Using a microscope

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Big idea: seeing the invisible

Big idea. Key concept: Change. The microscope changed what people could see, and what they could know, about living things.
Related concept: Models. A microscope shows us a magnified view of something tiny, and a scientific drawing is a simple model of what we see.
Global context: Scientific and technical innovation. Better instruments lead to new discoveries.
In 1665 Robert Hooke looked at a thin slice of cork through a microscope and saw tiny box-shaped spaces. He called them cells, because they reminded him of the small rooms where monks lived.
Soon after, Antonie van Leeuwenhoek used single lenses to see living things in pond water that no one had known existed.
In the 1930s the electron microscope was invented. It uses beams of electrons instead of light and shows much finer detail inside cells.

Robert Hooke’s microscope and cork cells

The parts of a light microscope

A light microscope uses light and glass lenses to make tiny things look bigger.
The eyepiece lens is the lens you look through. It is often ×10.
The objective lenses are the lenses just above the slide. A microscope usually has three, for example ×4, ×10 and ×40. They are mounted on a turning nosepiece.
The stage is the flat platform that holds the slide. Stage clips keep the slide still.
The light source (a lamp or a mirror) shines light up through the specimen so you can see it.
The coarse focus wheel makes big changes to bring the specimen roughly into focus. The fine focus wheel makes small changes to sharpen the image.

The parts of a light microscope

Using a microscope and finding the magnification

Always carry a microscope with two hands: one on the arm and one under the base.
Start with the lowest power objective. It gives the widest view, so the specimen is easiest to find.
Clip the slide on the stage. Look from the side while you use the coarse focus wheel to bring the objective close to the slide without touching it.
Then look through the eyepiece and use the coarse focus wheel to move the lens away from the slide until the image appears. Sharpen it with the fine focus wheel.
To see more detail, swing in a higher power objective. Only use the fine focus wheel now, because the lens is very close to the slide.
Total magnification = eyepiece magnification × objective magnification. A ×10 eyepiece with a ×40 objective gives ×400.

Preparing a slide

Specimens must be thin so that light can pass through them.
Put a drop of water or iodine solution on a clean glass slide. Iodine is a stain: it colours parts of the cell, such as the nucleus, so they stand out.
Use forceps to peel a very thin layer of onion epidermis from the inside of an onion layer. Lay it flat on the drop.
Hold a coverslip at an angle and lower it slowly using a mounted needle. This keeps out air bubbles, which would look like dark rings and hide the cells.
Blot away any extra liquid with paper towel.
Take care with glass and stains. Wash off any iodine that gets on your skin.

Preparing an onion-cell slide

Drawing cells and working out scale

A scientific drawing is a clear record of what you can see. Use a sharp pencil, a large simple outline and no shading or colouring.
Draw only what is really there. Draw a few cells carefully rather than trying to copy everything.
Label with straight lines ruled with a ruler. The lines must not cross and should touch the part they name.
Give the drawing a title and write the magnification beside it so that others can work out the real size.
Magnification = image size ÷ actual size. If a drawing of a cell is 40 mm long and the magnification is ×400, the actual length is 40 ÷ 400 = 0.1 mm.
Cells are so small that scientists use micrometres (µm). 1 mm = 1000 µm, so 0.1 mm = 100 µm.

Onion epidermis cells under a light microscope

Think like a scientist: which stain works best?

Question: does iodine or methylene blue show the nuclei of onion cells more clearly?
The independent variable is the type of stain. The dependent variable is how clearly you can see the nuclei, which you could score out of 5.
Control variables include the same microscope, the same objective, the same piece of onion and the same length of staining time.
Repeat with several slides and several cells. One good-looking cell is not enough evidence.
To evaluate your method, ask what might have made your results unreliable. Examples are air bubbles, thick peel or scoring that depends on opinion.
Inquiry task: plan a fair test to find out which objective lens gives the clearest view of onion cells. List your variables, say how you will score clarity and describe one way to make your results more reliable.

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1.Which part of a light microscope do you look through?
Easy
- AThe objective lens
- BThe stage
- CThe eyepiece lens
- DThe light source
2.What is the job of the stage on a microscope?
Easy
- ATo hold the slide in place
- BTo shine light through the specimen
- CTo magnify the specimen ten times
- DTo move the lenses up and down
3.Which part of a microscope lights up the specimen?
Easy
- AThe eyepiece
- BThe fine focus wheel
- CThe stage clips
- DThe lamp or mirror
4.Which objective lens should you use first when you start to look at a slide?
Easy
- AThe highest power objective
- BThe lowest power objective
- CWhichever one is closest to the slide
- DThe one with the largest number on it
5.Why do you start with the lowest power objective?
Easy
- AIt is the only lens that lets light through
- BIt magnifies the most, so the specimen is clearest
- CIt can never break the slide if it touches it
- DIt gives a wide view, so the specimen is easy to find
6.What does the coarse focus wheel do?
Easy
- AIt makes tiny changes to sharpen the picture up
- BIt brings the specimen roughly into focus in big steps
- CIt changes the brightness of the lamp in the base
- DIt swaps one objective lens for another one
7.Which wheel should you turn to sharpen the picture when the ×40 objective is in place?
Easy
- AThe fine focus wheel
- BThe coarse focus wheel
- CThe nosepiece
- DThe stage clips
8.What is a coverslip used for?
Easy
- ATo make the specimen look a lot bigger
- BTo colour the nucleus of each cell in it
- CTo keep the specimen flat and protect the lens
- DTo hold the slide firmly on the stage

Soal lainnya

9.What is the total magnification when a ×10 eyepiece is used with a ×40 objective?
Easy
- A×50
- B×400
- C×4000
- D×140
10.Why should you watch the objective lens from the side while you use the coarse focus wheel?
Medium
- ATo check that the lamp is switched on
- BTo make the picture much sharper
- CTo count how many cells there are
- DTo stop the lens hitting the slide
11.Which change makes the view MORE magnified?
Easy
- ASwapping a ×40 objective for a ×10 objective
- BTurning the lamp up
- CSwapping a ×10 objective for a ×40 objective
- DTurning the coarse focus wheel
12.You swing in the ×40 objective and the picture is blurry. What should you do?
Medium
- ATurn the fine focus wheel
- BTurn the coarse focus wheel
- CRemove the slide
- DSwitch back to the eyepiece
13.Why must the specimen be very thin?
Easy
- ASo that it dries out faster
- BSo that it looks darker
- CSo that light can pass through it
- DSo that it can be stained
14.Why is iodine solution added to an onion slide?
Medium
- AIt stains the nuclei so they show up
- BIt gets rid of any air bubbles in the water
- CIt makes the cells grow larger so they show
- DIt holds the coverslip down onto the slide
15.Why is a coverslip lowered slowly at an angle using a mounted needle?
Medium
- ATo make the cells move apart
- BTo stain the cells evenly
- CTo magnify the specimen
- DTo avoid trapping air bubbles
16.Robert Hooke called the tiny spaces he saw in cork “cells”. Why did he choose that word?
Medium
- AThey were alive and moved about on the slide
- BThey reminded him of monks’ small rooms
- CThey were green in colour, like plants
- DHe had already seen nuclei inside each one
17.What should a scientific drawing show?
Easy
- AEverything you expect to see, in colour
- BA realistic picture with lots of shading
- COnly the parts you already know the names of
- DOnly what you can really see, without shading
18.Which is the correct way to label a scientific drawing?
Medium
- AUse curly arrows that cross over each other
- BUse ruled lines that do not cross each other
- CWrite the labels on top of the drawing itself
- DUse a different colour for each of the labels
19.Why is the magnification written next to a scientific drawing?
Medium
- ASo that others can work out the real size
- BSo that the drawing looks a lot neater
- CSo that the title can be made shorter
- DSo that the labels can then be left out
20.A drawing of a cell is 50 mm long. The cell’s actual length is 0.25 mm. What is the magnification of the drawing?
Hard
- A×12.5
- B×50
- C×200
- D×2000
21.Why can an electron microscope show smaller structures than a light microscope?
Hard
- AIt uses a much bigger and brighter lamp
- BIt uses beams of electrons, not light
- CIt has a much longer eyepiece lens than usual
- DIt needs no specimen to be placed on it
22.How did better microscopes change scientists’ ideas about living things?
Medium
- AThey proved that cells cannot ever be seen
- BThey showed that only plants are made of cells
- CThey removed the need for experiments in science
- DThey showed cells and tiny organisms no one knew about
23.A student wants to find out whether iodine or methylene blue shows onion cell nuclei more clearly. Everything else stays the same. What is the independent variable?
Medium
- AThe clarity score of the nuclei
- BThe microscope used
- CThe type of stain
- DThe objective lens used
24.A student wants to know which objective lens gives the clearest view of onion cells. Which plan is a fair test?
Medium
- AUse one slide and the same light, and change only the objective
- BUse a different slide for each objective that is tried
- CChange the objective and the lamp brightness at the same time
- DUse only one objective and compare it with a friend’s slide
25.A student measures one onion cell, finds it is 0.3 mm long, and concludes that all onion cells are exactly 0.3 mm long. What is the main weakness?
Hard
- AShe should have measured in micrometres instead
- BOnion cells do not really have a length to measure
- CCells vary, so she should measure several and average them
- DShe should have used a ×4 objective lens instead
26.Which of these are parts of a light microscope? (select all that apply)
Easy
- AEyepiece lens
- BStage
- CObjective lens
- DNucleus
- EChloroplast
27.Which are sensible safety steps when using a microscope? (select all that apply)
Medium
- ACarry the microscope with two hands
- BPoint the mirror at the Sun to get more light
- CTake care with glass slides and coverslips
- DWash off any iodine that gets on your skin
- ELower the lens while looking only through the eyepiece
28.Which are good rules for a scientific drawing? (select all that apply)
Medium
- AUse a sharp pencil
- BColour it in to make it look realistic
- CDraw a large, clear outline
- DAdd a title and the magnification
- EUse a pen and cross out mistakes
29.Which would make a comparison of cells from two plants fairer and more reliable? (select all that apply)
Hard
- ALook at several cells from each plant
- BUse the same magnification each time
- CUse the same stain each time
- DChoose only the best-looking cell from one plant
- EUse a different objective for each plant
30.A light microscope uses lenses and light to magnify a specimen.
Easy
True or false?
31.You should start looking at a slide with the highest power objective.
Easy
True or false?
32.Total magnification is found by multiplying the eyepiece magnification by the objective magnification.
Medium
True or false?
33.You should use the coarse focus wheel when the ×40 objective is in place.
Medium
True or false?
34.A scientific drawing should be shaded to make it look realistic.
Easy
True or false?
35.Electron microscopes were invented before Robert Hooke looked at cork.
Hard
True or false?
36.Match each part of the microscope to its job.
Easy
- Eyepiece lens
- Stage
- Light source
- Fine focus wheel
- The lens you look through
- Holds the slide
- Shines light through the specimen
- Sharpens the image
37.Match each piece of equipment to its use when making an onion slide.
Medium
- Forceps
- Iodine
- Coverslip
- Mounted needle
- Peel a thin layer of onion
- Stain the nuclei
- Flatten and protect the specimen
- Lower the coverslip slowly
38.Match each length in millimetres to the same length in micrometres.
Medium
- 0.5 mm
- 2 mm
- 0.05 mm
- 0.2 mm
- 500 µm
- 2000 µm
- 50 µm
- 200 µm
39.Put the steps for focusing a microscope in the correct order.
Medium
- Bring the image roughly into focus with the coarse focus wheel
- Swing in a higher power objective and refocus with the fine focus wheel
- Turn the nosepiece to the lowest power objective
- Sharpen the image with the fine focus wheel
- Clip the slide onto the stage
40.Put the steps for making an onion slide in the correct order.
Medium
- Lower a coverslip slowly at an angle
- Put a drop of iodine on the slide
- Blot away extra liquid
- Peel a thin layer of onion with forceps
- Lay the onion layer flat on the drop
41.Put these lengths in order from the smallest to the largest.
Hard
- 200 µm
- 1 mm
- 50 µm
- 0.1 mm
42.Complete the sentence about total magnification.
Easy
Total magnification is found by multiplying the ____ magnification by the objective magnification.
43.Complete the sentence about starting to use a microscope.
Easy
You should always start with the ____ power objective lens.
44.Complete the sentence about covering a specimen.
Easy
A thin square of glass placed over a specimen is called a ____.
45.Complete the sentence about staining a slide.
Medium
Iodine is a ____ that makes the nucleus of each cell easier to see.
46.Complete the sentence about the history of cells.
Medium
In 1665 Robert Hooke looked at thin slices of ____ and named the tiny boxes he saw cells.
47.Complete the sentence about actual size.
Hard
Actual size is found by dividing the image size by the ____.
48.Describe how to prepare a slide of onion epidermis.
Medium
49.Explain why you should use only the fine focus wheel once a high power objective is in place.
Medium
50.Explain how improvements in the microscope have changed scientists’ ideas about living things.
Hard
51.An eyepiece lens is ×10 and the objective lens is ×10. Calculate the total magnification. Give your answer as a number after ×.
Easy
52.The total magnification is ×400 and the eyepiece lens is ×10. What is the magnification of the objective lens? Give your answer as a number after ×.
Medium
53.A student draws a plant cell 40 mm long. The magnification of the drawing is ×400. Calculate the actual length of the cell in millimetres.
Hard

Catatan ulasan

## Microscopes and change - Hooke named **cells** in 1665. Electron microscopes (1930s) show finer detail than light microscopes. ## Parts of a light microscope - **Eyepiece lens**, **objective lenses**, **stage**, **light source**, **coarse** and **fine focus wheels**. ## Using a microscope - Start on the **lowest power**, focus with the coarse wheel while looking from the side, then sharpen with the fine wheel. - **Total magnification = eyepiece × objective.** ## Preparing a slide - Thin specimen, drop of **stain**, **coverslip** lowered at an angle to avoid air bubbles. ## Drawing and scale - Sharp pencil, clear outline, no shading, ruled labels, title and magnification. - **Magnification = image size ÷ actual size.** 1 mm = 1000 µm. ## Inquiry - Name the independent, dependent and control variables, repeat, and evaluate your method.

Light microscope: An instrument that uses light and lenses to magnify tiny objects.
Eyepiece lens: The lens you look through on a microscope, often ×10.
Objective lens: One of the lenses just above the slide, for example ×4, ×10 or ×40.
Stage: The platform on a microscope that holds the slide.
Coarse focus wheel: The wheel that makes large movements to bring the specimen roughly into focus.
Fine focus wheel: The wheel that makes small movements to sharpen the image.
Total magnification: Eyepiece magnification multiplied by objective magnification.
Stain: A coloured solution, such as iodine, that makes parts of a cell easier to see.
Coverslip: A thin piece of glass placed over a specimen on a slide.
Scientific drawing: A clear, labelled record of what you can see, with a title and magnification.
Micrometre (µm): A unit of length equal to one thousandth of a millimetre.
Electron microscope: A microscope that uses beams of electrons and shows much finer detail than a light microscope.

Kartu flash

Who named cells, and when?

Robert Hooke, in 1665, after looking at cork.

What does the eyepiece lens do?

It is the lens you look through, and it magnifies the image.

What are the objective lenses?

The lenses just above the slide, such as ×4, ×10 and ×40.

What is the stage for?

It holds the slide in place.

Which objective do you use first?

The lowest power objective.

What does the coarse focus wheel do?

Brings the specimen roughly into focus with big movements.

What does the fine focus wheel do?

Sharpens the image with small movements.

How do you calculate total magnification?

Eyepiece magnification × objective magnification.

What is the total magnification of a ×10 eyepiece with a ×40 objective?

×400.

Why must a specimen be thin?

So that light can pass through it.

Why do we add iodine to an onion slide?

It stains the nuclei so they show up more clearly.

Why is a coverslip lowered at an angle?

To avoid trapping air bubbles.

What makes a good scientific drawing?

Sharp pencil, clear outline, no shading, ruled labels, title and magnification.

What is the formula for magnification?

Magnification = image size ÷ actual size.

How many micrometres are in 1 mm?

1000 µm.

Why can an electron microscope show more detail?

It uses beams of electrons, which can show much smaller structures than light.

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