PAPER 1 again

• Cells


  Can be seen with a normal light microscope, but subcellular structures are not visible. Electron microscopes have better resolving power and resolution to see finer details.
• Cell size


  Can be calculated by knowing the magnification of the microscope: Magnification = Image size / Object size
• Cell types


  • Eukaryotic cells (have a nucleus)
  • Prokaryotic cells (no nucleus, DNA in a ring called a plasmid)
• Eukaryotic and prokaryotic cells


  • Contain similar organelles or subcellular structures
• Cell membrane


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

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


  The liquid that makes up the cell, 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
• Plant cells


  • Contain chloroplasts with chlorophyll, where photosynthesis takes place
  • Contain a permanent vacuole to store sap
• Bacterial multiplication


  1. Binary fission, number doubles every 10 minutes

  2. Can be demonstrated through a practical using agar in a Petri dish and aseptic technique
• Diploid cells


  Cells with 23 pairs of chromosomes (e.g. human cells)
• Haploid cells


  Cells with 23 single chromosomes (e.g. gametes)
• Cell division


  Mitosis: Genetic material is duplicated, nucleus breaks down, chromosomes are pulled to opposite sides, new nuclei form, resulting in two identical cells
• Cell specialization


  • Cells specialize depending on their function (e.g. nerve, muscle, root hair, xylem, phloem, stem cells)
• Stem cells


  Unspecialized cells that can differentiate into various cell types, found in embryos and bone marrow
• Diffusion


  The movement of molecules or particles from an area of high concentration to an area of low concentration, down the concentration gradient, without requiring energy input
• Osmosis


  The diffusion of water across a semi-permeable membrane
• Factors affecting diffusion and osmosis

  Increased concentration difference, temperature, or surface area can increase the rate
• Practical on osmosis


  Cut equal-sized vegetable cylinders, weigh, place in varying sugar solutions, reweigh after a day, calculate percentage change in mass, plot against concentration to find the point of no change (same concentration inside and out)
• Active transport


  The movement of substances through a membrane against a concentration gradient, using energy
• Tissues


  Groups of similar cells connected and working together
• Organs


  Groups of tissues working together to perform a specific function
• Organ systems


  Groups of organs working together (e.g. circulatory, digestive)
• Enzymes


  Biological catalysts that break down larger molecules into smaller ones, specific to certain substrates due to the lock-and-key principle
• Factors affecting enzyme activity

  Increased temperature and optimal pH increase the rate, but extreme conditions can denature the enzyme
• Practical on enzyme activity

  Mix amylase with starch at different temperatures or pH, time how long it takes to break down all the starch, plot a curve to find the optimum conditions
• Food tests


  Iodine for starch, Benedict's solution for sugars, Biuret's reagent for proteins, ethanol for lipids
• Breathing vs respiration


  Breathing provides the oxygen for respiration to occur in cells
• Respiratory system

  • Air moves down the trachea, bronchi, bronchioles to the alveoli where gas exchange occurs
  • Oxygen binds to hemoglobin in red blood cells and is transported to cells
  • Carbon dioxide and water are expelled during exhalation
• Circulatory system


  A double circulatory system, with deoxygenated blood entering the right side of the heart, going to the lungs, then oxygenated blood returning to the left side of the heart and pumped to the body
• Heart


  • Has thicker walls in the left ventricle to pump blood to the whole body
  • Electrical pulses from the right atrium cause the heart to contract and beat
  • Coronary arteries supply the heart muscle with oxygen and nutrients
• Blood vessels


  Arteries carry oxygenated blood away from the heart, veins carry deoxygenated blood towards the heart, capillaries allow fast diffusion
• Non-communicable diseases


  Diseases caused by factors within the body, e.g. cardiovascular disease, autoimmune conditions, cancer
• Communicable diseases


  Diseases caused by pathogens that can be transmitted between organisms
• Coronary artery


  Delivers blood to the heart muscle to supply oxygen
• Coronary heart disease (CHD)


  Occurs when coronary arteries are blocked by fatty deposits, causing a heart attack
• Stent


  A small tube inserted into blood vessels to keep them open and allow blood flow
• Statins


  Drugs that reduce cholesterol and fatty deposits
• Faulty heart valves


  Result in backflow, can be replaced with artificial ones