National 5 Cell Biology Summary Notes

Cell Structure

• Types of cells: Animal, plant, yeast, and bacterial.
• Organelles and Functions:
  1. Cell membrane: Controls entry and exit of materials (All cells)
  2. Ribosome: Site of protein synthesis (All cells)
  3. Cytoplasm: Site of chemical reactions (All cells)
  4. Mitochondria: Site of aerobic respiration (Animal, plant, yeast cells)
  5. Nucleus: Controls cell activities (Animal, plant, yeast cells)
  6. Cell wall: Supports the cell; made of cellulose in plant cells (Plant, yeast, bacterial cells)
  7. Vacuole: Contains cell sap (Plant, yeast cells)
  8. Chloroplast: Site of photosynthesis (Plant cells)
  9. Plasmid: Small ring of DNA (Bacterial cells)
• Microscopy: Use of stains to visualize organelles.

Transport Across Cell Membranes

• Cell membrane composition: Proteins and phospholipids.
• Passive transport (No energy required):
  • Diffusion: Movement from higher to lower concentration. Important for glucose, oxygen intake, CO2 removal.
  • Osmosis: Movement of water from high to low concentration through a selectively permeable membrane.
• Active transport: Requires energy to move substances against the gradient.

DNA and the Production of Proteins

• DNA: Carries genetic information; made of genes which code for proteins.
• Structure: Double helix with bases adenine-thymine and guanine-cytosine pairing.
• mRNA: Carries genetic code from DNA to ribosome for protein assembly.
• Proteins: Made of amino acids; types include antibodies, hormones, receptors, structural proteins, and enzymes.
  • Enzymes: Biological catalysts; specific to substrates; affected by temperature and pH.

Enzyme Reactions

• Degradation: Breaking down molecules (e.g., Catalase: hydrogen peroxide → oxygen + water).
• Synthesis: Building up molecules (e.g., Potato phosphorylase: glucose-1-phosphate → starch).
• Optimum conditions: Temperature and pH levels where enzyme activity is highest.

Genetic Engineering

• Process:
  1. Identify and extract the required gene.
  2. Extract plasmid from bacteria.
  3. Insert gene into plasmid.
  4. Insert plasmid into host cell to create GM organism.
• Applications: Production of human proteins like insulin.

Respiration

• Purpose: Release chemical energy from glucose through enzyme-controlled reactions.
• ATP: Energy molecule used for cellular activities (e.g., cell division, muscle contraction).
• Aerobic respiration: Occurs with oxygen, yielding large ATP from pyruvate breakdown into CO2 and water.
• Fermentation: Occurs without oxygen; yields lactate in animals, CO2 and ethanol in plants/yeast.
• Location: Begins in cytoplasm; aerobic respiration completed in mitochondria; fermentation in cytoplasm.
• Energy demand: Cells needing more energy (e.g., sperm cells) have more mitochondria.

Summary Word Equations

• Aerobic Respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy
• Fermentation (Animal Cells): Glucose → Lactate + Energy
• Fermentation (Plant/Yeast Cells): Glucose → Carbon dioxide + Ethanol + Energy