The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.

Concentration gradient

The difference in concentration between two regions; particles diffuse down it (from high to low concentration).

Why is diffusion important for cells?

It allows essential substances (e.g. oxygen and dissolved nutrients) to move into cells and waste substances (e.g. carbon dioxide) to move out, without using energy.

Give one example of a substance that moves into a cell by diffusion and one that moves out.

In: oxygen (for respiration). Out: carbon dioxide (a waste product of respiration).

What provides the energy for particles to diffuse?

The random movement (kinetic energy) of the particles themselves — no energy from respiration is needed.

List the main factors that affect the rate of diffusion.

Surface area. Temperature. Concentration gradient. Distance (the diffusion path).

How does surface area affect the rate of diffusion?

A larger surface area provides more space for particles to cross, so the rate of diffusion increases.

How does the distance (diffusion path) affect the rate of diffusion?

The shorter the distance particles have to travel, the faster the rate of diffusion.

How are gas exchange surfaces (e.g. alveoli) adapted to maximise diffusion?

They have a large surface area. They have a short diffusion distance (thin walls). They have a good blood supply to maintain a steep concentration gradient.

The net movement of water molecules from a region of higher water potential (a dilute solution) to a region of lower water potential (a concentrated solution), through a partially permeable membrane.

Partially permeable membrane

A membrane that allows some molecules (e.g. water) to pass through but not others (e.g. larger solute molecules).

How is osmosis different from diffusion?

Osmosis is the diffusion of water molecules specifically, and it occurs across a partially permeable membrane. Diffusion can apply to any particles and does not require a membrane.

Which way will water move between a dilute solution and a concentrated solution separated by a partially permeable membrane?

Water moves from the dilute solution (higher water potential) into the concentrated solution (lower water potential).

In a potato osmosis experiment, what happens to a potato cylinder placed in pure (distilled) water?

Water moves into the cells by osmosis, so the cylinder increases in mass and length and becomes firm (turgid).

In a potato osmosis experiment, what happens to a potato cylinder placed in a concentrated sugar solution?

Water moves out of the cells by osmosis, so the cylinder decreases in mass and length and becomes soft (flaccid).

How do you calculate the percentage change in mass in an osmosis experiment?

Percentage change = (change in mass / initial mass) × 100.

At what point on a potato osmosis graph is the concentration of the solution equal to the concentration inside the cells?

Where the line crosses the x-axis (0% change in mass) — there is no net movement of water.

A plant cell that is firm and swollen because it has taken in water by osmosis, pushing the cell membrane against the cell wall.

When a plant cell loses so much water by osmosis that the cell membrane pulls away from the cell wall.

What happens to an animal cell (e.g. a red blood cell) placed in pure water?

Water enters by osmosis and the cell swells and may burst (lysis), because animal cells have no cell wall to resist the pressure.

What happens to an animal cell placed in a concentrated solution?

Water leaves the cell by osmosis, so the cell shrinks and becomes crenated (shrivelled).

Why does a plant cell not burst when placed in pure water, unlike an animal cell?

The strong, inelastic cellulose cell wall resists the inward pressure as water enters, so the cell becomes turgid rather than bursting.

Why does a plant wilt when it lacks water?

The cells lose water by osmosis and become flaccid, so they no longer provide support (loss of turgor pressure).

The movement of particles from a region of lower concentration to a region of higher concentration (against a concentration gradient), using energy from respiration.

Why can't active transport happen by diffusion alone?

Because the particles are moved against the concentration gradient (from a low to a high concentration), which requires energy from respiration.

Give one similarity and one difference between active transport and diffusion.

Similarity: both move substances across the cell membrane. Difference: active transport moves particles against the concentration gradient and needs energy, whereas diffusion moves them down the gradient with no energy.

Why would a cell carrying out lots of active transport contain many mitochondria?

Mitochondria carry out aerobic respiration to release the energy needed to power active transport.

Give an example of active transport in plants.

The uptake of mineral ions (e.g. nitrate ions) into root hair cells from the soil, where the ions are in lower concentration than inside the cell.

Does active transport need living cells? Explain.

Yes — it requires energy from respiration, so it can only occur in living cells (e.g. ones with many mitochondria).

Why can't mineral ions enter root hair cells by diffusion?

Their concentration is usually higher inside the cell than in the soil, so they must be moved against the concentration gradient by active transport.

Why is active transport important for the body even though it uses energy?

It allows cells to take up essential substances (e.g. glucose, mineral ions) that would otherwise be lost or could not be absorbed against the concentration gradient.

IGCSEScienceCambridge (CIE)Co-ordinated Sciences (Double Award)BiologyFlashcards3. Movement into & out of CellsDiffusion, Osmosis & Active Transport

Diffusion, Osmosis & Active Transport (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Biology): Flashcards

Exam code: 0654 & 0973

1/46

0Still learning

Know0

FrontDiffusion
Diffusion

Was this flashcard helpful?

Cards in this collection (46)

Diffusion
The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.
Concentration gradient
The difference in concentration between two regions; particles diffuse down it (from high to low concentration).
Diffusion is the net movement of particles from a region of concentration to a region of lower concentration.
higher
Diffusion is a process, meaning it does not require energy from respiration.
passive
Why is diffusion important for cells?
It allows essential substances (e.g. oxygen and dissolved nutrients) to move into cells and waste substances (e.g. carbon dioxide) to move out, without using energy.
Give one example of a substance that moves into a cell by diffusion and one that moves out.
In: oxygen (for respiration).
Out: carbon dioxide (a waste product of respiration).
What provides the energy for particles to diffuse?
The random movement (kinetic energy) of the particles themselves — no energy from respiration is needed.
List the main factors that affect the rate of diffusion.
Surface area.
Temperature.
Concentration gradient.
Distance (the diffusion path).
The steeper the concentration gradient, the the rate of diffusion.
faster
Increasing the temperature the rate of diffusion, because particles gain more kinetic energy and move faster.
increases
How does surface area affect the rate of diffusion?
A larger surface area provides more space for particles to cross, so the rate of diffusion increases.
How does the distance (diffusion path) affect the rate of diffusion?
The shorter the distance particles have to travel, the faster the rate of diffusion.
A larger surface area gives a rate of diffusion.
faster
How are gas exchange surfaces (e.g. alveoli) adapted to maximise diffusion?
They have a large surface area.
They have a short diffusion distance (thin walls).
They have a good blood supply to maintain a steep concentration gradient.
Osmosis
The net movement of water molecules from a region of higher water potential (a dilute solution) to a region of lower water potential (a concentrated solution), through a partially permeable membrane.
Partially permeable membrane
A membrane that allows some molecules (e.g. water) to pass through but not others (e.g. larger solute molecules).
Osmosis is the net movement of molecules through a partially permeable membrane.
water
In osmosis, water moves from a region of higher water potential to a region of water potential.
lower
How is osmosis different from diffusion?
Osmosis is the diffusion of water molecules specifically, and it occurs across a partially permeable membrane.
Diffusion can apply to any particles and does not require a membrane.
Which way will water move between a dilute solution and a concentrated solution separated by a partially permeable membrane?
Water moves from the dilute solution (higher water potential) into the concentrated solution (lower water potential).
In a potato osmosis experiment, what happens to a potato cylinder placed in pure (distilled) water?
Water moves into the cells by osmosis, so the cylinder increases in mass and length and becomes firm (turgid).
In a potato osmosis experiment, what happens to a potato cylinder placed in a concentrated sugar solution?
Water moves out of the cells by osmosis, so the cylinder decreases in mass and length and becomes soft (flaccid).
In a potato osmosis experiment, the percentage change in is usually calculated so results can be compared fairly.
mass
How do you calculate the percentage change in mass in an osmosis experiment?
Percentage change = (change in mass / initial mass) × 100.
At what point on a potato osmosis graph is the concentration of the solution equal to the concentration inside the cells?
Where the line crosses the x-axis (0% change in mass) — there is no net movement of water.
To make an osmosis experiment a fair test, the potato cylinders should all be the same size and left for the same at the same temperature.
time
Turgid
A plant cell that is firm and swollen because it has taken in water by osmosis, pushing the cell membrane against the cell wall.
Plasmolysis
When a plant cell loses so much water by osmosis that the cell membrane pulls away from the cell wall.
A plant cell that has lost water and become limp, with the contents no longer pushing on the cell wall, is described as .
flaccid
What happens to an animal cell (e.g. a red blood cell) placed in pure water?
Water enters by osmosis and the cell swells and may burst (lysis), because animal cells have no cell wall to resist the pressure.
What happens to an animal cell placed in a concentrated solution?
Water leaves the cell by osmosis, so the cell shrinks and becomes crenated (shrivelled).
Why does a plant cell not burst when placed in pure water, unlike an animal cell?
The strong, inelastic cellulose cell wall resists the inward pressure as water enters, so the cell becomes turgid rather than bursting.
Turgor pressure helps provide to plant tissues, keeping non-woody plants upright.
support
Why does a plant wilt when it lacks water?
The cells lose water by osmosis and become flaccid, so they no longer provide support (loss of turgor pressure).
Active transport
The movement of particles from a region of lower concentration to a region of higher concentration (against a concentration gradient), using energy from respiration.
Active transport moves particles against a concentration gradient, from low to concentration.
high
Unlike diffusion and osmosis, active transport requires released by respiration.
energy
Why can't active transport happen by diffusion alone?
Because the particles are moved against the concentration gradient (from a low to a high concentration), which requires energy from respiration.
Give one similarity and one difference between active transport and diffusion.
Similarity: both move substances across the cell membrane.
Difference: active transport moves particles against the concentration gradient and needs energy, whereas diffusion moves them down the gradient with no energy.
Why would a cell carrying out lots of active transport contain many mitochondria?
Mitochondria carry out aerobic respiration to release the energy needed to power active transport.
Give an example of active transport in plants.
The uptake of mineral ions (e.g. nitrate ions) into root hair cells from the soil, where the ions are in lower concentration than inside the cell.
Does active transport need living cells? Explain.
Yes — it requires energy from respiration, so it can only occur in living cells (e.g. ones with many mitochondria).
Root hair cells absorb mineral from the soil by active transport.
ions
Active transport allows cells to absorb substances even when they are at a lower concentration the cell than inside it.
outside
Why can't mineral ions enter root hair cells by diffusion?
Their concentration is usually higher inside the cell than in the soil, so they must be moved against the concentration gradient by active transport.
Why is active transport important for the body even though it uses energy?
It allows cells to take up essential substances (e.g. glucose, mineral ions) that would otherwise be lost or could not be absorbed against the concentration gradient.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Cell Structure & Size of SpecimensNext:Biological Molecules