snab topic 1 practicals notes

snab topic 1 practicals notes

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  • Created on: 09-06-14 19:22
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AS BIOLOGY
EXPERIMENT WRITE-UPS
Edexcel SNAB specification
Made by Nabilah Chowdhury
Copyrighted
References: SNAB Activity sheets + various internet resources
DAPHNIA EXPERIMENT
Topic: What affect does caffeine have on heart rate?
Aim: investigate how caffeine conc. can affect the heartbeat rate of daphnia
Background info:
If the environmental temperature changes, the daphnia's body
temperature does so too and it's metabolic rate will be expected to
rise or fall accordingly. So the temperature of the organism must be
kept constant during the procedure.
It has a transparent body so you can visibly count its heartbeats.
Prediction:
As the concentration of caffeine increases, the heartbeat rate will also increase.
Nabilah Chowdhury, 12RH
Copyrighted

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Hypothesis:
The heart follows the atria-ventricular cycle. During systole the heart contracts whilst during diastole the
heart relaxes. This way the blood pressure is maintained.
However caffeine makes the heart constrict by making the ventricles contract more. This in turn narrows
the arteries and blood is spurted out at high pressures. The constant contraction of the ventricles means
that blood is pumped faster around the heart in numerous spurts, thus increasing the heartbeat rate.…read more

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The results show a directly proportional trend ­ as the caffeine concentration increases so does the
number of heartbeats. Similar results are produces from each trial and therefore the results are repeatable
and reliable.
VITAMIN C EXPERIMENT
Topic: What is the Vitamin C content of different juices?
Aim: Investigate how much juice is required to turn DCPIP colourless
Background info:
Ascorbic acid (Vitamin C) is an antioxidant which is used to neutralise free radicals that are known to harm
cells.…read more

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DCPIP is a redox. Vitamin C (juice) is a reducing agent. The Vitamin C reduces the DCPIP and when it does,
the excess H+ from the acid in the juice binds to the DCPIP and changes it to a pale pink or colourless
solution.
If there is an increase in the amount of juice needed to "neutralise" the DCPIP, this means that it takes
more molecules to change the DCPIP into the colourless solution.…read more

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BEETROOT EXPERIMENT
Topic: Why does colour leak out of cooked beetroot?
Aim: use beetroot to examine the effect of temperature or alcohol on cell membranes.
Background info:
The dark red and purple pigments in beetroot are located in the cell vacuole and are chemical compounds
called betalains.
Prediction:
As you increase the concentration of alcohol, more of the cells content leaks out.
As you increase the temperature, more of the cell's contents will leak out.
DIRECTLY PROPORTIONAL.…read more

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liquid like. The bilayer may separate so that two chains of phospholipids remain, and all the cells contents
will leak out.
Temperature:
At physiological, or body temperature, the cells function their best. As
temperatures increase, both the cell membrane and the proteins can
be affected. The fatty acid tails of the phospholipid bilayer can "melt" at
high temperatures meaning that they become more fluid and allow
more movement.…read more

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Method for temperature
1. Use size 4 cork borer to cut sections of beetroot.
2. Cut x8 pieces of 1cm slices from these larger sections
3. Place slices in beaker of distilled water over night to wash away excess dye.
Next day...
4. Pour 5cm3 distilled water in x8 boiling tubes.
5. Place the boiling tubes in the water baths of different temps (at a regular range e.g. 10, 20, 30
degrees)
6. Wait 5mins for water to reach the required temp.
7.…read more

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Method for alcohol
1. Use size 4 cork borer to cut sections of beetroot.
2. Cut x8 pieces of 1cm slices from these larger sections
3. Place slices in beaker of distilled water over night to wash away excess dye.
Next day...
4. Place one slice in a 5cm3 boiling tube of distilled water ­ this will have a 0% alcohol conc.
5. Repeat with x7 boiling tubes containing the different concentrations of alcohol (at a regular range
e.g.…read more

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If 100% light is transmitted, then no light has been absorbed.
If 80% of light is transmitted, then 20% has been absorbed thus some pigment must have leaked out of
the beetroot cell in order to have absorbed the light.
Temperature Observation Calorimeter
(degrees reading (%
Celsius) absorbency)
Trial 1 Trial 2 Trial 3 Average
0 Clear 0 0 0 0
20 Pale pink 6 5 4 5
40 Pale pink 20 23 24 22.3
60 Pink 73 70 69 70.…read more

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At first, the rate of reaction increased steeply because doubling the concentration means that it also
doubles the number of enzymes acting upon the surface of the substrate.
However, when adding a high conc. of enzymes the rate will not increase as quickly, as the surface of the
substrate began to get almost completely covered with enzymes.…read more

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