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.