How are cells specialised for their jobs, and how do we use a microscope to see and measure them?
How named cells are adapted to their functions, the use of a light microscope to view cells, and calculating magnification and real size using the magnification equation.
A focused answer to the WJEC GCSE Science Double Award Unit 1 topic on specialised cells and microscopy, covering how named cells are adapted to their functions, using a light microscope, and calculating magnification and real size with the magnification equation.
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What this dot point is asking
WJEC Double Award Unit 1 wants you to describe how named cells are adapted to their functions, use a light microscope to view cells, and calculate magnification and real size using the magnification equation.
What "specialised" means
In a multicellular organism, different cells do different jobs, so they are adapted in different ways. The adaptation always links to the function: examiners want both the feature and the reason it helps.
Examples of specialised cells
- Root hair cell: has a long, thin "hair" giving a large surface area to absorb water and mineral ions; it has many mitochondria for active transport.
- Red blood cell: has no nucleus (so more room for haemoglobin) and a biconcave disc shape giving a large surface area to carry oxygen.
- Sperm cell: has a tail (flagellum) to swim to the egg and many mitochondria to release energy for swimming.
- Nerve cell (neurone): is very long to carry electrical impulses over a distance, with branched ends to connect to other cells.
- Palisade (leaf) cell: is packed with chloroplasts near the top of the leaf to absorb the most light for photosynthesis.
Using a light microscope
A light microscope uses lenses to magnify a thin specimen on a slide. To use one, you place the slide on the stage, start with the lowest power objective lens, and use the coarse then fine focus to bring the image into view. The total magnification is the eyepiece magnification multiplied by the objective magnification: a 10 times eyepiece with a 40 times objective gives 400 times magnification.
The magnification equation
The image size and the real size must be in the same units before you divide. Cells are often measured in micrometres (), where , so unit conversion is a common part of the question.
Preparing a slide to view cells
To see cells under a microscope you first prepare a thin slide. For onion epidermis, you peel a thin layer, place it flat on a slide, add a drop of iodine stain (which colours the nucleus and makes structures show up), then lower a cover slip at an angle to avoid trapping air bubbles. The specimen must be thin so light can pass through it, and staining is used because most cell structures are otherwise transparent. You then view it starting with the lowest power objective and focus carefully.
Light microscopes and what they reveal
A light microscope can magnify up to about 1500 to 2000 times, which is enough to see cells, the nucleus, the cell wall, chloroplasts and the vacuole. It cannot show the very smallest structures inside a cell, but for GCSE it is the standard tool. Always record the total magnification (eyepiece times objective) next to any drawing, because the same image looks very different at different magnifications, and the magnification is needed to work out the real size.
Try this
Q1. State the equation linking magnification, image size and real size. [1 mark]
- Cue. Magnification = image size / real size.
Q2. Give one reason a stain such as iodine is added when preparing a slide of cells. [1 mark]
- Cue. It colours structures (such as the nucleus) that are otherwise transparent, so they can be seen.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksDescribe two ways a root hair cell is adapted for absorbing water and mineral ions from the soil.Show worked answer →
A Unit 1 adaptation question worth 4 marks (2 adaptations, each with a reason). Reward: the root hair cell has a long thin extension (the hair) that gives a large surface area for absorbing water and ions faster; it has many mitochondria to release energy for the active transport of mineral ions against the gradient; and it has a thin cell wall so the distance for water to cross is short. Markers credit any two adaptations linked to their function. A common error is to describe the adaptation without saying why it helps.
WJEC style3 marksA cell measured under a microscope is 40 mm wide. The magnification is 200. Calculate the real width of the cell in micrometres (1 mm = 1000 micrometres).Show worked answer →
A Unit 1 calculation. Real size = image size divided by magnification: (1 mark for method, 1 for 0.2 mm). Convert to micrometres: (1 mark). Markers reward rearranging the magnification equation correctly and the unit conversion. A common error is to multiply instead of divide, or to forget the conversion to micrometres.
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