Study "BFI - Plants", a flashcard deck on FORKSAI.
How does the structure of chlorophyll a contribute to its function in photosynthesis?
Chlorophyll a has a porphyrin ring head containing a magnesium atom, which is the site where light energy is absorbed. Its hydrocarbon tail anchors the molecule within the hydrophobic pocket of proteins in the thylakoid membranes, positioning it correctly for light capture.
Define the relationship between the absorption spectrum and the action spectrum in photosynthesis.
The absorption spectrum illustrates the wavelengths of light absorbed by a specific pigment, such as chlorophyll a or b. The action spectrum, conversely, shows the rate of photosynthesis at different wavelengths of light, generally mirroring the combined absorption spectra of photosynthetic pigments, indicating which absorbed light is effectively used for photosynthesis.
Explain the role of the proton gradient in ATP synthesis during the light-dependent reactions.
During the electron transport chain, protons (H+) are pumped from the stroma into the thylakoid space, creating a proton gradient where the H+ concentration is much higher inside the thylakoid space. This gradient drives protons through ATP synthase back into the stroma, and this movement powers the synthesis of ATP from ADP and inorganic phosphate.
Distinguish between chlorophyll a and chlorophyll b based on their roles and structural differences.
Chlorophyll a is the primary pigment directly involved in capturing light energy and has a CH3 functional group. Chlorophyll b is an accessory pigment that absorbs light at different wavelengths and transfers this energy to chlorophyll a, characterized by a CHO functional group.
Why do plants appear green?
Plants appear green because chlorophyll molecules within the thylakoid membranes of chloroplasts absorb blue and red light for photosynthesis, but they transmit or reflect green light. This reflected green light is what our eyes perceive.
How does the Calvin Cycle utilize the products of the light-dependent reactions?
The Calvin Cycle uses the ATP and NADPH generated during the light-dependent reactions. ATP provides the energy, and NADPH provides the reducing power, both essential for converting carbon dioxide into glucose and regenerating RuBP.
Define photolysis and explain its significance in the light-dependent reactions.
Photolysis is the process where light energy absorbed by chlorophyll in Photosystem II is used to split water molecules (H2O). This process is significant because it releases oxygen as a byproduct, provides protons (H+) that contribute to the proton gradient, and supplies electrons (e-) for the electron transport chain.
What is the primary function of carotenoids in photosynthesis?
Carotenoids are accessory pigments that primarily absorb some blue light to protect chlorophyll from damage. They also absorb light energy and transfer it to chlorophyll a to be used in photosynthesis.
How does carbon fixation occur in the Calvin Cycle?
Carbon fixation begins when carbon dioxide from the atmosphere enters the stroma and is attached to a five-carbon sugar molecule called RuBP. This reaction is catalyzed by the enzyme rubisco, forming an unstable six-carbon compound that quickly splits into two molecules of a three-carbon compound.
What are the net products of the light-dependent reactions and what are their fates?
The net products of the light-dependent reactions are ATP, NADPH, and oxygen (O2). ATP and NADPH carry chemical energy and reducing power, respectively, to the Calvin Cycle to synthesize glucose. Oxygen is released as a byproduct.