NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions


Sympathetic nervous system induces

  • Heartbeat

  • Secretion of digestive juice

  • Secretion of saliva

  • All of the above



Medulla of brain has two regions affecting heart rate.

(i) Cardiac inhibitory centre.

(ii) Cardiac accelerator centre

Sensory nerves originating from the accelerator centre run parallel to the spinal cord and enter the sino-artial node. Stimulation by these nerves, which are the part of the sympathetic nervous system causes an increase in heartbeat.


The canal system is a characteristic feature of

  • Echinoderms

  • Helminths

  • Coelenterates

  • Sponges



Sponges possess an extensive system of interconnected cavities called canal system, which typically consists of in current canals, radial canals, excurrent canals and spongocoel. The system is useful for nutrition, respiration and excretion.


The layer of cells that secrete enamel of the tooth is

  • Dentoblast

  • Ameloblast

  • Osteoblast

  • Odontoblast



The pulp cavity contains a mass of dense but soft connective tissue which is called pulp. A single layer of odontoblast cells lines the pulp cavity. These cells secrete enamel, which is a bluish-white shiny translucent and the hardest substance of the body.


Solenocytes are the main excretory structures in

  • Annelids

  • Molluscs

  • Echinodermates

  • Platyhelminthes



Solenocytes (also called flame cells) are meant for excretion and osmoregulation in Platyhelminthes. Annelids have metanephridia for excretion, Molluscs have kidneys (although different from vertebrate kidneys) for excretion. In echinodermates, no special excretory organs are found for excretion. In them, excretion takes place through diffusion or osmosis or through active transport.


Calcitonin is a thyroid hormone which

  • Elevates potassium level in the blood

  • Lowers calcium level in a blood

  • Elevates calcium level in the blood

  • Has no effect on calcium


Lowers calcium level in a blood

Calcitonin is a polypeptide hormone which lowers calcium and phosphate levels of plasma by inhibiting bone degradation and stimulating their uptake by bone. Parathyroid hormone elevates calcium level in blood.


The exchange of gases in the alveoli of the lungs takes place by

  • Osmosis

  • Simple diffusion

  • Passive transport

  • Active transport


Simple diffusion

Oxygen diffuses from alveoli to deoxygenated blood, and carbon dioxide diffuses from deoxygenated blood to alveoli by simple diffusion. Diffusion is defined as, the flow of the substance (gases) from a region of their higher concentration to a region of lower concentration.


Carbon monoxide is a pollutant because it

  • Reacts with oxygen

  • Inhibits glycolysis

  • Reacts with haemoglobin

  • Makes nervous system inactive


Reacts with haemoglobin

Carbon monoxide, when inhaled, combines with blood haemoglobin to form carboxyhaemoglobin at a rate 210 times faster than the rate of oxygen forms oxyhaemoglobin. Thus, respiration is impaired.


The contraction of gall bladder is due to

  • Gastrin

  • Secretin

  • Cholecystokinin

  • Enterogastrone



Cholecystokinin (also called pancreozymin) is a hormone of the mucosa of the small intestine. It is related in response to chyme. It causes the pancreas to release pancreatic enzymes and gallbladder to eject bile.


A condition of failure of kidney to form urine is called

  • Deamination

  • Entropy

  • Anuria

  • None of these



The terms anuria, oligonuria, polynuria and dysuria are used for the absence of urine, scanty urine, large amounts of urine, and painful urination respectively. Deamination is the removal of amino (NH) group frequently from an amino acid by transaminase enzymes.


The functional unit of the contractile system in striated muscle is

  • Cross Bridge

  • Myofibril

  • Myofibril

  • Z-band



A skeletal muscle consists of a bundle of long fibres running the length of the muscle. Each fibre is a single cell with many nuclei.

Skeletal muscle is also called striated muscle because of the regular arrangement of the and dark bands. Each repeating pattern of light and dark bands. 

Each repeating unit is a sarcomere, the basic functional unit of the muscle. The borders of the sarcomere, the Z-lines are lined up in adjacent myofibrils and contribute to the striations visible with a light microscope. The thin filaments are attached to the Z-lines and project towards the centre of the sarcomere while the thick filaments are centred in the sarcomere. At rest, the thick and thin filaments do not overlap completely, and the area near the edge of the sarcomere where there are only thin filaments is called the I -band. 

The A-band is the broad region that corresponds to the length of the thick filaments. The thin filaments do not extend completely across the sarcomere. So, the H-zone in the centre of the A-band contains only thick filaments. This arrangement of thick and thin filaments is the key to how the sarcomere and hence, the whole muscle contracts.