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Biology – All Core Practicals

Using microscopes:

Parts to know: eyepiece lens, focusing wheel, objective lens and stage (specimen holder)
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Resolution = the smallest distance between two points on a specimen which can be
distinguished as two separate entities
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0001mm
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Units

1 metre/1000 = 1mm
1mm/1000 = 1μm (micrometre)
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Method
Safety = wear eye protection
A
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Place the cells on a microscope slide, and add a stain/drop of water to the slide
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Iodine can act well as a stain
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Use a toothpick to lay a coverslip over the specimen to keep it flat and hold it in
place
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Examine specimen with a microscope, starting with lowest magnification and
working way up to highest
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Draw cells without colouring or shading
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1
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2
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3
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When food is tested, measure 2cm3 of the food solution into a test tube and place in
a hot water bath to allow chemical reactions to occur more rapidly
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Glucose: Benedict’s solution will go from blue and become increasingly red depending on
the quantity of glucose present
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Problems: the test does not work for sugars which are non-reducing e
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sucrose

Protein: biuret test: sodium hydroxide is mixed with a solution of the food
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Lipids (fats and oils): ethanol emulsion test – food mixed with ethanol and shaken
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Fats and oils dissolved in the ethanol float
to surface forming cloudy emulsion
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Set up heating apparatus using tripod, gauze, heat-resistant mat, Bunsen burner and
large beaker half-full of water
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B
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C
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D
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E
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F
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Start timing as you stir the mixture
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Every 30 seconds, take a small amt
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Stop testing when the iodine solution stops
changing colour (from brown/orange to blue/black)
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Repeat experiment using different pH solutions
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Not always obvious to detect when the solution stops becoming blue-black – the colour
change tends to be gradual (may be a mix of blue-black/brown-orange)
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Solution: get several people to observe the spotting tile and
decide unanimously when the reaction has completed
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Potato is peeled, because the potato’s skin can affect osmosis
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Cork borer is used to produce three cylinders of potato – using a cork borer makes
all of the cylinders the same diameter
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Use a scalpel to trim the cylinders to the same length (around 3cm) – Not diameter
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Measure length of each cylinder (3cm) and the mass of each cylinder with an electric
scale – should be similar
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Place each cylinder into a test tube, add 10cm3 of 0
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6
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25 molar sugar solution to 2nd test tube, 10cm3 of distilled water to
3rd – (distilled contains no dissolved substances which may affect osmosis)
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Leave potato cylinders overnight to allow osmosis to take place
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Remove potato cylinders and roll them on a paper towel to remove surface
moisture
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Measure the length and the mass of the cylinders again
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Calculate percentage change in lengths and masses of each cylinder compared to
their starting values:


% change = change in value/original value x100

At lower concentrations (dilute solutions) potato mass will increase because water will
move into the potato via osmosis as there is less concentration of water in the potato than
outside of it
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5 molar) potato mass
will decrease as water moves out of the cells because the concentration of water outside
the potato is smaller
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Use an agar gel plate – agar gel in a Petri dish
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How bacteria are prepared onto an agar dish:
1
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2
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a
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Sterilise the inoculating loop by holding it over a Bunsen flame
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4
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5
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How the practical is carried out - method:
1
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2
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3
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4
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5
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6
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7
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Leave for a few days
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After this, a layer of bacteria should be observed with a zone of inhibition (a circle
gap) around most of the antibiotics – they have prevented bacteria from growing in
these zones
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Effectiveness of antibiotic can be measured by measuring the area of the zone of
inhibition, measure the radius then pi r squared
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Photosynthesis:

Investigate how light intensity affects the rate of photosynthesis
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1
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LED used because they do not release much heat – higher
temperatures may affect the experiment
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Pour 45cm3 of sodium hydrogen carbonate solution (1%) into the tube – this
substance releases carbon dioxide which is required for photosynthesis
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Put an 8cm long piece of pondweed, Cabomba into the boiling tube with a cut end at
the top – do this carefully using forceps, make sure pondweed not damaged/liquid
overflow
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Leave for five minutes to allow the pondweed to acclimatise to the conditions
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Bubbles of gas should be seen being produced from the cut end of the pondweed –
oxygen being produced by photosynthesis
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Start a stopwatch and count the no
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7
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8
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Independent = distance from light source in cm


Dependent = number of oxygen bubbles produced per minute

Control (stay same and are important) = piece of Cabomba pondweed, temperature,
concentration of sodium hydrogen carbonate

Safety = dry hands when handling lamp

A correct experiment would see less bubbles produced the further back the pondweed is
placed
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Revised
experiment would measure the volume of oxygen produced
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Inverse square law

Light intensity increases photosynthesis because photosynthesis is endothermic – it uses up
light energy to react water and carbon dioxide into producing oxygen and glucose
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The
initial straight line on the light intensity graph indicates that light intensity is directly
proportional to the rate of photosynthesis until a limiting factor (such as temperature) has
an effect on photosynthesis
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E
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Therefore If you double the distance from a light source (e
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10cm to 20cm) the light
intensity is ½2 – in other words, a quarter of the original
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g
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Extraction of DNA from living material

Safety: wear safety goggles

Method

1
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2
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Do not make the mixture foamy!

4
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Mash 50g of peas, placing the mashed peas into an empty beaker + adding solution
made in first steps, stir slowly for 1 minute
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Place beaker in a 60oC water bath for 15 minutes
7
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Place 10cm3 of filtrate into boiling tube
9
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Proteases break down the proteins in the pea
10
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DNA is insoluble in ethanol, so it forms a precipitate
11
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Investigation into factors affecting the distribution and abundance of a species

Method

1
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2
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Place a quadrat down and count the number of plant species found within
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Return to the starting point and use different random numbers to generate
coordinates to take measurements from, repeating these steps 14 times
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Certain locations may be used to measure the effect of an abiotic factor (e
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cutting
of grass)
6
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Population size = no
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- FORMULA:
o (No
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in 2nd)/number in 2nd previously marked

Investigation into factors affecting decomposition (milk)


Aim: to measure temperature’s effect on the rate of decomposition of milk
- Done through pH because bacteria in the milk convert lactose sugar into lactic acid
which is acidic, and thus can help us to measure the decay of milk

Method:
1
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Determine initial pH of each milk beaker using universal indicator
3
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Makes sure bacteria in the milk does not escape
4
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Use universal indicator paper to find out the pH of each beaker after 24, 48 and 72h
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8)

How to improve experiment: repeat to find a mean – improves reliability

Alternative experiment for same aim:
1
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5cm3 of urea to a test tube
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Add 1
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3
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4
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5
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6
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Theory:
- Decomposers secrete enzymes into the soil to speed up decomposition
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Factors affecting decomposition:
- Temperature: speeds up decomposition as enzymes are better able to catalyse
molecules as they have more kinetic energy so more collisions occur – but if
temperature = too high enzymes denature
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- Oxygen: speeds up decomposition – plentiful oxygen supply = aerobic respiration =
more growth = microorganism population increased so speeds up
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Carry out a risk assessment for using the scalpel:
a
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Examine the outside of the kidney – ureter, renal artery and renal vein all enter in
same area – draw a diagram of the kidney
3
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Observe the cut surface
5
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Draw diagram of kidney after dissection

Examination of artery + vein using a light microscope

Method
1
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S
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2
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Calculate the magnification: eyepiece lens mag
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3
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Work in pairs
2
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Drop ruler without the test subject expecting it, measure reaction time by the
distance at which they grab the ruler at
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Repeat 10 times (don’t calculate a mean)


NON-REQUIRED BUT COULD COME UP


Investigating aerobic respiration in germinating peas

Theory

-

Germinating peas grow rapidly
Growth process requires a lot of energy for cell division
So, rate of respiration in germinating peas is high
We can measure this in heat produced by aerobic respiration (an exothermic
reaction) in the peas
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Germinating peas
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Flask C – boiled, disinfected peas
- The control experiment
- Heat not produced

- Peas boiled to denature the enzymes responsible for catalysing aerobic respiration
- No microbes to respire and release heat either
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- This experiment is measuring temperature’s effect on the rate of oxygen uptake
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What is the purpose of sodium hydroxide solution?
- Absorbs carbon dioxide
- Makes sure that only oxygen uptake is being measured and prevents carbon dioxide
produced by respiration hindering the results
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Measuring the decrease in mass

Method
1
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Measure their mass
3
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Why?
- Most stomata found on bottom surface
- Avoids rainfall being absorbed by leaf
- + stops them transpiring too much in the Sun

2
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Set up this equipment:


Source: BBC Bitesize GCSE Eduqas Biology

2
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3
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4
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Timer is started, and a set time (e
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30s) is measured
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The distance the air bubble has travelled along the scale is recorded
7
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g
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Remove a green leaf from a plant
2
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Stops enzymatic reactions within cells in the leaf
3
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Extracts chlorophyll as ethanol dissolves lipids in cell membranes – green
pigment removed
4
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Softens leaf and allows iodine to penetrate
5
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Urine food tests to check for
- Healthy urine
- Someone with kidney disease
- Someone with uncontrolled diabetes

Method
- Add biuret reagent sample to check for protein
o Sodium hydroxide solution + drops of copper sulfate
- A colour change from pale blue to purple would be seen, without need for heating
- Add Benedict’s solution to check for glucose + heat strongly
o Blue to brick red = high glucose concentration
o Blue to green = low glucose concentration
o Blue to yellow = moderate concentration
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o Glucose not positive as it would be expected for the proximal convoluted
tubule to be reabsorbed into the blood
Uncontrolled diabetes = positive result with Benedict’s solution + biuret
o Glucose present as extremely high concentrations of glucose in the blood
would lead to a lack of reabsorption by the PCT into the blood
o Protein present thanks to damage to glomerular membrane
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- The concentrated sucrose solution is hypertonic in comparison to the surrounding
distilled water which is hypotonic = it has a higher concentration of solutes
- So, a net movement of water particles takes place (osmosis) from the water outside
the Visking tubing to the sugar solution inside
- (indicated by a rising water level in a capillary tube)
- Sucrose particles stay in the tubing as they are too large to pass through the partially
permeable membrane

1
The similarities between Visking tubing and a real gut are:
• the food molecules are contained in a tube whose walls are permeable only
to small molecules
• the food in the tube is a mixture of large and small molecules
• the tube is surrounded by liquid which contains a low concentration of food
molecules
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