Mr Exham IGCSE - Movement In And Out Of Cells

MAKING SENSE OFMOVEMENT IN AND OUT OF

CELLS

IGCSE Biology1.1 Life Processes

Movement in and out of cellsBrought to you by MrExham.com

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Learning Objectives• Can you write a definition for diffusion,

osmosis and active transport?• Can you explain how surface area to volume

ratio, temperature, and concentration gradient affect the rate at which these processes work?

• Can you describe a simple experiment to demonstrate diffusion using a non-living system?


The Cell• In order for the cell to carry out the many

chemical reactions it needs to, substances must enter and leave the cell.

• This happens in the following 3 ways:





Diffusion





Diffusion Active Transport





OsmosisDiffusion Active Transport


Diffusion• Diffusion happens when a substance is more

concentrated in one place than another.• This difference in concentration is called a

concentration gradient.• Molecules are moving randomly due to their

kinetic energy, but the net movement will be from a high concentration to a low concentration.

Particles moving from high to a low concentration.


Active Transport• Sometimes a cell needs to take in a substance

against a concentration gradient. • This requires energy released from respiration.• The process is called ACTIVE TRANSPORT.

Particles moving from low to a high concentration.


Active Transport• Active transport occurs in the roots of plants

to move minerals into them against the concentration gradient and also in the small intestine of animals.

Plant minerals Small Intestine


Osmosis• Water moves from a dilute solution to a more

concentrated one across the partially permeable cell membrane.

Rlawson at en.wikibooks


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Osmosis

– In osmosis, water moves from an area of high water concentration (pure water or a dilute solution) to an area of low water concentration (a more concentrated solution of sugar or another solute).

– Water passes through a partially permeable cell membrane. – This type of membrane has tiny holes (pores) through which very small

molecules (including water) can pass, but not larger molecules (such as sugar and proteins).

Sugar Molecule

Water Molecule

Partially permeable membrane

High water concentration

Low water concentration


– In osmosis, water moves from an area of high water concentration (pure water or a dilute solution) to an area of low water concentration (a more concentrated solution of sugar or another solute).

– Water passes through a partially permeable cell membrane. – This type of membrane has tiny holes (pores) through which very small

molecules (including water) can pass, but not larger molecules (such as sugar and proteins).

Sugar Molecule

Water Molecule

Partially permeable membrane

High water concentration

Low water concentration


Osmosis

Osmosis Demonstration

Visking tubing

0.5% Sugar solution

0.1% Sugar solution


Which way will the water

move?

Osmosis Demonstration

Visking tubing

0.5% Sugar solution

0.1% Sugar solution


Which way will the water

move?

Water moves from a dilute solution to a more concentrated one across the partially permeable cell membrane.

Factors affecting the rate of diffusion

Surface area to volume

ratioTemperature Concentration

gradient


Surface area to volume ratio


Surface area to volume ratio

The surface area of the second cell is much bigger than the first cell due to the folded membrane. The volume of the cells is very similar. Therefore the second cell has a much larger surface area to volume ratio and it increases the rate of diffusion.


Temperature

Low temp High temp


Temperature

Low temp High tempAt a higher temperature the particles have more kinetic energy and are moving around faster. Therefore in a given time more diffusion will occur.


Concentration gradient

Low concentration gradient High concentration gradient


Concentration gradient

Low concentration gradient High concentration gradient

When there is a big difference between the number of particles in one place and another diffusion will happen much faster then if they are already quite spread out.


Experiment to investigate surface area to volume ratio

• Three cubes of agar are prepared which contain the indicator phenolphthalein.

• These are placed in hydrochloric acid which will diffuse into the cubes.

• As it diffuses in it will turn the indicator colourless.

3cm

3cm

2cm

2cm

1cm

1cm



• As the size of the cube increases the surface area to volume ratio decreases.

3cm

3cm

2cm2

cm1cm

1cm

Width of cube (cm)

Surface area (cm2)

Volume (cm3)

Surface area: volume

1 6 1 6

2 24 8 3

3 54 27 2



• The cubes look like this after a few minutes.

• If these were real cells then the bigger cell would not have received what it needs to all parts of the cell.

• Therefore it would need a bigger surface area in order to rely on diffusion.

3cm

3cm

2cm

2cm

1cm

1cm



• Watch this video to see the experiment in action.


http://www.youtube.com/watch?v=xuG4ZZ1GbzI

Surface Area• As the rate of diffusion relies on the surface

area.• The parts of organisms that rely on diffusion

therefore tend to have a large surface area.

Root hairs Alveoli in the lungs


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