Biology Diffusion Topic Revision

Osmosis Defintion:

The movement of water from an area of high water concentration to an area of lower water concentration across a semi permeable membrane. It is a specialised form of diffusion (only water moves in osmosis)

How are leaves adapted for diffusion?

The rate of diffusion in plants is increased by broad, flat like structures called leaves. These increase the surface area for diffusion of CO2 into the leaf from the air and O2 out of the leaf into the air.

How is the small intestine adapted for diffusion?

The rate of diffusion is increased by hair like structures called microvilli. These increase surface area for diffusion of digested foods into the blood.

Equilibrium Definition:

an even distribution of all types of particle

What type of process is diffusion and osmosis?

passive

Why do passive processes not require energy?

It is a movement from high to low concentration. It is moving alongside the concentration gradient.

A small cube has a ........ SA : Vol ratio

large

After soaking potatoes in sugar solutions and water, which measurement gave the most useful results- % change in mass or change in length? Why?

% change in mass It showed a clear trend. The change in length didn't show a clear trend. Length wasn't a good measurement to take, as the potato cylinders width increased as they absorbed water- not length. The % change in mass was a much better measurement to take because it showed us direct information about the amount of water movement into/ out of the potato through the semi permeable membrane.

% change of mass =

(final - start) / start x 100

How do you set up a visking investigation? (4 steps)

1. Fill a boiling tube with dilute iodine solution. 2. Use a pipette to put starch solution into some visking tubing 3. Put the visking tubing with the starch solution in it into the boiling tube filled with dilute iodine solution 4. Wait for the reaction to take place

The exchange surfaces of multicellular organisms tend to have (3 things):

1. large surface area 2. very thin exchange surfaces (usually only one cell thick) 3. An efficient method for transporting aerials away from the exchange surface (e.g. efficient blood supply)

Explain how a sugar cube dissolves in water (5 steps):

1. sugar particles have low kinetic energy 2. they are put into water 3. sugar dissolves through diffusion (moving from an area of high to low concentration) 4. kinetic energy increases 5. particles of sugar are distributed evenly through the water (the concentration is even)

Turgid defintion:

A plant cell fully inflated with water

Plasmolysed defintion:

A plant cell that has lost water causing the cell membrane to be pulled away from the inside of the cell wall

Flaccid defintion:

A plant cell that is limp through a reduction of pressure inside the cell

What is active transport?

A process that requires energy

What is visking tubing?

A semi permeabel membrane

Examples of diffusion (2) :

Air freshener mixing with air particles Sugar cube dissolving

Why did soaking potatoes in sugar solutions and water show us? What's the conclusion?

As the concentration of sucrose increases the mass of the potato decreases because more water molecules move out of the potato as there are fewer water molecules outside the potato. More water molecules have to move in order to reach equilibrium. This causes the potato to lose or mass. The potato cylinders soaked in higher sugar solutions had the highest change in mass.

How does temperature affect rate of diffusion?

At higher temperatures, particles have more energy and move around more. This increases the rate of diffusion.

Which part of the cell is semi permeable?

Cell membrane

Why does active transport require energy?

It is a movement against the concentration gradient (from low to high concentration).

What practical could you do to investigate the rate of diffusion and surface area?

Different sized cubes of agar could be added to a solution of coloured dye in a beaker. The time taken for each cube of agar to soak up the dye solution could be recorded in a table. Then results could be compared.

2 examples of active transport

Digestion: active transport is used to absorb more nutrients from the gut into the blood Plant roots: Plants uses active transport to take up nutrients from the soil Respiration: Glucose concentration is higher inside the cell. The cell will use energy to move glucose from the lower concentration outside the cell to attain the glucose needed for respiration.

Why are fish gills adapted for diffusion?

Exchanging gases from water

Why are plant roots adapted for diffusion?

For absorbing water from the soil

Why are leaves adapted for diffusion?

For diffusing CO2 in and O2 out

Why is the small intestine adapted for diffusion?

For digestion across the wall of the intestine

Why are the lungs adapted for diffusion?

For gas exchange between the lungs and the blood

What does semi permeable mean?

It allows some, but not all, substances to pass through it

What happens to red blood cells (RBC) if too much water is lost?

It will shrink

After soaking potatoes in sugar solutions and water, which measurements should be have taken? Why?

Mass and volume This would have given us a more accurate and useful set of results. Then the results would have been comparable on a graph. The change in length didn't provide us with sufficient information.

What is a passive process?

One that doesn't require energy

NET movement definition:

Overall movement

Explain the results of dissolving potassium permanganate (or PP) ?

PP particles dissolve in the water. Over time, they diffuse from an area of high concentration to an area of lower concentration. By the end of the experiment the PP particles have been evenly mixed with the water particles. They are in equilibrium.

What are three factors that affect rate of diffusion?

Temperature, surface area and diffusion gradient

How does diffusion gradient affect the rate of diffusion?

The greater the concentration difference, the greater the rate of diffusion

What is the isotonic point on a graph showing the relationship between % change in mass and concentration of sucrose?

The isotonic point is where there is no change in mass. This means there is no NET movement of water. Therefore, water concentration in the sugar solution is equal to the water concentration in the potato.

Which organ ensures red blood cells (RBC) never explode or shrink? How?

The kidney by making sure the concentration of blood stays around the same as the concentration of solution inside the RBC. This prevents osmosis from taking place.

Explain the results of visking?

The liquid inside the visking tubing turns black where starch and iodine react. The iodine solution diffuses into the visking tubing, causing this reaction to happen. The starch was unable to diffuse out of the visking tubing and into the iodine solution because starch molecules are too large to pass through the visking tubing.

How are fish gills adapted for diffusion?

The rate of diffusion is increased by infolding's of membrane called gills. This allows oxygen to diffuse into the blood from the water and carbon dioxide to diffuse out of the blood into the water (gas exchange). Gills are the respiratory organs of fish.

How are plant roots adapted for diffusion?

The rate of diffusion is increased by long hair like structures called root hair cells. These increase the surface area for diffusion of water into the root from the soil.

How are the lungs adapted for diffusion?

The rate of diffusion is increased by small balloon like structures called alveoli. These increase the surface area for diffusion of oxygen into the blood from the lungs and carbon dioxide out of the blood into the lungs (gas exchange).

Single celled organisms can easily exchange materials by the process of diffusion. Why?

The surface are : volume ratio is very small for a single celled organism. There is only one cell for diffusion to take place in. There's only the cell membrane for the substance to diffuse through. This means it happens very quickly.

How does surface area affect rate of diffusion?

There is a greater amount of substance moved per unit time

Why is the rate of diffusion for multicellular organisms slower than the rate for single celled organisms?

They have small SA : Vol ratio because they're big

What happens to plants when water enters them by osmosis?

They have strong cell wall. This prevents them from swelling up when water enters. Instead they become stiff and hard (turgid).

What has the slow rate of diffusion meant for multicellular organisms?

This means that the materials multicellular organisms need cannot diffuse into them at the required rate. Thus, multicellular organisms have adapted to enhance the rate at which materials can be exchanged.

How does active transport use energy?

Transport proteins in the cell membrane use energy (from aerobic respiration in the mitochondria) to move molecules against their concentration gradient.

What are two examples of practicals used to investigate diffusion?

Visking and Dissolving potassium permanganate

Why do red blood cells (RBC) explode if they take in too much water?

Water enters RBC by osmosis. RBC have a very weak cell membrane and no cell wall. As the volume of water, and therefore pressure, increases the cell bursts open.

What happens to red blood cells (RBC) when placed in a sugar solution?

Water moves out of the RBC by osmosis. This causes it to shrink. This makes the cell appear wrinkled when viewed through a microscope.

When does diffusion happen?

When particles move from an area of high concentration to an area of lower concentration

Why do plants wilt when they lose water?

When plant cells lose water by osmosis they shrink a little. Normally, the vacuole exerts pressure on the cell wall, keeping the cell turgid. When water is lost the vacuole shrinks and no longer exerts pressure onto the wall. As the cell membrane is no longer being pushed agains the cell wall, it begins to shrink away from the cell wall. The cell wall is tough though, so keeps the cell's shape when the membrane inside shrinks away from it. This causes the cell to become limp and floppy (plasmolysed). As the cell becomes more flaccid, the plant starts to wilt.

iodine + starch makes which colour?

black

Lysis defintion:

bursting an animal cell by osmosis

The more uneven the particles are the .... diffusion takes place

faster because the greater the concentration difference the greater the rate of diffusion

Crenation defintion:

shrinking an animal cell by osmosis

A large cube has a ........ SA : Vol ratio

smaller

The higher the surface area : volume ratio, the greater...

the rate of diffusion