Biology

• Characteristics of Living Organisms

  • Move
  • Respire
  • Sensitivity
  • Growth
  • Excretion
  • Reproduction
  • Nutrition
• Eukaryotic cells


  Complex, e.g. animal and plant cells
• Prokaryotic cells


  Smaller and simpler, e.g. bacteria
• Types of Eukaryotic Organisms

  • Plants
  • Animals
  • Fungi
  • Protoctists
• Plants


  • Multicellular
  • Have chloroplasts to photosynthesise
  • Cell wall made of cellulose
  • Store carbohydrates as sucrose or starch
• Animals


  • Multicellular
  • No chloroplasts – no photosynthesis
  • No cell walls
  • Nervous coordination – respond to stimuli
  • Move around
  • Store carbohydrates as glycogen
• Fungi


  • Single-celled OR multicellular – have body called mycelium made up of hyphae
  • Can't photosynthesise
  • Cell walls made of chitin
  • Most feed by saprotrophic nutrition
• Protoctists


  • Single-celled and microscopic
  • Some have chloroplasts – similar to plant cells
  • Others are similar to animal cells
• Types of Bacteria


  • Lactobacillus bulgaricus (rod shaped, used for making yoghurt)
  • Pneumococcus (spherical)
• Bacteria


  • Single-celled and microscopic
  • No nucleus
  • Have circular chromosome of DNA
  • Some can photosynthesise
  • Most feed off other organisms – both living and dead
• Viruses


  • Particles smaller than bacteria
  • Reproduce inside living cells – so is a parasite
  • Infect all living things
  • Come in lots of different shapes and sizes
  • Have a protein coat around genetic material (DNA or RNA)
• Examples of Pathogens


  • Plasmodium (protoctist, causes malaria)
  • Pneumococcus (bacterium, causes pneumonia)
  • Influenza virus (causes flu)
• Organelles


  Tiny structures within cells – only seen through a microscope
• Organelles in Animal and Plant Cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Organelles Only in Plant Cells

  • Cell wall
  • Chloroplasts
  • Vacuole
• Tissue


  A group of similar cells working towards a particular function
• Tissues


  • Xylem in plants (for transporting water and mineral salts)
  • Phloem in plants (for transporting sucrose and amino acids)
• Organ

  A group of different tissues working towards a particular function
• Organs


  • Lungs in mammals
  • Leaves in plants
• Organ System


  A group of organs working together
• Organ Systems


  • Digestive system in mammals (stomach, intestine, pancreas, liver)
• Organism

  A multicellular living thing, usually made up of many organ systems
• Enzyme

  A biological catalyst which increases the speed of a reaction without being changed or used up at the end of the reaction
• Enzymes reduce the need for high temperatures to speed up reactions
• Enzymes speed up useful chemical reactions (metabolic reactions)
• Enzyme structure

  Large proteins made up of chains of amino acids folded up into unique shapes
• Enzyme specificity


  Every enzyme molecule has an active site – the part where the substrate joins onto the enzyme
• Enzyme function


  For an enzyme to work, the substrate needs to be the correct shape to fit into the active site – the 'lock and key' model
• Effects of temperature on enzymes

  • Increase temperature = increase rate as enzymes and substrates gain energy and move around more and collide more often, up to a certain temperature. After this optimum temperature, any more increase will denature the enzyme (bonds inside it breaking, changing its shape and making the shape of the active site change)
• Effects of pH on enzymes

  • If pH is too high or too low, this will interfere with the bonds holding the enzyme together, changing the shape of the active site and denaturing the enzyme
• Measuring enzyme activity - hydrogen peroxide decomposition

  1. Hydrogen peroxide → water + oxygen (catalysed by catalase)

  2. Set up experiment to measure oxygen produced in first minute at different temperatures

  3. Control all other variables such as pH, potato used, size of potato pieces
• Measuring enzyme activity - starch hydrolysis

  1. Starch → maltose (catalysed by amylase)

  2. Use iodine solution to detect presence of starch, measure time taken for starch to break down at different temperatures

  3. Control all other variables such as concentration of starch solution, concentration of amylase, volume of starch and amylase solution, volume of iodine solution, pH
• Diffusion


  The net movement of particles from an area of high concentration to an area of low concentration
• Factors affecting diffusion rate

  • Bigger concentration gradient, larger surface area
• Osmosis


  The net movement of water molecules across a partially permeable membrane, from a region of high water concentration to a region of low water concentration
• The net movement of water molecules stops when there is an equal concentration of water molecules on either side of the membrane
• Active transport


  Movement of particles from low concentration to high concentration (against the concentration gradient), using energy released in respiration
• Differences between diffusion/osmosis and active transport

  • Diffusion/Osmosis: High concentration to low concentration, does not require energy
  • Active Transport: Low concentration to high concentration, requires energy
• Factors affecting movement of substances

  • Surface area to volume ratio
  • Distance
  • Temperature
  • Concentration gradient
• Diffusion in a non-living system

  Cube with dilute sodium hydroxide and phenolphthalein (pink) added to dilute acid. After a while, the acid diffuses in, neutralises the alkali, making the cube turn colourless