Answer: Option D. -> parathyroid
:
D
The parathyroid glands are small, oval bodies that are usually four in number which lie at the back of thyroid glands. They secrete a hormone called as parathormone or parathyrin. It regulates the level of calcium in the blood plasma. Parathormone and a thyroid hormone called calcitonin work antagonistically (they work in opposite ways i.e. if one increases the calcium and phosphate levels, the other will decrease) to regulate the plasma calcium and phosphate levels.

Answer: Option D. -> diffusion of auxins towards the shady side of shoot.
:
D
Auxins are synthesized at the shoot tip and help the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

Answer: Option C. -> It primarily consists of fat reserves which act as perfect insulator.
:
C
Mylein sheath which covers the axon with certain gaps between two successive sheaths is composed of fatty material. Myelin with its various components is a perfect insulator and does not allow electric charges to pass through it.

Answer: Option B. -> (i) – (ii) – (iii)
:
B
The leaves of a mimosa plant close and droop down immediately after they are touched (thigmotropicmovements). Movement of sunflower in response to day and night happens much slowly (phototropic movement). Growth related movements take place even slowly.

Answer: Option B. -> CNS, PNS
:
B
In our nervous system, the role of the CNS (Central Nervous System) is to receive, process, analyze, interpret and organize the information coming from our primary senses and sends out the messages as instructions for the effector organs. On the other hand, the role of the PNS (Peripheral Nervous System) is to handle and transmit the impulses coming from the senses and going to the effector organs accordingly. SNS amd ANS refers to somatic and autonomic nervous systems respectively.

:
The movement of plant due to touch is called thigmotropic movement.

Answer: Option B. ->  I – (A), II – (A), III – (P), IV – (A)
:
B
Progesterone is a hormone that is secreted in females and is associated with menstrual cycle and pregnancy.
Thyroxine is a hormone that is secreted by the thyroid gland and regulates the metabolism of carbohydrates, proteins and fats and maintains the balance of growth.
Auxin is a plant hormone and is responsible for the growth of the shoot.
Adrenaline is a hormone secreted in the animal body and it affects the heart rate, dilation of pupils, etc.

Answer: Option A. -> Reflex arc, A - Receptor, B - Sensory neuron, C - Motor neuron, D - Relay neuron
:
A
The figure shown above represents the pathway of the impulse taken during a reflex action. The pathway is called reflex arc. The components of a reflex arc are:
  A: Receptor: The receptor acts as a sensory organ and detects the external stimulus.
  B: Sensory neuron: It takes the information detected by the receptor to the spinal cord. The spinal cord processes this information and gives a signal.
  C: Motor neuron: It takes the signal from spinal cord to the effector organ.
  D: Relay neuron: It connects the sensory neuron to the motor neuron.
The effector organ, in this case a muscle, does the action of pulling the hand away from hot pan.

Answer: Option A. -> Gibberellin – internodal elongation
:
A

Gibberellins promote internodal growth. Auxin helps in apical dominance. Cytokinin brings about cell division and ethylene promotes ripening of fruits.

Answer: Option A. ->  Sensory nerves
:
A

The pain message is sent to our brain through the sensory nerves. These nerves carry impulses from the sense organs to either the spinal cord or the brain. Motor nerves carry impulses from the brain and spinal cord to the muscle and glands. Cerebellum and cerebrum are parts of the human brain.