Detailed Notes - Topic 1: Cell Biology (AQA Biology GCSE)

Overview

• This material covers Cell Biology, a key section in the AQA GCSE Biology curriculum.
• Content is applicable for both separate and double award students.
• Some advanced content is highlighted for higher-tier students.

Cell Structure (1.1)

Eukaryotes and Prokaryotes (1.1.1)

• Eukaryotic cells: Found in animals and plants.
  • Contain cell membrane, cytoplasm, nucleus (with DNA).
• Prokaryotic cells: Smaller, found in bacteria.
  • Contain cell wall, cell membrane, cytoplasm, single circular DNA, and plasmids.
• Organelles: Structures within cells with specific functions.
• Orders of magnitude help describe size differences:
  • 10 times larger = 10^1 times, 1000 times = 10^3 times, and so on.
• Prefixes:
  • Centi (0.01), Milli (0.001), Micro (0.000001), Nano (0.000000001).

Animals and Plants (1.1.2)

• Animal and Plant Cell Structures:
  • Nucleus: Contains DNA, enclosed in nuclear membrane.
  • Cytoplasm: Site of chemical reactions, contains enzymes.
  • Cell membrane: Regulates entry and exit of substances.
  • Mitochondria: Site of aerobic respiration.
  • Ribosomes: Protein synthesis occurs here.
• Plant-Specific Structures:
  • Chloroplasts: Site of photosynthesis, contain chlorophyll.
  • Permanent vacuole: Maintains cell rigidity, stores cell sap.
  • Cell wall: Made of cellulose, provides strength.

Cell Specialisation (1.1.3)

• Differentiation: Process where cells gain new structures.
  • Stem cells can differentiate throughout life (in plants) or once (in animals).
• Examples of Specialized Animal Cells:
  • Sperm Cells: Streamlined for swimming, contain many mitochondria.
  • Nerve Cells: Transmit signals, have long axons and dendrites.
  • Muscle Cells: Contract to enable movement, contain proteins and mitochondria.
• Specialized Plant Cells:
  • Root Hair Cells: Absorb water and minerals.
  • Xylem Cells: Transport water and minerals.
  • Phloem Cells: Transport products of photosynthesis.

Microscopy (1.1.5)

• Light Microscopes:
  • Max magnification ~x2000, resolving power ~200nm.
  • Uses light and two lenses.
• Electron Microscopes:
  • Use electrons, higher magnification (up to x2,000,000).
  • Types: Scanning Electron Microscope (3D images), Transmission Electron Microscope (2D detailed images).

Culturing Microorganisms (1.1.6 - Biology Only)

• Methods:
  • Nutrient Broth: Shaken regularly for oxygen distribution.
  • Agar Gel Plates: Inoculating loop spreads microorganisms.
• Ensuring Sterility:
  • Sterilize Petri dishes/media to avoid contamination.
  • Use antibiotics to test bacterial growth inhibition.

Cell Division (1.2)

Chromosomes (1.2.1)

• Genetic information in chromosomes, 23 pairs in each cell except gametes.

Mitosis and the Cell Cycle (1.2.2)

• Stages:
  • Interphase: Growth and DNA replication.
  • Mitosis: Chromosomes separate.
  • Cytokinesis: Formation of two daughter cells.

Stem Cells (1.2.3)

• Types: Embryonic, Adult (bone marrow), Meristems (plants).
• Uses: Therapeutic cloning, research, disease treatment.
• Ethical Considerations: Destruction of embryos, potential for disease transmission.

Transport in Cells (1.3)

Diffusion (1.3.1)

• Process: Movement from high to low concentration, passive.
• Factors: Concentration gradient, surface area, temperature.

Osmosis (1.3.2)

• Process: Water movement through a partially permeable membrane.
• Effects:
  • Plant cells: Turgid (in dilute solution), plasmolysed (in concentrated solution).
  • Animal cells: Can burst or shrink depending on solution concentration.

Active Transport (1.3.3)

• Process: Movement against concentration gradient, requires energy.
• Examples: Mineral uptake in roots, nutrient absorption in the gut.

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This summary provides an overview of the key concepts in Cell Biology covered in the AQA Biology GCSE curriculum, including cell structure, specialization, microscopy, culturing microorganisms, cell division, and the processes of transport across cell membranes.