Biology by Bradford
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The subtopic in the middle and eleven tasks round it: label four diagrams, complete two tables, put a process in order and fill 52 gaps. Every standard level statement has a box; the three boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Water entering from a hypotonic solution swells the cell's contents until they press outwards with , and the cell is . Water leaving into a hypertonic solution shrinks them away from the edge of the cell: .
Cylinders in the weakest solutions mass: those solutions were hypotonic to the tissue. Where the curve crosses zero, the solution is with the tissue, here at about mol dm⁻³. The error bars show the ; where the bars of two means overlap, their difference may not be .
Water potential, Ψ, is the of water per unit volume. It cannot be measured absolutely, so pure water at atmospheric pressure and 20 °C is given the value , and values are usually in . Water moves from to lower water potential, losing energy as it goes, like a ball rolling downhill.
12Water molecules are : the oxygen is slightly negative and each hydrogen slightly positive. Surrounding solute particles with water molecules like this is , and it is why ions and polar molecules are .
A multicellular animal keeps its tissue fluid with its cells, so they neither swell nor shrink. Medicine does the same. A drip into a vein is 0.9% sodium chloride, , with the same solute concentration as blood . A kidney or heart awaiting is kept cold in a solution that matches its cells, so they keep their shape.
| Ψs / kPa | Ψp / kPa | Ψ / kPa | |
|---|---|---|---|
| Turgid cell | −700 | +300 | |
| Cell at full turgor in pure water | −500 | 0 | |
| Plasmolysed cell | 0 | −900 | |
| Xylem sap under tension | −100 | −600 |
Ψ = Ψs + Ψp. Solute potential is zero or ; pressure potential is usually inside cells, but not in xylem sap pulled up under tension.
A potato cell has Ψs = −600 kPa. In pure water, which is hypotonic, water enters until Ψp has risen to about kPa, making the cell's Ψ equal to that of the water. In a hypertonic solution of −1000 kPa, water leaves, Ψp falls to , and the cell becomes . Water keeps leaving until Ψs inside has fallen to kPa.
| Solution outside the cell | Its solute concentration, compared with the cell's | Net movement of water |
|---|---|---|
| Hypotonic | into the cell | |
| Isotonic | ||
| Hypertonic | higher |
Water moves by from the less concentrated solution to the concentrated one. In an isotonic solution it still crosses the membrane, as fast in as out: a .
With no wall to hold it, an animal cell that gains too much water swells and may ; one that loses water shrinks, its surface puckering: . A freshwater protist such as Paramecium uses contractile vacuoles to pump out the water that keeps entering by .
Number the steps in order.
Repeats at each concentration give a mean and a , which shows how spread out the results are.
Water molecules are polar: the oxygen is slightly negative and each hydrogen slightly positive. Surrounding solute particles with water molecules like this is solvation, and it is why ions and polar molecules are hydrophilic.
| Solution outside the cell | Its solute concentration, compared with the cell's | Net movement of water |
|---|---|---|
| Hypotonic | lower | into the cell |
| Isotonic | equal | none |
| Hypertonic | higher | out of the cell |
Water moves by osmosis from the less concentrated solution to the more concentrated one. In an isotonic solution it still crosses the membrane, as fast in as out: a dynamic equilibrium.
With no wall to hold it, an animal cell that gains too much water swells and may burst; one that loses water shrinks, its surface puckering: crenation. A freshwater protist such as Paramecium uses contractile vacuoles to pump out the water that keeps entering by osmosis.
Water entering from a hypotonic solution swells the cell's contents until they press outwards with turgor pressure, and the cell is turgid. Water leaving into a hypertonic solution shrinks them away from the edge of the cell: plasmolysis.
Repeats at each concentration give a mean and a standard deviation, which shows how spread out the results are.
Cylinders in the weakest solutions gained mass: those solutions were hypotonic to the tissue. Where the curve crosses zero, the solution is isotonic with the tissue, here at about 0.3 mol dm⁻³. The error bars show the standard error; where the bars of two means overlap, their difference may not be significant.
A multicellular animal keeps its tissue fluid isotonic with its cells, so they neither swell nor shrink. Medicine does the same. A drip into a vein is 0.9% sodium chloride, saline, with the same solute concentration as blood plasma. A kidney or heart awaiting transplant is kept cold in a solution that matches its cells, so they keep their shape.
Water potential, Ψ, is the potential energy of water per unit volume. It cannot be measured absolutely, so pure water at atmospheric pressure and 20 °C is given the value zero, and values are usually in kilopascals. Water moves from higher to lower water potential, losing energy as it goes, like a ball rolling downhill.
| Ψs / kPa | Ψp / kPa | Ψ / kPa | |
|---|---|---|---|
| Turgid cell | −700 | +300 | −400 |
| Cell at full turgor in pure water | −500 | +500 | 0 |
| Plasmolysed cell | −900 | 0 | −900 |
| Xylem sap under tension | −100 | −500 | −600 |
Ψ = Ψs + Ψp. Solute potential is zero or negative; pressure potential is usually positive inside cells, but not in xylem sap pulled up under tension.
A potato cell has Ψs = −600 kPa. In pure water, which is hypotonic, water enters until Ψp has risen to about +600 kPa, making the cell's Ψ equal to that of the water. In a hypertonic solution of −1000 kPa, water leaves, Ψp falls to zero, and the cell becomes plasmolysed. Water keeps leaving until Ψs inside has fallen to −1000 kPa.