Theory question 107
Nutrient Cycling(For candidates in Nigeria only)
(a) With the aid of annotated diagrams only, outline the water cycle.
(b) Describe an experiment to show that water is conducted in the xylem tissue of flowering plants.
Show the model answer
(a) Labelled/annotated diagram showing: evaporation from seas, rivers and lakes; transpiration from plants; evaporation from soil; respiration, sweating and excretion by animals; water vapour rising and condensing into clouds; precipitation (rain) falling; run-off into streams and water bodies; infiltration into underground water; absorption by plant roots; drinking by animals; decay returning water.
(b) Cut a young herbaceous shoot (e.g. balsam) under water; wash the roots/stem; stand it in a beaker of dilute dye (eosin or red ink) in sunlight for a few hours; remove, wash, and cut thin transverse sections of the stem; view under a microscope: only the xylem is stained red, showing water travels up in the xylem.
For (a) the marks are in the arrows and labels on the diagram, not in written paragraphs.