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
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| 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
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| 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
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| 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
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| Roots |
- Large SA
- Thin surface membrane for a short diffusion pathway
- Lots of mitochondria to provide energy from respiration for active transport
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| Leaves |
- Large SA
- Thin surface for short diffusion pathway
- Air spaces between cells
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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
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Animal cell
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- Hypotonic solution
- Net movement of water into cell by osmosis
- Cell swells, then burst
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- Isotonic solution
- No osmosis occurs
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- Hypertonic solution
- Net movement of water out of cell by osmosis
- Cell shrivels
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Plant cell
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- Hypotonic solution
- Net movement of water into cell by osmosis
- Cell turgid
- X burst coz cell membrane press against cell wall
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- Isotonic solution
- No osmosis occur
- Cell flaccid
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- Hypertonic solution
- Net movement of water out of cell by osmosis
- Cell membrane shrank away from cell wall (plasmolysis)
- Cell flaccid
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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
