From a Cell to an Organism Levels of Organization

From a Cell to an Organism
Levels of Organization
Key Concepts
What do you think? Read the three statements below and decide
whether you agree or disagree with them. Place an A in the Before column
if you agree with the statement or a D if you disagree. After you’ve read
this lesson, reread the statements and see if you have changed your mind.
Before
Statement
After
4. Unicellular organisms do not have all the
• How do unicellular and
multicellular organisms
differ?
• How does cell
differentiation lead to the
organization within a
multicellular organism?
characteristics of life.
5. All the cells in a multicellular organism are the
same.
6. Some organs work together as part of an
organ system.
3TUDY#OACH
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Life’s Organization
All matter is made of atoms. Atoms combine and form
molecules. Molecules make up cells. A large animal, such
as a Komodo dragon, is not made of one cell. Instead, it is
made of trillions of cells working together. The skin of the
Komodo dragon is made of many cells that are specialized
for protection. The Komodo dragon has other types of cells,
such as blood cells and nerve cells, which perform other
functions. Cells work together in the Komodo dragon and
enable the whole organism to function. This is the same way
that cells work together in you and in other multicellular
organisms.
Recall that some organisms are made of only one cell.
These unicellular organisms carry out all the activities
necessary to survive, such as absorbing nutrients and getting
rid of wastes. No matter their sizes, all organisms are made
of cells.
Reading Essentials
Make Flash Cards As you
read, write each vocabulary
word and key term from the
text on one side of a flash
card and its definition on the
other side. Use your cards to
review the material later.
Reading Check
1. Identify What are all
organisms made from?
From a Cell to an Organism
47
Unicellular Organisms
Unicellular organisms have only one cell. These organisms
do all the things needed for their survival within that one
cell. An amoeba is a unicellular organism. It takes in, or
ingests, other unicellular organisms for food to get energy.
Unicellular organisms also respond to their environment, get
rid of waste, grow, and reproduce. Unicellular organisms
include both prokaryotes and some eukaryotes.
Prokaryotes
A cell without a membrane-bound nucleus is a prokaryotic
cell. In general, prokaryotic cells are smaller than eukaryotic
cells. As shown below on the left, prokaryotic cells also have
fewer cell structures. A unicellular organism made of one
prokaryotic cell is called a prokaryote. Some prokaryotes live
in groups called colonies. Some can also live in extreme
environments. The heat-loving bacteria that live in hot
springs get their energy from sulfur instead of light.
Visual Check
2. Highlight each area
where the hereditary
material is located.
Gel-like capsule
m
Cell wall
Cell membrane
Cell membrane
Oral groove
Cytoplasm
Food vacuole
Anal pore
Cilia
Hereditary
material
Ribosomes
Macronucleus
Eukaryotes
A eukaryotic cell has a nucleus surrounded by a membrane
and many specialized organelles as shown above on the right.
This paramecium has an organelle called a contractile
vacuole. The contractile vacuole collects extra water from the
paramecium’s cytoplasm and pumps it out. The contractile
vacuole keeps the paramecium from swelling and bursting.
Reading Check
3. Identify one example of
a eukaryotic organism.
48
From a Cell to an Organism
A unicellular organism that is made of one eukaryotic
cell is called a eukaryote. There are thousands of different
unicellular eukaryotes. The alga that grows on the inside of
an aquarium and the fungus that causes athlete’s foot are
unicellular eukaryotes.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Flagellum
Contractile
vacuole
Micronucleus
Multicellular Organisms
A multicellular organism is made of many eukaryotic
cells working together. Each type of cell in a multicellular
organism has a specific job that is important to the survival
of the organism.
Cell Differentiation
Remember that all cells in a multicellular organism come
from one cell, a fertilized egg. Cell division starts quickly
after fertilization. The first cells made can become any type
of cell, such as a muscle cell, a nerve cell, or a blood cell.
The process by which cells become different types of cells is called cell
differentiation (dihf uh ren shee AY shun).
A cell’s instructions are contained in its chromosomes.
Nearly all the cells in an organism have identical sets of
chromosomes. If an organism’s cells have identical sets of
instructions, how can the cells be different? Different cell types
use different parts of the instructions on the chromosomes.
A few of the many different types of cells that can result
from cell differentiation are shown in the figure below.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Animal Stem Cells Not all cells in a developing animal
differentiate. Stem cells are unspecified cells that are able to develop
into many different cell types. There are many stem cells in
embryos but fewer in adult organisms. Adult stem cells are
important for cell repair and replacement. For example, stem
cells in your blood marrow can produce more than a dozen
different types of blood cells. These replace the cells that are
damaged or worn out. Stem cells in your muscles can
produce new muscle cells. These can replace torn muscle
fibers.
Key Concept Check
4. Describe How do
unicellular and multicellular
organisms differ?
Use a layered book to
describe the levels of
organization that make up
organisms.
L l off
Levels
Organization
g
Org
Organ
Organ Syste
System
y
Orga is
Organism
O
Visual Check
Egg
Red blood cell
5. Name two types of cells
that can result from cell
differentiation.
Fertilized egg
p
Reading Essentials
From a Cell to an Organism
49
Reading Check
Plant Cells Plants also have unspecialized cells, similar to the
stem cells of animals. These cells are grouped in areas called
meristems (MER uh stemz). Meristems are in different areas
of a plant, including the tips of roots and stems. Cell
division in meristems produces different types of plant cells
with specialized structures and functions. These functions
include transporting materials, making and storing food, or
protecting the plant. Meristem cells might become part of
stems, leaves, flowers, or roots. Meristems are shown in the
figure below.
6. Identify the three
possible functions of
meristems.
Visual Check
7. Identify Circle two
additional places where
meristem cells might be
located in plants.
In multicellular organisms, similar types of cells are
organized into groups. Tissues are groups of similar types of cells
that work together to carry out specific tasks. Most animals,
including humans, have four main types of tissues. These are
muscle tissue, connective tissue, nervous tissue, and
epithelial (eh puh THEE lee ul) tissue. Muscle tissue makes
movement possible. Connective tissue provides structure
and support. Nervous tissue carries messages to and from the
brain. Epithelial tissue forms the protective outer layer of
skin and the lining of major organs and internal body
cavities.
Reading Check
8. Compare animal and
plant tissues.
50
From a Cell to an Organism
Plants also have different types of tissues. The three main
types of plant tissue are dermal tissue, vascular (VAS kyuh lur)
tissue, and ground tissue. Dermal tissue provides protection
and helps reduce water loss. Vascular tissue transports water
and nutrients from one part of a plant to another. Ground
tissue provides storage and support. Photosynthesis takes
place in ground tissue.
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Tissues
Organs
Complex jobs in organisms require more than one type
of tissue. Organs are groups of different tissues working together to
perform a particular job. Your stomach is an organ that breaks
down food. It is made of all four types of tissue: muscle,
epithelial, nervous, and connective. Each type of tissue
performs a specific function necessary for the stomach to
work properly and break down food. Muscle tissue contracts
and breaks up food. Epithelial tissue lines the stomach.
Nervous tissue signals when the stomach is full. Connective
tissue supports the stomach wall.
ACADEMIC VOCABULARY
complex
(adjective) made of two or
more parts
Plants also have organs. A leaf is an organ specialized for
photosynthesis. Each leaf is made of dermal tissue, ground
tissue, and vascular tissue. Dermal tissue covers the outer
surface of a leaf. The leaf is an important organ because it
contains ground tissue that produces food for the rest of the
plant. Ground tissue is where photosynthesis takes place.
The ground tissue is tightly packed on the top half of the
leaf. The vascular tissue moves both the food produced by
photosynthesis and water throughout the leaf and plant.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Organ Systems
Most organs do not function alone. Instead, organ
systems are groups of different organs that work together to complete
a series of tasks. Human organ systems can be made of many
different organs working together. For example, the digestive
system is made of the stomach, the small intestine, the liver,
and the large intestine. These organs all work together to
break down food. Blood absorbs and transports nutrients
from food to cells throughout the body.
Plants have two main organ systems—the shoot system
and the root system. The shoot system includes leaves,
stems, and flowers. The shoot system transports food and
water throughout the plant. The root system anchors the
plant and takes in water and nutrients.
Reading Check
9. Identify the major
organ systems in plants.
Organisms
Multicellular organisms usually have many organ
systems. The cells of these systems work together and carry
out all the jobs needed for the organism to survive. There
are many organ systems in the human body. Each organ
system depends on the others and cannot work alone. For
example, the respiratory system and circulatory system carry
oxygen to the cells of the muscle tissue of the stomach. The
oxygen aids in the survival of muscle tissue cells.
Reading Essentials
Key Concept Check
10. Explain How does cell
differentiation lead to the
organization within a
multicellular organism?
From a Cell to an Organism
51
Mini Glossary
cell differentiation (dihf uh ren shee AY shun): the
process by which cells become different types of cells
organ: a group of tissues working together to perform a
particular job
stem cell: an unspecified cell that is able to develop into many
different cell types
tissue: a group of similar types of cells that work together to
carry out specific tasks
organ system: a group of organs that work together to
complete a series of tasks
1. Review the terms and their definitions in the Mini Glossary. Write two sentences
describing some of the different types of cells within an organism.
2. Fill in the chart below to show the different levels of organization in a multicellular
organism.
organism
3. How did making flash cards of the important terms in the text help you review the
material?
What do you think
Reread the statements at the beginning of the
lesson. Fill in the After column with an A if you
agree with the statement or a D if you disagree.
Did you change your mind?
52
From a Cell to an Organism
Connect ED
Log on to ConnectED.mcgraw-hill.com
and access your textbook to find this
lesson’s resources.
END OF
LESSON
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
tissue