(2.15-2.16) Movement of Substances

Define diffusion.

The passive net movement of particles from a region of high concentration to an area of low concentration.

(down a concentration gradient)

How does diffusion occur in a living organism?

Molecules move into or out of living cells across a partially permeable membrane.

How does the partially permeable nature of the membrane affect the diffusion?

Molecules that are too large to pass through can’t, so only smaller molecules can diffuse.

How does diffusion help in living organisms?

Gain nutrients and oxygen

Remove waste products

How and why does SA:V ratio affect the rate of diffusion?

The higher the SA:V ratio, the faster the rate of diffusion.

This is because there is more area through which molecules can travel.

How does SA:V ratio differ with the size of the cell?

The larger the cell, the smaller the SA:V ratio.

How and why does thickness of walls affect the rate of diffusion?

The thinner the walls → the smaller the distance travelled by the molecules → faster diffusion rate

How and why does temperature affect the rate of diffusion?

The higher the temp → the more energy the molecules have → the faster they move → the greater the chance and rate of movement

How and why does concentration gradient affect the rate of diffusion?

The greater the different in concentration → the more random collisions on the higher concentration side → the faster the movement

Define osmosis.

The movement of water molecules from a region of high water concentration (dilute) to a region of low water concentration (concentrated) through a partially permeable membrane.

Define a hypertonic solution.

A solution in which the concentration of solutes is higher compared to the cell.

What does water do in a hypertonic solution?

It flows out of the cell to the more concentrated area.

Define a hypotonic solution.

A solution with less solutes and more water than the cell.

What does water do in a hypotonic solution?

Water flows into the cell towards to more concentrated region.

Define an isotonic solution.

A solution in which the solute concentrations with the cell are equal.

What does water do in an isotonic solution?

Water flows in equal parts out of and into the cell, resulting in 0 net water flow.

What does the partially permeable membrane do in osmosis?

Ensure larger molecules don’t travel through but small water molecules can.

Why can the results of osmosis be severe in animal cells?

They have no supporting cell wall so it can lose and take in water to the extremes.

If an animal cell was placed into a hypertonic solution, what would happen?

cell would lose water by osmosis as the solution it is in is more concentrated than itself.

This would result in it becoming crenated (shrivelled).

If an animal cell was placed into a hypotonic solution, what would happen?

As there would be more water outside the cell than inside, the cell would gain water.

It would continue until the cell membrane is too stretched and bursts. (cell lysis)

What does a presence of a cell wall mean for plants in regards to osmosis?

It is protected from cell lysis (bursting) due to the support.

What happens to a plant cell in a hypertonic solution?

The water leaves the cell to the more concentrated solution, meaning the cell loses water.

The vacuole gets smaller.

The cell membrane shrinks away from the cell wall.

The cell becomes flaccid.

What happens to a plant cell in a hypotonic solution?

The water enters the more concentrated cell.

The vacuole grows, pushing the membrane against the cell wall.

The cell is turgid.

What are the benefits of turgid cells?

They provide structural support and prevent plants from wilting.

What is the relationship between osmosis and diffusion?

Osmosis is the diffusion of water.

Define active transport.

The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration.

Why is energy needed for active transport?

Needed because particles are being moved against the concentration gradient.

Where is the energy used in active transport from?

Released during cellular respiration.

Describe the process of active transport.

A carrier protein within the cell membrane binds onto the molecule that needs to be moved.

Energy (ATP) is used to make the protein change shape.

The molecule is released on the other side of the membrane.

The protein returns to pick up another molecule.

Where does active transport occur in animals?

The transport of glucose into the bloodstream from the small intestine when the sugar concentration in blood is higher.

Where does active transport take place in plants?

Root hair cells need to move mineral from the soil into the cytoplasm of the cell.