AP Biology 2.1 Cell Structure and Function Study Notes - New Syllabus Effective 2025
AP Biology 2.1 Cell Structure and Function Study Notes- New syllabus
AP Biology 2.1 Cell Structure and Function Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Explain how the structure and function of subcellular components and organelles contribute to the function of cells.
Key Concepts:
- Subcellular Components
- Cell Structure & Function
- Cells & Surface Area
- Specialized Exchange Strategies
2.1.A – Cell Structure & Function
🧬 Why Structure = Function in Cells
- Every organelle inside a cell has a specific structure that allows it to do a special job.
- Together, these parts help the cell survive, grow, and carry out life processes.
🧩 Key Organelles & Their Functions
| Organelle | Structure 🧱 | Function ⚙️ |
| Nucleus | Double membrane, contains DNA | Controls cell activities, stores genetic information |
| Ribosomes | Small, no membrane, free-floating or on RER | Make proteins using mRNA instructions |
| Rough ER (RER) | Membranes with ribosomes attached | Folds and transports proteins |
| Smooth ER (SER) | Membranes without ribosomes | Makes lipids and detoxifies harmful substances |
| Golgi Apparatus | Stacked, flattened membranes | Modifies, sorts, and ships proteins |
| Mitochondria | Double membrane, has own DNA, folded inner part | Converts glucose into ATP = energy (cell respiration) |
| Chloroplast (plants) | Double membrane, contains chlorophyll | Photosynthesis, makes sugars from sunlight |
| Lysosome | Membrane sac with digestive enzymes | Breaks down waste and worn-out parts |
| Vacuole | Large in plants, small in animals | Stores water, ions, waste, or nutrients |
| Cell Membrane | Phospholipid bilayer with proteins | Controls what enters/leaves, semi-permeable |
| Cytoskeleton | Network of protein fibers | Supports shape, helps with movement and transport |
| Centrioles (animal cells) | Cylindrical, made of microtubules | Help in cell division |
🧠 Summary:
- Each organelle has a unique structure that helps it do a specific function – this teamwork allows the cell to run like a factory!
2.1.A.1 – Ribosomes & Common Ancestry
🧬 What are Ribosomes?
- Ribosomes are tiny structures made of:
- rRNA (ribosomal RNA)
- Proteins
- They do NOT have a membrane, unlike many other organelles.
- Found in all forms of life – bacteria, archaea, and eukaryotes.
🧠 Function of Ribosomes
- Ribosomes are protein factories.
- They read mRNA sequences and build proteins using amino acids.
- This process is called translation (part of protein synthesis).
🌍 Why They’re Important in Evolution
- Because every living cell has ribosomes, scientists believe:
- All life on Earth shares a common ancestor.
- Ribosomes are a conserved feature – they’ve stayed mostly unchanged through evolution.
🔑 Key Terms
| Term | Meaning |
| rRNA | Ribosomal RNA – helps make up ribosomes and aids in protein assembly. |
| mRNA | Messenger RNA – carries instructions from DNA to make proteins. |
| Protein Synthesis | Building proteins based on genetic code. |
| Translation | The step where ribosomes “read” mRNA and link amino acids. |
✅ Quick Recap
- Ribosomes = non-membrane organelles made of rRNA + protein
- Found in all life forms → supports common ancestry
- They build proteins using mRNA instructions
2.1.A.2 – The Endomembrane System
📦 What is the Endomembrane System?
- A network of membrane-bound organelles inside the cell that work together to:
- Synthesize (make)
- Modify
- Package
- Transport proteins, lipids, and polysaccharides
- Works both inside the cell and for export outside the cell.
🏗️ Who’s in the Team? (Main Components)
| Organelle | Function |
| Endoplasmic Reticulum (ER) | Rough ER: Has ribosomes → makes proteins Smooth ER: Makes lipids & detoxifies |
| Golgi Complex (Apparatus) | Sorts, modifies, and packages proteins/lipids into vesicles for transport |
| Lysosomes | Break down waste, damaged organelles, and macromolecules using enzymes |
| Vacuoles | Storage (especially in plants), sometimes digestion |
| Transport Vesicles | Small sacs that carry materials between organelles or to the plasma membrane |
| Nuclear Envelope | Surrounds the nucleus, has pores that regulate what goes in and out |
| Plasma Membrane | Controls what enters and exits the cell; final barrier for export/import |
🚛 What Does It Do?
- Like a factory system:
- Ribosomes (on rough ER) make proteins.
- Proteins/lipids move to the Golgi for finishing touches.
- Packaged into vesicles.
- Sent to where they’re needed – inside the cell or exported.
- Lysosomes digest unwanted stuff.
- Vacuoles store nutrients, waste, or water.
🧠 Why It Matters
- Keeps the cell organized, efficient, and functional.
- Without this system, materials couldn’t be properly processed or transported.
🧩 Key Terms Recap
| Term | Meaning |
| Vesicle | A small membrane-bound transport bubble |
| Polysaccharide | A complex carbohydrate (like starch or cellulose) |
| Lipid | Fats and oils, made in the smooth ER |
| Protein | Made in ribosomes, modified in ER/Golgi |
✅ Summary
- The endomembrane system is like a cellular factory
- It moves, modifies, and ships proteins, lipids, and carbs
- Key players: ER, Golgi, lysosomes, vacuoles, vesicles, nuclear envelope, plasma membrane
2.1.A.3 – Endoplasmic Reticulum (ER)
🧱 What Is the ER?
- The endoplasmic reticulum (ER) is a network of membranes inside the cytoplasm.
- It provides mechanical support to help maintain cell shape.
- It’s involved in moving materials (like proteins & lipids) within the cell.
🔴 Types of ER:
- 1. Rough ER (RER):
- Has ribosomes attached → looks “rough” under a microscope.
- Function:
- Protein synthesis (with ribosomes).
- Compartmentalizes the cell → keeps protein production organized and separate.
- Sends proteins to Golgi in vesicles.
- 2. Smooth ER (SER):
- No ribosomes → looks smooth.
- Function:
- Lipid synthesis (like fats and steroids).
- Detoxification – breaks down harmful chemicals (like drugs & alcohol).
🧠 Why It’s Important:
- Keeps the cell organized and efficient.
- Works like a cellular highway and manufacturing unit:
- RER = makes proteins
- SER = makes lipids & detoxifies
- Both = help transport products to where they’re needed
✨ Quick Recap Table
| Feature | Rough ER | Smooth ER |
| Ribosomes | ✅ Yes | ❌ No |
| Main function | Protein synthesis | Lipid synthesis & detox |
| Shape role | Structural support & transport | Transport & metabolic roles |
2.1.A.4 – The Golgi Complex
🧱 What is the Golgi Complex?
- The Golgi complex (also known as the Golgi apparatus or Golgi body) is a membrane-bound organelle.
- Made of stacked, flattened membrane sacs called cisternae.
- Found in eukaryotic cells.
⚙️ Main Functions:
- 1. Folding & Modifying Proteins
- Receives newly made proteins from the rough ER.
- Helps fold proteins into their functional shapes.
- Can chemically modify them (e.g., adding sugars → glycoproteins).
- 2. Packaging & Shipping
- Packages proteins into vesicles for delivery:
- Inside the cell (e.g., to lysosomes)
- Outside the cell (secretion)
- Sorts and tags proteins to ensure they reach the correct destination.
- Packages proteins into vesicles for delivery:
🧠 Why It’s Important:
- Think of the Golgi as the “post office” of the cell.
- It processes, labels, and ships proteins and lipids.
- Without it, cells couldn’t properly transport molecules, leading to major dysfunction.
🧾 Quick Recap Table
| Feature | Function |
| Flattened membrane sacs | Structure for organizing & processing materials |
| Protein folding | Ensures proper shape/function |
| Chemical modification | Adds groups (e.g., sugars) to proteins |
| Packaging in vesicles | Sends proteins to correct cellular locations |
2.1.A.5 – Mitochondria & Their Role in Cellular Respiration
🏛️ Structure of Mitochondria:
- Mitochondria are double membrane-bound organelles found in all eukaryotic cells.
| Membrane | Description | Function |
| Outer membrane | Smooth surface | Protective barrier, regulates what enters/leaves. |
| Inner membrane | Highly folded (called cristae) | Increases surface area for ATP production. |
- Matrix: The inner fluid-filled space inside the inner membrane where the Krebs cycle occurs.
⚙️ Function: Aerobic Cellular Respiration
- Main job = make ATP (cell’s usable energy).
- Performs multiple metabolic reactions:
- Glycolysis products (pyruvate) enter the mitochondria.
- Krebs cycle takes place in the matrix.
- Electron Transport Chain (ETC) is located on the inner membrane.
- ATP synthase uses the proton gradient to make lots of ATP.
🧠 Why Are Cristae Important?
- More folds = more surface area.
- This allows more ETC proteins and ATP synthase enzymes to be packed in.
- Result: More efficient ATP production for the cell.
✨ Quick Recap
| Feature | Purpose |
| Double membrane | Separates different reaction spaces |
| Cristae (inner folds) | Maximize ATP production surface area |
| Matrix | Site of the Krebs cycle |
| Inner membrane | Location of ETC and ATP synthesis |
2.1.A.6 – Lysosomes: Structure & Function
🧫 What Are Lysosomes?
- Lysosomes are membrane-bound sacs found in animal cells.
- They contain hydrolytic enzymes that work best at an acidic pH.
- Think of them as the cell’s “recycling center” or “digestive system”.
🧬 Why Are Lysosomes Important?
- Keep the cell clean by removing waste.
- Help maintain homeostasis.
- Prevent accumulation of harmful materials.
- Allow controlled cell death during development or immune responses.
🔍 Functions of Lysosomes
| Function | Explanation |
| Intracellular digestion | Breaks down food particles, worn-out organelles, and cellular debris. |
| Autophagy | Recycles damaged cell parts for reuse. |
| Apoptosis | Plays a role in programmed cell death by releasing digestive enzymes. |
| Defense | Destroys invading pathogens like bacteria (especially in white blood cells). |
🧠 Quick Recap
| Feature | Details |
| Type | Membrane-enclosed organelle |
| Enzymes inside | Hydrolytic enzymes |
| Main jobs | Digest, recycle, defend, and trigger apoptosis |
| Found in | Mainly animal cells (rare in plants) |
2.1.A.7 – Vacuoles: Structure & Function
🧫 What Are Vacuoles?
- Vacuoles are membrane-bound sacs found in both plant and animal cells.
- They function as storage centers and help maintain cell structure in plants.
- Their role depends on the type of cell they’re in.
🪴 Vacuoles in Plant Cells
- Contain a large central vacuole that:
- Stores water, ions, nutrients, and waste.
- Maintains turgor pressure (internal pressure that keeps plant cells firm and upright).
- Helps support the structure of the plant.
🧠 Think of it as a water balloon that keeps the plant standing tall.
🧬 Vacuoles in Animal Cells
- Smaller and more numerous than in plant cells.
- Used mainly for storage of:
- Nutrients
- Waste
- Cellular materials (like ions, enzymes, and food particles)
📦 Functions of Vacuoles
| Function | Plant Cells | Animal Cells |
| Storage | Water, nutrients, waste | Nutrients, waste, cellular materials |
| Turgor Pressure | ✅ Maintains rigidity | ❌ Not applicable |
| Support/Structure | ✅ Yes (via central vacuole) | ❌ No structural role |
🧠 Quick Recap
- Plant cells: Large, central vacuole = support + storage
- Animal cells: Small, multiple vacuoles = storage
- Vacuoles help maintain balance in the cell’s internal environment and support its needs.
2.1.A.8 – Chloroplasts: Structure & Function
🌞 What Are Chloroplasts?
- Specialized organelles found in:
- 🌱 Plants
- 🧫 Photosynthetic algae
- These are the site of photosynthesis – the process where light energy is converted into chemical energy (sugars).
🧱 Structure of Chloroplasts
- Double membrane:
- Outer membrane: Smooth protective layer
- Inner membrane: Surrounds the internal fluid
- Outer membrane: Smooth protective layer
- Stroma: The fluid-filled space inside the inner membrane where the Calvin cycle happens.
- Thylakoids:
- Flattened, disc-like membranes stacked into grana.
- Contains chlorophyll (green pigment) to absorb sunlight.
- Light-dependent reactions happen here.
🔁 Function of Chloroplasts
- Perform photosynthesis:
- Convert CO₂ + H₂O + light → glucose + O₂
- Produce energy-rich molecules (glucose) used by the plant or stored.
- Generate oxygen as a by-product (essential for life on Earth).
📌 Key Facts to Remember
| Feature | Function |
| Double membrane | Separates and protects internal functions |
| Thylakoids | Site of light reactions (ATP & NADPH made) |
| Stroma | Site of Calvin cycle (glucose formed) |
| Chlorophyll | Absorbs light energy for photosynthesis |
🧠 Tip:
Think of chloroplasts as solar-powered food factories for the plant!