Diffusion through cell membranes

Gas Exchange happens in the lungs

  • The job of the lungs is to transfer oxygen to the blood and to remove waster carbon dioxide from it
  • Lungs contain millions of air sacs called alveoli where gas exchange takes place

Alveoli - specialised to mximise diffusion of oxygen and CO2

  • An enormous surface area
  • Moist lining for dissolving gases
  • Very thin walls
  • A good blood supply

Villi - Provide a reall really big surface area

  • The inside of the small intestine is covered by villi
  • They increase the surface area so digested food is absorbed faster into the blood
  • They have single layer of surface walls and a very good blood supply to assist absorption
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Active Transport

Active transport - substances need to be absorbed against a concentration gradient. i.e from a lower to a higher concentration

Root hairs are specialised for absorbing water and minerals

  • The cells on the surface of the plant roots grow into long hairs which stick into the soil
  • Gives the plant a big surface area for absorbing water and minerals from soil
  • Most of the water and minerals are absorbed into the plant by the root hair cells

Root hairs take in minerals using active transport

  • The concentration of minerals is usually higher in the root hair cell than the soil
  • Normal diffusion doesnt explain how minerals are taken up into the root hair cell
  • Active Transport is responsible
  • This allows the plant to absorb minerals from a dilute solution, against a concentration gradient
  • Essential for growth
  • Active Transport needs ENERGY from respiration to make this work
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Active Transport in the body

Active transport is used in the gut when there is a low concentration of nutrients in the gut, but a high concentration of nutrients in the blood.

  • when there is higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood
  • But- sometimes there is a lower concentration of nutrients in the gut than there is in the blood.
  • This results in then concentration gradient being the wrong way.
  • This process is Active Transport

Active Transport allows nutrients to be taken into the blod, despite the concentration gradient the wrong way.

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Water Flow Through Plants

Ploem tubes transport food

  • Columns of living cells with small holes
  • Allows stuff to flow through
  • The transport goes in both directions
  • Food substances such as dissolved sugars made in the leaves to growing regions

Xylem tubes take water up

  • Made of dead cells
  • Joined end to end with no end walls between them
  • A hole down the middle
  • They carry water and minerals from the roots to the stem and leaves
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