Biology paper 2

• Suggest one reason the scientists used BIOMASS instead of the number of individuals of each plant species when collecting data to measure diversity

  1. Too small to count individuals
• What is meant by the all or nothing principle

  1. An action potential is only generated above the threshold
  2. Increasing the pressure creates a generator potential
• Explain the action of acetylcholine

  1. It blocks the Ca2+ channels
  2. Therefore Ca2+ can not move into the presynaptic knob by facilitated diffusion
  3. Therefore vesicles do not merge with the presynaptic membrane and nothing is released
  4. No neurotransmitters diffuse across the synaptic cleft and they do not attach to the receptors on the postsynaptic membrane
  5. Na+ do not diffuse in so no action potential occurs as the membrane does not depolarise
• Suggest two reasons why drugs should be injected into their cerebrospinal fluid rather than a pill

  1. Directly reaches the spinal cord
  2. It's too large to be absorbed
• Describe how carbon dioxide is fixed and organic substances are produced during the LIR

  1. Carbon dioxide and RuBP join to form GP
  2. This reaction is catalysed by rubisco
  3. ATP + NaDPH -> GP + triose phosphate
  4. Triose phosphate is then used to regenerate RuBP
• State why the scientists need the sample to be random

  1. to remove bias
• Explain the relationship between leaf area and number of flowers

  1. More leaf area means more photosynthesis occurring
  2. It increases the amount of sugar produced
  3. So that means more cellulose is made
• Describe the role of ATP in muscle contraction

  1. It breaks actinmyosin
  2. It then bends the myosin head
• Suggest and explain how transport proteins are useful during exercise

  1. More glucose enters the cells
  2. It enters via facilitated diffusion
  3. This then gives more fatty acids for the krebs cycle
• An increase in muscle activity causes an increase in heart rate, describe and explain how

  1. An increase in CO2 makes the blood more acidic, chemoreceptors pick this up
  2. They send impulses to the medulla oblongata
  3. This causes more impulses from the SAN
  4. Via the sympathetic nervous system
• Scientists used a radioactive labelled DNA probe to show a cell contained a specific gene. How did they do this

  1. Extract the gene and add restriction endonuclease
  2. Separate the fragments using gel electrophoresis
  3. Treat the DNA to form single strands
  4. The probe will bind to the specific gene
  5. Use autoradiography to show the gene
• What is a DNA probe

  1. Short single stranded DNA
  2. Has bases complementary to the specific gene
• Describe how enzymes can insert a gene into a plasmid

  1. Restriction endonuclease is used
  2. Ligase joins the gene and the plasmid
• Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis

  1. Mass of the amino acid
  2. R group
• What is the role of reverse transcriptase in PCR

  1. produces cDNA from mRNA
• What is the role of DNA polymerase in PCR

  1. Join nucleotides to form DNA
• Any DNA is hydrolysed by enzymes before the sample is added to the reaction mixture in PCR. Why?

  1. To remove any DNA present
  2. Because this DNA would be amplified, which you do not want
• Why does DNA replication eventually stop in PCR

  1. Limited number of nucleotides
• Describe and explain how PCR is used to amplify a DNA fragment.

  1. You need; DNA polymerase, DNA primers and nucleotides
  2. Heat the sample to 95 degrees to break the hydrogen bonds
  3. Reduce the temperature so primers bind to the DNA
  4. Increase the temperature, DNA polymerase joins nucleotides
• Why would inhibiting the krebs cycle decrease the uptake of oxygen in respiration

  1. Less reduced NAD
  2. Oxygen is the terminal electron acceptor
• What will autosomal linkage mean

  1. The genes occur at the same point in the chromosome
  2. There will be no Heterozygous offspring
  3. There is no crossing over
• How do you determine mean percentage coverage

  1. use a random coordinate generator
  2. Place a large amount of quadrats down
  3. Divide the total percentage by the number of quadrats
• Explain how succession results in a wide variety of fish living on coral reefs

  1. Increases the variety
  2. Means there will be more food types
• Explain why glucose is found in the urine of a person with untreated diabetes

  1. There is a high concentration of glucose in the blood
  2. Not all the glucose can be reabsorbed into the cell in the proximal convoluted tubule
  3. The co-transport proteins are working at their maximum
• The two alleles F and f of a different gene, which is not sex-linked, interact with the gene controlling fur colour. Name the type of interaction

  Epistasis
• How are colours seen

  1. Colour vision involves cone cells
  2. Each photoreceptor has a different pigment
  3. Greater absorption by certain wavelengths to give colour
• How are the proximal convoluted tubules adapted to allow the rapid readsorption of glucose into the blood

  1. Microvilli provide a large surface area
  2. Many carrier proteins for active transport
  3. Many mitochondria for active transport
• Name two parts of the nephron that have binding sites for ADH

  1. Collecting duct
  2. Distal convoluted tubule
• Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect the blood pressure

  1. Aorta
  2. ADH increases the re adsorption of water
  3. Increases the volume of the blood and pressure
• Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem

  1. Heat loss from respiration
  2. Food not digested
  3. Excretion
• How are DNA strands cut at specific genes

  1. Using restriction endonucleases
  2. It cuts the DNA at specific base sequences
• Why is it important to know the base sequences when doing PCR

  1. For the primers
  2. To produce a complementary base sequence
• Describe and explain how taking creatine supplements and carb loading can improve performance of different muscle types

  1. Fast fibre muscles are used in short intense exercise
  2. Slow fibre muscles are used during long term exercise
  3. Creatine is used to form phosphocreatine
  4. This phosphocreatine combines with ADP to form ATP
  5. The carbohydrates are stored as glycogen
  6. The glycogen is then hydrolysed to release glucose which is used in respiration