JAMB Biology 1983

B: Epidermis of roots

A root hair is a tubular extension of a root epidermal cell. It increases the surface area available for absorbing water and mineral ions. The pericycle lies deeper inside the root and gives rise to lateral roots rather than root hairs.

A: Position of 7

The central star-shaped xylem, with phloem between its arms, is characteristic of a young dicot root. Dicot stems instead usually have separate vascular bundles arranged in a ring. A circular outline alone does not distinguish a root from a stem.

B: Produce more of 5 and 7

The vascular cambium divides to produce secondary xylem towards the inside and secondary phloem towards the outside. It therefore adds more of the tissues labelled 7 and 5. Cork is produced by cork cambium, a different meristem.

D: Produce lateral roots

Lateral roots arise from the pericycle, the cell layer just inside the endodermis. New root primordia develop internally and grow out through the surrounding tissues. Root hairs instead arise from epidermal cells on the root surface.

D: Contain chloroplasts

In a typical dicot leaf epidermis, guard cells contain chloroplasts whereas ordinary epidermal pavement cells usually do not. Guard cells also possess nuclei and vacuoles. Their changes in turgor regulate the opening of the stomatal pore.

C: Have nonwoody stems

In botanical usage, herbs are herbaceous plants with nonwoody above-ground stems. Shrubs retain woody stems. Herbs can be annual, biennial or perennial, and the word does not mean that the plant must be medicinal.

B: Carbohydrates

Many common carbohydrates have hydrogen and oxygen atoms in a 2:1 ratio, as in glucose, C₆H₁₂O₆. This ratio is a useful introductory clue, but it does not alone prove that an unknown compound is a carbohydrate; there are exceptions and other compounds with the same ratio.

A: Magnesium and iron

Magnesium is the central metal atom in chlorophyll. Iron is required for processes involved in chlorophyll synthesis, although it is not the central atom of the chlorophyll molecule. Deficiency of either can therefore impair normal green pigmentation.

D: Nastic movement

A nastic movement is a plant-part response whose direction is independent of the direction from which the stimulus arrives. In a tropism, the direction of growth depends on the stimulus direction. Phototropism concerns light, and thigmotropism concerns directional touch.

C: Cerebellum

The cerebellum integrates sensory feedback and helps coordinate posture, balance and precise movements. It compares intended movement with incoming information and contributes corrective signals. Other brain regions also participate, but the cerebellum is the best answer here.

D: 3

An axillary or lateral bud can grow into a daughter bulb, allowing vegetative multiplication. The fleshy scales supply stored food, the basal stem bears these tissues and the roots absorb water and minerals. The labelled lateral bud is part 3.

E: Fleshy leaf bases

The onion bulb stores much of its food in thick, fleshy leaf bases or scales. These surround a short basal stem. The dry outer protective scales are not the principal succulent storage tissue.

C: Aggregate fruit

An aggregate fruit develops from several separate carpels of a single flower. Each carpel contributes a fruitlet. A multiple fruit instead develops from flowers grouped in an inflorescence, while a simple fruit comes from one ovary.

B: Maize rust

Maize rust is caused by fungi, such as Puccinia sorghi in common rust. The other listed diseases are viral: rinderpest, Newcastle disease, swine fever and cassava mosaic disease. A fungal rust pathogen is biologically different from a virus.

D: A homozygote

An organism with two identical alleles at a particular gene locus is homozygous at that locus. For example, AA and aa are homozygous genotypes, whereas Aa is heterozygous. Diploid describes chromosome-set number rather than whether the two alleles match.

C: produce suckers

Banana, plantain and pineapple can all produce suckers used for vegetative propagation. These shoots can grow into new plants. Pineapple is a multiple fruit, but banana and plantain are not, so fruit type does not unite all three.

D: Dog

An adult dog has, on each side, three upper and three lower incisors, one canine in each jaw, four premolars in each jaw, two upper molars and three lower molars. Doubling the one-side total gives 2 × (3 + 3 + 1 + 1 + 4 + 4 + 2 + 3) = 42 teeth.

B: They attract insects only for pollination

Insectivorous plants attract some insects as prey, not solely as pollinators. Digestion of prey supplies nutrients such as nitrogen, helping these plants live in nutrient-poor habitats. They generally still use photosynthesis to make carbohydrates.

D: Atlas, axis, remaining cervical, thoracic, lumbar

The atlas is the first cervical vertebra, C 1, and the axis is the second, C 2. The remaining cervical vertebrae follow, then the thoracic vertebrae and then the lumbar vertebrae. Atlas and axis are therefore part of the cervical region, not separate regions.

D: Auxin accumulating on the shaded side and promoting greater elongation there

Under one-sided illumination, auxin becomes more concentrated on the shaded side of a coleoptile. At growth-promoting concentrations, cells there elongate more than cells on the illuminated side. The unequal elongation bends the shoot towards the light.

D: Lacks axillary buds

Cassava’s swollen storage organ is a storage root. It lacks the axillary buds associated with nodes on a stem tuber. Storing food alone does not make an organ a stem: roots and modified stems can both act as food stores.

A: Transmission of vibrations

The malleus, incus and stapes form a chain that transmits vibrations from the eardrum to the oval window of the inner ear. This transfer helps sound energy enter the fluid-filled inner ear. Balance is mainly sensed by the vestibular apparatus, not the ossicles.

B: Secchi disc

A Secchi disc is lowered into water to measure the depth at which it disappears from view, providing a measure of water transparency. Cloudier water usually reduces this depth. The reading is a clarity indicator, not a direct laboratory turbidity reading in NTU.

E: 2 → 3 → 1 → 4 → 5

A plausible chain begins with Mucuna, the producer, followed by a plant-eating grasshopper, an insect-eating toad, a snake and a hawk. Arrows run from food to consumer, showing the direction in which energy passes along the chain.

C: Glycogen

Rhizopus is a fungus, and glycogen is a fungal storage polysaccharide. It consists of branched chains of glucose units. Starch is the usual plant storage polysaccharide, while oil is a lipid rather than a carbohydrate.

C: Unaffected by humidity

Humidity affects the water-vapour gradient between a leaf and the air. At otherwise comparable conditions, high humidity generally reduces evaporation from the leaf. Temperature, light, air movement and water supply can also influence transpiration.

D: Snail

A snail is a mollusc and lacks the jointed appendages characteristic of arthropods. Its shell is an external protective structure, but it is not the articulated arthropod skeleton. Cockroaches, spiders, millipedes and dragonflies are arthropods.

E: A total of six molars

The complete permanent dentition has three molars in each of four quadrants, giving twelve molars. There are eight incisors, four canines and eight premolars, for a total of thirty-two teeth. Each jaw contains sixteen teeth.

D: Loses water and its protoplast shrinks

Water leaves the cell by osmosis towards the lower water potential outside. The protoplast loses volume and can pull away from the cell wall, causing plasmolysis. The rigid wall does not simply shrink along with the cell contents.

A: Liver

The liver converts nitrogen from amino-acid breakdown into urea through the urea cycle. Blood then carries urea to the kidneys for excretion in urine. The urinary bladder stores urine; it is not the main site of urea synthesis.

E: Ileum → hepatic portal vein → hepatic vein → vena cava → heart

Absorbed glucose reaches the liver through the hepatic portal vein. Blood passes through liver sinusoids, leaves through hepatic veins and enters the inferior vena cava on the way to the heart. The listed vessel sequence leaves the intervening liver tissue implicit.