YT import

• All life consists of cells
• Light microscope


  Can see cells and maybe the nucleus, but not subcellular structures
• Electron microscope


  Can see finer details and subcellular structures, has better resolving power and higher resolution
• Calculating cell size


  1. Measure image size

  2. Divide by magnification
• Cell types


  • Eukaryotic cells
  • Prokaryotic cells
• Eukaryotic cells


  • Have a nucleus where DNA is found
  • Examples: plant and animal cells
• Prokaryotic cells


  • Don't have a nucleus, DNA is in a ring called a plasmid
• Cell organelles


  • Cell membrane
  • Cell wall (plant cells and bacteria)
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chloroplasts (plant cells)
  • Vacuole (plant cells)
• Enzymes


  Biological catalysts that break down larger molecules into smaller ones
• Enzymes


  • Specific - only break down certain molecules
  • Work on a lock and key principle with substrates
• Enzyme activity rate


  Increases with temperature (until active site is denatured)
• Enzyme activity rate


  Affected by pH (can be denatured by too high or too low pH)
• Practical on enzyme activity

  1. Mix enzyme and substrate

  2. Measure time taken for reaction to complete

  3. Plot graph to find optimum temperature or pH
• Food tests


  • Iodine turns black for starch
  • Benedict's solution turns orange for sugars
  • Biuret reagent turns purple for proteins
  • Ethanol goes cloudy for lipids
• Diffusion


  Movement of molecules/particles from high to low concentration, down concentration gradient, passive
• Osmosis


  Diffusion of water across a semi-permeable membrane
• Factors affecting diffusion/osmosis rate

  • Concentration difference
  • Temperature
  • Surface area
• Practical on osmosis


  1. Cut equal potato cylinders

  2. Weigh and place in sugar solutions

  3. Reweigh after time

  4. Calculate % change in mass

  5. Plot graph to find no change concentration
• Active transport


  Using energy to move substances against a concentration gradient
• Diploid cells


  Have 23 pairs of chromosomes
• Haploid cells


  Have 23 single chromosomes
• Mitosis


  1. Genetic material duplicated

  2. Nucleus breaks down

  3. Chromosomes pulled to opposite sides

  4. New nuclei form, resulting in two identical cells
• Cell specialisation


  Cells take on specific functions e.g. nerve, muscle, root hair
• Stem cells


  Unspecialised cells that can develop into different cell types
• Parts of the nervous system

  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (nerves)
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical signal to spinal cord

  3. Signal bypasses brain and goes straight to effector
• Reaction time experiment


  Measure time taken for person to catch falling ruler
• Parts of the brain

  • Cerebral cortex (higher functions)
  • Cerebellum (motor skills, balance)
  • Medulla oblongata (unconscious actions)
• MRI scans


  Safely show brain activity
• Accommodation


  Eye's ability to change lens shape to focus light
• Pupil


  Hole in iris that changes size with light intensity
• Meiosis


  1. Chromosomes copied and paired

  2. Cell divides twice to form 4 haploid cells
• Asexual reproduction


  Daughter cells are genetically identical clones
• Genome


  All the genetic material in an organism
• Gene


  Section of DNA that codes for a specific protein
• Genotype


  Genetic code stored in DNA
• Phenotype


  How the genetic code is expressed in an organism's characteristics
• Nucleotides


  Monomers that make up DNA, consisting of a sugar, phosphate and one of 4 bases
• Protein synthesis


  1. DNA sequence copied to mRNA

  2. mRNA taken to ribosome

  3. Amino acids assembled in sequence
• Mutations


  Changes to genes that can result in non-functional proteins