Biology
Name:
Observing Differences in Leaf Structures
Principal scientific skills we’re practicing here: observation, comparative method, deductive reasoning, microscopy.
Write a prelab:
The purpose should include some science linking the function and structure of leaves in general. Go online to carry
out some research about how plants adapt to differing levels of water availabity.
Create a table to record observations and leave space for a labeled sketch of the leaf structure
Instructions:
1. Pick up a slide labeled “Dicot leaf types,” mount it on your microscope stage, and focus (it’s best to start under low
power, then move to higher power as you explore finer details). There are three types of leaf cross-sections on your
slide: one from a plant that is adapted to hydric environments, one to mesic environments, and one to xeric
environments (very wet, moderate, and dry, respectively). I’m not telling you, which is which, but I will tell you that
one of these is a water-lily.
2. Identify some of the typical leaf structures we’ve discussed. Although it’s interesting to look at the central vein, the
stereotypical leaf cross-section is more easily seen away from the central vein.
Make a list of similarities and differences that you observe between these leaf types. Below are some possible
dimensions of similarities/differences you might examine (this is not an exhaustive list!).
Plant #1
Relative leaf thickness
(thickest, medium, thinnest)
Cuticle thickness
(thickest, medium, thinnest. Can you
see one?)
Epidermal thickness
(thickest, medium, thinnest, compare
the top to bottom of the leaf)
Palisade mesophyll thickness
(lots/little compared to spongy layer,
any gaps, number of cells, % of total
cell thickness)
Spongy mesophyll thickness
(lots/little compared to palisade layer,
% of total cell width)
Stomate location and density
(many/few; where on leaf?, are they
indented, in crypts, flush with the
surface, hairs?)
These website might help you.
virtualplant/ANATOMY/prac3.htm
http://botweb.uwsp.edu/anatomy/dicotleafxs.htm
Plant #2
Plant #3
3. Make a labeled sketch of each cross section. (make sure it is large and in pencil). You must
show guard cells and stomata. You may want to include a smaller more detailed sketch to show
details of the stoma area for some leaves. Also include the microscope power at which this
drawing was made. (e.g. x100)
4. Based on your observations, can you figure out which one cross section is adapted to which
environment (Xeric, hydric and mseic? Can you figure out which is the water-lily? Justify your
reasoning by giving 3 -4 reasons for your classification. Make sure you refer to your
drawings. I would paste a drawing next to your explanation to help me.
5. Look at the three plants on the side of the room. Draw very simple drawing of these leaves.
How are they different for the typical model of a “normal” leaf? Use these difference to try and
say something about these plants.
Grading Rubric For Leaf Structure Lab
Pre-lab Layout:
Title, Date, Name, partner
Introduction:
Summary of the science behind the experiment /2
Purpose of the Lab
/34
8
/1
Results:
Data table with results
/2
Conclusion:
Correct identification of plants
/3
Reasons behind classification:
Explanations of results xeric plant
Explanations of results hydric plant
Explanations of results mesic plant
/4
/4
/3
Drawings:
Drawing of xeric plant
Drawing of hydric plant
Drawing of mesic plant
/3
/3
/3
Extra plants:
Explanations of results plant A
Explanations of results plant B
Explanations of results plant C
11
9
6
/2
/2
/2