Topic 1: Cell Biology - AQA Biology GCSE

Cell Structure (1.1)

Eukaryotes and Prokaryotes (1.1.1)

• Eukaryotic Cells (Animal and Plant):
  • Components: Cell membrane, Cytoplasm, Nucleus containing DNA.
• Prokaryotic Cells (Bacterial):
  • Components: Cell wall, Cell membrane, Cytoplasm, Single circular strand of DNA, Plasmids.
  • Smaller than eukaryotic cells.

Orders of Magnitude

• Helps understand the size comparison between cells.
• Example: If an object is 10 times bigger, it's 10^1 times bigger.

Prefixes for Measurement

• Centi: 0.01
• Milli: 0.001
• Micro: 0.000001
• Nano: 0.000000001

Animals and Plants (1.1.2)

Subcellular Structures

• Animal and Plant Cells:

  • Nucleus: Contains DNA, enclosed in a nuclear membrane.
  • Cytoplasm: Site of chemical reactions, contains enzymes and organelles.
  • Cell Membrane: Regulates what enters and exits the cell.
  • Mitochondria: Site of aerobic respiration, provides energy.
  • Ribosomes: Protein synthesis, found on rough endoplasmic reticulum.

• Only in Plant Cells:

  • Chloroplasts: Site of photosynthesis, contains chlorophyll.
  • Permanent Vacuole: Contains cell sap, maintains cell rigidity.
  • Cell Wall: Made from cellulose, provides structural support.

Cell Specialisation (1.1.3)

• Differentiation: Process by which cells become specialized.
• Animal Cells Examples:
  • Sperm Cells: Streamlined for swimming, many mitochondria, acrosome contains enzymes.
  • Nerve Cells: Long axon for impulse transmission, dendrites for connections, neurotransmitter production.
  • Muscle Cells: Contract for movement, contain proteins myosin & actin, store glycogen.
• Plant Cells Examples:
  • Root Hair Cells: Large surface area, absorb water & minerals.
  • Xylem Cells: Transport water & minerals, lignin strengthens cells.
  • Phloem Cells: Transport food, sieve plates allow movement.

Cell Differentiation (1.1.4)

• Stem cells differentiate by gene activation/inactivation.
• Animal Cells: Differentiate early, mitosis for replacement.
• Plant Cells: Retain ability to differentiate and re-differentiate as needed.

Microscopy (1.1.5)

Light Microscopes

• Used for viewing tissues and cells.
• Maximum magnification of x2000.
• Resolving power of 200nm.

Electron Microscopes

• Two types: Scanning (3D images) and Transmission (2D images).
• Magnification up to x2,000,000.
• Higher resolving power than light microscopes.

Culturing Microorganisms (1.1.6 - Biology Only)

• Methods of Growth:
  • Nutrient broth solution.
  • Agar gel plates.
• Steps for Preparing Agar Plates:
  • Sterilize Petri dishes and inoculating loops.
  • Seal dishes partially to avoid contamination.
  • Incubate at 25 degrees to prevent harmful bacteria growth.

Cell Division (1.2)

Chromosomes (1.2.1)

• Chromosomes contain DNA; 23 pairs in each body cell.
• Gametes have 23 chromosomes in total.

Mitosis and Cell Cycle (1.2.2)

• Stages:
  • Interphase: Cell growth, DNA replication.
  • Mitosis: Chromosomes align and separate.
  • Cytokinesis: Division of cytoplasm, forming two daughter cells.
• Essential for growth, repair, asexual reproduction.

Stem Cells (1.2.3)

• Types:
  • Embryonic: Differentiate into any cell type.
  • Adult: Found in bone marrow, limited differentiation.
  • Plant Meristems: Retain differentiation ability for life.
• Therapeutic Cloning:
  • Produces cells with patient’s DNA.
  • Potential medical applications.

Transport in Cells (1.3)

Diffusion (1.3.1)

• Movement from high to low concentration.
• Influenced by concentration gradient, surface area, temperature.

Osmosis (1.3.2)

• Movement of water across membranes from high to low water potential.
• Affects cell turgor in plants, can cause animal cells to burst.

Active Transport (1.3.3)

• Movement against concentration gradient, requires energy.
• Important in root hair cells and nutrient absorption in the gut.