Practical Mechanisms Flashcards
Explain in full practical detail how you could find the effect of age upon membrane permeability in red cabbage leaves
Health and safety:
- put scalpel in a tray when moving it or not using it
Reliability:
- Choose cabbages of at least 5 different ages
- ideally choose cabbages with ages at regular intervals, e.g. 1 week, 2 week, 3 week etc.
- Same volume of water in the 5 test tubes
- Choose leaves of the same surface area, shape and from the same part of the (cabbage) plant
- put the 5 test tubes in a water bath at 30 Degrees Celsius
- leave the test tubes in for 5 minutes
Colorimeter:
- take the test tubes out after the 5 minutes
- Drain the fluid into a cuvette and place into a colorimeter which has been calibrated with distilled water beforehand.
- Take repeat readings and calculate the mean values from colorimeter from each age of cabbage
Analysis of data:
- plot the results and data in a scatter graph
- plot age on the x-axis
- plot mean % absorbable of light on the y-axis
How to produce a glucose-calibration curve
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Precautions of chromatography
- Remove chromatography paper once solvent has reached end of paper.
Describe how a colorimeter is calibrated
Set colorimeter to zero absorbable and fill with distilled water
Why is it important to calibrate a colorimeter?
So that values of light/wavelength absorption are valid/accurate
Chromatography full mechanism
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For TLC, state 3 variables that need to be controlled
- Temperature of system/lab
- Volume of mobile phase solvent
- Humidity of the lab
Explain why some of the ingredients in a substance may not have been separated in results of TLC
- Some ingredients may only form a colourless spot upon the plate
- In this way they may not have been spotted as a constituent
- Some pigments may overlap, due to having similar size/polarity
- They may be counted as only one pigment
Setting up a microscope mechanism
6 Marks
- The specimen on a slide is placed on a stage and clipped into place
- Rotate the nosepiece to pick the lowest power objective lens
- Adjust the coarse focus knob
- look into eyepiece until image seen is clear and in focus - Whilst viewing the image
- adjust iris diaphragm for optimum light - Look down ocular tube
- use fine focus knob to focus the image - Repeat step 5, using a higher power lens
Different staining chemicals
- Acetic orcein binds to DNA and stains chromosomes dark red
- Eosin stains cytoplasm
- Sudan red stains lipids
- Iodine stains cellulose in plant cell walls yellow
- Iodine stains starch granules blue/black
Explain why biological specimens under a microscope may be stained.
(2 Marks)
- enhance visualisation of certain cells or cellular organelles/components under a microscope
- differentiate between different cellular components and cell types
- to investigate the compositions of different cell organelles
Explain why differential staining was used when producing a blood smear.
(2 Marks)
- stains some structures darker and provides contrast
- allows for shape of the nucleus to be seen
- allows the type of (blood) cell to be identified
What is the eyepiece graticule?
- Meauring device
- placed in eyepiece of microscope
- acts as a ruler when viewing object under a microscope
What is the stage graticule?
- precise measuring device
- small scale placed on a microscope tags
- used to calibrate value of eyepiece division at different magnifications
Preparation of a slide
- Dehydrate the specimens
- Embed in wax to prevent distortion during slicing
- create sections using a special instrument
- stain and mount in special chemical to preserve
