You need a strong understanding of cell structure and function to succeed in AP Biology Unit 2.
Cells build all living things. Every process inside an organism starts at the cellular level.
This guide breaks down important ideas into simple, easy-to-read notes — perfect for a quick and clear review!
Table of Contents
Here’s what we’ll cover:
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What Is Cell Structure and Function?
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The Cell Theory: 3 Main Ideas
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Types of Cells: Prokaryotic vs. Eukaryotic
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Cell Organelles and Their Functions
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Cell Membrane Structure and Plasma Membrane Function
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The Endosymbiotic Theory
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Quick Summary Table: Organelles and Their Functions
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Final Tips for AP Biology Unit 2 Success
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Conclusion
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FAQ
What Is Cell Structure and Function?
Let’s start with the basics.
Cell structure describes how a cell is built — what parts it has and how they fit together.
Cell function explains what each part does to keep the cell alive and working.
When you connect both ideas, you’ll realize that even the tiniest cell acts like a busy city!
🔹 Example: The nucleus acts like city hall, storing important information.
🔹 The mitochondria work like power plants, producing energy.
The Cell Theory: 3 Main Ideas
The cell theory forms one of the basic foundations of biology.
Scientists have agreed on three main ideas:
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All living things are made up of cells.
- Everything from tiny bacteria to giant whales starts with cells.
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Cells are the basic unit of life.
- They carry out all the processes that define life.
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All cells come from existing cells.
- Cells divide and create new cells.
Real-world example: When you cut your finger, new skin cells form to heal the wound.
Types of Cells: Prokaryotic vs. Eukaryotic
Cells fall into two major groups. Knowing the difference helps you a lot in AP Biology Unit 2.
Prokaryotic Cells
- Don’t have a nucleus (DNA floats freely).
- Stay small and simple.
- Don’t contain membrane-bound organelles.
- Example: Bacteria and Archaea.
Eukaryotic Cells
- Contain a true nucleus.
- Pack in many membrane-bound organelles.
- Show more complexity.
- Example: Plants, animals, fungi, and protists.
🔹 Tip: Prokaryotes appeared first in Earth’s history. Eukaryotes evolved later!
Cell Organelles and Their Functions
Cells act like tiny factories.
Each cell organelle does a specific job to keep the factory running smoothly.
Here’s a simple list:
Nucleus Function
- Stores the DNA.
- Directs cell activities.
- Has a double membrane (nuclear envelope).
Ribosomes Function
- Build proteins.
- Float freely or stick to the rough ER.
Mitochondria Function
- Produce ATP (cell energy).
- Carry their own DNA.
Chloroplast Function
- Capture sunlight for photosynthesis.
- Appear only in plant cells and some protists.
Smooth and Rough ER
- Rough ER: Makes proteins (covered in ribosomes).
- Smooth ER: Produces lipids and detoxifies harmful substances.
Golgi Apparatus Role
- Sorts, packages, and ships proteins and lipids.
- Works like a shipping center.
Lysosomes and Peroxisomes
- Lysosomes: Break down waste and damaged parts.
- Peroxisomes: Break down fatty acids and neutralize toxins.
Vacuoles Function
- Store water, nutrients, and waste.
- Plant cells have one huge central vacuole.
Cytoskeleton in Cells
- Supports the cell’s shape.
- Helps move materials inside the cell.
Cell Membrane Structure and Plasma Membrane Function
The cell membrane (also called the plasma membrane) protects the cell and manages what enters and leaves.
Structure:
- A double layer of phospholipids with proteins scattered throughout.
Functions:
- Protects the cell.
- Regulates movement of materials.
- Communicates with the environment.
🔹 Example: Oxygen enters a cell, while carbon dioxide exits, through the plasma membrane.
The Endosymbiotic Theory
Scientists use the endosymbiotic theory to explain how complex cells evolved.
Main Idea:
- Early eukaryotic cells swallowed free-living bacteria.
- These bacteria survived and became parts of the cell, like mitochondria and chloroplasts.
Evidence:
- Both organelles have their own DNA.
- They reproduce similarly to bacteria.
- They have double membranes.
🔹 Fun Fact: Mitochondria are still ancient bacteria living inside you!
This idea plays a big role in AP Biology Unit 2 exams.
Quick Summary Table: Cell Organelles and Their Functions
| Organelle | Function |
|---|---|
| Nucleus | Stores DNA, directs cell |
| Ribosomes | Build proteins |
| Mitochondria | Create energy (ATP) |
| Chloroplasts | Perform photosynthesis (plants) |
| Rough ER | Produce proteins |
| Smooth ER | Make lipids, detoxify |
| Golgi Apparatus | Package and ship materials |
| Lysosomes | Break down waste |
| Peroxisomes | Neutralize toxins |
| Vacuoles | Store nutrients and waste |
| Cytoskeleton | Provide support and movement |
Final Tips for Cell Structure and Function AP Biology Unit 2 Success
You can absolutely master cell structure and function if you stay consistent.
Here’s what you can do:
✅ Sketch diagrams of cells and label them.
✅ Teach yourself out loud — explain functions like you’re the teacher.
✅ Make flashcards for all organelles.
✅ Solve practice problems — especially past AP Biology Unit 2 questions.
✅ Review often, even when you feel confident!
Also, check Refresh Kid’s AP Biology resources if you need extra help.
Cells may seem small, but they make a huge impact.
When you understand cell structure and function, you build a strong foundation for learning biology.
Take your time to study.
Practice a little every day.
Stay curious and keep asking questions.
You’re well on your way to doing great in AP Biology Unit 2!
Frequently Asked Questions on Cell Structure and Function
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What does the cell membrane do?
The cell membrane protects the cell and controls what comes in and goes out.
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How do prokaryotic and eukaryotic cells differ?
Prokaryotic cells don’t have a nucleus, while eukaryotic cells do.
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Why do people call mitochondria the powerhouse of the cell?
Because mitochondria create most of the energy (ATP) the cell needs to survive.
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What evidence supports the endosymbiotic theory?
Mitochondria and chloroplasts have their own DNA and reproduce like bacteria.
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Which organelles exist only in plant cells?
Chloroplasts, a large central vacuole, and a cell wall.
Having covered unit 2, don’t forget to go back and review Unit 1: Chemistry of Life.
