Year 12s: what will be the first way you research your future options? >>

Biology - Hormones in Plants - Tropisms ( please help )

Hello, I have a question that I feel a little unsure of.

In an investigation into the effect of light intensity on the growth of young shoots some seedling were grown in bright light and some in the dark.

1. Predict the results of the experiment. (1 mark)
2. Explain the results in terms of the auxin content of the seedings.(3marks)
3. What steps should be taken to make the investigation valid and reliable?(4 marks)
4. Suggest the survival value of to the seedings of the behaviour investigated in questions 1-3.(3 marks)

For the first question I do not know how to answer, it is only worth one mark. The question does not state whether the light is one sided, or if there is any light source in the dark. If shoots are in all round light/ darkness then the shoots will grow evenly and their stems would grow straight, because auxin concetration is equal. The shoot in darkness would be tall, thin, straight and yellow (becasue of absence of chlorophyll manaufacturing due to there being no light). The shoot in the light would be healthy and green growing straight upwards.

For question 2, the auxin content will be lower in the shoot grown in bright light becasue bright light destroys auxins. In addition, the shoot in bright light will grow shorter than the plant in the darkness, becasue of the decreased auxin concentration. However, because there is light all around, the growth regions will recieve equal quantities of auxins, which causes the shoot to grow straight and the cells grow at the same rate.
The shoot in the dark will have a higher auxin concentration becasue of the lack of light. The auxin concentration will be even is the growth cells, causing the shoot to grow longer than the plant in light and the shoots will be straight.

Question 3: In order for the investigation to be valid, the same species and age of seedlings should be used. In addition, the light intensity, temperature and water content of the soil should also be kept constant. Furthermore, for this investigation to be reliable the experiment should be repeated in case of any mistaken readings or anomalous results.

Question 4: I am not sure how to answer this. The shoot in the light could have the the survival value of growing in light for photosynthesis to take place?

I really do not know how to answer the last question, or if my previous answers are correct. I would appreciate any clarifications or help 😀