Why can these molecules pass through the cell membrane?
They are small enough (Big molecules i.e. starch, proteins are too large)
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How is urea excreted?
Urea diffuses out of cells in the kidney into the blood plasma down its concentration gradient.
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Give 3 factors that affect the rate of diffusion
1. Difference in concentration gradient 2. Temperature 3. Surface area of membrane
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Explain how the rate of diffusion changes if conc gradient is greater
Greater conc= faster rate of diffusion. Net movement from one side is greater.
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Explain how the rate of diffusion changes if temp is greater
Higher temp= faster rate of diffusion. Particles have more energy so move around faster
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Explain how the rate of diffusion change if surface area of membrane increases
Larger surface area of membrane = faster rate of diffusion. More particles can pass through at once (i.e. epithelial cells in small intestines have finger-like projections)
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How do single-celled organisms exchange their substances?
Gases and dissolved substances can diffuse across the cell-membrane.
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Why is this possible?
They have a large surface area to volume ratio; substances can move fast enough to meet their needes/
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What do multicellular organisms have to have and why is this?
Multicellular organisms have specialised surfaces and organ systems to exchange. This is because they have a small surface area to volume ratio and a large number of cells.
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Give 4 ways the effectiveness of an exchange surface can be increased
1. Large surface area 2. Thin membrane--> short diffusion path 3. Efficient blood supply (in animals) 4. Well ventilated (in gas exchange)
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What is the specialised gas exchange surface is present in the lungs?
Alveoli
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How are the gills in fish specialised for gas exchange? Give 3 reasons
1. Many gill filaments to give a large surface area 2. Many lamallae on each gill filament to increase surface area 3. Lamelle have lots of blood capillaries to maintain steep conc gradients
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4.1.3.2- OSMOSIS
4.1.3.2- OSMOSIS
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What is osmosis?
The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
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What do isotonic drinks contain, when are they given and why?
Water and ions, often given after exercise, to replenish the water and ions lost during exercise through sweating to ensure cells do not shirnk.
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*REQUIRED PRACTICAL 3- OSMOSIS
*REQUIRED PRACTICAL 3
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4.1.3.3- ACTIVE TRANSPORT
4.1.3.3- ACTIVE TRANSPORT
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What is active transport?
The movement of substances from a more dilute solution to a more concentrated solution (against conc gradient) using energy transferred in respiration.
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Give an example of where and why is active transport used in plants?
In the roots to absorb mineral ions from the soil.
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Why is active transport used to absorb the mineral ions?
The concentration of mineral ions in the soil is lower (more dilute) than inside of the plant
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Why do plants need mineral ions?
Mineral ions are needed for healthy growth
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Give an example of where and why active transport is used in humans
In the guts to absorb sugar molecules into the blood
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Why is active transport used to absorb the glucose?
The concentration of glucose is lower (more dilute) in the gut than what is in the blood
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Why do humans need glucose?
For use in respiration.
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How are alveoli specialised for gas exchange? Give 3 reasons
1. Large surface area (many of them) 2. Very thin walls 3. Good blood supply to maintain steep conc gradients
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Other cards in this set
Card 2
Front
What is diffusion?
Back
Diffusion is the net movement of particles (of any substance in solution, or particles of gas), from an area of HIGHER --> LOWER concentration.
Card 3
Front
Name 4 molecules that can diffuse through cell membranes
Back
Card 4
Front
Why can these molecules pass through the cell membrane?
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