Every Core Practical AS Biology Unit 2
This article was written with students of the Edexcel SNAB biology syllabus in mind. The summaries below are tailored to answering the questions used in the exams, which are always in the form of 'describe an experiment to find X' and will usually have the same answer in every test too.
These questions are usually worth 5-6 marks and are by far some of the easiest marks to acquire. However, it is necessary to learn the standard format in which you need to answer the questions.
Take note that answering in bullet points is an accepted and by some advised method of answering these questions.
- Heat 2cm3 of 1 mole HCl acid in a 60oC waterbath.
- Cut off 1-2cm garlic root tips.
- Put the garlic root tips in a watch glass containing 2cm3 of acetic alcohol for 12 minutes.
- Remove the tips from the acetic acid and place them into a different watch glass containing 5cm3 of ice cold distilled water.
- After 5 minutes remove them and leave them to dry.
- Then place the tips into the warmed HCl acid for 5 minutes.
- Repeat 1-6 to make the tips even more fragile.
- Transfer a tip to a microscope slide and then cut 5mm off the end of the tip.
- Macerate using a mounted needle.
- Stain using 1 drop of toludine blue and leave root tips for 2 minutes.
- Add coverslip and blot with filter paper.
- View under a microscope and identify the stages of mitosis.
(Overview of treatment to 1-2cm tips: 2cm3 acetic alcohol -> 5cm3 ice cold water -> dry -> 2cm3 60oC HCl acid -> repeat -> Cut 4-5mm tip off root tip -> macerate using mounted needle -> stain with toludine blue -> blot with filter paper -> view)
Mint or Garlic in Toothpaste
1. Seed agar plates using aseptic techniques.
2. Crush 3g of mint leaves using a pestle and mortar in 10cm3 of methylated spirit.
3. Pipette 0.1cm3 of the mint leaf solution onto a paper disc.
4. Repeat 1-3 using garlic leaves instead of mint leaves.
5. Allow the discs to dry for 10 minutes.
6. Using sterilised forceps place the discs onto a petri dishes.
7. Use a blank disc as a control in the petri dish.
8. Tape the lid onto the petri dish, leaving a sufficient air supply so that dangerous anaerobes do not grow.
9. Incubate the petri dish for 24 hours at 25oC.
10. Measure the diameter of the rings of affect around the different discs and record the data in a table.
11. Repeat 1-10 at least 3 times and calculate mean averages.
12. Create a graph in order to better see the differences between the antibacterial effects of mint and garlic.
13. Larger diameters of the rings of affect suggest more antibacterial strength.
For a more in-depth (not tailored to SNAB) version of this experiment, see: Garlic and Mint Experiment
Totipotency and Tissue Culture
- Acquire seeds that are starting to unfold their cotyledons.
- Cut the tops of the seeds just below the shoot apex using sharp scissors.
- Place the stem of the new explants into agar gel in McCartney bottles.
- Cover the McCartney bottles with cling film and place on a sunny windowsill.
Factors that may affect the results:
- Agar gel may become contaminated with pathogens (which kill the cotyledons) because of the nutritious and moist environment it provides.
- The wrong part of the plant may be cut off and placed into the agar gel.
The Strength of Plant Fibres
- Soak plant material in water for at least one week to soften the fibres for easier extraction.
- Ret the plant material for its fibres.
- Clamp a fibre between two clamp stands and add mass to the centre of the fibre until it snaps (record the weight at which it does so).
- Repeat at least 3 times and calculate the average.
- Repeat using other plant fibres
- Plot data in a bar graph to compare fibre strengths.
- Ensure that the lengths of the fibres are equal each time.
- Ensure that the plants are the same age at the time of extraction as older fibres will be more brittle than younger counterparts.
Investigating Plant Mineral Deficiencies
- Prepare bottles of varying mineral content starting from a control of distilled water (lacking all nutrients) and ending with a solution containing all nutrients (with no potassium, no phosphorus, no magnesium etc. in other bottles).
- Cover bottle openings with foil and then perforate the centre of the foil lids.
- Place a plant of the same species in each bottle by putting its roots through the opening that was perforated so that the roots may absorb the solution.
- Place on a sunny windowsill.
- Record observations.
Note: see photo below for major roles of each nutrient.