Photosynthesis Flashcards
What is the primary purpose of photosynthesis?
Photosynthesis converts light energy into chemical energy in the form of sugars, which provide energy and fixed carbon for organisms.
What are the two main products of photosynthesis?
Glucose (a sugar that provides energy and fixed carbon) and oxygen (a byproduct).
What are photoautotrophs?
Organisms that use light to synthesize their own food, such as plants, algae, and some bacteria.
What are heterotrophs?
Organisms that cannot convert carbon dioxide to organic compounds and must obtain their fixed carbon by consuming other organisms, like animals and fungi.
Where does photosynthesis primarily take place in plants?
In the mesophyll cells of leaves, which contain chloroplasts.
What are chloroplasts?
Organelles in plant cells that contain chlorophyll and carry out the process of photosynthesis.
What is the role of chlorophyll in photosynthesis?
Chlorophyll absorbs light energy, which is necessary for the light-dependent reactions of photosynthesis.
What are the two stages of photosynthesis?
The light-dependent reactions, which occur in the thylakoid membrane, and the Calvin cycle, which occurs in the stroma.
What happens during the light-dependent reactions?
Light energy is absorbed by chlorophyll, and this energy is used to produce ATP and NADPH, while water molecules are split, releasing oxygen.
What happens during the Calvin cycle?
The Calvin cycle uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars (G3P), which can form glucose.
How are photosynthesis and cellular respiration related?
They are near-opposite processes: photosynthesis captures energy from light to produce glucose, while cellular respiration breaks down glucose to release energy.
What is the electron transport chain’s role in both photosynthesis and cellular respiration?
It generates a proton gradient across membranes, which drives ATP synthesis through chemiosmosis.
What is chlorophyll?
hlorophyll is a pigment found in the thylakoids that absorbs light energy, which is used to produce carbohydrates during photosynthesis.
What are thylakoids?
Thylakoids are disc-like structures within chloroplasts that help absorb light energy for photosynthesis.
What is the overall reaction of photosynthesis?
The overall reaction of photosynthesis is: 6CO2+6H2O+lightenergy→C6H12O6+6O2. This converts carbon dioxide and water into glucose and oxygen, using light energy.
What is the stroma?
The stroma is the fluid-filled space surrounding the grana in a chloroplast.
Where does the Calvin cycle occur, and what does it require?
The Calvin cycle takes place in the stroma and does not directly require light; it uses ATP and NADPH from the light-dependent reactions to create sugars.
Flashcard 13:
What is the visible spectrum?
The visible spectrum is the part of the electromagnetic spectrum that can be seen by the human eye, with wavelengths between 400 nm and 700 nm.
Where do the light-dependent reactions occur in plant cells?
The light-dependent reactions take place in the thylakoid membranes of chloroplasts.
What are the two types of photosystems involved in the light-dependent reactions?
Photosystem I (PSI) and Photosystem II (PSII).
What are the special pairs of chlorophyll in photosystems I and II?
The special pair in PSII is called P680, and in PSI, it is called P700.
How does light energy affect the electrons in photosystem II?
Light energy excites electrons in the P680 special pair of PSII, causing them to be passed to a primary electron acceptor.
What happens when water is split in photosystem II?
Water is split into oxygen (O₂), protons (H⁺), and electrons, contributing to the proton gradient used for ATP synthesis.
What is the Calvin cycle also known as?
the Calvin cycle is also known as the light-independent reactions.
Where do the reactions of the Calvin cycle take place?
In the stoma of the chloroplast
What molecules provide energy for the Calvin cycle?
ATP and NADPH from the light reactions
What happens during the carbon fixation stage of the Calvin cycle?
A CO₂ molecule combines with a five-carbon molecule, RuBP, forming an unstable six-carbon compound that splits into two 3-carbon chains with phosphate
What enzyme catalyzes the carbon fixation reaction in the Calvin cycle?
The enzyme rubisco (RuBP carboxylase/oxygenase) catalyzes the carbon fixation reaction.
What happens during the reduction stage of the Calvin cycle?
ATP and NADPH convert 3-PGA molecules into G3P (glyceraldehyde-3-phosphate), a three-carbon sugar.
What happens during the regeneration stage of the Calvin cycle?
Some G3P molecules are used to make glucose, while others are recycled to regenerate RuBP, requiring ATP.
How many turns of the Calvin cycle are required to make one G3P molecule that can exit the cycle?
Three turns of the Calvin cycle are needed to produce one G3P molecule.
What are the key molecules that enter the Calvin cycle?
What are the key molecules that enter the Calvin cycle?
How many ATP and NADPH are used in the Calvin cycle to make one net G3P?
9 ATP and 6 NADPH are used to make one net G3P.
What is Rubisco and why is it important in photosynthesis?
Rubisco is an enzyme that catalyzes the fixation of CO₂ into organic molecules during the Calvin cycle. It plays a key role in the first step of photosynthesis.
What is Rubisco’s “bad habit”?
Rubisco can bind O₂ instead of CO₂, initiating photorespiration, which wastes energy and reduces the efficiency of carbon fixation.
Under what conditions does photorespiration increase?
Photorespiration increases under hot, dry conditions when stomata close, raising the O₂/CO₂ ratio inside the leaf.
How does temperature affect Rubisco’s affinity for CO₂ and O₂?
At mild temperatures, Rubisco strongly favors CO₂. At high temperatures, Rubisco binds O₂ more often, leading to increased photorespiration.
What are the two molecules produced when Rubisco binds O₂ to RuBP?
The reaction produces 3-PGA (a normal Calvin cycle intermediate) and phosphoglycolate (which cannot enter the Calvin cycle).
Why is photorespiration considered wasteful?
Photorespiration removes fixed carbon from the Calvin cycle as CO₂ and uses energy without producing sugar.
What is photorespiration?
A wasteful pathway where rubisco binds to O2 instead of CO2, using up fixed carbon and wasting energy.
Why does photorespiration occur more at high temperatures?
Plants close stomata to conserve water, reducing CO2 levels and increasing O2 levels inside leaves.
What are C3 plants?
Plants that use only the Calvin cycle for carbon fixation, producing a three-carbon compound (3-PGA). Examples include rice, wheat, and soybeans.
What enzyme fixes CO2 in C4 plants, and why is it effective?
PEP carboxylase; it does not bind to O2 , ensuring efficient carbon fixation.
What is the primary adaptation of CAM plants?
They separate CO2 fixation and the Calvin cycle in time, opening stomata at night to conserve water.
How do CAM plants store CO2 captured at night?
As organic acids (e.g., malate) in vacuoles.
