question_answer

                The graph shows how the amount of carbon dioxide taken in or given out by a plant varies through a 24-hour period. (a) At what time did photosynthesis start? (b) At what time was the rate of photosynthesis greatest? (c) At what time of the day did it get dark? (d) (i) What processes causes carbon dioxide to be given out?               (ii) Does this process only occur when  it is dark?                           (e) What other factors could affect the rate   of photosynthesis?   

Answer:

                  (a) 7.00am                                                               (1)    (b) The rate of photosynthesis was greatest at 12 noon as the amount of carbon dioxide taken in  was greatest at that time.               (1) (c) 9.00pm                                                          (1) (d) (i) Respiration                                          (1/2) (ii) No, respiration occurs 24 hours a day.   During daylight, photosynthesis takes in more carbon dioxide than is released by   respiration.                                                    (1/2) (e) Factors which affect the rate of photosynthesis are humidity, temperature and concentration  levels of carbon dioxide in the air. There are optimum levels for each factor above, after which  photosynthesis will start to decrease.                                             (1)