Transport in cells

1.3.1 Diffusion

  • Spreading out of particles of any substance in solution, or particles of a gas, causing a net movement from an area of higher concentration to an area of lower concentration

What substances in animals & plants are transported in & out of cells by diffusion?

  • O2 & CO2 in gas exchange
  • Urea (waste product) from cells into blood plasma for excretion in the kidney

Factors affect rate of diffusion

Concentration gradient ↑ concentration gradient, ↑ rate
Temperature ↑temp, particles ↑KE, move faster, ↑rate
Surface area ↑SA, ↑particle exposed, ↑availability to react, ↑rate

How ____ is adapted for exchange?

Small
  • Small intestine is very long, which gives plenty of time to complete absorption
intestine
  • Villi are covered with microvilli, which increases SA to absorb quicker
  • Villi contain blood capillaries, which provide rich blood supply to maintain a steep concentration gradient to assist quick absorption
  • Villi have thin walls for short diffusion pathways into blood
  • Have lots of mitochondria to provide energy from respiration
Lungs
  • Lots of alveoli to increase SA
  • Thin membrane for a short diffusion pathway
  • Good ventilation and lots of blood capillaries to provide rich blood supply to maintain a steep concentration gradient
Gills in fish
  • Gills has threads to increase SA
  • Thin surface membrane for a short diffusion pathway to increase exchange
  • Good ventilation and lots of blood capillaries to provide rich blood supply to maintain a steep concentration gradient
Roots
  • Large SA
  • Thin surface membrane for a short diffusion pathway
  • Lots of mitochondria to provide energy from respiration for active transport
Leaves
  • Large SA
  • Thin surface for short diffusion pathway
  • Air spaces between cells

1.3.2 Osmosis

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

Isotonic – concentration of solutes in solution outside & inside cells are same

Hypertonic – concentration of solutes in solution outside higher than inside of cell

Hypotonic – concentration of solutes in solution outside lower than inside of cell

  • Net movement of water into bag by osmosis
  • Volume of water in bag increases
  • Bag expand & increases water level

Animal cell

  • Hypotonic solution
  • Net movement of water into cell by osmosis
  • Cell swells, then burst
  • Isotonic solution
  • No osmosis occurs
  • Hypertonic solution
  • Net movement of water out of cell by osmosis
  • Cell shrivels

Plant cell

  • Hypotonic solution
  • Net movement of water into cell by osmosis
  • Cell turgid
  • X burst coz cell membrane press against cell wall
  • Isotonic solution
  • No osmosis occur
  • Cell flaccid
  • Hypertonic solution
  • Net movement of water out of cell by osmosis
  • Cell membrane shrank away from cell wall (plasmolysis)
  • Cell flaccid

1.3.3Active transport

  • Movement of substances across a membrane from a low to high concentration of solution (against a concentration gradient)
  • Process requires energy from respiration
  • In animals, absorption of sugar in the gut from a low to high concentration into blood for cell respiration
  • In plants, absorption of mineral ions into plant root hairs for healthy growth