1. What are the plant growth responses to light and gravity called ?
Answer
The plant growth responses to light and gravity are called phototropism (light) and geotropism or gravitropism (gravity).
2. A student investigated plant growth responses using newly germinated mustard seedlings. The seeds were grown on cotton wool in a plastic dish for three days, then placed in a box with a hole cut in the side and a lamp positioned next to the hole. The seedlings were left in the box for five days. Describe the growth response of the shoot after five days and explain why this growth response is useful for the shoot.
Answer
The shoot grows towards the light, which is called positive phototropism. In this way, the shoot and leaves receive more light for photosynthesis, leading to increased production of glucose for energy, glucose for cell wall synthesis, and protein for growth.
3. Explain what causes the shoot above to curve in this growth response.
Answer
Plant hormones called auxins accumulate on the shaded side of the shoot and cause cell elongation, which makes the shoot curve.
4. Suggest how the method above could be modified to investigate the effect of light intensity on the growth responses of mustard seeds. Identify the control variables the student should keep constant when carrying out this investigation.
Answer
The student could put the lamp different distances from the box to vary light intensity and could measure the length of each seedling at the start and end of the investigation. He must keep constant the same number of seeds or seedlings in each plastic dish, the same amount of water on the cotton wool, the same type of seed or seedling, and the same temperature.
5. Which of the following is not a use of auxins ?
a) As selective weed killers
b) As rooting powders
c) For promoting growth in tissue culture
d) For increasing fruit sweetness in plants
Answer
d) For increasing fruit sweetness in plants
6. Selective weed killers kill some plants. Explain how the use of weed killers affects biodiversity.
Answer
Insects may rely on the weeds for food so killing the weeds may result in loss of some insects which other animals relied on for food, and so biodiversity is decreased.
7. Ethene is a plant growth hormone used in the food industry. Explain why bananas are picked and transported when they are green, then stored in a room containing ethene gas.
Answer
Bananas are easier to transport when unripe then ethene promotes ripening before the bananas are sold.
8. Why might a gardener soak seeds in a solution containing gibberellins before planting ?
a) To increase chlorophyll production in leaves
b) To end dormancy and trigger germination
c) To enhance root hair formation directly
d) To strengthen the seed coat against pests
Answer
b) To end dormancy and trigger germination
9. Why might a gardener spray tomato plants with a solution containing gibberellins ?
a) To increase tomato size b) To improve soil nutrient absorption c) To promote leaf fall d) To enhance resistance against fungal infections
Answer
a) To increase tomato size