the potato cylinders?
(c) Name and define the process which is responsible for the movement of substance mentioned in answer (b).
(d) Write specific names of the processes which occur in beakers B and C [kinds of processes defined in answer (c)].
(e) Would there be any difference in the weight of the potato cylinder in beaker A after 48 hours? Give reason.
The figure given below is a diagrammatic representation of a part of the cross-section of the root in the root hair zone. Study the same and then answer the questions that follow:

(a) The parts labelled as 1, 2, 3 and 4 are :
- Root hair, Xylem vessel, Soil particles, Cortex respectively.
- Xylem vessel, Soil particles, Root hair, Cortex respectively.
- Root hair, Xylem vessel, Cortex, Soil particles respectively.
- Cortex, Soil particles, Xylem vessel, Root hair respectively.
(b) The process that enables the passage of water from soil into the root hair is :
- Diffusion
- Active transport
- Osmosis
- Passive absorption
(c) The kind of force which exists between a liquid and any surface is called as :
- Cohesive force
- Adhesive force
- Capillarity
- Suction force
(d) The kind of force between the same kind of liquid molecules is :
- Capillary force
- Transpirational pull
- Adhesive force
- Cohesive force
(e) Sometimes exudation of water occurs from the margin of the leaves in early morning or night. It is termed as :
- Transpiration
- Bleeding
- Guttation
- Osmosis
Study the experimental setup in the figure and then answer the questions that follow.

(a) What phenomenon is being studied by this setup?
(b) Explain the phenomenon mentioned in (a) above.
(c) What is meant by 'semipermeable membrane'?
(d) What will you observe in the setup after about half an hour? Give a reason for your answer.
Given below is the figure of a plant cell showing different kinds of pressure acting upon it. Study the figure and answer the questions that follow:

(a) In the figure, 1, 2 and 3 represent :
- Cytoplasm, Nucleus, Vacuole respectively
- Vacuole, Cytoplasm, Cell wall respectively.
- Cytoplasm, Cell membrane and vacuole respectively.
- Cytoplasm, Cell wall and Vacuole respectively.
(b) B in the figure represents :
- Osmotic pressure
- Turgor pressure
- Wall pressure
- Diffusion pressure
(c) A in the figure represents :
- Imbibition pressure
- Wall pressure
- Turgor pressure
- Osmotic pressure
(d) C in the figure represents :
- Turgor pressure
- Osmotic pressure
- Wall pressure
- Imbibition pressure
(e) Draw a neat and labelled diagram of a plasmolysed plant cell.