Long Set Biology Answers Flashcards
what are reducing sugars
what is is the benedict’s test for REDUCING SUGARS
what is a qualitative test
all monosaccharides and disaccharides are reducing sugars EXCEPT SUCROSE
1) add your sample to a test tube and add an equal volume of benedict’s solution to it
2) place your test tube in a water bath and heat to 95°C
3) a positive result is BLUE to BRICK red
this test is a qualitative benedict’s test because we cannot compare results from different samples. we only get a positive or negative result
semi quantitative benedict’s test
This is useful when comparing the concentration of reducing sugar in different solutions/samples e.g. types of lemonade.
• Control variables must be standardised by using the same volume of Benedict’s solution, the same volume of the sample solutions and the samples must be heated for the same period of time at the same temperature.
• The resulting colour (or the amount of precipitate seen) is then used to compare the concentration of reducing sugar. An intense brick red colour (lots of precipitate) indicates a high concentration of reducing sugar whereas a yellow or green colour shows a low concentration was present.
• A problem with this method is it can be difficult to judge colour - it is subjective (different people may have different views).
describe quantitate benedict’s test
This is carried out to obtain numerical data to compare the concentration of reducing sugar in different samples.
It is an objective test (not influenced by opinion).
This method can also be used to find the
concentration of an unknown sample:
• Perform the Benedict’s test on reducing sugar solutions of known concentrations.
• Control variables must be standardised: add the same volume of sugar solution and same volume of Benedict’s solution and heat in a water bath for the same length of time at the same temperature.
• Use a colorimeter to measure the absorbance of each of the known solutions.
• Plot a graph of known concentration (on x-axis) against absorbance value (on y-axis). This is called a calibration curve. Add a line of best fit.
Repeat the Benedict’s test with the unknown sample (using the same volume of sample, same volume of Benedict’s and heat in a 95°C water bath for the same amount of time).
• Use the absorbance value of the unknown to read off the calibration curve to find its concentration
test for non reducing sugar
Take a small sample and heat in a 95°C water bath with Benedict’s solution to confirm a negative result.
• Hydrolyse another sample of the sucrose by heating in a 95°C water bath with dilute acid (e.g.HCl).
• When cooled, neutralise the acid with an alkali (e.g. NaOH).
• Add the same concentration of Benedict’s solution and heat in a 95°C water bath.
• A positive brick red colour (precipitate) indicates a non-reducing sugar (sucrose) was originally present.
how do you identify starch
add 2/3 drops of iodine
orange to blue black solution
how to test for lipids
1) add sample to test tube and add ethanol
2) shake the mixture to make sure fat dissolves
3) add water
4) white emulsion forms
how can lipids be hydrolysed (2 ways)
1) heating with acid or alkali
3) lipase enzyme and optimum ph and temperature
how can proteins be hydrolysed
1) heating with acid
2) protease enzymes
test for proteins
biuert solution blue to lilac
what is the effect of substrate concentration in enzyme reactions
for a given concentration of enzyme molecules, an increase of substrate concentration will increase the rate of reaction to a point where rate reaches a constant maximum rate (Vmax)
• initially rate increases as collisions between enzyme and substrate is more likely to form enzyme substrate complexes
• the rate of reaction then levels out when more active sites of enzymes are being taken up by substrate molecules and therefore less frequency of collisons
• the active sites are saturated
• at this point the rate of reaction is limited by concentration of enzyme
• we can overcome this by adding more enzyme
graph is x axis = substrate conc
graph y axis = rate of reaction
it looks like a hill
effect of enzyme conc
When the concentration of substrate is in excess (i.e. it is abundant and not a limiting factor then an increase in enzyme concentration increases the rate of reaction.
• This is because when there are more enzyme molecules there are more active sites available.
• This increases the number of collisions between active sites and substrates to form more enzyme-substrate complexes.
effect of temp in enzyme
An increase in temperature provides the molecules with more kinetic energy resulting in more collisions between the active site of enzymes and substrate molecules and therefore more enzyme-substrate complexes are formed.
This increases the rate of reaction up to the optimum temperature where the rate of reaction is at a maximum.
Increasing the temperature above this causes the tertiary structure of the enzyme to denature as hydrogen and ionic bonds are broken.
The rate of reaction decreases as the substrate has difficulty binding to the altered active site. The active site has changed shape and is no longer complementary,so less
enzyme-substrate complexes form.
Denaturation of proteins at temperatures above 50°C is usually permanent as the tertiary structure is irreversibly altered and the substrate cannot bind to the active site.
inspiration
Inspiration or “breathing in” is an active process.
- External intercostal muscles contract pulling the ribs upwards and outwards, while the internal intercostal muscles relax.
- The diaphragm muscle contracts pulling the diaphragm down so it flattens.
- Both these actions increase the volume of the thoracic cavity.
- The pressure inside the lungs decreases below atmospheric pressure and air enters the lungs along a pressure gradient.
Expiration or “breathing out” is mainly a passive process as it uses less energy than inspiration.
- The internal intercostal muscles
contract pulling the ribcage
downwards and inwards, while
the external intercostal muscles relax - The diaphragm muscle relaxes
and the diaphragm moves upwards to its dome shape. - These actions decrease the
volume of the thoracic cavity. - The pressure inside the lungs
increases above atmospheric
pressure and air is forced out of
the lungs. - Elastic recoil of the lung tissue
helps to force air out of the lungs
during expiration.
expiration
