Figure (a) appears more accurate because it is showing positive geotropic movement in roots and negative geotropic movement in stem.

Iodised salt in diet is advisable because it contains iodine, which is essential element for the synthesis of thyroxine hormone by thyroid gland. In case, iodine is deficient in our diet, there is a possibility of suffering from goitre.

(a) Dwarfism if less hormone; Gigantism if secreted more.
(b) Diabetes
(c) Goitre
(d) Masculine characters will not develop properly in male.

Auxin and gibberellin.

It is a spontaneous, involuntary and unconscious response to a stimulus.

Nerves which originated from the brain are called cranial nerves.

(a) Auxin
(b) Giberellin
(c) Cytokinin
(d) Abscissic acid

Auxins promote cell elongation and are present at the shoot tip. When tendril comes in contact with a support, auxin stimulates faster growth of the cells on the opposite sides. Thus, the tendril coils around the support.

The flow of signals through neurons takes place in the form of specialized chemicals; called neurotransmitters. The neurotransmitters. The neurotransmitters can only enter a neuron through dedicated receptor channels. Such receptor channels a5re only present at the dendritic end but not at the axonal end. Hence, the flow of signals in a synapse happens from axonal end of one neuron to dendritic end of another neuron but not in the reverse direction.

Various plant hormones and their effects are as follows:
(i) Auxin : Promotes cell elongation and thus promotes growth of a plant part.
(ii) Gibberellins : Promotes growth.
(iii) Cytokinin :  Promotes cell division and thus promotes growth.
(iv) Abscissic acid : Inhibits growth and is responsible for shedding or older parts.

(a) General metabolism.
(b) Controls blood sugar level.
(c) Prepare the body for 'fight or flight' response.
(d) Promotes growth and development.
(e) Triggers sperm production and is responsible for the development of secondary sexual characters in males.

Voluntary actions are under the control of our will, it needs thinking. e.g. talking, walking. Involuntary actions are not under the control of our will, they are automatic. eg. salivation, heart beat.

Information passes through neuron in the form of electro-chemical signals. These signals are called impulse.
When an impulse reaches the end of the axon it sets off the release of some chemicals. These chemicals cross the gap or the synapse and start a similar electrical impulse in a dendrite of the next neuron. A similar synapse allows the delivery of impulses from the neurons to other cells, like muscle cells or glands.

(i) Regions included in central nervous system are the brain and the spinal cord. The brain and the spinal cord. The brain is further divided into three parts - forebrain, midbrain, and hindbrain.
(ii) Three of the functions of the brain are:
Forebrain controls intelligence, learning, memory, thinking, speech, etc.
Midbrain is associated with the sense of sight and hearing.
Hindbrain controls all involuntary actions such as breathing, peristalsis, etc.