ATP & the Flow of Energy — Practice · Grade 10 Science

Chapter: Matter & Energy in Living Systems

What this practice covers

By the end of ATP & the Flow of Energy you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: ATP, ADP, autotroph, heterotroph, energy coupling.

Problem 1

ATP is best described as
  1. the organelle where respiration happens
  2. the cell's main energy currency
  3. the molecule that stores genetic information
  4. a green pigment that absorbs light
Answer and explanation

the cell's main energy currency

ATP is the small, spendable energy-carrying molecule cells use to power almost every activity — its nickname is the cell's energy currency.

Problem 2

What is the main difference between ATP and ADP?
  1. ATP contains DNA while ADP does not
  2. They are identical molecules with different names
  3. ATP has three phosphate groups and ADP has two
  4. ATP has two phosphate groups and ADP has three
Answer and explanation

ATP has three phosphate groups and ADP has two

ATP has three phosphate groups; ADP has two. Hydrolysis forms ADP and inorganic phosphate.

Problem 3

Under stated standard biochemical conditions, ATP hydrolysis releases 7.3 kcal/mol. Using that value, how much free energy is released by 5 mol?
Answer and explanation

36.5 kcal

5 × 7.3 = 36.5 kcal under the stated conditions; actual cellular values depend on conditions.

Problem 4

Explain why ATP is called a 'rechargeable' energy molecule rather than a disposable one.
Answer and explanation

When ATP releases energy it becomes ADP plus a phosphate, but it isn't discarded — the cell adds energy from food or sunlight to reattach the phosphate and turn ADP back into ATP. This ATP–ADP cycle repeats over and over, like recharging a battery.

Problem 5

Which of these organisms is an autotroph?
  1. A gray wolf
  2. A mushroom
  3. A human
  4. An oak tree
Answer and explanation

An oak tree

An oak tree makes its own food from sunlight, carbon dioxide, and water, so it is an autotroph (producer). The wolf, mushroom, and human are heterotrophs that must eat other organisms.

Problem 6

Why must an active cell keep regenerating ATP? Explain the reasoning in your own words.
Answer and explanation

Continuous regeneration keeps production matched to ongoing demand.

Cell work continually converts ATP to ADP and phosphate.

Available ATP is limited, so metabolic processes must replenish it.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

Why can a cell stop pumping if ATP regeneration fails? Show the reasoning, not just the conclusion.
Hints

Account for both hydrolysis and regeneration.

Answer and explanation

Energy-coupled transport cannot continue normally without sufficient chemical energy supply.

Problem 8

Does a large ATP turnover rate imply every ATP molecule is stored forever?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. ATP is repeatedly regenerated and used, so turnover and standing amount differ.

Problem 9

ATP supports work through a chemically coupled reactionATP supports work through a chemically coupled reactionATPCoupled transportor synthesisADP + phosphate must be rebuilt using another energy input.
Original ATP-work coupling abstraction, not a fixed free-energy-per-molecule measurement.
Interpret the supplied visual. Why does counting ATP molecules not alone give the total energy supplied by food?
Answer and explanation

The pathway, reaction conditions, coupling and other energy transfers matter; ATP count is only one defined output.

ATP hydrolysis can support an energetically linked change, such as a transport protein’s conformational cycle. The useful change depends on the overall reaction and coupling, not on energy being released by breaking one isolated bond. ADP and inorganic phosphate can be used to rebuild ATP through other energy-transferring processes. ATP therefore serves repeated short-term transfers rather than a perpetual source. Count a stated ATP demand separately from the food input or the rate of ATP production; molecule count and energy amount are different quantities.

The pathway, reaction conditions, coupling and other energy transfers matter; ATP count is only one defined output.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 10

A defined process receives 240 energy units and delivers 72 to the selected useful output. Find efficiency and explain where the remainder belongs in an energy account.
Answer and explanation

Efficiency is 72/240×100 = 30%; 168 units goes to other transfers/storage under the boundary. It is not destroyed, and identifying particular outputs requires a complete measured account.

Efficiency is 72/240×100 = 30%; 168 units goes to other transfers/storage under the boundary. It is not destroyed, and identifying particular outputs requires a complete measured account.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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