cell biology

• 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
• Bacteria divide by binary fission
• Growing uncontaminated bacterial cultures

  Sterilise equipment

  Inoculate agar plate

  Incubate at 25°C

  Seal plate to prevent contamination
• Testing antibiotics/antiseptics


  Place antibiotic discs on agar with bacteria

  Measure area of bacterial death around discs
• Cell cycle


  Growth and DNA replication

  Mitosis - chromosomes line up and separate

  Cytoplasm and cell membrane divide
• Stem cells


  Undifferentiated cells that can develop into specialised cells
• 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. 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. Remove nucleus from patient body cell

  2. Remove nucleus from human egg cell

  3. Insert patient nucleus into egg cell

  4. Clone to produce stem cells for medical 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
• Active transport examples


  • Sugar absorption in small intestine
  • Mineral ion absorption in plant root hair cells
• Surface area to volume ratio

  Ratio of surface area to volume, decreases as organism size increases
• Adaptations for exchange in larger organisms

  • Villi and microvilli in small intestine
  • Alveoli in lungs
  • Stomata in leaves
  • Gill filaments in fish
• Osmosis


  Diffusion of water from dilute to concentrated solution through a partially permeable membrane
• Investigating effect of solutions on plant tissue mass

  1. Prepare solutions of different concentrations

  2. Cut equal-sized plant tissue samples

  3. Measure mass before and after immersion in solutions

  4. Calculate percent change in mass

  5. Plot results on graph
• 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