Biology Paper 1 Part 3

• Why might temperature need to be controlled when working out sugar concentration of plant tissue?

  If the temperature is warmer, the water will have more kinetic energy. Therefore moving across the membrane quicker by osmosis.
• Why do you place cling film over the test tube while osmosis is occurring ?

  To prevent evaporation and reducing the water concentration.
• What does the word equilibrium mean in terms of osmosis?

  The water concentration is the same as both sides of the membrane, therefore there is no net movement
• When working out water concentration of plant tissue, how would you use this information to work out water uptake ?

  Mass gain divided by time.
• How do use iodine to test for starch?

  If it goes brown to blue / black if starch is present.
• How do You use Benedict's to test for sugar?

  Add Benedict's and heat water in a Bath , if it turns blue to orange or brick red. Sugar is present
• How do you use buirets to test for protein or amino acid?

  Add buirets and it will go blue to purple if protein or amino acids are present.
• What are the limitations of food tests?

  Qualitative- You get a positive or negative result and do not tell you numbers (quantitative).
• How would you test the effect of PH on the rate it an enzyme controlled reaction?

  Place starch and a pH buffer in test tube, the buffer keeps PH the same.

  Place in water bath to control temperature, use thermometer.

  Remove some and check it will test positive with iodine at the start.

  Add amylase

  Remove some of solution every 30 seconds

  When it stops testing positive with iodine all the starch has been broken down.
• How would you control the PH in an experiment?

  PH buffer , reduces the effect of an acid or alkali being added. Keeps PH the same.
• What is starch broken down into?

  Maltose first then glucose
• Other than testing for iodine every 30 seconds how else could you see how quickly amylase breaks down starch?

  Colorimeter - measures how much light passes through a solution if iodine, starch and amylase.

  
  

  As starch is broken down less iodine will go blue / black so more light can pass through.
• Why does a light microscope require a thin specimen to study?

  Light needs to be able to pass through.

  Too thick and fells will not be clear because they are piled on top of eachother.
• If the eyepiece lens is 10X and the objective lens reads 20X, what would be the total magnification?

  200X - you multiply them together
• What should be included on a diagram when you draw cells or any biological drawing?

  A scale bar - see magnification

  Lines with no arrows - identify different sections

  Single lines with no shading
• Why do you use a stain on cell preparations?

  To see the cells as otherwise most would be colourless.
• A coverslip is lowered at an angle onto the cells when preparing a slide. Suggest why?

  Squeeze out any air bubbles.

  Any remaining can be removed by drawing the water through with tissue paper.
• How do you calculate modal average?

  Look for most common result.
• How do calculate median ?

  Removing highest to lowest result until you are left with one
• Place the following in size order, largest to smallest: nucleus , ribsosomes, mitochondria, cell , tissue , organ system

  Organ system

  Tissue

  Cell

  Nucleus

  Mitochondria

  Ribosome
• On the microscope, scientists could see other objects and that were hard to identify and did not let light through, what could be the issue?

  Small pieces of dust that appear large in the microscope.
• Why do we focus upwards rather then downwards when using a microscope?

  The higher magnifications could damage the lens as it is possible not lower it into the slide.
• How would you work out the effect of light intensity on the rate of photosynthesis?

  Cut a 5cm piece of pondweed. Place under a funnel in large piece of water. Count bubbles.

  Divide volume of gas or bubbles by time. Repeat with lamp further away.
• How could you make sure that the heat of a lamp has less of an effect of measuring light intensity in photosynthesis?

  Use a clear heat shield which would absorb heat but let light through.
• Why might heat effect measuring light intensity in photosynthesis?

  Enzymes are used and they are effected by heat.
• Why is collecting gas from a plant not a good measure of photosynthesis?

  The gas could be carbon dioxide from respiration . Some of the oxygen produced by photosynthesis could be used by the plant in respiration and not released.
• What would you control when working out the effect of light intensity on the rate of photosynthesis?

  Species of pondweed.

  Temperature by placing experiment in a water bath or using heat shield.
• Why might you not be able to throw the pondweed away in the bin?

  Some species may invade waterways, damaging ecosystems.
• What needs to happen to a scientific experiment before we accept the results?

  A peer review journal. Other scientists view methods and decide if it was done correctly.
• What is the problem if a group of scientists work for a company that make money out of the products they are testing?

  They will be bias and might want their results to come out a certain way.
• Why might scientific results that are published online and in papers not be accurate?

  I hehe might not have been submitted by a peer review journal ( checked by other scientists ).
• What is the difference between measured and perceived risk?

  Measured risk is the percentage of chance scientists have calculated of a safety issue occurring.

  Perceived risks is how likely someone believes a safety issue may happen.
• Why might perceived ( estimated ) risk be different to measured ( calculated ) risk?

  People might not be able to see the hazard making people more anxious. If the hazard is unfamiliar, people might be confident knowing the actual risk.
• What would you look for to know it an experiment was relaible?

  Number of repeats

  Number of people in sample

  Did they get a mean average and exclude anomalous results ( odd ones out )
• What is a random error?

  Careless in taking readings or improper carrying out methods might make the results differ by varying amounts each time.
• Why do we repeat results?

  To calculate mean averages and identify anomalous results and exclude them. Reliability.
• How would you calculate 30% of a number?

  Multiply by 0.3
• What is uncertainty?

  The smallest number of your results can be rounded to. ( a ruler measured to nearest 1mm to hen the uncertainty either side would be 0.5)
• How many significant figures should you go to when doing calculations?

  The same as the question.

  I.e if the paper has gone to 1 S.F then so do you
• How do you calculate mean?

  Add up results and divide by how many there are, ignore any anomalous results.