Cell Structure and Microscopy - Worksheets, Questions and Revision

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GCSE · Biology

B1a Cell Structure and Microscopy

AQA 8464 · Calculator allowed · about 72 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Seeing the Unseen: Microscopes and the Cell Theory

Original text written for Revision Library.

In 1665, the English scientist Robert Hooke used one of the earliest microscopes to examine a thin slice of cork. He observed a pattern of small, box-like compartments and named them cells, after the small rooms used by monks. A few years later, Antonie van Leeuwenhoek built simple microscopes powerful enough to observe living cells and microorganisms for the first time. Since then, microscope technology has continued to improve. Light microscopes use lenses to bend visible light and can magnify a sample up to about x2000, letting scientists see whole cells and some larger organelles. Electron microscopes use a beam of electrons instead of light. Because electrons have a much shorter wavelength, electron microscopes have a far higher resolution, revealing tiny sub-cellular structures, such as ribosomes and plasmids, that a light microscope cannot distinguish. This topic covers how cells are classified, how sub-cellular structures are adapted for their function, and how magnification and resolution are calculated and compared.

This question is about structures found in cells.

(a)Which cell structure controls which substances enter and leave a cell?(1)

A) Cytoplasm
B) Cell membrane
C) Nucleus
D) Ribosome

(b)State the function of the nucleus.(1)

(c)State the function of the cytoplasm.(1)

(d)State the function of the mitochondria.(1)

(e)State the function of the ribosomes.(1)

(Total for Question 1 is 5 marks)

Bacteria are prokaryotic organisms, made of a single prokaryotic cell. Animals and plants are eukaryotic organisms, made of eukaryotic cells. For each statement below, state whether it is true or false.

(a)Prokaryotic cells contain a nucleus.(1)

(b)Prokaryotic cells are generally smaller than eukaryotic cells.(1)

(c)A prokaryotic cell may contain one or more small rings of DNA called plasmids.(1)

(d)All eukaryotic cells contain chloroplasts.(1)

(Total for Question 2 is 4 marks)

Plant cells contain some structures that are not found in animal cells.

(a)Plant cells (but not animal cells) have a cell wall. State what the cell wall is made of, and describe its function.(2)

(b)State the function of the chloroplasts found in plant cells.(2)

(c)State the function of the permanent vacuole found in plant cells.(2)

(Total for Question 3 is 6 marks)

Cells become specialised (differentiated) to carry out a particular function.

(a)Describe one way a sperm cell is adapted for its function, and explain how this adaptation helps the cell.(2)

(b)Describe one way a root hair cell is adapted for its function, and explain how this adaptation helps the cell.(2)

(c)Describe one way a red blood cell is adapted for its function, and explain how this adaptation helps the cell.(2)

(d)Describe one way a ciliated epithelial cell is adapted for its function, and explain how this adaptation helps the cell.(2)

(Total for Question 4 is 8 marks)

A student is preparing a temporary mount of some plant cells to view using a light microscope (required practical).

(a)State the purpose of using a mounted needle when lowering the coverslip onto the sample.(1)

(b)State the purpose of the coverslip.(1)

(c)State the purpose of using a small piece of paper towel to remove excess stain from the edge of the coverslip.(1)

(Total for Question 5 is 3 marks)

A student wants to observe onion epidermal cells using a light microscope (required practical).

(a)Describe how the student should prepare a temporary mount of the onion epidermal cells, from obtaining the sample to viewing it under the microscope.(4)

(Total for Question 6 is 4 marks)

Onion epidermal cells are almost transparent and colourless when unstained.

(a)Explain why iodine solution is used to stain the sample before it is viewed under the microscope.(2)

(Total for Question 7 is 2 marks)

A light microscope has an eyepiece lens and a set of interchangeable objective lenses.

(a)The eyepiece lens has a magnification of x10 and the objective lens in use has a magnification of x25. Calculate the total magnification of the microscope.(2)

(Total for Question 8 is 2 marks)

An animal cell has an actual diameter of 25 micrometres (um).

(a)The cell is viewed under a total magnification of x600. Calculate the diameter of the image of the cell, giving your answer in millimetres (mm).(3)

(Total for Question 9 is 3 marks)

A micrograph (a photograph taken through a microscope) shows a chloroplast.

(a)In the micrograph, the chloroplast has a length of 12 mm. The micrograph was produced at a total magnification of x2400. Calculate the actual length of the chloroplast, in micrometres (um).(2)

(b)Give your answer to part (a) in standard form, in metres (m).(1)

(Total for Question 10 is 3 marks)

Write each of the following lengths in standard form, in metres (m).

(a)0.02 mm(1)

(b)15 um(1)

(d)4 nm(1)

(Total for Question 11 is 4 marks)

A typical animal cell has a diameter of about 20 micrometres (um). A mitochondrion inside the cell has a diameter of about 1 micrometre (um).

(a)Calculate how many times greater the diameter of the cell is than the diameter of the mitochondrion.(2)

(Total for Question 12 is 2 marks)

While preparing a slide, a student lowered the coverslip quickly instead of at an angle, and trapped an air bubble underneath it.

(a)Suggest how the student could tell the difference between a trapped air bubble and a cell when viewing the slide.(1)

(b)Suggest one change to the technique that would reduce the risk of trapping air bubbles in future.(1)

(c)Suggest why it can be useful to compare an observation made from an unfamiliar sample with a reference photograph taken by an experienced microscopist.(1)

(Total for Question 13 is 3 marks)

Bacterial cells are prokaryotic. Animal cells are eukaryotic. Scientists studying bacteria often need to use an electron microscope, rather than a light microscope, to see internal detail clearly.

Compare the structure of a prokaryotic cell with the structure of a eukaryotic (animal) cell, and explain why an electron microscope allows more of a bacterial cell's internal structure to be seen than a light microscope does.

(Total for Question 14 is 6 marks)

Higher tier only. A student increases the magnification of a light microscope from x400 to x1500 while viewing a bacterial cell, but no extra detail becomes visible; the image just becomes larger and blurred.

(a)Explain why increasing the magnification did not reveal any extra detail.(3)

(Total for Question 15 is 3 marks)

A student views a sample of onion epidermal cells under a light microscope.

(a)The diameter of the field of view is 1.5 mm. The student counts 10 onion cells lying end to end across the full diameter of the field of view. Estimate the mean length of one onion cell, giving your answer in micrometres (um).(2)

(Total for Question 16 is 2 marks)

Higher tier only. A bacterial cell has an actual length of 2 micrometres (um).

(a)A scientist produces an image of the cell using a transmission electron microscope (TEM) with a total magnification of x25000. Calculate the length of the image, giving your answer in centimetres (cm).(3)

(Total for Question 17 is 3 marks)

Higher tier only. The resolution of a light microscope is approximately 200 nanometres (2 x 10^-7 m). The resolution of a transmission electron microscope (TEM) is approximately 0.2 nanometres (2 x 10^-10 m).

(a)Calculate how many times better (smaller) the resolution of the TEM is compared with the resolution of the light microscope.(2)

(b)Suggest one advantage, other than resolution, that a light microscope has over a transmission electron microscope for viewing onion cells.(1)

(Total for Question 18 is 3 marks)

Mark scheme · B1a Cell Structure and Microscopy

Question 1

(a) B1 B (cell membrane)
(a) Answer: B (cell membrane)
(b) B1 contains the genetic material (DNA) and controls the activities of the cell, oe
(b) Answer: Contains the genetic material and controls the cell's activities.
(c) B1 gel-like substance in which most of the cell's chemical/metabolic reactions take place, oe
(c) Answer: The gel-like substance in which most chemical reactions of the cell take place.
(d) B1 site of aerobic respiration, which releases/transfers energy for the cell, oe
(d) Answer: Site of aerobic respiration, releasing energy for the cell.
(e) B1 site of protein synthesis, oe
(e) Answer: Site of protein synthesis.

Question 2

(a) B1 False
(a) Answer: False
(b) B1 True
(b) Answer: True
(c) B1 True
(c) Answer: True
(d) B1 False (only plant cells and algal cells contain chloroplasts)
(d) Answer: False

Question 3

(a) B1 made of cellulose
(a) B1 provides strength/structural support to the cell, and prevents the cell bursting, oe
(a) Answer: Made of cellulose; provides strength and support and stops the cell bursting.
(b) B1 absorb light energy, using the chlorophyll they contain, oe
(b) B1 used to produce glucose/sugars by photosynthesis, oe
(b) Answer: Absorb light energy (using chlorophyll) and use it to produce glucose by photosynthesis.
(c) B1 contains cell sap (a solution of sugars and salts), oe
(c) B1 helps to keep the cell turgid/rigid, providing support to the plant, oe
(c) Answer: Contains cell sap; keeps the cell turgid, helping to support the plant.

Question 4

(a) B1 adaptation, e.g. has a long tail (flagellum) / has many mitochondria in the mid-piece / has an acrosome containing enzymes
(a) B1 linked explanation, e.g. the tail allows the cell to swim towards the egg cell; OR many mitochondria release energy (by respiration) for the tail to move; OR the acrosome enzymes digest through the egg cell membrane, oe
(a) Answer: E.g. long tail (flagellum), which allows the sperm cell to swim towards the egg cell.
(b) B1 adaptation: has a long, hair-like extension (the root hair)
(b) B1 explanation: this increases the surface area of the cell, increasing the rate of absorption of water and mineral ions from the soil, oe
(b) Answer: Long hair-like extension, which increases surface area for absorbing water and mineral ions.
(c) B1 adaptation, e.g. biconcave disc shape / no nucleus / contains haemoglobin
(c) B1 explanation, e.g. biconcave shape increases surface area for the diffusion of oxygen; OR having no nucleus leaves more space to carry haemoglobin/oxygen, oe
(c) Answer: E.g. biconcave disc shape, which increases surface area for the diffusion of oxygen.
(d) B1 adaptation: has cilia (tiny hair-like structures) on its surface
(d) B1 explanation: the cilia beat/move to waft mucus (and trapped particles/pathogens) away from the lungs, oe
(d) Answer: Has cilia on its surface, which waft mucus and trapped particles away from the lungs.

Question 5

(a) B1 to lower the coverslip slowly/at an angle so that air bubbles are not trapped underneath, oe
(a) Answer: To lower the coverslip slowly and at an angle so air bubbles are not trapped.
(b) B1 keeps the sample flat and in place, and protects the sample and the objective lens, oe
(b) Answer: Keeps the sample flat and in place, and protects the sample and the lens.
(c) B1 draws excess stain/liquid away from under the coverslip so it does not obscure the view/pool on the slide, oe
(c) Answer: Removes excess stain so it does not obscure the view of the cells.

Question 6

(a) B1 peel/cut a thin section of epidermal tissue from the inner surface of an onion, using forceps or a scalpel
(a) B1 place the tissue sample flat in the centre of a clean microscope slide, and add a drop of water or iodine solution using a pipette
(a) B1 lower a coverslip onto the sample at an angle, using a mounted needle, to avoid trapping air bubbles
(a) B1 place the slide on the microscope stage and view under the lowest-power objective lens first, before increasing the magnification
(a) Answer: Peel a thin epidermal section, mount it in water/iodine on a slide, lower a coverslip at an angle with a mounted needle to avoid air bubbles, then view starting on the lowest magnification.

Question 7

(a) B1 cells/cell structures are naturally transparent/colourless, so are difficult to see clearly (lack contrast), oe
(a) B1 iodine stains structures such as the nucleus and cell wall, adding contrast so they can be seen/identified more easily, oe
(a) Answer: Cells are naturally transparent; iodine stains structures like the nucleus, adding contrast so they can be seen clearly.

Question 8

(a) M1 total magnification = eyepiece magnification x objective magnification, oe
(a) A1 x250 cao
(a) Answer: x250

Question 9

(a) M1 image size = actual size x magnification, oe
(a) A1 25 x 600 = 15000 um, oe (intermediate value)
(a) A1 15 mm cao (allow 15000 um)
(a) Answer: 15 mm (15000 um)

Question 10

(a) M1 converts 12 mm to 12000 um, then actual size = image size / magnification, oe
(a) A1 5 um cao
(a) Answer: 5 um
(b) B1 5 x 10^-6 m, ft from their (a) answer converted correctly to standard form
(b) Answer: 5 x 10^-6 m

Question 11

(a) B1 2 x 10^-5 m cao
(a) Answer: 2 x 10^-5 m
(b) B1 1.5 x 10^-5 m cao
(b) Answer: 1.5 x 10^-5 m
(c) B1 7.5 x 10^-7 m cao
(c) Answer: 7.5 x 10^-7 m
(d) B1 4 x 10^-9 m cao
(d) Answer: 4 x 10^-9 m

Question 12

(a) M1 20 / 1, oe
(a) A1 20 (times) cao
(a) Answer: 20 times

Question 13

(a) B1 an air bubble appears as a distinct, dark-edged, round/circular shape with no cell structures (e.g. no nucleus/cell wall) visible inside it, oe
(a) Answer: An air bubble looks like a dark-outlined circular shape with no internal cell structures visible.
(b) B1 lower the coverslip slowly, at an angle, starting from one edge (using a mounted needle), oe
(b) Answer: Lower the coverslip slowly, at an angle, starting from one edge, using a mounted needle.
(c) B1 helps to check whether unusual/unexpected structures seen are genuine cell structures or artefacts (e.g. air bubbles, dirt, fibres), improving the reliability of the observation, oe
(c) Answer: It helps the student check whether what they saw is a real cell structure or an artefact, improving reliability.

Question 14

Level 3 (5-6): A detailed, logically sequenced answer that compares at least three structural features of prokaryotic and eukaryotic cells AND gives a scientifically correct explanation of why electron microscopes reveal more internal detail than light microscopes, linking this to resolution/wavelength.
Level 2 (3-4): The answer compares some structural features of prokaryotic and eukaryotic cells and attempts an explanation of why electron microscopes show more detail, with some correct scientific ideas but limited linkage or detail.
Level 1 (1-2): One or two isolated relevant points are made about cell structure or about microscope technology, with little or no linkage between them.
Level 0 (0): No relevant content.
Indicative content:
- Prokaryotic cells (e.g. bacteria) do not have a nucleus; their genetic material is a single loop of DNA free in the cytoplasm.
- Prokaryotic cells may also contain one or more small rings of DNA called plasmids.
- Prokaryotic cells do not have membrane-bound organelles such as mitochondria or chloroplasts.
- Prokaryotic cells are generally much smaller than eukaryotic cells.
- Eukaryotic (animal) cells have a nucleus enclosing the genetic material as linear chromosomes.
- Eukaryotic cells contain membrane-bound organelles, such as mitochondria (site of aerobic respiration) and ribosomes.
- Light microscopes use visible light, which has a relatively long wavelength, limiting their resolution (the smallest distance apart two points can be and still be seen as separate) to around 200 nanometres.
- Electron microscopes use a beam of electrons, which have a much shorter wavelength than light, giving them a much higher resolution, able to distinguish points far less than 1 nanometre apart.
- This higher resolution means an electron microscope can reveal smaller sub-cellular structures (e.g. plasmids, ribosomes, detailed internal membranes) that appear as a single blurred point, or are invisible, using a light microscope.
- Simply increasing the magnification of a light microscope further would not reveal this detail, because its resolution is fixed by the wavelength of light used (empty magnification).

Question 15

(a) B1 resolution is the ability to distinguish between (see as separate) two points that are very close together, oe
(a) B1 a light microscope has a limited/fixed resolving power (about 200 nm), set by the wavelength of light used, oe
(a) B1 increasing the magnification beyond this limit only makes the (already blurred) image bigger; it does not increase the resolution, so no new detail is revealed, oe
(a) Answer: Resolution (not just magnification) limits detail; a light microscope's resolving power is fixed by the wavelength of light (about 200 nm), so magnifying further just enlarges the blur without revealing new detail.

Question 16

(a) M1 mean cell length = diameter of field of view / number of cells, oe (1.5 / 10)
(a) A1 150 um cao (allow 0.15 mm)
(a) Answer: 150 um (0.15 mm)

Question 17

(a) M1 image size = actual size x magnification, oe
(a) M1 2 x 25000 = 50000 um, oe
(a) A1 5 cm cao
(a) Answer: 5 cm