Cells and Diffusion

Investigating Cells

SG Biology

Key Facts

• Cells are the building blocks of life

• All living things are made up of cells

• A living thing is called an organism

• Plants and animals are organisms

Life Processes

• In order to be “alive” an organism must

show these 7 life processes

– Movement

– Reproduction

– Sensitivity

– Growth

– Reproduction

– Excretion

– Nutrition

Animal Cell

Nucleus Controls cell activities,

contains genetic

information

Cytoplasm Where all

chemical

reactions take place.

Cell Membrane Controls what passes into and out

of cell (partially

permeable)

Plant Cell

Nucleus

Cell

membrane

cytoplasm

Vacuole Contains a weak

solution of salt and

water called cell sap.

Gives cell support Chloroplast Contains chlorophyll, which absorbs the

sun’s energy to make food in photosynthesis

Cell Wall Made of cellulose Gives cell strength

and support

Comparing Plant and

Animal cells Animal Cells Plant Cells

Nucleus Nucleus

Cytoplasm Cytoplasm

Cell membrane Cell membrane

Cell wall

Chloroplast

vacuole

Microscope

Using a microscope • Turn the microscope’s nosepiece until the low power

objective clicks into position above the hole in the stage.

• Adjust the mirror until light is seen to pass up through the microscope.

• Place the prepared slide so that the specimen is in the centre of the hole in the stage.

• With your eyes level with the stage, use the coarse adjustment handle to lower the objective to a position about 5mm from the slide.

• Look down the microscope through the eyepiece and slowly raise the objective until the specimen comes into focus.

• Change from low to high power by turning the nose piece.

Magnification

Magnifying

power of

eyepiece

lens

Magnifying

power of

objective lens

Total

magnification

of

microscope

Low

power

Medium

power

High

power

Magnification

Magnifying

power of

eyepiece

lens

Magnifying

power of

objective lens

Total

magnification

of

microscope

Low

power X 10 X 4 X 40

Medium

power X 10 X 10 X 100

High

power X 10 X 40 X 400

Preparing a

microscope

Slide

Observing Cells

• Place the slide onto the stage of the microscope.

• Focus carefully onto the onion skin using the lowest power objective lens in your microscope.

• Turn on to the high power objective lens to see details of the onion cells.

• Repeat Stages 1 – 4, using iodine to mount the cells instead of water.

• Repeat your observations

Quick Test - cells

1. name three differences between a

plant and an animal cell.

2. Name three similarities between an

animal cell and a plant cell.

3. What does the cell membrane do?

4. What does the cell wall do?

5. What substance do chloroplasts

contain and what does it do?

6. What is the job of the nucleus?

What is Diffusion?

In your books try to write an explanation of

what is happening in the cartoon.

Purple Crystals into water

Draw a diagram to explain what has

happened in this situation

Purple molecules have

spread out by DIFFUSION

Purple molecules have

spread out by DIFFUSION

Diffusion

• Diffusion is – The movement of molecules from an area of high

concentration to an area of low concentration

– Until evenly spread out

• Two rules – The larger the molecule the slower the rate of

diffusion

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

• The difference is called concentration gradient.

Demonstration

Demonstration

• Ammonia at one side of tube

• HCl at the other

• Bungs on end

• Describe what happens, try to explain

the results.

Example of diffusion in an

animal cell

Diffusion in humans

Diffusion in the body

Example of diffusion in plants

• Carbon dioxide

diffuses into the

stomata

• Oxygen and

water diffuse

out of the

stomata

Quick Test - Diffusion

1. What is diffusion?

2. Give an example of diffusion in plant

cells.

3. Give an example of where diffusion

takes place in an animal.

4. The greater the concentration

difference the the

diffusion rate.

Osmosis

Investigating Cells

SG Biology

Key Fact

• Each cell is surrounded by a cell

membrane which has tiny holes in it.

• This membrane is partially permeable.

• It allows small molecules to pass

through, but not larger ones.

Osmosis

• Osmosis is

– The net movement of water molecules from an area of high water concentration (weak

solution) to an area of low water

concentration (strong solution) through a

partially permeable membrane.

Osmosis a special case of diffusion