Bio paper 1-Practicals

What are the step to Slide Preparation: Viewing Onion Cells

• Start with a clean microscope SLIDE.

• Add a single DROP OF WATER to the slide.

• Carefully cut an onion and separate it into layers.

• With TWEEZERS, peel off a piece of the EPIDERMAL tissue and place it onto the drop of water on your slide.

• Add a drop of IODINE SOLUTION as a stain to highlight cell features.

• Place a COVER SLIP over the specimen carefully to avoid air bubbles which can obstruct the view.

what are the steps to using a light microscope?

• Secure the slide on the stage of the microscope.

• Begin with the LOWEST-POWERED OBJECTIVE LENS.

• Adjust the COARSE ADJUSTMENT KNOB to bring the stage close to the lens without it touching.

• Look through the EYEPIECE and use the COARSE ADJUSTMENT KNOB to find the focus.

• Fine-tune the focus with the FINE ADJUSTMENT KNOB for a clear image.

• For greater detail, switch to a higher-powered objective lens and refocus.

What are the steps to drawing your observations for the microscopy practical?

• Draw what you observe with a PENCIL.

• Ensure the drawing occupies at least half of the space provided.

• Use clear, UNBROKEN LINES, and avoid coloring or shading.

• Draw cells proportionally, labelling important features like the nucleus or chloroplasts with straight lines.

• Include a TITLE and the MAGNIFICATION LEVEL.

How do you prepare your samples for the osmosis practical?

• Begin by CUTTING POTATO CYLINDERS of the same size.

• Immerse the cylinders in DIFFERENT SUGAR SOLUTIONS with varying concentrations (e.g., 0.2 mol/dm³, 0.4 mol/dm³, etc.) to see how different solute concentrations affect osmosis.

• One cylinder should be placed in PURE WATER as a CONTROL.

What are the 2 steps to measuring mass changes-osmosis practical?

• Using a MASS BALANCE, record the initial mass of the potato cylinders and then place them in the beaker of solution

• After around 24hrs, take the cylinders out, blot them with a PAPER TOWEL to remove surface moisture and REWEIGH to determine mass change.

What are the steps to analysing the results-osmosis practical?

• If cylinders in sugar solutions GAIN mass, water has moved INTO the cells by osmosis, indicating the solutions had a HIGHER WATER CONCENTRATION than the inside of the potato. 

• If cylinders in sugar solutions LOSE mass, water has moved OUT OF the cells by osmosis, indicating the solutions had a LOWER WATER CONCENTRATION than the inside of the potato. 

• If cylinders in sugar solutions stay the SAME mass, water has neither moved out, nor moved into the cells, this is because the solutions had the SAME WATER CONCENTRATION as the inside of the potato. 

What are the variables in the osmosis practical?

• The CONTROLLED VARIABLES in this experiment include, the volume of the solution, temperature, time, and type of sugar/salt. These should be kept the SAME across all samples to ensure a fair test.

• The DEPENDENT VARIABLE is the MASS of the potato cylinders

• the INDEPENDENT VARIABLE is the sugar solution CONCENTRATION.

How do you find the effect of the sugar solution on osmosis?

By calculating the percentage change in mass for each sugar connectration using the formula: Percentage change in mass= change in mass/intial mass(g) x100

How do we minimize errors in the osmosis practical?

• Ensure the potato cylinders are FULLY SUBMERGED in the solutions without touching the sides of the beaker.

• FULLY DRY the potato cylinders before measuring their mass

• REPEAT the experiment multiple times to calculate a MEAN PERCENTAGE CHANGE, reducing random errors.

What is the aim on the enzyme practical?

To see the effect of pH on enzyme activity

→The enzyme used is AMYLASE which breaks down STARCH into MALTOSE.

→The reaction will involve the amylase reacting with starch solution and this reaction can be monitored using IODINE solution, which changes from brown-orange to blue-black with starch.

What would happen if the enzyme does it’s job and the reaction is successful?

The starch will turn into maltose and the iodine solution will be BROWN-ORANGE

What would happen if the enzyme doesn’t do it’s job(Denature) and the reaction is successful?

The reaction is NOT CARRIED OUT, starch will remain present and the iodine solution will be BLUE-BLACK.

What is used to change the pH of the reaction?

A BUFFER solution is used to change the pH of the reaction

What are the 1st step for the enzyme activity experiment?

Add iodine solution to each well of a SPOTTING TILE.

What are the 2nd step for the enzyme activity experiment?

Set up a WATER BATH at 35°C using a beaker of water and a thermometer for consistent temperature control during the experiment.

What are the 3rd step for the enzyme activity experiment?

Combine 1 cm³ of amylase solution with 1 cm³ of a buffer solution with a pH of 5 in a test tube.

What are the 4th step for the enzyme activity experiment?

Place the tube in the water bath for five minutes using test tube holders

What are the 5th step for the enzyme activity experiment?

Add 5 cm³ of starch solution to the amylase and buffer mixture and start timing the reaction using a stopwatch.

What are the 6th step for the enzyme activity experiment?

Every 30 seconds, use a DROPPING PIPETTE to add a drop of the mixture to the iodine on the spotting tile and note the color of the iodine

What are the final step for the enzyme activity experiment?

Record when the iodine no longer turns BLUE-BLACK, indicating starch breakdown and repeat with buffers of different pH values to see the effect of pH on amylase activity. 

How do we understand the results of the enzyme practical?

• The pH at which the iodine stops turning blue-black the FASTEST, will be the OPTIMUM pH

• If the iodine remains BLUE-BLACK at a particular pH for the full amount of time, the amylase is assumed to have DENATURED, meaning the starch has NOT been broken down

• Comparing rates across different pH levels will highlight the pH sensitivity of amylase

How do the control variables ensure it’s a fair test-enzyme practical?

They Ensure a FAIR TEST by keeping other variables constant, such as amylase concentration and temperature

How do we understand the results of the enzyme practical-iodine solution?

The sooner the color of the iodine solution stops turning BLUE-BLACK, the FASTER the rate of reaction, and the better the enzyme works.

→The pH at which the iodine stops turning blue-black the FASTEST, will be the OPTIMUM pH

General prep for food tests

• Start by breaking down the food using a PESTLE AND MORTAR.

• Transfer the ground food into a BEAKER with distilled water.

• STIR the mixture to dissolve some food particles.

• FILTER the mixture to remove solid residues.

Testing for Sugars: BENEDICTS REAGENT-Steps

• Add the food sample to a test tube, mix in Benedict's solution.

• Heat the tube in a WATER BATH at 75°C for 5 minutes.

• A color change indicates the presence of reducing sugars, with the color varying from BLUE to GREEN to YELLOW or BRICK-RED depending on sugar concentration.

Testing for Starch: IODINE SOLUTION-Steps

• Place the sample in a test tube and add iodine solution.

• A color change from BROWN-ORANGE to BLUE-BLACK signifies the presence of starch.

Testing for proteins: BIURET TEST-Steps

• Combine the food sample with Biuret solution in a test tube.

• Gently shake; a change to PURPLE indicates protein. If no protein, the solution remains BLUE

Testing for Lipids: SUDAN III TEST-Steps

• Add the food sample and Sudan III stain solution to a test tube without filtering.

• Gently shake the tube. Lipid presence will show as a separate BRIGHT RED LAYER.

Steps for photosynthesis practical

• Set the light source at a SPECIFIC DISTANCE from the pondweed.

• Allow the pondweed to photosynthesize for a set amount of time, collecting oxygen in the capillary tube.

• Use the SYRINGE to draw the oxygen bubble alongside the ruler.

• Measure the length oxygen bubble with the ruler to determine the volume of oxygen produced and hence the rate of photosynthesis

• TEMPERATURE and the DURATION of exposure to light are CONTROLLED..

• Repeat the experiment several times and find a MEAN and then repeat the whole process again with the light source at different distances from the pondweed.

Inverse square law and light intensity

• When considering the effect of light on photosynthesis, the INVERSE SQUARE LAW is a key concept. It states that light intensity is INVERSELY PROPORTIONAL to the SQUARE of the distance from the light source

→Mathematically, this is expressed as Light intensity(au)= 1/distance(cm)2

→This means if the distance from the light source to the plant DOUBLES, the light intensity at the plant's location is reduced to ONE-FOURTH and you can work out LIGHT INTENSITY by using the inverse square law.

When you bring a lamp at 5 cm from the pondweed, it has a light intensity of 16au then Calculate the light intensity if the lamp is moved 10cm from the pondweed

Distance: 5cm →10cm ( x2)

Light intensity: 16au→4au (x1/2 to the power of 2)

What is the Light intensity equation?

Light intensity(au) = 1/distance2(cm)