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4 Body Systems in Balance

in the previous activity, you learned about some of the factors that
influence world health and disease. Scientists who study a particular
disease gather information about how that disease affects the organism.
They look at all levels of the organism, from molecules and cells to tissues
and organs, as well as the whole organism. Look at Figure 4.1 and consider
this question: In what ways could disease disrupt the normal functioning
of the respiratory system at different levels of organization?

System Organ Tissue Cell

lungs lung tissue lung cell

FIGURE 4.1: Levels of Organization in the Respiratory System

Guiding Question

How do levels of a human body system work together to
perform body functions?

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Materials

FOR EACH GROUP OF FOUR STUDENTS

set of 20 Structure and Function cards
set of 4 Homeostasis Disrupted cards
set of 4 Restoring Homeostasis cards

FOR EACH STUDENT

Student Sheet 4.1, “Body Systems and Disease”

Procedure

Part A: Examining Structure And Function

1. Spread out the 20 Structure and Function Cards on a table.
2. With your group of four, sort the cards into four different body

systems. Work together to agree which cards belong with which
system. Remember to listen to and consider other group members’
ideas. If you disagree with anyone in your group, explain why you
disagree.
3. Review the first five column headings on Student Sheet 4.1, “Body
Systems and Disease.”
4. Spread out the cards for one of the human body systems. Discuss with
your group which cards fit into which level of organization for a
particular system by evaluating both structure and function. Use the
column headings on Student Sheet 4.1 as a guide. Record your notes
on Student Sheet 4.1.
5. Repeat Step 4 until you have completed all four human body systems.
6. Share your work with the class. Discuss any differences in your
responses, and make changes to your organization levels as needed.
7. Discuss the following questions with your group:

• How might two of these systems work together to perform a single

function?

• The cards model the structure and function of levels of organization

in a human body system. How could you improve this model?

• How does each system contribute to the human body’s homeostasis?

What might happen when that homeostasis is disrupted?

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BODY SYSTEMS IN BALANCE ACTIVITY 4

Part B: Restoring Homeostasis

8. Spread out the four Homeostasis Disrupted and four Restoring
Homeostasis cards on the table.

9. With your group, pair each Homeostasis Disrupted card with a
Restoring Homeostasis card, and decide which pairs belong with which
system. Record your notes in the last two columns of Student Sheet 4.1.

10. With your group, discuss the following questions:

• What is the relationship between the structures of a body system

and their functions?

• In what ways does disease affect the functioning of a body system?
• How do different body systems interact to maintain homeostasis?
• Can you name at least two examples of how medical treatments can

be used to restore homeostasis?

Build Understanding

1. In this activity, you used cards to model the levels of organization in
human body systems, their functions, and the effects of disease on
each system.
a. What are the strengths and weaknesses of this model?
b. Explain how you would improve this model.

2. Choose a human body system that was not modeled in this activity,
such as the urinary, skeletal, nervous, muscular, or reproductive
system.
a. Explain how each level of organization of this system (system,
organ, tissue, cells) works with the other levels to perform a single
function.
b. Explain how your chosen system works in conjunction with
another body system to maintain homeostasis.

3. How do human body systems interact to maintain homeostasis of fluid
levels in the body? In your response, draw on what you’ve learned in
the last few activities.

4. True or false: Human health depends on the different levels of
organization within the body being able to perform specific functions.
Support your answer with evidence from this activity.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

5. As you can see in Figure 4.2, the ratio of infectious to noninfectious
diseases has changed since 1990. Why do you think that noninfectious
diseases were rising faster than infectious diseases up to 2017?

100% Injuries

80%
Infectious, maternal,
neonatal, and

60% nutritional diseases

40%
Noninfectious
diseases

20%

0% 1995 2000 2005 2010 2017
1990

FIGURE 4.2: Total Global Disease Burden By Cause, 1990–2017

KEY SCIENTIFIC TERMS

cell
homeostasis
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system
tissue

U.S. WEATHER FATALITIES 30 YEAR AVERAGE FOR 1991 2000

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5 Evidence of Disease

how do doctors diagnose what’s wrong when someone is sick?

One strategy is to gather evidence from the human body. Some scientists,
like cell biologists, use microscopes to study the structure and function of
cells in organisms, from humans to plants, insects, and microbes. A
microbe is a microscopic cellular organism or a virus, and some microbes
cause infectious diseases. One way to detect and study many diseases is to
compare blood from healthy and sick individuals under a microscope. In
this activity, you will examine samples of blood from healthy and diseased
people. Imagine the following scenario:

You are a doctor who has recently seen two patients who reported similar symptoms.
From your examination of each patient, you have gathered the following information.

HISTORY FROM PATIENT A

– Patient reports periods of feeling sick but feels well most of the time.
– Patient recently returned from working in Nigeria with the Peace Corps.
– Patient reports frequent fevers.

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and legs.

Symptoms Noted During Today’s Examination

– Patient has vision problems.

– There is visible yellowing of the eyes and skin.
– Abdominal area is tender to the touch.

HISTORY FROM PATIENT B B-39
– Patient reports becoming sick shortly after returning from a trip to Africa in the past month.
– Patient reports severe headaches and fatigue for the past few weeks.
– Patient reports a fever and muscle and joint pain in the past week.

Symptoms Noted During Today’s Examination
– There is visible yellowing of the eyes.

– Abdominal area is tender to the touch.

CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How do diseases affect organisms at the cellular level?

Materials

FOR EACH GROUP OF FOUR STUDENTS

prepared slide, “Patient A Blood”
prepared slide, “Patient B Blood”

FOR EACH PAIR OF STUDENTS

prepared slide, “Typical Human Blood”
microscope

SAFETY

Always carry a microscope properly with both hands: one
hand underneath, and one holding the microscope arm.

Procedure

1. Prepare a chart in your science notebook like the one shown here.

Observations of Blood Samples Color of cells Number of cells
Slide Shape of cells in field of view

2. With your partner, obtain a slide labeled “Typical Human Blood.” This
blood sample will serve as your reference. Observe the slide on
medium or high magnification, and record your observations in the
chart. Add a sketch of a typical red blood cell to your notes.

3. Consider which of four possible diseases the patient’s symptoms
suggest, based on the patient’s history and today’s examination.
a. Read the descriptions of possible diseases in Table 5.1.
b. For each disease in Table 5.1, draw a sketch of what you predict you
would observe in a blood sample under the microscope as
compared to the typical human blood you just observed.

B-40

EVIDENCE OF DISEASE ACTIVITY 5

TABLE 5.1: Possible Diseases

POSSIBLE DISEASES weakness, disturbed vision, headache, An abnormality in the bone marrow
Polycythemia vera dizziness, enlarged liver, abdominal causes an overproduction of red blood
pain due to an enlarged spleen cells, almost double in some cases. This
Sickle cell disease joint and muscle pain, anemia, vision increases blood volume and thickness,
problems, abdominal pain, yellowish leading to life-threatening blood clots.
color of skin and eyes, and frequent An inherited genetic mutation (error)
infections changes the hemoglobin protein,
Spherocytosis causing the proteins to stack on one
yellowish color of skin and eyes, another within the red blood cells.
Malaria abdominal pain from an enlarged This produces a sickle- or banana-
spleen, pale skin, and weakness shaped blood cell. Sometimes under
fever, headaches, extreme fatigue, the microscope the sickle cells appear
mild yellowish color of skin and eyes, flattened.
abdominal pain, and A genetic disorder causes the
body aches red blood cells to become small,
spherically shaped and fragile. These
cells are destroyed by the spleen. It is
often diagnosed in childhood.
An infectious disease, malaria is caused
by a single-celled parasite of the
genus Plasmodium and is ­carried by
mosquitoes. A Plasmodium appears
as an irregular purple spot containing
dark dots when a sample is stained and
viewed under a microscope.

4. Obtain the slides of “Patient A
Blood” and “Patient B Blood.”
Decide with your group which
pair will first observe Patient
A’s blood and which will first
observe Patient B’s. Observe
and draw what you see on the
slide sample at medium or
high magnification. Compare
your drawing to your
prediction from Step 3b.

5. Switch slides with the other FIGURE 5.1
pair in your group, and repeat
Step 4 for the other patient.

6. In your science notebook, write your hypotheses for which disease is
affecting each patient. Include the information from the slide samples
you observed and Table 5.1 to support your hypotheses.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Build Understanding

1. What abnormalities did you observe in each patient’s blood?
2. Based on your observations, which patient has an infectious disease?

Support your answer with at least two pieces of evidence, and explain
how disease disrupted the human body’s functioning at more than one
level of organization.
3. Observe Figure 5.2. Which patient would you diagnose with sickle cell
disease? Explain, using evidence from this activity.

Patient 1 Patient 2
FIGURE 5.2: Patient Blood

4. How does knowing how levels of organization in the human body 3377 SEPUP SGI 3e Cell SB
system interact help doctors and scientists diagnose and study Figure: 3377CellSB 05_02
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changes can affect the prevalence of infectious disease. Select one
example of an environmental change from the table, and discuss the
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the three pillars of sustainability (social, economic, and
environmental).

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EVIDENCE OF DISEASE ACTIVITY 5

TABLE 5.2: Effects of Environmental Change on Human Infectious Diseases

ENVIRONMENTAL EXAMPLE DISEASES PATHWAY OF EFFECT
CHANGES Schistosomiasis
Dams, canals, Malaria ▲ Snail host habitat, human contact
irrigation Helminthiasies ▲ Breeding sites for mosquitoes
River blindness ▲ Larval contact due to moist soil
Agricultural Malaria ▼ Blackfly breeding, ▼ disease
intensification Venezuelan haemorraghic Crop insecticides and ▲ vector resistance
Urbanization, urban fever ▲ Rodent abundance, contact
crowding Cholera
Dengue ▼ Sanitation, hygiene; ▲ water contamination
Deforestation and Water-collecting trash, ▲ Aedes aegypti mosquito
new habitation Cutaneous leishmaniasis breeding sites
Malaria ▲ Proximity, sandfly vectors
Reforestation ▲ Breeding sites and vectors, immigration of
Ocean warming Oropouche susceptible people
Elevated Visceral leishmaniasis ▲ Contact, breeding of vectors
precipitation Lyme disease ▲ Contact with sandfly vectors
Red tide ▲ Tick hosts, outdoor exposure
Rift valley fever ▲ Toxic algal blooms
Hantavirus pulmonary ▲ Pools for mosquito breeding
syndrome ▲ Rodent food, habitat, abundance

▲ increase ▼ decrease

KEY SCIENTIFIC TERMS

cell
disease
infectious
levels of organization
microbe
sustainability
system
tissue

B-43



6 Specialized Cells and Disease

in the previous activity, you examined red blood cells, which are

specialized for carrying oxygen to the cells and carrying carbon dioxide
away from the cells in the body. Many types of cells have specialized
structures that allow them to perform specific functions in order to maintain
homeostasis. Often, their functions are carried out by proteins that are made
in the specialized cells. Understanding normal cell structures and their
functions helps scientists understand what happens when disease occurs.
Figure 6.1 shows different types of specialized cells. Some are healthy cells,
and some are diseased. What do you notice about these cells? Is it possible
to tell which are diseased and which are healthy? In this activity, you will
take a closer look at some specialized cells and how they carry out their
normal functions, and you will investigate how diseases can disrupt the
normal functions of specialized cells.

FIGURE 6.1: These images of specialized cells (a. red blood cell; b. white blood cell)
were captured by scanning electron microscopy.

a b

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How does disease disrupt the normal functions of
specialized cells, tissues, and organs?

Materials

FOR EACH PAIR OF STUDENTS

computer with Internet access

FOR EACH STUDENT

Student Sheet 6.1, “Specialized Cells”
Student Sheet 6.2, “Cellular Disease Diagrams”

Procedure

Part A: Structure and Function of Normal Cells

1. In your science notebook, use a full page to draw a diagram of what
you think a typical cell looks like, including its internal structures. On
your diagram, write labels for as many parts of the cell as you can. If
you know the function of the part, write a brief description of it next to
the label.

2. Compare your cell diagram to your partner’s diagram and work
together to create a common cell diagram that you can use for
reference.

3. With your partner, use Student Sheet 6.1, “Specialized Cells,” to guide
you through a computer simulation of the structures and functions of
specialized human cells. Investigate the following questions:

• What is the specialized cell shown in each animation?
• What is the function of each specialized cell shown?
Part B: The Effect of Disease on Cells

4. Read the information about the effects of diseases on human cells in
Table 6.1.

B-46

SPECIALIZED CELLS AND DISEASE ACTIVITY 6

TABLE 6.1: Effect of Disease on Cells

DISEASE SYMPTOMS DESCRIPTION
Diabetes Increased thirst, frequent
(type 2) urination, hunger, • A noninfectious chronic condition that affects the way the
fatigue, and blurred
Sickle cell vision. Other symptoms body processes blood sugar (glucose).
disease include skin infections,
slow-healing cuts and • P ancreatic cells produce the protein insulin, which sends
Cholera sores, and damage to
nerves and other organs. signals to other cells to take in and store glucose.
Joint and muscle pain,
anemia, vision problems, • W ith type 2 diabetes, the body either doesn’t produce enough
abdominal pain,
yellowish color of skin insulin or it doesn’t respond to the insulin, limiting the body’s
and eyes, and frequent ability to process and use sugars for energy. The sugars
infections. instead stay in the bloodstream, where they can make the
blood thicker and can restrict blood flow.
Watery diarrhea and
dehydration. Shock, • A noninfectious inherited condition caused by a mutation
seizures, or death may
occur in severe cases. in the gene for the hemoglobin protein, which is specifically
made in red blood cells.

• T he mutation causes the hemoglobin proteins to stick to one

another within the red blood cells.

• T his causes the red blood cells to change shape from a round

cell to a sickle-shaped cell.

• S ickle-shaped cells can have trouble moving through blood

vessels and can get stuck in small blood vessels.

• S ickle-shaped red blood cells also die early, causing a shortage

of blood cells.

• A n infectious disease caused by eating food or water

contaminated with the bacteria Vibrio cholerae.

• C ells that line the inside of the small intestine (lumen)

normally absorb most of the fluid that is ingested, and only a
small amount of fluid is excreted in the feces.

• T he bacteria secrete a protein toxin (poison) that binds to the

cells of the small intestinal lumen and causes the cells to expel
large amounts of water.

5. Work with your group to identify which specialized cell from the
simulation is affected by each disease.

6. Using Student Sheet 6.2, “Cellular Disease Diagrams,” work with your
group to develop a model for how each disease might impact the
normal functioning of the specialized cell. Build on the model
provided in each diagram by adding additional drawings and labels,
and include a caption that explains your model.

Remember to listen to and consider other group members’ ideas. If
you disagree with anyone in your group, explain why you disagree.

7. Follow your teacher’s instructions for sharing your models with
the class.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

8. With your group, discuss the following questions:

• What is the relationship between the structures of a specialized cell

and its function?

• In what ways can disease affect the functioning of a specialized cell?
• Think about the role of proteins in the functioning of specialized

cells. Identify a protein that is essential to the functioning of one
specialized cell. What do you think would happen if the protein was
unable to function?
9. Based on the presentations and your group’s discussion, revisit your
models on Student Sheet 6.2 and make any needed changes.

Extension 1

How does the disease COVID-19 disrupt the normal functioning of lung
cells? View the fourth animation in the “What Do Specialized Cells Do?”
simulation on the SEPUP SGI Third Edition page of the SEPUP website at
www.sepuplhs.org/high/sgi-third-edition. Use Student Sheet 6.3,
“Extension 1,” to guide you through the animation.
Use the information in Table 6.2 to develop a model of how COVID-19
might impact the normal functioning of the lung alveolar cells. Build on
the model provided in Diagram 4 on Student Sheet 6.3 by adding
additional drawings and labels. Include a caption that explains your model.

TABLE 6.2: Effect of COVID-19 on Cells

DISEASE SYMPTOMS DESCRIPTION
COVID-19 Infection may occur
1–14 days before • A n infectious disease caused by a
developing symptoms
such as fever, tiredness, virus called the severe acute respiratory
and dry cough. May syndrome coronavirus 2 (SARS-CoV-2),
be severe and even which enters the body primarily
fatal in some cases, through air-borne droplets.
in particular with the
elderly and/or those • T he virus multiplies in infected cells,
with other medical
conditions (such as damaging the cells and causing
asthma, diabetes, or inflammation.
heart disease).
• T he virus accesses host cells via the

enzyme ACE2, a type of protein that
helps control blood volume and blood
pressure. In the lungs, ACE2 is most
abundant in type II alveolar cells.

• T he virus uses a special surface

glycoprotein, called a “spike,” to connect
to ACE2 and enter the host cell.

B-48

SPECIALIZED CELLS AND DISEASE ACTIVITY 6

Build Understanding

1. Compare the different diseases presented in this activity and how they
disrupt normal functioning in specialized cells.
a. Are there any similarities in how the diseases disrupt the function
of each specialized cell?
b. What are the differences you noticed about the way that each
disease affects cell function?
c. For sickle cell disease, explain why the disease affects only red
blood cells and not other cells. Include in your explanation how the
disease affects the genetic code and how that disrupts the specific
function of red blood cells.

2. Explain how a change in the function of a cell can result in disease at
the human body level and disrupt homeostasis. Support your
explanation with evidence from this and other activities.

3. Explain how the disruptions caused by the diseases you investigated in
this activity might impact multiple body systems. Use your models on
Student Sheet 6.2 to help develop your explanation. Think about the
body system that these cells function in and how that body system
might interact with other systems.

4. Issue connection: What is a global change in climate that could affect
the prevalence of cholera? Think about how changes in climate might
increase the likelihood of getting an infectious disease.

FIGURE 6.2

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

KEY SCIENTIFIC TERMS

cell
disease
infectious
levels of organization
noninfectious
organelle
tissue

Extension 2

What are proteins, and what do they do in the human body?
Visit the SEPUP SGI Third Edition page of the SEPUP website at
www.sepuplhs.org/high/sgi-third-edition for links to a journal article
that provides more information about proteins and their functions.

B-50

7 Homeostasis and Medical Treatment

your immune system recognizes and fights disease-causing
microbes. Most people are able to fight off infectious diseases like colds
quickly and return to full health within a week or so. Other diseases,
like COVID-19, are often more severe. Such diseases are much more
likely to have serious effects, or even lead to death, in a larger portion
of the population.
Look at Figure 7.1, which shows death rates from several infectious
diseases for the years 2000–2015. What conclusions do you draw from this
data? What role do you think modern medicine has played? What do you
think this graph might look like today?

160 Low-income
economies
Lower-middle-
140 income economies

120 Upper-middle-
income economies
Crude death rate High-income
100 economies

80 Global

60

40

20

0 2015 Respiratory diseases (including
2000 in uenza and pneumonia)
Diarrheal diseases
FIGURE 7.1: Global Mortality Rates from Infectious Disease by Parasitic and vector diseases
Economy Type, 2000–2015 (including measles)

LabAids SEPUP SGI Cells 3e
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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

In what ways does modern medicine help maintain human
health?

Materials

FOR EACH STUDENT

Student Sheet 7.1, “Three-Level Reading Guide: Homeostasis and Medical
Treatment”

Procedure

1. Refer to Student Sheet 7.1, “Three-Level Reading Guide: Homeostasis and
Medical Treatment,” to guide you as you complete the following reading.

Reading

Infectious Disease Outbreaks: Coronaviruses

Although noninfectious diseases are the leading cause of death in most
developed nations, infectious diseases are a major public health concern in
the United States and around the world. The number of infectious disease
outbreaks has increased significantly since 1980. Some of these outbreaks
were from diseases that existed in animal populations. For example,
coronaviruses are a large family of viruses that usually cause mild to
moderate illness. There are hundreds of coronaviruses, and most are found
among animal populations, including pigs, camels, bats, and cats.
Sometimes these animal viruses can transfer to humans and cause disease.
Since 2000, there have been three major coronavirus disease outbreaks in
humans: SARS (severe acute respiratory syndrome), which emerged in late
2002 and disappeared by 2004; MERS (Middle East respiratory syndrome),
which emerged in 2012 and is still found among human and camel
populations; and COVID-19, which emerged in December 2019 and is
caused by the virus known as SARS-CoV-2.

Interacting Body Systems Control Breathing

Coronaviruses affect the respiratory system (and may also affect other
systems). The human respiratory system—which consists of the nose,
mouth, airways, and lungs—brings in oxygen and releases carbon dioxide
from the body. The respiratory system must interact with other systems to
function normally. Parts of the skeletal system, such as the nasal septum

B-52

HOMEOSTASIS AND MEDICAL TREATMENT ACTIVITY 7

and the ribs, provide structure and protection to the soft structures of the
respiratory system. Contraction and relaxation of muscles such as the
diaphragm cause air to be drawn in and released from the lungs, while the
nervous system sends signals that control the rate of breathing. Blood in
the arteries carries oxygen away from the lungs for delivery to other parts
of the body, while blood in the veins brings carbon dioxide back to the
lungs to be released into the air.
Homeostasis is maintained in the respiratory system through a negative
feedback loop that maintains oxygen and carbon dioxide levels in the body
within a healthy range. Look at Figure 7.2, which shows a negative feedback
loop for breathing. When a disease (or other condition) causes carbon dioxide

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Normal carbon High blood
dioxide and carbon dioxide
blood pH
levels

Disease raises Drop in
blood carbon blood pH
dioxide levels

Blood carbon
dioxide levels
fall, pH of the
blood returns

to normal

Low pH detected
by chemoreceptors

Increased rate of
removal of carbon dioxide

from the body

Brain
stimulates
increased rate
and depth of
breathing

FIGURE 7.2: Breathing: A Negative Feedback Loop
You have learned that a negative feedback loop is one in which the body recognizes a change and
brings conditions back to normal. Follow the arrows in the diagram to see how the body responds to a
disease that raises carbon dioxide levels.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

The Effects of Disease on Interacting Body Systems

With a mild case of COVID-19, the body is able to
maintain homeostasis despite the infection.
COVID-19 enters your body when you breathe it in
(for example, after an infected person coughs or
sneezes nearby), or when you touch a contaminated
surface and then touch your eyes, nose, or mouth. The
virus infects the cells that line your throat, airways,
and lungs. Like other diseases caused by viruses,
coronavirus diseases work by replicating inside your
cells, creating more copies of the virus that go on to
infect more of your cells.

COVID-19 is a mild infection for many people, and FIGURE 7.3: SARS-CoV-2 virus
some may not experience any symptoms. For those
who do, symptoms may include fever, dry cough,
shortness of breath, headache, muscle pain, and fatigue. A fever is one
way that your body works to restore homeostasis in response to a disease.
Most viruses (and bacteria) do well when your body is at your normal
temperature. But if you have a fever, it is harder for microbes to survive.

Your body is using the fever as one method to try to kill the virus that is
causing the infection. Your immune system recognizes the virus as foreign
and signals to the rest of the body that something is wrong by releasing
chemicals. The brain responds by raising the body temperature: Blood moves
to the body’s core, heating the body overall but cooling the surface (which
can result in chills). At the same time, your immune system produces
antibodies that bind to the virus, identifying it so that white blood cells can
engulf and destroy it. In some mild cases of the disease, your body is able to
be successful at fighting off the disease and restoring homeostasis.

Restoring Homeostasis Through Medical Intervention

Some mild cases of COVID-19 may simply require bed rest, increased fluid
intake, and a fever or pain reducer such as acetaminophen. In severe cases,
the virus can result in more severe conditions such as pneumonia, an
inflammation of the lungs; sepsis, where the body’s reaction to the infection
causes damage to multiple organs; and heart muscle inflammation and
injury. In addition, SARS-CoV-2 has been found in other organs, such as
the kidneys, where it can cause other internal damage, and it has also been
associated with blood clotting disorders.

Inflammation is one of the immune system’s normal responses to infections.
Immune system cells travel to the site of the infection and widen local blood
vessels so that there is an outflow of fluid and immune cells into
surrounding tissues. Signals from the local cells (immune and non-immune)

B-54

HOMEOSTASIS AND MEDICAL TREATMENT ACTIVITY 7

also cause blood vessels to dilate. This can be amplified by further
inflammatory signaling by recruited immune cells. White blood cells leave
the bloodstream and move into the tissue to clean up the inflammation, as
too much of it can cause damage. But instead of cleaning up and moving on,
white blood cells stay in the tissue, and more white blood cells come in
behind them. This accumulation can cause damage to internal organs, like
the lungs, and can lead to death. Extensive inflammation in the lungs keeps
the body from getting enough of the oxygen it needs to survive. It can cause
blood pressure to drop to dangerously low levels and organs to stop working
properly or fail completely. Researchers are working to determine whether
heart muscle inflammation is also caused by this response or by the virus
entering heart tissue. In some cases, the use of anti-inflammatory drugs that
suppress this immune response have helped COVID-19 patients.
Shortness of breath, another symptom, is a result of low levels of oxygen in
the blood. Some people may need a ventilator to help them breathe; the
ventilator blows air into airways through a breathing tube and helps get
oxygen-rich air into the lungs. Other patients may require an artificial lung
that takes blood out of the body through thick tubes, oxygenates it, and
pumps it back in. If the virus damages the tiny air sacs in the lungs, it can
disrupt the ability of oxygen to diffuse into the bloodstream, depriving other
major organs of oxygen, including the liver, kidney, and brain. This damage
can reach fatal levels, at which organs can no longer keep the body alive.

FIGURE 7.4

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Maintaining Homeostasis Through Prevention FIGURE 7.5: Human
Blood Cells
Using face masks, maintaining physical distance, and avoiding large
gatherings, especially indoors, have been some of the methods used to help
prevent the spread of COVID-19. One challenge in preventing its spread is
that some infected individuals do not have symptoms and do not realize
they are spreading the disease. Modern medicine has slowed or stopped
the spread of many infectious diseases through the use of vaccines. A
vaccine is a substance used to stimulate the production of antibodies in the
immune system, which helps prepare your body to fight off the disease-
causing agent in advance of getting sick.

Immunization is one of the most successful
and cost-effective health interventions,
preventing millions of deaths every year.
Vaccines are available against diseases caused
by both viruses and bacteria. Immunization
protects against diseases such as diphtheria,
measles, pertussis (whooping cough),
pneumonia, polio, rotavirus, rubella, and
tetanus. There are also vaccines being
developed to work against other microbes.

When a person is infected by a virus or
bacteria, these microbes attack the body’s
systems and multiply in number. This
infection is what causes illness. The immune
system uses several tools to fight infection.
Blood contains red blood cells, for carrying
oxygen to tissues and organs, and white
blood cells or immune cells, for fighting
infection. The first time the body encounters
a particular microbe, the body produces
responses that will help it get over the infection. Afterward, the immune
system learns to recognize that specific microbe, and responds faster and
more aggressively the next time it encounters that microbe.

Vaccines help develop immunity by signaling the immune system to
recognize and prepare to fight a specific disease without the person actually
getting sick. Mild side effects, such as a low fever or body aches, are
symptoms of the immune system being activated but do not mean that the
person is sick with the disease.

Because each vaccine is specific to a particular microbe, vaccines do not
exist for emerging diseases. In addition, some vaccines do not provide
long-term immunity or can require more than one dose to be effective.

B-56

HOMEOSTASIS AND MEDICAL TREATMENT ACTIVITY 7

Normally, it takes two to five years to produce a new vaccine. With the
COVID-19 outbreak, scientists across the globe worked together, shared
information and research, and built on existing knowledge from years of
research. Many governments and organizations provided funding and
other support. As a result, scientists were able to develop several
COVID-19 vaccines quickly and to safely release them for global use in
December 2020, approximately one year after the first known case.

Build Understanding

1. Return to the graph at the beginning of this activity.
a. Which infectious diseases appear to be increasing over time?
b. What could explain this trend? Support your answer with evidence.

2. How does the immune system help maintain homeostasis in the
human body?

3. Select a human body system, such as the respiratory or nervous
system. Construct an explanation that includes the following:

• At least four different levels of organization of the system, the

relationship between them, and their size progression

• How these different levels contribute to the functioning of the

system

• How this system interacts with another body system to perform one

or more essential functions in the human body
4. Issue connection: What does the rapid spread of COVID-19 tell you

about the challenges to sustaining global health? In your response,
address how COVID-19 had impacts on the three pillars of
sustainability (social, economic, and environmental).
5. In early 2020, when COVID-19 was first identified and the disease was
rapidly spreading around the world, many cities and countries
instituted a lockdown. Residents were asked to stay home and to leave
only for the most essential reasons. Travel was restricted, and only
workers identified as essential were expected to go to their workplace.
Do you think lockdown should be used as a method of reducing the
spread of infectious disease? Support your answer with evidence from
this activity, and identify the trade-offs of your decision.

B-57

KEY SCIENTIFIC TERMS

cell
disease
homeostasis
infectious
levels of organization
model
negative feedback loop
noninfectious
sustainability
system
vaccine

Extension

What are the latest findings on COVID-19? Visit the SEPUP SGI Third
Edition page of the SEPUP website at www.sepuplhs.org/high/
sgi-third-edition to get started on your research by reading a journal
article on COVID-19. Think about what questions you still have about
COVID-19, and do additional research to see what you can learn. You
can use Student Sheet 7.3, “Evaluating Websites,” to guide you in
examining the resources you find.

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8 Feedback Loops in Humans

in the last activity, you learned more about the increasing

prevalence of infectious respiratory diseases worldwide. Figure 8.1 shows
the global death rate by age from upper respiratory infections. What do
you think could explain this data? In this activity, you will plan and
conduct an investigation to gather data on how your respiratory and
circulatory systems interact to maintain homeostasis.

70+ year-olds
Under age 5

50–69 years old
5–15 years old

15–49 years old
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

FIGURE 8.1: Death Rate from Upper Respiratory Infections By Age, 2017

LabAids SEPUP SGI Evolution 3e
Figure: Evo3e SB 08_12
MyriadPro Reg 9.5/11

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How do body systems interact to restore homeostasis?

Materials

FOR THE CLASS

access to a wall clock or watch that displays seconds

FOR EACH PAIR OF STUDENTS

calculator

SAFETY

Do not participate in this activity if you have any condition
that prevents you from exercising. If you begin to feel dizzy
or short of breath during exercise, stop exercising immediately and
tell your teacher.

Procedure

Part A: Quantitative Data on Body Systems

1. In your group, discuss the following questions:

• How can you collect quantitative data about your cardiovascular

system?

• How can you collect quantitative data about your respiratory

system?
2. Work with your group to agree on an approach for collecting data.

Then measure your own data for each system for one minute. Record
your results in your science notebook.

Part B: Interacting Body Systems and Homeostasis

3. Design an investigation of your own cardiovascular and respiratory
systems that provides evidence that these two systems work together
to maintain homeostasis.

Hint: Think about what you do that causes change in one of these
systems, as well as how these two systems interact.

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FEEDBACK LOOPS IN HUMANS ACTIVITY 8

4. As you design your investigation, think about the following questions:

• What is the purpose of your investigation?
• How will you collect quantitative data?
• How will these data help you make a conclusion?
• How will you record these data?
• What is your hypothesis?
• What is your procedure?

5. Record your hypothesis and your planned procedure in your science
notebook.

6. Make a table that has space for all the data you need to record. You will
fill it in during your investigation.

7. Follow your teacher’s instructions for sharing your investigation design
with your group, getting feedback, and revising your design as needed.

8. Obtain your teacher’s approval of your final investigation design.
9. Conduct your investigation, and record your results.
10. Analyze your data, and record your conclusions. Be sure to explain

how your investigation provided evidence that feedback loops
maintain homeostasis within the body.

Build Understanding

1. What evidence do you have that your circulatory and respiratory
systems work together to maintain stable conditions in your body?
Explain what was happening inside your body, supporting your
answer with evidence from your investigation.

2. What other body systems are affected by exercise? Explain your
reasoning.

3. What do you think would happen if systems such as the cardiovascular
and respiratory systems did not work together to maintain
homeostasis?

4. Issue connection: Based on what you learned in this activity, why do
you think both the very young and the very old have the highest rates
of death from respiratory disease? What do you think this means for
global health and sustainability?

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

KEY SCIENTIFIC TERMS

homeostasis
feedback loop
model
organ
qualitative
quantitative
sustainability
system

Extension: Engineering Connections

Today, many people use technology, such as phones or other devices, to
measure how many steps they take in a day. In what other ways might
technology support human health? Brainstorm some ways that technology
could be used to prevent, monitor, or treat a noninfectious or infectious
condition. Describe one of your ideas, making sure to explain what data you
would collect and how your idea could be used to improve people’s health.

FIGURE 8.2

B-62

9 Global Nutrition

extreme heat events and disease are just two factors that can
affect human health. One of the most basic human needs is food.
Malnutrition—a lack of proper nutrition—is a global concern. In some
parts of the world, malnutrition means undernutrition: individuals not
getting the amount or quality of food needed for good health.
Undernutrition can lead to child stunting (low height for their for age) or
wasting (low weight for their height). Although the global percentage of
undernourished children has generally declined over the past few decades,
nearly half of all deaths in children under 5 are a consequence of
undernutrition. Malnutrition also refers to overnutrition, in which
individuals get an oversupply of the food they need. This can lead to health
problems such as obesity. Over 10 times more children and adolescents
were obese in 2016 (124 million) than in 1975 (11 million).
Note: If you need to review basic concepts about food, matter, and energy,
you will find a short reading at the end of this activity.

Investigative Phenomenon

Examine Figure 9.1. Population in developing countries (millions) 8,000 < 2,000 kcal/person/day 2,000–3,000 kcal/person/day 7,671
What do you observe? 7,000 2,000–2,500 kcal/person/day > 3,000 kcal/person/day 3,362
What do you think this 6,000
means for global health 5,000 6,839 4,069
in the present and in the 4,000 240
future? How sustainable 3,000 5,218 5,879 2,631 2050
is this trend, and how 2,000 711 2,261
might it be affected by 4,099
changes in the food 281 2,233
1,559
1,166

3,489

supply? You will 1,000 1,850 2,047 2,349 683
investigate these 0 480 104 2030
questions in this 1990/1992 227 2015
learning sequence. You’ll 2005/2007

begin by more closely FIGURE 9.1: Per Person Food Consumption in Developing Countries
examining the The energy provided by food is measured in Calories. A kilocalorie (kcal), or
relationship between Calorie, is the amount of heat required to raise the temperature of one
food and health. kilogram of water 1° Celsius.

CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How does food availability and quality affect human health?

Materials

FOR EACH PAIR OF STUDENTS

computer with Internet access

FOR EACH STUDENT

Student Sheet 9.1, “Global Food Patterns”

Procedure

Part A: Daily Calorie, Protein, and Fat Supply

1. Macronutrients are substances in food that people require in relatively
large amounts. Macronutrients include carbohydrates, proteins, and fats.
These three substances are made of carbon-based molecules, and they
can all be used for energy or to build the molecules needed for the body
to grow and function. Review the information in Table 9.1 about the
Calories, protein, and fat in the average food supply in 12 countries.

TABLE 9.1: Average Calories, Protein, and Fat Supply Per Person

Argentina AVERAGE AVERAGE AVERAGE FAT SUPPLY
Cambodia FOOD SUPPLY PROTEIN SUPPLY ( G R A M S / C A P I TA / D AY )
China ( C A LO R I E S / C A P I TA / D AY ) ( G R A M S / C A P I TA / D AY )
Ethiopia 116
Haiti 3,229 103 36
Honduras 2,477  67 96
India 3,108 98 26
Russia 2,131 60 49
United Kingdom 2,091 48 73
United States 2,641 65 52
Yemen 2,459 60 106
Zambia 3,361 103 138
3,424 103 162
3,682 110 48
2,223 59 42
1,930 55

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GLOBAL NUTRITION ACTIVITY 9

Russia

United
Kingdom

United States China Cambodia
Haiti
India
Honduras Yemen

Ethiopia
Zambia

Argentina

FIGURE 9.2: World Map

2. Use the data in Table 9.1 to identify the five countries that have the
highest availability of (a) total Calories, (b) protein, and (c) fat. Record
your response on Student Sheet 9.1, “Global Food Patterns.” You may

LabAids SEPUPfiSnGdI Cietlhlse3lepful to list the countries in order (from highest to lowest) and
MFigyuriraed:PCreollRs3eegtS9oB.5rF/e1igc1uorred09th_0e3specific number of Calories (e.g., Argentina: 3,229).

3. Use the data in Table 9.1 to identify and record the five countries that
have the least availability of (a) total Calories, (b) protein, and (c) fat.
Record your response on Student Sheet 9.1, “Global Food Patterns.”
You may find it helpful to list the countries in order (lowest to highest)
and to record the specific number of Calories.

4. Consider that the average recommended daily intake per person of
Calories, protein, and fat is 2,100 Calories, 50 grams of protein, and 63
grams of fat (daily maximum). Record your predictions to thec7m0y0k9
c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

Maps1 Maps2 folloMapws3 ingMapqs4 uesMtaipso5 ns on Student Sheet 9.1, and then share your
reasoning with your partner.
c0 m30 y70 k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

a. Based on the above information, in which five countries do you
think residents are most at risk of overnutrition (obesity)?
c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90

b. In which five countries are residents most at risk of undernutrition
(stunting or wasting)?

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

5. Compare your predictions with the most current data on obesity and
undernourishment around the world:

• Go to the SEPUP SGI Third Edition page of the SEPUP website at

www.sepuplhs.org/high/sgi-third-edition.

• Follow the link for country-specific data on obesity (which is

generally due to overnutrition). Scroll down the page to find the
map on the share of adults who are obese. Move your cursor over
the different countries to see country-specific data.

• Follow the link for country-specific data on undernourishment.

Scroll down the page to find the map for the share of the population
that is undernourished. Move your cursor over the different
countries to see country-specific data.
6. Discuss the following questions with your partner.

• Were your predictions correct? What did you predict correctly or

incorrectly, and why?

• What other factors could have affected the accuracy of your

predictions?

Part B: Micronutrient Intake

In addition to macronutrients, your body needs nearly 30 vitamins and
minerals that it cannot manufacture in sufficient amounts on its own.
These substances needed in small amounts are called micronutrients
(micro means small).
7. Read about three common micronutrient deficiencies in Table 9.2.
8. Based on what you now know about

Calorie, protein, and fat intake,
which three countries do you think
have the highest frequency of (a)
iron deficiency (anemia) in children,
(b) vitamin A deficiency in children,
and (c) zinc deficiency? Record your
predictions on Student Sheet 9.1,
and share your reasoning with your
partner.

FIGURE 9.3
B-66

GLOBAL NUTRITION ACTIVITY 9

TABLE 9.2: Common Micronutrient Deficiencies

MICRONUTRIENT DESCRIPTION OF MICRONUTRIENT EFFECTS OF MICRONUTRIENT
Iron (anemia) AND SYMPTOMS OF DEFICIENCY DEFICIENCY
Iron is found in meat, fish, lentils, May lead to a rapid or irregular heartbeat.
Vitamin A beans, spinach, and broccoli. Without Heart must pump more blood to make up
iron, blood cannot produce enough for the lack of oxygen in the blood. Can
Zinc hemoglobin, a substance in red blood lead to an enlarged heart or heart failure.
cells that enables them to carry oxygen In infants and children, severe anemia can
to the body’s tissues. Symptoms of iron lead to delayed growth and development
deficiency include extreme fatigue, and to increased susceptibility to
shortness of breath, lightheadedness, infections.
and poor appetite.
Vitamin A is found in leafy green Leading cause of preventable blindness in
vegetables, carrots, sweet potatoes, children worldwide. Can also lead to “night
pumpkin, eggs, and cantaloupe. It is blindness,” the inability to see well at night
important in vision, growth, cell division, or in poor light.
reproduction, and immunity. Symptoms (Note: Too much vitamin A can also be
of vitamin A deficiency include dry harmful.)
eyes, dry skin, delayed growth, chest
infections, and poor wound healing. Results in slow growth in infants and
Zinc is found in meat, shellfish, lentils, children, delayed sexual development in
beans, nuts, and dairy products. It is used adolescents, and age-related vision loss.
for fighting off infections and producing In developing countries, children often die
cells. Symptoms of zinc deficiency from severe diarrhea.
include unexplained hair loss, poor
wound healing, diarrhea, and reduced
sense of taste and smell.

9. Compare your predictions with the most current data on
micronutrient deficiencies around the world:

• Return to the SEPUP SGI Third Edition page of the SEPUP website

at www.sepuplhs.org/high/sgi-third-edition.

• Scroll down the page to the data for each micronutrient. For

childhood anemia, you will see a Table button at the bottom of the
chart; click on it to scroll through country-specific data.

• For childhood vitamin A deficiency and zinc deficiency, move your

cursor over the different countries to see country-specific data.

10. Discuss the following questions with your partner.

• Were your predictions correct? What did you predict correctly or

incorrectly, and why?

• What other factors could have affected the accuracy of your

predictions?

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Build Understanding

1. Macronutrients include the carbohydrates, proteins, and fats needed in
relatively large amounts in the diet. Calories are a measure of the total
energy provided by the macronutrients in food.
a. Why do you think scientists gather data specifically on protein and
fat consumption in addition to total Calorie consumption?
b. Nutrition is the process of obtaining the food necessary for health
and growth. Based on this definition, what do you think the term
empty calories means?
c. How would you define a quality food supply?

2. What are some possible solutions for undernourishment and obesity?
3. Draw on what you’ve learned about homeostasis and infectious disease

to answer the following questions.
a. What do you think the relationship is between homeostasis and

nutrition?
b. What does Figure 9.4 tell you about the relationship between

nutrition and infectious disease?

UNDERNUTRITION

increased appetite immunity
energy needs nutrient absorption risk of disease
calories needed to ght infection

INFECTIOUS
DISEASE

FIGURE 9.4: Nutrition and Infectious Disease

SGI Cells
Figure: SGI3e Cells SB 9_02
MyriadPro Semibold 18/14, Regular 12

c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

Maps1 Maps2 Maps3 Maps4 Maps5

B-68

c0 m30 y70 k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90

GLOBAL NUTRITION ACTIVITY 9

4. A region of the brain called the hypothalamus plays a role in
controlling normal eating behavior. As the intake of calories or
nutrients increases, the hypothalamus signals fullness, and eating
stops. When the intake of calories or nutrients decreases, the
hypothalamus signals hunger, and eating is activated.

Draw a model to show how the two feedback loops described above
maintain normal eating behavior. Be sure to include descriptive labels
that explain what is happening in your drawing.

5. Issue connection: Some scientific studies have found that global
changes in climate and carbon dioxide levels are reducing the protein
and micronutrient content of grains. One study conducted at Harvard
University found that when critical food crops like wheat, corn, rice,
and soy are exposed to carbon dioxide at the levels predicted for 2050,
the plants lose as much as 10% of their zinc, 5% of their iron, and 8%
of their protein content. Another international study predicts even
larger reductions in zinc, iron, and protein in crops.

Based on your analysis of the data in this activity, explain how these
findings might impact nutrition on a global level.

KEY SCIENTIFIC TERMS

feedback loop
homeostasis
macronutrients
malnutrition
micronutrients
nutrition

Extension

Do you have questions about a healthy diet or what people eat in different
parts of the world—like: What is the relationship between diet and
sustainability? What effects do food choices have on human health and the
environment? What barriers or challenges prevent people from eating a
healthy diet? Visit the SEPUP SGI Third Edition page of the SEPUP website
at www.sepuplhs.org/high/sgi-third-edition to read a journal article on
the connections between people, their diets, and the environment.

B-69

CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Review and Refresh: The Need for Food

All animals, including humans, must get food that rearrange the atoms in the molecules of
by eating plants or other animals. Food is a the starting substances into new molecules.
source of both matter and energy for the cells This process of digestion of proteins and
that make up the animal’s body. The matter is carbohydrates is summarized in Figure 9.5.
used by cells as building material to produce
more cells as needed for growth or This breakdown is necessary because
maintenance of the organism. The energy is only small molecules can move from the
used by cells to fuel the many processes intestines and into the blood vessels and
needed to keep the animal healthy and alive. then the cells of the body. For example,
carbohydrates are broken down into glucose
The substances provided by food include (sugar). These smaller molecules cross from
proteins, carbohydrates, and fats. Before the the intestines into the bloodstream and are
substances in food can be used by cells, their carried to cells throughout the body, where
molecules must first be broken down into they cross the cell membranes and enter the
smaller molecules by the digestive system. cells, providing the matter and energy
This involves a series of chemical reactions needed for cells to function.

Hamburger contains protein Esophagus

and bun contains carbohydrate.
Mouth

Mouth breaks apart the food and
begins digesting the carbohydrate
into smaller pieces.
Protein

Carbohydrate

FIGURE 9.5: Stomach begins breaking
Human Digestion protein into amino acids.
B-70
Small intestine continues
digestion to produce sugars
and amino acids.
Large intestine
Rectum
Anus

larger molecules
smaller molecules

10 Burning Calories

Standard Vertical

nutritional sustainability is the ability of a food Nutrition Facts
system to provide sufficient energy and the amounts of essential
nutrients required to maintain the good health of the population 8 servings per container
without compromising the ability of future generations to meet Serving size 2/3 cup (55g)
their nutritional needs. In this activity, you will investigate how
much stored energy can be obtained from various foods and Amount per serving 230
then compare the nutritional and sustainability value of those
foods. Stored energy is any type of energy that can be used at a Calories
later time.
In the previous activity, you explored Calories in the human diet. % Daily Value*
You are probably familiar with the Calorie information displayed
on many food labels, such as the one shown in Figure 10.1. In this Total Fat 8g 10 %
activity, you will further investigate Calories—what are they and
how are they measured? Saturated Fat 1g 5%

Guiding Question Trans Fat 0g

How do scientists measure the Calories in various foods? Cholesterol 0mg 0%

Sodium 160mg 7%

Total Carbohydrate 37g 13 %

Dietary Fiber 4g 14 %

Total Sugars 12g

Includes 10g Added Sugars 20%
Protein 3g

Vitamin D 2mcg 10%
Calcium 260mg 20%
Iron 8mg 45%
Potassium 235mg
6%

* The % Daily Value (DV) tells you how much a nutrient in
a serving of food contributes to a daily diet. 2,000 calories
a day is used for general nutrition advice.

FIGURE 10.1: A Food Label

SAFETY 1

Notify your teacher if you are allergic to any food items.

Be sure to wear safety eyewear during this investigation.
Long hair must be tied back, and loose sleeves rolled up. If anything
besides the food item begins to burn, inform your teacher
immediately. Be especially careful not to get clothing or your hair
near the flame. Keep a cup of water nearby as a fire safety
precaution. Note that the can may become quite hot during the
investigation. Carefully follow all instructions from your teacher.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Materials

FOR EACH GROUP OF FOUR STUDENTS

SEPUP food holder
50-mL graduated cylinder
glass thermometer
metric ruler
cup of room-temperature water
aluminum foil
wire coat hanger
aluminum beverage can
food items (such as a nut, cheese puff, or mini-marshmallow)
wooden matches or lighter
tongs or pot holder

FOR EACH STUDENT

Student Sheet 10.1, “Anticipation Guide: Energy and Matter from Food”
Student Sheet 10.2, “Cellular Respiration Model”
chemical splash goggles

Procedure

Part A: Burning Calories

1. Carefully place the food on the food holder.
2. Pour 100 mL of water into the can.
3. Construct a calorimeter, a device used to

measure the amount of heat involved in
physical changes or chemical reactions.
Hang the can from the bent coat hanger as
shown in Figure 10.2. Position the bottom
of the can about 3 cm (1 in) above the top
of the food. It needs to be above the flame
of the burning food but not so low that it
will extinguish the flame.

FIGURE 10.2: Calorimeter Setup

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BURNING CALORIES ACTIVITY 10

4. Just before lighting the food, record the following:

• The starting temperature of the water
• Your prediction for the final temperature of the water after burning

the food
5. Light the food according to your teacher’s instructions. When it begins

to burn, slide it under the can, and let it burn completely. If you think
the food stopped burning before all its energy was released, ask your
teacher for advice on relighting it.
Tips to get the food to light:

• If it’s a nut, have its thinnest edge or the point of the nut pointing down.
• Hold the match to the thinnest part of the food.
• Make sure that there are no drafts blowing on the match.
• Hold the match below the food so that the top of the flame

completely touches the food.
6. As soon as the food stops burning, use the thermometer to stir the

water gently inside the can. Record its final temperature.
7. Calculate the temperature change of the water caused by thermal

energy transferred as the food burns.
8. A calorie is defined as the amount of thermal energy it takes to raise

the temperature of 1 gram (g) of water by 1°C. Calculate and record,
in calories, the amount of thermal energy the water gained by using
this formula:

energy released (calories) = temperature change of water (°C) x mass of water (g)

Note: 1 mL of water has a mass of 1g.
9. In the last activity, you examined kilocalories, or Calories. A Calorie is

1,000 calories, or 1 kilocalorie. Determine how many Calories were in
the food, and record it in your science notebook.
10. Follow your teacher’s instructions for sharing your data with the class.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

FIGURE 10.3

Part B: Modeling Energy Transfer from Food

11. With your partner, draw a very simple model (like the one in Figure
10.4) showing what happened to the energy stored in the food in this
activity. Your model should include:

• the food and oxygen
• where the energy was before and after burning the food
• the transfer of energy
• the kind of energy present before and after burning the food
• a brief caption that explains the model

Reactants Produce Products
food molecules + oxygen carbon dioxide + water

FIGURE 10.4: Reactants and Products
The reaction of food molecules with oxygen when you burned the food can be
described by this equation. The reactants are the substances at the start of the
reaction, and the products are the substances at the end of the reaction.

12. Examine the graphs in Figure 10.5. Which graph do you think best
represents the change in the amount of stored energy in this reaction
system before, during, and after you burned the food (including the
energy transferred from lighting the food)? Discuss your ideas with your
partner and record them in your science notebook. Be prepared to:

• explain the energy changes modeled by each graph
• present an evidence-based argument, including your evidence from

the activity and your reasoning, for which graph best represents the
energy changes as the food was burned

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LabAids SEPUP SGI Cells 3e

BURNING CALORIES ACTIVITY 10

REACTION ENERGY CHANGES

A B
Reactants
Stored Reactants
Energy
Stored
Energy

Products Products

Reaction Time (Progress) Reaction Time (Progress)

C Products D
Products
Stored
Energy Stored
Energy
Reactants
Reactants
Reaction Time (Progress)
FIGURE 10.5: Energy Graphs Reaction Time (Progress)

Build Understanding

1. Based on the class’s results from the investigation in Part A:

a. Which food item had the most calories?
b. Is this method a good way for consumers to compare the calories

in a serving of the different foods? Explain your thinking.

2. Your friend says that the energy stored in food, such as a peanut,
originally came from nutrients in the soil. Is your friend right?
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food when it is burned (as in this
conducts cellular respiration.

a. What are the similarities between these chemical reactions? c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

Maps1 Maps2 Maps3 Maps4 Maps5
b. What are the differences between these chemical reactions?

c. Explain what people mean when they say they are “burning c0m30y70k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0
c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90

calories” when they exercise. What happens if a person doesn’t
burn enough calories over time?
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c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

4. A snack of potato chips and a snack of apple slices and nuts both
provide energy that can be used by the human body.
a. From the perspective of health and nutrition, why might a person
choose one snack over the other?
b. How do you think this choice might relate to global health
patterns?
KEY SCIENTIFIC TERMS
calorie
Calorie
nutritional sustainability
product
reactant
stored energy
thermal energy

Extension: Engineering Connections

As you’ve learned in previous activities, data is accurate if it is close to
the true value of the quantity being measured, and it is precise if the
measurements are close in value. How could you improve the design of
the classroom calorimeters to get more accurate and precise data?
Describe and/or draw how you would improve the design, using readily
available materials. Explain why you think your design would give
more accurate results.

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11 How Plants Make Food

about 60% of the world’s population get the majority of their

dietary protein from plants. People rely on plants, and animals that eat
plants, for food. Plants are at the base of the food chain because they make
their own food through photosynthesis.

FIGURE 11.1

Many scientists have studied the question of how plants grow. Over the
centuries, the combined results of reproducible investigations have
provided evidence supporting the modern scientific understanding of
photosynthesis. Consider an experiment conducted in the 1700s by Jan
Ingenhousz, a Belgian physician. He placed three jars containing leaves in
various locations: in the shade, in the sun, and near a fire.

A jar full of walnut tree leaves [and water] was placed under the
shade . . . so that no rays of the sun could reach it. It stood there the
whole day, so that the water in the jar had received . . . about the same
degree of warmth as the surrounding air. . . . I placed some leaves in
[another] jar and kept it near the fire to receive a moderate warmth.
[I placed] a similar jar, filled with leaves of the same plant, in the open
air in the sun [so that it too received a moderate warmth]. The result
was that the air obtained by the fire was very bad, and that obtained
in the sun was [good] air.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

What do you think Ingenhousz meant by “good” and “bad” air? What
can you conclude from his results? How does his experiment compare
to the experiment you conducted in the previous activity? In this
activity, you will examine some of the experiments that led to how
scientists understand photosynthesis today.

Guiding Question

How did scientists gather and interpret evidence for how
plants provide energy for living organisms?

Materials

FOR EACH GROUP OF FOUR STUDENTS

set of 10 History of Photosynthesis Experiments cards
set of 10 Scientific Conclusions cards

FOR EACH STUDENT

Student Sheet 11.1, “History of Science Timeline”

Procedure

1. With your partner, read the information on the 10 History of
Photosynthesis Experiments cards.

2. Discuss with your group what scientific conclusions you can make
from each experiment, and record a brief summary of your ideas in
your science notebook. Remember to listen to and consider other
group members’ ideas. If you disagree with anyone in your group,
explain why you disagree.

3. Obtain the 10 Scientific Conclusions cards. Spread out both sets of
cards, and match each Experiment card with its corresponding
Scientific Conclusions card.

4. Compare the Scientific Conclusions cards to your group’s summaries
of each experiment. Identify how the conclusions are similar or
different.

5. Obtain Student Sheet 11.1, “History of Science Timeline,” which shows
the date that each experiment was conducted. Work with your group
to determine which experiment occurred when.

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HOW PLANTS MAKE FOOD ACTIVITY 11

Hint: Use information from both sets of cards to guide you. Work as a
group to place the cards in order from oldest to most recent and then
match them to the timeline.

6. On Student Sheet 11.1, record when each scientific development
occurred, using only the bold or underlined words on each card to
record your answers. Be sure to record both the scientist and the
scientific conclusion.

Build Understanding

1. Use what you’ve learned about photosynthesis in this and previous
activities, as well as in this course, to respond to the following:
a. Describe the process of photosynthesis in plants. Be sure to include
the transfer of energy in your explanation.
b. Write a word equation for photosynthesis to support your
explanation.

2. In the Ecology unit, you learned about the carbon cycle—the series of
processes by which carbon moves through the environment.
a. Explain the role of photosynthesis in the carbon cycle. Support
your answer with evidence from the history of photosynthesis
experiments.
b. Construct a model showing the flow of energy and matter into and
out of a plant during photosynthesis. Be sure to label the inputs and
outputs as either matter or energy.

3. What did you observe about the scientists featured on the History of
Photosynthesis Experiment cards? Who do you think is missing? Why
do you think these gaps exist in the history of science?

4. Issue connection: New food products have been created as a result of
increasing knowledge of the cellular and chemical nature of plants and
other food sources. For example, plant-based proteins are now being
used to make meat substitutes, such as plant-based burgers. How
might this trend lead to more sustainable food production?

KEY SCIENTIFIC TERMS

chemical energy
energy
photosynthesis
sustainability

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12 Photosynthesis and the Environment

crop yield—the amount of crops harvested per area of land—

depends on plant growth. Plant growth depends on plants getting the
matter and energy they need through photosynthesis and cellular
respiration. How are these processes affected by changing environmental
conditions? In this activity, you will design a lab to investigate how the rate
of photosynthesis is affected by changing conditions.

Guiding Question

How do changing conditions affect the rate of
photosynthesis in plants?

FIGURE 12.1

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

Materials

FOR THE CLASS

aluminum foil
colored filters: red, blue, and green
thermometers
bicarbonate solution
source of light
source of heat (or hot and cold water)

FOR EACH PAIR OF STUDENTS

20-mL syringe
50-mL graduated cylinder
straw
clear plastic cup containing 20 mL bicarbonate solution
timer
1–2 spinach leaves

FOR EACH STUDENT

chemical splash goggles

SAFETY

Wear chemical splash goggles while working with chemicals.
Do not touch chemicals or bring them into contact with your eyes
or mouth.

PROCEDURE

Part A: Measuring the Rate of Photosynthesis

1. Obtain the materials needed for this
investigation. With your partner, use the
straw to cut out 10 circles from your
spinach leaves, as shown in Figure 12.2.

2. Remove the plunger from the syringe, and
carefully put the leaf disks in the barrel of
the syringe. Try to avoid having them stick
to the side. Gently tap the discs down to
the syringe tip.

3. Carefully replace the plunger. Be sure to be
gentle if you accidentally touch a leaf disk
with the plunger.
FIGURE 12.2

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PHOTOSYNTHESIS AND THE ENVIRONMENT ACTIVITY 12

4. Your cup contains approximately 20 mL of bicarbonate solution. Place
the tip of the syringe into the solution and draw about 15 mL of
solution into the syringe. The disks should float.

5. Hold the syringe with the tip pointing up, and expel all the air by
gently pushing on the plunger.

6. Cover the tip of the syringe tightly with your fingertip and pull
strongly on the plunger to create a vacuum, as shown in Figure 12.3.
Hold the vacuum for a few seconds and release the plunger. Some of
the disks may begin to sink. Repeat this process until all the disks have
sunk to the bottom of the solution.

7. Place the syringe directly under a light source, and create a data table
like the one shown here. Record the starting time to help you keep
track of the minutes.

Start time: Number of disks floating FIGURE 12.3
TABLE 12.1: Number of Floating
Minutes Disks Over Time
1
2
3
4
5
6
7
8
9
10
11
12
13
14

8. In your data table, record what happens every minute after the start time.
(It is possible that nothing may happen for several minutes.) Be sure to
record when the first disk floats and when each remaining disk floats.

Note: You may need to extend the amount of time that you observe the
disks beyond 14 minutes. Make adjustments to your data table as
needed.

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CELLS SCIENCE & GLOBAL ISSUES: BIOLOGY

9. Discuss your results with your partner. What do these results tell you
about photosynthesis in plants? Think about the variable you
controlled and how you might conduct the experiment differently.

Part B: Investigating the Rate of Photosynthesis

10. Work with your group to design an experiment to investigate the rate
of photosynthesis in plants. Remember that if a plant is to survive, it
must be kept in water.
a. As a group, brainstorm a list of variables you might test.
b. Consult with your teacher to determine one variable that you can
test in this activity.

11. Think about the following questions as you design your experiment:

• What is the purpose of your experiment?
• What variable are you testing?
• What variables will you keep the same?
• What is your hypothesis?
• How many trials will you conduct?
• Will you collect qualitative and/or quantitative data? How will these

data help you make a conclusion?

• How will you record your data?

12. Record your hypothesis and your planned experimental procedure in
your science notebook.

13. Make a data table that has space for all the data you need to record. You
will fill it in during your experiment.

14. Obtain your teacher’s approval of your experiment.
15. Conduct your experiment, and record your results.

Build Understanding

1. Review your laboratory results.
a. In Part A, why did the leaf disks float after being exposed to light?
b. How does this investigation demonstrate that plants produce
oxygen during photosynthesis? Support your answer with evidence
from your observations.

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