GCSEBiology B3 Higher Tier Revision Cards

Osmosis

• The movement of water from a dilute solution to a more concentrated solution.
• The water must pass through a partially permeable membrane.
• Osmosis is passive.

Diffusion

• Substances move from a high concentration to a low concentration.
• Substances must be either soluble or a gas.
• This is how oxygen leaves the leaf.

Active Transport

• Substances move against the concentration gradient.
• Particles move from a low concentration to a high concentration.
• Requires energy to take place.
• This is how plants take in minerals through their roots.

Exchange surfaces in humans

• The surface area of the lungs is increased by the alveoli.
• The surface area of the small intestine is increased by the villi.

Exchange in the lungs

• The epithelium of the alveoli is very thin, which shortens the diffusion distance.
• There are capillaries running over the surface of the alveoli, which removes carbon dioxide and takes oxygen to the cells for respiration.
• The alveoli aid gaseous exchange by providing a large surface area, having a moist surface and having a copious blood supply.

Exchange in the gut

• Villi and microvilli increase the surface area of the small intestine. This increase in surface area aids the absorbtion of digested products.
• The villi have a rich blood supply which produces a steep concentration gradient for efficient diffusion.
• Villi also have a thin wall (around 1 cell thick) which shortens the diffusion distance.

• Gasses diffuse in and out of the stomata, found on the underside of the leaves.
• Leaves have a large surface area.
• Air spaces within the leaves increases the surface area inside.
• Guard cells control the size of the stomata.

Inside a leaf

• Upper epidermis
• Cuticle
• Chloroplast - palisade layer
• Xylem, phloem and air spaces - spongey layer
• Stomata and guard cells - lower epidermis

Organisms

• Worms breathe through their skin (no lungs)
• Insects breathe through spiracles on the sides of their bodies (no lungs)
• Dolphins breathe through their blowholes (lungs)
• Land snails breathe through their mantle, a thin layer of tissue (lungs)
• Water snails breathe through their gills (lungs)
• Gasses diffuse across the surface of amoeba.

Transpiration

• Transpiration is the loss of water from the leaves through the stomata.
• Plants lose water in the form of water vapour.
• Capillary action is when water moves up the plant via fibres in the xylem.
• Water molecules are cohesive, they stick together.

Speeding it up

• Flatter, thinner leaves
• Hot, dry, windy weather
• Larger stomata
• More stomata

Slowing it down

• Humid climate
• Small stomata
• Fewer stomata
• Waxy leaves

Blood flow

• (Through the veins) From lungs --> left atrium --> left ventricle --> (through arteries) body tissues --> (through veins) right atrium --> right ventricle --> (through arteries) lungs.