Biology paper 1 weak areas

• I micrometer = 0.001mm
• I nanometre = 0.000001mm
• Magnification is how many times bigger an image is compared to the actual size of a specimen
• The resolution is the smallest observable difference between two points on an instrument
• Magnification = image size/ actual size
• Electron microscopes have a higher magnification and resolution than light microscopes
• Microscopy practical


  1. prepare an onion by taking thin layer and place on Slide, stain with iodine and place a cover slip on top
  2. clip on stage and use lowest Powered objective lens
  3. Use coarse focusing wheel and fine focusing wheel to get image in focus
  4. To get higher magnification, use higher powered objective lens
• binary fission is how bacteria divides and they divide once every 20 minutes in ideal conditions
• 2^n where n is the number of divisions
• the ideal conditions for bacteria to divide is warm temps(37°C in labs but 25°C in schools ) and adequate nutrients
• Sterile methods 


  • work carried out in front of bunsen burner
  • only open petri dish a bit
  • Lid only secured with a few bits of tape
  • Don’t incubate above 25°C
• Culturing microbes practical 


  1. Sterilise hands and tables
  2. Use a sterilised inoculating loop to spread culture on petri dish
  3. place 4 paper discs in 4 sections soaked with a different antibiotic but one control with only water
  4. Incubate for 48 hours at 25°C and calculate zone of inhibition using $pir^2$
• Mitosis is used for growth and repair
• Stages of mitosis 


  • cell enlarges and chromosomes and organelle duplicate
  • Nucleus dissolves and each set of chromosomes is pulled to the opposite sides
  • Cytoplasm and cell membrane divide forming two daughter cells
• A stem cell is an undifferentiated cell
• Embryonic stem cells are found in embryos and can become any cell
• Adult stem cells are found in bone marrow and can only become blood cells
• Meristem cells are found in the roots and shoots and can become all plant cells
• Therapeutic cloning


  • nucleus is removed from skin cell and is replaced with an egg cell from donor
  • This develops into an embryo and can differentiate into any cell
  • This means the cell can’t get rejected
• issues With stem cells


  • stem cells in labs could become mutated or infected
  • Lack of peer reviewed success
  • Embryo rights
• The benefits of plant stem cells is that they can clone plants with beneficial traits such as pest resistance
• SA:V ratio is bigger the smaller an object is
• SA:V ratio affects the rate of subject exchange as the distance between cell membrane and centre of cell is short so no diffusion etc is needed
• The bigger an object, the lower the SA:V ratio so they have to use exchange systems such as villi, lungs and roots
• The bigger an object, the lower the SA:V ratio so they have to use exchange systems such as villi, lungs and roots
• Osmosis practical 


  1. Get 5 potato cylinders of same size using cork borer and ruler
  2. Place them in 5 sugar solutions ranging from 0 mol/dm^3 to 1 mol/dm^3 after weighing them
  3. Leave for 24 hours
  4. Remove and blot dry and reweigh
  5. Find out percentage change and plot on graph and where the line meets the x axis is the concentration of sugar inside the potato
• Digestion is used to build new carbohydrate, lipids and proteins for cells
• amino acids are used to build enzymes and antibodies and the products of lipids are used to make cell membranes and hormones
• Food tests practical

  1. break up food using pestle and mortar and mix with water and strain to get solution
  2. iodine = orange to blue/black
  3. Benedicts = blue to green if little, yellow if moderate and brick red if a lot
  4. biuret = blue to lilac
  5. Ethanol = colourless to cloudy emulsion
• Enzymes practical 


  1. add iodine to spotting tiles
  2. Mix ph buffer solution and amylase
  3. Mix solution with starch and start timer
  4. Add drop of solution to each iodine spot every 10 seconds until no colour change
  5. Repeat steps with different ph buffer solutions
• Adaptations of alveoli 


  large surface area for faster diffusion

  Thin walls for shorter diffusion pathway

  Good blood supply to maintain high gradient
• The Intercoastal muscles are between the ribs and cause inhalation and exhalation
• The left side of the heart is thicker as it has to pump blood to the whole body
• The right side of the heart pumps deoxygenated blood
• The septum in the heart prevents mixing of blood
• The pacemaker cells are in the right atrium and control heart rate by sending impulses
• Of pacemaker cells are faulty, artificial pacemakers can be fitted to correct irregular heartbeat
• Coronary heart disease is the buildup of cholesterol in the arteries leading to a blockage which hardens as plaque
• The buildup of cholesterol in arteries lead to less blood flow which leads to less O2 to heart which leads to lack of respiration which leads to lack of contractions so less O2 gets to cells so it causes shortness of breath and fatigue
• partial blockages cause anginas whereas full blockages can cause heart attacks