Cell Biology Overview

Cell Composition

• Cells are primarily composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).
• Cells are the fundamental units of life.

Cell Theory

• Robert Hooke first observed cells in 1665.
• The cell theory proposes that all living things are made of cells and that cells originate from prior existing cells.

Cell Size and Shape

• Cell size is limited by its membrane.
• Cell shape reflects its function.
• Cells are categorized as prokaryotic (lack a nucleus) or eukaryotic (have a nucleus).

Cell Organelles

• Organelles vary in their structure and function depending on the cell's role.
• Cells have membranes to regulate what enters and exits.

Cell Membrane

• Cell membranes are composed of a phospholipid bilayer.
• The hydrophilic heads of the phospholipids face outward, and the hydrophobic tails face inward.
• Integral and peripheral proteins are embedded within the membrane.
• Cholesterol is a steroid also found within the bilayer.
• The membrane's protein patterns are dynamic, known as the fluid-mosaic model.

Microscopes

• Light microscopes magnify objects up to 1000x, requiring that the object be thin or cut thin enough for light to pass through.
• Electron microscopes use beams of electrons to magnify objects more greatly. Transmission electron microscopes (TEM) examine thin sections of the object while scanning electron microscopes (SEM) examine the surface of a specimen. False color is often added to improve visibility.

Cellular Homeostasis

• Single-celled organisms maintain stable internal conditions (homeostasis).
• Multicellular organisms divide labor among cells through specialization.

Cellular Communication

• Cells in multicellular organisms communicate using receptors.

Cell Transport

• Passive transport moves substances across the membrane with no energy input, down a concentration gradient. Examples are diffusion, osmosis, and facilitated diffusion.
• Active transport moves substances against their concentration gradient requiring energy. Examples are the sodium-potassium pump and bulk transport (endocytosis and exocytosis).

Osmosis and Solutions

• Cells respond to different solutions (hypertonic, hypotonic, and isotonic).
• Hypertonic solutions cause water to leave the cell, potentially shrinking it or leading to plasmolysis.
• Hypotonic solutions cause water to enter the cell, potentially causing it to swell or resulting in cytolysis.
• Isotonic solutions maintain equilibrium.