Section 1: Cell biology
Plant and animal cells (eukaryotic cells) 1.
The diagram shows an animal cell.
A
a Which letter shows the structure responsible
E
for controlling substances entering and leaving the cell?
[1 mark]
D B
C
b Which structure(s) can only be seen with an
electron microscope?
[1 mark]
Part C:
[1 mark]
Function:
[1 mark]
c Identify part C. What is the function of part C?
2.
a What are plant cell walls made of?
[1 mark]
b State three functions of a plant cell wall.
1 2 3
3.
a Name this organelle.
b Write down the name of one type of cell where many of these
[3 marks]
[1 mark] length
organelles are found.
[1 mark]
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1 c The organelle has been magnified 12 000 times.
Maths
Calculate the actual length of this organelle in μm.
Worked Example
[3 marks]
Length on diagram = 15 mm real size =
size of image 15 = magnification 12 000
The student gets all three marks for this answer. She has measured the length of the image and used the correct formula to work out the real size of the organelle. She has converted mm to μm correctly by multiplying by 1000 – because there are 1000 μm in 1mm.
= 0.00125 mm = 1.25 μm
Bacterial cells (prokaryotic cells) 1.
Which of the following statements are true? Tick two boxes. Bacteria are easily seen with under a light microscope with low power Bacterial cell walls are not made of cellulose Bacterial cells contain DNA in a nucleus Bacteria contain loops of DNA called plasmids
2.
[2 marks] C
The diagram shows a bacterial cell. a Name structure B and state its function.
Structure B: Function:
B
[1 mark] [1 mark]
b Which group of organisms do bacteria belong to?
A
[1 mark]
[1 mark]
[1 mark]
c What is the outside coating on some bacterial cell walls?
d Why is this coating important?
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3.
In a culture of bacteria, the initial concentration is 2000 cells/cm3.
Maths
Each cell divides once every 30 minutes. Calculate how long it will take for the concentration to become greater than 60 000 cells/cm3.
Answer = 4.
hours
[1 mark]
[4 marks]
Compare a bacterial cell with a plant cell.
Size of cells and cell parts 1.
Write the following cell parts in order of size starting with the smallest. Nucleus
smallest
Mitochondrion Plant cell vacuole Ribosome 2. Maths
largest
An egg cell is one of the largest human cells, with an average diameter of 120 µm. Write this in mm. Answer
mm [1 mark]
[2 marks] Maths Converting units can be confusing. Remember there are 1000 micrometres (μm) in every millimetre (mm). So, to convert μm to mm you need to divide by 1000 because you are converting a smaller unit to a bigger one.
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3. Maths
1 Emily used an eyepiece lens with a magnification of ×20 and an objective lens with a magnification of ×40 to look at a specimen. The image size of the specimen is 8 mm. Calculate the real size of the specimen. Write your answer in micrometres.
Answer 4. Maths
μm
[3 marks]
Alex measured the distance between the two ends of a plant cell on a picture. She found the length was 60 mm. The actual length of the cell was 150 μm. What is the magnification of the cell picture?
Magnification = 5.
[2 marks]
[1 mark]
[1 mark]
Ali looked at some onion cells under a light microscope.
Required practical
a He used a dye to stain the cells. Suggest the name of the dye.
b He used a coverslip over the specimen. Explain why.
c Ali tried to lower the coverslip carefully, putting one side down first before the other.
Suggest why.
[1 mark]
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d Ali used a ×10 eyepiece lens with a ×20 objective lens to view the onion cells. What was
Maths
the total magnification?
Magnification =
Maths Higher Tier only Worked Example
e Ali calculated the length of one onion cell to be 150 μm.
Express this in standard form.
1 μm = 0.000 001 m = 1 × 10 −6 m
[1 mark]
[2 marks] Maths When measuring in standard form, we convert measurements in mm or μm to sizes in metres.
150 μm = 150 × (1 × 10 −6) = 1.5 × 10 −4 m So, the onion cell is 1.5 × 10 −4 m long.
Electron microscopes 1.
Using the correct words from the box below, complete the following sentences. colour range higher lower molecules organelles organs resolving power similar An electron microscope has a greater A light microscope has a an electron microscope.
than a light microscope. magnification compared with
An electron microscope can show fine details of 2.
in a cell.
[3 marks]
Name the type of microscope needed to see ribosomes. Explain why. Type of microscope: Explanation:
[1 mark]
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