Diffusion, Osmosis and Active Transport

Diffusion, Osmosis and Active Transport

Diffusion: An Overview

  • Diffusion is the movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached.
  • This is a passive process and does not require energy.
  • It is caused by the random motion of particles.
  • Factors that can affect the rate of diffusion are the concentration gradient, temperature, surface area, and the size of the molecule diffusing.

Examples of Diffusion in Biological Systems

  • Within the body, oxygen from the lungs diffuses into the blood, while carbon dioxide diffuses out of the blood into the lungs.
  • Nutrients from the food we eat diffuse into the blood from the small intestine.
  • Waste products such as urea diffuse from the cells into the blood, ready for excretion.

Osmosis: Understanding the Process

  • Osmosis is the movement of water molecules across a semi-permeable membrane from a region of lower solute concentration to a region of higher solute concentration.
  • Osmosis is also a passive process, meaning it does not require energy.
  • Semi-permeable membranes allow substances to pass through but block others.

Osmosis in Cells

  • Osmosis is crucial in maintaining the balance of water within cells.
  • If too much water enters a cell by osmosis, the cell may burst, a process known as lysis.
  • If too much water leaves a cell by osmosis, the cell may become dehydrated and shrivel, a process known as plasmolysis.

Active Transport: How It Operates

  • Active transport is the movement of molecules against their concentration gradient, from an area of lower concentration to an area of higher concentration.
  • Active transport requires energy in the form of ATP (adenosine triphosphate).
  • As it moves against a concentration gradient, it can be used to transport substances into areas that are already saturated or highly concentrated.

Active Transport in Biological Systems

  • Active transport is mainly used to transport ions such as potassium and sodium in and out of cells.
  • It allows cells to maintain a balance of ions, necessary for nerve impulses and muscle contractions.
  • Glucose, an essential molecule for energy, is another substance that is absorbed via active transport in the small intestine and kidneys.