Theory question 102
Transport in Plants(a) Explain briefly the process of translocation of food in plants.
(b) A student obtained a green leaf from a plant that has been exposed to sunlight for six hours and wants to test it for starch in the laboratory. Complete the table below by stating four steps that would be involved in the experiment and give one reason for each of the steps.
Table columns: Four steps involved in the experiment | One reason for the step
(c) Complete the table below on enzymes
Table columns: Enzyme | Organ/gland where enzyme is produced | Site of action | Substrate that enzyme acts on
Rows: Ptyalin; Trypsin; Sucrase
Show the model answer
(a) Translocation is the movement of manufactured food (mainly sucrose and amino acids) from the leaves where it is made to other parts (growing points, storage organs, fruits) through the phloem sieve tubes, in both directions.
(b) 1. Boil the leaf in water for a few minutes - to kill the cells and stop enzyme action, and make the cells permeable.
2. Put the leaf in alcohol (methylated spirit) in a test tube heated in a water bath - to remove the chlorophyll (decolourise the leaf).
3. Dip the leaf in warm water - to soften it, as alcohol makes it brittle.
4. Spread the leaf on a white tile and add iodine solution - a blue-black colour shows starch is present.
(c) Ptyalin - salivary glands - mouth - starch (cooked starch) to maltose.
Trypsin - pancreas - duodenum (small intestine) - proteins/peptones to polypeptides.
Sucrase - wall of small intestine (intestinal glands) - small intestine (ileum) - sucrose to glucose and fructose.
Never heat alcohol over a direct flame; use a water bath.