Chapter 3: Cells – Structure, Function, and Cellular Processes

Introduction to Cells

Overview of Cellular Biology

Cells are the fundamental units of life, and most anatomical and physiological processes occur at the cellular level. The study of cells became possible with the invention of the microscope about 400 years ago, leading to the development of the cell theory.

• Microscopy: The use of microscopes to observe cellular structures.

• Cell Theory: A foundational concept in biology describing the properties and functions of cells.

Cell Theory

Basic Concepts

The cell theory was developed from the research of Robert Hooke and others. It provides the basis for understanding the role of cells in living organisms.

• Cells are the building blocks of all plants and animals.

• All cells come from the division of preexisting cells.

• Cells are the smallest units that perform all vital physiological functions.

• Each cell maintains homeostasis at the cellular level.

• Cytology: The study of cellular structure.

Cell Size and Shape

Variation in Cellular Morphology

Cells vary greatly in size and shape, which is related to their function. The size of cells is typically measured in micrometers (μm).

• Distinctive shapes: Cells possess unique shapes suited to their roles (e.g., spherical, elongated, flat).

• Size range: Most cells are between 7.5 μm and 200 μm in diameter.

• Measurement: 1 micrometer (μm) = 1 × 10-6 meters.

Types of Cells

Sex Cells vs. Somatic Cells

Cells in the human body are classified into two main types: sex cells and somatic cells.

• Sex cells (germ cells):

  • Reproductive cells: Male sperm and female oocyte (egg precursor).

  • Haploid (1n): Contain half the number of chromosomes.

  • Formed by meiosis.

• Somatic cells (soma = body):

  • All body cells except sex cells.

  • Diploid (2n): Contain a full set of chromosomes.

  • Formed by mitosis.

Key Terms and Definitions

• Cell: The smallest structural and functional unit of an organism.

• Microscopy: The technique used to view cells and their components.

• Homeostasis: The maintenance of stable internal conditions at the cellular level.

• Cytology: The branch of biology concerned with the structure and function of plant and animal cells.

• Meiosis: The process by which sex cells are formed, resulting in haploid cells.

• Mitosis: The process by which somatic cells divide, resulting in diploid cells.

Examples and Applications

• Red blood cells: Biconcave shape increases surface area for gas exchange.

• Muscle cells: Elongated shape allows contraction and movement.

• Nerve cells: Long extensions (axons) facilitate transmission of electrical signals.

Additional info: The provided images illustrate basic cell structure, including the nucleus, mitochondria, ribosomes, and endoplasmic reticulum, which are key organelles involved in cellular function.