Biology 2021 Jamb Examination

To determine the water content of the soil:
Mass of soil before heating = 29g - 10g = 19g
Mass of soil after heating = 18g - 10g = 8g
Mass of water lost = 19g - 8g = 11g

The percentage of water is calculated as:$$\text{Percentage of water} = \dfrac{\text{Mass of water}}{\text{Mass of wet soil}} \times 100 = \dfrac{11}{19} \times 100 \approx 57.89\% \approx 60\%$$Hence, the correct answer is 60%.

The contractile vacuole is an organelle in protozoa that regulates water balance by expelling excess water.
Other options are incorrectly matched: Stomata are in plants, alveoli in lungs, and Malpighian tubules in insects.

In fish, water enters the mouth, passes over the gills where gas exchange occurs, and exits via the operculum.
This unidirectional flow ensures efficient oxygen uptake and carbon dioxide removal.

Blood group AB has both A and B antigens and no antibodies, making AB individuals universal recipients but they can only donate to AB because their blood contains both antigens which could be attacked by antibodies in A, B, or O recipients.

Xerophytes are adapted to arid conditions and have features such as thick cuticles, reduced leaves, and deep root systems to minimize water loss and survive prolonged drought.

Insects (Insecta) constitute the largest and most diverse class of animals, with millions of species described and many more undiscovered.
They occupy nearly all habitats, have high reproductive rates, and play vital roles in ecosystems.

Nastic movements are non-directional responses to stimuli such as light, touch, or temperature, e.g., the folding of leaves in Mimosa pudica when touched.
Unlike tropisms, they do not depend on the direction of the stimulus.

Hugo de Vries proposed the mutation theory, suggesting that new species arise from sudden hereditary changes (mutations) rather than gradual modification, providing an alternative mechanism to natural selection.

Both parents are heterozygous: Aa x Aa.
Using a Punnett square, offspring genotypes: AA, Aa, Aa, aa.
Probability of recessive (aa) = $$\dfrac{1}{4}$$.

Double circulation refers to the passage of blood through the heart twice during a complete circuit: once through the pulmonary circuit (to the lungs) and once through the systemic circuit (to the body).
This ensures efficient oxygenation and separation of oxygenated and deoxygenated blood.