Mr Exham IGCSE - Movement In And Out Of Cells
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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?
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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:
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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
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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 Active Transport
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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:
OsmosisDiffusion Active Transport
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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.
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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.
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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
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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
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– 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
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Osmosis
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Osmosis Demonstration
Visking tubing
0.5% Sugar solution
0.1% Sugar solution
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Which way will the water
move?
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Osmosis Demonstration
Visking tubing
0.5% Sugar solution
0.1% Sugar solution
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Which way will the water
move?
Water moves from a dilute solution to a more concentrated one across the partially permeable cell membrane.
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Factors affecting the rate of diffusion
Surface area to volume
ratioTemperature Concentration
gradient
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Surface area to volume ratio
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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.
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Temperature
Low temp High temp
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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.
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Concentration gradient
Low concentration gradient High concentration gradient
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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.
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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
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Experiment to investigate surface area to volume ratio
• 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
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Experiment to investigate surface area to volume ratio
• 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
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Experiment to investigate surface area to volume ratio
• Watch this video to see the experiment in action.
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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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