In an experiment to investigate the effects of light intensity on the rate of photosynthesis, a shoot of elodea (water weed)was used.

In an experiment to investigate the effects of light intensity on the rate of photosynthesis, a shoot of elodea (water weed) was used. The shoot was immersed in 2% sodium hydrogen carbonate solution maintained at 15^oC in an apparatus which allowed for collection of a gas evolved from the shoot. The gas given off was collected for five minutes at each light intensity and its volume recorded as shown below.

​(a) Using the data given in the table plot a suitable graph of gas evolved against light intensity (6mks)

see graph
NB

• ​correct plotting
• Smooth curve 1mk
• Axes correctly labeled -2mks
• Scale -2mks

(b) Account for the rate of gas evolved

(i) 1 and 18 arbitrary units (3mks)

Gas evolved  increase with increase in light intensity; increase in light leads to more splitting of water molecules into hydrogen ions and oxygen; hence increase in rate of photosynthesis

(ii) 26-46 arbitrary units (2mks)

Amount of gas evolved remained constant as rate of photosynthesis constant due to limiting factors

Glucose formed is converted into starch for storage in the tissue.

​(c) Explain why a green leaf is normally tested for the presence of starch instead of glucose (2mks)

Glucose formed in converted into starch is osmotically in activated hence stored

(d) How is the dry mass of a leaf determined (3mks)

By heating the leaves in an oven at 110^oC and weighing them; then heating and weighing is repeated several knows till constant weight i​s obtained

​(e) Describe how the chloroplast is adapted to its functions (4mks)

Has stroma where Carbon (IV) oxide fixation takes place; has a grana containing; chlorophyll that traps light energy for photosynthesis. Has integranna lamellae that hold the grana position