Gas exchange - determining stomatal density Flashcards
What is stomatal density?
The number of stomata per unit of area.
Why is stomatal density a useful measurement for biologists?
To assess the plant’s likely response to a dry spell of weather and to predict its behaviour in windy or wet climates.
What can be assessed using stomatal density measurements?
How stomatal density varies from species to species.
List the apparatus needed to determine stomatal density.
- 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
What are the steps in the method for determining stomatal density?
- Select a leaf from a live plant and cut it off the plant
*Place the leaf upside down on a flat surface such as a tile or worktop - Paint clear nail varnish onto the underside of the leaf
- Wait for the nail varnish to dry (approx. 5 minutes)
- Peel off the layer of varnish using sellotape
- Place the dried varnish impression on a microscope slide
- Count stomata
What types of plants are recommended for this experiment?
Geraniums and spider plants.
Are a coverslip and a drop of water required to observe a varnish impression under a microscope?
No, a coverslip is not required as it is not a biological sample, just an impression of one. A drop of water is not required either.
What is the ideal number of stomata to count in the field of view?
Between 15 and 100.
True or False: A stoma partially visible at the edge of the view should be counted.
True.
What is the purpose of using a stage micrometer?
To measure the diameter of the field of view.
What increases the reliability of quantitative data?
Repeating measurements.
What are anomalous measurements?
Measurements that deviate from the expected measurements.
Why is it important to repeat stomatal counts?
To identify anomalous measurements and calculate a mean.
What is the effect of repeated stomatal counts delivering similar results?
The data is said to be reliable.
Fill in the blank: Reliability refers to the level of trust that we can place in _______.
numerical measurements.
What type of data is gathered during stomatal counts?
Quantitative data.
What is a limitation of using solvent-based nail varnish?
It can destroy some of the cell structure it comes into contact with.
What is a safer alternative to solvent-based nail varnish?
Water-based nail varnish.
Fill in the blank: Taking repeated measurements will help to identify _______.
anomalous measurements.
