1. Agenda 2/6 Environmental Factors Notes Plant Projects
Turn in: Concept Map, Video Notes
Homework:
1. Plant adaptations video and notes
2. C4, CAM, C3 Worksheet

2. Warm Up
Describe two environmental factors that would increase the rate of photosynthesis. Explain your answer

3. Photosynthesis: A Recap
Based on this equation, how could the rate of photosynthesis be measured?
The photosynthetic equation:
Provides the carbon to produce organic compounds during the Calvin Cycle
The organic compound ultimately produced during the Calvin Cycle
light
6 H2O
6 CO2
6 O2
C6H12O6
Emphasize to students the importance of understanding how and when each component of the photosynthetic equation is used; this is much more valuable (and less intimidating!) than simply having them memorize the equation!
Most realistically, the rate of photosynthesis could be measured by using the:
Decrease in environmental CO2 (in a closed system)
Increase in environmental O2 (in a closed system)
Increase in glucose (perhaps measured using radioactive carbon)
Split during the light reactions to replace electrons lost from Photosystem II
Produced as a byproduct of the splitting of water during the light reactions
Excites electrons during the light reactions

4. Environmental Factors & Photosynthesis
The rate (or speed) of photosynthesis can vary, based on environmental conditions.
Light intensity
Temperature
Oxygen concentration

5. Environmental Factors & Photosynthesis
Light intensity
As light intensity increases, so too does the rate of photosynthesis.
This occurs due to increased excitation of electrons in the photosystems.
However, the photosystems will eventually become saturated.
Above this limiting level, no further increase in photosynthetic rate will occur.
light saturation point
- Emphasize to students what it means to be saturated – as “full” as an item can be, or at its full capacity. A sponge is a good example to illustrate saturation; if a sponge is fully saturated with water, it can be left in a bucket of water overnight and will not gain any more water. In the same way, electrons in photosystems can be excited more often as light intensity increases, but eventually a “maximum” rate of excitation will be achieved; increasing light intensity beyond this point of light saturation will not yield an increase in photosynthetic rate. Be certain students don’t confused “stopped increasing the rate” with “ceases”!

6. Environmental Factors & Photosynthesis
Temperature
The effect of temperature on the rate of photosynthesis is linked to the action of enzymes.
As the temperature increases up to a certain point, the rate of photosynthesis increases.
Molecules are moving faster & colliding with enzymes more frequently, facilitating chemical reactions.
However, at temperatures higher than this point, the rate of photosynthesis decreases.
Enzymes are denatured.
-Ask students what type of “situation” is pictured here. They should answer an “optimum” situation is represented by this graph.
-This is an excellent opportunity to review the structure & function of enzymes as 3-D proteins with three or four levels of structure (primary, secondary, tertiary, quaternary) that are subject to external stresses such as temperature extremes. Emphasize to students the increased rate of molecular motion as temperatures increase, as well as the process of denaturation on protein structure and the resultant loss of molecular function.
- Emphasize to students the enzymes involved in photosynthesis, even though their names and specific functions do not need to be memorized. NADP+ reductase, Rubisco, and ATP synthase are all examples of enzymes involved in the process of photosynthesis.

7. Environmental Factors & Photosynthesis
Oxygen concentration
As the concentration of oxygen increases, the rate of photosynthesis decreases.
This occurs due to the phenomenon of photorespiration.

8. Photorespiration
Photorespiration occurs when Rubisco (RuBP carboxylase) joins oxygen to RuBP in the first step of the Calvin Cycle rather than carbon dioxide.
Whichever compound (O2 or CO2) is present in higher concentration will be joined by Rubisco to RuBP.
Photorespiration prevents the synthesis of glucose AND utilizes the plant’s ATP.
- Photorespiration is a negative process for photosynthetic organisms.
Photosynthesis occurs; glucose is produced
Rubisco joins CO2 to RuBP
More CO2
Photorespiration occurs; glucose is NOT produced
More O2
Rubisco joins O2 to RuBP

9. Photorespiration
Photorespiration is primarily a problem for plants under water stress.
When plants are under water stress, their stomata close to prevent water loss through transpiration.
However, this also limits gas exchange.
O2 is still being produced (through the light reactions).
Thus, the concentration of O2 is increasing.
CO2 is not entering the leaf since the stomata are closed.
Thus, as the CO2 is being used up (in the Calvin Cycle) and not replenished, the concentration of CO2 is decreasing.

10. Photorespiration
As the concentration of O2 increases and the concentration of CO2 decreases (due to the closure of the stomata to prevent excessive water loss), photorespiration is favored over photosynthesis.
Some plant species that live in hot, dry climates (where photorespiration is an especially big problem) have developed mechanisms through natural selection to prevent photorespiration.
C4 plants
CAM plants
Again, emphasize to students that photorespiration is unfavorable for photosynthetic organisms. It consumes ATP and does not produce glucose; the strong selective pressure against photorespiration has favored the proliferation of adaptations that increase the evolutionary fitness of those organisms who possess these adaptations.
This is another opportunity to stress how evolutionary adaptations come to exist. A mutation occurs, which may increase or decrease an organism’s chance of survival. If the mutation allows the organism that possesses it to reproduce more than other members of his/her/its population, the mutation will be favored through natural selection and will become more common in the population as organisms that possess the favorable mutation (adaptation) survive and reproduce at higher rates than members of the population which do not possess this adaptation.

11. C3 Plants
C3 plants, which are “normal” plants, perform the light reactions and the Calvin Cycle in the mesophyll cells of the leaves.
The bundle sheath cells of C3 plants do not contain chloroplasts
palisade mesophyll
spongy mesophyll
bundle sheath cells

12. C4 and CAM Plants
C4 plants and CAM plants modify the process of C3 photosynthesis to prevent photorespiration.
Overview:
C4 plants perform the Calvin Cycle in a different location within the leaf than C3 plants.
CAM plants obtain CO2 at a different time than C3 plants.
Both C4 and CAM plants separate the initial fixing of CO2 (carbon fixation) from the using of CO2 in the Calvin Cycle.
Both C4 and CAM plants fix CO2 with an enzyme other than Rubisco (both use PEP carboxylase) so they are able to fix CO2 in spite of the relatively high concentrations of O2. Then they use that CO2 separately in a normal Calvin cycle.

13. C4 Plants: Preventing Photorespiration
Plants that use C4 photosynthesis include corn, sugar cane, and sorghum.
In this process, CO2 is transferred from the mesophyll cells into the bundle-sheath cells, which are impermeable to CO2.
This increases the concentration of CO2.
Thus, the Calvin Cycle is favored over photorespiration.
The bundle-sheath cells of C4 plants do contain chloroplasts.
- Remember, Rubisco will join whichever compound is present in highest concentration (O2 or CO2) to RuBP; by shuttling CO2 into the bundle-sheath cells from which CO2 cannot escape, the concentration of CO2 is increased, which leads to the joining of CO2 to RuBP and the resultant production of organic compounds through the Calvin Cycle.

14. CAM Plants: Preventing Photorespiration
Plants that use CAM photosynthesis include succulent plants (like cacti) and pineapples.
In CAM (crassulacean acid metabolism) photosynthesis, plants open their stomata at night to obtain CO2 and release O2.
This prevents them from drying out by keeping their stomata closed during the hottest & driest part of the day.

15. CAM Plants: Preventing Photorespiration
When the stomata are opened at night, the CO2 is converted to an organic acid (via the C4 pathway) and stored overnight.
During the day – when light is present to drive the Light Reactions to power the Calvin Cycle – carbon dioxide is released from the organic acid and used in the Calvin Cycle to produce organic compounds.
Remember:
- Emphasize to students that the Calvin Cycle is not performed at night by CAM plants (or any other!). It is impossible for the Calvin Cycle to occur while it is dark because ATP and NADPH (from the Light Reactions) are required to run the Calvin Cycle. Instead, CAM plants store their CO2 as part of malic acid overnight until it can be released and used when the Light Reactions start again during the lighted hours.
Even though the CO2 is taken in at night, the Calvin Cycle cannot occur because the Light Reactions can’t occur in the dark!

16. Avoiding Photorespiration
Both C4 and CAM plants – which are primarily found in hot, dry climates – have evolutionary adaptations which help prevent photorespiration.
C4 plants perform the Calvin Cycle in the bundle-
sheath cells.
CAM plants open their stomata at night and store the CO2 until morning.
- Again, stress the location difference of the Calvin Cycle between C3 and C4 plants, and the temporal difference of the uptake of CO2 between C3 and CAM plants. Both mechanisms are adaptations that promote adequate CO2 levels to promote the Calvin Cycle over photorespiration while preventing desiccation.

17. Plant Adaptations Project
In your group, pick a specific type of plant and investigate what type of plant it is and what adaptations it has.
Include a summary of light dependent and calvin cycle
State whether it is a C4, C3, or CAM plant
Explain how the plant avoids photorespiration
Draw a diagram explaining the adaptations it has
Draw a picture of the plant overall and describe/label structural adaptations
Explain three other evolutionary adaptations that the plant posses
*When you group is finished do the environmental factors WS on the website!