SNC1D1
The Interaction of Living Things
MATERIALS:
2000 mL beaker
150 mL beaker
50 mL beaker
manganese dioxide powder
candle
scoopula
stopwatch
30% hydrogen peroxide
INQUIRY ACTIVITY
Relationship Between Chemical Reactions (Demo)
Demonstration 1: Place a candle on a 150 mL beaker and light. Cover the candle with a 2000 mL
beaker and start the stopwatch. Stop the timer when the candle is extinguished and record
observations on the board.
Demonstration 2: Place about 15 mL 30% hydrogen peroxide in a 50 mL beaker. Add a very small
amount of manganese dioxide in the beaker and repeat Demonstration 1.
Hypothesis:
Design:
Independent Variable: ____________________________
Dependent Variable:
_____________________________
Controlled Variables:
__________________________________________
__________________________________________
Observations:
Demonstration
1
2
Conclusion:
Materials
candle
candle + hydrogen peroxide
Time (s)
The Relationship Between Living Things
GOAL: To understand how plants and animal life are connected as part of a simple cycle.
KEY TERMS:
Organic
Inorganic
Combustion
Photosynthesis
Cellular Respiration
BACKGROUND: Ecosystems are incredibly complex systems. All living things are composed of matter
(atoms) that move through food chains, but they must be constantly recycled back to the environment
as waste products or by decomposers. Organic substances are compounds that contain carbon,
hydrogen and other atoms such as oxygen and nitrogen. These are found in all living things. Inorganic
substances do not contain carbon and hydrogen together, such as water (H2O), carbon dioxide (CO2) and
ammonia (NH3). Organic substances undergo changes as they move through living things in an
ecosystem and eventually return to the environment as inorganic substances.
Studying ecosystems can be difficult, but by using carefully controlled experiments we can better
understand how living things are related. Joseph Priestley (1733-1804) was a famous chemist best
known for his studies of gases. He discovered oxygen using an experiment similar to one you have
observed in class, as well as other gases such as ammonia and carbon monoxide. Priestley also studied
the relationship between living things and the gases he discovered.
Priestley’s First Experiment: Priestley carried out an experiment with 2 sealed jars to study the
relationship between a burning candle and a plant (Figure 1). Examine the diagrams and answer the
following questions on a separate page.
`
A
B
a) Why did the candle in jar A go out after 3 minutes?
b) Write a hypothesis (prediction and explanation) for what happened to the candle in jar B.
c) Priestley observed that the candle in jar B burned for 5 minutes. What gas is produced by the
plant?
d) What gases are produced by the burning candle?
e) Priestley was careful to control the variables he was not interested in. How would the time of
burning be affected by the following changes? Give a reason for each answer.
i) a larger bell jar was used (increased volume).
ii) a larger candle was used
iii) a larger plant was used
Priestley’s Second Experiment: Using three sealed jars, Priestley now studied the relationship between
the plant and two mice (Figure 2). Both mice eventually died, but the mouse in jar E lived longer .
C
C
D
E
a) Why did the mouse in jar D die?
b) Why did the mouse in jar E live longer?
c) After a long period of time, the plant in jar C appeared wilted and sickly. Write a possible
explanation. How could you test your hypothesis?
d) In jar E, the mouse lived longer and the plant appeared healthier. What is a possible
explanation for this ?
e) To study living things, biologists often sacrifice the life of animals, particularly mice and rats. Do
you agree or disagree with using animals in experiments? Explain your reasoning.
We will now examine two processes that link plants and animals together.
Analysis Questions:
1. Which substances involved in photosynthesis and cellular respiration are organic? Which ones
are inorganic substances?
2. How is the candle in the first experiment and the mouse in the second experiment similar?
3. One problem with space exploration is the need to bring oxygen for astronauts to breathe.
How might this problem be solved?
4. Within the biosphere, a balance between oxygen and carbon dioxide is maintained by the
processes of photosynthesis and cellular respiration. Combustion also puts carbon dioxide and
water into the atmosphere. How could combustion affect this balance and how may
ecosystems respond to this change?
5. Scientists often use living things in experiments. Write a set of rules that you would impose on
scientists who wished to use living things in experiments.
The Interaction of Living Things
Combustion
A chemical reaction that converts fuel and oxygen gas into carbon dioxide and
water.
Reactants
Products
fuel
+
oxygen
carbon dioxide
+
water
fuel
+
O2
CO2
+
H2O
Photosynthesis
The process carried out by plants and algae to use the energy of sunlight to
convert carbon dioxide and water into sugar and oxygen.
carbon dioxide
+
water
sugar
+
oxygen
CO2
+
H2O
C6H12O6
+
O2
Cellular Respiration
Most living things use oxygen to break down sugar as a source of energy.
sugar
+
oxygen
carbon dioxide
+
water
C6H12O6
+
O2
CO2
+
H2O
Plants also use cellular respiration but they generate much more oxygen through
photosynthesis than they consume. Many organisms therefore rely on the
oxygen released by plants in order to produce energy.