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Chapter 3
Cellular Hierarchy
ALABAMA 7TH GRADE SCIENCE STANDARDS COVERED IN THIS CHAPTER INCLUDE:
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Relate major tissues and organs of the skeletal, circulatory, reproductive,
muscular, respiratory, nervous and digestive systems to their functions.
CELLULAR HIERARCHY
In Chapter 2, you learned about the structure ofplant and animal cells. How does this
relate to actual plants and animals? As you may have already guessed, the
microscopic differences between plant and animal cells translate into macroscopic
(larger) differences in organisms. This fact is explained by the cellular hierarchy. As
we will discover during this chapter, differences in cells mean differences in larger
structures like tissues or organs. You can think of it like the foundational difference
between two different types of houses in a neighborhood
build a different
foundation, get a different house.
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The cellular hierarchy starts with one cell and works its way to more complex
structures that eventually form the most complex ofliving things: an organism. Take
a look at the cellular hierarchy flow diagram in Figure 3 1 You should recognize
most of the words; they relate to systems within the human body.
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Cellular Hierarchy
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Cells
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Figure 3.1 Cellular Flow Diagram
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—>
Organism
Cellular Hierarchy
CELLS
Recall, multicellular organisms are composed of
many cells that work together to carry out life
processes. In multicellular organisms, cells group
together and divide the labor. Cells in a multicellular
organism are specialized to perform specific
functions. These specializations usually cause the
figure 3.2
Figure 3.3
Red Blood Cells cells in a multicellular organism to take on special
Nerve Cell
shapes. Examine Figures 3.2 and 3.3. These images
show the differences in external structures of two different types of cells. Figure 3.2
shows the round disk shape of red blood cells. This shape maximizes surface area,
allowing lots of oxygen and carbon dioxide to move into and out ofthe red blood cells.
Essentially, their disk shape allows red blood cells to transport gases efficiently. Figure
3.3 shows a nerve cell; you can see it has many long finger-like extensions. This shape
helps transmit information over long distances, throughout the entire human body.
There are thousands of examples of cellular specialization in plants and animals. Some
more examples of cells are skin cells, liver cells, leaf cells and root cells.
TISSUES
Cells group together to perform the same function and are called tissues. The human
body is made up of four basic types of tissue: epithelial, connective, muscle and
nervous. Epithelial tissue usually surrounds and protects the things beneath it.
Epithelial cells can also filter, secrete and absorb substances. Some examples include
skin, ducts, glands and the outer layer of your eye called the sciera (the white part).
Connective tissue connects and supports body parts. Cartilage and blood are two
examples ofconnective tissue. Muscle tissue helps move the body. Muscle tissue moves
bones, digestive organs and the heart. Nervous tissue carries messages from the body
and environment to the brain and back.
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ORGANS
Several types of tissues group together and form an organ. The brain,
heart, stomach and lungs are some examples of organs. Organs usually
perform a complex task. Figure 3.4 shows a four chambered human
heart. This organ is made of specialized tissues that act as a pump to
move blood (and other fluids) through the body. Cardiac muscle tissue
contracts and causes the heart to beat. Nervous tissue in the heart Figure 3.4 Heart
receives signals from the brain to make the heart beat at the correct rate.
Epithelial tissue (called the pericardium) forms a protective sac around the heart.
Connective tissues form the valves ofthe heart, preventing the backflow ofblood in the
heart’s chambers. Not to mention blood itself is a type of connective tissue mentioned
earlier in this text.
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Chapter 3
ORGAN SYSTEM
An organ system is a group of organs working together for a particular function.
Examples of organ systems are the digestive system, circulatory system and nervous
system. The organ systems ofmulticellular organisms work together to carry out the life
processes of the organism, with each system performing a specific function. All the
organ systems combine to make up the organism.
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Tissues combine
organs combine
to make small
to make digestive
Organ systems
combine to make
intestine organ
organ system
an organism
Figure 3.5 Cellular Hierarchy
As living things become more complex, their cells become more specialized, forming
specific types oftissues and organs.
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Activity
Fill in the blanks in the table below.
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Lymphocyte
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Organ
Tissue
Cell
Organ System
Spleen
Lymph fluid
Muscular system
Tendon
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Bone marrow
Liver*
Digestive system
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BONUS: Complete the last row all on your own.
*Hjnt. The liver is the largest gland in the human body and secretes many substances used in
digestion.
Activity
Use a sheet of paper to draw your own cellular hiearchy image similar to Figure 3.5.
tissue —> organ —> organ
:IBe sure to show each level of organization from cell
system —> organism.
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Cellular Hierarchy
CHAPTER
3
REVIEW
1. A(n)
is a group of different tissues that work together to perform a
certain function.
A
B
C
B
:
organ system
organ
cell
organelle
2. Your heart functions because of tissues like cardiac muscle, blood and
connective tissues. At which level of organization is your heart?
A
B
an organ system
an organ
C
B
a cell
an organelle
3. The central nervous system (CNS) consists of the brain and spinal cord. What
is the CNS an example of?
A
B
organ system
organ
C
B
cell
organelle
4. Which of the following is listed from least to most complex?
A
B
C
D
organ, organism, cells
cells, tissues, organism, organ system
cells, organ, organism
tissues, organism, organ
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5. Which of the following is an example of a tissue?
A
B
C
D
chloroplast
stomach
human
bicep
E
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