Biology Paper 2, WASSCE (PC), 2016

Question 1

  1. Explain briefly how soil water gets to the leaves of a plant. [5 marks]
  2. State five reasons for classifying organisms. [5 marks]
  3. Explain briefly how the following structures of mammals are adapted to their functions:
    1. veins; [6 marks]
    2. arteries. [4 marks]


This question was not a popular one amongst the students as many did not attempt it and those who answered it performed below average. In (a), some candidates focused their answers on transpiration, instead of essentially writing on turgidity, osmosis and plasmolysis. Many candidates did not write anything on the root pressure, capillarity and transpiration pull by cohesive and adhesive forces.
Many candidates answered (b) by listing the different groups of microorganisms instead of writing on how, why and stating the advantages of having names for organisms. Candidates stated the functions of the blood vessels rather than stating the structures with their functions for adaptation in (c).

The expected answers are:


(a) How soil water gets to the leaves of plants

- Soil water is absorbed/enters root hairs by osmosis;

- soil water is less concentrated than sap of root hair cells;

- cell sap becomes more diluted than the cortical cells of the root adjacent to root hairs;

- this process continues until water enters the xylem of the root;

- root pressure pushes the column of water in the xylem of the stem to a certain height;

- water moves up by capillarity/capillary action;

- transpiration pull/lifts water in a column up the xylem vessels of the leaves; by the cohesive forces of water molecules;

- as well as the adhesive forces for the walls of the xylem.


(b) Reasons for classifying organisms

- to sort out organisms into specific groups;

- to show the relationships between organisms;

- for easy identification/provide universally accepted names/nomenclature;

- to trace the possible origin/ancestor/evolution of organisms;

- for easy reference;

- for easy study/research.


(c)(i) Adaptations of Veins

- presence of wide lumen; to allow the volume of blood flow;

- presence of valves; to prevent reflux/backflow of blood;

- presence of thin/less muscular wall; to allow smooth flow of blood;

- presence of non-elastic wall; to compensate for low blood pressure;

- superficially located under skin; to facilitate easy removal of some excretory products /heat/water vapour/sweat.

(ii) Adaptations of Arteries

- absence of valves; to allow easy flow of blood;

- thick/muscular wall; to withstand high blood pressures;

- elastic wall expands/contracts/dilates/constricts; to allow for regulation of blood volume;

- deeply situated in muscles; to protect against fatal injuries leading to loss of blood;

- small lumen; to increase pressure of blood flow.

Note: Structure must correspond to function to score for c (i) and c (ii).
Structure x 1 mark; function x 1 mark.
Function alone should not score; Structure alone scores.