Can you guess what this is a photograph of? It is a singlegrain of sand all the way from the Sahara desert, shownat �100 magnification! The image has been capturedusing a high-powered modern microscope, and it showshow far technology has come since the very firstmicroscopes were developed.

6 a An early microscope.

Microscopesthrough the agesthrough the ages

b A very modern vacuum microscope.

Microscopes

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CELLS, TISSUES AND ORGANS

7

1938 Ernst Ruska develops the

electron microscope to improve

the magnification and resolution.

Viruses and molecules are studied

1932 Frits Zernike invents a

microscope to study transparent

and colourless specimens18th Century improvements in

microscopes result in their greater

use by scientists1675 Anton van Leeuwenhoek

uses a simple microscope to look

at blood, insects and pond water.

He was the first person to

describe cells and bacteria

1667 Robert Hooke makes a

microscope to study various

objects

1590 Dutch lens grinders Hans and

Zacharias Janssen make the firstmicroscope by placing

two lensesin a tube

1 What is a microscope used for?

2 Name three jobs where amicroscope is used.

3 When were the first microscopesused?

4 Why did scientists only find outmore about the blood in the1670s?

5 Why could viruses not be seenbefore 1938?

6 What optical structure do allmicroscopes contain?

7 Which microscope would beused to study the contents of anucleus?

8 Look at the timeline above for thedevelopment of the microscope.How have microscopes changedover this time?

9 Why do schools not haveelectron microscopes?

10 Briefly explain howimprovements in microscopesmay have benefited scientists.

What do you know?

Microscopes opened up a previously unseen worldto scientists. This was a very exciting time forscientists – they used their microscopes to studyall forms of small animals, body fluids and water.Then scientists in other areas of science realisedthat microscopes would be useful to them –chemists studied crystals, technologists checkedsilicon chips used in computers and engineerslooked at faults in metal structures.

Today scientists use microscopes totrace very tiny particles entering thebody as part of their research intocures for diseases such as cancer.

By the end of this unit you will knowmore about the various organs in thebody and their functions. You will be

able to describe how they are composedof tissues, and how the tissues are

composed of cells. You will also be ableto explain how and why some cells arealike, and others are different. You willhave developed your skills of observing

and interpreting what you see.

BIG IDEASBIG IDEAS

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Setting up a microscopeThere are two lenses in a simplemicroscope – the eyepiece lens and the objective lens.

To set up a microscope in order to look at an object you need to follow these steps.

Hold the microscope by its base.

Place it near a light source. (Do not look directly at the Sun.)

Adjust the mirror until light isreflected up the microscope.(Check this by looking downthe microscope.)

Turn the objective lens to itslowest magnification.

What is meant bymagnification?

Why must you not look atthe sun?

How many lenses are usedto focus on an object?

MagnificationThemagnification of amicroscope is the product of theobjective lens and the eyepiecelens magnifications:

… eyepiece lens … magnification

Using amicroscope

Using amicroscope

8

Total�

objective�

eyepiece lensmagnification magnification magnification

Remember the magnification isworked out by multiplying thelens sizes together, not byadding them.

Work out the magnification for the objects whenthe eyepiece is �10 and the objective lens is:a �20 b �40.

Which lens is changed on a microscope when themagnification is changed?

You are learning to:� Set up a microscope� Calculate the

magnification for amicroscope

� Make observationsusing a microscope

BIG IDEASBIG IDEAS

FIGURE 1: Asimplemicroscope.

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Questions

1 Roughly how much bigger did the hand-lens appear to make the objects?

2 The hand-lens has a magnification of �10. Explain what this means.

3 What was strange about the writing in the newspaper that you looked at?

4 What might happen if you wound the lens down towards the glass slide rather thanaway?

5 When you look at objects under high magnification what happens to the brightness?

6 What problem is caused when you look at an object that is not flat?

Using hand-lenses and microscopesScientists use microscopes to help them develop new materials that combine desirablefeatures. GORE-TEXR is a material used a lot in clothing for climbers and walkers. It iswaterproof and breathable.

You are going to use a hand-lens (or a twisted wire) and amicroscope to look at some objects.

Your teacher will provide you with the apparatus that youmay need for your observations.

Method:

1 Use a hand-lens to look at the following objects. Write inyour notebooks what you see for each one.

coin newspaper print scale on a ruler

2 Now use a microscope to study the following objects. Follow steps 3 to 6 carefully.Write in your notebooks what you see for each object.

coin lined paper

newspaper print tissue paper

3 Place a slide on the microscope stage.

4 Looking at the side of the microscope, carefully move the objective lens down (byturning the knobs) so that it is as near to the slide as possible. (Watching from the sideas the lens comes down stops you breaking the slide.)

5 Looking down the microscope, slowly turn the focusing knob so the lens moves up andaway from the slide. Do this until the specimen is in focus.

6 Keeping the tissue paper slide on the microscope stage, switch to a higher power bycarefully turning the objective lens until the higher power lens ‘clicks’ into positiondirectly above the slide. Slowly turn the focusing knobs to bring the tissue paper intofocus at the higher magnification. Write in your notebook what you see.

… microscope … objective lens 9

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Building blocks inplantsPlant cells are the ‘building blocks’ found in allplants. Each plant cell has the same features asan animal cell and also contain some otherstructures too.

Look at the plant cell shown in Figure 2 – it shows themain structures found in all plant cells, for examplein the roots and the leaves.

Look again at the plant cell in Figure 2.What shape is it?

Name one type of plant cell.

Studying plant cellsHowever, not all plant cells are exactly the same. For example:

a root cell does not need chloroplasts (these absorb sunlight)as its job is to absorb water and minerals from the soil

to grow a plant needs to ‘make’ new cells. New plant cells are formed from simple cells found inthe growing regions of a plant – the root tip, buds or growth rings. These simple cells are calledstem cells.

Differences betweenplant and animal cellsThe plant cell has the following structures that are notfound in animal cells.

Cell wall – an outer protective layer that keeps the cell rigid.

Chloroplast – a structure that contains a green pigment that traps light.

Cell vacuole – a fluid-filled space inside the cell that gives the cell its shape.

Which three structures are found in both plants and animals?

Which three structures are only found in plant cells?

In a plant cell what is the role of the:a cell wall b chloroplast c cell vacuole?

… cell … cell vacuole … cell wall … cellulose

Studying plantcells

Studying plantcells

10

You are learning to:� Explain the role of a plant cell� Describe the difference between

plant and animal cells� Record the structure of

different types of plantcells

BIG IDEASBIG IDEAS

FIGURE 1: Different parts of aplant are made up of the samebasic cells but with smalldifferences depending on wherethey are in the plant.

vacuole

cell wall(made of

cellulose)

cellmembrane

nucleus

cytoplasm

FIGURE 2: Thedifferent partsof a plant cell.

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Be a plant detective!

You are going to prepare and then look at onion cells under the microscope and then drawwhat you see. You are then going to be a plant detective and match some mystery plantcells to the plants they are taken from. You are then going to make a model of a plant cell.Your teacher will provide you with the apparatus that you need for your investigation.

Method:

1 Collect the plant sample slides labelled ‘A’ to ‘C’ and the piece of onion.

2 Take off a piece of onion tissue and carefully peel off the outer layer and place this on aslide. Place a coverslip over the onion sample. Place your slide on the microscope stage.

3 Using the ‘�10’ magnification focus the microscope on the sample.

4 Draw what you see in your notebook. (Hint: use the photograph of the onion cells aboveto help you.) Remember to label your drawing.

5 Now look at each slide in turn labelled ‘A’ to ‘C’ under the microscope. Using what yousee down the microscope and the photographs on this page match slides ‘A’ to ‘D’ withthe plant that they are taken from. Write down your answers.

Scientists sometimes make models of what they are looking at to help theirunderstanding. This can be a difficult skill, but it does help them to remember what theyfind out.

6 You are now going to have a go at building a plant cell model. Hopefully it will help youto remember what a plant cell looks like! Your model can be 2-D or 3-D. Explain to thegroup what your model shows.

… chloroplast … root cell … stem cell 11

Questions1 Which structures cannot be seen in the onion cell?

2 Which structure has made the cells green in the leaves of the pond weed?

3 What structures did you see in all the plant cells except for the potato scrapings?

4 How does your model plant cell differ from a model of an animal cell?

5 The growth cells of a plant are small, colourless and consist of cytoplasm and a nucleus.What changes must occur to form a leaf cell?

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