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Cell Size Measurement in Biology

Sep 4, 2025

Overview

This lecture explains how to describe the size of cells using metric prefixes such as centi-, milli-, micro-, and nano-, and introduces standard form for expressing very small measurements in biology.

Metric Units for Measuring Size

  • Scientific measurements use the meter as the base unit.
  • 1 meter (m) is often too large for measuring cells and cell structures.
  • 1 centimeter (cm) is 1/100th of a meter (1 cm = 1 × 10⁻² m).
  • 1 millimeter (mm) is 1/1000th of a meter (1 mm = 1 × 10⁻³ m).
  • 1 micrometer (μm) is 1/1,000,000th of a meter (1 μm = 1 × 10⁻⁶ m).
  • 1 nanometer (nm) is 1/1,000,000,000th of a meter (1 nm = 1 × 10⁻⁹ m).

Application to Biology

  • Prokaryotic (bacterial) cells are much smaller than eukaryotic (animal and plant) cells.
  • Typical animal cells are about 10–20 micrometers (μm) in size.
  • Structures inside cells, like ribosomes, are measured in nanometers.
  • Proteins such as hemoglobin are roughly 5 nm in diameter.
  • Using standard form notation is important for expressing these small sizes in exams.

Key Terms & Definitions

  • Centimeter (cm) — 1/100th of a meter (1 × 10⁻² m)
  • Millimeter (mm) — 1/1,000th of a meter (1 × 10⁻³ m)
  • Micrometer (μm) — 1/1,000,000th of a meter (1 × 10⁻⁶ m)
  • Nanometer (nm) — 1/1,000,000,000th of a meter (1 × 10⁻⁹ m)
  • Standard form — a way of writing very large or very small numbers using powers of ten (e.g., 1 × 10⁻⁶ m for 1 μm)

Action Items / Next Steps

  • Practice using metric prefixes and standard form to describe and compare the sizes of biological objects.
  • Review exam questions on cell sizes using provided workbooks or resources.