Diffusion, osmosis and active transport

What is diffusion?

It is the net movement of particles from an area of high concentration to an area of low concentration. It is a passive process (doesn't require energy) which involves the random movement of particles.

What are the processes that allow substances to move in and out of cells?

By diffusion, osmosis and active transport

In which substances does diffusion occur? Why?

In fluids like gases and liquids because particles in these substances are free to move around randomly

In which substances will diffusion occur faster?

In gases because they have more kinetic energy.

What is a passive process?

Process that doesn't require additional energy from the organism (ATP)

What factors affect the rate of diffusion?

Concentration gradient, temperature, distance particles must travel, surface area to volume ratio and the size of particle.

What is a concentration gradient?

The difference in concentration between two areas.

How does the concentration gradient affect the rate of diffusion?

The greater the concentration gradient, the faster the rate of diffusion.

How does temperature affect the rate of diffusion?

The higher the temperature, the faster the rate of diffusion. This is because the particles have more kinetic energy so they move around faster, therefore causing the rate of diffusion to increase.

How does the distance particles must travel affect the rate of diffusion?

The shorter the distance the faster the rate of diffusion will be. This is because particles will diffuse faster if they have a shorter distance to go.

How does the surface area to volume ratio affect the rate of diffusion?

The larger the surface area to volume ratio the faster the rate of diffusion. This is because more surface area exposed for particles to collide will lead to a faster rate of diffusion.

How does the size of the particle affect the rate of diffusion?

The smaller the particles the faster the rate of diffusion. This is because smaller particles are lighter so they travel faster, meaning diffusion happens quicker.

Practical: demonstration of diffusion in a jelly
What type of jelly to use? What are the two chemicals used + where? Method?

Agar jelly dyed purple with potassium manganate(VII) and put into dilute hydrochloric acid. When they react, purple colour disappears.
In a beaker add dilute HCl and add the same time, carefully drop 3 cubes of diff sizes. After x minutes take them out and cut them to measure how many mm turned colourless in each cube

Explain 2 factors that the student should keep constant in this investigation

M1. temperature (increased);
M2. particles have more (kinetic) energy / move faster / more movement / eq;

M1 concentration of dye (increased);
M2 increased concentration gradient / more particles / eq;

M1 concentration/density of agar (increased);
M2 reduces speed of particle movement / eq;

Explain how the results of the student's investigation support the idea that large organisms need a circulation system (3)

1. dye does not reach middle of cube / takes longer to reach middle of cube / reaches lower proportion;
2. large organisms / large cubes have small SA:VOL;
3. (in large organisms) diffusion is slow / diffusion takes too long / diffusion is insufficient / diffusion is affected by distance / eq;
4. need to get oxygen / glucose to cells / all of the body;

CUBE RESULT EXPERIMENT

IMAGENES

What is osmosis?

It is the net movement of water molecules across a partially permeable membrane from a high concentration of water, a solvent, (dilute solution) to a lower concentration of water (solution with high levels of solute)

What is a freely permeable membrane and a partially permeable membrane? Give examples

A freely permeable membrane (e.g. cell wall) is one that allows every kind of particles to pass through, no matter the size.
A partially permeable membrane separates two solutions (e.g. cell membrane) and only allows small particles to pass through its 'pores' — like water. Big molecules such as starch or proteins can't fit through the membrane.term-7

Describe what happens in this image (two solutions separated by membrane) topic de diffusion, osmosis y active transport.

Two solutions with different concentrations are separated by a partially permeable membrane. Water molecules are moving randomly in and out of the membrane, but sugar molecules are too big to pass through. Because one side is more dilute than the other, the net flow of water with be into the region with a higher concentration (e.g. sucrose solution) which would mean that it would dilute the sucrose solution to equalize the concentrations.

What happens to a red blood cell in a hypertonic solution?

The cell shrinks which means which means it passes through crenation. This is because in a hypertonic solution there will be a lower concentration of water so there will be a net movement of water molecules out of the cell. The mass would decrease.

What happens to a red blood cell in a hypotonic solution?

Lysing, which means the cell swells and could burst. This is because since the cell is in a dilute solution, there would be a net movement of water into the cell. The mass would also increase

What happens to a red blood cell and a plant cell in a isotonic solution?

The cell would remain the same, conserving it's mass. This is because the concentration of water is the same outside and inside the cell so the net movement of water would reach an equilibrium.

What happens to a plant cell in a hypertonic solution?

Turgid pressure, seen as wilting, falls. It becomes flaccid and reaches plasmolysis (when the cell membrane detaches from the cell wall) This is because in a hypertonic solution there will be a lower concentration of water so there will be a net movement of water molecules out of the cell.

What happens to a plant cell in a hypotonic solution?

Turgor pressure increases so the cell becomes turgid (firm). But it would not burst because it has a cell wall. This is because since the cell is in a dilute solution, there would be a net movement of water into the cell. The mass would also increase

Practical: investigating effect of osmosis on potato tuber tissue (a plant storage organ so convenient tissue to investigate effects of osmosis on mass) How to find percentage change in mass?

(Final - initial)/ initial x 100

What is active transport?

It is the movement of particles against a concentration gradient using energy released during respiration (ATP)

Where would active transport occur?

In the small intestine when there is a low concentration of nutrients there, but a high concentration of nutrients in the blood. Nutrients have to be absorbed into the blood.
Roots of plants to take in mineral ions

What are the main differences between diffusion, osmosis and active transport?

Osmosis and diffusion are passive processes while active transport is not + explanation

Diffusion doesn't require a partially permeable membrane but osmosis and active transport MUST have one.