Download ORGANIZATION IN PLANTS AND ANIMALS

ORGANIZATION IN PLANTS AND ANIMALS
reflect
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
stimuli: things that an
environment and send signals throughout the body. For
organism can sense
example, nervous tissue in the stomach sends signals to the
brain to let a person know when he or she is hungry. Nervous
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 system is
made of a number of organs. The stomach stores food and
helps with digestion. The intestines digest food and absorb
glands: organs that make
nutrients. The liver works as part of the digestive system
and release chemicals
by secreting bile, which is a substance that helps with the
called hormones;
break down of fats, or lipids. A single organ can work with
hormones control and
multiple organ systems. For example, the liver also works
regulate body processes
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
what do you think?
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.
look out!
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 well-defined 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
Sponges commonly live and
used by doctors to help diagnose organ or organ
grow on coral reefs.
system diseases. The procedure 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
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ORGANIZATION IN PLANTS AND ANIMALS
grey from 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.
These plant cells
group together to
form tissue.
• 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.
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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.
what do you think?
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.
look out!
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
connecting with your child
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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