Enrichment: Chemical Changes in Plants
and Animals
Read the passage and complete the activity below. Then use a separate sheet of paper to
answer the questions that follow.
Plants and animals have a lot in common. They are both made of matter and undergo physical and
chemical changes. They are made of the same elements, primarily carbon, oxygen, and hydrogen. It may
not look like it, but plant leaves are made of the same elements as a polar bear’s fur. The arrangement of
atoms in molecules gives matter unique physical and chemical properties that create substances that look
and behave in different ways.
Perhaps the most amazing similarity between plants and animals is a fundamental chemical reaction that
makes life possible. All plants, with the help of energy from the sun, utilize carbon dioxide and water to
produce glucose and gaseous oxygen molecules. In a way, the plant “breathes in” carbon dioxide from
the atmosphere and “breathes out” oxygen. Warm-blooded animals, however, do the opposite during a
process called respiration. They breathe in oxygen and, with the help of the chemical energy stored in
glucose molecules, generate heat and expell carbon dioxide. In this way, plants and animals each play a
part in ensuring that the other has what it needs to survive. The next time you see a tree, thank it for the
air you breathe!
(photosynthesis)
carbon dioxide water glucose/sugar oxygen
6CO2 + 6H2O + heat

–––––––→ C6H12O6 + 6O2
←––––––––
(respiration)
Number of Number of
Elements: C___ Elements: C___
O___ O___
H___ H___
Analyze and Interpret Data
1. Reason Quantitatively In the reaction above, some molecules have a number in front of
the formula showing how many molecules it takes for the reaction to occur. Tally the
number of elements on each side of the reaction and record the values above.
2. Describe Patterns Describe how the number of elements compare on each side of the
reaction, and explain how this relates to the law of conservation of mass.
3. Explain Phenomena Identify which chemical reaction is endothermic and which is
exothermic. How can you tell?
4. Support Your Explanation All life requires an energy source and a source of carbon.
Based on the reactions above, identify each of these for plants and warm-blooded animals.