TRANSPIRATION AND WATER CONDUCTION Flashcards
is the loss of water in the form of water vapor from the leaves of plants through the stomata. It is necessary because it is the mechanism by which water and the dissolved solutes are transported to all parts of the plant. It is also unavoidable in the sense that the leaves must have gas exchange with the environment in order to acquire carbon dioxide for photosynthesis.
Transpiration
Gadget used to determine Effect of Some Environmental Factors on Transpiration Rate
Potometer
This paper is impregnated with _______ and it is blue when dry and pink when moist.
Cobalt Chloride Paper
stomatal density formula
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OCR Gateway GCSE Biology
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GCSEBiologyOCR GatewayRevision Notes7. Practical Skills7.1 Practical Skills7.1.9 Practical - Measurement of Stomatal Density
7.1.9 Practical - Measurement of Stomatal Density
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Stomatal Density
Measurement of stomatal density on the surface of a leaf
This isnot a required practicalbut is excellent practice fordeveloping microscope skillsand use ofmathematicalprocessing of data
Thedensity of stomata(the number of stomata per unit of area) can be a useful measurement to biologists
To assess the plant’slikely responseto a dry spell of weather
Topredict its behaviourin windy or wet climates if the plant was being moved for agricultural / horticultural reasons
This technique can be used to assess howstomatal density variesfrom species to species
Apparatus
A plant to sample a leaf from
Clear nail varnish (ideally solvent based)
Sellotape
Microscope
Microscope slides
Stage micrometer
Counting device (clicker/ phone app etc.)
Calculator
Method
Select a leaf from alive plantand cut it off the plant
Geraniumsandspider plantsmake good subjects for this experiment
Place the leaf upside down on a flat surface such as a tile or worktop
Paintclear nail varnishonto the underside of the leaf
Wait for the nail varnish todry(approx. 5 minutes)
Peel offthe layer of varnish using sellotape
Discard the leaf
Place the dried varnish impression on amicroscope slide
Acoverslip is not requiredas this isn’t a biological sample, just an impression of one
Adrop of wateris not required either, so long as the sample is laid flat on the slide
Use the usual steps tofocuson the sample
Adjust the zoomsuch that acountable numberof stomata are visible in the field of view
Between15 and 100is ideal
Even if a stoma is partially visible at the edge, still count it as 1
Count the stomatain that field of view
You may wish to use aclickerorphone appso you don’t lose count!
Move the field of viewto another area of the nail varnish layer and repeat
Count at least 3 separate fields of view and take a mean value
Repeat readings allow you toeliminate anomalous resultsand calculate areliable mean
Measurements to take
Use astage micrometerto measure thediameterof the field of view
This has to beat the same magnificationpower that you used when counting the stomata
The stage micrometer will be calibrated in micrometers
A typical microscope allows the scientist to look at a field of view of about 0.5 mm diameter when on full power (× 400)
You will have calculated a mean number of stomata per field of view from the previous stage
Worked example
A study reveals a mean count of16 stomataper field of view at a magnification of × 400. The stage micrometer calculates thediameterof the field of view at a magnification of × 400 to be0.46mm
Calculate the stomatal density based on these data. Give units in stomata per mm2
Use a value of π = 3.14 and give your answer to the nearest whole number of stomata.

Step 1: Calculate the radius of the field of view
Radius = Diameter ÷ 2
Radius = 0.46 mm ÷ 2 = 0.23 mm
Step 2: Calculate the area of the field of view
Area = πr2= π × 0.232
Area = 0.1662 mm2
Step 3: Divide the mean number of stomata by the area of the field of view to calculate density
Density = 16 ÷ 0.1662 = 96.27 stomata per mm2
Step 4: Round to the required precision (nearest whole number)
Density = 96 stomata per mm2
Rise of the Transpiration Stream solution
Eosin
