1. Investigating Cells
Cells
G Davidson

2. Investigating Cells
The detailed structure of animals and plants cannot be seen with the naked eye.
The microscope is an instrument which enlarges things.
Total magnification = eyepiece x objective
07 December 2018
G Davidson

3. Light Microscope Eyepiece Objective lens Focus knob Specimen Stage
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G Davidson

4. Light Microscope
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G Davidson

5. Light Microscope Eyepiece Focus knob Lens tube Fine focus knob
Nosepiece
Objective lenses
Objective lens
Stage clips
Handle
Stage
Condenser
Swivel
Lamp
Base
07 December 2018
G Davidson

6. Preparing Material
Living material which is to be viewed under the microscope should allow light to pass through.
It is, therefore, necessary to look at very thin pieces of material.
Living material must also be kept moist; a drop of water or similar liquid must be added.
Stains can be added to colour certain parts of the specimen to make them easier to see.
07 December 2018
G Davidson

7. Identifying Cells Cells are the basic units of all living organisms.
Although they vary in shape, they do all have the same structures in common.
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G Davidson

8. Differences Between Plant & Animal Cells
All living things consist of one or more cells.
The majority of living organisms have more than one cell and are called multicellular organisms.
The human body contains at least 100 million, million cells.
07 December 2018
G Davidson

9. Differences Between Plant & Animal Cells
Unicellular organisms e.g. protozoa, bacteria and some algae, are made up of only one cell.
Each individual cell is very small – diameters usually vary from 0.01mm to 0.1mm.
Most cells are transparent.
07 December 2018
G Davidson

10. Plant Cells
When plant cells are examined under the microscope they are found to contain the following structures:
Nucleus
Cytoplasm
Cell membrane
Vacuole
cell wall
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G Davidson

11. Palisade mesophyll cell
Identifying Cells
Palisade mesophyll cell
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12. Identifying Cells
Nerve cell
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13. Identifying Cells Root hair cell Cell membrane Cell Wall Vacuole
Cytoplasm
Nucleus
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G Davidson

14. Plant Cells
The vacuole is a large cavity in the centre of the cell and is filled with a watery solution of salts and sugars (Cell Sap).
The cell wall is made of CELLULOSE and forms a rigid structure on the outside of the cell.
07 December 2018
G Davidson

15. Plant Cells
It is difficult to see the membrane as it lies close to the cell wall.
Plant cells taken from the green parts of a plant contain structures called CHLOROPLASTS.
These contain a green pigment called CHLOROPHYLL which is needed to trap sunlight for making food by a process called photosynthesis.
07 December 2018
G Davidson

16. Animal Cells
Animal cells are usually much smaller than plant cells and have no supporting wall on the outside.
They are surrounded only by a cell membrane which is fairly flexible.
Animal cells do not have a definite shape.
It is determined by the pressure of the adjacent cells pushing on it.
Show pictures of different animal cells.
07 December 2018
G Davidson

17. Looking at Sections
Special machines called microtomes are used to cut thin slices, called sections.
When looking at sections we have to try and build up a complete picture – i.e. a picture in 3D.
Section of the shopping bag.
07 December 2018
G Davidson

18. Estimating Cell Size
It is possible to estimate the sizes of cells while observing them under the microscope.
Before we can measure cell size, it is necessary to measure the field of view.
07 December 2018
G Davidson

19. Estimating Cell Size Method:
Place a ruler on the stage under low power.
Move it until the edge goes across the centre.
Record the size that you can see (mm).
Do the same for medium and high power.
We can now estimate the size of cells using this information.
07 December 2018
G Davidson

20. Micro-organisms
There is a whole world of organisms called micro-organisms which are too small to be seen with the naked eye, but can be viewed with a microscope.
Although man was unaware of the existence of micro-organisms before the 17th Century, he has made use of some of their products for at least 2000 years.
07 December 2018
G Davidson

21. Magnification
A microscope makes each object viewed appear to be larger than it really is.
The power of 100x makes 1mm look like 100mm!
Magnification = eyepiece x objective
07 December 2018
G Davidson

22. Magnification
Example – if the eyepiece has a magnification of 10x and the objective has a magnification of 20x, we multiply the 2 numbers.
In this case 10 x 20 = 200x
If the object we are looking at is 0.1mm, it’s apparent size is 200 times greater than that – so 0.1mm x 200 = 20mm.
07 December 2018
G Davidson

23. Magnification Eyepiece Objective Magnification Size of object viewed
Apparent size 5x
20x
0.01mm
10x
50x
5mm
800x
0.02mm
30x
900x
0.001mm
400x
0.04mm
07 December 2018
G Davidson

24. Cell Functions
Animals and plants are made up of many different kinds of cells.
These cells are adapted to carry out different functions.
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G Davidson

25. Cell Functions Cell Type Function Adaptation Epidermis Guard Cell
Mesophyll cells
Xylem
Phloem
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G Davidson