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Lesson 2
How Do Cells Work Together?
Fast Fact
Liquid Tissue In the blood vessel shown here, red blood cells are carrying oxygen to
other parts of the body. In the Investigate, you'll see different types of cells that
work together to keep organisms functioning. ,
Investigate
Cells and Tissues
Materials
 prepared slides of a plant root, a plant leaf, and a plant stem
 microscope
 colored pencils
 Procedure
Procedure
1. Place the slide of the plant root on the stage of the microscope. Turn the focus knob
until you can see the cells clearly. Observe the root cells. Use the colored pencils to
record your observations in a drawing.
2. Repeat Step 1, using the slide of the plant leaf. Again, use the colored pencils to
record what you observe.
3. Repeat Step 1, using the slide of the plant stem. Record your observations.
4. Compare the cells from the different parts of a plant. What similarities did you
observe? What differences?
Draw Conclusions
1. You observed cells from three different parts of a plant. Based on your observations,
what conclusion can you draw about cells that look similar in all three parts?
2. Inquiry Skill When scientists compare objects, they often infer reasons for any
differences. What can you infer about why leaf cells contain more green structures
than do stem cells?
Investigate Further
Form a hypothesis about similarities and differences among animal cells. Using
prepared slides of animal cells, test your hypothesis.
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Reading in Science
VOCABULARY
tissue p. 40
organ p. 41
organ system p.42
digestive system p. 42
SCIENCE CONCEPTS
 how tissues are formed of similar cells
 how tissues work together in organs
 how body systems are groups of organs that work together
READING FOCUS SKILL
COMPARE AND CONTRAST Look for ways that tissues, organs, and organ systems
are alike and different.
alike - different
Cell, Tissue, Organ
Your body is made up of trillions of cells. Each cell is able to carry out its own life
functions. But your body's cells—like those in other organisms made up of many
cells—also work together. Cells that work together to perform a certain function
form a tissue. There are four kinds of tissue in your body.
Your body is covered and lined with epithelial (ep•ih•THEE•lee•uhl) tissue. Epithelial
tissue is in your skin. It also lines your internal organs.
Most of your body mass is muscle tissue. Whenever you move, muscle tissue contracts
and relaxes to move your skeleton. The bones and cartilage of your skeleton are
made of connective tissue. Tendons and ligaments are connective tissue, too.
Tendons connect bones to muscles. Ligaments connect bones to bones.
Signals from another kind of tissue, nervous tissue, "tell" muscles when to contract.
Nervous tissue is found in the brain, spinal cord, and nerves.
Muscle tissue is made up of cells that contract when they receive signals from the
brain. The contraction and relaxation of muscle tissue moves the skeleton.
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The heart is an organ made up of muscle tissue, epithelial tissue, nervous tissue,
and connective tissue. These tissues work together to pump blood to all parts
of your body.
Just as cells work together to form tissues, tissues work together to form organs. An
organ is several kinds of tissue working together for the same function. Your skin
is in organ. It is made up of many layers of epithelial tissue. It also has muscle
tissue, nervous tissue, and a layer of connective tissue. These tissues work together
to protect your body.
Your heart is an organ that pumps blood to all parts of your body. It contains each of the
different kinds of tissue. The heart Is mostly muscle tissue, but it also has
connective tissue. It is lined and covered with epithelial tissue. Nervous tissue in
the heart receives signals from the brain to make it beat faster or slower.
The lungs are organs that take in oxygen from the air. They are made up of epithelial
tissue and connective tissue.
The lungs, the heart, and all other organs rely on a very special kind of connective
tissue—blood. The red cells in blood deliver oxygen to all other cells of the body.
The liquid part of blood, called plasma, delivers nutrients and helps remove wastes
from body cells. White blood cells help your body fight diseases. And platelets help
blood clot if you qet cut.
COMPARE AND CONTRAST How are muscle tissue and connective tissue
alike? How are they different?
The lungs are made up of epithelial tissue and connective tissue. These tissues
work together to take in oxygen from the air and move it into the blood.
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The Digestive System
Organs that work together to do a job for the body are called an organ system. There
are ten major organ systems in your body. One of the major systems is the
digestive system. The digestive system breaks food down into chemical nutrients
that body cells need for energy, growth, and repair.
As food passes through the digestive system, chemicals made in the stomach,
pancreas, and small intestine break the food down. Nutrients from the food
help the body's cells grow and stay healthy.
For a more detailed look at the digestive system, see the Health Handbook.
Nutrients pass into the blood through the walls of the villi in the small intestine.
The digestive system helps the body get the nutrients it needs from food. First,
chemicals break food down into nutrients. Then, nutrients are moved into the
blood. Blood moves the nutrients to each of the body's cells.
Most people think the stomach is the first body organ involved in digestion. But
digestion of certain foods starts as soon as you take a bite! As you chew, food is
broken into smaller pieces. Glands in your mouth produce saliva. Saliva contains
chemicals that begin breaking down some carbohydrates. Together, chewing and
saliva begin digesting starchy foods. Starchy foods, like breads and pasta, begin to
break down into sugars. You can investigate this yourself. Try chewing an unsalted
cracker for a minute or two. You'll notice that its starchy taste soon becomes sweet.
From the mouth, food travels down the esophagus, a long tube that leads to the stomach.
In the stomach, strong muscles churn the food with acid and other chemicals that
break down proteins.
From the stomach, partly digested food moves into the small intestine. Chemicals
produced there, along with chemicals from the pancreas and gallbladder, complete
digestion.
Once digestion is complete, nutrients are absorbed into the blood. The small intestine is
lined with finger-like bumps called villi (vIL•eye). Villi have many blood vessels.
Nutrients move from the small intestine into the blood vessels of the villi. Then
they are carried by the blood throughout the body.
COMPARE AND CONTRAST How are villi like the roots of a plant? How are
they different?
Peristalsis (pair•uh•sTAHL•sis) is the wavelike contraction of muscles in the
organs of the digestive system. It helps move food through the system.
Insta-Lab
Make a Model
You can make a model of food moving through the digestive system. Cut the foot off
one leg of a pair of pantyhose. Put an inflated balloon into the other end. Then use
both hands to squeeze the balloon along the length of hose. How does this model
peristalsis?
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Body Organization
Suppose you join a local sports team. The team might be part of a regional league that is
part of a state or national organization. From the smallest unit—you to the national
organization, all parts of the group work together to do the same thing—to help you
learn, play, and enjoy a sport.
Your body is also organized for one function—to keep you alive and healthy. Each of
your cells works to keep itself healthy. But cells also work with other cells to form
tissues. Tissues work together in organs, organs work together in systems, and
systems work together to keep your body functioning.
---see picture
Cells to Systems
1. This is a specialized cell of the digestive system. It produces acid to help break
down food.
2. Digestive cells form a type of epithelial tissue that helps in digestion.
3. Layers of different kinds of tissue form a digestive organ—the stomach.
4. The stomach is part of the digestive system—an organ system that breaks food
down into nutrients and moves the nutrients into the blood.
COMPARE AND CONTRAST How are cells like systems? How are they
different?
Eating a sandwich may seem simple, but it takes cells, tissues, organs, and an
organ system to get nutrients from food.
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Reading Review
1. COMPARE AND CONTRAST Draw and complete the graphic organizer by
writing Yes or No in place of the circled letters.
---see chart
2. SUMMARIZE Use the graphic organizer to write a lesson summary.
3. DRAW CONCLUSIONS What part of the digestive system isn't working properly
in people who cannot absorb nutrients? Explain.
4. VOCABULARY Use the lesson vocabulary and other lesson terms to write a
paragraph about the digestive system.
Test Prep
5. Critical Thinking What is the relationship between the digestive system and the
circulatory system?
6. Which is an example of a tissue?
A. the heart
B. a nucleus
C. a muscle
D. a vacuole
Writing
Narrative Writing Write a creative story describing an adventure through the
digestive tract. Tell about the "stops" you make along the way, including the
various organs.
Math
Calculate
Count how many times your heart beats in 15 seconds. Multiply by 4 to find how many
times your heart beats in a minute. Run in place for two minutes and repeat. How
much faster is your heartbeat rate now?
Health
Lifeblood
Blood is a vital tissue. When a person loses a lot of blood due to an injury, a transfusion
can save his or her life. Contact your local blood bank to learn about blood
transfusions.
For more links and activities, go to www.hspscience.com
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