Comprehensive Study Notes: Biology B1-B9

Eukaryotic and Prokaryotic Cells

• Eukaryotic Cells:     * Definition: Cells that possess a nucleus where their genetic material is stored.     * Examples: Animal cells and plant cells are the primary examples of eukaryotic organisms.     * Key Features: They contain various membrane-bound organelles such as mitochondria and ribosomes.

• Prokaryotic Cells:     * Definition: Cells that are significantly smaller than eukaryotic cells and lack a defined nucleus.     * Genetic Material: Their DNA is not contained within a nucleus; instead, it is free within the cytoplasm and typically forms a single, continuous loop.     * Examples: All bacteria are classified as prokaryotes.     * Bacterial Cell Specific Structures:         * Plasmids: Small, circular rings of extra bacterial DNA.         * Flagella: Tail-like structures that provide motility, allowing the bacterial cell to move around (note: not all bacteria possess these).         * Slime Capsule: An outer layer used for protection and to prevent the cell from drying out (note: not all bacteria possess these).

Components of Cells and Their Functions

• Common to Animal and Plant Cells:     * Nucleus: This organelle controls all cell activity and contains the organism's DNA (genetic material).     * Cytoplasm: A liquid gel-like substance where the majority of chemical reactions within the cell take place.     * Cell Membrane: A biological barrier that controls the movement of substances into and out of the cell.     * Mitochondria: The site of aerobic respiration, which releases energy for the cell to use for various processes.     * Ribosomes: The site of protein synthesis; they are responsible for making proteins.

• Found Only in Plant Cells:     * Cell Wall: A structure that strengthens the cell. In plants and algae, it is composed of a strong substance known as cellulose.     * Chloroplasts: The site of photosynthesis. These organelles contain a green pigment called chlorophyll, which traps energy from sunlight.     * Permanent Vacuole: A space within the cytoplasm filled with cell sap. Its primary function is to keep the cell turgid (swollen and rigid) to provide structural support for the plant.

Studying Cells: Microscopy and Magnification

• Light Microscopes:     * Used to view cells with a magnification potential of up to $\times 2000$.

• Electron Microscopes:     * Possess a much higher magnification and resolution compared to light microscopes.     * These allow scientists to observe very small internal structures, such as ribosomes.

• Key Definitions:     * Magnification: This refers to how many times larger the image appears compared to the actual size of the object.     * Resolution: The ability of a microscope to distinguish between two separate points. Higher resolution results in finer detail in the image.

• Calculating Magnification:     * $\text{Total Magnification} = \text{Eyepiece Lens} \times \text{Objective Lens}$     * $\text{Magnification} = \frac{\text{Image Size}}{\text{Object Size}}$

• Orders of Magnitude:     * If an object is 10 times larger than another, it is 1 order of magnitude larger ($10^1$).     * If an object is 100 times larger, it is 2 orders of magnitude larger ($10^2$).

• Unit Conversions:     * $1\,\text{cm} = 10\,\text{mm}$     * $1\,\text{mm} = 1000\,\mu\text{m}$     * $1\,\mu\text{m} = 1000\,\text{nm}$     * To convert from mm to $\mu\text{m}$, multiply by $1000$. To go from $\mu\text{m}$ to mm, divide by $1000$.

• Size Examples:     * Salmonella bacterium: Width $0.5\,\mu\text{m}$, Length $1\,\mu\text{m}$.     * Cheek cell: Width $70\,\mu\text{m}$.

Transport In and Out of Cells

• Requirement for Transport: Cells must intake useful substances such as glucose and oxygen for respiration and eliminate waste products like carbon dioxide and urea. They must also regulate water content.

• Diffusion:     * Definition: The net movement of particles from an area of high concentration to an area of low concentration, moving down a concentration gradient.     * Passive Process: It does not require energy.     * Factors Affecting Rate:         * Temperature: Increased temperature causes particles to move faster, increasing the rate of diffusion.         * Surface Area: Larger surface areas (often created by folds in membranes) provide more space for diffusion to occur, increasing the rate.         * Concentration Gradient: A larger difference in concentrations creates a steeper gradient, which increases the rate.

• Osmosis:     * Definition: The movement of water molecules from a dilute solution to a concentrated solution across a partially permeable membrane.     * Passive Process: It does not require energy.     * In Animal Cells: In a concentrated solution, cells lose water ($H_2O$ out) and shrink. In a dilute solution, they gain water ($H_2O$ in).     * In Plant Cells: In a hypotonic (dilute) solution, water enters and the cell becomes a normal turgid cell. In a hypertonic (concentrated) solution, the cytoplasm shrinks away from the cell wall (plasmolysis).

• Active Transport:     * Definition: The movement of substances from an area of low concentration to an area of high concentration, moving against a concentration gradient.     * Requirement: This process requires energy.     * Examples:         * Root Hair Cells: Absorb mineral ions from a low concentration in the soil into the higher concentration within the cell.         * Small Intestine: Glucose is absorbed from a low concentration in the gut into a higher concentration in the blood.

Exchanging Substances and Surface Area to Volume Ratio

• Large Multicellular Organisms: These have a small surface area to volume (SA:V) ratio, meaning they cannot rely on simple diffusion from their surroundings to meet nutrient needs.

• Exchange Surfaces: Specialized organs adapted for efficient exchange include the lungs, small intestine, leaves, alveoli, and fish gills. Common adaptations include:     * Large surface area to maximize diffusion.     * Thin walls/membranes to provide a short diffusion path.     * Efficient blood supply to maintain a steep concentration gradient.     * Ventilation (in animals) to maintain a steep concentration gradient.

Cell Specialisation and Differentiation

• Cell Differentiation: The process by which cells change and acquire new structures to become specialized for a specific function.

• Examples of Specialised Animal Cells:     * Nerve Cell (Neurone):         * Dendrites and nerve endings: Make connections to communicate with other cells.         * Long Axon: Extends the cell to connect different body parts.     * Sperm Cell:         * Tail: Enables swimming to the egg cell.         * Mitochondria (Midpiece): Provides energy from respiration for the movement of the tail.         * Acrosome: Contains enzymes to penetrate the egg cell membrane.         * Haploid Nucleus: Contains half the DNA required to form an embryo.     * Muscle Cell:         * Fused Cells: Form muscle fibers that contract together for strong pulling force.         * Many Mitochondria: Release energy required for muscle contraction.

• Examples of Specialised Plant Cells:     * Phloem Vessels:         * Sieve Plates: Broken cell walls with holes that allow dissolved sugars to move through the plant.         * Companion Cells: Help keep phloem cells alive as they lack many internal structures.     * Xylem Vessels:         * Dead Cells: Fused to form a hollow, uninterrupted tube for water and mineral ion transport.         * Lignin: Thickens and strengthens walls to resist water pressure and support the plant.     * Root Hair Cell:         * Long Extension: Increases surface area for water and mineral absorption.         * Thin Walls: Provide a short pathway for transport.         * Large Vacuole: Increases the rate of osmosis into the cell.         * Many Mitochondria: Provide energy for the active transport of rare mineral ions.

Required Practical: Microscopy of Biological Specimens

• Preparing Stained Onion (Plant) Cells:     1. Place a drop of water on a microscope slide using a pipette.     2. Peel a thin layer of onion tissue and place it on the slide.     3. Add a drop of iodine stain.     4. Lower a cover slip onto the tissue, avoiding air bubbles.

• Preparing Stained Cheek (Animal) Cells:     1. Place a drop of water on a slide.     2. Swab the inside of the mouth with a clean cotton bud.     3. Transfer cells to the slide by rubbing the bud in the water.     4. Add a drop of methylene blue stain.     5. Lower a cover slip.

• Viewing the Slide:     1. Place slide on the stage.     2. Select the lowest power objective lens.     3. Move the stage up until just below the objective using the coarse adjustment knob.     4. Look through the eyepiece and move the stage down until the image is roughly focused.     5. Use the fine adjustment knob for a clear image.     6. Rotate the nosepiece for higher power objectives.     7. Draw with pencil, label with title and magnification (Eyepiece $\times$ Objective).

Required Practical: Osmosis in Plant Tissue

• Procedure:     1. Use a cork borer to cut five potato cylinders of identical diameter. Trim them to the same length and remove skin.     2. Blot the cylinders and measure the initial mass (or length).     3. Place each cylinder in a different concentration of salt/sugar solution.     4. Leave for one hour.     5. Remove, blot dry, and measure the final mass.

• Analysis:     * $\text{Percentage Change in Mass} = \frac{\text{Mass at End} - \text{Mass at Start}}{\text{Mass at Start}} \times 100$     * Percentage change allows comparison despite different starting masses.

• Variables:     * Independent: Concentration of the solution.     * Dependent: Change in mass of the potato.     * Control: Cylinder diameter/length, potato source, skin removal, temperature (water bath).

• Graph Interpretation:     * Positive change: Water entered by osmosis (solution was more dilute than cell contents).     * Negative change: Water left by osmosis (solution was more concentrated than cell contents).     * X-intercept (0% change): The concentration of the solution is equal to the concentration of the cell contents.

Cell Division and the Cell Cycle

• Chromosomes and DNA:     * The nucleus contains chromosomes made of DNA molecules.     * Each chromosome carries many genes.     * In body cells, chromosomes are usually found in pairs (one from each parent).

• The Cell Cycle and Mitosis:     * Mitosis is necessary for growth and repair, producing two identical daughter cells.     * Stage 1: DNA replication and production of new subcellular structures (ribosomes, mitochondria).     * Stage 2 (Mitosis): One set of chromosomes is pulled to each end of the cell, and the nucleus divides.     * Stage 3: The cytoplasm and cell membrane split to form two identical cells.

Stem Cells

• Definition: An undifferentiated cell capable of dividing to produce more stem cells or differentiating into specialized cells.

• Animal Stem Cells:     * Embryonic Stem Cells: Formed from a zygote; can differentiate into most cell types (muscle, blood, bone).     * Adult Bone Marrow: Can form many types of cells, including blood cells.

• Plant Stem Cells:     * Meristem Tissue: Located in roots and shoots; can differentiate into any plant cell type throughout the life of the plant.     * Uses: Producing clones quickly and cheaply, protecting rare species from extinction, and cloning crops with disease resistance.

• Therapeutic Applications and Risks:     * Stem cells can treat conditions like Type 1 Diabetes (replacing insulin cells) and paralysis (replacing nerve cells).     * Therapeutic Cloning: Creating an embryo with the same genes as the patient so stem cells are not rejected.     * Risks/Ethics: Viral transfer risks, ethical/religious objections regarding the use of embryos, and the issue of consent from the embryo.

• Therapeutic Cloning Steps:     1. Remove nucleus from a human egg cell.     2. Remove nucleus from patient's cell and transfer it to the donor egg.     3. Stimulate the cell to divide into an embryo.     4. After 4-5 days, remove and culture stem cells.

Organization and the Digestive System

• Hierarchical Levels: Cells $\rightarrow$ Tissues (similar cells) $\rightarrow$ Organs (different tissues) $\rightarrow$ Organ Systems (different organs).

• Chemistry of Food:     * Carbohydrates (e.g., Starch): Found in bread/pasta; used for energy. Broken down into glucose (sugar) by Amylase (a carbohydrase). Produced in salivary glands, pancreas, and small intestine.     * Proteins: Found in meat/eggs; used for growth and repair. Broken down into amino acids by Protease. Produced in the stomach, pancreas, and small intestine.     * Lipids (Fats/Oils): Found in butter; used for energy and cell membranes. Broken down into glycerol and 3 fatty acids by Lipase. Produced in the pancreas and small intestine.

• Efficiency of Digestion:     * Stomach: Acidic environment kills bacteria and provides optimum pH for protease.     * Bile: Made in liver, stored in gallbladder. Neutralizes stomach acid in the small intestine and emulsifies fat (breaks large drops into small droplets) to increase surface area for lipase.

Enzymes as Biological Catalysts

• Function: Speed up chemical reactions without being used up. They can build, break down, or change molecules.

• Lock and Key Theory:     1. The substrate has a shape complementary to the enzyme's active site.     2. The substrate fits into the active site.     3. The substrate is split into products.     4. Products leave; the enzyme remains unchanged.

• Factors Affecting Enzymes:     * Temperature: Increases rate up to the optimum; exceeding this alters the active site shape, and the enzyme is denatured.     * pH: Deviation from the optimum pH alters the active site shape and denatures the enzyme.

Food Tests (Required Practical 4)

• Preparation: Always crush food using a pestle and mortar first.

• Test for Sugar (Benedict's): Add solution and heat for 5 minutes. Blue $\rightarrow$ light green (little sugar); Blue $\rightarrow$ brick red (a lot of sugar).

• Test for Protein (Biuret): Add reagent and shake. Blue $\rightarrow$ lilac.

• Test for Starch (Iodine): Add reagent and shake. Orange $\rightarrow$ blue/black.

• Test for Lipids (Ethanol): Add water and ethanol and shake. Formation of a milky white emulsion.

The Circulatory System

• Purpose: Transport oxygen (from lungs) and glucose (from digestion) to cells for respiration; remove waste like $CO_2$ and urea.

• Blood Components:     * Red Blood Cells: Carry oxygen; biconcave shape for SA; contain haemoglobin.     * White Blood Cells: Immune system; perform phagocytosis (engulfing pathogens) or produce antibodies.     * Platelets: Cell fragments that cause clotting at wounds.     * Plasma: Straw-colored fluid; carries dissolved substances ($CO_2$, glucose, urea) and cells.

• Blood Vessels:     * Arteries: Carry blood Away from heart; thick muscular/elastic walls for high pressure; small lumen.     * Veins: Take blood Into the heart; thinner walls; large lumen; contain valves to prevent backflow.     * Capillaries: 1 cell thick; tiny lumen; allow diffusion of oxygen and $CO_2$ in lungs and tissues.

• Double Circulatory System: Blood visits the heart twice per journey. This increases pressure for delivery to cells.

The Heart and Heart Disease

• Heart Structure:     * Right Atrium: Contains pacemaker cells to control heart rate.     * Left Ventricle: Has a very thick muscular wall to pump blood to the entire body via the aorta.     * Pathway: Vena Cava $\rightarrow$ Right Atrium $\rightarrow$ Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs (oxygenation) $\rightarrow$ Pulmonary Vein $\rightarrow$ Left Atrium $\rightarrow$ Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Body.

• Coronary Heart Disease (CHD): Fatty material narrows coronary arteries, reducing oxygen to the heart muscle.

• Treatments:     * Statins: Reduce blood cholesterol level to slow fatty deposit rate.     * Stents: Keep coronary arteries open.     * Pacemakers: Electrical device to correct irregular heart rhythms.     * Valves: Biological (pig/human) or mechanical (man-made) to replace leaky valves.     * Transplants: From human donors for heart failure; artificial hearts used while waiting.

Respiratory System and Gas Exchange

• Pathway: Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli.

• Alveoli Adaptations:     * Thin walls: Short diffusion distance.     * Huge Surface Area: Due to large numbers and round shape.     * Capillary Network: Constant blood flow maintains a steep concentration gradient.

Plant Organ Systems and Transport

• Root Hair Cells: Absorb water (osmosis) and ions (active transport).

• Xylem Tissue: Transports water and minerals from roots to leaves (Transpiration). Made of hollow dead cells strengthened with lignin.

• Phloem Tissue: Transports dissolved sugars around the plant (Translocation). Made of elongated cells with end pores; supported by companion cells.

• Transpiration Factors:     * Temperature: Higher temp increases evaporation, increasing transpiration.     * Humidity: High humidity decreases evaporation, decreasing transpiration.     * Wind: Increases evaporation and transpiration.     * Light Intensity: Bright light opens stomata for photosynthesis, increasing transpiration.

Leaf Structure and Photosynthesis

• Layers:     * Waxy Cuticle: Waterproof; prevents water loss from the top.     * Epidermis: Transparent to allow light through.     * Palisade Mesophyll: Contains many chloroplasts; located at the top to trap light.     * Spongy Mesophyll: Air spaces for gas exchange ($CO_2$ to palisade cells).     * Stomata & Guard Cells: Pores on the underside; guard cells open them for pulses of $CO_2$ and close them at night.

• Photosynthesis Reaction: Endothermic (takes in sunlight).     * $\text{Carbon Dioxide} + \text{Water} \xrightarrow{\text{light}} \text{Glucose} + \text{Oxygen}$     * $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

• Glucose Uses: Respiration, conversion to starch, making fats/oils, cellulose for cell walls, and amino acids (with nitrate ions).

• Limiting Factors: Light intensity, temperature, $CO_2$ concentration, and chlorophyll amount.

• HT Rule: Inverse Square Law: $\text{Light Intensity} \propto \frac{1}{\text{distance}^2}$.

Health, Disease, and Drugs

• Communicable diseases: Caused by pathogens (Viruses, Bacteria, Protists, Fungi).     * Measles/HIV/TMV: Viruses.     * Salmonella/Gonorrhoea: Bacteria.     * Malaria: Protist.     * Rose Black Spot: Fungus.

• Vaccination: Introducing dead/inactive pathogens. White blood cells produce antibodies. Upon re-infection, they produce them faster and in higher concentrations.

• Drug Development:     * Digitalis: Foxgloves; Aspirin: Willow; Penicillin: Fleming's mould.     * Stages: Preclinical (cells, tissues, animals); Clinical (healthy volunteers for toxicity, then patients for efficacy/dose).     * Double-blind trials: Placebo used; neither doctor nor patient knows who has the real drug.

• Non-Communicable Diseases: Not infectious; linked to risk factors (Smoking, Diet, Alcohol).     * Causal Mechanisms: Proven biological explanations (e.g., smoking $\rightarrow$ lung cancer via carcinogens in tar).     * Cancer: Uncontrolled cell division. Benign (contained, non-cancerous); Malignant (invades other tissues, cancerous, forms secondary tumours via blood).

Respiration and Metabolism

• Aerobic Respiration: Exothermic; moves energy to environment.     * $\text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water}$     * $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$

• Anaerobic Respiration: Without oxygen.     * Animals: $\text{Glucose} \rightarrow \text{Lactic Acid}$     * Yeast: $\text{Glucose} \rightarrow \text{Ethanol} + \text{Carbon Dioxide}$ (Fermentation).

• Exercise Response: Heart and breathing rates increase to deliver oxygen/glucose and remove $CO_2$. Insufficient oxygen leads to anaerobic respiration and oxygen debt.

• Metabolism: All chemical reactions in the body. Includes converting glucose to starch/glycogen, making lipids from glycerol and fatty acids, and breaking down proteins into urea in the liver.