Cells are open systems – they exchange both matter and energy with their environment.
Cellular Open Systems: Examples of Exchange
- In: Water, oxygen, nutrients, solar energy (in plants)
- Out: Carbon dioxide, waste, thermal energy, kinetic energy
Cellular Needs and Organ System Functions
| Need | Organ System |
|---|
| Nutrient intake & use | Digestive |
| Gas exchange | Respiratory, circulatory |
| Movement & growth | Musculoskeletal |
| Response to stimuli | Nervous |
| Waste removal | Excretory, respiratory, digestive |
| Reproduction | Reproductive |
Surface Area to Volume Ratio (SA:V)
Cells work best with a high SA:V ratio (more membrane per unit of volume).
- Small cells = high SA:V → efficient transport
- Large cells = low SA:V → less efficient
SA:V Ratio Calculation Formulas
- Surface Area of cube: 6 × (side × side)
- Volume of cube: side × side × side
- SA:V Ratio: Surface Area ÷ Volume
Animal vs. Plant Cell Differences
| Animal Cells | Plant Cells |
|---|
| Centrioles (cell division) | Cell wall (structure/support) |
| Many small vacuoles | 1 large central vacuole |
| Store energy as fat | Store energy as oil/starch |
| No chloroplasts | Chloroplasts (photosynthesis) |
| All other organelles shared | All other organelles shared |
Key Organelles and Their Functions
| Organelle | Function |
|---|
| Cell membrane | Controls what enters/exits cell (selectively permeable) |
| Cytoplasm | Suspends organelles, contains nutrients |
| Nucleus | Contains DNA; controls cell activities |
| Mitochondria | Site of cellular respiration (sugar → energy) |
| Ribosomes | Makes proteins from amino acids |
| Rough ER | Has ribosomes; protein synthesis |
| Smooth ER | Synthesizes fats/oils |
| Golgi apparatus | Packages materials for transport |
| Lysosomes (animal only) | Digestion, defense |
| Centrioles (animal only) | Helps in cell division |
| Chloroplast (plant only) | Photosynthesis; contains chlorophyll |
| Vacuole | Stores water/nutrients |
| Cell wall (plant only) | Rigid support; allows material exchange through pores |
Cell Organelles and Human System Analogies
| Organelle | Human System Equivalent |
|---|
| Nucleus | Nervous system |
| Lysosomes | Digestive + immune systems |
| Centrioles | Reproductive system |
💧 Cell Membrane & Transport
🧱 Cell Membrane Structure: Fluid Mosaic Model
- Fluid Mosaic Model = Flexible + made of many parts
- Phospholipid Bilayer = 2 layers
- Hydrophilic heads (water-loving)
- Hydrophobic tails (water-fearing)
- Proteins = Channels + carriers for transport
⚖️ Concentration & Gradients
- Concentration = Ratio of solute to solvent
- Gradient = Difference in concentration
- Movement direction:
- High → Low = With gradient (passive)
- Low → High = Against gradient (active)
The Particle Model of Matter Principles
- All matter is made of particles
- Particles are always moving
- Particles attract each other
- Particles have space between them
Cellular Transport Mechanisms
| Type | Needs Energy? | Gradient Direction | Uses Proteins? | Moves... |
|---|
| Diffusion | ❌ No | High → Low | ❌ No | Small, fat-soluble molecules |
| Facilitated Diffusion | ❌ No | High → Low | ✅ Yes | Large/non-fat-soluble molecules |
| Osmosis | ❌ No | High water → Low water | ❌ No | Water only |
| Active Transport | ✅ Yes | Low → High | ✅ Yes | Any molecule (e.g., nutrients, ions) |
| Endocytosis | ✅ Yes | Into the cell | ❌ (uses vesicle) | Large molecules like proteins |
| Exocytosis | ✅ Yes | Out of the cell | ❌ (uses vesicle) | Wastes, proteins, hormones |
Osmosis: Cell Behavior in Different Solutions
| Type | Solution Solute | Water Movement | Effect on Animal Cells | Effect on Plant Cells |
|---|
| Hypotonic | Less than cell | Water into cell | Swells, may burst (lyse) | Turgid (healthy) |
| Isotonic | Same as cell | No net movement | Normal | Limp/floppy |
| Hypertonic | More than cell | Water leaves cell | Shrivels, may die (crenate) | Plasmolysis (wilting) |
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