PRACTICALS Flashcards
QUANTITATIVE BENEDICTS: What is a supernatant?
A supernatant is the soluble liquid reaction of a sample after centrifugion of precipitation of insoluble solids
QUANTITATIVE BENEDICTS: Why is the red filter used in the colorimeter?
The red filter is used as it absorbs blue lights and reflects red light, and as blue solution is being used a filter that absorbs the cells will need to be used
QUANTITATIVE BENEDICTS: Why is glucose called a reducing sugar?
Glucose is called a reducing sugar because it acts as a reducing agent as it donates electrons to other elements
QUANTITATIVE BENEDICTS: Explain the colour change in the Benedict’s solution in terms of copper ions and electrons.
The colour changes from blue to red because the copper (II) ions in the Benedict’s solution are reduced to copper (I) ions which cause the colour change
QUANTITATIVE BENEDICTS: Explain how the absorbance (or % transmission) readings relate to glucose concentration.
High glucose concentration means that there are more Cu+ ions so less blue solution means there is low absorption and high % transmission
LIGHT MICROSCOPE TO MEASURE PALISADE CELLS: Why are palisade cells near the top surface of a leaf?
Palisade cells are the top surface of a leaf because they contain chloroplasts which are the main components to conduct photosynthesis, so being at the top of the leaf is more efficient as it is closer to the sun
LIGHT MICROSCOPE TO MEASURE PALISADE CELLS: Why would a sample, such as a leaf cross section, need to be stained?
A sample, such as a leaf cross section will need to be stained to enhance visualisation and to identify which part of the sample is being viewed
LIGHT MICROSCOPE TO MEASURE PALISADE CELLS: Why should CLEAPSS be considered when staining microscope slides?
CLEAPSS should be considered when staining microscope slides as some stains may be toxic and cause irritant
LIGHT MICROSCOPE TO MEASURE PALISADE CELLS: Describe the four stages involved in the pre-preparation of a microscope slide.
The first stage in the pre-preparation of a microscope slide is fixing, where specimens are preserved in chemicals such as formaldehyde. Then specimens are sectioned, meaning they are dehydrated with alcohol and sliced with a microtome. Specimens may then be stained and finally, they are mounted and secured to the slide with a coverslip placed at an angle to prevent any air bubbles
AMINO ACID CHROMATOGRAPHY: Why might not all of the amino acids known to be present in the mixture have appeared on the chromatogram?
Not all amino acids known may appear on the chromatogram as amino acids are on top on each other
AMINO ACID CHROMATOGRAPHY: How could you improve this practical procedure?
To improve the procedure, you could make sure each amino acid is used in an equal amount on the chromatogram
AMINO ACID CHROMATOGRAPHY: Why are you advised to handle the chromatography paper as little as possible?
You are advised to handle the paper as little as possible as human sweat on hands also contains amino acids, which may interfere with the experiment
AMINO ACID CHROMATOGRAPHY: Why does having a lid over the running tanks improve the data obtained?
A lid over the running tank will improve the results as the lid prevents the solvent from evaporating in the tanks, letting the amino acids absorb the solvent for longer
AMINO ACID CHROMATOGRAPHY: What other substances could be separated using chromatography?
Using chromatography, ink, paint, blood and most compound substances can be separated
AMINO ACID CHROMATOGRAPHY: Why is it important to have the same solvent when separating amino acids?
It is important to keep the same solvent as some amino acids separate differently when exposed to different solvents
AMINO ACID CHROMATOGRAPHY: How does chromatography separate substances?
Chromatography separates substances as the substances making up the compound absorb the solvent and are moved up to the solvent front
AMINO ACID CHROMATOGRAPHY: What is gel electrophoresis and how is it similar to and different from thin layer chromatography?
Gel electrophoresis is used to separate mixtures of DNA, RNA or proteins. It, like chromatography, consists of a stationary and mobile phase. However, they differ as it requires an electrical current
DNA EXTRACTION: Why is it necessary to cut the onion into small pieces before beginning the procedure?
It is necessary to cut the onion because it increases surface area to break down the cell membrane quicker
DNA EXTRACTION: Why does the detergent break down cell membranes?
The detergent breaks down cell membranes because the detergent can bind to the hydrophobic end of the membrane and form a solution with water
DNA EXTRACTION: Why might the addition of NaCl cause the DNA molecules to coalesce?
The addition of NaCl causes the DNA molecules to coalesce as the charge of DNA becomes neutralised and the molecule becomes less hydrophillic
DNA EXTRACTION: Why is the 60 degree water bath an essential part of the procedure?
The water bath is essential as it creates the optimum environment for the DNAase enzymes to work properly
DNA EXTRACTION: Why does the mixture need to be cooled in an ice bath following heating?
The mixture will need to be cooled as the cold water protects the DNA by slowing down the enzymes that break it apart
DNA EXTRACTION: Why does the mixture need to be liquidised prior to the extraction of DNA?
The mixture needs to be liquidised prior to the extraction of DNA because DNA is soluble in water and allows the DNA to precipitate
DNA EXTRACTION: Which biological molecules would be found in the filtrate?
In the filtrate, DNA nucleotides would be expected
