Biology B1

# 🧬 B1 CELL BIOLOGY – DETAILED REVISION NOTES These are the key points you should know for each topic. --- # 🔬 1. MICROSCOPES ### What is a microscope? * A tool used to see objects too small to be seen with the naked eye. * Used to study cells and microorganisms. ### Light microscope * Uses visible light. * Can observe living cells. * Lower magnification. * Lower resolution. ### Electron microscope * Uses a beam of electrons. * Much higher magnification. * Much higher resolution. * Shows organelles and viruses in detail. * Cannot observe living cells. ### Magnification * How many times bigger an image is than the real object. * Formula: [ \text{Magnification}=\frac{\text{Image size}}{\text{Real size}} ] ### Resolution * Ability to distinguish two close points as separate. * Higher resolution = clearer image. ### Advantages of microscopes * Observe cells and organelles. * Diagnose diseases. * Scientific research. --- # 🧫 2. ANIMAL AND PLANT CELLS ## Animal Cell ### Nucleus * Contains DNA. * Controls cell activities. ### Cytoplasm * Jelly-like substance. * Site of chemical reactions. ### Cell membrane * Controls movement of substances into and out of the cell. ### Mitochondria * Site of aerobic respiration. * Releases energy (ATP). ### Ribosomes * Site of protein synthesis. --- ## Plant Cell Contains everything an animal cell has plus: ### Cell wall * Made of cellulose. * Supports and strengthens cell. * Prevents bursting. ### Chloroplasts * Contain chlorophyll. * Site of photosynthesis. ### Vacuole * Contains cell sap. * Maintains turgor pressure. * Helps support the plant. --- # 🦠 3. PROKARYOTIC AND EUKARYOTIC CELLS ## Eukaryotic Cells * Plants, animals, fungi. * Larger and more complex. * DNA enclosed in nucleus. * Membrane-bound organelles present. Examples: * Animal cells * Plant cells --- ## Prokaryotic Cells * Bacteria. * Smaller and simpler. * No nucleus. * DNA free in cytoplasm. * No membrane-bound organelles. ### Structures * Cell membrane * Cytoplasm * Cell wall * Circular DNA * Plasmids --- ## Comparison ### Eukaryotic * Larger * Nucleus present * Organelles present ### Prokaryotic * Smaller * No nucleus * No membrane-bound organelles --- # 🧬 4. SPECIALISED ANIMAL CELLS ## Sperm Cell ### Adaptations * Long tail for swimming. * Many mitochondria for energy. * Enzyme-filled acrosome to penetrate egg. * Haploid nucleus (half DNA). ### Function * Fertilise egg cell. --- ## Nerve Cell ### Adaptations * Long axon carries impulses. * Branched ends connect to other cells. * Insulating sheath speeds transmission. ### Function * Carries electrical impulses. --- ## Muscle Cell ### Adaptations * Contractile fibres. * Many mitochondria. ### Function * Contracts to create movement. --- # 🌿 5. SPECIALISED PLANT CELLS ## Root Hair Cell ### Adaptations * Long extension increases surface area. * Thin cell wall. * Many mitochondria. ### Function * Absorb water and minerals. --- ## Palisade Cell ### Adaptations * Many chloroplasts. * Tall shape. * Located near upper leaf surface. ### Function * Photosynthesis. --- ## Xylem Cell ### Adaptations * Hollow tubes. * Thick lignin walls. * Dead cells. ### Function * Transport water and minerals. * Provide support. --- ## Phloem Cell ### Adaptations * Sieve plates. * Living cells. ### Function * Transport sugars. --- # 🌊 6. DIFFUSION ## Definition * Net movement of particles from high concentration to low concentration. ## Features * Passive process. * No energy needed. * Moves down concentration gradient. ## Factors affecting diffusion ### Temperature * Higher temperature = faster diffusion. ### Concentration gradient * Bigger difference = faster diffusion. ### Surface area * Larger surface area = faster diffusion. ### Distance * Shorter distance = faster diffusion. --- ## Examples * Oxygen into blood. * Carbon dioxide out of blood. * Gas exchange in leaves. --- # 💧 7. OSMOSIS ## Definition * Net movement of water molecules through a partially permeable membrane. * From high water concentration to low water concentration. --- ## Key Terms ### Hypotonic * More water outside cell. * Water enters cell. ### Hypertonic * Less water outside cell. * Water leaves cell. ### Isotonic * Equal concentrations. * No net movement. --- ## Animal Cells ### Water enters * Swells. * May burst. ### Water leaves * Shrinks. --- ## Plant Cells ### Turgid * Water enters. * Cell firm and supported. ### Flaccid * Water leaves. * Cell loses support. ### Plasmolysed * Severe water loss. * Cell membrane pulls away from wall. --- # 🌱 8. OSMOSIS IN PLANTS ### Importance * Maintains support in plants. * Controls water balance. ### Practicals * Potato cylinders in different concentrations. * Measure mass change. * Calculate percentage change. ### Interpretation * Gain mass = water entered. * Lose mass = water left. --- # ⚡ 9. ACTIVE TRANSPORT ## Definition * Movement of substances from low concentration to high concentration. * Requires energy from respiration. --- ## Features * Uses ATP. * Against concentration gradient. * Uses carrier proteins. --- ## Examples ### Root Hair Cells * Absorb mineral ions. ### Small Intestine * Absorb glucose into blood. --- ## Importance * Allows uptake when concentration outside is lower. --- # 🌬️ 10. EXCHANGE SURFACES ## Purpose * Allow rapid movement of substances. --- ## Adaptations ### Large surface area * More diffusion. ### Thin membrane * Short diffusion distance. ### Good blood supply * Maintains concentration gradient. ### Ventilation * Refreshes air. --- ## Examples ### Alveoli * Gas exchange in lungs. ### Villi * Absorb nutrients in small intestine. ### Leaves * Gas exchange through stomata. ### Root Hair Cells * Absorb water and minerals. --- # 📐 SURFACE AREA TO VOLUME RATIO ### Small organisms * High SA:V ratio. * Exchange materials easily. ### Large organisms * Low SA:V ratio. * Need specialised exchange surfaces. ### Why important? * Cells need oxygen and nutrients. * Waste must be removed efficiently. --- # ⭐ ABSOLUTE MUST-KNOW DEFINITIONS * **Diffusion:** Movement of particles from high to low concentration. * **Osmosis:** Movement of water through a partially permeable membrane from high to low water concentration. * **Active transport:** Movement from low to high concentration using energy. * **Magnification:** Image size ÷ real size. * **Resolution:** Ability to distinguish detail. * **Eukaryotic cell:** Cell with a nucleus. * **Prokaryotic cell:** Cell without a nucleus. If you can confidently explain every bullet point above, you're covering essentially the entire Cell Biology unit shown on your specification.

What is a microscope?

A tool used to see objects too small to be seen with the naked eye, used to study cells and microorganisms.

What are the two main types of microscopes?

Light microscope and electron microscope.

What are the characteristics of a light microscope?

Uses visible light, can observe living cells, has lower magnification and lower resolution.

What are the characteristics of an electron microscope?

Uses a beam of electrons, has much higher magnification and resolution, shows organelles and viruses in detail but cannot observe living cells.

How is magnification calculated?

Magnification = Image size / Real size.

What is resolution in microscopy?

The ability to distinguish two close points as separate; higher resolution equals a clearer image.

What are the advantages of using microscopes?

They allow the observation of cells and organelles, aid in diagnosing diseases, and facilitate scientific research.

What are the main components of an animal cell?

Nucleus, cytoplasm, cell membrane, mitochondria, ribosomes.

What are the additional components of a plant cell compared to an animal cell?

Cell wall, chloroplasts, vacuole.

What are eukaryotic cells?

Larger and more complex cells that have DNA enclosed in a nucleus and membrane-bound organelles, found in plants, animals, and fungi.

What are prokaryotic cells?

Smaller and simpler cells, such as bacteria, without a nucleus, with DNA free in the cytoplasm, and no membrane-bound organelles.

What are specialized adaptations of a sperm cell?

Long tail for swimming, many mitochondria for energy, enzyme-filled acrosome to penetrate the egg, haploid nucleus.

What is the function of a nerve cell?

Carries electrical impulses.

What is the primary function of muscle cells?

Contracts to create movement.

What are the adaptations of a root hair cell?

Long extension for increased surface area, thin cell wall, and many mitochondria.

What is the function of a palisade cell?

Photosynthesis.

What defines diffusion?

The net movement of particles from a region of high concentration to one of low concentration.

What factors affect the rate of diffusion?

Temperature, concentration gradient, surface area, distance.

What is osmosis?

The net movement of water molecules through a partially permeable membrane from a region of high water concentration to low.

What happens to animal cells during osmosis in a hypotonic solution?

Water enters the cell, making it swell or may burst.

What happens to plant cells during osmosis in a hypertonic solution?

Water leaves the cell, making it flaccid and potentially plasmolysed.

What is active transport?

The movement of substances from a region of low concentration to high concentration, requiring energy from respiration.

What are the adaptations of exchange surfaces?

Large surface area, thin membranes, good blood supply, and ventilation.

Why is surface area to volume ratio important for organisms?

Smaller organisms have a high SA:V ratio allowing for easier exchange of materials; larger organisms need specialized exchange surfaces.

Define diffusion.

Movement of particles from high to low concentration.

Define osmosis.

Movement of water through a partially permeable membrane from high to low water concentration.

Define active transport.

Movement from low to high concentration using energy.

Define magnification.

Image size ÷ real size.

Define resolution.

Ability to distinguish detail.

What is a eukaryotic cell?

A cell with a nucleus.

What is a prokaryotic cell?

A cell without a nucleus.