Diffusion

The energy for diffusion is derived from the kinetic energy of the random movement of molecules and ions. Increased temperature leads to faster movement and, therefore, a faster rate of diffusion.

Some substances, like oxygen and carbon dioxide, move into and out of cells by diffusion through the cell membrane. The cell membrane is partially permeable, allowing only small, non-polar molecules to pass directly.

Oxygen is important for aerobic respiration, generating energy for the cells. Carbon dioxide diffuses into the leaf for photosynthesis to make food and diffuses out as a waste product of respiration.

Oxygen is transported from the lungs to respiring tissues in the body, facilitating energy release. Carbon dioxide moves from the respiring tissues to the lungs and gets exhaled as waste.

A larger surface area increases the rate of diffusion. The small intestine has villi to increase surface area for efficient absorption of digested food into the bloodstream.

An increase in temperature increases the rate of diffusion. Higher temperatures provide more kinetic energy to the molecules, causing them to move faster and increasing diffusion rate.

A steeper concentration gradient (larger difference in concentration) increases the rate of diffusion. The greater the difference, the faster the net movement of particles.

A shorter distance decreases the time it takes for diffusion to occur, increasing the rate. Diffusion is only efficient over short distances because the rate of diffusion is inversely proportional to the square of the distance.

Small, non-polar molecules like oxygen (O2), carbon dioxide (CO2), and urea readily move across cell membranes via diffusion due to their chemical properties. Large or polar molecules need carrier/channel proteins.