CORE PRACTICALS biology

CP1- looking at cells- step 1

Peel off an epidermal layer on the onion using forceps.

CP1- looking at cells- step 2

Mount onto the microscope slide with a drop of water using a pipette, making sure the tissue lies flat.

CP1- looking at cells- step 3

Add 2 drops of iodine solution to stain the cells so that internal structures

CP1- looking at cells- step 4

Place the cover slip on by first placing one edge down on the slide and slowly lowering the other side of the cover slip using forceps. Make sure no air bubbles are trapped.

CP1- looking at cells- step 5

Remove any excess stain by soaking it with paper towels.

CP1- looking at cells- step 6

Place the slide on the stage of the microscope.

CP1- looking at cells- step 7

Turn the nosepiece to select a low power objective.

CP1- looking at cells- step 8

Set up the microscope - don't look into the eyepiece yet. Instead, use the coarse adjustment knob to raise the stage until the cover slip just touches the objective.

CP1- looking at cells- step 9

Now look into the eyepiece and turn the coarse adjustment knob to move the stage away until the image comes into focus (doing this helps avoid you breaking the slide).

CP1- looking at cells- step 10

Turn the nosepiece to select a high power objective.

CP1- looking at cells- step 11

Repeat the same process as above and then look into the eyepiece and turn the fine adjustment knob until the image comes into focus.

CP1- looking at cells- step 12

Make a labelled drawing of a few of the cells you can see, including any features eg. cell wall, nucleus. Write down the magnification.

CP1- looking at cells- step 13

Repeat these steps using a prepared slide.

CP2- pH and enzyme activity- step 1

On a tile, label each well with the time and add a drop of iodine solution to each well.

CP2- pH and enzyme activity- step 2

Add 2 cm'3 of each buffer solution using a syringe (ranging from pH 3.0 to 7.0) into each labelled test tube.

CP2- pH and enzyme activity- step 3

Immerse the starch solution, amylase solution, and the test tubes of buffer solution in a water bath at 25°C.

CP2- pH and enzyme activity- step 4

Allow a few minutes for the temperature to equilibrate.

CP2- pH and enzyme activity- step 5

Use a syringe to add 2 cm'3 of amylase into a test tube of buffer solution.

CP2- pH and enzyme activity- step 6

Use a syringe to add 2 cm'3 of starch into the same test tube and start timing immediately.

CP2- pH and enzyme activity- step 7

Use the glass rod to transfer a drop of the mixture to the well labelled 'O' on the tile.

CP2- pH and enzyme activity- step 8

Repeat step 6 every 30 seconds, rinsing the glass rod in between every test, until the iodine solution remains brown and does not turn blue-black i.e. all the starch has been digested.

CP2- pH and enzyme activity- step 9

Repeat steps 1-8 twice more and take a mean time required for iodine solution to remain brown.

CP2- pH and enzyme activity- step 10

Calculate the rate of enzyme reaction by using 1/ time taken for iodine solution to remain brown.

CP2- pH and enzyme activity- step 11

Repeat steps 2-8 for buffer solutions with different pH values. Plot a graph of the rate of enzyme reaction against pH.

CP3- food tests (results if present)- starch

iodine test, brown to blue black

CP3- food tests (results if present)- reducing sugars

benedicts solution (water bath 60 degrees celcius), blue to brick red

CP3- food tests (results if present)- protein

biurets test, blue to purple

CP3- food tests (results if present)- lipids

emulsion test (ethanol), white to cloudy

CP4- osmosis- step 1

Use a cork borer to cut 5 potato cylinders.

CP4- osmosis- step 2

Accurately measure and record the mass of each cylinder.

CP4- osmosis- step 3

Measure 10 cm'3 of the 1.0M sugar solution and transfer to the first boiling tube and label.

CP4- osmosis- step 4

Repeat step 3 for other concentrations of the solution and distilled water.

CP4- osmosis- step 5

Add one potato cylinder (of known mass) to each boiling tube.

CP4- osmosis- step 6

Add one potato cylinder to each boiling tube, making sure the mass of each cylinder is known.

CP4- osmosis- step 7

Leave the cylinders in the boiling tubes for at least 15 minutes in a test tube rack.

CP4- osmosis- step 8

Remove the cylinders from the boiling tubes and dry with paper towels.

CP4- osmosis- step 9

Measure the mass of each cylinder and record your measurements in the table. Calculate the percentage changes for each cylinder.

CP4- osmosis- step 10

Plot a graph of change in mass against the concentration of sugar solution. Find the x-intercept to determine the concentration of sugar solution that is isotonic to the potato cells.

CP5- microbial cultures- step 1

On the bottom of the agar plate (not the lid) mark with a wax pencil / permanent marker: 3 segments, a dot in the middle of each segment, name of bacteria, initials

CP5- microbial cultures- step 2

Wash your hands with antibacterial handwash. Place the different antiseptics onto different filter paper discs.

CP5- microbial cultures- step 3

Lift the lid of the agar plate at an angle and use forceps to place each filter paper disc onto the dots. Note down the antiseptic applied to each zone.

CP5- microbial cultures- step 4

Tape the lid onto the agar plate securely, but loosely enough that oxygen can still reach the bacteria.

CP5- microbial cultures- step 5

Place the agar plate in the incubator at 25°C for 48 hours.

CP5- microbial cultures- step 6

Measure the diameter of the zones of inhibition after 48 hours using a ruler. Take a second measurement at 90 degrees from your first measurement and take a mean for the diameter. Do not remove the lid when taking measurements.

CP5- microbial cultures- step 7

The area of the zones of inhibition can be calculated using the formula pi R squared.

CP6- photosynthesis- step 1

A lamp with an LED bulb is set up at different distances from the plant in a beaker of water (An LED bulb is best as this will not raise the temperature of the water)

CP6- photosynthesis- step 2

Sodium hydrogen carbonate is added to the water to supply the reactant carbon dioxide to the plant

CP6- photosynthesis- step 3

The light intensity is proportional to distance - it will decrease as the distance away from the bulb increases.

CP6- photosynthesis- step 4

The bubbles produced over one minute periods are recorded. The rate of photosynthesis is the number of bubbles produced per minute- light intensity= 1/distance^2

CP7- respiration- step 1

The apparatus consists of two tubes, one containing the living organisms and the other with glass beads to act as a control.

CP7- respiration- step 2

Both tubes contain an alkali such as sodium hydroxide to absorb any carbon dioxide given off during respiration. This ensures that any volume changes measured in the experiment are due to oxygen uptake only.

CP7- respiration- step 3

Once the apparatus has been set up, the movement of the coloured liquid towards the insect will give a measure of the volume of oxygen taken up by the insect for respiration.

CP7- respiration- step 4

The reduction of volume in the tube increases pressure causing the coloured liquid to move.

CP7- respiration- step 5

The distance moved by the liquid in a given time is measured will provide the volume of oxygen taken in by the insect per minute.

CP7- respiration- step 6

Volume is given by volume of a cylinder V=πr2h, where h is the distance moved by the coloured liquid. The unit of rate of respiration is cm3/min.

CP8- quadrats- step 1

choose a starting point on the school field in an area where the grass is often cut

CP8- quadrats- step 2

use random numbers to generate a set of coordinates to place your first quadrat

CP8- quadrats- step 3

count the number of different plant species within this quadrat (the species richness)

CP8- quadrats- step 4

return to your starting position and repeat steps two and three a further 14 times using different random numbers

CP8- quadrats- step 5

repeat steps one to four for a part of the school field which the grass is infrequently cut

CP8- quadrats- step 6

compare your results by calculating a mean for each location

CP8- belt transects- step 1

Lay down a tape measure from the base of a tree to an open area of ground

CP8- belt transects- step 2

Place the quadrat along the end of the tape measure

CP8- belt transects- step 3

Count the number of plants and record it in a table

CP8- belt transects- step 4

Place the quadrat 5 m up the tape measure and repeat step 3.

CP8- belt transects- step 5

Repeat step 4 at 5 m intervals until you reach the end of the transect line.

CP8- belt transects- step 6

Gather data from your class to find the mean number of plants at each point along the transect.