topic 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
  • Nucleus
• Muscle cell


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


  • No end plates
  • No cytoplasm
  • Rings of lignin
• 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 low resolving power

  Electron microscopes have high magnification and high resolving power
• Calculating magnification


  Magnification = Size of image / Size of real object
• Magnification calculations


  • Root hair cell image 5 mm, real size 20 μm, magnification 250x

  Sperm cell image 10 mm, magnification 2000x, real length 5 μm
• Culturing microorganisms


  Binary fission for rapid division

  Provide nutrients like glucose and amino acids

  Incubate at 25°C to encourage growth
• Growing uncontaminated cultures


  Sterilise equipment and work area

  Use inoculating loop to transfer bacteria to agar gel

  Seal petri dish to prevent contamination

  Incubate at 25°C
• Testing antibiotics/antiseptics


  Place antibiotic/antiseptic discs on agar with bacteria

  Measure area of dead bacteria around discs

  Control variables: disc area, concentration, volume
• Cell cycle and mitosis

  Stage 1: Cell growth and DNA replication

  Stage 2: Chromosomes line up and separate

  Stage 3: 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. Patient body cell nucleus removed and inserted into empty human egg cell

  2. Cloned to produce stem cells

  3. Stem cells differentiated to make 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
• Examples of diffusion in living things

  • Oxygen diffusing into cells from blood
  • Carbon dioxide diffusing out of cells into blood
  • Urea diffusing out of cells
• Examples of active transport in living things

  • 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
• Larger organisms need exchange and transport systems due to low surface area to volume ratio
• Adaptations for exchange in larger organisms

  • Villi and microvilli in small intestine
  • Alveoli in lungs
  • Stomata in leaves
  • Gill filaments in fish gills
• 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. Immerse samples in solutions

  4. Measure mass change after time
• Potato tissue in more concentrated solution

  Water moves out of potato, potato loses mass