Biology Chapter 3 – Movement of Substances (Diffusion, Osmosis & Active Transport)

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30 Q&A flashcards summarising key definitions, processes, examples, and effects of diffusion, osmosis, and active transport from the lecture notes.

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29 Terms

1
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What is the definition of diffusion?

The net movement of molecules or ions from a region of higher concentration to a region of lower concentration down a concentration gradient, without using energy.

2
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During diffusion, molecules move ___ a concentration gradient.

Down

3
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How does the steepness of the concentration gradient affect the rate of diffusion?

A steeper concentration gradient results in a faster rate of diffusion.

4
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Give an everyday example that illustrates diffusion.

The spreading of the smell of perfume through a room.

5
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Name two small molecules that enter or leave cells by diffusion.

Oxygen and carbon dioxide (others include glucose).

6
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Describe how oxygen enters the bloodstream from the alveoli.

Oxygen concentration is higher in the alveoli than in the blood capillary, so oxygen diffuses through the alveolar wall into the blood until concentrations equilibrate.

7
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Why can gases diffuse rapidly across cell membranes?

Cell membranes are thin and partially permeable, and gases are small, non-polar molecules that pass easily through lipid bilayers.

8
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State the four ‘Golden Rules’ for answering diffusion/osmosis questions.

1) Compare concentrations (or water potentials). 2) State the movement of molecules and its direction. 3) Name the process (diffusion or osmosis). 4) Give the outcome/result.

9
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What is meant by a permeable membrane?

A membrane that allows both the solvent (water) and dissolved solutes to pass through freely.

10
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What is meant by a partially permeable membrane?

A membrane that allows certain substances (e.g., water) to pass through but restricts others (e.g., larger solutes).

11
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Define osmosis.

The net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

12
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In osmosis, water moves from ___ water potential to ___ water potential.

Higher; lower

13
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Why does water rise in arm A when two sucrose solutions of different concentrations are separated by a partially permeable membrane?

The solution in arm B has a higher water potential than the solution in arm A; water moves by osmosis from B to A, raising the level in A.

14
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What happens to a plant cell placed in a solution of higher water potential than its cell sap?

Water enters by osmosis, the vacuole enlarges, the cell becomes turgid, and the cell wall prevents bursting.

15
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Explain the term turgor pressure.

The pressure exerted by the water in a plant cell’s vacuole against the cell wall when the cell is turgid.

16
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Why is turgor pressure important to plants?

It maintains the shape of soft tissues, keeps leaves and young stems erect, and drives movements such as stomatal opening and closing.

17
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What happens to an animal cell placed in a solution of higher water potential than its cytoplasm?

Water enters by osmosis; the cell swells and may burst (lysis).

18
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What is plasmolysis?

The process in which the cytoplasm and cell membrane of a plant cell shrink away from the cell wall after water leaves the cell by osmosis.

19
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Describe what happens to a plant cell in a solution of lower water potential.

Water leaves by osmosis, the vacuole shrinks, the cytoplasm pulls away from the cell wall (plasmolysis), and the cell becomes flaccid.

20
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What is crenation in animal cells?

Shrinking and the appearance of spiky projections on an animal cell’s surface when it loses water in a solution of lower water potential.

21
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What occurs when a cell is in a solution of the same water potential?

There is no net movement of water molecules; the cell remains the same size and shape.

22
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Define active transport.

The movement of molecules or ions through a cell membrane from a region of lower concentration to a region of higher concentration against a concentration gradient, using energy from respiration.

23
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Why is energy required for active transport?

Because substances are moved against their concentration gradient, which is an energetically uphill process.

24
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Where does the energy for active transport usually come from?

ATP produced during cellular respiration.

25
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Why does active transport occur only in living, respiring cells?

It requires energy in the form of ATP, which is generated only in metabolically active cells.

26
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Give one example of active transport in plants.

Uptake of mineral ions by root hair cells from soil where the ion concentration is lower than inside the root hair.

27
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Give one example of active transport in humans.

Absorption of glucose (and amino acids) by the cells of the villi in the small intestine when luminal concentrations are lower than in the bloodstream.

28
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Contrast diffusion and active transport in terms of energy use.

Diffusion is passive and does not require energy, whereas active transport is an energy-consuming process.

29
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Contrast osmosis and diffusion in terms of the substance moved.

Osmosis specifically involves water movement through a partially permeable membrane, while diffusion can involve any particles (gases, ions, small molecules) moving down their concentration gradient.