Biology revision

• The nucleus is the control centre of the cell, containing DNA which controls all activities within the cell.
• Plasma membrane:

  • Cells exist in a watery environment of extracellular fluid
  • Controls the movement of substances between extracellular and intracellular fluid
  • Forms a boundary
• Multicellular extracellular fluid:

  • More complex organisms have more control in their environment
  • Regulates temperature, pH, osmotic pressure, and oxygen levels
• Plasma membrane composition:

  • Structure described by the Fluid Mosaic model
  • Consists of two layers of phospholipid molecules
  • Includes proteins, carbohydrates, and cholesterol
• Phospholipids:

  • Have a hydrophobic tail and a hydrophilic head
  • Heads face outwards and inwards, tails are in the middle
  • Make the plasma membrane impermeable to water-soluble particles, ions, and polar molecules
  • Fluidity depends on the % of unsaturated fatty acids
• Cholesterol:

  • Provides stability to the membrane without affecting fluidity
  • Reduces permeability to small water molecules
• Proteins:

  • Integral proteins are permanent parts of the membrane (channel and carrier)
  • Peripheral proteins are temporary parts
  • Globular proteins are needed for immune response
• Carbohydrates:

  • Linked to protruding proteins (glycoprotein) or lipids (glycolipids) on the membrane surface
  • Play a role in recognition and adhesion between cells
• Active transport:

  • Requires energy (ATP)
  • Moves substances against the concentration gradient (low to high)
  • Two types: protein-mediated transport and bulk transport
• Endocytosis and Exocytosis:

  • Endocytosis: movement of substances into the cell
  • Exocytosis: movement of substances out of the cell
  • Exocytosis requires energy (ATP)
• Cell theory:

  • All cells come from pre-existing cells
  • All types of cells perform similar basic processes and may have specialized functions
  • Cells require a lot of energy
• Types of cells:

  • Prokaryotes: composed of prokaryotic cells, no nucleus, no membrane-bound organelles, less complex
  • Eukaryotes: composed of eukaryotic cells, more complex, contain membrane-bound organelles, have a nucleus
• Common features of cells:

  • Plasma membrane (phospholipid bilayer)
  • Cytoplasm (liquid)
  • DNA
  • Ribosomes (make protein RNA)
• Organelles:

  • Nucleus: contains most DNA, site of DNA replication
  • Ribosomes: sites of protein synthesis
  • Endoplasmic reticulum: rough (RER) and smooth (SER)
  • Golgi apparatus: center of manufacturing, storing, sorting, and shipping
  • Lysosome: digests and breaks down unwanted matter
• Energy transformations:

  • Mitochondria: powerhouse of the cell, site of cellular respiration
  • Chloroplast: found in plants, trap light energy for glucose production
• Storage and Cell structure:

  • Vacuoles: store enzymes and molecules, provide structural support in plants
  • Plasma membrane: controls cell entry and exit
  • Cell wall: support and prevents expansion in plants
  • Cytoplasm: contains organelles and substances for cell metabolism
• Cilia and flagella:

  • Cilia: short, numerous hair-like structures for movement
  • Flagella: long, whip-like structure for movement
• Key scientific skills:

  • Graphing: appropriate heading, labeled axes, correct results, appropriate graph type
  • Errors: personal errors, systematic errors, random errors