Unit 1

• The specification is an important starting point for revising for GCSE Science tests and exams
• Exam papers are written from the specifications, not from revision guides or textbooks
• Mark schemes have reference points to where the questions came from in the specification
• Eukaryotes


  Animals and plants
• Animal cell


  • Nucleus
  • Cytoplasm
  • Cell membrane
• Plant cell


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Sap vacuole
  • Chloroplast
• Prokaryotes


  Bacterial cells with no nucleus or subcellular structures with membranes
• Approximate sizes: Animal cell 10 micrometers, Plant cell 50 micrometers, Prokaryote 5 micrometers
• Nerve cell


  • Cell body
  • Dendrites
  • Axon
  • Insulating sheath
  • Axon terminals
• Sperm cell


  • Mid piece with mitochondria
  • Tail
  • Acrosome
• Muscle cell


  • Fibers for contraction
  • Mitochondria
  • Glycogen store
• Xylem cell


  • No end plates
  • No cytoplasm
  • Lignin rings for support
• Phloem cell


  • Little cytoplasm
  • End plates with pores
  • Companion cells
• Root hair cell


  • Large surface area
  • Many mitochondria
• Microscopes


  Simple microscopes have low magnification and resolving power

  Electron microscopes have high magnification and resolving power
• Calculating magnification


  Magnification = Size of image / Size of real object
• Culturing microorganisms


  Sterilise equipment

  Inoculate agar plate with sample

  Incubate at 25°C

  Test antibiotics/antiseptics
• Cell cycle


  Growth and DNA replication

  Mitosis (chromosomes line up, divide, cytoplasm divides)

  Daughter cells genetically identical
• Stem cells


  • Embryonic stem cells are undifferentiated

  Can differentiate into any cell type
• Cell growth and division

  1. Cell grows and increases number of subcellular structures

  2. DNA replicates to form two copies of each chromosome

  3. Chromosomes line up along center and are pulled to each end of cell

  4. Nucleus divides

  5. Cytoplasm and cell membranes divide to form two genetically identical cells
• Mitosis


  The process of cell division described above
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Plant stem cells (meristem tissue)
• Embryonic stem cells


  • Undifferentiated
  • Can be cloned
  • Can differentiate into most other cell types
• Adult stem cells


  • Found in bone marrow
  • Can differentiate into many cell types, mainly blood cells
• Plant stem cells


  • Found in meristem tissue in root and shoot tips
  • Can differentiate into any plant cell
• Therapeutic cloning


  1. Patient body cell nucleus removed

  2. Nucleus inserted into enucleated human egg cell

  3. Cloned and stem cells produced

  4. Stem cells differentiated into specialized cells/tissues for treatment
• Diffusion


  Spreading out of particles in a solution or gas, with net movement from higher to lower concentration
• Factors affecting rate of diffusion: concentration gradient, temperature, surface area
• Active transport


  Movement of particles from lower to higher concentration, requires energy
• Diffusion in living things

  • Oxygen diffusing into cells from blood
  • Carbon dioxide diffusing out of cells into blood
  • Urea diffusing out of cells
• Single-celled organisms


  • Have high surface area to volume ratio, allowing sufficient transport of molecules
• Larger organisms


  • Have smaller surface area to volume ratio, require exchange and transport systems
• Adaptations for exchange in larger organisms

  • Small intestine: Villi and microvilli increase surface area
  • Lungs: Alveoli provide large surface area, thin walls for short diffusion distance
  • Leaves: Flat shape, thin, stomata, air spaces for gas exchange
  • Fish gills: Gill filaments provide large surface area, thin walls for short diffusion distance, water flow maintains concentration gradient
• Osmosis


  Diffusion of water from a dilute to a concentrated solution through a partially permeable membrane
• Plant cells do not burst during osmosis due to cell wall
• Investigating effect of solutions on plant tissue mass

  1. Prepare solutions of different concentrations

  2. Cut equal-sized plant tissue samples

  3. Immerse samples in solutions for set time

  4. Measure mass before and after

  5. Calculate percent change in mass

  6. Plot results on graph to find point of no net water movement
• Potato loses mass


  Solution outside is more concentrated than inside, so water moves out by osmosis
• Potato gains mass


  Solution inside is more concentrated than outside, so water moves in by osmosis