answer me please only question no19
Answers
A growth of a plant in the direction of it's light source is called phototropism. Phototropism occurs when a plant responds to the light by bending towards it. Photo means light and tropism is the growth of a plant as a response to the stimulus.Plants are very sensitive so they are involved in many kinds of tropisms which is necessary for their survival.
The phototropism happens because - as plants need food to survive by converting the light energy into chemical energy by the process of photosynthesis, they bend towards the light to capture as much as light energy they can for it's survival.
Occurence
(i) When sunlight falls straight on the plant, the auxin hormone synthesised at the tip of the stem spreads uniformly down the stem and due to equal concentration of auxin, stem grows straight.
(ii) When sunlight fells on only one side of the plant, the auxin diffuses towards the shady side of shoot. The concentration of auxin stimulates the cells to grow longer. Therefore, the stem appears to bend towards the source of light.
Answer:
Hello Friend!
I am so sorry to tell you that I can't see the Question 19 in detail.But I can tell you the answer of Question 20.
Explanation:
(i) Phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs.
(ii) When sunlight fells on only one side of the plant, the auxin diffuses towards the shady side of shoot. The concentration of auxin stimulates the cells to grow longer. Therefore, the stem appears to bend towards the source of light.
(iii) Activity: Take 2 seedlings of mustard plant. Keep them in a small bottle containing water. Now close bottle with a split cork, then keep it inside a wooden box that is provided with a small opening on one side. Now keep box near to a light source in such a way that “opening in box faces light source”.