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1.15
Cell Specialization
thin cell
wall
middle
lamellae
a Thin-walled plant cells are found in the
flexible tissues of the leaf, flower, fruit,
and root. Most edible plant roots, such
as potatoes and radishes, ar e
composed of these cells.
thicker
cell wall
b Thick-walled plant cells are specialized
for support. Their stretchable cell walls
are flexible. The tough strings of the
celery stalk are made of these cells.
thickest
cell wall
c Very thick cell walls provide rigid
support. The cell wall can get so thick,
as the plant matures, that it becomes
difficult for nutrients to enter the cell.
The cell usually dies, leaving an empty
chamber surrounded by a thick wall.
Fabrics such as linen are made from
these cells.
Figure 1
Plants, like animals, are made of tissues
and organs. Each kind of tissue contains
a special type of cell.
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Unit 1
Imagine how difficult life would be
without specialists. Could you build
your own television? Grow your own
food? Do your own surgery?
Unicellular organisms are not
specialists. Each cell must carry out
all the functions of life. Multicellular
organisms, such as you, benefit from
cell specialization. We have cells that
come in a variety of sizes and shapes,
each designed to car ry out a special
function.
Specialized Plant Cells
Nerve cells tend to be
long and thin. Many nerve
cells are protected by
a coating of insulation
that prevents short
circuits.
1
3 Blood tissue
The long, thin strings inside a celery
stalk, the pit in an apricot, the thin
leaves of the lettuce are all evidence
that there is a variety of different
types of plant cells (Figure 1).
The cell wall is one very
noticeable feature of plant cells. As
plants develop, a primary cell wall is
formed around each cell. Once the
plant stops growing, an additional
secondary cell wall may form inside
the primary cell wall. This structure
provides added strength.
The spaces between plant cells,
referred to as the middle lamellae,
contain a sticky, sugary substance
called pectin. Pectin acts like cement,
sticking plant cells together. The
sticky syrup that often forms on the
top of a baked apple pie is pectin.
5 Fat tissue
1 Nerve tissue
5
In fat cells,
most of the
cytoplasm is
occupied by a
vacuole that
stores fat
molecules.
a Red blood cells carry
oxygen in a special
protein called
hemoglobin. The
cells are filled with
this protein.
b White blood cells
protect the body from
invaders by engulfing
them and digesting
them, or by killing
them with antibodies.
3
a
b
Specialized Animal Cells
Understanding Concepts
The shape of animal cells provides a clue to their function.
Many of the features of unicellular organisms can be
found in animal cells as you can see in Figure 2.
Figure 2
Some specialized cells found
in human bodies.
2 The respiratory system
2
a
a Particles that attempt to
enter your lungs are trapped
in mucous and then swept
away from the lungs by cells
with cilia.
b Cells of the lung are very
thin. This allows gases to
exchange rapidly between
the air and the blood.
1. What are the advantages of cell
specialization for an organism?
2. Predict what might happen
to multicellular plants if a
microorganism that digests
pectin was accidentally released
from a laboratory.
3. What is the advantage of a
highly folded cell membrane?
4. What advantage does a thick,
flexible plant cell wall provide
over a thick, rigid cell wall?
5. Examine the cell shape in Figure 3:
Figure 3
4 The stomach
Your stomach contains a
powerful acid. Cells of the
lining of the stomach ar e
protected from the acid by a
layer of mucous. These cells
also have many Golgi
apparatuses to store the
proteins that break down food.
b
4
Three cell shapes
(a) Which cell would be best
suited as an egg cell? Give
your reasons.
(b) Which cell would be best
suited for movement? Give
your reasons.
(c) Which cell would be best
suited as a covering for an
organ? Give your reasons.
6. Identify body cells that have a
structure similar to that of a
unicellular organism.
Reflecting
7. Why are specialized cells
dependent on other specialized
cells?
6
6 The small intestine
Cells that line the small
intestine absorb food.
Fingerlike projections
increase the surface
area for absorption.
Is the structure of the
cell that you are building
suited for its special
function? What changes
should you make in your
design now that you
know more about
specialized cells?
Cells, Tissues, Organs, and Systems
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