Control and Coordination: questions with answers

At the gap between two neurons, a chemical is released that crosses the gap and starts a new signal in the next neuron. There is no direct cytoplasmic link, the signal does not cross as electricity alone, and blood is not involved.

A synapse works only one way because one neuron releases the chemical signal, and only the other neuron has receptors to receive it. This arrangement does not support reverse transmission.

Nerve impulses travel quickly to a precise target. Hormones travel through the blood, so they act more slowly and their effect often lasts longer and reaches many organs, as in growth over months.

Adrenaline raises both heart rate and breathing rate, sending more blood and oxygen to the muscles for quick action.

The central nervous system is made up of the brain and spinal cord. Cranial nerves and spinal nerves come out of them and link them to the body, so they belong to the peripheral nervous system.

A motor neuron carries the signal from the spinal cord to the muscle. A sensory neuron carries signals toward the spinal cord, not away from it.

A reflex arc passes through the spinal cord, which is part of the central nervous system. The action is quick and needs no thinking by the brain.

In a reflex such as pulling the hand from a hot object, the spinal cord receives the information and sends the quick response. The information also travels up to the brain, so the brain is informed too.

The medulla controls involuntary actions such as breathing, heartbeat and blood pressure. The cerebellum keeps balance and makes voluntary movements precise. Thinking is done by the forebrain.

The skull encloses the brain, a membrane covers it, and fluid around the brain cushions it from shock. Together these three give the brain full protection.

A shoot growing upward, away from gravity, shows negative geotropism. A tropism is a directional growth response, not a rapid muscle movement.

Abscisic acid is the plant hormone that inhibits growth; it also helps a plant cope with stress, for example by closing stomata. Auxin, gibberellin and cytokinin promote growth processes such as cell elongation and cell division.

Endocrine glands have no duct. They release their hormone straight into the blood, which carries it to the rest of the body.

When thyroxine rises, the signal to the thyroid gland falls, so less is released. When thyroxine falls, the signal rises, so more is released. This keeps thyroxine close to its normal level.

Pituitary growth hormone is especially important during childhood and adolescence, when it drives normal body growth. Deficiency or excess during this period alters growth.