Edexcel IGCSE revision

• Who wrote the Edexcel IGCSE Revision notes?

  Tim Filtness
• What are the characteristics of living organisms?

  • Movement
  • Respiration
  • Sensitivity
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
• What do all living organisms contain that is essential for their functions?

  All living organisms contain nucleic acids (DNA).
• What ability do all living organisms have regarding their internal conditions?


  They have the ability to control their internal conditions.
• How many groups are living organisms classified into?

  Five groups
• What are the characteristics of plants?

  1. Multicellular organisms
  2. Cells contain chloroplasts and can photosynthesize
  3. Cells have cellulose cell walls
  4. Store carbohydrates as starch or sucrose
• What are the characteristics of animals?

  1. Multicellular organisms
  2. Cells do not contain chloroplasts and cannot photosynthesize
  3. Cells have no cell walls
  4. Have a nervous system
  5. Store carbohydrates as glycogen
• What are the characteristics of fungi?

  1. Saprophytic, feeding by excreting digestive enzymes
  2. Cells do not contain chloroplasts and cannot photosynthesize
  3. Cells form threads called hyphae
  4. Cell walls made from chitin
  5. Store carbohydrates as glycogen
• What are the characteristics of bacteria?


  1. Made from single cells
  2. Cells do not contain a nucleus, but have circular DNA
  3. Some can carry out rudimentary photosynthesis, most are saprophytes
  4. Have a specific structure
• What are the characteristics of protoctists?


  1. Mostly single-celled organisms
  2. Can have animal-like characteristics (e.g. Amoeba)
  3. Can have plant-like characteristics (e.g. Chlorella)
  4. Some are multicellular (e.g. seaweeds)
• What are the characteristics of viruses?

  1. Much smaller than bacteria and not made from cells
  2. Totally parasitic, reproducing inside host cells
  3. Infect every type of living cell
  4. Have a specific structure

  
• What is the function of the envelope in viruses?

  The envelope is used to gain entry into host cells.
• What is the function of the capsid in viruses?

  The capsid is a protein coat that protects the genetic information.
• What do the DNA or RNA in viruses contain?

  The DNA or RNA contains the code for building new viruses.
• What is the hierarchy of structures in living organisms?

  1. Organelles
  2. Cells
  3. Tissues
  4. Organs
  5. Organ Systems
• What are the functions of the organelles in a cell?

  • Cytoplasm: site of chemical reactions
  • Cell Membrane: controls entry/exit of substances
  • Nucleus: contains nucleic acids for protein synthesis
  • Mitochondrion: site of respiration
  • Chloroplast: site of photosynthesis
  • Cell Wall: strengthens the cell
  • Sap Vacuole: stores water, sugars, or waste products

  
• What is the unit of measurement for cells?

  Micrometers (µm)
• What are the differences between plant and animal cells?

  | Organelle | Animal Cell | Plant Cell |

  |----------------|-------------|------------|

  | Chloroplast | X | √ |

  | Cell Wall | X | √ |

  | Sap Vacuole | X | √ |

  | Chlorophyll | X | Found in chloroplast |

  | Size | Roughly 50µm long | Roughly 150µm long |

  | Shape | No fixed shape | Rectangular |
• What are the main food groups?

  • Carbohydrates
  • Lipids
  • Proteins
• What are the components of carbohydrates, proteins, and lipids?

  • Carbohydrates: made from one or more sugars
  • Proteins: polymers of amino acids
  • Lipids: made from one glycerol and three fatty acids
• What are the functions of the main food groups?

  • Lipids: long-term energy store, protection, insulation
  • Carbohydrates: provide energy in respiration
  • Proteins: used for growth and repair
  • Fibre: regulates bowel movement
  • Water: solvent for chemical reactions, transport
  • Vitamins and Minerals: essential for enzyme and protein function

  
• What are the characteristics of enzymes?

  • Are proteins
  • Biological catalysts
  • Specific to one substrate
  • Affected by temperature and pH
  • Not used up in reactions
• What happens to enzymes when the temperature exceeds the optimum?

  The enzyme begins to change shape and becomes denatured.
• What happens to enzymes when the pH exceeds the optimum?

  The enzyme begins to change shape and becomes denatured.
• What is the equation for the breakdown of hydrogen peroxide by catalase?

  $2H_2O_2 \rightarrow O_2 +$$2H_2O$
• What is diffusion?

  Diffusion is the movement of molecules from high concentration to low concentration down a concentration gradient.
• What is osmosis?

  Osmosis is the movement of water molecules from high concentration to low concentration through a partially permeable membrane.
• What is active transport?


  Active transport is the movement of molecules from low concentration to high concentration against the concentration gradient, requiring energy.
• What factors affect the rate of diffusion?

  • Temperature
  • Stirring
  • Surface area for diffusion
  • Thickness/distance for diffusion
  • Size of concentration gradient
  • Surface area to volume ratio
• What happens to plant cells when they lose water?

  • They become flaccid, losing strength and starting to wilt.
  • Eventually, they can become plasmolysed, killing the cell.
• What are good examples of diffusion?

  • Ink chromatography
  • Diffusion of KMnO4 crystals in water
  • Diffusion of gases in the lung or leaf
• What are good examples of osmosis?


  • Visking tubing
  • Potato chips in salt solutions of different concentrations
• What is the process of photosynthesis in flowering plants?

  • Plants are photoautotrophic, generating food using sunlight.
  • The equation is: $6CO_2 +$$6H_2O \rightarrow 6O_2 +$$C_6H_{12}O_6$
• What do plants use glucose for?

  • Respiration
  • Stored as starch
  • Turned into cellulose
  • Used to make fats and oils
• What are the rate-limiting factors for photosynthesis?

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• What minerals do plants need for photosynthesis?

  • Nitrate: for amino acids
  • Magnesium: part of chlorophyll
  • Potassium: essential for cell membranes
  • Phosphate: part of DNA and cell membranes
• What experiment shows how the rate of photosynthesis is affected by limiting factors?

  Using pond weed (Elodea) to measure the rate of bubble production as it photosynthesizes.
• What experiment proves that light and CO2 are essential for starch production?

  • Use a Geranium plant.
  • Leaves turn blue-black in iodine solution if starch is present.
  • Boil in ethanol to remove chlorophyll.
  • One leaf in aluminum foil and another in lime water do not turn blue-black.

  
• What is the structure of a leaf and its adaptations for photosynthesis?

  • Cuticle: prevents water loss
  • Epidermis: transparent protective layer
  • Palisade cells: packed with chloroplasts for photosynthesis
• How is the rate of bubble production related to photosynthesis?

  The rate of bubble production is approximately proportional to the rate of photosynthesis.