Energy & Photosynthesis (College Board AP® Biology): Flashcards
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Why do all living systems require a constant input of energy?
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Cards in this collection (47)
Why do all living systems require a constant input of energy?
To maintain their ordered systems.
Energy transfer to the surroundings (as heat) is constant, so an input of energy is needed to balance this loss and keep the system ordered.
True or False?
Energy input must exceed energy loss for a cell to maintain order and power its processes.
True.
If energy input does not exceed loss, the system cannot maintain order; significant loss of order or energy flow results in death.
What does it mean for an energy-releasing process to be coupled with an energy-requiring process?
The energy released by one reaction (e.g. breakdown of ATP) is used to drive another reaction that requires energy (e.g. building a larger molecule).
A significant loss of order or energy flow in a living system results in .
A significant loss of order or energy flow in a living system results in death.
Why are energy-related pathways in cells broken into a sequence of steps?
So energy is transferred in a controlled way.
Releasing all the energy of a molecule such as glucose in one step would cause cell damage.
How is the product of one step in a metabolic pathway usually used?
It is typically the reactant (substrate) for the next step in the pathway.
Example: pyruvate is a product of glycolysis and a substrate in the Krebs cycle.
Define conserved metabolic pathway.
Conserved metabolic pathway is a core pathway, such as glycolysis or oxidative phosphorylation, found across all domains of life — Archaea, Bacteria, and Eukarya.
Why is glycolysis thought to be an ancient, universal pathway?
It occurs in the cytoplasm of all domains, works without oxygen, uses widely available substrates, and needs only a few simple cofactors.
True or False?
The fact that core metabolic pathways are shared across all domains of life supports the idea of common ancestry.
True.
Conserved pathways such as glycolysis and oxidative phosphorylation are found in Archaea, Bacteria, and Eukarya, supporting common ancestry.
Why is it incorrect to say energy is 'produced' or 'made' in a cell?
Energy is never created — it is only released or transferred.
The correct language is that energy is released or transferred, not produced.
Define photosynthesis.
Photosynthesis is the series of reactions that use carbon dioxide, water, and light energy to make carbohydrates and oxygen.
Photosynthesis uses carbon dioxide, water, and to make carbohydrates and oxygen.
Photosynthesis uses carbon dioxide, water, and light energy to make carbohydrates and oxygen.
What happens to the energy captured during photosynthesis?
It is stored within the bonds of the organic compounds (carbohydrates) that are produced.
These carbohydrates can be used in other biological processes (e.g. cellular respiration) or stored (e.g. as starch).
In what type of organism did photosynthesis first evolve?
Prokaryotic organisms, such as cyanobacteria.
True or False?
Prokaryotic photosynthetic pathways provided the foundation for the evolution of eukaryotic photosynthesis.
True.
Eukaryotic photosynthesis is built on pathways that first evolved in prokaryotes such as cyanobacteria.
How did early cyanobacteria change Earth's atmosphere?
Their photosynthesis released oxygen, gradually producing an oxygenated atmosphere where previously there was none.
Define endosymbiotic theory.
Endosymbiotic theory proposes that chloroplasts are modified cyanobacteria that were engulfed by an early eukaryotic cell.
What features of chloroplasts provide evidence that they evolved from cyanobacteria?
A double membrane (from engulfment)
A circular genome
70S ribosomes (like bacteria, not eukaryotic 80S)
They divide like bacteria
Photosystems and chlorophyll a that closely match cyanobacteria
Define stroma.
Stroma is the fluid within the inner chloroplast membrane and outside the thylakoid; it is the site of the carbon fixation (Calvin cycle) reactions.
Define grana.
Grana are stacks of thylakoids within the chloroplast where the light reactions of photosynthesis occur.
The thylakoid membranes contain chlorophyll pigments organized into two .
The thylakoid membranes contain chlorophyll pigments organized into two photosystems.
What happens to the electrons in chlorophyll when it absorbs light energy?
The electrons are boosted to a higher energy level within photosystems I and II.
True or False?
In linear electron flow, photosystem I passes its electrons to photosystem II.
False.
Photosystem II passes its electrons along the electron transport chain to photosystem I; PSI was simply discovered first.
What replaces the electrons lost from photosystem II?
Electrons released by the splitting of water (photolysis) replace those lost from photosystem II.
What two products of the light-dependent reactions are passed to the Calvin cycle?
ATP
NADPH
These power the production of organic molecules in the light-independent reactions.
Where in the chloroplast do the light-dependent reactions take place?
In the thylakoid membranes, where the photosystems and electron transport chain are located.
What happens when chlorophyll in photosystems I and II absorbs light?
The light energy boosts electrons to a higher energy level.
These energized electrons are then passed along the electron transport chain.
Electrons lost from photosystem II are replaced when is split.
Electrons lost from photosystem II are replaced when water is split.
How is the proton (H⁺) gradient across the thylakoid membrane established?
As electrons pass along the electron transport chain, the energy released is used to actively transport protons from the stroma into the thylakoid lumen.
This creates a high proton concentration in the lumen and a low concentration in the stroma.
Define chemiosmosis.
Chemiosmosis is the movement of protons back across the thylakoid membrane through ATP synthase, providing the energy to synthesize ATP.
Which enzyme synthesizes ATP as protons flow back into the stroma?
ATP synthase.
Protons flow through it by facilitated diffusion, driving the formation of ATP from ADP and inorganic phosphate.
The production of ATP using light energy in the light-dependent reactions is called .
The production of ATP using light energy in the light-dependent reactions is called photophosphorylation.
What is NADPH formed from at the end of the electron transport chain?
Electrons and protons combine with the carrier molecule NADP⁺, reducing it to NADPH in photosystem I.
True or False?
The light-dependent reactions produce oxygen as a result of splitting water.
True.
Splitting water to replace lost electrons also releases oxygen as a by-product.
True or False?
ATP synthase actively pumps protons into the thylakoid lumen using energy from ATP.
False.
Protons are pumped into the lumen using energy from the electron transport chain. ATP synthase does the reverse — protons flow back through it, and this drives ATP synthesis.
Define Calvin cycle.
Calvin cycle is the light-independent stage of photosynthesis, occurring in the stroma of the chloroplast, in which carbon dioxide is used to produce carbohydrates.
Where in the chloroplast does the Calvin cycle take place?
In the stroma, the fluid that surrounds the thylakoids.
The Calvin cycle is the stage of photosynthesis.
The Calvin cycle is the light-independent stage of photosynthesis.
Which two products of the light reactions supply the energy for the Calvin cycle?
ATP and NADPH.
True or False?
The Calvin cycle occurs in the grana of the chloroplast.
False.
The Calvin cycle occurs in the stroma; the light reactions take place in the grana.
What is the source of carbon for the Calvin cycle?
Carbon dioxide (CO2), which is absorbed from the air and enters the chloroplast.
Define carbon fixation.
Carbon fixation is the incorporation of inorganic carbon dioxide into organic molecules during the Calvin cycle.
What type of organic molecules does the Calvin cycle produce?
Carbohydrates, such as sugars, as well as starch, sucrose, and cellulose.
During the Calvin cycle, carbon dioxide is into organic molecules.
During the Calvin cycle, carbon dioxide is fixed into organic molecules.
True or False?
The Calvin cycle can proceed without the products of the light reactions.
False.
The Calvin cycle depends on the ATP and NADPH generated by the light reactions.
Why is the Calvin cycle described as "light-independent"?
Because it does not use light directly; it is instead powered by the ATP and NADPH made during the light reactions.
The energy for the Calvin cycle is supplied by ATP and from the light reactions.
The energy for the Calvin cycle is supplied by ATP and NADPH from the light reactions.
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