Question 6
- Explain briefly the process of perceiving smell in humans. [4 marks]
- State the adaptive features of the egg of a domestic fowl. [6 marks
- (i) What are autotrophs? [2 marks]
(ii) Name two unicellular organisms that are autotrophs. [2 marks] - State five functions of the World Health Organization (WHO). [5 marks]
- Name two examples each of plants and animals that live in a freshwater pond. [4 marks]
- State five differences between the skin of a mammal and the epidermis of a leaf. [5 marks]
- A farmer has two plots of land: Plots A and B, On Plot A, the farmer planted several seeds of maize. On Plot B, the farmer planted several seeds of maize and pepper in a small area.
What type of competition would be observed on:
(i) Plot A:
(ii) Plot B. [2 marks]
Observation
Many candidates could not answer (a) well by explaining the procedure of perceiving smell in humans properly.
6 (b) and (c) (i) were well answered. In c) (ii), some candidates could not name unicellular organisms that are autotrophs. Some candidates could answer (d) properly while (f) was answered poorly. Some candidates interchanged the answers in question (g).
The expected answers are:
- The process of perceiving smell
- Chemical substances/odour carried in the air pass through the air/nasal cavity;
- The molecules dissolve in the moist membrane of the nasal cavity;
- Sensory cells are stimulated;
- Impulses are formed;
- Which pass through the nerve endings to the olfactory nerves; - Which pass into the cerebrum of the brain/brain;
- The brain interprets the impulses;
- And the sensation of smell is produced/smell is perceived.
- Adaptive features of the egg of a domestic fowl
- Porous shell; for gaseous exchange/provides shelter/protects the embryo against mechanical damage/desiccation;
- Shell membranes; allow gaseous exchange/for protection;
- Yolk; contains high level of proteins and fats/provides food for embryonic growth;
- Egg white/albumen; consists of water to absorb shock/ proteins/food;
- Air space; provides surface for gaseous exchange;
- Chalaza; holds the yolk/embryo in position.
Note: Function must correspond with the structure to score;
Structure alone can score 1 mark if function is wrong;
Function alone cannot score. -
(i)Autotrophs
Organisms that do not rely on other organisms for food/they manufacture their own food; from using simple inorganic compounds; can be chemosynthetic/photosynthetic.(ii) Examples of unicellular autotrophs
Chlamydomonas; Euglena; Chemosynthetic bacteria/sulphur bacteria; blue-green algae/Anabaena; Nostoc/Oscillatoria; Chlorella/diatoms; Nitrosomonas; Nitrobacter/any correctly named example.
Note: Spelling must be correct to score.
- Functions of WHO
- Provides grants for medical research;
- Improves public health/promotes environmental health;
- Prevents the spread of diseases/vaccination;
- Provides vaccines/drugs in cases of emergences;
- Informs/creates awareness/educates the public of any research findings/outbreak of diseases;
- Assists by sending medical personnel/logistical support to countries upon request;
- Helps in the training of medical personnel;
- Keeps health statistics;
- Promotes nutritional/sanitary products.
Note: Any correctly named function should score.
-
Examples of plants and animals that live in a freshwater pond
Plants: Water arum; diatoms; Ceratophyllum/hornwort; Utricularia/bladderwort; Arrowhead/sedge; Pistia; Salvinia/water fern; water lily; Wolffia/duckweed any other correctly named example.
Animals: Cyclops; Daphnia/water flea; Hippopotamus; crocodile; water snake; tadpoles; pond skaters; zooplanktons; mosquito larvae; water bugs; water scorpions; leeches; water snails; catfish/Tilapia/fishes etc/any correctly named freshwater animal.
Note: Spelling must be correct to score in plants and animals
- Differences between skin of a mammal and epidermis of leaf
-
Type of competition on
(i) Plot A Intraspecific/intraspecies competition
(ii) Plot B Interspecific/interspecies competition