Science [1 Mark Questions]

As the electrical impulse reaches the axon terminal in the region of axon-dendrite synapse, it stimulates the exocytosis of vesicles containing neurotransmitter (e.g. acetylcholine). Neurotransmitter attaches to the chemoreceptor sites of the membrane covering the dendrite end of synapse. It creates a new impulse that travels through cell body and axon of the second neuron. At synapse, the axon end does not contain any chemoreceptor sites so that reverse flow of electrochemical impulses is not possible.

Dwarfism. Growth hormone.

Thyroid gland produces thyroxine and triiodothyronine. Thyroxine has four iodine atoms, while triiodothyronine has three iodine atoms. The dietary iodine serves as source and thus iodine deficient diet renders the gland unable to synthesize the hormones. Thyroid hormones deficiency inhibits metabolic rate, growth and development.
A person might suffer from goitre in case of iodine deficiency in the body.

Abscisic acid.

Auxin.

1. Dendrite.
2. Cell body.
3. Axon.
4. Nerve ending.

Figure (a) is more accurate as it shows appropriate response of both shoot and root to the vector of gravity. Shoot is negatively geotropic. It, therefore, bends upwardly. Root is positively geotropic. It, therefore, bends downwardly.

Growth.

Sperm production, development of secondary sexual characters during puberty.

Endocrine Gland in Males only Testis.

Controls general metabolism and growth in the body.

Endocrine Gland Associated with Kidneys. Adrenal glands.

Puberty changes in females. Oestrogen.

Controls blood sugar level.

Blood Sugar. Insulin.

Prepares the body for emergency situations and hence is also called ‘Fight and flight’ hormone.

Iodine Hormone. Thyroxine.

Endocrine Gland Associated with Brain. Pituitary.

The movements which are in a particular direction in relation to the stimulus are called tropic movements. Tropic movements happen as a result of growth of a plant part in a particular direction. There are four types of tropic movements, viz. geotropic, phototropic, hydrotropic and thigmotropic.
Example: Roots usually show positive geotropic movement, i.e. they grow in the direction of the gravity. Stems usually show negative geotropic movement.

The junction between two neurons is called synapse. When electrical impulse reaches the axonal end of a neuron, it sets off the release of neurotransmitters in the synapse. These neurotransmitters enter the dendrite of another neuron to set off electrical signal in that neuron. That is how electrical impulse travels from one neuron to another.

Gibberellin.

Cytokinin.