Edexcel Biology GCSE - Topic 1: Key Concepts in Biology

Edexcel Biology GCSE

Topic 1: Key Concepts in Biology

Table of Contents

• 1.1 - Eukaryotic and Prokaryotic Cell Functions

• 1.2 - Specialised Cells and their Functions

• 1.3 - Microscopy

• 1.4 - Size, Scale and Estimations

• 1.5 - Units and Standard Form

• 1.6 - Core Practical - Investigating Biological Specimens

• 1.7 - Enzyme Action

• 1.8 - Enzyme Denaturation

• 1.9 - Changing Enzyme Activity

• 1.10 - Core Practical - Effect of pH on Enzyme Activity

• 1.11 - Rate Calculations

• 1.12 - Enzymes as Biological Catalysts

• 1.13B - Higher and Biology Only Core Practical - Investigating Macronutrients

• 1.14B - Higher and Biology Only Calorimetry

• 1.15 - Cell Transport

• 1.16 - Core Practical - Investigate Osmosis in Potatoes

• 1.17 - Calculating Percentage Gain and Loss

1.1 - Eukaryotic and Prokaryotic Cell Functions

• All living things are made of cells, which can be classified into two main types: prokaryotic and eukaryotic.

• Eukaryotic Cells
    - Found in animals and plants.
    - Key structures include:
      - Cell membrane
      - Cytoplasm
      - Nucleus containing DNA

• Prokaryotic Cells (example: bacterial cells)
    - Much smaller than eukaryotic cells.
    - Key structures include:
      - Cell wall
      - Cell membrane
      - Cytoplasm
      - Single circular strand of DNA and plasmids (small rings of DNA found in the cytoplasm).

• Organelles
    - Defined as structures within cells that perform specific functions.
    - Organelles in Animal and Plant Cells:
      - Nucleus:
        - Contains DNA coding required for protein synthesis essential for building new cells.
        - Enclosed in a nuclear membrane.
      - Cytoplasm:
        - The liquid medium where the majority of chemical reactions occur.
        - Contains biological catalysts known as enzymes.
        - Organelles are suspended within it.
      - Cell membrane:
        - Controls the influx and efflux of substances into and out of the cell.
      - Mitochondria:
        - Site of aerobic respiration, generating energy for the cell.
      - Ribosomes:
        - Location of protein synthesis; associated with rough endoplasmic reticulum.

1.2 - Specialised Cells and Their Functions

• Cell Specialisation
    - Occurs through a process called differentiation where cells acquire new organelles appropriate for their specific roles.
    - In animals, most cells differentiate only once; whereas in plants, many retain the ability to differentiate throughout their lives (these are called stem cells).

• Examples of Specialised Cells in Animals
    1. Sperm Cells:
       - Function: Transport male DNA to the egg cell (ovum) for fertilization.
       - Characteristics:
         - Streamlined head and long tail facilitating swimming.
         - Many mitochondria to provide energy for movement.
         - Acrosome at the head contains enzymes for penetrating the egg membrane.
         - Haploid Nucleus: Contains 23 chromosomes (half the number in typical body cells).
    2. Egg Cells:
       - Function: Accept a single sperm cell and develop into an embryo.
       - Characteristics:
         - Special cell membrane that becomes impermeable after a sperm has entered.
         - Numerous mitochondria for energy provision during embryo development.
         - Large size and abundant cytoplasm facilitate rapid division as the embryo forms.
    3. Ciliated Epithelial Cells:
       - Function: Transport mucus and trapped bacteria to the stomach where bacteria are destroyed.
       - Characteristics:
         - Long cilia waft mucus containing trapped bacteria down towards the stomach.

• Examples of Specialised Cells in Plants
    1. Root Hair Cells:
       - Function: Uptake water and minerals from the soil.
       - Characteristics:
         - Large surface area to enhance water absorption.
         - Permanent vacuole affects the speed of water movement from soil to cell.
         - Mitochondria provide energy for active transport of minerals.
    2. Xylem Cells:
       - Function: Transport water and minerals from roots to shoots.
       - Characteristics:
         - Formed by cells that die and become hollow tubes reinforced with lignin.
         - Lignin is deposited in spirals for structural integrity against water pressure.
    3. Phloem Cells:
       - Function: Distribute products of photosynthesis throughout the plant.
       - Characteristics:
         - Form sieve plates from cell wall breakdown allowing substance movement.
         - Depend on companion cells for energy supplied by mitochondria.

1.3 - Microscopy

• Microscopes are essential for observing tiny structures such as cells.

• Light Microscope
    - Historical Note: First observed in cork by Robert Hooke in 1665.
    - Characteristics:
       - Contains two lenses and illuminates samples from underneath.
       - Maximum magnification is approximately 2000x with a resolving power of 200nm.
       - Good for viewing tissues, cells, and larger organelles.

• Electron Microscope
    - Developed in the 1930s, uses electrons to form images due to their shorter wavelength compared to light.
    - Types:
       - Scanning Electron Microscope (SEM): Produces 3D images but at lower magnification.
       - Transmission Electron Microscope (TEM): Provides detailed 2D images.
    - Capabilities:
       - Magnification up to 2,000,000x with resolving power of 10nm (SEM) and 0.2nm (TEM).
    - Applications: Useful for observing organelles like mitochondria, viruses, and structures such as ribosomes in detail.

1.4 - Size, Scale, and Estimations

• Common calculations related to microscopy:
    1. Magnification Calculation:
       - Formula: $ext{Magnification} = ext{Eyepiece Magnification} imes ext{Objective Magnification}$
    2. Size of an Object:
       - Formula: $ext{Size of Object} = rac{ ext{Size of Image}}{ ext{Magnification}}$

• Standard Form:
    - Useful for handling very large or small numbers, typically represented as a product of a number between 1 and 10 and a power of ten.
    - Examples:
       - $1.5 imes 10^{-5} = 0.000015$
       - $3.4 imes 10^{3} = 3400$

• Estimations:
    - Aids in biological studies when exact counts are impractical.
    - Example of estimating the number of dandelions in a field:
      - In a 1m x 1m square containing 15 dandelions within a field measuring 50m x 50m, calculate total dandelions:
      - Field contains 2500 squares of 1m x 1m:
        - Total Dandelions = 15 × 2500 = 37,500.
    - Prefixes for Measurements:
      - Centi (0.01), Milli (0.001), Micro (0.000001), Nano (0.000000001).

1.6 - Core Practical: Investigating Biological Specimens

• Familiarity with the parts and usage of a light microscope is essential:
    - Eyepiece: The lens through which specimens are viewed.
    - Barrel: The adjustable part for focusing.
    - Turret: The rotating part to change magnification.
    - Stage: Flat surface for placing the specimen.

• Procedure for Using a Light Microscope:
    1. Position slide on the stage.
    2. Look through eyepiece and adjust focus with the focus wheel.
    3. Start with the lowest magnification and gradually increase.

• Proper specimen slide preparation:
    1. Prepare thin layers of cells.
    2. Apply chemical stains as instructed for visibility.
    3. Place cell samples on a glass slide.
    4. Lower the coverslip gently to avoid bubbles.

• Magnification Calculation:
    - Overall Magnification:
        - $ext{Magnitude} = rac{ ext{Measured Size}}{ ext{Actual Size}}$
        - Actual Size = $rac{ ext{Measured Size}}{ ext{Magnification}}$

1.7, 1.8 & 1.9 - Enzymes: Mechanisms, Denaturation, and Factors Affecting Activity

• Enzymes: Biological catalysts that increase reaction rates without altering their form.
    - Role: Can break down large molecules or synthesize smaller ones.
    - Structure: Proteins with a specific active site shape for substrate binding.

• Lock and Key Hypothesis:
    - Describes how enzymes interact with substrates:
      1. The substrate's shape is complementary to fits the enzyme's active site, forming an enzyme-substrate complex.
      2. The reaction occurs and the products are released from the active site.
    - Enzyme specificity limits enzyme-catalyzed reactions to certain substrates.

• Factors affecting Enzyme Activity:
    1. Temperature:
        - Optimal temperature for human enzymes is around 37°C.
        - Reaction rate rises with temperature until reaching optimal peak, beyond which it declines due to denaturation.
    2. pH Levels:
        - Most enzymes operate optimally at pH 7, though some pathogens have different optimal pH levels.
        - Deviations from optimal pH can lead to denaturation.
    3. Substrate Concentration:
        - Increasing substrate concentration initially raises reaction rates until reaching the saturation point—beyond which reaction rates plateau.

1.10 - Core Practical - Effect of pH on Enzyme Activity

• Investigation: Examining how pH values influence amylase activity (enzyme that breaks down starch into maltose).

• Materials:
    - 1% amylase solution, 1% starch solution, iodine solution, buffer solutions at varying pH levels.

• Method:
    1. Place iodine drops on wells of a tray.
    2. Heat buffer solution at the desired pH in a water bath for 3 minutes.
    3. Mix amylase, starch, and buffer in a test tube and start timing.
    4. Test drops for starch presence using iodine until the color remains unchanged.
    5. Repeat for various pH levels.

• Optimal pH Expectation: Should occur at the pH where the shortest reaction time is noted, likely around pH 7.

1.11 - Rate Calculations for Enzyme Activity

• Calculating the rate of enzyme-catalyzed reactions is essential:
    - Formula:
      $ext{Rate} = rac{ ext{Change}}{ ext{Time}}$
    - Example: If 5g of protein is converted over 30 minutes:
      - $ext{Rate} = rac{5g}{30 ext{ minutes}} = rac{5g}{0.5 ext{ hours}} = 10g/ ext{hour}$

1.12 - Enzymes as Biological Catalysts

• Types of Enzymes:
    1. Carbohydrases: Break down carbohydrates into simple sugars (e.g., amylase converts starch to maltose).
       - Found in salivary glands, pancreas, and small intestine.
    2. Proteases: Break down proteins into amino acids (e.g., pepsin located in the stomach).
    3. Lipases: Convert lipids into fatty acids and glycerol (produced in pancreas and small intestine).

• Products of digestion are absorbed into the bloodstream to construct new biomolecules and provide energy for cellular respiration.

1.13B Higher and Biology Only - Core Practical: Investigating Macronutrients

• Tests to identify presence of key nutrients in food samples:
    1. Starch:
       - Reagent: Iodine solution changes from orange to blue-black if starch is present.
    2. Reducing Sugars:
       - Test: Benedict's solution turns reddish-brown upon boiling with reducing sugars.
    3. Protein:
       - Test: Biuret test (add potassium hydroxide followed by copper sulfate) changes from blue to violet with proteins.
    4. Lipids:
       - Test: Emulsion test (adding ethanol then water), resulting in a white emulsion indicates presence of lipids.

1.14B Higher and Biology Only - Calorimetry

• Calorimetry: Measuring energy in reactions, specifically in food samples.

• Procedure:
    1. Start with 50ml of cold water and record its temperature.
    2. Hold a burning food sample beneath the test tube.
    3. Record the final temperature of the water once food burns out.

• Energy Calculation:
    - $ext{Energy Transferred} = ext{Mass of Water} imes 4.2 imes ext{Temperature Increase}$
      - Units: Energy in Joules (J), Mass in grams (g), Temperature increase in °C, specific heat capacity of water is 4.2 J/g.

1.15 - Cell Transport

• Essential for maintaining cellular function by transporting substances like oxygen and glucose.

• Types of Transport:
    1. Diffusion:
       - Passive transport; molecules spread from high to low concentration.
    2. Osmosis:
       - Passive transport but specifically for water, moving from dilute to concentrated solutions across a selectively permeable membrane.
    3. Active Transport:
       - Requires energy from ATP; works against concentration gradients from low to high concentration.

1.16 - Core Practical - Osmosis in Potatoes

• Investigation: Exploring how potato cells change mass in sucrose solutions of varying concentrations.

• Procedure:
    1. Cut potato into uniform 2cm diameter disks.
    2. Blot excess moisture and measure initial mass.
    3. Place disks in different concentrations of sucrose (1%, 2%, etc.), then mass again.
    4. Record mass difference and calculate percentage change using:
       - $ext{Percentage Change} = rac{ ext{Change in Mass}}{ ext{Initial Mass}} imes 100$

• Variables:
    - Independent: Concentration of sucrose
    - Dependent: Change in mass of potato disks
    - Control: Diameter of potato discs

• Outcome: Osmosis will result in water movement from lower to higher sucrose concentration, affecting mass.

1.17 - Calculating Percentage Gain and Loss of Mass

• To calculate:
    - Use the percentage change formula specified above to understand how sucrose concentration affects the potato chips.

• Conclusions on Osmosis: Water flows from areas of higher water potential (in potato) to areas of lower water potential (in sucrose solution), affecting the integrity and mass of the potato cells.

END OF NOTES