Transport in cells

Diffusion

The net movement of particles from an area of high concentration to an area of low concentration across a partially permeable membrane. When concentration becomes equal it stops

Substances that can move

• Gas molecules

• Liquid molecules

• Dissolved solid ions

Diffusion 5 affecting factors

• Temperature

• Concentration gradient

• Size of particle

• Diffusion distance

• Surface area : volume ratio

Temperature affects diffusion

Increased temperature allows for more kinetic energy in particles so the rate of diffusion is faster

Concentration gradient affects diffusion

Greater concentration gradient, the more particles randomly diffuse / unit of time

Size of particle affects diffusion

Smaller particles move quicker

Diffusion distance affects diffusion

Further substances have to diffuse, the slower the rate of diffusion

Surface area : volume ratio affects diffusion

The smaller the organism the larger the surface area : volume ratio so a larger surface area provides more space for molecules to cross leading leading to a higher rate of diffusion

3 adaptions of alveoli in gas exchange

• Thin alveolar wall

• Many alveoli

• Surrounded by many capillaries

Thin alveolar wall affects gas exchange

Short diffusion distance so quicker rate of reaction

Many alveoli affects gas exchange

Higher surface area

Many capillaries affects gas exchange

Good blood supply maintaining concentration gradient

3 factors affecting diffusion in leaves

• Thin leaves

• Many stomata

• Concentration gradient

Thin leaves affecting leaves

Short diffusion distance so quicker rate of diffusion

Many stomata affecting leaves

Many stomata increases surface area

Concentration gradient maintained in leaves

Maintained by photosynthesis in day, respiration in day and night and iwnd

Osmosis

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

Dilute solution of sugar

High concentration of water and a low concentration of sugar

Concentrated solution of sugar

Low concentration of water and a high concentration of sugar

Osmosis in animals

• Too much water enters the cell, it swells and bursts

• Too much water leaves the cell, it shrivels up and dies

Osmosis in plants

• Rely on osmosis to support stems and leaves

• Water moves into plant cells by osmosis

• Vacuole swells and presses against the cell wall - turgor pressure

Active transport

Movement of substances from a lower concentration to a higher concentration through a partially permeable membrane. Against the con. Requires energy

Plants using active transport

Absorb different minerals in different amounts to select which minerals it requires

Active transport in fish

Gills pumping salt back in the salty sea water

Active transport in kidney

Cells reabsorb sodium ions from urine

Active transport in the small intestine

Absorb glucose from gut into blood