1. Plant Metabolism & Productivity Tutorial

2. The Sun!! Photosynthesis
Where does the energy come from that sustains all life at the earth’s surface?
The Sun!!

3. Summarizing reaction of photosynthesis!
C6H12O6
Thought Questions:
How do plants acquire these starting reactants?
What do plants do with these products?
Record your answers to all of the though questions posed in this tutorial in the homework for Lab #4 in you lab manual. Review the entire tutorial before you attempt to answer any questions!

4. Who photosynthesizes?
Plants!

5. Marine and Freshwater phytoplankton – single celled and colonial algae
Rhodophyta (red algae)
Volvox
Who photosynthesizes?
Zooplankton (an animal)
Diatom
Chlorophyta (green algae)
Coccolithophore
Phaeophyta (brown algae)
Marine and Freshwater phytoplankton – single celled and colonial algae
Non-planktonic multicellular algae

6. Who photosynthesizes? Cyanobacteria
Found in the hot springs of Yellowstone N.P.

7. Anatomy of Photosynthesis in Plants
Photosynthesis occurs in the chloroplasts which are located in the cells of plant leaves. It is here that important light harvesting molecules called photosynthetic pigments are located.

8. The anatomy of a plant cell
Note that plant cells have both mitochondria for cell respiration and chloroplasts for photosynthesis!

9. Phytoplankton also undergo both cell respiration and photosynthesis!
Euglena – single cell freshwater phytoplankton
chloroplast
mitochondrion
nucleus
5 µm
Phytoplankton also undergo both cell respiration and photosynthesis!

10. The concept map on the following slide summarizes the important connections between cellular respiration and photosynthesis within and between plant cells.
As you toggle through this map see if you can determine where the sun’s energy is being used to facilitate the production of new plant tissues needed for plant growth. Also see if you can determine what energy is not available to sustain the growth of new tissues.

11. Plant Leaf Mesophyll Cell
H2O from soil O2
CO2 from atmosphere
starch
Energy from sunlight
Chloroplast
Cellulose
Exported to other plant cells to build
Amino acids
nucleotides
Note that these leaf cells, like many cells in plants, contain BOTH chloroplasts for photosynthesis and mitochondria for cellular respiration!
Plant Leaf Mesophyll Cell
Also converted to
Glucose (C6H12O6)
sucrose
Fuels cell respiration
Fatty acids
Mitochondrion
i.e. root cell
ATP
Exported to fuel respiration in other plant cells lacking chloroplasts
ATP
CO2
CO2

12. Provides the material resources to build plant cells and tissues to support plant growth and reproduction

13. What do you think this is?
Productivity is a measure of the amount of the sun’s energy captured by plants which is used to sustain the energy demands of life and provide energy for growth and reproduction.
We can estimate productivity by measuring something that is taken up by a plant which is proportional to energy uptake.
What do you think this is?
Carbon dioxide! - Used in the Calvin Cycle in photosynthesis to make carbohydrates. The rate of uptake of CO2 is directly proportional to the uptake of light energy from the sun.
The difference between these two provides a measure which is proportional to the amount of energy that is left over to fuel growth and reproduction!
Carbon dioxide is also a by-product of cellular respiration, so the rate of release of CO2 is directly proportional to how much energy is ultimately used by plants to run cellular processes.

14. Gross Primary Productivity (GPP) is…
…the total amount of the sun’s energy that a plant converts into chemical energy (stored in the bonds of organic molecules).
Think of it like your total earnings from a job!
Net Primary Productivity (NPP)
The total amount of the sun’s energy a plant converts into chemical energy subtracting out the amount of chemical energy a plant uses to fuel cellular respiration.
NPP or Energy available for growth and reproduction
or Gross (Total) Productivity – Cellular Respiration =
Total Pay rent & living expenses!
Money left over to grow your bank account =
Like…

15. CO2 concentration (*ppm)
Let’s say that we put some plant leaves in a sealed bottle and exposed it to 10 minutes of light and then 10 minutes of dark. During this time we used a CO2 sensor to measure changes in the concentration of CO2 in the bottle. The following results were obtained.
*ppm = part per million
Light
Dark
CO2 concentration (*ppm)
Slope = ppm/min
Slope = 20 ppm/min 10 20
Time (minutes)
The next 3 slides summarize the changes in CO2 in the bottle with respect to the metabolic processes occurring in the plant during the light and dark phases of the experiment.

16. Remember…
As we calculate productivity the sign of the slope (rate of change of [CO2]) for each measurement is important because they tell us whether CO2 is being taken up or released by the plant in your chamber!
A negative slope (i.e. -55 ppm/min/g) means the plant is TAKING UP CO2 from the chamber.
A positive slope (i.e. 34 ppm/min/g) means the plant is RELEASING CO2 into the chamber.

17. ? ?  CO2 uptake CO2 release  Light
Remember that the plant is doing both photosynthesis & cell respiration in the light!
Light
 CO2 uptake CO2 release 
The plant is actually taking up more CO2 than this through photosynthesis, but we cannot “see” this in the light because CO2 is also being released through cell respiration at the same time, and we don’t know how much!
Some amount of CO2 released from cell respiration ? ?
CO2 uptake  sugars Photosynthesis
Rate of Change in CO2 concentration (ppm/min)
-35.0 ppm/min = the rate of change of [CO2] due to BOTH respiration and photosynthesis which is Net Photosynthetic Productivity (NPP)

18. ?  CO2 uptake CO2 release  Dark Light …these should be equal!
During the dark, the plant is only doing cell respiration so….
…these should be equal!
So…to calculate gross (or total) primary productivity (the whole green box)…
…, we need to add the dark [CO2] change to the light, but in the negative direction. ?
Rate of Change in CO2 concentration (ppm/min)
We do this by subtracting the dark from the light!
-35.0 ppm/min (rate of change of [CO2] in the light)
-35.0 – 20.0 = (-20.0) = ppm/min

19. Here is another possibility!
Light
Dark
CO2 concentration (ppm)
Slope = 30.0 ppm/min
Slope = 10.0 ppm/min 5 10
Time (minutes)

20. ?  CO2 uptake CO2 release  Dark Light
We know that this plant is photosynthesizing because the rate of release of CO2 is greater in the dark than in the light!
+30dark slope
…but more CO2 is given off through respiration
In the light some amount of CO2 is used in photosynthesis… ?
Rate of Change in CO2 concentration (ppm/min)
To get gross primary productivity (GPP)…
10.0 ppm/min = the rate of change of [CO2] in the light due to BOTH respiration and photosynthesis
…again subtract the dark slope from the light slope
10.0 – 30.0 = -20.0

21. This plant is using up more of the energy it harvested from the sun to fuel cellular respiration than it is gaining through photosynthesis. This is indicated by the positive slope in the light!
Using our earnings analogy from earlier…this is like the person who’s rent and living expenses are GREATER than their total pay!
Like this plant which is using more energy just to stay alive than it is bringing in through photosynthesis! To stay alive, in the short term, this plant will have to use energy stored in organic molecules like starch.
This person is spending more than he is earning, and therefore must be depleting his savings in the bank!

22. Record your answer in your homework for Lab #4!
Team think and share…
A plant may be using more energy to fuel life processes (cell respiration) than it is taking in through photosynthesis either because its cell respiratory rate is elevated or because photosynthetic rate is diminished.
What is one potential reason why a plant may be forced to elevate its cell respiratory rate?
What is one potential reason for why a plant may experience diminished photosynthetic rates?
Record your answer in your homework for Lab #4!

23. Record your answer in your homework for Lab #4!
Thought Question!
Calculate the gross and net photosynthetic productivity for the plant in this experiment. What do you think is happening in this plant with regard to the relationship between cellular respiration and photosynthesis, and why might a living plant be exhibiting these metabolic characteristics?
Light
Dark
CO2 concentration (ppm)
Slope = 10.0 ppm/min
Slope = 10.0 ppm/min 5 10
Time (minutes)
Record your answer in your homework for Lab #4!