Question

For the cell to survive it must be able to take in elements and at the same time rid of some others. Discuss how the movement of substance throughout the cell happen and contribute to its maintenance/survival.

Answer 1

Transport of substances across cell membranes occurs mainly by passive transport, active transport and bulk transport.

Passive transport occurs when substances can cross the semipermeable plasma and organelle membranes and move down the concentration gradient without using energy. This happen through diffusion, facilitated diffusion and osmosis. In diffusion small substances diffuse down the concentration gradient, cross membranes by dissolving in the lipid part of the membrane and passing through water- filled channels. Facilitated diffusion is a passive process and is used by some substances that are unable to diffuse through the semipermeable membrane unaided. Osmosis is passive movement of water down its concentration gradient towards equilibrium across a semipermeable membrane.

In active transport, substances are transported up their concentration gradient from a lower to a higher concentration. The sodium - potassium pump is an active transport mechanism which maintains homeostasis of the electrolytes sodium and potassium. Ir

When there is transfer of particles too large to cross cell membranes occurs by pinocytosis or phagocytosis. These particles are engulfed by extension of the cytoplasm, which enclose them forming a membrane- bound vacuole. When the vacuole is small, pinocytosis occurs. In phagocytosis lsrger particles are taken into the cell. Lysosomes then adhere to the vacuole membrane, releasing enzymes which digest the contents.