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| 1. |
Explain the transport of substances across the plasma membrane.Or, Write notes on(a) Passive transport2.2.(b) Active transport. |
| Answer» <p>The plasma membrane surrounding animal cells is where the exchange of substances inside and outside of cells takes place. Some substances need to move from the extracellular fluid outside cells to the inside of the cell, and some substances need to move from the inside of the cell to the extracellular fluid.</p><p>Some of the proteins that are stuck in the plasma membrane help to form openings (channels) in the membrane. Through these channels, some substances such as hormones or ions are allowed to pass through. They either are “recognized” by a receptor (a protein molecule) within the cell membrane, or they attach to a carrier molecule, which is allowed through the channels. Because the plasma membrane is choosy about what substances can pass through it, it is said to be selectively permeable.</p><p>Permeability describes the ease with which substances can pass through a border, such as a cell membrane. Permeable means that most substances can easily pass through the membrane. Impermeable means that substances cannot pass through the membrane. Selectively permeable or semipermeable means that only certain substances are able to pass through the membrane.</p><p>Transporting substances across the plasma membrane can require that the cell use some of its energy. If energy is used, the transport is called active. If molecules can pass through the plasma membrane without using energy, the molecules are using passive transport.</p><p>(a) Passive transport is a type of cellular transport where substances move along the concentration gradient. Since it is associated with downhill movement of substances (i.e. from an area of higher concentration to an area of lower concentration) it does not require a chemical energy.</p><p>(b) Active transport is the process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient - and therefore require an input of energy from the cell. </p> | |