Q4. Give reasons for the following:
a) Neurons are often long and wire like.
b) Alveoli in lungs have thin membrane.
c) Plasma membrane plays an important role in generating immune responses.
d) Nucleus occupies a peripheral position I mature plants cells.
Answers
Explanation:
a) to conduct messages from brain to body parts and from body parts to brain
b) for efficient diffusion of gases to enable gaseous exchange
c) they have glycolipids and glycoproteins which distinguishes the cell from harmful organisms
d) in plants there is a large central vacuole which provides turgidity to cell and stores nutrients so nucleus occupies peripheral position
Answer:
a) Neurons transmit electrical signals from the brain to different ‘parts of the body’ and vice versa. The longest neurons are those that connect the brain and the legs and these are wire like and thin to endure reduction of surface area for fast transmission of signals.
b) Alveoli in the ‘lungs’ are sites of gas exchange. The deoxygenated blood exchanges oxygen at the surface of the alveoli. The thin membrane is required for easy and fast gaseous exchange.
c) The plasma membrane is the main site for initiation of immune responses. The B and T cells of humoral and cellular immune system have receptors on its surface to identify immunogens and initiate the immune activity.
d) Plant cells contain large vacuole filled with cell sap that occupies most of the space inside the cell. Hence the nucleus is pushed to the periphery.