diffusion, osmosis and active transport

what is diffusion

diffusion is the net movement of substances from an area of higher concentration to lower concentration through a partially permeable membrane. it is a passive process therefore it requires no energy. it occurs differently in liquids and gases

diffusion in the lungs

oxygen diffuses from inside the alveoli into the blood. the blood now has a higher concentration of oxygen and the higher concentrated blood is moved away to the tissues and blood. carbon dioxide diffuses in the opposite direction. it diffuses from the higher concentration in the cells to a lower concentration in the blood. it is then diffused from the blood to the lungs, where it is exhaled.

adaptations of the alveoli

→ large surface area to volume ratio. this helps increase the rate of diffusion because there is more surface for the particles to move across

→ they have thin capillary walls, which are one cell thick. this means the distance the particles have to move across is short, increasing the rate of diffusion

→ they have a rich blood supply. this means the capillaries surrounding the alveoli have a steep concentration gradient, making diffusion more efficient

diffusion in the small intestine

nutrients such as glucose and amino acids diffuse from the small intestine to the blood capillaries and lacteals

adaptations of villi

→ large surface area to volume ratio. this helps increase the rate of diffusion because there is more surface for the particles to move across. additionally, villi also as many microvilli, which additionally increases the surface area

→ they have thin walls, which are made from intestinal epithelium. this means the distance the particles have to move across is short, increasing the rate of diffusion

→ they have a rich blood supply. this makes a steep concentration gradient for nutrients, meaning they are rapidly transported to over parts of the body

adaptations of fish gills

→ large surface area to volume ratio. the gill filaments are covered in thin structures called lamellae, which increase the surface area. this helps increase the rate of diffusion because there is more surface for the particles to move across

→the walls of the lamellae are very thin. this means the diffusion of carbon dioxide out and oxygen into the blood would be faster

→ they have a rich blood supply. the capillaries in the gills maintain a steep concentration gradient, which allows for continuous diffusion

→ they have a counter current system. this is where blood flows in the opposite direction to the water passing over the gill. this maximises the oxygen uptake by maintaining a concentration gradient over the entire surface of the gill, allowing for more efficient diffusion.

what is osmosis?

osmosis is the diffusion of water molecules from a higher concentration gradient to a lower concentration gradient, across a partially permeable membrane. it is passive and requires no energy

how do plants take in water

by osmosis

what is active transport

active transport is the movement of particles against the concentration gradient. it isn’t passive and requires energy, and requires carrier proteins to transport molecules

where does the energy for active transport come from

ATP, which comes from respiration

factors that affect transport

→ surface area

→ temperature

→ concentration gradient