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

Chapter: Matter & Energy in Living Systems

What these drills covers

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

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

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

Problem 1

Why is ATP not a long-term energy store?
Answer and explanation

It turns over rapidly in energy-transfer reactions; cells use other molecules for bulk longer-term storage.

Problem 2

Energy enters almost every ecosystem as
  1. heat from the ground
  2. light from the sun
  3. ATP from producers
  4. nitrogen from the air
Answer and explanation

light from the sun

Photosynthetic producers capture light energy and store it in chemical bonds; almost all other organisms depend on that capture.

Problem 3

An organism that makes its own food from inorganic materials and an energy source is
  1. a heterotroph
  2. an autotroph
  3. a decomposer only
  4. a consumer
Answer and explanation

an autotroph

Autotrophs build organic molecules from inorganic sources; heterotrophs obtain organic molecules by consuming others.

Problem 4

A cell regenerates 9.0 × 10⁶ ATP molecules per second and uses 9.0 × 10⁶ per second. What is the net change in ATP count per second?
Answer and explanation

0

Use equals regeneration, so the pool stays constant. ATP supply is maintained by turnover, not by storing a large amount.

Problem 5

Of 1,000 kJ of light energy reaching a plant, about 10 kJ ends up in new plant tissue. What percentage is that?
Answer and explanation

1 %

10 / 1,000 × 100 = 1 percent. Most incoming light is reflected, transmitted, or lost as heat rather than stored.

Problem 6

Explain why matter cycles in an ecosystem while energy does not.
Answer and explanation

Atoms are rearranged but not destroyed, so carbon, nitrogen, and other elements pass between organisms, air, water, and soil and can be reused indefinitely. Energy changes form at every transfer and some becomes heat that disperses into the surroundings, where it is no longer available to do cellular work. An ecosystem therefore needs a continuous input of energy but not a continuous input of matter.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 7

Describe the ATP–ADP cycle and explain why ATP is called a currency rather than a store of energy.
Answer and explanation

ATP is hydrolysed to ADP and inorganic phosphate, releasing energy that is coupled to cellular work, and ADP is then recombined with phosphate using energy released by the breakdown of fuels. The cycle runs continuously. ATP is a currency because cells hold only a few seconds' worth and regenerate it as fast as they spend it; the long-term store is in fuel molecules such as glycogen and fat, which are converted into ATP as needed.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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