Science
During a field trip, Mohan and Rohit observed that shoots of sunflower plants bend towards the sunlight. Whereas, leaves of ‘Touch me not’ plant begin to fold and droop soon after touching even during the day. They were curious to know how these movements occur in plants.
Attempt either subpart A or B.
(a) What causes the bending of shoots in the sunflower plants towards sunlight?
OR
(b) What causes the folding of the leaves in ‘Touch me not’ plants when touched by hand?
(c) Compare the movement of growth of the pollen tube towards ovule with the bending of shoots of sunflower plant towards sunlight.
(d) Compare the movement in folding of leaves of ‘Touch me not’ plants with the movement of body parts in the animals.
Answer
(a) The bending of shoots in the plants :
- Bending of shoots of plants is a response to the stimulus and a directional, growth-related movement.
- When growing plants detect sunlight, a hormone called auxin, synthesized at shoot tip helps the cells to grow longer.
- When light is coming from one side of the plant, auxin diffuses to the shady side of the shoot.
- This concentration of auxin stimulates the cells of the shoot to grow longer on the side of the shoot which is away from the light. Thus, plant appears to bend towards light.
(b) The folding of the leaves in ‘Touch me not’ plant :
- Leaves of ‘Touch me not’ plant respond to the stimulus by showing growth independent movement.
- These plants use electrical–chemical means to convey the information from cell to cell.
- Movement happens at a point different from the point of touch.
- Plant cells change shape by changing the amount of water in them, resulting in swelling or shrinking, and therefore in changing shape.
(c) Growth of pollen tubes towards the ovule is an example of chemotropism whereas bending of shoots towards sunlight is an example of phototropism.
(d)
- Although both plants and animals show electrical–chemical means to convey the information from cell to cell but unlike nerve cells in animals there is no specialized tissue in plants for conduction of information.
- In animal cells, change in shape occurs because of the specialized proteins found in muscle cells; plant cells change shape by changing the amount of water in them.
Related Questions
(a) Distinguish between ethanol and ethanoic acid experimentally.
Attempt either subpart B or C.
(b) Give the IUPAC name of the first member of Alkene which is formed by addition of conc. sulphuric acid to it. Illustrate the change with the help of a chemical equation.
OR
(c) “All combustion reactions are oxidation but all oxidation reactions are not combustion.” Justify.
Mohan and Rohit observed that shoots of a plant growing in shade bend towards the sunlight. Whereas, leaves of ‘Touch me not’ plant fold and droop soon after touching. They were curious to know how these movements occur in plants.
In order to help them understand the movements in the plants, answer the following questions:
Attempt either subpart A or B.
(a) What causes the bending of shoots in the plants as shown in figure A?
OR
(b) What causes the folding of the leaves in ‘Touch me not’ plant as shown in figure B?
(c) Compare the movement of growth of the pollen tube towards ovule with the movements shown in part A of the above figure.
(d) Compare the movement shown in figure B with the movement of body parts in the animals.
The below image is that of a reflecting telescope. Reflecting telescopes revolutionised our ways of looking into the sky. They employ mirrors to gather and focus light, rather than relying solely on lenses as in their refracting counterparts. These telescopes utilise precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where it forms an image for observation.
(a) What kind of image of the star is seen by the observer at the eyepiece?
(b) What kind of mirror is used in this reflecting telescope?
Attempt either subpart C or D.
(c) Explain with reason what kind of optical device (type of lens or mirror) that is used at the eyepiece.
OR
(d) What is the role of the plane mirror in the telescope?
Azim Taraporewala was a traveller and science enthusiast. During one of his travels he found himself on the edge of an island without any mode of communication. As he had read in many stories, he thought he would light a fire on the beach and travelling boats or ships could see that fire and come to give him a ride. He had run out of lighters and match-sticks but had a reading glass. Being a science enthusiast he knew some tricks and used that lens and a scrap of paper to light a fire, with the help of scorching rays from the sun.
(a) Which lens can be used by Azim to create the fire?
(b) What property of the lens helps Azim to create the fire?
Attempt either subpart C or D.
(c) List two more uses of this kind of lens.
OR
(d) Explain with reason the condition under which the lens can form both real as well as virtual images.