teacher’s notes
student’s notes
Carbon cycle: releasing
dinosaur breath in the lab
(teacher’s notes)
Level
This material is designed for students aged 12 to 14
(years 8 and 9).
Topic
This activity is one of five aimed to teach students
about the nature of carbon, the different types of
compounds it exists in (eg charcoal, glucose, carbon
dioxide), the biochemical reactions it takes part in
(photosynthesis and respiration), the range of
processes that carbon and carbon compounds are
involved in on Earth, and how these link together to
form the carbon cycle.
The other activities are
Carbon cycle: where is this crucial carbon?; a teacher-
led discussion interspersed with demonstrations in
which the teacher burns a range of materials over a
Bunsen flame, forming charcoal, to illustrate that they
contain carbon.
Carbon cycle in the lab: carbon products and the
processes that link them; which involves working in
small groups to place examples of the carbon cycle
products in the correct places on a diagram of the
cycle.
Cycling carbon: seeing how plants use carbon dioxide
in the lab; a short pupil practical exploring the uptake
of carbon dioxide from the atmosphere by plants for
photosynthesis.
Carbon cycle: exchanging carbon dioxide between the
atmosphere and ocean; a short pupil practical
comparing how well carbon dioxide dissolves in sea
water compared with fresh water.
Context
An understanding of the carbon cycle is essential to
the debate about global warming, an environmental
issue that most students will have heard about. Since
the Earth’s atmosphere formed, it seems to have
always contained carbon dioxide in varying amounts
Carbon dioxide is a ‘greenhouse gas’ through which
light radiation can pass but which absorbs some of the
heat radiation produced by light irradiating the Earth’s
surface. This causes the Earth’s surface and
atmosphere to be warmer than it would otherwise be
and without the ‘greenhouse effect’ the Earth would
probably be completely frozen. Humans, as all life on
Earth, have always been part of the carbon cycle, but
now (since the industrial revolution) the large scale
burning of oil, coal and natural gas, along with
deforestation, is leading to increasing atmospheric
carbon dioxide levels. This in turn is related to an
enhanced greenhouse effect and consequent climatic
change. An understanding of the factors affecting
global warming leads to an understanding of the
measures required to reduce their impact. This can link
into economic and political debates on the subject.
Students should have already covered photosynthesis
and respiration in order to do this activity effectively.
Teaching points
In this activity, carbon dioxide is released from some
chalk (calcium carbonate) by reacting it with vinegar (a
solution containing a weak acid). Millions of years ago
the carbon (in the carbon dioxide released) was used
by the fossil marine organisms that make up the chalk
to make their hard parts and has been stored there
ever since (until we came along and poured acid onto
them!).
Animals get their carbon by eating plants and/or other
animals. When oxygen combines with food in cells
during respiration, carbon dioxide is released into the
atmosphere during exhalation.
Some of the carbon dioxide from the atmosphere is
stored in the ocean which acts as a carbon sink. Some
of this dissolved carbon dioxide is used by marine
organisms to make their ‘hard parts’ of calcium
carbonate, for example the shells of shelly organisms
and the discs of calcareous algae that form much of
the chalk. Limestone, including natural chalk, is made
of the remains of marine organisms that lived and died
millions of years ago (Chalk is largely made of
calcareous parts of planktonic algae and so is formed
mostly of plant remains, not animal remains.) When
limestone and chalk are formed carbon is locked away
(as calcium carbonate) for millions of years.
Students should work on this activity in pairs.
Apparatus and materials
Each group of pupils will need:
Eye protection
Crushed natural chalk
Vinegar (alternatively use dilute hydrochloric acid (1
mol dm-3), which has the advantage of not smelling)
Flask
Balloon
Test-tube
Limewater (calcium hydroxide solution)
Safety
Wear eye protection
Activity
Students follow the activity sheet by pouring limewater
into a test tube; then placing crushed chalk into a flask;
adding vinegar (or hydrochloric acid) to the flask and
placing a deflated balloon tightly over the flask neck so
that no gas can escape. When the reaction has stopped
they pinch the balloon tightly at the balloon neck, so
no gas can escape, remove it from the flask and over to
the test tube. They squeeze it so that the gas goes into
the limewater, observing it as they do so.
Once they have done this, the students should record
their observations by answering the following
questions:
Q 1. What colour was the limewater to begin with? =
Colourless.
Q 2. What happened to the limewater when you
added the gas from the balloon? = It became cloudy.
Q 3. Where did the gas in the balloon come from? =
The chalk.
Q 4. What reaction was responsible for creating it? =
The reaction of calcium carbonate with acid.
Q 5. What gas was released from the chalk by the
reaction? = Carbon dioxide.
Then they should attempt the following extension
questions which require more thought, and should
enable them to place their experiment in the context
of the carbon cycle and to think about how the carbon
cycle works over very long time scales:
Q 1. Where did the dinosaurs get their carbon from?
= Eating plants and/or animals
Q 2. Why could you say that “dinosaur breath” was
released from the chalk? How did it get there? = Chalk
is made of the hard parts of millions of tiny organisms.
They used carbon, to make their hard parts (calcium
carbonate) which they obtained from the sea water in
which they lived in the form of dissolved carbon
dioxide (many of these tiny organisms were
photosynthesisers). The carbon dioxide in the ocean
got there via gas exchange with the atmosphere.
Carbon dioxide in the atmosphere, in turn, got there
from animals (including dinosaurs) exhaling. So, the
carbon dioxide is released from chalk might have been
breathed out by a dinosaur (although, of course the
carbon has been through many stages and has been
combined in a range of other molecules in between
times).
Q 3. Draw a dinosaur on the geological carbon cycle
diagram and draw arrows to show the steps from how
the dinosaurs got carbon to how carbon dioxide from
the dinosaur got into the chalk. =