Diffusion and gas excahnge

Diffusion is the passive movement of particles from an area of high concentration to low concentration 

*  it happens in both liquids and gases because particles in these substances are free to move around randomly.the simplies type of diffusion is when different gases diffues through each other. this is whats happening when a smell is diffused around a room

only things like glucose, amino acids, water and oxygen can go in and out of the cell.

big molecules like starch and proteins cant fit through the membrane.

a) distance - substances diffuse ore quickly when they haven't as far to move.

b) concentration difference (gradient) - substances diffuse faster if there's a big difference in concentration. if there are lots more particles on one side, there are more there to move across.

c.surface area - the more surface area there is available for molecules to move across, the faster they can get from one side to the other.

Alveoli carry out gas exchange in the body

The lungs contain millions and millions of little air sacs called alveoli where gas exchange happens

The blood passing next to the alveoli has just returned to the lungs from the rest of the body, so it contains lots of carbon dioxide and very little oxygen. Oxygen diffuses out of the alveolus (high concentration) into the blood (low concentration). Carbon dioxide diffuses out of the blood (high concentration) into the alveolus (low concentration) to be breathed out.

. When the blood reaches body cells oxygen is released from the red blood cells (where there's a high concentration) and diffuses into the body cells (where the concentration is low). It’s then carried back to the lungs.

Small food molecules can be diffused into the blood

Food is digested in the gut to break it down into pieces small enough to be absorbed into the blood by diffusion.

The absorption happens in the small intestine, after big molecules like starch and proteins have been broken down into small ones like glucose and amino acids.

These molecules can diffuse into the blood from the small intestine because their concentration is higher than it is in the blood.

When blood reaches cells that need these substances because their concentration is low, they can diffuse out easily from an area of higher concentration to an area of lower concentration.