Biology Practicals

If you want to look at a specimen under a light microscope, you need to put it onto a micrsocope slide first. Slide - clear glass/plastic onto which the specimen is mounted.

1) Add a drop of water to the middle of a clean slide

2) Cut up an onion, separate it into layers. 

3) Using tweezers, peel off some epidermal tissue from the bottom of one of the layers

4) Place the tissue on the slide using tweezers

5) Add a drop of iodine solution ( a stain - used to highlight objects in a cell by adding colour to them)

6) Place a cover slip on top by standing it upright on the slide and then tilting it till it covers the specimen. 

*Try not to get any air bubbles - they'll obstruct the view.

1) Clip prepared slide to stage

2) Select lowest powered objective lens 

3) Use coarse adjustment knob to move stage up to just below objective lens

4) Look down eyepiece. Use CA knob to move stage downwards until image is roughly in focus

5) Adjust focus with fine adjustment knob, until you get a clear image if what's on the slide

6) Swap to higher powered objective lens and refocus if you need to see slide in greater magnification.

1) Use a sharp pencil to draw what's under the microscope.

2) Your drawing should take up half the space or more and should be drawn in clear unbroken lines.

3) No colouring or shading should be done.

4) If drawing cells, the subcelluar structures should be drawn in proportion

5) Include a title and the magnification you were observing under

6) Label important features 

• Amylase catalyses the breakdown of starch to maltose. Can detect starch using iodine solution - it will change from brownyorange to blueyblack if starch is present.

1) Put a drop of iodine solution into every well of a spotting tile

2) Place a Busen Burner on a heat-proof mat and a tripod and gauze over the B.Burner. Put a beaker of water on top and heat until it's 35oc. Try to keep the water temp constant throughout.

3) Use a syringe to add 1cm3 of amylase solution & 1cm3 of buffer solution with a pH of 5 to boiling tube. Using test tube holders, put tube into beaker and wait for 5 mins.

4) Use different syringe to add 5cm3 of starch solution to boiling tube.

5) Immediately mix contents of b.tube and start stop clock.

6) Use continous sampling to record how long it takes for the amylase to break down all the starch (use a dropping pipette to take fresh sample from b.tube every 30 secs & out drop in well. When iodine remains brownyorange no starch is present.)

7) Repeat with buffer solutions of different pH. Remember to control variables (conc & vol of A)

1) Get a piece of food, break it up using a pestle and mortar

2) Transfer ground up food to beaker and add some distilled water

3) Give mixture a good stir with a glass rod to dissolve some of the food

4) Filter solution using a funnel lined with filter paper to get rid of solid buts of food

Test for Reducing Sugars

1) Prepare Food Sample, transfer 5cm3 to test tube

2) Prepare water bath so it's set to 75oc 

3) Add some Bendicts solution to test tube using a pipette

4) Place test tube in water bath using test tube holder, leave there for 5 mins. Make sure tube is pointing away from you.

5) If food sample contains a reducing sugar, solution will change from normal blue colour to 

 green yellow or brick red depending on how much sugar is in the food.

Tests for Starch e.g pasta, rice, potatoes

1) Make a food sample, transfer 5cm3 into test tube

2) Add few drops of iodine solution and gently shake tube to mix contents.

If sample contains starch, colour of solution will change from browney orange to black/blueyblack.

Biuret Test

Test for Protein e.g. meat, cheese

1) Prepare FS, transfer 2cm3 to test tube

2) Add 2cm3 of biuret solution to test tube and shake t.tube gently to mix well

If sample contains protein, solution will change from blue to pink or purple 

Test for Lipids e.g. olive oil, margarine and milk

1) Prepare sample of food - you don't need to filter it. Transfer 5cm3 into Test Tube

2) Use pipette to add 3 drops of Sudan III stain solution to test tube and gently shake tube 

3) Sudan III stain solution stains lipids. 

If sample containd Lipids, mixture will separate into 2 layers. Top layer will be bright red.

Reaction Time - the time is takes to respond to a stimulus (often <second) can be affected by factors e.g. age, gender, drugs

1) Person should sit with arm resting on edge of table (to stop their arm moving up/down in test)

2) Hold a ruler vertically betwenn thumb & forefinger. Make sure 0 end of ruler is level with their thumb and finger. Let go without giving any warning.

3) Person being tested should try to catch the ruler as quickly as they can. 

4) Reaction time measured by No on ruler when it's caught. Number should read from top of thumb. Further down ruler = slower reaction time.

5) Repeat several times, calculate mean

6) Give person being tested caffeinated drink. After 10 mins, repeat experiment.

7) Control variabes to ensure it's a fair test e.g. use same person and same hand, ruler should always be dropped from same height, no caffeine before experiment.

Quadrat - square frame 

1) Place a 1m2 quadrat in ground at random point within first sample area e.g. divide the area into a grid and use a random number generator to pick co-ordinates.

2) Count all organisms within Quadrat

3) Repeat steps 1 & 2 as any times as you can

4) Work out mean No of organisms per quadrat within first sample area

5) Repeat steps 1-4 in second sample area

6) Compare the 2 means.