WAEC SSCE - Biology - 2016 (Practical)
Question 1 Report
(a)(i) Cut a pieces of specimen A, place it on the white tile. Add a few drops of iodine solution. Record the observation and result in a tabular form.
(ii) Squeeze a few drops of specimen E on another clean white tile provided, add a few dre Record the observation and result in a tabular form.
(b)(i) State two observables differences between specimens A and B. (ii) Suggest two factors that are likely to be responsible for the state of specimen B.
(iii) With the aid of hand lens/magnifying lens, observe.specimen B. and name an organism that is likely growing on it. (iv) State the mode of feeding of the organism on specimen B (c) ) Make a drawing 6cm-8 cm long, of specimen C and label fully. one function each of any three parts labeled.
Answer Details
(a)(i) Iodine test on specimen A (bread)
| Test | Observation | Result (inference) |
|---|---|---|
| A piece of specimen A is placed on the white tile and a few drops of iodine solution are added | The brown iodine solution turns blue-black | Starch is present in specimen A |
(a)(ii) Iodine test on specimen E (orange juice)
| Test | Observation | Result (inference) |
|---|---|---|
| A few drops of specimen E are squeezed onto a clean white tile and a few drops of iodine solution are added | The iodine solution remains brownish / yellowish (no colour change) | Starch is absent in specimen E |
(b)(i) Two observable differences between specimens A and B
| Specimen A (fresh bread) | Specimen B (stale bread) |
|---|---|
| White / cream in colour | Dark brown / black in colour |
| Soft in texture, fresh, with no mould | Hard in texture, stale / decaying, bearing mould (Rhizopus / Mucor) |
(b)(ii) Two factors likely responsible for the state of specimen B
- Presence of moisture / humidity.
- Presence of warmth (a suitable temperature), together with fungal spores acting over time, which allowed micro-organisms to grow and spoil the bread.
(b)(iii) Organism likely growing on specimen B
A mould (fungus), for example Rhizopus (bread mould) or Mucor.
(b)(iv) Mode of feeding of the organism
Saprophytic: it feeds on the dead organic matter of the bread by secreting enzymes for external (extracellular) digestion and then absorbing the digested nutrients.
(c) Drawing of specimen C (boiled egg)
Below is a labelled drawing, 6 cm to 8 cm long, of the longitudinal section of the boiled egg (specimen C).
(ii) One function of any three labelled parts
| Labelled part | Function |
|---|---|
| Shell | Protects the egg and its contents, gives shape and allows gaseous exchange (aeration) |
| Albumen (egg white) | Supplies protein and water to, and cushions, the developing embryo |
| Yolk | Stores food (fat and protein) for the growth and nourishment of the embryo |
Other parts labelled include the shell membrane and the air space, both of which aid gaseous exchange for the embryo.
