Download Biology 173, Spring 2008

Biology 173
McNeely
Winter 2016
Activity #1
Plant map and stoichiometry
Due Weds, Jan 20. The two maps are GROUP assignments. The stoichiometry questions
are an INDIVIDUAL assignment. Please plan to turn the maps in during your discussion
section. Please turn your stoichiometry questions in via Canvas.
In this exercise we will trace the path of 6 important elements from the environment into the
molecules where they are most abundant in plant tissue. Our goals are 1) understand plant
nutritional requirements in terms of chemicals that make up plant cells, 2) relate plant nutritional
requirements to plant traits – physiological and ecological, and 3) introduce the concept of
organismal stoichiometry – thinking about organisms in terms of ratios of their elemental
constituents. You may find the following material from your textbooks helpful: pgs 64-65, 68-80, 8688, 163-165, and 187.
If we were to write a chemical equation for the “typical” plant, as if the entire plant was one
molecule, the equation might look like this (some micronutrients omitted, water is included):
H3,500,000O1,475,000C123,000N3,500K837Ca405Mg726P209S102Cl9Fe6B6Mn3Zn1
Plants are variable in their nutrient make-up (compared to animals), so the coefficients might vary
from plant to plant, but the relative abundance of nutrients will follow this pattern.
For the rest of this activity we will focus on C, N, O, P, and S. We will consider primarily
the constituents of plant biomass (dried plant tissue), excluding free water.
The first portion of this activity (drawings) is a GROUP assignment.
These directions include some fairly specific instructions. To avoid losing points, make
sure you complete all portions of each step. It may help to reread them slowly and carefully
after you have done the step to make sure you didn’t miss anything.
1. Obtain an oversized piece of paper and a packet of markers. On one side, draw a diagram of a
plant indicating the following structures: root, root hair, xylem, phloem, stem, leaf, stoma. For
each element C, N, O, P, S, show the pathway through which it enters the plant and travels to a
leaf cell. Use colored dot stickers to code for each element and provide a key on the side of the
paper to indicate which color codes for which element. You should be thinking about these
elements primarily as constituents of organic molecules (not free water). Indicate which
uptake processes require the plant to use energy (you can use star stickers to indicate
energy use if you want).
2. What is the form for each of C, N, O, P, S in the environment that is taken up by the plant?
Write the chemical formula for each in the appropriate part of your diagram.
3. On the other side of your paper, draw a plant cell with these structures: cell wall, cell
membrane, nucleus, chloroplast (one of many), a mitochondrion (one of many) and a ribosome
(one of many).
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Biology 173
McNeely
Winter 2016
4. On your drawing, at the site of the appropriate cell structure, write out equations for 1)
photosynthesis and 2) cellular respiration. Which of the elements C, N, O, P, S are incorporated
into organic molecules during photosynthesis? Indicate them using the colored dot stickers.
5. Where in the plant cell do you find the most cellulose? Draw a cartoon of the structure of a
cellulose molecule near this structure on your map. Do you think cellulose is constructed near
this structure or elsewhere in the plant cell? What precursor molecules are required? (Answer
these questions on your map, near the drawing/cartoon of cellulose). Which of the C, N, O, P,
S elements are found in cellulose? Indicate them with your colored dot stickers.
6. In plants, nitrogen is first incorporated into organic molecules through the synthesis of
glutamic acid in the mitochondria. In or near the mitochondrion on your map, draw the
molecular structure of glutamic acid. Circle the two chemical groups that are present in all
amino acids. Identify which of these two groups is added during this synthesis. Indicate the
chemical form of nitrogen required. Contemplate the fact that the vast majority of the
nitrogen in all our proteins is originally incorporated into organic molecules from
inorganic nitrogen by plants via this mechanism. Place the dot sticker for nitrogen next to
your drawing of glutamic acid. Finally, draw an arrow from the mitochondrion to the structure
where amino acids are synthesized into proteins, and then draw some arrows to other cell
structures that require a lot of protein.
7.
On your drawing, at the site of a cell structure that includes this molecule, draw the molecular
structure of a nucleotide. Use a colored dot sticker to indicate the phosphorous present. Which
other C, N, O, or, S are found in nucleotides? Finally, use arrows or symbols to indicate other
cell structures containing high concentrations of nucleotides.
8. On your drawing, at this site of a cell structure that includes this molecule, draw a cartoon of the
molecular structure of a phospholipid. Use a dot sticker to indicate the phosphorous present.
9. What type of biomolecule contains most of the sulfur in a plant cell? What cellular organelle
synthesizes this type of molecule? Place a colored dot sticker by this organelle.
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Biology 173
McNeely
Winter 2016
Answer the following questions about plant stoichiometry.
Each student in the group should turn in INDIVIDUAL answers.
Please type your answers, save your file in .docx or .pdf format and submit through CANVAS. You
will find this document on Canvas as well.
In organismal stoichiometry, ratios of other elements are expressed relative to the abundance of
carbon (C:X); therefore the questions will ask you to determine when C:N or C:P ratios would be
relatively high or low.
1. Why do you think elemental ratios are expressed relative to carbon (rather than compared to a
different element or compared to wet weight, for example)?
2. Based on their molecular constituents, what molecules, organelles, and or structures within plant
cells are likely to contain a relatively high ratio of N compared to other elements (low C:N ratio)?
3. Based on their molecular constituents, what molecules, organelles, and or structures within plant
cells are likely to contain a relatively high ratio of P compared to other elements (low C:P ratio)?
4. Based on their molecular constituents, what molecules, organelles, and or structures within plant
cells are likely to contain little N or P (high C:N and C:P ratios)?
5. Would you expect a plant with very large woody stem such as a Douglas fir tree to have a higher
or lower C:N ratio than a plant without a woody trunk such as a daisy growing beneath the tree?
6. Plants (and other organisms) that grow very quickly require a high density of ribosomes within
their cells to rapidly produce new proteins. Would the C:P ratio of a fast growing plant or a slow
growing plant be higher?
What to turn in, when:
1. Today at the end of class, turn in your pre-lab questions, 1 PER GROUP.
2. Wednesday, 20 Jan, 11 am turn in your drawings, 1 PER GROUP.
3. On or before Wednesday, 20 Jan, 11 am turn in answers to stoichiometry questions above, 1
PER STUDENT, ON CANVAS.
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