Paper 1

• All life consists of cells
• Cells can be seen with a normal light microscope, but subcellular structures are not visible
• Electron microscopes allow us to see finer details of subcellular structures
• Magnification is equal to image size divided by object size
• Eukaryotic cells have a nucleus where DNA is found, while prokaryotic cells have DNA in a ring called a plasmid
• Both eukaryotic and prokaryotic cells contain similar organelles or subcellular structures
• Cell membrane


  • Keeps everything inside the cell, semi-permeable allowing certain substances to pass through
• Plant cells and most bacteria

  • Have an extra cell wall made of cellulose providing a rigid structure
• Cytoplasm

  • Liquid where most chemical reactions take place
• Mitochondria

  • Where respiration takes place, releasing energy for the cell to function
• Ribosomes


  • Where proteins are assembled or synthesized
• Chloroplasts

  • Contain chlorophyll where photosynthesis takes place
• Permanent vacuole in plant cells

  • Stores sap
• Bacteria multiplication


  By binary fission, doubling every say 10 minutes
• Practical on bacteria multiplication


  Producing a culture on agar in a Petri dish using aseptic technique
• Eukaryotic cell nuclei contain DNA stored in several chromosomes
• Humans have 23 pairs of chromosomes in every nucleus, making them diploid cells
• Gametes have half the number of chromosomes, making them haploid cells
• Cells specialize depending on the function they need to fulfill
• Stem cells are those that haven't yet specialized
• Stem cells are found in human and animal embryos and the meristems of plants
• Stem cells are made in bone marrow throughout life
• Types of cells

  • Nerve
  • Muscle
  • Root
  • Xylem
  • Stem cells
• Stem cells


  Cells that haven't yet specialized, found in human and animal embryos and the meristem of plants
• Stem cells are made in your bone marrow throughout your life but can only specialize into blood cells
• Stem cells can be used to combat conditions like diabetes and paralysis
• From the movie The Island: 'People are now getting clones of themselves made then harvesting the stem cells as these won't be rejected by the patient'
• Cloning plants can be used to prevent species from becoming extinct or produce crops with specific characteristics
• Diffusion


  The movement of molecules or particles from an area of high concentration to an area of low concentration
• Diffusion is passive and doesn't require any energy input
• Osmosis


  The diffusion of water across a semi-permeable membrane
• Rate of diffusion or osmosis can be increased by increasing the difference in concentrations, temperature, or surface area
• Practical on osmosis

  Cut equal size cylinders from a potato or other vegetable, weigh them, place in test tubes with varying concentration of sugar solution, remove excess water after a day, re-weigh, calculate percentage change in mass
• Active transport

  Movement of substances through a membrane using energy
• Cells get organized together to form tissues
• Tissues form organs, for example, heart tissue
• Organs work together in an organ system, like the circulatory system or digestive system
• Enzymes are biological catalysts that break down larger molecules into smaller ones
• Enzymes are specific and work on a lock and key principle
• Enzymes break down specific molecules like carbohydrates, proteins, and lipids