Unit 2: Characteristics of Life & Cell Structure

1. Characteristics of Living Things

All living organisms share these key traits:

• Cells – The basic unit of life (unicellular or multicellular).

• Organization – Structured in an orderly way (cells → tissues → organs → systems).

• Growth & Development – Increase in size and complexity over time.

• Energy Use – Metabolism converts energy for survival.

• Homeostasis – Maintaining internal balance (e.g., body temperature).

• Response to Stimuli – Reacting to environmental changes (e.g., pupils dilating in dim light).

• Reproduction – Producing offspring (sexual or asexual).

• Evolution & Adaptation – Genetic changes over generations for survival.

2. Cell Types, Structures, and Functions

• Prokaryotic Cells – Simple, no nucleus (e.g., bacteria).

• Eukaryotic Cells – Complex, with a nucleus and organelles (e.g., plant & animal cells).

• Organelles & Their Functions:

  • Nucleus – Stores genetic material (DNA).

  • Mitochondria – Produces energy (ATP) via cellular respiration.

  • Ribosomes – Makes proteins.

  • Endoplasmic Reticulum (ER) – Processes and transports proteins/lipids.

    • Smooth ER - Makes and changes proteins

    • Rough ER - makes lipids and helps clean out harmful substances from the cell.

  • Golgi Apparatus – Modifies and packages proteins.

  • Lysosomes – Breaks down waste.

  • Cell Membrane – Controls what enters and exits the cell.

  • Cell Wall (plants) – Provides structure and protection.

  • Vacuoles – Stores water, nutrients, and waste.

3. Solutions & Their Effects on Cells

• Hypotonic Solution – Water enters the cell, causing it to swell.

• Isotonic Solution – Water movement is balanced, maintaining cell shape.

• Hypertonic Solution – Water leaves the cell, causing it to shrink.

4. Chloroplasts & Endosymbiosis

• Chloroplasts – Organelles in plant cells that perform photosynthesis.

• Endosymbiotic Theory – States that mitochondria and chloroplasts evolved from ancient prokaryotic cells that were engulfed by larger cells, forming a symbiotic relationship. Evidence includes:

  • Both have their own DNA.

  • Both replicate independently.

  • Both have double membranes.

Connections Between Concepts

• Cells are the foundation of life, and all living things share fundamental characteristics.

• Cell structure determines function—organelles work together to keep the cell alive.

• Osmosis and solutions affect cell survival, impacting water balance.

• Chloroplasts and mitochondria show how cells evolved, supporting the idea of symbiosis in early life forms.