science shorts

• All life consists of cells
• Light microscope


  • Can see cells and 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
• Prokaryotic cells


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


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


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

  • Increase reaction rate without being consumed or altered
  • Increase reaction rate without altering chemical equilibrium
• Enzyme specificity


  Enzymes only break down certain molecules (lock and key principle)
• Enzyme activity and temperature


  Rate increases with temperature until active site is denatured
• Enzyme activity and pH


  Rate is optimum at certain pH, can denature at too high or too low pH
• Food tests can identify nutrients: iodine for starch, Benedict's solution for sugars, Biuret's reagent for proteins, ethanol for lipids
• Diffusion


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


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

  Concentration gradient, temperature, surface area
• Investigating osmosis


  1. Cut equal cylinders from potato

  2. Weigh and place in sugar solutions

  3. Reweigh after a day

  4. Calculate percentage change in mass

  5. Plot against sugar concentration
• Active transport


  Using energy to move substances against a concentration gradient
• Genetic material


  • DNA
  • Chromosomes
• Diploid cells


  Have 23 pairs of chromosomes
• Haploid cells


  Have 23 single chromosomes
• Cell division by mitosis


  1. Genetic material duplicated

  2. Nucleus breaks down

  3. Chromosomes pulled to opposite sides

  4. New nuclei form
• 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)
• Nerve impulse transmission


  1. Receptor detects stimulus

  2. Electrical signal travels to spine

  3. Signal crosses synapse by neurotransmitter

  4. Signal travels to brain

  5. Brain sends signal back to effector
• Reflex arc


  Electrical signal bypasses brain and goes straight from spine to effector
• Parts of the brain


  • Cerebral cortex
  • Cerebellum
  • Medulla oblongata
• MRI scans

  Safely show brain activity
• Eye


  • Accommodation - lens changes shape to focus light
  • Pupil changes size to control light intensity
  • Cornea, lens, retina
• Meiosis


  1. Chromosomes copied and paired

  2. Cell divides twice to form 4 haploid cells
• Reproduction methods


  • Sexual (gametes)
  • Asexual (mitosis)
• 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 are the monomers that make up DNA, consisting of a sugar, phosphate and one of 4 bases (A, T, C, G)
• Protein synthesis

  1. DNA sequence copied to mRNA

  2. mRNA taken to ribosome

  3. Amino acids assembled in sequence
• Harmful mutations can change a gene so the resulting protein doesn't function properly