Download Organization in Plants and Animals

Organization in Plants and Animals
What is your body made of? You might say that you
are made of atoms or cells. You might even say you
are made of organs, like skin and a heart. These
answers are all correct. Each focuses on a different
level of organization of the human body. Atoms are a
nonliving unit of the body. But cells and organs are
living units. How do these different living units relate to
each other? Where do body systems, like the digestive
system, fit into these levels of organization?
Organization in Animals
In all living things, the cell is the smallest unit of life. Some organisms are unicellular. They are
made of a single cell functioning on its own. Bacteria and yeasts are two examples of single celled
organisms.
Animals are multicellular, meaning they are composed
of more than one cell. In fact, the human body is made
up of about 100 trillion cells! Cells have a variety of
different shapes and structures because they each
have a different function. For example, muscle cells
tend to be long to allow for contraction. Nerve cells tend
to have many branches to help with communication.
One main function of red blood cells is to transport
oxygen from the lungs to other cells throughout the
body. An important function of certain bone cells is to
release hormones that help form bones.
Nerve cells have many
branches that help them send
signals throughout the body.
Cells that are similar in structure and function form
tissues. The cells that make up tissues work together to perform a specific activity. Animals have
four main types of tissue:
•
Muscular tissue is involved in movement. For example, skeletal muscles help move the body.
The stomach has smooth muscle tissue, which helps to churn foods and break the foods down
into smaller pieces. The smooth muscle of the stomach can also expand to hold large amounts
of food and then relax when empty.
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Organization in Plants and Animals
•
Epithelial tissue is found on the surface of organs and lines the inner spaces of the organs.
This tissue type also covers the entire body because it forms skin. The main functions of
epithelial tissue are protection, secretion (producing and releasing materials) and absorption
(taking in materials). Epithelial tissue that lines the stomach secretes chemicals that help with
digestion.
•
Nervous tissue functions to sense stimuli from the environment and send signals throughout
the body. For example, nervous tissue in the stomach sends signals
stimuli: things that an
to the brain to let a person know when he or she is hungry. Nervous
organism can sense
tissue also works with muscle tissue to help the body move. For
example, when you touch a hot object, the nervous tissue in your
hand sends signals to the brain to contract your muscles in order to
move your hand away.
•
Connective tissue has a variety of functions. This type of tissue connects and holds together
structures in the body, providing support and structure. Connective tissue includes bones and
fat tissue. Connective tissue is also found under epithelial tissue and helps to support the cells
of the epithelial layer. In the stomach, connective tissue can be found under its epithelial tissue
also.
The next level of organization in animals is the organ. Each organ is made of tissues with similar
structure and function. Examples of organs include the heart, skin (the largest human organ),
lungs, and stomach.
The organ systems are the next level of organization. An organ system consists of two or more
organs working together to perform a specific function for the organism. The human body is
organized into several main organ systems: circulatory, nervous, skeletal, muscular,
integumentary, endocrine, digestive, immune, reproductive, excretory, and respiratory systems.
Each system performs specific functions. For example, the integumentary system is made of the
skin, hair, nails, and glands. This system receives stimuli from the external environment and
protects the body’s deeper tissues and organs. The digestive
glands: organs that make
system is made of a number of organs. The stomach stores food
and release chemicals
and helps with digestion. The intestines digest food and absorb
called hormones;
nutrients. The liver works as part of the digestive system by
hormones control and
secreting bile, which is a substance that helps with the break down
regulate body processes
of fats, or lipids. A single organ can work with multiple organ
systems. For example, the liver also works with the circulatory
system to filter wastes in the blood.
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Organization in Plants and Animals
The final and most complex level of organization in animals is the organism. Organisms are entire
living things that perform basic life processes. Organisms take in materials, release energy from
food, release wastes, grow, respond to the environment, and reproduce.
Simple
The living units of organization from smallest to largest are cells,
tissues, organs, organ systems, and organisms. The images here
show, from left to right, are an epithelial cell, epithelial tissue, a
stomach, the digestive system, and a human body. Note that the
images are not to scale.
Complex
Suppose one organ in an organ system failed to work properly. How would the organ system be
affected? Would it still be able to function? Explain your reasoning.
Not all animals have the same levels of organization. For
example, sponges are simple aquatic animals. They are
multicellular; however, their cells are not organized into welldefined tissues. They do not have organs or organ systems. A
sponge’s essential life functions are carried out on the cellular
level.
Getting Technical: Magnetic Resonance Imaging Magnetic
Resonance Imaging, or MRI, is a procedure used by doctors to
Sponges commonly live and
help diagnose organ or organ system diseases. The procedure
grow on coral reefs.
uses magnets and radio signals to generate images of the
inside of the body. The magnets and the radio signals in an
MRI machine interact with the water in a patient’s body. The machine is then able to measure how
much water is present in any given area. This creates an image with various shades of grey from
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Organization in Plants and Animals
light (where there is a lot of water) to dark (where there is little water). Because the magnetic coils
are able create a magnetic force encircling the entire body, the MRI machine is able to image the
body in three dimensions, or in 3-D. This is displayed as a series of pictures showing one slice of
the body at a time. Doctors examine the images to look for structural abnormalities that may be
present in the organs.
An MRI machine generates a
magnetic force that encircles the
entire body.
An MRI machine
generated this image
of the brain and other
structures.
Organization in Plants
Like animals, plants are made of specialized cells that are organized
into tissues. For example, xylem is a tissue that moves water, while the
phloem is a tissue that moves sugars.
Plant tissues are organized into tissue systems. Plants have three
tissue systems:
•
The dermal tissue system covers the outside of the plant and
provides protection. The dermal tissue system includes epidermal
tissue and tiny openings, called stomata, that open and
close to allow for gas exchange.
•
The ground tissue system is a general tissue system
with a variety of functions including photosynthesis and
food storage. The ground tissue contains the
photosynthetic cells (chloroplasts) of the plant.
These plant cells
group together to
form tissue.
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Organization in Plants and Animals
•
The vascular tissue system is the system responsible for the transport of materials, including
water and nutrients, throughout the plant. Xylem and phloem are parts of the vascular tissue
system.
Which tissue system in plants is most similar to the integumentary system in animals? Explain
your reasoning.
Plant tissue systems are organized into organs. Plants have four main organs:
•
Leaves are the main organs used to capture sunlight used in
photosynthesis.
•
Roots are the main organs used to absorb water and nutrients from the
soil.
•
Stems are the main organs used to transport materials between leaves
and roots.
•
Reproductive organs (like flowers) produce seeds that grow into new
plants. Flowers usually consist of colorful petals that attract insects and
other pollinators.
Plant organs group together to form the two main organ systems of plants: the root system and the
shoot system. The root system is typically underground and includes the root and associated fibers
that branch off the main root. This system functions to anchor the plant and absorb water and
nutrients from the soil. The shoot system is typically above the ground and includes the stem, the
leaves, and the reproductive organs, such as flowers. This system has many functions including
photosynthesis and reproduction. As with animals, the organ systems of plants work together to
make up the structure and function of the entire organism.
The general organization in plants, from smallest to largest units, is shown below.
cells
tissues
tissue
system
organ
organ
system
organism
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Organization in Plants and Animals
A specific example of this organization begins with long, narrow, specialized plant cells that work
together to form the xylem, which is a tissue. The xylem works with the phloem (another tissue) to
form the vascular tissue system. The vascular tissue system works with the dermal tissue system
and the ground tissue system to form leaves, which are organs. Finally, leaves work with other
organs (roots, stems, and reproductive structures) to make up a plant.
Not all plants have all the tissue systems and organs. Mosses do not have vascular tissue. Without
vascular tissue, mosses cannot transport water long distances. This is why they can only grow in
wet areas and why they cannot grow very tall. Mosses also do not reproduce using flowers. They
use a simplified reproductive cycle involving tiny structures called spores.
What do you know?
The chart on the next page includes images of different structures found in animals or plants. For
each structure, describe the smaller living unit that makes up the structure. Also, describe the next
largest living unit. Write your answers directly in the chart next to each image. Watch out! Some
structures may not have a smaller or larger living unit. The first one is done for you.
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Organization in Plants and Animals
Plant
Tissue systems make up leaves. Leaves group together to
form part of the shoot system.
Leaf
Nerve Cells
Circulatory System
Ground Tissue System
Brain
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Organization in Plants and Animals
Identifying Plant Structures
To help students learn more about units of
organization in plants, dissect plant organs
and identify the tissue systems found within
the organs. You will need a veined leaf (such
as an oak or maple leaf), a stalk of celery, a
carrot, a knife, and a hand lens (if available).
Begin by identifying the veins of the leaf. The
veins represent the vascular tissue system of
the leaf, which is an organ. The dermal tissue
system can be peeled off carefully to show
the ground tissue system beneath. To peel off
the dermal tissue system, bend the leaf in half
until it snaps, and then peel back the clear
dermal tissue system. Be sure to do this in an
area of the leaf that is furthest from the thick
veins.
Next, explain to your child that the part of
celery that we eat, the stalk, is actually a
stem. Make a cross section of the stem; the
dermal tissue system is on the outside. The
vascular tissue system will look like clusters
of circles. This is easiest to see if a hand lens
is available. The rest of the cells in the stem
are in the ground tissue system.
Now explain to your child that the part of a
carrot that we eat is a root. Make a crosssection of the carrot. The root will look much
like the stem, but the vascular tissue system
is generally found in a single large bundle in
the center of the root.
Here are some questions to discuss with
students:
•
What was the smallest living unit of a
plant that you were able to observe?
•
What was the largest living unit you were
able to observe?
•
What might happen if a plant organ, such
as a leaf or stem, became damaged?
How would the organism be affected?
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