Biology (B2) Notes

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*Brief notes for the majority of Biology B2 (AQA) from the 2011 specification


  • Living things made of cells
  • Structures of cells are related to functions
  • Cells are specialised to carry out a job

Cell Structure

  • Most cells have:
    • Nucleus - controls activities of cell
    • Cytoplasm - where chemical reactions take place
    • Cell membrane - controls passage of substances
    • Mitochondria - where energy is released in respiration
    • Ribosomes - where protein synthesis occurs
  • Chemical reactions are controlled by enzymes in mitochondria (in cytoplasm)

Plant Cells

  • Also have:
    • Cell wall - to strengthen the cell
    • Chloroplasts - absorb light to make food
    • Vacuole - filled with cell sap

Other Cells

  • Bacterial cells don't have a nucleus, but they have:
    • Cytoplasm
    • Cell membrane
    • Cell wall
  • Yeast is a single-celled fungus with:
    • Nucleus
    • Cytoplasm
    • Cell membrane
    • Cell wall

Movement of Substances

  • Cells have to replace used substances e.g. glucose + oxygen
  • They have to remove waste e.g. carbon dioxide
  • Gases and solutions can pass through the cell membrane by diffusion


  • The spreading of gas or solution particles
  • Movement from an area of high concentration to one of low concentration
  • The greater the concentration difference, the faster the diffusion rate


  • Large multicellular organs develop systems
  • As the organisms develop, cells differentiate to perform different jobs
  • Tissues are groups of cells with a similar structure + function, e.g:
    • Muscular tissue contracts to bring about movement
    • Glandular tissue produces substances
    • Epithelial tissue covers organs


  • Made of tissues; may contain several
  • E.g. the stomach contains:
    • Musclular tissue to churn contents
    • Glandular tissue to produce digestive juices
    • Epithelial tissue to line and cover the stomach

Organ Systems

  • Groups of organs that carry out a function, e.g. the digestive system:
    • Pancreas + salivary glands to produce digestive juices
    • Stomach + small intestine where digestion occurs
    • Liver to produce bile which breaks down fat
    • Small intestine where soluble food is absorbed into the blood
    • Large intestine where water is absorbed, producing faeces
  • Humans have other organ systems e.g. excretory, circulatory and reproductive systems

Plant Organs

  • Stems, roots and leaves
  • Tissues include:
    • Epidermal substances to cover the plant
    • Mesophyll where photosynthesis occurs
    • Xylem and phloem to transport substances


  • Plants make food using sunlight
  • Occurs in light-exposed cells
  • Light energy absorbed by chlorophyll (found in chloroplasts)
  • Four things needed:
    • Light
    • Carbon Dioxide
    • Water
    • Chlorophyll
  • Light energy converts carbon dioxide + water into glucose + oxygen (a by-product)
  • carbon dioxide + water → glucose + oxygen
  •  6CO2  +  6H2O  →   C6H12O +  6O2

How Plants Use Glucose

  • Glucose from photosynthesis may be:
    • Stored as insoluble starch
    • Used in respiration
  • Some is used to produce:
    • Fat + Oil
    • Cellulose ( to strengthen cell walls)
    • Proteins
  • Proteins are also produced using nitrate ions from the soil.

Factors Affecting Photosynthesis

  • Temperature
  • Carbon dioxide concentration
  • Light intensity


  • As temperature increases, so does the rate of photosynthesis
  • At 45 C the rate drops to zero; enzymes have been destroyed

Carbon Dioxide Concentration

  • As the concentration…


Aaron Kirsopp


Brilliant notes. Im sure this will help me out alot. Thank you Ginevra!

Sophie Choi


Wow! You've definatly spent lots of time on this!! Thank you



Thank you very much!

Shannon Tennant-Smith - Team GR


Thank you all for the feedback :)

Damilola Fasoyiro


this notes are so useful, thank you so much :-D

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