Microscopy

Microscopes are used in biology to see objects too small for the human eye.

A student makes a microscope slide of a layer of onion epidermal cells.

The student uses a coverslip to make the slide.

Describe the function of the coverslip.

When the student looks down the microscope, they see an image like the one below.

Identify subcellular structure X and describe its function.

The student prepared the slide by covering the onion epidermal cells with water.

The student looks at the cells again after one hour and the vacuoles look larger.

Explain why the vacuoles look larger.

Use your knowledge of transport in cells.

What is the definition of resolution ?

A How large an image is compared to the object.

B The shortest distance apart that two objects can be and still be seen as separate objects.

C The magnification of an eyepiece and an objective lens multiplied together.

D The wavelength of light used to view an object.

How is this image of a cell generated?

A Electron microscope

B Hand lens

C Light microscope

D X-ray machine

The image shows cheek cells magnified at 550×.

Calculate the actual length of the cell marked X.

Use the line on the image.

State the function of the sub-cellular structure labelled Y.

A student prepares a microscope slide to view colourless plant cells.

Which type of substance is used to colour the cells?

A Acid

B Hormone

C Lipid

D Stain

The total magnification of an image viewed using a light microscope is calculated using a formula.

What is the correct formula for total magnification?

A Total magnification = eyepiece lens magnification × objective lens magnification

B Total magnification = eyepiece lens magnification – objective lens magnification

C Total magnification = eyepiece lens magnification + objective lens magnification

D Total magnification = eyepiece lens magnification ÷ objective lens magnification

The length of a bacteria cell is 5.3 m.

What is the length of this cell in mm ?

(1 mm = 1000 m)

5.3 × 10^–6 A

5.3 × 10^–3 B

5.3 × 10³ C

5.3 × 10⁶ D

The resolution of a microscope is limited to half the wavelength of light used to see the image.

Our eyes only detect light with a wavelength greater than 400 nm.

What is the approximate resolution of a light microscope?

(1000 nm = 1 m)

A <0.2 m

B ~0.2 m

C ~0.4 m

D >0.4 m

Fig. 14.1 is a diagram of a healthy heart. Fig. 14.2 shows a heart with a defect.

Fig. 14.1
Fig. 14.2

* Describe the heart defect shown in Fig. 14.2. Explain how this defect would affect oxygen transportation around the body.

Include the names of the chambers affected by the defect.

The photograph shows part of an artery seen using a light microscope.

The actual thickness of the wall at X–Y is 2 mm.

Calculate the magnification of the image.

Magnification = ×........

The diagram shows a prokaryotic cell.

Which structure labelled in the diagram would not be found in a eukaryotic plant cell?

Tick (✓) one box.

Prokaryotic cells are much smaller than most eukaryotic plant cells.

Explain why an electron microscope is used to view smaller prokaryotic cells instead of a light microscope.

Some prokaryotic cells contain chlorophyll in their cytoplasm.

Where is chlorophyll found inside eukaryotic plant cells?

What is one advantage of a light microscope compared to an electron microscope?

A Only light microscopes are able to observe live specimens.

B Only light microscopes are able to use stains.

C Light microscopes have a greater magnification.

D Light microscopes have a greater resolution.

15* (a) Sickle cell disease is a blood disorder causing some red blood cells to become sickle shaped.

The diagram shows red blood cells from a person with sickle cell disease.

The change in shape causes the cells to clump together. This makes sickle shaped red blood cells less efficient at carrying out their role.

Symptoms of sickle cell disease are tiredness and a lack of energy.

Explain why someone with sickle cell disease has these symptoms. Include information from the diagram.

The photograph shows part of an artery seen using a light microscope.

The image has been magnified 8 times.

Calculate the actual thickness of the artery between points X and Y in m.

Give your answer in standard form.

Actual size =........ m

Explain how the structure of a vein is adapted to its function.

A microscope has a ×10 eyepiece lens and a ×40 objective lens.

What is its magnification?

A ×10

B ×40

C ×50

D ×400

The diameter of a human ovum is 100 000 nm. The diameter of the HIV pathogen is 100 nm.

How many orders of magnitude larger is the diameter of a human ovum compared to an HIV pathogen?

A 3

B 10

C 99

D 1000

The diameter of a human ovum is 100 000 nm. The diameter of the HIV pathogen is 100 nm.

How many orders of magnitude larger is the diameter of a human ovum compared to an HIV pathogen?

A 3

B 10

C 99

D 1000

Complete these sentences about different factors that affect the ecosystem.

Use the words or phrases in the list.

abiotic biotic carbon dioxide food oxygen

pH in soil predators temperature

Living organisms affecting the ecosystem are known as........ factors.

Physical factors that affect living organisms are described as........ factors.

Physical factors that can directly affect the rate of photosynthesis include

........ and........ concentration.

A student investigates the relationship between bean plants and the bacteria that live in the roots of the bean.

They think the bacteria live inside root nodules.

Fig. 12.1 shows root nodules on a bean plant.

Fig. 12.1

The student takes a thin section of the nodule and looks at it under a light microscope.

Fig. 12.2 shows bacteria inside the root nodule.

Fig. 12.2

Describe how to take a thin section of the nodule and prepare it to view under a light microscope.

The bacteria were not visible clearly using a light microscope.

The student found an image taken using a different type of microscope.

Fig. 12.3 shows this image.

Fig. 12.3

The maximum resolution of a light microscope is 200 nm.

What type of microscope is used to take this image?

The bacteria live inside the bean plant cells in root nodules. The bacteria are able to take nitrogen gas from the air and turn it into nitrates. The plants use nitrates to make amino acids.

Explain the relationship between the bacteria and the bean plant. Include ideas about photosynthesis in your answer.

Which term describes a microscope with a higher resolution than a light microscope?

A Digital microscope

B Electron microscope

C Neutron microscope

D Proton microscope

A student uses a light microscope to observe onion cells.

They magnify the cells 400×. The magnification of the eyepiece is 20×.

What is the magnification of the objective lens?

A 20×

B 200×

C 420×

D 8000×

Describe the relationship between health and disease.

HPV (human papilloma virus) causes cervical warts.

Fig. 13.1 is a diagram representing the size of HPV as it would be seen using an electron

The HPV shown in Fig. 13.1 has a diameter of 50 mm. The actual HPV has a diameter of 55 nanometres.

Calculate the magnification of the HPV shown in Fig. 13.1.

Give your answer to 2 significant figures.

Magnification = ×........

Women can be given a vaccine to protect against HPV.

Explain why the vaccine produces an immune response to HPV but does not cause cervical warts.

Describe two ways scientists test new vaccines to ensure they are safe for humans.

Which term describes the ability to see two points as separate points and not merged into one?

A Depth of field

B Magnification

C Power

D Resolution

Look at the bacterial cell that causes disease.

The human eye can see objects 0.1 mm in size.

What minimum magnification will be needed before the eye can see this bacterial cell?

A 1.25×

B 12.5×

C 125×

D 1250×

The resolution of an electron microscope is 1×10^–10 m. 7

The resolution of a light microscope is 2×10^–7 m.

How many times greater is the resolution of the electron microscope compared to the light microscope?

5×10^–4 A

2×10^–3 B

5×10² C

2×10³ D

A student draws this image of a prokaryotic cell.

The cell image drawn by the student is 55 mm long.

The actual length of the prokaryotic cell is 1 m.

What is the magnification of the student’s drawing?

A 55×

B 550×

C 5500×

D 55 000×

Look at the sperm cell.

The eye can see objects 0.1 mm.

What minimum magnification will be needed before the eye can see the head of this sperm cell?

A 0.167×

B 1.67×

C 16.7×

D 167×

Plant material decomposes to make compost.

Gardeners add compost to their soil to increase crop yield.

Give one reason why compost increases crop yield.

Gardeners use compost activator to speed up the decomposition of plant material.

Compost activator contains bacteria.

Scientists are developing a new compost activator. To do this they need to isolate samples of bacteria.

They prepare agar jelly plates containing streaks of different bacteria. Fig. 14.1 shows a scientist preparing an agar jelly plate.

In Fig. 14.1 the scientist uses a sterile glass rod to transfer the bacteria.

Suggest why this is better than just pouring the liquid directly from the bottle.

Some bacteria grow faster at 37 °C than at 25 °C.

The scientist chooses to grow the bacteria at 25 °C.

Suggest why this would be safer than growing them at 37 °C.

What is the final dilution factor in tube five ?

The scientist puts 1 ml from each tube onto a separate agar plate.

The scientist then leaves the bacteria to grow so that the bacterial colonies become visible.

They use this formula to calculate the number of bacteria in the original sample:

number of bacteria in the original sample = number of CFU in sample × dilution factor

There are 29 CFU grown from the sample taken from tube 5.

Calculate the number of bacteria in the original sample.

Give your answer in standard form.

Number of bacteria in the original sample =........ CFU per ml

The picture shows plant cells as they are seen using a light microscope.

The actual length of plant cell X is 75 m.

You can use this fact to calculate the magnification of the image.

Explain how.

The same cells can be observed using an electron microscope.

Magnification of the cells can be increased using an electron microscope.

Explain how and why the image may also look different.

A student investigates different conditions that affect photosynthesis.

He sets up four different sets of apparatus, A, B, C and D.

The plants used are all of a similar age and size. Each plant is left under cover at room temperature.

After three days one leaf from each plant is tested for the presence of starch.

Describe all the stages required to test the leaves for the presence of starch.

What are the expected results of the starch test on each plant?

Write down reasons for your answers.