4.1.3 Transport in Cells

Factors that affect the rate of diffusion

The difference in concentrations (concentration gradient), the temperature and the surface area of the membrane

What factors increase the effectiveness of an exchange surface?

Having a large surface area, a membrane that is thin -to provide a short diffusion path, (in animals) having an efficient blood supply, (in animals, for gaseous exchange) being ventilated.

What is diffusion?

Net movement of particles from an area of high concentration to an area of low concentration

What kind of SA:V ratio do single-celled organisms have?

High SA:V ratio

What happens to the SA:V ratio as an objects size increases

SA:V ratio decreases

How are the lungs adapted for gaseous exchange?

Lungs contain millions of little air sacs called alveoli. They have: a large surface area, a moist lining (for dissolving gases), very thin walls and a good blood supply for efficient exchange (transfer oxygen to blood, remove waste CO2)

How is the small intestine adapted for digestion?

The inside of the small intestine is covered in villi. Villi increase the surface area greatly, so the digested food is absorbed much quicker into the blood. They have a single layer of surface cells and a very good blood supply (to assist quick absorption.)

How are leaves adapted for gaseous exchange?

Underneath the leaf, there’s an exchange surface: it’s covered in stomata. The size of stomata is controlled by guard cells, its flat shape increases area for exchange, air spaces inside leaf: increase S.A and allow more CO2 to get into cells

How are fish gills adapted for gaseous exchange?

Each gill consists of thin plates called gill filaments. Gill filaments are covered in tiny structures called lamellae (increases S.A.) Lamellae have: lots of blood capillaries (speeds up diffusion), thin surface layer of cells (minimises distance travelled by gases), blood& water flow in opposite directions maintaining a large conc. gradient.

What is Osmosis?

Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

What is Active transport?

Movement of substances from a dilute to a more concentrated solution- against conc. gradient. This requires energy from respiration.