Explanation

A nerve impulse involves electrical signals along the neuron and chemical signals (neurotransmitters) at synapses.

This combination allows rapid communication between neurons and target cells.

Explanation

The Golgi apparatus consists of flattened, stacked sacs called cisternae.

It modifies, sorts, and packages proteins and lipids for transport within or outside the cell.

Explanation

Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum.

It spreads mainly through sexual contact and can affect multiple organs if untreated.

Explanation

If fertilization does not occur, the endometrium (inner lining of the uterus) sheds during menstruation.

This prepares the uterus for a new cycle of potential implantation.

Explanation

The knee-jerk reaction is a reflex action, not controlled consciously by the brain.

It helps test the integrity of the spinal cord and nervous system.

Explanation

Explanation

Natural selection favors individuals with traits that increase survival and reproduction.

Over time, these beneficial traits become more common in the population.

Explanation

The cross RRYY × rryy produces F1 generation all RrYy.

Selfing F1 (RrYy × RrYy) gives F2 with 1 RRYY : 1 rryy for the homozygous combinations.

Explanation

During ventricular systole, the ventricles contract, and the atrioventricular (tricuspid and bicuspid) valves close.

This prevents backflow of blood into the atria while blood is pumped into arteries.

Explanation

In biotechnology, vaccines are made by cloning the gene that codes for a pathogen’s antigen.

This allows the body to recognize and mount an immune response without exposure to the actual pathogen.