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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

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. 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