Year 9 Biology Revision Notes

Cell Structure

  • Types of Cells:

    • Cells are classified into two main types:
    • Prokaryotes:
      • Size: Smaller
      • Genetic Material: Circular DNA not enclosed in a nucleus; may contain plasmids.
      • Mitochondria: None
    • Eukaryotes:
      • Size: Larger
      • Genetic Material: DNA organized into chromosomes within a nucleus; no plasmids.
      • Mitochondria: Present

  • Animal and Plant Cell Structures:

    • Animal Cells:
    • Nucleus: Controls cell activities.
    • Cytoplasm: Site of chemical reactions.
    • Cell Membrane: Regulates passage of molecules.
    • Mitochondria: Site of aerobic respiration (energy release).
    • Ribosomes: Site of protein synthesis.
    • Plant Cells:
    • Chloroplasts: Photosynthesis site.
    • Permanent Vacuole: Maintains turgor pressure.
    • Cell Wall: Composed of cellulose, provides structure.

Cell Differentiation

  • Definition:
    • The process where cells become specialized for specific functions as organisms develop.
  • Characteristics:
    • Most animal cells differentiate early, while plant cells can differentiate throughout life.

Specialised Cells

  • Root Hair Cell:
    • Adaptations: Large surface area for absorption; large vacuole; many mitochondria for active transport.
  • Palisade Cell:
    • Adaptations: Column shape, tightly packed with chloroplasts.
  • Xylem Cells:
    • Adaptations: Hollow tubes, lignin-reinforced walls for transportation.
  • Phloem Cells:
    • Adaptations: Sieve-like walls allowing free movement of sugars.
  • Nerve Cells (Neurones):
    • Adaptations: Elongated; dendrites for connections; myelin sheath for insulation.
  • Sperm Cell:
    • Adaptations: Large nucleus; tail for movement; many mitochondria; acrosome with enzymes.
  • Muscle Cell:
    • Adaptations: Contains contractile proteins; high mitochondria; stores glycogen.

Microscopy

  • Light Microscope:
    • Limited magnification, suitable for larger structures (e.g., nucleus).
  • Electron Microscope:
    • High magnification, suitable for smaller structures (e.g., mitochondria).
  • Magnification Formula:
    ext{magnification} = rac{ ext{size of image}}{ ext{size of actual object}}

Culturing Microorganisms

  • Bacterial Multiplication:
    • Via binary fission; occurs every 20 minutes under optimal conditions.
  • Culturing Methods:
    • In liquid nutrient broth or on solid agar plates.

Cell Division

  • Mitosis:
    • Produces genetically identical daughter cells.
    • Involves replication of DNA and organelles.
  • Human Chromosomes:
    • 46 chromosomes (23 pairs); contain genes for protein coding.

Stem Cells

  • Definition:
    • Undifferentiated cells capable of division into various cell types.
  • Sources:
    • Early embryos, meristem tissue in plants, bone marrow in adults.
  • Ethical Concerns:
    • Stem cells from embryos raise ethical issues; potential for cancer, and virus transmission.

Therapeutic Cloning

  • Process:
    • Cells from a patient create a cloned embryo for generating stem cells, which differentiate into tissues.
  • Applications:
    • Potential treatments for conditions such as diabetes and paralysis.

Transport in Cells

  • Diffusion:
    • Movement from high to low concentration.
    • Factors affecting rate include concentration gradient, temperature, surface area, and distance.
  • Osmosis:
    • Movement of water across a semi-permeable membrane from high water concentration to low.
  • Active Transport:
    • Movement against concentration gradient, requiring energy from respiration.

Organizational Structure in Animals

  • Levels of Organization:
    • Cells → Tissues → Organs → Organ Systems → Organisms.

Enzymes - Biological Catalysts

  • Function:
    • Speed up reactions without being consumed.
  • Active Site:
    • Specific shape for substrate binding (Lock and Key model).
  • Factors Affecting Action:
    • Temperature and pH can denature enzymes, affecting efficiency.

Digestive System

  • Digestive Enzymes:
    • Carbohydrases: Break down starch into sugars.
    • Proteases: Breakdown proteins into amino acids.
    • Lipases: Breakdown fats into fatty acids and glycerol.
  • Absorption of Nutrients:
    • Microvilli increase surface area for nutrient absorption in the small intestine.

The Circulatory System

  • Components:
    • Heart, blood vessels, blood.
  • Heart Function:
    • Pumps blood through two circuits (pulmonary and systemic).

Blood Composition and Functions

  • Red Blood Cells:
    • Carry oxygen via haemoglobin.
  • Platelets:
    • Involved in blood clotting.
  • Plasma:
    • Transports nutrients and wastes.

Health Issues

  • Disease Types:
    • Communicable (infectious) and Non-communicable (caused by lifestyle).
  • Tumours:
    • Benign (non-invasive) vs. malignant (invasive, cancerous).

Plant Tissues and Transport

  • Types of Plant Tissues:
    • Epidermal, palisade, spongy mesophyll, xylem, phloem, and meristem tissues.
  • Water and Mineral Uptake:
    • Roots are adapted for absorption; transpiration stream maintains water supply.
  • Translocation of Sugars:
    • Phloem transports sugars from photosynthesis to growth/storage areas.