Biology Paper 1

• 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
• Eukaryotic cell nuclei


  • Contain DNA stored in several chromosomes, humans have 23 pairs (diploid cells)
  • Gametes have half the number of chromosomes (haploid cells)
• Cell division


  Mitosis: Genetic material is duplicated, nucleus breaks down, one set of chromosomes 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, a passive process
• Osmosis


  The diffusion of water across a semi-permeable membrane
• Factors that increase the rate of diffusion and osmosis:
• Practical on osmosis


  Cut equal size cylinders from a vegetable, weigh, place in varying sugar solutions, reweigh after a day, calculate percentage change in mass, plot against sugar concentration to find the concentration with no change (same as inside the cells)
• 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 speed up chemical reactions, specific to certain substrates due to the lock and key principle
• Factors affecting enzyme activity

  • Rate increases with temperature up to the optimum, then decreases as the enzyme denatures
  • Rate also affected by pH, with an optimum pH range
• Practical on enzyme activity


  Mix enzyme (e.g. amylase) with substrate (e.g. starch), test for presence of substrate at intervals using iodine, plot time taken for complete reaction against temperature or pH to find optimum
• Food tests


  Iodine turns black with starch, Benedict's solution turns orange with sugars, Biuret's reagent turns purple with proteins, ethanol goes cloudy with 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


  • Double circulatory system, deoxygenated blood enters right side of heart, pumped to lungs, oxygenated blood returns to left side and is pumped to body
  • Heart has thicker walls on left side to pump blood to whole body
  • Blood vessels: Arteries carry oxygenated blood away from heart, veins carry deoxygenated blood towards heart
• Coronary arteries


  Supply the heart muscle with oxygen and nutrients
• Cardiovascular disease


  Non-communicable disease caused by factors within the body, e.g. coronary heart disease, faulty heart valves
• 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
• Cardiovascular (CV) disease


  An example of a non-communicable disease, caused by factors within the body
• Examples of non-communicable diseases


  • Cardiovascular disease
  • Autoimmune conditions
  • Cancer
• Communicable disease


  Caused by a pathogen that enters the body, resulting in viral, bacterial or fungal infection