Photosynthesis I & II Flashcards
Define photosynthesis
The process by which plants and other photoautotrophs use light energy to synthesize organic compounds from CO2
What is the overall reaction for photosynthesis?
6 H2O + 6 CO2 –> C6H12O6 + 6O2
Which reactant in photosynthesis is reduced?
Atmospheric CO2 is reduced to a carbohydrate molecule (glucose)
Which product of photosynthesis is oxidized?
Water
What is produced as a byproduct of water being oxidized?
molecular oxygen (O2)
In this lab, what is used as an assay of photosynthetic rate?
Oxygen production
If the photosynthetic rate is greater, will the leaf disks rise to the surface more quickly or slowly?
quickly
What was the additional source of CO2 used in this experiment?
Sodium bicarbonate aka baking soda
What is the summary of the equation for baking soda in water?
NaHCO3 + H+ –> Na+ + H2O + CO2
What type of energy is needed to synthesize organic compounds via photosynthesis?
Light energy
What was the plant species used for the leaf disk assay? Give the common and latin name
Spinach
Spinacia oleracea
After all the air has been removed from the leaf disks, what is produced that causes the leaf disks to float again?
oxygen
What is the purpose of the syringe?
To create a vacuum
What is the purpose of creating a vacuum within the syringe?
to remove all the gases from the intercellular spaces within the leaf disks and make the leaf disks sink
What happens to the leaf disks when the vacuum has been successfully made?
They sank
T or F: all the leaf disks cut will contain the same number of chloroplasts and will therefore photosynthesize at the same rate
False
What do photoautotrophs obtain the nutrients they require from?
water, soil minerals and atmospheric carbon dioxide
The conversion of atmospheric CO2 into organic materials provides the foundation for what four major things?
4 major macromolecules:
proteins
nucleic acids
carbohydrates
lipids
Photosynthesis occurs in the presence of what 2 things?
enzymes
light energy
Which organelles of plants conduct photosynthesis? Where are they located?
The chloroplasts located in the mesophyll tissues of leaves
What are the 2 major stages of photosynthesis?
- light dependent reactions
2. light independent reactions aka the Calvin Cycle
Where do the light dependent reactions occur?
in the thylakoid membranes of chloroplasts
Overall, what occurs during the light dependent reactions?
the stages of photosynthesis that convert light energy into chemical energy in the form of ATP and NADPH
What is NADPH?
the reduced form of NADP+
Briefly outline the steps of the light dependent reaction
- a water molecule is broken apart to provide a supply of electrons and protons
- oxygen gas is produced as a byproduct - electrons and protons release from the water are transferred to the acceptor NADP+ –> reducing it to NADPH
- Chemiosmosis joins a phosphate group to ADP to synthesize ATP during photophosphorylation
What are the products of the light reactions?
NADPH and ATP
Oxygen gas as a byproduct
Where does the Calvin Cycle occur?
the stroma of the chloroplasts
Overall, what occurs during the Calvin Cycle?
the stages of photosynthesis that convert inorganic CO2 into sugars
What happens when inorganic CO2 enters the stroma?
inorganic CO2 is converted into an organic form through CARBON FIXATION with the help of the rubisco enzyme
Which enzyme aids in carbon fixation in the Calvin Cycle?
rubisco
What is the final product of carbon fixation per one molecule of CO2 in the Calvin Cycle?
two 3-phosphoglycerate molecules
What happens to the 3-phosphoglycerates produced by carbon fixation in the Calvin Cycle?
Both of them are separately bonded to a phosphate group released from ATP to form 1,3-bisphosphoglycerate
What happens to 1,3-bisphosphoglycerate in the Calvin Cycle?
It is reduced by NADPH to produce glyceraldehyde 3-phosphate (G3P)
What is the product of the Calvin Cycle?
glyceraldehyde 3-phosphate (G3P), a carbohydrate
What is the function of the final stage of the Calvin Cycle?
regenerates the rubulose bisphosphate (RuBP) sugar to maintain the continuous fixation of inorganic CO2
What was the purpose of this experiment?
to determine whether the rate of photosynthesis by spinach is affected by varying concentrations of sodium bicarbonate
How was the rate of photosynthesis determined?
By measuring the time for 50% of the leaf disks to float
Why can it be predicted that photosynthetic rates will become greater/faster with a higher concentration of sodium bicarbonate?
because sodium bicarbonate is the source of CO2 in this experiment and CO2 is essential for the producing carbohydrates during photosynthesis
Which hypothesis was rejected based on the results?
The null hypothesis
What was the supported hypothesis?
the alternative:
the concentration of sodium bicarbonate (%) in tap water will have an effect on the rate of photosynthesis (seconds) by spinach, Spinacia oleracea.
Briefly describe the steps of the procedure for this experiment
- pour water into clear cup
- add amount of sodium bicarbonate to the water and gently mix
- obtain a few leaves from the spinach and use a straw to cut out X amount of disks per replicate
- gently put the leaf disks into the syringe and push the plug to the bottom carefully
- draw 2-3 mL of the sodium bicarbonate solution into the syringe and expel all the air out
- create the vacuum by covering the top of the syringe with thumb and pushing and pulling on the plunger until all the leaves sink
- label a plastic cup to indicate treatment and mark 3cm
- transfer leaf disks and solution into cup
- fill cup to 3cm mark with sodium bicarbonate solution
- use pipette to spread out leaf disks so they’re not overlapping
- place light source 10 cm above cup
- record time until 50% of leaf disks float or no change occurs after 20 minutes
- repeat steps for all replicates and treatments
Is it possible for the leaf disks to float in the control group?
yes, there is still a small amount of sodium bicarbonate present in tap water
What was the control group?
the solution without any additional CO2 added/no baking soda added
Why did the leaf disks float at different times?
chloroplast density will differ throughout different sections of the leaf
chloroplasts are where photosynthesis occurs so if there are less chloroplasts in one leaf disk, the rate of photosynthesis will be reduced compared to a leaf disk with a higher density
