Practical 12 - Investigation into stomatal numbers in leaves

Question 1

What are stomata and where can they be found?

Answer 1

pores surrounded by 2 guard cells on the aerial parts of plants

Question 2

Where in a plant are stomata more densely packed and what does this mean for us?

Answer 2

leaves
suitable experimental material

Question 3

Where in a plant are stomata more densely packed and what does this mean for us?

Answer 3

leaves
suitable experimental material

Question 4

What’s the aim of this pracitcal?

Answer 4

measure stomatal density in the lower epidermis of a leaf

Question 5

What are the steps to making a replica of the epidermis?

Answer 5

-leaf on white tile with lower epidermis facing upwards
-stretch leaf between 2 fingers with one hand, and apply a layer of colourless nail varnish/PVA with the other, between the veins, and allow it to dry
-apply a second layer and allow it to dry
-hold the pair of fine forceps horizontally and insert one point between the epidermis and the nail varnish/PVA layer - grip and peel away from you, maintaining tension in the peeled later - this is your replica of the lower epidermis
-place on a microscope slide and use a scalpel to cut a sample, ensuring it doesn’t fold
-apply 2 drops of water and cover with a cover slip

Question 6

What do we paint onto the leaf and where?

Answer 6

Clear nail varnish/PVA glue
Lower epidermis

Question 7

how do we count the stomata on the replica of the lower epidermis of a leaf?

Answer 7

-focus on the replica using x10 objective, then refocus using x40 objective
-count the number of stomata in the field of view
-repeat for 3 fields of view and calculate a mean

Question 8

How do we calculate stomata distribution in the lower epidermis of a leaf?

Answer 8

calculate the area of the field of view

area of field of view (mm2)

Question 9

How do we calculate the area of the field of view?

Answer 9

measure the diameter
convert to actual size (mm)
Pi x r^2 for area

Question 10

Which type of leaf contained the most stomata per field of view in our practical and what does this mean for it?

Answer 10

bay leaf
a higher stomatal density

Question 11

What does it mean for bay leaves compares to ivy leaves due to the fact that they have a higher stomatal density?

Answer 11

more likely to lose more water vapour
obtain more CO2 for gas exchange

Question 12

Why did the bay leaves have a higher stomatal distribution than ivy leaves in our practical?

Answer 12

could have been due to the environments they’d grown in