Light Reactions 1
Where do the light reactions take place?
Thylakoid membrane
Where do ATP and NADPH go to after they are made in the light reactions?
The Calvin Cycle
Where does the Calvin Cycle occur?
How does light intensity affect the rate of photosynthesis?
Photosynthesis increases as light increases. More light = more excited electrons = ATP is produced more frequently (light rxns) = more glucose produced = more overall ATP produced (cell resp)
Why can photosynthesis and cellular respiration be considered to be in a cycle?
Cellular respiration uses the products of photosynthesis as reactants (O2 and glucose) and photosynthesis uses the products of cellular respiration as reactants (H2O, CO2)
Why do the light reactions take place within a membrane?
The light reactions require an Electron Transport Chain in its process: the ETC is embedded into a membrane.
What pigment is involved in absorbing the sun's energy in the light reactions?
Chlorophyll
What are the products of the Calvin Cycle?
ADP, NADP+, C6H12O6 (glucose)
What organelle is responsible for photosynthesis? What are 3 important structures within this organelle?
Chloroplast. 1) Thylakoid 2) Stroma 3) Chlorophyll (photosystems in thylakoid membrane)
Autotrophs produce energy via photosynthesis & cellular respiration. Heterotrophs eat autotrophs for energy. Heterotrophs give off CO2 needed for autotrophs to make energy.
What are the products of the light reactions?
ATP, NADPH, and O2 (oxygen)
What are the reactants of the light reactions?
Sunlight and H2O
If ATP is made during the Light Reactions, why is glucose made during the Calvin Cycle?
A very small amount of ATP is used to power the Calvin Cycle to make glucose. This glucose is used in the mitochondria in cellular respiration to make a lot of ATP (38 ATP)
What is the relationship between photosynthesis and cellular respiration? (provide their chemical equations)
They are reverse reactions.
Photo: 6CO2 + 6H2O + sun -> C6H12O6 + O2
Cell Resp: C6H12O6 + O2 -> 6CO2 + 6H2O + ATP
Where in the chloroplast and in the mitochondria are there Electron Transport Chains?
ETC in chloroplast = thylakoid membrane
ETC in mitochondria = inner membrane of mitochondria (cristae)
What is the job of water in the light reactions?
Water is split at the beginning of the ETC to replenish it with electrons (oxygen is a byproduct of this).
What happens to the oxygen produced in light reactions (as a result of water splitting)?
1) Transported to the mitochondria to power cellular respiration in the plant
2) Given off into the atmosphere
Explain what happens to ADP and NADP+ after they are made in the Calvin Cycle.
ADP and NADP+ are transported to the end of the ETC (in the thylakoid membrane). NADP+ is an electron acceptor at the end of the ETC and ADP will turn into ATP with the addition of a phosphate.
How would an increase in CO2 concentration affect the rate of photosynthesis in the following conditions:
1) Adequate amount of light
2) No light
1) Increased CO2 concentration would increase the rate of photosynthesis (has adequate amounts of ATP to make glucose from CO2)
2) Increased CO2 concentration would increase the rate of photosynthesis for a short time (while the plant uses its ATP storage), and after that, would not be able to increase the rate of photosynthesis due to lack of ATP from Light Rxns
How are the ETCs in photosynthesis and cellular respiration related/similar?
Both utilize the process of chemiosmosis. Electrons are transported down proteins in a membrane to create a concentration gradient of protons. These protons power ATP Synthase to make ATP.
Explain how chemiosmosis is used in the light reactions.
The ETC produces a concentration gradient of protons on one side of the thylakoid membrane. When the concentration becomes high, diffusion occurs and the protons diffuse through ATP Synthase, creating ATP.
How does ATP Synthase make ATP?
Protons move through ATP Synthase (due to chemiosmosis). This movement powers the addition of a phosphate molecule to ADP, creating ATP.
In the last step of the Calvin Cycle, what molecule is used to make glucose?
G3P - Glyceraldehyde 3-phosphate
What happens to plants that are not watered? (your answer must be at the molecular level)
No water = no replenished electrons for the ETC = ETC cannot make ATP to power Calvin Cycle = glucose cannot be made = cellular respiration cannot make ATP for the plant to survive
How is the ETC different in the light reactions compared to cellular respiration?
ETC in light reactions uses photosystems that are powered by light energy to excite electrons to make ATP. Electrons are replenished by H2O.
ETC in cellular respiration use electron carriers (NADH and FADH2) to replenish electrons, and uses proteins to transport electrons to make ATP.