Download How does the food you eat provide energy to cells in

How does the food you
eat provide energy to cells
in your toes?
Why do doctors measure
their patients' blood
pressure?
r
Y
In your Science Log.
describe how a horse
obtains water and
how a tree obtains
water. Then describe
the system you think
each organism has
inside its body to
deliver water to all its
cells. At the end of this
chapter, look back to
see how your ideas
have changed.
().St cell,, of nlulticell(1lar organisms Such as a horse Or a
ho\\ biolO,^ists think of cells as I)ein0,
tree or \'oursclf are not in direct Con -
ortianir,ed into S\Stenls. "I he interac-
tact with the Olllsille e11v ii.Ollllle1lt. ti0
tions of-s\-stenls OI cell,, maintain a
h()\\, (10 the cells in the hind legs of a
stable en\vironnlent inside nlulticellu-
horse get oxvgen= I IO\\. do cells in
Iar organisnls, even though con-
the )-()()is of a tree het food (sugars)--
ditions Illav Change outside their
'li) think about this I)roblenl,
bodies. \Vhat happens \\ hen a system
inr l gin e that all the cell.,, of an animal
does not \\orl: 1)rol)crl} = I)rohlenl,, in
()1. 1)I:illt al•c orga niz ed into (hll ercllt
the (rgalll/atloll and Iunct1On ()f Cells
s\:sten l s. Filc h s \'St elll has a particular
and sy stem s can cause ill ness.
I'u11ct1OIl to 1)el'101'lll. l 'Or exa mple,
c hapt er
on e S\' s t e i n
66 (:ells kind I''u(ly System,
In this chalner, you will learn
c arries oxygen thl'Oll`^'h-
also explores ho\\ h ea lthy
lifestyle Choices ca n help
1)1-c\cllt
the
out the body to every' cell. Other
O nset
systems (hake sure that each cell
chal)t er b\ taking your pulse under
receives food, and so on. "lo-ether,
difl cre nt conditions. 'I'h e pulse is one
the systems keep all the cells of the
g u ide to h()\\- well
body functioning I)rol)erI}.
s \' st eill is \\ ()I•klllg.
of Illness and disease. Start this
yo ur
circulatory
The Advantages of Being Multicellular
Imagine von are a microSCopiC, unicellular organism. lour whole body is one cell.
This one cell must carry out all the functions needed to keep you alive. It must be
able to move, obtain food, reproduce, and respond to the environment. "There are
many living organisms that consist of only one cell. What disadvantages do you
think they have, compared With muulticellular organisms?
In the last chapter, you learned of one disadvantage. Unicellular organisms cannot grow very lark. Also, because they must take in all the materials they need
through their cell membranes, most unicellular organisms can only live in watery,
food-rich surroundings.
Multicellular organisms have several advantages compared to unicellular living
things. they can live ill a wide variety of environments. "They are able to grow
very large - as large as a whale or a Douglas fir. Multicellular animals can obtain
their energy from a wide variety of foods. "Their bodies are more complex. By
specializing ill particular functions, each cell in a multicellular organism can work
much more efficiently than the cell of a unicellular organism, which must do every
Job itself
In multicellular organisms, speciali zed cells of a similar kind work closely
together, and are usually found grouped closely together ill the body. Groups of
specialized cells, ill turn, work ill harmony With other groups. You will investigate
this organi zation of cells ill the next chapter.
Check Your Understanding
1. Why do cells ill your body need to be specialized?
2. Why do nerve cells have long fibres, whereas red blood cells are thin and
disklike?
3. 1V'hv do unicellular organisms live mainly ill a watery environment?
4. Apply Most people think of the skin as just a body covering. How do you
think skin cells are important to other body cells=
62 Cells and Body Sytitenx
2.4 Speci ized Cells
Imagine an orchestra made up of only a hundred trumpet players or
a hundred
violins. Such an orchestra would be very limited! To play every kind
of music, an
orchestra needs a variety of musical instruments - some flutes, some
oboes, a
piano, drums, and so on. In the same way, a multicellular organism
cannot be made
up only of identical cells. As Figure 2.13 shows, although multicellular
organisms
grow from single cells that repeatedly divide, their cells are not all the
same.
red blood cell
ti•
Figure 2 .13 Different cells have different shapes and functions.
Like the instruments in an orchestra, different cells have different appearances
and
perform different jobs. They are said to be specialized for particular tasks.
For
example, your muscle cells are shaped to move parts of your body, and your
skin
cells are built to protect your body from the drying rays of the Sun. Human
s have
about a hundred different types of cells, each with their own particular structu
re
and functions.
A nerve fibre in the
neck of a giraffe can be
up to 1 m in length.
However, the main part
of the cell from which
it comes is about the
same size as a human
nerve cell.
60 Cells and Body Systems
Look at the examples of plant and animal cells in Figure 2.13. How
do their
shapes relate to their functions? Nerve cells have long, branched fibres
running from
the main part of the cell, shaped to carry nerve signals from one part
of the body to
another. Red blood cells, which carry oxygen in the bloodstream, have
a thin, disklike shape. This gives them a large surface area to pick up large amount
s of oxygen.
The water-conducting cells of a plant are tubelike, with thick walls and
a network
of holes that lets water pass easily through them. Onion skin cells are
flat and brickshaped, so they can fit closely together to form a continuous protective
layer.