How do cells store and release the energy they need to do work?
Explain how cells use ATP as their energy currency, how energy is released when ATP is broken down, and how this links to photosynthesis and respiration (NYSSLS LS1, energy and matter; systems and system models).
A NYSSLS-level answer on cellular energy for the New York Life Science: Biology Regents: ATP as the cell's energy currency, how energy is released and stored, and how photosynthesis and respiration supply the energy cells use.
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What this topic is asking
NYSSLS LS1 treats the cell as an energy system. The Life Science: Biology Regents wants you to know that cells use ATP as their immediate energy supply, and to connect ATP to the larger picture: photosynthesis captures energy and respiration releases it. The crosscutting concept is energy and matter: energy flows through living systems, changing form but not appearing from nothing.
ATP, the energy currency
Cells do not use glucose directly to power most jobs. Instead they release energy from glucose in controlled steps and use it to make ATP, then spend ATP wherever energy is needed. ATP is ideal as a currency because it releases a usable amount of energy in a single step, can be made and broken quickly, and is the same molecule throughout the cell.
Releasing and storing energy
When a cell does work, ATP is broken down: ATP becomes ADP plus phosphate, and energy is released. When energy is available (from respiration), the cell rebuilds ATP by joining a phosphate back to ADP. This ATP-ADP cycle runs constantly, so a cell makes and uses enormous amounts of ATP without storing much at a time. Energy-requiring processes that depend on ATP include active transport across membranes, muscle contraction, nerve impulses, cell division and building large molecules.
Where ATP comes from
Most ATP is produced by cellular respiration, largely in the mitochondria, which release the chemical energy stored in glucose. This is why hard-working cells, such as muscle cells, contain many mitochondria. A small amount of ATP can be made without oxygen (anaerobically), but aerobic respiration produces far more. Respiration is covered in cellular respiration.
Tracing the energy back to sunlight
This is the crosscutting concept of energy and matter in action. The exam often asks you to trace the energy in ATP back to the sun, or to explain why energy must keep entering an ecosystem (because it flows through and is lost as heat, unlike matter, which cycles). The ecosystem-scale version is in energy flow and matter cycling.
Try this
Q1. State what ATP is broken down into when a cell uses energy. [1]
- Cue. ADP and a phosphate group.
Q2. Explain why a cell that cannot make ATP can no longer carry out active transport. [2]
- Cue. Active transport requires energy supplied by ATP; with no ATP there is no energy source, so the cell cannot move substances against their gradient.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (Life Science sample, 2024)2 marksActive transport, muscle contraction and protein synthesis all require energy supplied by ATP. (a) State where in the cell most ATP is produced. (b) Explain why a process such as active transport stops if a cell can no longer make ATP.Show worked answer →
A 2-point constructed-response item assessing energy and matter and systems reasoning.
(a) 1 point: most ATP is produced in the mitochondria (by cellular respiration).
(b) 1 point: active transport needs energy from ATP to move substances against their gradient; with no ATP there is no energy supply, so the process cannot continue.
Markers reward linking the loss of the ATP supply to the failure of an energy-requiring process.
Regents (Life Science CR, 2025)2 marksATP is described as the energy currency of the cell. (a) Explain what happens to ATP when a cell uses its energy. (b) Explain how the energy released by respiration is connected to the energy originally captured by photosynthesis.Show worked answer →
A 2-point item on ATP and the flow of energy.
(a) 1 point: ATP is broken down (a phosphate is removed) to release energy for the cell's work, forming ADP.
(b) 1 point: photosynthesis captures light energy and stores it in glucose; respiration releases that stored chemical energy from glucose to make ATP, so the energy in ATP originally came from sunlight.
Markers reward the chain light to glucose to ATP.
Related dot points
- Explain how enzymes act as biological catalysts, how the active site and substrate fit, and how temperature and pH affect enzyme activity (NYSSLS LS1, structure and function; analyzing data).
A NYSSLS-level answer on enzymes for the New York Life Science: Biology Regents: how enzymes lower activation energy, the active site and substrate fit, and how temperature and pH change the rate of enzyme-controlled reactions.
- Explain how photosynthesis converts light energy, carbon dioxide and water into glucose and oxygen, identify where it occurs, and analyze how limiting factors affect its rate (NYSSLS LS1, energy and matter; analyzing data).
A NYSSLS-level answer on photosynthesis for the New York Life Science: Biology Regents: the inputs and outputs, the role of chloroplasts and chlorophyll, the word and balanced equations, and how light, carbon dioxide and temperature limit the rate.
- Explain how cellular respiration releases energy from glucose to make ATP, compare aerobic and anaerobic respiration, and relate respiration to the role of the mitochondria (NYSSLS LS1, energy and matter; structure and function).
A NYSSLS-level answer on cellular respiration for the New York Life Science: Biology Regents: how glucose is broken down to release energy as ATP, the equation, the role of mitochondria, and the difference between aerobic and anaerobic respiration.
- Explain how photosynthesis and respiration together cycle carbon and oxygen while energy flows one way, and trace atoms of matter through these processes (NYSSLS LS1, energy and matter; systems and system models).
A NYSSLS-level answer on the cycling of matter and the flow of energy for the New York Life Science: Biology Regents: how photosynthesis and respiration link, why matter is conserved and cycles while energy flows one way, and how to trace atoms through living systems.
- Explain how the cell membrane controls the movement of materials by diffusion, osmosis and active transport, and relate membrane structure to selective permeability (NYSSLS LS1, structure and function; stability and change).
A NYSSLS-level answer on the cell membrane for the New York Life Science: Biology Regents: the structure of the membrane, selective permeability, diffusion and osmosis, active transport, and how cells maintain a stable internal environment.
Sources & how we know this
- New York State P-12 Science Learning Standards (Life Science) — New York State Education Department (2016)
- Educator Guide to the Regents Examination in Life Science: Biology — New York State Education Department (2025)