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Bio paper 1
Required practicals
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Cards (36)
Optical
microscope
Used to look at
cells
on a
prepared
microscope slide
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Optical
microscope
Has a
stage
to place the microscope slide
Has a
light
source (lamp or mirror) to illuminate the slide
Has objective lenses with different magnifications (4x,
10x
,
40x
)
Has an
eyepiece
lens with 10x magnification
Has
coarse
and
fine
focusing dials
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Using
an optical microscope to view a prepared slide
1. Place slide on stage and secure with clips
2. Select lowest power (
4x
) objective lens
3. Slowly turn coarse focus dial to lower lens near slide
4. Look through eyepiece and turn coarse focus dial to bring cells into focus
5. Use fine focus dial to sharpen focus
6. Calculate total magnification by multiplying eyepiece (10x) and objective (
4x
, 10x,
40x
) magnifications
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What you might see under an optical microscope
Animal
cells:
nucleus
, cytoplasm, cell membrane, possible mitochondria
Plant cells: cell wall,
cytoplasm
,
nucleus
, possible vacuole and chloroplasts
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An
optical microscope
can only show
limited
detail compared to other microscopes
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Drawings made from an optical microscope should include a
magnification
scale
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This is a required
practical
that could come up as a
6-mark essay
question in the exam
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Preparing
uncontaminated bacterial culture using aseptic technique
1.
Sterilize
petri dishes, bacterial nutrient broth, and
agar
to kill unwanted microorganisms
2.
Transfer
bacteria using a sterilized inoculating loop
3. Attach lid with
adhesive
tape to prevent contamination
4. Incubate plate upside down at
25°C
to reduce chances of harmful bacteria growth
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Investigating
effect of antibiotics on bacterial growth
1. Clean bench with disinfectant
2. Sterilize
inoculation
loop
3. Open sterile agar plate near
Bunsen burner
flame
4. Use loop to spread chosen
bacteria
evenly on plate
5. Place sterile
filter paper disks
containing antibiotic onto plate
6. Incubate plate at
25°C
for a few days
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Bacterial
culture
Bacteria
can double in number every
20
minutes with enough nutrients and suitable temperature
Nutrient
broth solution contains all nutrients bacteria need to
grow
and divide
Agar gel plates
contain nutrient broth solidified into a jelly, allowing bacteria to grow into
visible
colonies
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Zone
of
inhibition
Region where
bacteria
are not growing around the
antibiotic disk
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Calculating
area of zone of
inhibition
Area = π x R^2, where R is the
radius
of the zone of inhibition
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Plenty
of questions on culturing microorganisms and this required practical in the
revision workbook
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Osmosis
Diffusion
of
water
from a dilute solution to a concentrated solution through a partially permeable membrane
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Plant cells placed in water
Water moves into the cell by
osmosis
, causing the cell to
expand
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Plant
cells placed in concentrated solution
Water moves out of the plant cell by
osmosis
, causing the cell to
shrink
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Investigating
the effect of osmosis on plant tissue
1. Peel potato
2. Use cork board to produce cylinders
3. Trim cylinders to same
length
4. Measure
length
and
mass
of cylinders
5. Place cylinders in
test tubes
with
different
solutions
6. Leave
overnight
7. Remove cylinders, gently
roll
on paper towel
8. Measure
length
and
mass
of cylinders again
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Distilled water
Contains
no dissolved substances
that could affect the weight of
osmosis
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Percentage change
Calculated as: (
change
in value / original value) x
100
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Graph of percentage changes in mass or length against concentration of sugar solution shows gain in
water
in dilute solution, loss in concentrated solution, and no change at the
concentration
inside the cell
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Carrying
out chemical tests for carbohydrates, proteins and lipids
1. Grind food sample with
distilled
water using mortar and pestle to make a
paste
2. Transfer paste to beaker and add more
distilled
water
3. Stir to
dissolve
chemicals
4.
Filter
solution to remove
suspended
food particles
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Carbohydrates
Include
starch
and
sugars
such as glucose
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Test
for starch
1. Place 2cm3 of food solution in test tube
2. Add a few drops of iodine solution
3.
Blue-black colour
indicates presence of starch
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Test
for sugars (e.g. glucose)
1. Place 2cm3 of food solution in test tube
2. Add 10 drops of Benedict's solution
3.
Heat
test tube in hot
water bath
for 5 minutes
4.
Colour
change indicates amount of
reducing sugars
present
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Benedict
's test
Only works for
reducing
sugars, not non-reducing sugars like
sucrose
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Test
for proteins
1. Place
2cm3
of food solution in test tube
2. Add
2cm3
of Biuret solution
3.
Purple
/
lilac
colour indicates presence of proteins
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Test
for lipids/fats
1. Grind food with
distilled
water using
mortar
and pestle (do not filter)
2. Transfer
2cm3
of solution to test tube
3. Add a few drops of
distilled
water and
ethanol
4.
Shake
gently
5. White cloudy
emulsion
indicates presence of
lipids
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All chemicals used in these tests are potentially
hazardous
, so safety
goggles
must be worn
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Ethanol
is highly flammable, so no naked
flames
should be present
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Investigating
the effect of light intensity on the rate of photosynthesis
1. Take a boiling tube
2. Place 10 cm away from an LED light source
3. Fill boiling tube with sodium hydrogen carbonate solution
4. Put a piece of pond weed into the boiling tube
5. Leave for 5 minutes to acclimatize
6. Start stopwatch and count bubbles produced in 1 minute
7. Repeat 2 more times and calculate mean
8. Repeat experiment at 20 cm, 30 cm, and
40
cm
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Problems
with the practical
Number of
bubbles
can be too fast to count accurately
Bubbles are not always the same
size
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Solving the problems
1. Measure the volume of
oxygen
produced instead of counting
bubbles
2. Use equipment to catch the
bubbles
in a
measuring
cylinder filled with water
3. Use the
measuring
cylinder to measure the volume of
oxygen
produced
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Doubling
the distance from the light to the pondweed
Number of
bubbles
per minute falls by a factor of
4
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Inverse square law
If we double the distance, the light intensity falls by
4
times, which causes the number of
oxygen bubbles
to fall by 4 times
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Higher tier students need to understand the
inverse square law
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You
'll find plenty of questions on this required practical in the
revision workbook
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