WAEC SSCE - Biology - 2012 (Practical)

(a)(i) Mode of nutrition of specimen D (tick): parasitic (it sucks blood from its host).

(a)(ii) One way each is of economic importance

• C (grain weevil): it destroys stored grains and lowers their quality, reducing the farmer's income.
• D (tick): it infests cattle and dogs, sucking blood and making them anaemic, and it transmits diseases.
• E (rat): it destroys and contaminates stored food and spreads diseases.

(b)(i) Classification into phyla and classes

(b)(ii) Three observable characteristic features of each class

• Insecta (C): body in three divisions (head, thorax, abdomen); three pairs of jointed walking legs; a pair of antennae; compound eyes (and usually wings).
• Arachnida (D): body in two divisions (cephalothorax and abdomen); four pairs of legs; no antennae; simple eyes; feeding appendages (pedipalps and chelicerae).
• Mammalia (E): body covered with hair/fur; external ears (pinnae); mammary glands; four limbs; heterodont dentition.

(b)(iii) Two observable differences between C and D

(c) Four observable sensory features of specimen E (rat): the eyes (sight), the external ears/pinnae (hearing), the nostrils (smell) and the whiskers (touch).

(a)(i) Types of fruit in specimens A and B, with reasons

Specimen A (garden egg): a berry. Reason: it has a fleshy pericarp with many seeds embedded in it.

Specimen B (Tridax fruit): a cypsela. Reason: it is a dry, single-seeded fruit that develops from an inferior ovary and bears a hairy pappus (parachute) formed from the modified calyx.

(a)(ii) Labelled drawing of the lateral (side) view of specimen B (Tridax fruit)

The drawing below shows the lateral view of the Tridax cypsela, made 8-10 cm long and fully labelled.

(b) Modes of dispersal of specimens A and B

Specimen A (garden egg): dispersed by animals. The fleshy, edible fruit is eaten by animals; the seeds pass through the gut unharmed and are voided in the droppings some distance away.

Specimen B (Tridax fruit): dispersed by wind. The light, dry fruit bears a crown of feathery pappus hairs (a parachute) that increases its surface area, so it is easily carried away by air currents.

(c) Five differences between specimens A and B

(a)(i) Class of each specimen

• Specimen J (tilapia): Class Osteichthyes (bony fishes).
• Specimen K (toad): Class Amphibia.
• Specimen L (lizard): Class Reptilia.

(a)(ii) Three reasons for placing each specimen in its class

Specimen J (Osteichthyes):

• The body is covered with thin, overlapping bony scales.
• It possesses paired fins (pectoral and pelvic fins).
• A lateral line runs along each side of the body.
• The gills are covered by a bony operculum (gill cover).

Specimen K (Amphibia):

• The skin is moist and warty (glandular), without scales.
• The hind limbs bear webbed digits.
• It has large, bulging eyes.
• A visible ear drum (tympanum) lies behind each eye.

Specimen L (Reptilia):

• The skin is dry and covered with horny scales.
• It has two pairs of limbs bearing clawed digits.
• The teeth are all alike (homodont dentition).
• It possesses a well-developed, retractable tongue.

(b) Two structural adaptations for escaping predators

Specimen K (toad):

• Poison (parotoid) glands in the skin secrete an irritant substance that repels predators.
• Long, muscular hind limbs enable it to leap swiftly away from danger, while counter-shading of the dorsal and ventral surfaces camouflages it.

Specimen L (lizard):

• The tail is detachable (autotomy); it can be shed to distract a predator while the lizard escapes.
• The skin colouration blends with the surroundings (camouflage), concealing it from predators.

(c) Drawing, 8 - 10 cm long, of the lateral view of specimen J (tilapia)

The lateral (side) view of the tilapia is shown below, drawn 8 - 10 cm long with the parts clearly labelled.

(d)(i) Two similarities between specimens J and L

• Both possess eyes and a pair of nostrils on the head.
• Both have a body covered with scales and bear a tail.

(d)(ii) Two observable differences between J and L