3.1
Cells, Matter, and Energy
E X P E C TAT I O N S
solar energy
Figure 3.1 Although only a
small fraction of the total energy
emitted by the Sun reaches
Earth’s surface to be used by
plants and algae to produce
food, that small share is enough
to sustain life on our planet.
You have learned that all organisms are composed
of cells, whether they are plants, animals, algae,
fungi, or micro-organisms. They all need food to
provide the energy and matter they need for growth
and reproduction. As the above flowchart shows,
the organisms that photosynthesize obtain their
energy directly from the Sun. What about other
organisms? What is the source of their energy? The
herbivores (plant eaters) obtain it directly from the
plants they eat. The carnivores (meat eaters) obtain
it from the herbivores they eat, and the top
carnivores obtain energy from the herbivores and
other carnivores they eat. Notice that the boxes
MINI
herbivores
carnivores
top carnivores
thermal energy returned
to the atmosphere
containing the names of organisms (e.g. carnivores)
become smaller and smaller. This is done to
illustrate an important point — not all of the
energy the photosynthesizers obtain from the Sun
is passed on to the herbivores that eat them, and so
on. Why not? Think about it. Some of the energy
that a dog, for example, obtains from its food is
used for everyday processes — walking, running,
catching a stick, even blinking its eyes. Some is
transformed to other forms of energy, such as
sound (as it barks) and thermal energy (heat that
keeps its body warm). Thus, some energy escapes
LAB
Matter and Energy Carousel
Living things use energy to organize matter. How are energy
and matter related to the processes of life? Do this activity
to find out about this question.
Your class will divide into small groups. Each group will be
assigned one coloured marker. The black marker will be
used to show the paths of carbon atoms. The red marker
will show the paths of oxygen atoms. The blue marker will
show the paths of hydrogen atoms, and the green marker
will represent the transfer of energy.
There will be six stations set up around the room, each with
a different scene. One station will have a picture showing a
picnic scene, another will have a forest scene, yet another
80
photosynthesizers
energy transformed to heat
Explain the molecular
principles and mechanisms
that govern energytransforming activities in all
organisms.
2% of solar energy reaching
Earth’s atmosphere
decomposers
S E C T I O N
MHR • Cellular Functions
will have an underwater scene, etc. At each station your
group will use the marker assigned to you to mark coloured
arrows on the diagram or photograph, showing the path of
the type of atom, or energy, for which your group is
responsible. A sheet of lined paper is available at each
station for your group to write additional comments. You
will remain at the last station, and your group will be
responsible for reporting all the results of that station.
Analyze
1. One member of your group will report on the collective
findings of all the groups for the station.
2. Was there agreement on what happens to each kind of
atom and to energy? If not, what are some questions to
which you still need to find answers?
from the food chain at each of the feeding or
so-called trophic levels (see Figure 3.1).
What about the matter? Does matter escape from
the food chain as energy does, or is it simply
cycled over and over and over again?
no exceptions have been found to this enormously
important idea.
Consider this chain of transformations. A
baseball is thrown into a mitt on your hand. You
hear a thud as it hits your mitt. You have just
observed evidence of energy transformation. The
energy of the incoming ball was in the form of
kinetic energy (of motion). As the ball hits your
mitt, some kinetic energy was transformed into
sound energy. A sensitive thermometer would also
detect an increase in the mitt’s temperature where
the ball struck it. In this transformation, kinetic
energy was converted to thermal energy. Note that
none of the ball’s energy has been “lost,” it is
simply transformed.
Figure 3.2 What activities use the energy supplied by the
food the fox eats? That energy will no longer be available
to the eagle or bear that attacks the fox, or to the
decomposers if it dies a natural death.
Thinking About Energy
The following brief review of energy concepts will
ensure you understand the nature of energy before
you proceed with this chapter. You will probably
recall from your previous studies that energy is the
capacity to do work. You are already familiar with
some everyday forms of energy — light energy, sound
energy, electrical energy, etc. Potential energy is
stored energy. An apple hanging from a stem on a
tree has potential energy as does the water stored
behind a dam, but that energy must be released
before it can actually do any work. Kinetic energy
is the energy of motion, such as the energy of an
apple falling to the ground from the tree or water
flowing over a dam (its energy can then be
harnessed to run turbines to generate electricity, for
example). Chemical energy is the energy stored in
the bonds between atoms in molecules. Thus,
chemical energy is potential energy. Once the
chemical bonds are broken, the atoms have extra
kinetic energy. They have the ability to move, to do
work, to make things happen. By 1859, strong
evidence persuaded scientists to accept the Law of
Conservation of Energy, which states the idea that
energy can neither be created nor destroyed, but
simply converted to another form of energy. So far,
Figure 3.3 What energy transformations occur when the
ball hits your baseball mitt?
Chemical reactions also involve energy
transformations: that is, a change of energy from
one form to another. As long as a cell remains alive
it retains the ability to control the chemical
reactions occurring within it. If too little energy is
transformed during certain reactions, the cell dies.
The intricate chemical balance that cells are
capable of maintaining is difficult to imagine.
Taken together, the total of all of the chemical
reactions that occur within a cell are known as its
metabolism. Metabolism includes all of the
building up and breaking down of substances in a
cell as well as the energy changes that occur
simultaneously. A cell’s metabolism relies on
chemical energy. The next section will reveal
where that chemical energy comes from.
Cells, Energy, and Technology • MHR
81
SECTION
1.
REVIEW
K/U Look at the two photographs shown here to
check your understanding of energy. Identify areas in
the photographs where an energy transformation is
taking place. Some will be useful, ensuring that work
is done. Others will be conversions to energy forms
that cannot be (or, at least, are not being) used to do
work. Identify, as well, where potential energy may be
used to do work in the future.
2.
K/U
Why do cells need energy?
3.
K/U Identify five ways your body uses energy during
an average day.
4.
K/U Glucose is a common source of energy in cells.
Where is the energy in glucose?
5.
C Energy can not be created or destroyed. The flow
diagram in Figure 3.1 seems to show a loss of
energy.
(a) Explain this apparent loss of energy.
(b) Assume that the atmosphere of the Earth
changed so that energy from the Sun could reach
the surface of Earth but visible light could not.
How would the flow diagram change?
6.
C Make a flow diagram showing the chain of energy
transformations for each of the following situations:
(a) This book falls off a table.
(b) You walk home after eating a meal.
7.
K/U Define the term metabolism. Then, do the
following:
(a) List three metabolic processes you have studied
in previous chapters.
(b) For one of these processes, identify how energy
is used.
8.
I Amylose and cellulose are carbohydrates. We can
eat both, but can only use amylose as a source of
energy. Some animals can digest cellulose and use
the energy stored in this carbohydrate. Which
molecule has the greatest potential energy? Propose
one way to answer this question.
9.
C The flow diagram in Figure 3.1 shows the Sun as
the source of energy for life on Earth. Design a
diagram to show the path followed by oxygen among
living things on Earth.
10.
MC Constant solar energy supports the processes
of life on Earth. How, then, can we have energy
shortages?
UNIT INVESTIGATION PREP
How does energy flow through communities of
organisms? How much energy is transferred from
herbivores to carnivores, for instance? Energy is also
stored in various molecules, including the fat, protein,
and carbohydrate in milk. Which of these molecules is
your body most likely to use? What is the ultimate source
of this energy? Write your thoughts in preparation for
your Unit 1 Design Your Own Investigation.
82
MHR • Cellular Functions