Biology 1

• Prokaryotic cells


  Smaller and simpler cells, e.g. bacteria
• Subcellular structures in animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Bacterial cell structure


  No chloroplasts or mitochondria, single circular strand of DNA in cytoplasm, may contain plasmids
• Electron microscopes

  Use electrons instead of light, have higher magnification and resolution than light microscopes
• Stains are used to highlight objects in a cell by adding colour to them
• Cell differentiation


  The process by which a cell changes to become specialised for its job
• Mitosis


  1. Cell grows and increases subcellular structures

  2. DNA is duplicated and forms X-shaped chromosomes

  3. Chromosomes line up at cell centre and are pulled apart

  4. Membranes form around new nuclei

  5. Cytoplasm and cell membrane divide to form two new daughter cells
• Mean division time


  Average amount of time it takes for one bacterial cell to divide into two
• Things that help maximise the rate of binary fission

  • Warm environment
  • Lots of nutrients
• Testing the action of antibiotics on bacterial growth


  1. Place paper discs soaked in antibiotics on agar plate with bacteria

  2. Antibiotic diffuses into agar

  3. Antibiotic-resistant bacteria continue to grow, non-resistant strains die forming inhibition zone

  4. Use a control disc with sterile water

  5. Leave plate for 48 hours at 25°C
• Comparing inhibition zones of different antibiotics

  The larger the inhibition zone, the more effective the antibiotic
• Differentiation


  Process by which a cell changes to become specialised for its job
• Stem cells


  Undifferentiated cells that can divide to produce more undifferentiated cells and differentiate into different cell types
• Embryonic stem cells can turn into any type of cell, adult stem cells can only turn into certain cell types
• Stem cells can be used to replace faulty cells in diseases, but there are risks involved
• Arguments against stem cell research

  • Embryos shouldn't be used as they are potential human lives
  • Scientists should focus on finding other sources of stem cells
• In plants, stem cells are found in the meristems and can be used to produce clones of whole plants
• Diffusion


  The spreading out of particles from an area of higher concentration to an area of lower concentration
• Diffusion happens in both solutions and gases because the particles are free to move about randomly
• Higher temperature


  Faster diffusion rate
• Diffusion of gases


  • Perfume particles diffusing in the air
• The bigger the concentration gradient

  The faster the diffusion rate
• A higher temperature


  Gives a faster diffusion rate because the particles have more energy, so move around faster
• Cell membranes


  • They hold the cell together BUT they let stuff in and out as well
• Diffusion through cell membranes

  Dissolved substances can move in and out of cells by diffusion
• Molecules that cannot diffuse through cell membranes

  • Starch
  • Proteins
• Particles flow through the cell membrane

  From where there's a higher concentration to where there's a lower concentration
• Partially permeable membrane


  A membrane with very small holes in it, so small that only tiny molecules (like water) can pass through them, and bigger molecules (e.g. sucrose) can't
• Osmosis is a type of diffusion-passive movement of water particles from an area of higher water concentration to an area of lower water concentration
• How root hair cells take in minerals

  They use active transport, which requires energy from respiration to work
• Active transport in the gut

  It allows nutrients to be taken into the blood, despite the fact that the concentration gradient is the wrong way
• The alveoli in the lungs are adapted to maximise the diffusion of oxygen and carbon dioxide
• Multicellular organisms are well adapted for getting the substances they need to their cells
• Specialised cells carry out a particular function
• Organs in the digestive system

  • Glands (e.g. pancreas and salivary glands)
  • Stomach and small intestine
  • Liver
  • Small intestine
  • Large intestine
• Organ systems work together to make entire organisms
• Living things have thousands of different chemical reactions going on inside them all the time
• Catalyst

  A substance which increases the speed of a reaction, without being changed or used up in the reaction
• Enzyme


  A large protein that acts as a biological catalyst to speed up useful chemical reactions in the body
• Enzymes


  • They have an active site with a unique shape that fits onto the substance involved in a reaction
  • They usually only catalyse one specific reaction
  • The active site changes shape a little as the substrate binds to it to get a tighter fit (induced fit model)