Diffusion Osmosis And Active Transport

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Diffusion

Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration (down a concentration gradient).
Movement occurs due to the random motion (Brownian motion) of particles; energy comes from their kinetic energy.
The cell membrane is partially permeable – it allows some molecules to cross easily but restricts others (e.g., based on size).
Diffusion helps organisms obtain requirements (e.g., oxygen, carbon dioxide) and remove waste products (e.g., carbon dioxide).
Examples: oxygen diffusing into cells for respiration; carbon dioxide diffusing out of cells; carbon dioxide diffusing into leaf cells for photosynthesis.

Diffusion across the cell membrane

Factors that Influence Diffusion

Surface area to volume ratio: larger surface area speeds up diffusion; cells like root hair cells and ileum cells have folded surfaces to increase area.
Distance: shorter distance increases rate; e.g., capillary and alveolus walls are one cell thick.
Temperature: higher temperature gives particles more kinetic energy, increasing diffusion rate.
Concentration gradient: steeper gradient increases rate because more collisions occur on the high-concentration side.

Osmosis

Osmosis is the diffusion of water molecules from a dilute solution (high water potential) to a concentrated solution (low water potential) across a partially permeable membrane.
Water moves down its concentration gradient; the membrane allows small water molecules through but not larger solute molecules.
Water potential describes the tendency of water to move: dilute solutions have high water potential; concentrated solutions have low water potential.

Osmosis and the partially permeable membrane

Osmosis Experiments

Common practical: cut cylinders of potato or radish, weigh, place in distilled water or sucrose solutions of increasing concentration, leave 20–30 min, dry and reweigh.
If mass increases: water moved into tissue by osmosis; external solution is more dilute (higher water potential) than the tissue.
If mass decreases: water moved out of tissue; external solution is more concentrated (lower water potential) than the tissue.
If mass unchanged: no net movement; internal and external concentrations are equal.

Osmosis in radish tissue

Osmosis in Animals & Plants

Plant cell in dilute solution: water enters by osmosis, pushes membrane against cell wall, cell becomes turgid (increased turgor pressure).
Plant cell in concentrated solution: water leaves, cell becomes flaccid; if severe, plasmolysis occurs (membrane pulls away from cell wall).
Animal cell in dilute solution: water enters, cell swells and may burst (no cell wall).
Animal cell in concentrated solution: water leaves, cell crenates (shrivels).

Effect of osmosis on animal cells

Active Transport

Active transport is the movement of particles across a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient).
Requires energy from respiration (ATP).
Enables cells to take up substances even when they are in low concentration outside.

The process of active transport

Importance of Active Transport

Uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron.
Uptake of ions from soil water by root hair cells in plants.

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练习题

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1.Osmosis is:
Easy
- AThe active movement of molecules from a region of their lower concentration to a region of their higher concentration.
- BThe movement of water through a partially permeable membrane from a more concentrated to a more dilute solution.
- CParticles from a region of lower concentration to a region of higher concentration using energy from respiration.
- DThe movement of water through a partially permeable membrane from a more dilute to a more concentrated solution.
2.How does a water vapour molecule move out of the air space of a leaf into the atmosphere on a dry day?
Easy
- AActive transport
- BDiffusion
- CEvaporation
- DTranspiration
3.What causes the diffusion of carbon dioxide out of a living cell?
Easy
- AActive transport
- BRandom movement of molecules
- CRespiration
- DPhotosynthesis
4.Which of the structures below is best adapted for diffusion?
Medium
- Aileum
- Bbronchioles
- Catria
- Dcapillary
5.Which of the following statements would be correct for both diffusion and osmosis?
Medium
- Adoes not require energy from the cell ✓; molecules must be separated by a partially permeable membrane ✓; molecules move from a dilute to a more concentrated solution ✗
- Bdoes not require energy from the cell ✗; molecules must be separated by a partially permeable membrane ✗; molecules move from a dilute to a more concentrated solution ✓
- Cdoes not require energy from the cell ✓; molecules must be separated by a partially permeable membrane ✗; molecules move from a dilute to a more concentrated solution ✗
- Ddoes not require energy from the cell ✓; molecules must be separated by a partially permeable membrane ✗; molecules move from a dilute to a more concentrated solution ✓
6.A number of red blood cells were immersed in a pure solution of water before being observed under a microscope. There was a dramatic change in their appearance. Which row of the table below correctly describes and explains what happened to the red blood cells?
Hard
- Adirection of water movement: in; from higher to lower concentration: ✓; from higher to lower water potential: ✗; effect: cells burst
- Bdirection of water movement: in; from higher to lower concentration: ✗; from higher to lower water potential: ✓; effect: cells burst
- Cdirection of water movement: out; from higher to lower concentration: ✓; from higher to lower water potential: ✗; effect: cells shrink
- Ddirection of water movement: out; from higher to lower concentration: ✓; from higher to lower water potential: ✓; effect: cells shrink
7.A plant absorbs a number of substances into its roots. Which row of the table below correctly shows the substances absorbed by the roots and how these substances are absorbed?
Medium
- Aminerals: active transport; oxygen: diffusion; water: osmosis
- Bminerals: active transport; oxygen: not absorbed; water: transpiration
- Cminerals: diffusion; oxygen: diffusion; water: osmosis
- Dminerals: active transport; oxygen: not absorbed; water: osmosis
8.Solution W is a dilute sugar solution and solution X is a concentrated sugar solution, separated by a partially permeable membrane. Which of the statements below is true?
Medium
- AThere is no net movement of water from W to X
- BThere would be movement of water molecules from W to X
- COsmosis of sugar molecules would occur from the dilute solution (W) to the concentrated solution (X)
- DSolution X is more dilute and therefore has a higher water potential than solution W

更多题目

9.Define diffusion.
Easy
10.What is diffusion?
Easy
- AThe net movement of molecules from a region of higher concentration to a region of lower concentration
- BThe net movement of molecules from a region of lower concentration to a region of higher concentration
- CThe movement of water through a partially permeable membrane
- DThe movement of molecules using energy from respiration
11.Which of the following factors does NOT affect the rate of diffusion?
Easy
- ASurface area to volume ratio
- BDistance
- CTemperature
- DLight intensity
12.In an osmosis experiment, potato cylinders are placed in different concentrations of sucrose solution. After 30 minutes, the potato cylinder in distilled water has increased in mass. Which statement explains this?
Medium
- AWater moved out of the potato cells by osmosis because the distilled water has a lower water potential than the potato cells.
- BWater moved into the potato cells by osmosis because the distilled water has a higher water potential than the potato cells.
- CSucrose moved into the potato cells by active transport.
- DWater moved out of the potato cells by diffusion because the potato cells have a higher concentration of water.
13.What happens to a red blood cell when it is placed in pure water?
Easy
- AIt shrinks because water moves out by osmosis.
- BIt bursts because water moves in by osmosis.
- CIt remains unchanged because the cell membrane prevents water movement.
- DIt swells but does not burst because of the cell wall.
14.Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration. Which of the following is required for active transport?
Easy
- AA partially permeable membrane
- BA concentration gradient
- CEnergy from respiration
- DA high temperature
15.A plant cell is placed in a concentrated sugar solution. After some time, it becomes plasmolysed. What does this mean?
Medium
- AThe cell has taken in water and become turgid.
- BThe cell membrane has pulled away from the cell wall.
- CThe cell wall has burst.
- DThe cell has increased in size.
16.Which of the following are examples of diffusion in living organisms? (Select all that apply)
Medium
- AOxygen moving from alveoli into blood
- BCarbon dioxide moving from blood into alveoli
- CUptake of glucose by villi in the small intestine
- DMovement of water into root hair cells
17.The energy for diffusion comes from the kinetic energy of the random movement of particles.
Easy
True or false?
18.Diffusion is the net movement of molecules from a region of their higher concentration to a region of their lower concentration. What provides the energy for this movement?
Easy
- AKinetic energy of random movement of molecules
- BEnergy from respiration
- CLight energy from the sun
- DChemical energy from ATP
19.Which of the following factors would increase the rate of diffusion of oxygen into a cell?
Medium
- AIncreasing the thickness of the cell membrane
- BDecreasing the temperature
- CIncreasing the concentration gradient of oxygen
- DDecreasing the surface area of the cell
20.Osmosis is the movement of water molecules from a region of lower water potential to a region of higher water potential across a partially permeable membrane.
Medium
True or false?
21.Which of the following statements about osmosis are correct? Select all that apply.
Medium
- AOsmosis requires energy from respiration.
- BOsmosis involves the movement of water molecules.
- COsmosis occurs across a partially permeable membrane.
- DOsmosis results in the movement of solute molecules.
- EOsmosis is a type of diffusion.
22.Place the following events in the correct order to describe the process of plasmolysis in a plant cell placed in a concentrated sugar solution.
Medium
- Water moves out of the cell by osmosis.
- Cell membrane pulls away from the cell wall.
- Cell becomes flaccid.
- Plant cell is placed in concentrated sugar solution.
23.A red blood cell is placed in pure water. What will happen to the cell?
Easy
- AIt will shrink and become crenated.
- BIt will swell and burst.
- CIt will remain unchanged.
- DIt will undergo plasmolysis.
24.Which of the following are required for active transport to occur? Select all that apply.
Medium
- AA partially permeable membrane
- BA concentration gradient (high to low)
- CEnergy from respiration
- DCarrier proteins in the membrane
- EWater molecules
25.During transpiration, water enters leaf cells from the xylem by osmosis, then evaporates from the mesophyll cell walls into the air spaces, and finally diffuses out of the leaf through the stomata as water vapour. Which sequence describes the correct order of these three processes?
Hard
- AEvaporation, then osmosis, then diffusion
- BOsmosis, then evaporation, then diffusion
- CDiffusion, then osmosis, then evaporation
- DOsmosis, then diffusion, then evaporation
26.Two identical square pieces of beetroot, each of mass 3.0 g, are placed in different solutions. S is placed in concentrated salt solution, T in pure water. After 3 hours, what are the likely masses?
Medium
- AS: 3.0 g, T: 3.2 g
- BS: 2.7 g, T: 3.0 g
- CS: 2.9 g, T: 3.2 g
- DS: 3.1 g, T: 2.9 g
27.The image below shows molecules in two solutions separated by a membrane. In which direction would there be movement?
Medium
- Awater molecules: right to left; solute molecules: no net movement
- Bwater molecules: left to right; solute molecules: right to left
- Cwater molecules: left to right; solute molecules: no net movement
- Dwater molecules: right to left; solute molecules: left to right
28.Which of the following are required for active transport to occur? (Select all that apply)
Medium
- AA partially permeable membrane
- BEnergy from respiration
- CA concentration gradient (higher to lower)
- DCarrier proteins in the membrane
- EA difference in water potential
29.Diffusion is the net movement of molecules from a region of lower concentration to a region of higher concentration.
Easy
True or false?
30.Match each process with its correct description.
Medium
- Diffusion
- Osmosis
- Active transport
- Movement of water across a partially permeable membrane
- Movement of particles down a concentration gradient without energy
- Movement of particles against a concentration gradient using energy
31.A group of students carried out an investigation into osmosis using cylinders of potato. The results from their experiment are shown below. concentration of salt solution / mol dm⁻³: 0.2 mass of potato cylinder at start / g: 2.5 mass of potato cylinder after 24 hours / g: 2.7 Which statement below correctly explains this change in mass?
Medium
- Amovement of water out of the potato cells; the salt solution has a lower water potential than the potato cells.
- Bmovement of water out of the potato cells; the salt solution has a higher water potential than the potato cells.
- Cmovement of water into the potato cells; the salt solution has a lower water potential than the potato cells.
- Dmovement of water into the potato cells; the salt solution has a higher water potential than the potato cells.
32.A group of students carried out an investigation into osmosis using cylinders of potato. The results from their experiment are shown below. concentration of salt solution / mol dm⁻³: ? length of potato cylinder at start / mm: 35 length of potato cylinder after 24 hours / mm: 33 Which statement below correctly explains this change in length and shows the concentration of the sugar solution?
Hard
- Aconcentration of sugar solution: 0.0; the sugar solution is more concentrated than the solution inside the potato.
- Bconcentration of sugar solution: 0.6; the solution in the potato is more dilute than the solution around the potato.
- Cconcentration of sugar solution: 0.6; the solution in the potato is less dilute than the solution around the potato.
- Dconcentration of sugar solution: 0.0; the sugar solution is less concentrated than the solution inside the potato.
33.Which of the following is the definition of diffusion?
Easy
- AThe net movement of molecules from a region of higher concentration to a region of lower concentration
- BThe net movement of molecules from a region of lower concentration to a region of higher concentration
- CThe movement of water molecules across a partially permeable membrane
- DThe movement of particles using energy from respiration
34.Complete the sentence.
Medium
Active transport moves particles from a region of ____ concentration to a region of ____ concentration, using energy from ____.
35.A potato cylinder has an initial mass of 3.50 g. After being placed in a salt solution for 24 hours, its mass increases to 3.85 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Medium
36.Complete the sentence about plant cells in a concentrated solution.
Easy
When a plant cell is placed in a concentrated sugar solution, water moves ____ of the cell by osmosis, causing the cell to become ____.
37.State one factor that increases the rate of diffusion.
Easy
38.In an osmosis experiment, a potato cylinder of length 50 mm is placed in a sucrose solution. After 24 hours, its length is 46 mm. Calculate the percentage decrease in length.
Medium
39.A red blood cell is placed in a solution with a water potential lower than that inside the cell. Calculate the percentage change in mass if the cell loses 0.2 g from an initial mass of 2.0 g.
Medium
40.Complete the sentence about the effect of osmosis on plant cells in a concentrated solution.
Easy
When a plant cell is placed in a concentrated sugar solution, water moves ____ the cell by osmosis, causing the cell to become ____.
41.A potato cylinder has an initial mass of 3.50 g. After being placed in a salt solution for 24 hours, its mass increases to 3.85 g. Calculate the percentage change in mass. Give your answer to one decimal place.
Easy
- A12 %
- B11 %
- C9 %
- D10 %
42.In an osmosis experiment, a potato cylinder of length 50 mm is placed in a sucrose solution. After 24 hours, its length is 46 mm. Calculate the percentage decrease in length.
Easy
- A8 %
- B9 %
- C7 %
- D10 %
43.A red blood cell is placed in a solution with a water potential lower than that inside the cell. Calculate the percentage change in mass if the cell loses 0.2 g from an initial mass of 2.0 g.
Medium
- A9 %
- B10 %
- C11 %
- D12 %
44.Which of the following is an example of active transport in plants?
Easy
- AMovement of carbon dioxide into a leaf
- BMovement of oxygen out of a leaf
- CUptake of mineral ions by root hair cells
- DMovement of water through a plant
45.State one example of active transport in plants.
Easy
46.Explain why active transport is necessary for the uptake of glucose by epithelial cells in the small intestine.
Hard

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