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Key concepts in biology

Edexcel GCSE Combined ScienceTopic 1 of 1453 lessons

Revision notes for Key concepts in biology in Edexcel Combined Science (1SC0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. Core practical: Microscopes, magnification and scientific drawingsA light microscope is used to look at thin specimens such as onion epidermis or cheek cells.
  2. Core practical: The effect of pH on enzyme activityEnzymes work best at one pH, called the optimum pH.
  3. Core practical: Osmosis in potatoesOsmosis is the movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
  4. Sub-cellular structures in animal, plant and bacterial cellsAnimal and plant cells are eukaryotic: their genetic material is inside a nucleus.
  5. Specialised cells: sperm, egg and ciliated epithelial cellsSpecialised cells have features, called adaptations, that help them do one job.
  6. How microscope technology has changed our view of cellsThe first microscopes used light and glass lenses.
  7. Number, size and scale, and estimationLiving things come in a huge range of sizes, from a bacterium about 1 µm long to a whale many metres long.
  8. Units for cells: milli, micro, nano and picoCells and the structures inside them are far too small to measure sensibly in metres, so biologists use smaller units.
  9. How enzymes work: the active site and specificityEnzymes are biological catalysts.
  10. Denaturing of enzymesAn enzyme is a protein folded into a precise three-dimensional shape.
  11. Effects of temperature, substrate concentration and pHThe rate of an enzyme-controlled reaction depends on conditions.
  12. Rate calculations for enzyme activityThe rate of a reaction tells you how fast it happens.
  13. Enzymes as biological catalysts in synthesis and breakdownCells carry out thousands of chemical reactions, and most would be far too slow at body temperature.
  14. Transport into and out of cells: diffusion, osmosis and active transportSubstances move into and out of cells in three main ways.
  15. Calculating percentage gain and loss of mass in osmosisWhen a piece of plant tissue such as a potato cylinder is left in a solution, water moves by osmosis.
  16. How Mendeleev arranged the elements in his periodic tableIn 1869 the Russian chemist Dmitri Mendeleev set out to bring order to the elements known at that time.
  17. How Mendeleev used his table to predict undiscovered elementsMendeleev's table was so useful because it could do more than organise known elements.
  18. Metals and non-metals in the periodic table and their atomic structureThe periodic table can be divided into metals and non-metals.
  19. Electronic configurations of the first 20 elementsThe electrons in an atom are arranged in shells (energy levels) around the nucleus.
  20. Electronic configuration and position in the periodic tableThe position of an element in the periodic table tells you its electronic configuration.
  21. Ionic bonding and dot and cross diagramsIonic bonding happens between a metal and a non-metal.
  22. IonsAn ion is an atom or group of atoms with a positive or negative charge.
  23. Protons, neutrons and electrons in simple ionsYou can work out the particles in an ion from its atomic number and mass number.
  24. Formation of ions in ionic compoundsAtoms form ions so that they have a full outer shell, the same electronic configuration as a noble gas.
  25. The endings -ide and -ate in compound namesThe name of a compound tells you which elements it contains.
  26. Formulae of ionic compoundsAn ionic compound has no overall charge, because the total positive charge of its ions equals the total negative charge.
  27. Ionic lattice structureAn ionic compound is made of positive and negative ions.
  28. Formation of a covalent bondAtoms of non-metal elements usually bond by sharing electrons rather than transferring them.
  29. Covalent bonding and moleculesWhen atoms are joined to each other by covalent bonds, the result is a molecule.
  30. Size of atoms and small moleculesAtoms are extremely small.
  31. Dot and cross diagrams of simple moleculesA covalent bond forms when two atoms share a pair of electrons.
  32. Types of substance and their propertiesElements and compounds can be sorted into four types by their structure and bonding.
  33. Properties of ionic compoundsAn ionic compound is a giant lattice of oppositely charged ions held together by strong electrostatic forces.
  34. Properties of simple molecular substancesSimple molecular substances, such as water, methane, carbon dioxide and hydrogen chloride, are made of small molecules.
  35. Graphite and diamondThe element carbon exists in more than one form.
  36. Structures of graphite and diamondIn diamond each carbon atom is joined to four other carbon atoms by strong covalent bonds.
  37. Uses of graphite and diamondGraphite and diamond are both made only of carbon atoms, but their structures and bonding are different, so they are used for different jobs.
  38. Properties of fullerenes and grapheneFullerenes are molecules made only of carbon atoms, arranged in hexagons and sometimes pentagons, forming hollow shapes.
  39. Poly(ethene) and simple polymersPolymers are very large molecules made by joining many small molecules together.
  40. Properties of metalsMetals have a giant structure.
  41. Limitations of models and representationsScientists use models to show the structure and bonding of substances.
  42. Properties of metals and non-metalsYou can often tell a metal from a non-metal by its physical properties.
  43. Relative formula mass and percentage by massThe relative formula mass (Mr) of a compound is found by adding up the relative atomic masses (Ar) of all the atoms in its formula.
  44. Empirical formulae from massesThe empirical formula of a compound is the simplest whole-number ratio of the atoms of each element in it.
  45. Empirical and molecular formulaeA molecular formula shows the actual number of atoms of each element in one molecule.
  46. Finding the empirical formula of magnesium oxideThe empirical formula of magnesium oxide can be found by heating magnesium in air and measuring the mass change.
  47. The law of conservation of massThe law of conservation of mass says that no atoms are made or destroyed in a chemical reaction.
  48. Calculating reacting massesA balanced equation shows the ratio in which substances react.
  49. Concentration of solutions in g/dm3A solution forms when a solute dissolves in a solvent.
  50. The mole and the Avogadro constantAtoms and molecules are far too small to count one by one, so chemists count them in moles.
  51. Calculations with moles and particlesThe number of moles in a sample links its mass to its relative particle mass: moles = mass (g) ÷ relative formula mass Mr (or Ar for an element)…
  52. Limiting reactants and the mass of productThe balanced equation shows the ratio in which reactants combine.
  53. Deducing stoichiometry from massesThe stoichiometry of a reaction is the ratio in which the substances react and form, shown by the numbers in front of the formulae in the balanced…

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