Solved Exercise, Bio-12, Ch-17


(i) Neurotransmitter molecules bind to the receptors on the _______ membrane at synapse. (post-synaptic)

(ii) Excess of _______ hormone is secreted in Addison’s disease. (Melanophore stimulating hormone)

(iii) Operant learning has been demonstrated and studied by ______ and ______. (Thorndike & B.F. Skinner)

(iv) _______ are plant hormones which delay the life of fresh leaf crops. (Cytokinins)

(v) All membranes of neurons have very active _______ and _______ pumps. (sodium & potassium)


(i) Impulses travel much more rapidly along myelinated neurons. (TRUE)

(ii) All glial tissue consists of glial cells. (TRUE)

(iii) Saltatory conduction is carried out by those nerve fibres that have nodes of Ranvier. (TRUE)

(iv) The myelin sheath of neuron is particularly good conductor of electric impulse. (FALSE)

CORRECT: The myelin sheath of neuron is particularly good insulator of electric impulse.

(v) The resting membrane potential is maintained largely by the sodium pump. (FALSE)

CORRECT: The resting membrane potential is maintained largely by the sodium-potassium pump.

(vi) Hormones initiate new biochemical reactions in the body. (TRUE)


(i) The neuron net of Hydra lacks.

(a) Neurons

(b) Dendrites

(c) Connections

(d) Direction of impulse flow

EXPLANATION: Unlike complex nervous systems with defined pathways, Hydra’s nerve net lacks a specific direction for impulses. Signals can flow in any direction through the network.

(ii) A nerve is a:

(a) Collection of neurons

(b) Bundles of axons or dendrites of neurons

(c) Concentration of dendrites and axons

(d) Bundle of axons or dendrites bounded by connective tissue.

EXPLANATION: A nerve is like a bunch of electrical wires (axons) wrapped together, protected by a sheath (connective tissue). These wires carry messages (nerve impulses) throughout your body, letting you feel, move, and function.

(iii) Thyroid glands produce.

(a) Thyroxines, T3 & T4 and calcitonin

(b) Calcitonin

(c) Tri-iodothyronine

(d) Tetra-iodothyronine

EXPLANATION: The thyroid glands produce thyroxines (T3 & T4) and calcitonin. Thyroxines are hormones that regulate metabolism, and calcitonin helps control calcium levels in the blood.

(iv) What is the number of cranial and spinal nerves in man.

(a) 12 & 31

(b) 24 & 62

(c) Both a & b

(d) None of the above

EXPLANATION: In humans, there are 12 pairs of cranial nerves and 31 pairs of spinal nerves. So, there are 12 cranial nerves and 31 spinal nerves in total.

(v) The one which is not related to others is.

(a) Cretinism

(b) Myxedema

(c) Exophthalmic

(d) Diabetes mellitus

EXPLANATION: Diabetes mellitus is not related to the thyroid disorders listed in the other options. Cretinism, myxedema, and exophthalmic goiter are conditions associated with thyroid dysfunction.

Q.04: SHOR



“Biorhythms showing periodicity of about 24-hours are called circadian Rhythms.”

The term circadian has a Latin origin, circa=about, dies=day, which means about one day. So, they are also called diurnal rhythms.

CNS or Central Nervous System:

(1) Central nervous system (CNS) consists of brain and spinal cord.

(2) It is the main control center that makes decisions and sends orders.

PNS or Peripheral Nervous System:

(1) Peripheral nervous system (PNS) includes all nerves and ganglia outside the CNS.

(2) It connects the CNS to the rest of the body, transmitting information to and from the CNS.

Functions of Parathyroid Gland:

(1) Parathyroid glands produce a hormone called parathormone.

(1) The primary function of parathormone (PTH) is to regulate calcium levels in the blood. It acts to increase the concentration of calcium in the blood by:

  • Stimulating the release of calcium from bones.
  • Increasing the reabsorption of calcium in the kidneys.
  • Promoting the activation of vitamin D, which enhances the absorption of calcium in the intestines.

(1) Thus, over-activity of PTH would lead to a demineralization of the bones similar to rickets, as well as to the formation of massive kidney stones. Both conditions may be fatal. While, under-activity causes a drop in blood Ca++ ions which in turn leads to muscular tetany.


“Hormones are chemical messengers produced by glands in the endocrine system that regulate various physiological processes like growth, metabolism & reproduction, by transmitting signals between cells and tissues in the body.”

Hormones are organic compounds of varying structural complexity. Chemically, they may be:

  • Proteins (insulin & glucagon),
  • Amino acids & derivatives (Thyroxine, epinephrine & norepinephrine),
  • Polypeptides (vasopressin or anti-diuretic hormone & oxytocin) and
  • Steroids (estrogens, testosterone & cortisone)  

Commercial Applications of Auxins:

Synthetic auxins, such as naphthaleneacetic acid (NAA), 2,4-Dichlorophenoxy acetic acid, have several commercial applications in agriculture and horticulture as:

(1) NAA (Naphthalene acetic acid) Indole propionic acid:

It stimulates fruiting, helps natural fruit set. Sometimes, it causes fruit setting in absence of pollination (parthenocarpy).

(2) 2,4-Dichlorophenoxy acetic acid:

  1. It is selective weed-killer, and kills broad leaved species (dicots). It is used in cereal crops and lawns to eliminate weeds.
  2. It inhibits sprouting of potatoes.
  3. Prevents premature fruit drop (retards abscission)

Types of Tropisms:

The word tropic is derived from Greek word ‘Tropos’ meaning ‘turn’.

“Tropism is the movement in curvature of whole organ towards or away from stimuli such as light, gravity, and touch.”

Following are the common types of tropic movements:

  1. Phototropism: Movement in response to stimulus of light.
  2. Thigmotropism: Movement in response to stimulus of touch.
  3. Chemotropism: Movement in response to some chemicals.
  4. Hydrotropism: Movement of plant parts in response to stimulus of water.
  5. Geotropism: Movement in response to the gravity.

Alzheimer’s Disease:

(1) Alzheimer’s disease was first described by Alois Alzheimer in 1907.

(2) It is characterized by the decline in brain function.

(3) Its symptoms are similar to those diseases that cause dementia (memory loss).

(4) There is a genetic predisposition to the disease in some people, so it tends to run in families.

(5) There is also evidence that high levels of aluminium may contribute to the onset of this disease.

(6) There is also decline in brain function with age.


Consult textbook at page 83 — 84.

Consult textbook at page 83 — 84.

Consult textbook at page 62 — 64.

Consult textbook at page 66 — 67.

Consult textbook at page 68 — 69.

Consult textbook at page 73 — 74.

Leave a Reply

Your email address will not be published. Required fields are marked *