A2.2

Campbell IB Bio 1 CHS

Cell Theory

Cell Theory

A scientific theory stating that all living things are composed of cells, which are the smallest unit of life, and that cells arise only from pre-existing cells.

Mitosis

A process of cell division that results in two identical daughter cells, essential for growth and repair.

Meiosis

A type of cell division that generates gametes (sperm and eggs) for sexual reproduction.

Theory

A well-substantiated explanation of some aspect of the natural world, based on a body of facts and repeatedly confirmed through observation and experimentation.

Viruses

Entities that are not considered alive because they lack cells, do not maintain homeostasis, do not grow, cannot reproduce independently, and cannot perform metabolism.

Life

Defined as a self-sustaining chemical system capable of undergoing Darwinian evolution.

Common Cellular Structures

Basic components found in all cells, including the plasma membrane, cytosol, and organelles.

Plasma Membrane

A bilayer formed from phospholipids that separates the cell's exterior from its interior and allows for homeostasis.

Cytosol

The fluid component of the cytoplasm, essential for metabolism and dissolving solutes, primarily composed of water.

Cytoplasm

The fluid plus all contents within the cell, including organelles.

Deoxyribonucleic Acid (DNA)

The genetic material necessary for making new cells, reproduction, and evolution.

Ribosomes

Cellular structures that synthesize proteins using the information encoded in DNA; prokaryotes have 70s ribosomes, while eukaryotes have 80s ribosomes.

Discrepancies to Cell Theory

Exceptions to the cell theory, including red blood cells, aseptate fungal hyphae, skeletal muscles, and phloem sieve tubes.

Red Blood Cells (Erythrocytes)

Cells that transport oxygen but lack a nucleus, mitochondria, and DNA as they mature.

Aseptate Fungal Hyphae

Tubal projections of multicellular fungi that form a network with continuous cytoplasm and multiple nuclei.

Skeletal Muscles

Large cells formed by the fusion of multiple cells during development, resulting in multinucleated structures to produce proteins efficiently.

Phloem Sieve Tubes

Specialized cells in phloem that transport sugars, losing their nucleus and organelles during development to maximize transport space, with companion cells providing necessary organelles.