Paper 1

• Eukaryotic cells


  They have genetic material (DNA) that forms chromosomes and is contained within a nucleus
• Specialised cells


  • Cells in animals and plants differentiate to form different types of cells
  • Cells in animals have a single cell stage of development, whereas a plant's cells remain undifferentiated through the early stage of development
• Prokaryotic cells


  • Bacteria have the following characteristics: single-celled, have a single loop of DNA, have small rings of DNA called plasmids, DNA free in the cytoplasm
• Light microscope


  Uses light to form images
• Electron microscope


  Uses a beam of electrons to form images
• Electron microscopes allow you to see sub-cellular structures, such as ribosomes that a light microscope cannot
• To calculate the magnification of an image

  magnification = image size / actual size
• Specialised cells


  • Muscle cell: contains protein fibres which can contract to allow movement
  • Nerve cell: contains advanced endings called dendrites to make connections with other neurons or effectors, has a myelin sheath to increase the transmission speed of electrical signals
• Specialised plant cells


  • Palisade cell: enables photosynthesis in the leaf
  • Root hair cell: long projection to increase the surface area for absorption of water and mineral ions, has lots of mitochondria to release energy for active transport of mineral ions from the soil
• Factors affecting the rate of diffusion

  • Difference in concentration
  • Temperature: the higher the temperature, the faster the rate of diffusion
  • Surface area of the membrane: the larger the membrane surface, the faster the rate of diffusion
• Adaptations for exchanging substances

  • Single-celled organisms have a large surface area to volume ratio
  • Multicellular organisms have specialised organ systems and exchange surfaces to allow enough molecules to be transported into and out of their cells
  • Exchange surfaces work most efficiently when they have a large surface area, a thin membrane, and a good blood supply
• Examples of exchange surfaces

  • Villi in the small intestine
  • Alveoli in the lungs
  • Fish gills
  • Root hair cells
• Levels of organisation in animals

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organisms
• Breathing in


  1. Air moves through mouth and nose

  2. Down the trachea

  3. Into the bronchi

  4. Through the bronchioles

  5. Into the alveoli (air sacs)
• Oxygen exchange


  Oxygen goes into the blood in the network of capillaries over the surface of the alveoli
• Digestion


  1. Food enters the mouth

  2. Travels to the stomach

  3. Mixes with digestive enzymes

  4. Travels to the small intestine

  5. Nutrients absorbed into the blood
• Blood vessels


  • Arteries - carry blood away from the heart, thick and muscular walls
  • Veins - carry blood to the heart, thin walls
  • Capillaries - connect arteries and veins, one cell thick walls
• Heart


  • Made of cardiac muscle tissue
  • Supplied by coronary artery
  • Right atrium and ventricle pump blood to the lungs
  • Left atrium and ventricle pump blood around the body
• Double circulatory system


  Blood passes through the heart twice for every circuit around the body
• Heart rate control


  Electrical impulses generated by cells in the right atrium act as a pacemaker
• Artificial pacemaker


  Used to control irregular heartbeats
• Components of blood


  • Red blood cells
  • Plasma
  • Platelets
  • White blood cells
• Lock and key theory

  The active site of an enzyme has a specific shape that fits a specific substrate
• How enzymes catalyse reactions

  1. Substrate binds to active site

  2. Enzyme lowers activation energy

  3. Reaction occurs

  4. Products released
• As temperature increases


  Reaction rate increases
• At very high temperatures


  Enzyme becomes denatured and stops working
• Denaturation


  At extremes of pH or temperature, the shape of an enzyme's active site can change, preventing the substrate from binding
• The substrate can no longer bind to the denatured enzyme's active site, so the enzyme cannot catalyse the reaction
• Digestive enzymes


  Convert food into small, soluble molecules that can then be absorbed into the bloodstream
• Digestive enzymes


  • Carbohydrases
  • Proteases
  • Lipases
• Carbohydrases break down carbohydrates into simple sugars
• The products of digestion can be used to build new carbohydrates, lipids, and proteins
• Some of the glucose produced is used in respiration
• Sites of production


  • Salivary glands
  • Pancreas
  • Small intestine
  • Stomach
• Reaction catalysed by proteases

  Proteins to amino acids
• Reaction catalysed by carbohydrases

  Starch to maltose (simple sugars)
• Reaction catalysed by lipases


  Lipids to fatty acids and glycerol
• Different enzymes have different optimum pH values
• This allows enzymes to be adapted to work well in environments with different pH values
• Parts of the digestive system greatly differ in pH