2019 JAMB BIOLOGY PAST QUESTIONS AND ANSWERS

The fastest rate of growth is represented by the steepest part of the curve, where growth is rapid. In a typical growth curve, this corresponds to the exponential phase, often found before the leveling off at the stationary phase.

The grand period of growth is the part of the curve where growth accelerates, generally seen in the middle part of the curve. This is where growth is rapid before reaching the maximum potential.

Sensory neurons receive stimuli from the body or environment and carry signals to the central nervous system. Other neuron types like motor neurons transmit signals from the central nervous system to muscles and glands.

A climax community is a stable, mature ecological community that remains relatively unchanged until environmental or climatic changes occur. It is the final stage in ecological succession. Other options refer to earlier succession stages or characteristics.

A population consists of organisms of the same species that interbreed freely in a shared habitat. While they may behave similarly or occupy the same area, interbreeding is key to defining a biological population.

In a food chain, as energy is transferred, organisms become progressively larger and fewer, with energy loss at each trophic level. Secondary and tertiary consumers are larger predators at the top of the food chain.

The top of the pyramid, represented by the tertiary consumer level, has the least stored energy due to energy losses at each trophic level. Each subsequent level retains only about 10% of the energy from the previous level.

In the given ecological pyramid, the shark represents a tertiary consumer, feeding on secondary consumers like Tilapia. Algae, on the other hand, are producers at the base of the food chain.

Mangrove swamps develop where freshwater from rivers meets seawater, creating a brackish environment with specific vegetation adapted to fluctuating salinity. This habitat often supports diverse marine life.

Clay has the finest particles among soil types, retaining water well but draining poorly. Other soil types like sand have larger particles and do not hold water as effectively.

Malaria symptoms result from the destruction of red blood cells by the malaria parasite’s lifecycle stages within the bloodstream, releasing toxins that cause fever and chills.

All daughters will be carriers as they inherit one X chromosome from the haemophilic father and one from the non-carrier mother. Sons will not inherit haemophilia as they receive the unaffected X from the mother and a Y chromosome from the father.

The mitochondrion is known as the powerhouse of the cell and is responsible for cellular respiration, where ATP is produced. This process provides energy for cell functions. Other organelles like the endoplasmic reticulum and ribosome have different roles in protein and lipid synthesis.

A tissue is an aggregate of similar cells that perform the same function. This organization allows cells to work together efficiently. For example, muscle tissue consists of muscle cells that contract to produce movement.

The correct life cycle involves a progression from prothallus to egg/sperm formation, fertilization, and development into a leafy plant that produces spores. Ferns have a unique alternation of generations. Other sequences do not capture this biological process accurately.

Platyhelminthes, or flatworms, have a third tissue layer, the mesoderm, which coelenterates (like jellyfish) lack. This development allows for more complex body structures and organ systems. Other differences are less defining or specific to each phylum.

Hydra is diploblastic (has two tissue layers), while tapeworms are triploblastic (have three layers). This structural difference underpins the complexity of these organisms’ body plans and modes of feeding. Other options describe additional but non-structural differences.

The duration of sunlight, or photoperiod, affects the flowering time of plants by signaling when to reproduce. This adaptation ensures optimal conditions for pollination and seed dispersal. Other factors like temperature also influence growth but not as directly.

Structure X resembles a digestive structure, similar to how humans use the intestine to digest food and absorb nutrients. Options such as the trachea and oesophagus serve different functions in human physiology and do not match the digestive role.

Structure Y in the organism is a contractile vacuole, used to expel excess water and maintain osmotic balance, much like kidneys in humans. Other structures such as the food vacuole and nucleolus have different functions within the cell.

Termites undergo incomplete metamorphosis, which involves egg, nymph, and adult stages without a pupal stage. Complete metamorphosis includes a pupal stage and is seen in insects like butterflies and flies.

An onion has a reduced stem and thick, fleshy leaves that store nutrients, characteristic of a bulb. Tubers, on the other hand, are modified stems or roots that store nutrients differently.

Guard cells control the opening and closing of stomata, regulating the exchange of gases and water vapor between the leaf and the environment. Other structures like lenticels and air spaces do not have this regulatory function.

Fungi lack chlorophyll, so they cannot perform photosynthesis. They obtain nutrients by absorbing organic material from other organisms, which defines them as heterotrophic. Other options describe characteristics unrelated to their mode of nutrition.

Photosynthesis primarily occurs in the palisade parenchyma cells, which contain a high concentration of chloroplasts. The epidermis layers do not contain chloroplasts and are not involved in photosynthesis.

The appearance of a purple color indicates proteins due to the Biuret reaction. This color change does not occur with other macromolecules like glucose or fats.

The hepatic portal vein transports nutrient-rich blood from the intestines to the liver, where it undergoes further processing. Other vessels like the hepatic artery supply blood directly from the heart.

In birds, air sacs act as reservoirs that allow for continuous air flow through the lungs, enhancing gas exchange efficiency during both inhalation and exhalation. Other structures like bronchi are primarily pathways, not sites of gas exchange.

In anaerobic conditions, pyruvic acid is converted to ethanol (in yeast) or lactic acid (in muscles) instead of entering the citric acid cycle. This allows glycolysis to continue producing small amounts of ATP without oxygen.

Insects excrete waste via Malpighian tubules, which help in osmoregulation and removal of nitrogenous wastes. Other options, like flame cells, are found in flatworms and nephidia in annelids.

Structure 5 is the sweat gland, which is involved in temperature regulation and waste excretion through sweat production. Other structures, like blood vessels and sebaceous glands, have different functions.

Melanin, responsible for skin pigmentation, and keratin, a protein that strengthens skin and hair, are produced in the epidermis (part labeled 3). Other layers like the dermis do not produce these proteins.

The atlas is the first cervical vertebra that supports the skull, allowing for nodding movements. The axis, which comes after the atlas, provides rotational movement. Other options like the odontoid process are parts of these vertebrae.

Pancreatic juice contains enzymes such as amylase, lipase, and trypsin, which aid in the digestion of carbohydrates, fats, and proteins. Other combinations, like ptyalin or pepsin, are found in saliva and the stomach, respectively.

The part labeled 3 is the synovial fluid, which lubricates the joint, reducing friction during movement. Other parts like cartilage and ligament have different structural roles within the joint.

Part 1 secretes a fluid that lubricates the joint, facilitating smooth movement. This fluid, known as synovial fluid, minimizes friction between bones. Other options describe functions unrelated to joint lubrication.

Double fertilization results in the formation of both the embryo and the endosperm, which nourishes the developing seed. This process is unique to angiosperms and is vital for seed development and viability.

The yolk supplies nutrients to the developing embryo, providing essential energy and materials for growth. Other options like shock absorption do not describe the yolk’s role in mammals, where it serves as an energy reserve.

In hypogeal germination, the epicotyl elongates, keeping the cotyledons below ground. This is seen in seeds like peas. In contrast, epigeal germination involves the elongation of the hypocotyl, bringing cotyledons above ground.

Parthenocarpic fruits develop without fertilization, resulting in seedless varieties, such as seedless grapes. This process bypasses the typical fertilization pathway that produces seeds.

The segment labeled M represents the fastest rate of growth, corresponding to the exponential or log phase where cell division and growth occur rapidly before slowing down in the stationary phase.

The grand period of growth, where cells grow and divide rapidly, is represented by the section labeled M in the growth curve. This phase precedes the plateau as resources begin to deplete.