Digestion, Absorption & Food Molecules — Practice · Grade 7 Science

Chapter: Body Organization, Transport & Movement

What this practice covers

By the end of Digestion, Absorption & Food Molecules you should be able to:

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

Vocabulary used: digestion, enzyme, absorption, small intestine, surface area.

Problem 1

Why is grinding alone not complete chemical digestion?
Answer and explanation

It changes piece size and surface area but does not necessarily break the relevant chemical bonds into absorbable components.

Problem 2

Why is the stomach-only model incomplete?
Answer and explanation

Processing, transport, digestive contributions, and much absorption occur through several organs, especially the small intestine.

Problem 3

How does more exchange area help the absorption model?
Answer and explanation

It provides more surface across which materials can move under suitable conditions, rather than making food molecules appear from nothing.

Problem 4

Does absorbing sugar mean all its energy has already been used?
Answer and explanation

No. Absorption makes material available for transport; later cellular processes transfer its stored energy or use its matter.

Problem 5

Illustrative comparison: Sample A remains in one large piece; equal-mass Sample B is divided into small pieces. Both experience the same stated enzyme conditions; B breaks down faster. Explain a surface-area mechanism, distinguish observation from inference, and connect digestion with absorption.
Answer and explanation

Faster breakdown in B is consistent with increased exposed surface for enzyme contact under the stated conditions. The result is evidence about breakdown rate, not proof that absorption or energy use has already occurred. Further measurements could check the products and their passage across an exchange surface. Other changed conditions would weaken the isolated surface-area explanation.

Identify comparable mass and conditions.

Connect smaller pieces with more exposed surface.

Separate breakdown from later boundary crossing.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A diagram says food energy is created in the stomach. Correct it.
Answer and explanation

Food already contains chemical energy. Digestion processes molecules and absorption makes products available; cellular processes transfer energy into usable forms rather than create it.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which describes absorption?
  1. Food crosses the intestinal lining into transport
  2. Chewing reduces piece size
  3. A diagram label gets larger
  4. All energy is created
Answer and explanation

Food crosses the intestinal lining into transport

Absorption is boundary crossing; chewing is mechanical processing.

Problem 8

Why can equal masses in smaller pieces be processed faster under matched conditions?
Answer and explanation

Smaller pieces can provide more exposed surface for contact. The explanation requires comparable materials and reaction conditions.

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