Cell Structure and Function: Study Notes

Cell Structure and Function

Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life. It provides the foundation for understanding the structure and function of all living organisms.

• All living things are composed of cells. Every organism, from the simplest bacteria to complex plants and animals, is made up of one or more cells.

• A single cell is the smallest unit that exhibits the characteristics of life. Cells carry out all necessary life processes, such as metabolism, growth, and reproduction.

• All cells come only from preexisting cells. New cells are produced by the division of existing cells, ensuring continuity of life.

Sizes of Living Things

Living organisms and their components vary greatly in size, from molecules to multicellular organisms. Understanding these size differences is important for studying cell structure and function.

• Metric conversions: 1 m = 100 cm = 1000 mm = $10^6$ μm = $10^9$ nm

• Examples: Proteins and viruses are measured in nanometers (nm), while most bacteria and organelles like chloroplasts are measured in micrometers (μm). Human cells and eggs are larger, visible under a light microscope.

Application: Electron microscopes are required to view structures smaller than 0.2 μm, such as viruses and proteins, while light microscopes can be used for most cells and larger organelles.

Cell Size

Cell size is limited by the surface area-to-volume ratio, which affects the ability of the cell to exchange materials with its environment.

• Small cell size is advantageous for multicellular organisms because:

  • Nutrients such as glucose can efficiently enter the cell.

  • Wastes such as carbon dioxide ($CO_2$) can efficiently exit the cell.

• Surface area affects material exchange: As cells increase in volume, the proportionate amount of surface area decreases, limiting the rate of exchange.

Formula: Surface area of a sphere: $4\pi r^2$; Volume: $\frac{4}{3}\pi r^3$

Additional info: This ratio explains why most cells are microscopic.

Types of Cells

Cell Types

Cells are classified into two fundamental types based on their internal structure: prokaryotic and eukaryotic.

• Prokaryotic cells: Lack a membrane-bound nucleus. Examples include Archaea and Bacteria.

• Eukaryotic cells: Possess a membrane-bound nucleus. Found in all other organisms, including animals, plants, fungi, and protists.

Prokaryotic vs. Eukaryotic Cells

Prokaryotic and eukaryotic cells differ in complexity, structure, and the presence of organelles.

• Prokaryotes:

  • Structurally simple and unicellular

  • Metabolically diverse

  • Adapted to most types of environments

• Eukaryotes:

  • Structurally complex

  • Have a nucleus

  • Possess membrane-bounded organelles

  • Make up animals, plants, fungi, and protists

Comparison Table:

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No	Yes
Membrane-bound organelles	No	Yes
Cell type	Unicellular	Unicellular or multicellular
Examples	Bacteria, Archaea	Animals, plants, fungi, protists