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Transcript of Starter Activity: Answer the following question in your classwork jotter 1.What type of fibres are...
Starter Activity:
Answer the following question in your classwork jotter
1. What type of fibres are the cell walls of plants made of?
2. Name the small rings of DNA found in bacterial cells.
3. Name the process by which yeast cells reproduce.
4. What is the function of a) ribosomes? b) mitochondria?
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Be able to describe the structure of the cell
membrane• Understand the terms passive and active transport • Understand the term diffusion and give examples
of diffusion in cells• Understand the term osmosis and its effect on
cells• Understand the idea of concentration gradient
The Function of the Cell Membrane
Twig Video Clip: The Cell Membrane
Whilst you are watching the video clip write down key words on a show me board.
Structure of the cell membrane
• The cell membrane is very thin.
• It is able to control the movement of materials into and out of cells.
• When seen under an electron microscope, it can be seen to consist of a double layer.
Cytoplasm of cell
Cell membrane
Structure of the cell membrane
• It has a double layer made of molecules called phospholipids.
• Phospholipid molecules have a head and a tail end.
• All the tails point inward and the heads point outwards.
Head end
Head end
Tails
Structure of the cell membrane• There are also proteins embedded in the
membrane.• These proteins have various functions.• Some are involved in the transport of
materials across the membrane.
proteins
Phospholipid double layer
Fluid mosaic model• The membrane is a very flexible structure
which can move and change shape easily.• It is often described as a fluid mosaic model. • Fluid refers to the moving phospholipids and
mosaic refers to the patchy arrangement of the proteins.
Homework task - Make a 3D cell membrane model
• Your task is to make a 3D model of the cell membrane.
• You can use any materials you can find at home, especially recycling materials.
• Your model should show the proteins and the phospholipids with their head and tail ends.
• The component parts should be labelled or there should be a key to identify them.
• Examples of materials you could use include paper, cardboard, plastic bottle lids, plasticene, playdoh, straws, cotton buds, cocktail sticks, buttons, ribbons, fabric, lolly sticks, dry pasta, lego, stickle bricks, k’nex.
• THE POSSIBILITIES ARE ENDLESS SO HAVE FUN!
Selectively permeable membrane
• Permeability means the ability of a surface to allow molecules to pass through it.
• The cell membrane is usually described as selectively permeable.
• This means that it allows some molecules to move through it easily, but others move more slowly, and some cannot move across it at all.
Visking tubing
• Visking tubing is a selectively permeable material that acts like a cell membrane.
• We can use it to demonstrate which molecules are able to pass through the membrane, and which are not.
• Your teacher will show you how to use the visking tubing in an experiment.
Visking tubing experiment
Water
Visking tubing bag
Starch and glucose solution
Test water for starch and glucose after 20 minutes
Visking tubing experiment1. Soften a length of visking tubing under running
water until you can open it up.2. Tie a firm knot in one end.3. Add equal volumes of starch and glucose
solutions using droppers.4. Tie a firm knot in the other end. Cut off any
excess tubing to leave 1cm tails.5. Wash the bag thoroughly under running water.6. Place bag in a test tube, cover with water and
leave for 20 minutes. Remove the bag.7. Transfer a drop of the water to a spotting tile
and test for starch using iodine.8. Test the remaining water for glucose by adding
Benedicts solution and heating to 80°C for 5 minutes.
Visking tubing experimentResults:
Colour change observed
Result of test – positive or negative
Starch test (iodine)
Glucose test(Benedicts)
Conclusion : The ______was able to pass through the visking tubing but the _______was not. This is because starch has ________ molecules but glucose has ________molecules.
Selectively Permeable Membranes
• Cell membranes allow small molecules like glucose, oxygen and water to pass through them freely.
• This is because the membrane has tiny holes in it called pores that make it permeable. Large molecules like starch are unable to pass through.
Selectively Permeable Membranes
• Pores in the membrane are small, so only small molecules such as glucose, water, oxygen and carbon dioxide can get through.
• Large molecules such as starch cannot pass through.
• Selectively permeable membranes allow certain molecules to pass through but not others.
nucleus
selectively permeable membrane
cytoplasm
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Be able to describe the structure of the cell
membrane• Understand the terms passive and active transport • Understand the term diffusion and give examples
of diffusion in cells• Understand the term osmosis and its effect on
cells• Understand the idea of concentration gradient
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the terms passive and
active transport • Understand the term diffusion and
give examples of diffusion in cells
Passive transport
• passive transport is the movement of a substance across a cell membrane down a concentration gradient
• It does not require energy. • The two types of passive transport
are:1. Diffusion2. Osmosis
Diffusion
•Diffusion is the movement of
molecules in a liquid or gas from high
to low concentration until they are
evenly spread out.
•Diffusion moves down a
concentration gradient. Diffusion clip
Diffusion in liquids
• Diffusion in liquids can be seen by adding dye to a beaker of water.
Add dye to one side only
Water
Do not shake or stir. Leave for 20 minutes.
Diffusion in liquids
Red dye in water
Red dye molecules and water molecules have moved until they are evenly spread – this is DIFFUSION.
Direction of diffusion
Diffusion always occurs from high concentration of a molecule to low concentration of that molecule.
Concentration Gradient
The difference in concentration of two solutions is called a concentration gradient.
In diffusion, molecules will always move down the concentration gradient from high concentration to low concentration.
Concentration Gradient
high ground
gradient (slope)
low ground
ball ball rolls down gradient
ball stops
•Like a ball on a slope, molecules diffuse down a concentration gradient from high to low.
Concentration Gradient
• A concentration gradient exists when there
is a difference in concentration from one
area to another.
• Molecules move down a concentration
gradient from high to lower concentration.
The molecules will stop moving when the
two concentrations are equal.
Cells and diffusion
• Many substances can enter or leave cells by diffusion.
• This happens across the cell membrane.
• Animal cells take in glucose, oxygen and amino acids by diffusion.
• Carbon dioxide and waste materials leave animal cells by diffusion.
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the terms passive and
active transport • Understand the term diffusion and
give examples of diffusion in cells
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term osmosis and its
effect on cells• Understand the idea of concentration
gradient
Osmosis• Water can also diffuse into and out of cells across the cell membrane.
• Osmosis is the special diffusion of water from an area of high concentration to an area of low concentration through a selectively permeable membrane.
High water concentration
Low water concentration
Twig Video Clip - Osmosis
Visking tubing
• Visking tubing is a selectively permeable material that can be used to show the effect of osmosis on cells.
• The visking tubing behaves like a cell membrane, so we can use it to make model cells.
Osmosis experiment
A B
Visking tubing bag
10% sugar solution
water
Boiling tube
1. Wash and dry bags when filled.2. Weigh both bags.3. Place in test tubes for 20 minutes then dry and reweigh.
TEACHER DEMONSTRATION
Results
A B
Mass of bag and contents at start (g)
Mass of bag and contents after 20 minutes (g)
Difference in mass (g)
Conclusion
• Bag A increased/decreased in mass. This was because water moved in/out by osmosis.
• Bag B increased/decreased in mass. This was because water moved in/out by osmosis.
• Water always moves from ________ water concentration to ______ water concentration.
Answer the following questions in sentences:
1. Why was the visking tubing bag dried in a paper towel before being weighed?
2. Why was visking tubing used in this experiment? What property does it have that makes it a good model cell?
3. What would happen to an onion cell placed in pure water?
4. What would happen to a cheek cell placed in 10% sucrose solution?
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term osmosis and its
effect on cells• Understand the idea of concentration
gradient
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term osmosis
Understand the effect of osmosis on plant cells
Osmotic Effect On Cells
Water concentrations • If we think about solutions in terms of
their water concentrations, it is easier to recognise which direction water molecules will flow in.
• A dilute sugar solution will have a high concentration of water, whereas a concentrated sugar solution will have a lower water concentration.
Dilute Sugar Solution
Concentrated Sugar
Solution
Low water concentration
High sugar concentration
High water concentration
Low sugar concentration
Water Concentrations
H2O concentration
>
The surrounding solution has a higher water concentration than the water concentration within the cell, so water enters by osmosis.
cell
Direction of water
movement
Cell in pure water
Water ConcentrationsCell in concentrated salt solution
cellH2O
concentration <
The surrounding solution has a lower water concentration than the water concentration within the cell, so water leaves the cell by
osmosis.
Water Concentrations
cellH2O concentration =
Cell in solution with equal concentration to cell contents.
The surrounding solution has a water concentration that is equal to the water concentration within the cell, so there is
no gain or loss of water by osmosis.
Investigating osmosis in potato tissue
1. Copy the title and the aim from the instruction card.
2. Prepare a results table.3. Set up the experiment by
following the instructions on the card.
Results
Conclusion
Evaluation
Bathing solution
Initial mass (g)
Final mass (g)
% Change in mass
Water
Strong sucrose solution
Plant Cells and OsmosisPure water: there is more water outside of the cell than inside, therefore water will move into the cell by osmosis. This causes the cell to swell and become turgid.
Strong salt solution: there is more water inside the cell than outside, therefore water will move out of the cell by osmosis. This causes the cell to become softer or flaccid.
Cell in pure water
Cell in strong salt solution
Plant Cells and Osmosis
Cell in pure water - turgid
Normal cell Cell in strong salt solution - plasmolysed
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term osmosis
Understand the effect of osmosis on plant cells
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term osmosis
Understand the effect of osmosis on animal cells
Viewing plasmolysed cells
• In this practical, you will expose onion cells to a solution of salt to observe plasmolysis. You will also prepare cells in water for comparison (as a control experiment).
• You will view the cells under the microscope and make drawings of what you see.
• You will need a pencil and a circular object (eg beaker) to draw round.
• Follow the instructions on the card provided.
Plasmolysis in onion cells• The photo shows
onion cells which have been bathed in strong salt solution and have become plasmolysed.
• Notice how the cytoplasm and cell membrane have shrunk inwards away from the cell wall.
cell wall
cell membrane
nucleus
cytoplasm
Osmosis in red cabbage cellsYour task in this experiment is to identify liquids A and B by looking at the results.
1. Label two boiling tubes A and B.2. Half fill tube A with liquid A and tube B
with liquid B.3. Cut 10 discs from red cabbage using a
cork borer.4. Wash the leaf discs in a small beaker of
water and dry them gently.5. Add 5 discs to each test tube.6. Leave for 20 minutes and observe any
colour change in the liquids.
Osmosis in red cabbage cells
Results:
Test tube A Test tube B
Appearance of liquid
Conclusion:Which test tube contained strong sucrose solution? How do you know this?Which test tube contained water?How do you know this?
Animal Cells & Osmosis
• The effects of osmosis on animal cells are totally different to plant cells because animal cell structures are different.
• Animals cells do not have:Cell wallsVacuoles
Animal Cells & Osmosis
• Red blood cells (RBCs) float in a liquid called plasma which is the same water concentration as the cells.
• RBCs in plasma do not change size because the water has no concentration gradient to follow.
• RBCs will change if there is a concentration gradient for water to follow.
Normal red blood cell
RBC in strong salt
solution
RBC in equal concentration solution
RBC in pure water
Cell loses water by osmosis
and shrinks.
No net osmosis, cell stays the same.
Cell takes in water
by osmosis,
swells and eventually
bursts.
Animal Cells & Osmosis
Osmosis in eggs
• Your teacher will show you a demonstration experiment involving eggs placed in different solutions.
• Write a description of this experiment in your notebook. Include the following:
TitleDiagramMethod ResultConclusion
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term osmosis
Understand the effect of osmosis on animal cells
Transport across cell membranes
Learning Intention:Learning Intention:Investigate the cell membrane and the movement of molecules across it
Success Criteria:Success Criteria:• Understand the term active transport
and its effect on cells• Understand the idea of concentration
gradient
Passive transport
• Diffusion and osmosis are examples of passive transport.
• This always involves movement of molecules down a concentration gradient.
• Passive transport does not need any energy input.
Active transport• Some molecules and ions are moved
across the membrane by active transport. • This involves movement of molecules and
ions against a concentration gradient. • Active transport does need energy input.• Membrane proteins are involved in this
process.
Transport across cell membranes (Glow)
The sodium potassium pump
Sodium pumped out
Potassium pumped in
OUTSIDE THE CELL
INSIDE THE CELL
CELL MEMBRANE
•This is an example of active transport which occurs in nerve cells.•Sodium ions are pumped out of cells against the concentration gradient.•Potassium ions are pumped into cells against the concentration gradient.
Membrane proteins
Active transport in cells
• When a cell is alive, the membrane can use active transport to make sure that suitable molecules are allowed to build up in the cell, and unsuitable or harmful molecules are kept out of the cell.
Practical application of this idea
• You will probably have had antibiotics at some time for an infection.
• Many antibiotics work by destroying the membranes of live bacteria in your body.
• The damaged membranes allow vital nutrients to escape and poisonous substances to enter and kill the bacterial cells.