Biology paper 1

• Advantages of light microscopes

  Cheaper to buy and can see general outline of cells
• Advantages of electron microscopes


  Higher magnification and resolution but they are more expensive
• Formula for magnification

  magnification = image/actual
• Making cultures aseptic technique


  1. Lift lid of Petri dish towards flame to sterilise

  2. Put a drop of culture on agar/spread evenly

  3. Put drops/discs of antibiotics on culture if needed

  4. Use a few bits of tape to hold the Petri dish shut (but also allow aerobic respiration)

  5. Incubate at 25 degrees Celsius

  6. Measure the area with no bacterial growth
• How many chromosomes do regular human cells have compared to gametes


  Regular have 23 pairs

  Gametes have only 23 (not pairs)
• Stages of mitosis

  1. Nucleus dissolves and genetic material is duplicated

  2. The two sets of chromosomes move to opposite sides of the cell

  3. Mitochondria,ribosomes and other organelles are duplicated

  4. The cell divides and forms two new genetically identical cells
• Where are stem cells found in humans and plants

  Found in animal embryos and the meristem of the plant, some stem cells are made in the bone marrow but can only specialise into blood cells
• What can stem cells be used to treat

  Anemia

  Paralysis

  Diabetes
• Definition of diffusion

  The movement of particles from an area of high concentration to an area of low concentration across a partially permeable membrane (neutral as it does not use energy)
• Osmosis definition


  Diffusion of water across a partially permeable membrane from an area of high concentration to an area of low concentration (also passive as it does not use energy)
• Active transport definition

  The net movement of particles from an area of low concentration to an area of high concentration across a partially permeable membrane using energy from respiration
• OSMOSIS PRACTICAL

  1. Weigh and place identical cylinders from same vegetable in sugar solutions of varying concentration

  2. After a set time, remove cylinders and remove excess water before reweighing

  3. Calculate percentage change in mass using

  (Final mass-initial mass)/initial mass times 100

  4. Plot the percentage change in mass against concentration.using the line of beat fit find where the percentage change in mass =zero
• Ways to increase rate of osmosis and diffusion

  Increase difference in concentrations

  Increase surface area
• Outline the digestive pathway

  - Teeth break down food mechanically and saliva contains amylase

  - nutrients like glucose are absorbed by the villi in the small intestine into the blood

  - water is absorbed into the bloodstream in the large intestine

  -liver produces bile, stored in gall bladder and goes to small intestine, bile emulsifies lipids to form droplets with a larger surface area and neutralises pH so enzymes are at optimal pH

  -pancreas secretes amylase which breaks down starch into glucose in small intestine
• What are enzymes


  Enzymes are special proteins that act as biological catalysts, often breaking down molecules into smaller ones (polymers into monomers)

  Enzyme are SPECIFIC so only break down substrates that fit the active site (lock and key)
• Digestive enzymes


  Carbohydrates break down carbohydrates into simple sugars

  Proteases break down proteins into amino acids

  Lipases break down lipids into glycerol and fatty acids
• How does activity (rate of reaction). Change with temperature regarding enzymes


  Activity increases with temperature until the enzyme denatures (active site changes shape)

  This is also true with pH
• ENZYME PRACTICAL

  -mix amylase with starch and start timer

  -remove a few drops every ten seconds and add to a spotting tile with iodine

  - record time taken for no starch to be produced (iodine will remain orange)

  -repeat at different temperatures

  Plot points on a graph and use line of best fit to find optimum temperature (bottom of curve)
• FOOD TESTS

  Starch- turns iodine from orange to black

  Sugars- turns Benedict's solution from blue to orange

  Protein- turns biurets reagent from blue to purple

  Lipids(fats)- turn cold ethanol cloudy
• Pathway of air

  Trachea-bronchi-bronchioles-alveoli

  -oxygen diffuses into the bloodstream and binds to the heamoglobin in red blood cells to be transported

  - carbon dioxide and water diffuse from the blood to the lungs to be exhaled

  -alveoli have a large surface area to allow gaseous exchange to occur at a faster rate
• Pathway of blood

  —deoxygenated blood enters the heart through the vena cave to the right atrium

  -the deoxygenated blood then enters the right ventricle where a valve prevents backflow

  -deoxygenated blood then goes out the pulmonary artery to the lungs to be oxygenated

  -the now oxygenated blood then enters the left atrium through the pulmonary vein before entering the left ventricle and leaving to the rest of the body through the aorta
• Structure and function of arteries

  - carries blood away from the heart

  -always carries oxygenated blood EXCEPT the pulmonary artery

  - thick walls and thin lumen to withstand high pressure
• Structure and function of veins

  -carries blood back into the heart

  - thin walls and wide lumen

  - valves to prevent backflow
• Capillaries

  -one cell thick to allow fast diffusion
• Coronary heart disease and treatment

  When the coronary artery (supplies blood for the heart) becomes blocked by a build up of fatty deposits. Fat can build up in arteries that restricts blood flow. Can be treated by a stent that is inserted into the blood vessel and a balloon expands the stent before being removed to leave a structure that holds the blood vessel wider open. Can also be treated by statins (a drug) that reduces these fatty deposits
• What does blood carry

  - red blood cells

  -White blood cells

  -Platelets

  
  

  Everything except oxygen is dissolved in the plasma
• Leaves

  - site of photosyntheses

  -where water evaporates out
• Xylem

  - continuous tubes that carry water+dissolved mineral ions upwards

  - transpiration (unidirectional) rate increases with increased air movement and/or temperature

  - strengthened by lignin
• Phloem

  - Tubes of cells that transport dissolved sugars from leaves to the rest of the plant

  - cell sap can move from one phloem cell to another through pores in the walls
• Flower


  Reproductive organs
• Roots

  Water enters through osmosis

  Mineral ions enter through active transport
• Meristem

  Stem cell production
• Communicable disease

  Caused by a pathogen
• Non communicable disease

  Cause comes from inside the body
• Examples of non communicable disease and what increases the risk

  Diabetes-obesity and poor diet increase risk

  Heart disease- diet,smoking, lack of exercise

  Liver disease- alcohol
• Cancer

  Auto immune condition resulting from genetic mutation causing cells to multiple uncontrollably (tumour)

  Increased risk with carcinogens

  Malignant- spreads through body in the blood

  Benign-doesn't spread through the body
• Structure of the leaf

  Waxy cuticle-waterproof to stop water loss from the top of the leaf

  Upper epidermis-transparent to let light through

  Spongey mesophyll- gaps to allow gaseous exchange

  Palisade mesophyll-most photosynthesis takes place here

  Vascular bundle- xylem and phloem

  Lower epidermis- bottom of the leaf, contains stomata to allow gases in and out. Stomata size controlled by guard cells
• What is a pathogen

  A microorganism that causes disease, includes bacteria viruses fungi and protists
• How do viruses reproduce

  By inserting genes into a cell which causes them to produce more copies
• Examples of viruses

  measles

  HIV

  tobacco mosaic virus