A red blood cell in hypotonic, isotonic and hypertonic solutions, why a plant cell does not burst, and active transport against the concentration gradient.
Step 1 of 6 · Pure water
Step 1 of 6
Pure water
Now the partially permeable membrane is a red blood cell’s, holding haemoglobin and salts at about 300 mOsm/L, like the plasma the cell swims in. The solution round the cell can be:
- hypotonic: weaker than the cell.
- isotonic: the same concentration as the cell.
- hypertonic: stronger than the cell.
Step 2 of 6
Swelling
In a solution only a little weaker than the cell, it swells but does not burst. How much does it swell? Nearly half a red blood cell is haemoglobin and other material that does not flow, and only the water in it swells.
Step 3 of 6
Seawater
In a hypertonic solution the gradient runs the other way.
Step 4 of 6
A safe drip
Outside the cell is free, and starts at pure water.
Step 5 of 6
Plant cells
A plant cell has, outside its membrane, a strong wall of cellulose, and in its middle a large vacuole full of solution.
Step 6 of 6
Against the gradient
Diffusion and osmosis are passive transport: substances flow by themselves, down the concentration gradient, and the cell spends no energy. But sometimes a cell needs to take in a substance it already has plenty of, or push out one that is more plentiful outside. For that its membrane has pump proteins that use the energy of ATP, the molecule the mitochondria make.
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Each step sets up the Scene for you, and a control marked “fixed” stays put for that step.
Practice · Predict, then look
Inside the red blood cell is 300 mOsm/L, as in plasma. We will move it into Pure water. What will happen to it?
Practice · Predict, then look
Inside the red blood cell is 300 mOsm/L, as in plasma. We will move it into Pure water. What will happen to it?
Practice · Calculate
Outside the cell is 200 mOsm/L, inside it 300. Only 60% of the cell’s volume is water that can flow; the rest, mostly haemoglobin, does not change. How many times bigger will the cell become?
Practice · Calculate
Outside the cell is 200 mOsm/L, inside it 300. Only 60% of the cell’s volume is water that can flow; the rest, mostly haemoglobin, does not change. How many times bigger will the cell become?
Practice · Predict, then look
Now we move the cell into Seawater, 1000 mOsm/L. What will happen to it?
Practice · Predict, then look
Now we move the cell into Seawater, 1000 mOsm/L. What will happen to it?
Practice · Reach the target
A drip into a patient’s vein must not harm the blood cells. Change Outside the cell until the red blood cell keeps its volume, then press Check.
Practice · Reach the target
A drip into a patient’s vein must not harm the blood cells. Change Outside the cell until the red blood cell keeps its volume, then press Check.
Practice · Choose
What happens to a lettuce leaf cell placed in pure water?
Practice · Choose
What happens to a lettuce leaf cell placed in pure water?
Practice · Choose
Inside a plant’s root hairs nitrate ions are a hundred times more concentrated than in the soil water, yet the root keeps taking in more. How?
Practice · Choose
Inside a plant’s root hairs nitrate ions are a hundred times more concentrated than in the soil water, yet the root keeps taking in more. How?
Lesson complete. Every practice question here is done.