bio paper1 RPS

rp1 microscopy practical method

1. Use tweezers to remove a thin layer of onion epidermis

2. Place it flat on a slide

3. Add one drop of iodine to stain and show structures

4. Carefully lower a coverslip at an angle to prevents air bubbles

5. start with the lowest magnification

6. Place slide on the stage and clip it

7. Focus using the coarse focus, then fine focus

8. Increase magnification only after focusing

9. Adjust the light for a clear image

magnification calculation

Magnification = Image size ÷ Real size

safety precautions for microscopy practical

• Carry microscope with two hands

• Don’t touch the lens with fingers

• Clean spills immediately

• Keep liquids away from electrics

rp2 microbiology method

1. Label the agar plate into sections for each antiseptic/antibiotic and a control.

2. Spread the bacteria evenly over the surface of the agar using a sterile spreader or swab.

3. Soak paper discs in different antiseptics/antibiotics.

4. Place one disc onto each labelled section of the agar plate.

5. Add a control disc soaked in sterile water.

6. Tape the lid lightly and incubate the plate at 25°C for 24–48 hours.

7. After incubation, measure the diameter of the clear zones (zones of inhibition) around each disc

8. Compare results — the largest clear zone shows the most effective antiseptic/antibiotic.

microbiology aseptic techniques

Use aseptic technique:

1. Sterilise equipment

2. Open the lid only slightly

3. Work quickly to avoid contamination

independent dependent and control variables for microbiology RP

Independent variable (change): type or concentration of antiseptic

Dependent variable (measure): size of zone where bacteria can’t grow).

Control variables (same): same volume of bacteria, same incubation time/temperature, disc sizes

RP3 osmosis method

1. Cut five potato cylinders of the same diameter so their the same length (about 3 cm)

2. Measure and record the initial mass and length of each potato cylinder using a scale and ruler.

3. Prepare labelled boiling tubes with different concentrations of sugar (or salt) solution and one with distilled water.

4. Place one potato cylinder into each tube

5. Leave the cylinders overnight in the tubes so osmosis can occur.

6. Remove the potato pieces, blot them dry with paper towels and measure the final length and mass of each cylinder.

7. Record all results in a table showing initial and final mass/length.

8. Calculate the change in mass and length for each cylinder (final minus initial).

9. Plot a graph of change in mass on the y-axis against solution concentration on the x-axis

independent dependent and control variables for osmosis RP

Independent Variable

• Concentration of sugar/salt solution

Dependent Variable

• Change in mass or length of potato

Control Variables

• Size and type of potato pieces

• Volume of solution

• Time left in solution

• Temperature

what is an Isotonic solution

where there is no net movement of water

• Percentage change = 0

• It shows the solution has the same water potential (concentration of water is the same inside and outside the cells) as potato cells

test for starch

• Put the food sample in a test tube or on a spotting tile.

• Add a few drops of iodine solution.

• Look for a colour change.

Positive Result:
➡ Turns blue-black if starch is present
Negative Result:
➡ Stays brown/orange

Test for Reducing Sugars

• Add Benedict’s solution to the food sample in a test tube.

• Heat in a hot water bath for a few minutes.

Positive Result:
➡ Solution changes from blue to green/yellow/orange/brick-red, depending on amount of sugar present
Negative Result:
➡ Remains blue (no reducing sugar)

Test for Proteins

1. Add a few drops of Biuret solution to the food sample.

2. Mix gently and wait a minute.

Positive Result:
➡ Solution turns purple/violet
Negative Result:
➡ Stays blue (no protein)

Test for Lipids (Fats)

1. Add a few cm³ of ethanol to the food sample.

2. Then pour this into equal volume of water.

Positive Result:
➡ A milky white emulsion forms (lipids present)
Negative Result:
➡ No cloudy layer (no lipids

food test safety precautions

• Wear safety goggles.

• Keep ethanol away from flames (flammable).

• Be careful with biuret reagents (can irritate).

• Don’t taste or eat any samples.

rp5 enzymes method

1. Label wells on a spotting tile with time intervals (0 s, 30 s, 60 s,…). Add a drop of iodine in each well.

2. Measure 2 cm³ of each buffer solution into separate test tubes (different pH values)

3. Place the starch, amylase, and the test tubes of buffer into a water bath at a 25 °C

4. Wait a few minutes to equilibrate the temperature.

5. Use a syringe to add 2 cm³ amylase and 2 cm³ starch and to a test tube of buffer, start the stopwatch immediately.

6. Every 30 seconds, use a glass rod to transfer a drop of the reaction mixture to the well on the tile.

7. Continue until the iodine stays brown (means no starch left).

8. Record the time taken for starch to be completely broken down.

9. Calculate the rate of reaction

11. Repeat Steps 2–10 with buffer solutions at different pH values.

12. Plot a graph of rate of reaction vs pH to identify the optimum pH.

rate of reaction formula

independent dependent and control variables for enzyme rp

Independent variable - pH

Dependent variable - Time taken for starch to be broken down

Control variables - Temperature, volume of amylase and volume of starch

photosynthesis rp6 method

1. Place a piece of pondweed in a beaker of water.

2. Add sodium hydrogencarbonate to ensure carbon dioxide is not limiting.

3. Position a lamp at a 10cm from beaker with a metre stick beside.

4. Allow 5 minutes for the plant to acclimatise.

5. Measure the rate of photosynthesis by: Counting bubbles per minute OR measuring volume of oxygen produced using a gas syringe for higher accuracy

6. Repeat at different distances of the lamp to change light intensity.

7. Record results in a table.

8. Plot a graph of light intensity against rate of photosynthesis.

independent dependent and control variables for photosynthesis rp

Independent variable - Light intensity/distance from beaker

Dependent variable - Rate of photosynthesis
(measured by oxygen volume per time or bubbles per minute)

Control variables -

• Temperature

• Carbon dioxide concentration

• Length/type of pondweed

• Same apparatus and volumes

how to improve reliability rp6

repeat and calc mean

measure oxygen with gas syringe

keep conditions constant

in osmosis practical - explain why the result for the potato pieces at 1mol/dm3 was different from the result at 0.6mol/dm3

pieces at 1.0mol/dm3 lost more mass bc more water left the potato

bc of a steeper conc gradient