WebLab STEM

Biology · 1. Cells and microscopy

Cells as the basic unit of life

Learn cell structure through scaled observation, separating visible evidence from inferred structures.

40 minutesContent version: 2.1
Start the interactive pathwayOpen the virtual experiment

Driving question

How can a micrograph support valid conclusions about cell structure and size?

Curriculum coverage

Vietnam Biology 6 and 10; Cambridge IGCSE/AS cell structure and microscopy.

Model scope and limitations

Light microscopes cannot resolve ribosomes or very small internal membranes; textbook colours often come from stains or false colouring. Some specialised cells, such as mature mammalian red blood cells, have lost their nucleus and most organelles.

Learning objectives

  • Compare plant, animal and bacterial cells.
  • Calculate magnification or actual size with correct units.
  • Prepare and observe a slide safely.

Prerequisite knowledge

  • Convert mm, µm and nm.
  • Basic ideas of living things and organs.

Core knowledge

Shared structure

A typical living-cell model includes a membrane, cytoplasm, genetic material and ribosomes; prokaryotes lack a nucleus, and specialised cells can lose some structures.

Resolution

Magnification enlarges an image; resolution determines whether nearby points remain distinguishable.

Image scale

Magnification = image size/actual size after converting to the same unit.

Worked example

A cell is 40 mm on an image and actually 80 µm. Since 40 mm = 40,000 µm, magnification = 40,000/80 = 500×.

Misconceptions to avoid

  • The cell wall lies outside the cell membrane; plant cells have both.
  • Onion bulb epidermal cells usually lack chloroplasts because they grow underground.

Virtual experiment procedure: Microscopy and cell structure

  1. Start on low power, centre the slide and adjust illumination.
  2. Use coarse focus on low power; use only fine focus at high power.
  3. Use clear single lines, a title, ruled labels and a scale bar where data permit.

Safety and cautions

  • Glass and microscopes can be damaged; carry with two hands and never drive the objective into the slide.

Evidence to collect

  • A labelled observation with total magnification and at least three cell comparisons.
Open the virtual experiment
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<iframe src="https://visuallab.win/bio-lab/?experiment=microscopy" width="100%" height="560" frameborder="0" allow="fullscreen" loading="lazy"></iframe>

Diagnostic check

1. Which structure is in plant but not animal cells?

  1. Cellulose wall
  2. Cell membrane
  3. Ribosome
Show answer and explanation

Correct answer: Cellulose wall

Animal cells have membranes and ribosomes but no cellulose wall.

2. A 10× eyepiece and 40× objective give what total magnification?

  1. 400×
  2. 50×
  3. 4×
Show answer and explanation

Correct answer: 400×

Multiply the lens magnifications: 10 × 40 = 400.

Application practice

1. A 30 mm image of a 60 µm object has what magnification?

  1. 500×
  2. 2×
  3. 50×
Show answer and explanation

Correct answer: 500×

30 mm = 30,000 µm; 30,000/60 = 500.

2. Why start with the low-power objective?

  1. Wider field, easier to locate specimen
  2. Always gives most detail
  3. Needs no focusing
Show answer and explanation

Correct answer: Wider field, easier to locate specimen

A wide field and greater working distance make locating the specimen safer.

3. What bacterial structure is not enclosed in a nucleus?

  1. Circular DNA
  2. Chloroplast
  3. Mitochondrion
Show answer and explanation

Correct answer: Circular DNA

Bacteria are prokaryotes; their main DNA lies free in the cytoplasm.

Academic references

  1. Cambridge IGCSE Biology 0610 — official syllabus and resources
  2. Cambridge AS & A Level Biology 9700 — official syllabus
  3. OpenStax Biology 2e — peer-reviewed foundational biology

This lesson is maintained against the cited sources below. Simulations are learning models and do not replace supervised physical-laboratory safety procedures.

Content publisher
WebLab STEM
Technical maintainer
Đức Tiến — Control & Automation Engineer