MYP Biology Topic Osmosis Revision Notes

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MYP Biology Topic Osmosis Revision Notes | RevisionDojo

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What Exactly Is Osmosis?

Osmosis is the diffusion of water, it follows the same principles, but only water molecules move.
So similarly, water molecules move from dilute to concentrated solutions.
Or in other words, from areas of low to high solute concentrations.
1. Dilute solution = lots of water molecules, few solute particles (high water concentration).
2. Concentrated solution = fewer water molecules, lots of solute particles (low water concentration).

Definition

Osmosis

The net movement of water molecules from an area of higher water concentration (dilute solution) to an area of lower water concentration (concentrated solution), across a partially permeable membrane.

Why Does Water Move but Not Solutes?

The membrane controls what passes through:
1. Water molecules are tiny (about 0.3 nanometers), easily fitting through membrane pores.
2. Solute particles are much larger (glucose is 1 nanometer, proteins are even bigger), making them too big to fit through the pores.
The membrane prevents solute from moving:
1. Solute particles would naturally diffuse to spread out evenly.
2. But the membrane blocks them.
3. Only water can move to balance things out.

Tip

Diffusion and osmosis happen simultaneously, but osmosis specifically describes what happens when there's a partially permeable membrane that blocks solute but allows water through.
Without a membrane (normal diffusion):
- Both solute particles AND water would spread out evenly.
- Everything diffuses until equilibrium.
With a partially permeable membrane (osmosis):
- Solute particles are physically blocked by the membrane - they're too large to fit through the pores.
- Water molecules are small enough to pass through.
- Since solute can't move to balance concentrations, water moves instead.
- Water moves from high water concentration to low water concentration.

Note

The membrane doesn't actively block anything, it's passive.
Large molecules physically cannot fit through the tiny pores in the membrane structure.
It's like how a sieve works

What Happens to Cells in Salty or Sugary Environments?

The effect of osmosis on cells depends on the surrounding solution:

Cells in hypertonic solutions (concentrated)

Definition

Hypertonic solution

A solution with lower water concentration than the cell contents (more concentrated). Water moves out of the cell by osmosis.

Animal cells:

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MYP Biology Osmosis Notes

What Exactly Is Osmosis?

Why Does Water Move but Not Solutes?

What Happens to Cells in Salty or Sugary Environments?

Cells in hypertonic solutions (concentrated)

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What Exactly Is Osmosis?

Why Does Water Move but Not Solutes?

What Happens to Cells in Salty or Sugary Environments?

Cells in hypertonic solutions (concentrated)

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Cells7 subtopics

Organisms7 subtopics

Processes10 subtopics

Metabolism4 subtopics

Evolution7 subtopics

Interactions with environment6 subtopics

Interactions between organisms5 subtopics

Human interactions with environments3 subtopics

Biotechnology3 subtopics

MYP Biology Osmosis Notes

Cells7 subtopics

Organisms7 subtopics

Processes10 subtopics

Metabolism4 subtopics

Evolution7 subtopics

Interactions with environment6 subtopics

Interactions between organisms5 subtopics

Human interactions with environments3 subtopics

Biotechnology3 subtopics

What Exactly Is Osmosis?

Why Does Water Move but Not Solutes?

What Happens to Cells in Salty or Sugary Environments?

Cells in hypertonic solutions (concentrated)

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

What Exactly Is Osmosis?

Why Does Water Move but Not Solutes?

What Happens to Cells in Salty or Sugary Environments?

Cells in hypertonic solutions (concentrated)

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account