Biology 2025 Jamb Examination

The mammalian epidermis consists of several layers. The outermost is the cornified layer (stratum corneum), which consists of dead cells. The malpighian layer (which includes the stratum basale and stratum spinosum) is the innermost layer. It is the actively dividing layer where new skin cells are produced to replace those shed at the surface. Capillaries are actually located in the dermis, not the epidermis.

To find the probability, we use a Punnett square. The gametes from the first parent are R and r, and from the second parent are r and r.
The resulting genotypes are:
1. \( R \times r = Rr \)
2. \( R \times r = Rr \)
3. \( r \times r = rr \)
4. \( r \times r = rr \)
Since 2 out of 4 offspring are Rr, the probability is \( \frac{2}{4} \), which simplifies to \(\frac{1}{2}\) or 50%.

Centrioles are barrel-shaped organelles found in animal cells. They play a critical role in organizing the microtubule network. Specifically, they give rise to basal bodies, which serve as the anchoring structures and templates for the formation of cilia and flagella. Plastids are found in plants, golgi bodies process proteins, and lysosomes are involved in intracellular digestion.

The lumbar vertebrae are located in the lower back between the thoracic vertebrae and the sacrum. They are the largest and strongest bones in the spine because they support the weight of the upper body. Their large transverse processes provide the primary site for the attachment of the powerful abdominal and back muscles. Cervical bones are in the neck, and thoracic bones are attached to the ribs.

Carnivores (flesh-eaters) have highly developed, long, and pointed canine teeth. These teeth are specifically adapted for piercing, gripping, and tearing the flesh of their prey. In contrast, herbivores often have a gap (diastema) where canines would be, or very small ones, as their diet consists of plant matter that requires grinding rather than tearing.

Translocation is the process by which organic nutrients (sucrose/manufactured food) produced during photosynthesis are transported from the leaves to other parts of the plant. This transport occurs through the phloem cells (specifically sieve tubes). Xylem vessels, on the other hand, are responsible for the upward transport of water and dissolved minerals from the roots.

In terms of evolutionary complexity:
1. *Paramecium* is a unicellular protozoan (simplest).
2. *Hydra* is a diploblastic coelenterate (tissue level).
3. *Planaria* is a triploblastic flatworm (organ level).
4. The earthworm is an annelid, which is a triploblastic coelomate with a segmented body and a well-developed circulatory and digestive system, making it the most advanced on this list.

The Savanna is characterized by distinct wet and dry seasons. The Baobab tree is famously adapted to this environment through its thick, succulent trunk, which is capable of storing vast amounts of water to survive the long drought periods. While it also has a thick bark (option D) that protects it from bushfires common in the savanna, the water storage is its most iconic physiological adaptation. Based on standard JAMB marking, thick bark or water storage are key, but the thick bark is a common choice for protecting the cambium from fire.

Albinism is a genetic condition characterized by a complete or partial absence of pigment (melanin) in the skin, hair, and eyes. It is an inherited trait caused by recessive genes. A person must inherit two copies of the recessive allele (one from each parent) to manifest the condition. It is specifically due to the lack of an enzyme called tyrosinase, which is needed to produce melanin.

A reflex action is an involuntary, rapid, and automatic response to a stimulus that does not involve conscious thought. Coughing is a protective reflex triggered by irritation in the respiratory tract. Writing, talking, and walking are voluntary actions or learned behaviors that require coordination and conscious control by the higher centers of the brain.