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Chapter 3
Life Science
Organization of Life
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A cell is smaller than the period at the end of
this sentence, yet a single cell has all the
items necessary to carry out life’s activities.
Not all of your cells look or act the same. You
have about 200 different kinds of cells, and
each type is specialized to do a particular job.
You are made of about 100 trillion cells.
Tissues
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A tissue is a group of cells that work together
to perform a specific job in the body.
Blood, fat, and muscle cells are just a few of
the many cells that make tissues in your
body.
Organs
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When two or more tissues work together to perform
a specific job, the group of tissues is called an
organ.
Some examples of organs are your stomach,
intestines, heart, lungs, and skin.
Plants also have different kinds of tissues that work
together.
A leaf is a plant organ that contains tissue that traps
light energy to make food.
Other examples of plant organs are stems and
roots.
Organ Systems
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Organs work together in groups to perform
particular jobs called organ systems.
Your body has several organ systems.
One example is the digestive system.
Organisms
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Anything that can live on its own is called an
organism.
If a single cell is living on its own, it is called a
unicelluar organism.
You are a multicellular organism. This means
that you can exist only as a group of cells and
that most of your cells can survive only if they
remain a part of your body.
Populations
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Although organisms can live on their own,
they rarely do.
A group of organisms that are of the same
kind and that live in the same area make up a
population.
Communities
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Two or more different populations living in the
same area make up a community.
Your hometown is a community that includes
all of the people, dogs, cats, and other
organisms living there.
Ecosystems
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The community and all of the nonliving things
that affect it, such as water, soil, rocks,
temperature, and light, make up an
ecosystem.
Ecosystems on land are called terrestrial
ecosystems
Ecosystems in water are called aquatic
ecosystems
The Cell Theory
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All organisms are composed of one or more
cells.
The cell is the basic unit of life in all living
things.
All cells come from existing cells.
Cells
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All cells are surrounded by a cell membrane.
When new cells are made, they receive a
copy of the hereditary material of the original
cells. This material is DNA.
All cells have chemicals and structures that
enable the cell to live, grow, and reproduce.
The structures are called organelles.
The chemicals and structures of a cell are
surrounded by a fluid called cytoplasm.
Cells
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You are made up of 100 trillion cells, and it
would take 50 of these cells just to cover up
the dot on the letter i.
As the cell’s volume increases, its outer
surface grows too. But the volume of a cell
increases at a faster rate than the area of its
outer surface.
Multicellular organisms grow by producing
more small cells, not larger cells.
Cells
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A single cell cannot do all the things that
many different cells can do.
Having many different cells that are
specialized for specific jobs allows
multicellular organisms to perform more
functions than unicellular organisms.
Cells
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Cells can be divided into two groups:
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Prokaryotic – Cells that do not have a nucleus
Eukaryotic – Cells that do have a nucleus
Prokaryotic cells are also called bacteria.
They are the world’s smallest cells, and they do not
have a nucleus.
Bacteria do not have any membrane-covered
organelles but they do have tiny, round organelles
called ribosomes.
These organelles work like little factories to make
proteins.
Cells
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Eukaryotic cells are more complex than prokaryotic
cells.
All living things that are not bacteria are made of
one or more eukaryotic cells.
This includes plants, animals, fungi, and protists.
An advantage of having the cell divided into
compartments is that it allows many different
chemical processes to occur at the same time.
Cells
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Instead of being circular, the DNA molecules
in eukaryotic cells are linear.
All eukaryotic cells have a cell membrane,
and some of them have a cell wall.
Those that have cell walls are found in plants,
fungi, and some unicellular organisms.
Difference Between Cells
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Prokaryotic Cells
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No nucleus
No membrane-covered
organelles
Circular DNA
Bacteria
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Eukaryotic Cells
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Nucleus
Membrane-covered
organelles
Linear DNA
All other cells
Cells
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Cells are so small that the details of their
structure could not be seen until better
methods of magnifying and staining were
developed.
We know that cells are very complex,
especially eukaryotic cells.
Cell Membrane
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All cells are covered by a cell membrane.
The job of the cell membrane is to keep the
cytoplasm inside to allow nutrients in and
waste products out, and to interact with
things outside the cell.
Cell Wall
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The cells of plants and algae have a hard cell
wall made of cellulose.
The cell wall provides strength and support to
the cell membrane.
When too much water enters or leaves a
plant cell, the cell wall can prevent the
membrane from tearing.
Nucleus
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The largest and most visible organelle in a
eukaryotic cell is the nucleus.
The nucleus has often been called the control
center of the cell.
The nucleus stores the DNA.
The dark spot inside the nucleus is called the
nucleolus.
Ribosomes
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Proteins, the building blocks of all cells, are
made up of chemicals known as amino acids.
These amino acids are hooked together to
make proteins at very small organelles called
ribosomes.
Ribosomes are the smallest but most
abundant organells.
Ribosomes are not covered with a
membrane.
Endoplasmic Reticulum
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Eukaryotic cells have an organelle called the
endoplasmic reticulum.
The ER is a membrane-covered
compartment that makes lipids and other
materials for use inside and outside the cell.
It is also the organelle that breaks down
drugs and other chemicals that could damage
the cell.
Mitochondria
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ATP can be made at several locations in
eukaryotic cells, but most of it is produced at
bean-shaped organelles called mitochondria.
The reason you breathe air is to make sure
your mitochondria have the oxygen they need
to make ATP.
Highly active cells, such as those in the heart
and liver, may have thousands of
mitochondria, while other cells may have only
a few.
Chloroplasts
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Plants and algae have an additional kind of energyconverting organelle, called chloroplast.
These are flattened, membrane-covered sacs that
contain an important chemical called chlorophyll.
Chlorophyll is what makes chloroplasts green.
The energy of sunlight is trapped by chlorophyll and
used to make sugar.
This process is called photosynthesis.
Golgi Complex
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When proteins and other materials need to
be processed and shipped out of a eukaryotic
cell, the job goes to an organelle called the
golgi complex.
The golgi complex looks like the ER, but it is
located closer to the cell membrane.
Vesicles
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All eukaryotic cells have membrane-covered
compartments called vesicles.
Vacuoles
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Most plant cells have a very large membranecovered chamber called a vacuole.
In plants, large central vacuoles store water
and other liquids.
Lysosomes
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Lysosomes are specials vesicles in animal contains
enzymes.
Lysosomes destroy warn-out or damaged organs.
They get rid of waste materials and protect the cell
from foreign invaders.
Sometimes lysosome membranes break, and
enzymes spill into the cytoplasm, killing the cell.
This is what happened to you when you were born.
Lysosomes caused the destruction of cells formed
the webbing between your fingers.
Plant or Animal?
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How can you tell the difference between a
plant cell and an animal cell?
They both have a cell membrane, and they
both have nuclei, ribosomes, mitochondria,
endoplasmic reticula, golgi complexes, and
lysosomes.
Plan cells have cell wall, chloroplast, and a
large vacuole. Animal cells do not have
these.