Question

Exchange of substances between a cell and its environment is mediated through
(a)Osmosis
(b)Active transport
(c)Diffusion
(d)All of the above

Answer 1

Hint: Exchange of substances between a cell and its environment takes place through the cell membranes and if it is a plant cell, then the cell wall is also present. The cell wall is freely permeable to all substances which means it does not stop anything from entering and exiting. The cell membrane is however selectively permeable which means it selects what to allow inside and exit outside according to the demands of the cell.

Complete answer:
All of the processes mentioned osmosis, active transport and diffusion are responsible for the mediation of substances between a cell and its environment. Let us understand in detail what these processes are.
Osmosis: Osmosis is used to refer specifically to the diffusion of water across a semipermeable or a selectively permeable membrane such as the cell membrane. It occurs spontaneously in the direction of the driving force which is the movement of water from its high concentration to the region of its low concentration. When water moves inside the cell it is known as endosmosis and when it moves out it is known as exosmosis.
Active transport: Active transport is defined as the movement of substances against their concentration gradient by pumps present in the cell membrane. This uphill movement (against the gradient) is achieved by utilizing energy. The pumps used are specific membrane proteins that move substances from their lower concentration to their higher concentration.
Diffusion: It is known as the passive movement of substances across the cells as there is no expenditure of energy. This is because the molecules move in a random fashion from their high concentration to lower concentration. Diffusion which occurs using membrane proteins is known as facilitated diffusion.
So, the correct option is ‘All of the above’.

Note: -In a plant cell, along with the cell membrane, the membrane of the central vacuole known as tonoplast determines the movement of substances in and out of the cell.
-Since active transport and facilitated diffusion are dependent on proteins, they are susceptible to saturation and inhibition.
-Saturation is when all the pumps are being used and the movement of substances cannot be increased anymore.