Download Animal and Plant Classification

Animal and Plant
Classification
The Building Blocks
of Living Things
Think about the building blocks you played
with when you were younger. You started with
just one block. If you put a few blocks together,
you could build a house. If you put many blocks
together, you could build something complicated,
like a castle with towers. All living things—
plants and animals—are made of cells.
A cell is the smallest unit of a living thing.
You can think of cells as building blocks. Some
living things are made of just one block, or cell.
Most plants and animals are made by putting
thousands, millions, or even billions of cells
together.
Cells can have many jobs. Some cells help a
living thing to be healthy. Other cells help it to
adapt to its environment.
Microscopes make objects appear larger
than they really are. By looking at cells under a
microscope, scientists can see inside them and
learn how they work.
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The Parts of a Cell
Cells have different parts, and each part has a
specific job to do. The nucleus is like the “brain”
of the cell. The instructions for the cell’s job are
stored in the nucleus.
The cell membrane is a thin covering all
around the cell. It has two jobs. It separates the
cell from things around it. It also acts as a guard
that decides what can come into and go out of
the cell.
Cytoplasm holds everything a cell needs to
carry out its life processes. It is a material similar
to jelly that fills the cell. The nucleus floats in the
cytoplasm.
Plant cells have the same parts as animal
cells— plus some extras. The cell wall is outside
of the cell membrane. The walls of all the cells
help hold up a plant. Chloroplasts are the
parts of a cell that trap energy from sunlight so a
plant can make its own food.
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From Cells to Organisms
Cells have different shapes, depending on
the kinds of jobs they do. For example, nerve
cells are very thin. They act like wires that send
messages through the body. Nerve cells can be as
long as your arm or as short as the period at the
end of this sentence.
Cells that look alike and have the same shape
do the same job. These cells combine to build
tissue. For example, nerve tissue is made of
nerve cells.
Tissues of the same type combine to form
organs. For example, the brain is an organ that
is made of nerve tissue.
Organs that work together form an organ
system. Two organs—the brain and the spinal
cord—build the central nervous system in your
body. An organism is the complete living thing
that is made when all the parts are combined.
An organism is made of many cells. Unlike
an organism, a virus is a very tiny particle with
similarities to both living and nonliving things.
It uses plant and animal cells to make more
viruses.
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Sorting Living Things
Into Groups
There are more than a million organisms.
Who keeps track of them all? Biologists! In
order to identify, compare, and study all these
organisms, biologists use a classification system.
Using this system, they place every kind of
organism into a group. All the organisms in a
group have common characteristics.
Biologists would ask questions like these to
help them decide if a shark and a dolphin belong
in the same group.
Do sharks and dolphins have one cell or many
cells? They have many cells. That is a common
characteristic, so they belong in the same group.
Where do sharks and dolphins live? They
live in the ocean. That is another common
characteristic, so they still belong in the
same group.
How do sharks and dolphins get oxygen?
Sharks get oxygen from the water. Dolphins
get oxygen from the air. That is a different
characteristic, so they belong in different groups.
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Kingdoms—The Largest Group
Kingdoms are the largest groups in the
classification system. Many scientists divide
organisms into six kingdoms. The kingdom that
an organism belongs to depends mostly on how
many cells it has, what cell parts it has, where it
lives, and how it gets its food.
Dividing the Kingdoms
Sorting living things into six kingdoms is
only the beginning! Next, scientists divide the
members of each kingdom into smaller and
smaller groups. They use organisms’ features
to decide which organisms are in each group.
After kingdoms, the groups are divisions, classes,
orders, and families. The last two groups are
genus and species. Scientists use these last groups
to name animals. A genus is a group of animals
that are similar in many ways. For example,
a dog and a wolf are members of the same
genus. Their genus is Canis. The genus group is
divided one more time into groups of species. A
species is a group of animals whose members
can reproduce. The species name often describes
where the animal lives or what color it is.
The first part of an animal’s scientific name
is the genus. The second part is the species. So,
although you might name your pet dog Max, his
scientific name would be Canis familiaris.
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How Scientists
Classify Plants
To sort plants into groups, scientists look at
two main characteristics. One is the way that a
plant transports water and nutrients. The other is
how a plant reproduces.
Moving Water and Food
Some plants, called vascular plants, have
parts that look like tubes. Water and nutrients
from the soil move up and down these tubes to
the roots, stems, and leaves. Vascular plants are
all around you. You may have stepped on some
this morning, if you walked on grass. If you had
celery with your lunch, you ate one! The tissue
that makes up the tubes supports a plant’s stems
and leaves. Because of this, vascular plants can
grow to be very tall.
Plants without these tubes are called
nonvascular plants. These plants pass water and
nutrients through cell walls, from one cell to the
next. This process is very slow, so nonvascular
plants usually grow close to the ground. That
way, water and nutrients do not have to travel so
far. Some nonvascular plants are mosses, lichen,
and algae.
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Reproduction
The second way that scientists classify plants
is by how they reproduce, or make new plants.
One group reproduces by making seeds. A seed is
a structure with a protective covering. Inside the
seed is a young plant. In plants with flowers, the
seeds are in the flowers.
Conifers are plants that make seeds but do
not have flowers. In conifers, the seeds are in the
cones. Some plants have no seeds at all. They
use spores to reproduce. A spore is a single cell
surrounded by a cell wall. It can grow into a new
plant if it falls on a place where it can get the
water and food it needs. Ferns and mosses
have spores.
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How Scientists Classify
Animals
The animal kingdom is divided into two
main groups. One group is vertebrates, or
animals with a backbone. The other group is
invertebrates, or animals without a backbone.
Vertebrates
Scientists have divided vertebrates into five
smaller groups. This group includes mammals,
birds, reptiles, amphibians, and fish.
Reptiles
Let’s take a closer look at one group of
vertebrates—reptiles. Reptiles include lizards,
snakes, turtles, crocodiles, and alligators. These
animals live in the water and on land. As you
can see from the chart, reptiles breathe air with
their lungs. Many people are very surprised
when they touch a reptile for the first time. They
expect them to be wet and slimy, but they have
dry skin covered with scales.
People often confuse crocodiles and alligators
because the bodies of these reptiles are similar
in many ways. An easy way to tell them apart is
to look at their mouths. You can see a crocodile’s
teeth when its mouth is shut, but you cannot see
an alligator’s teeth in that position.
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The Life Cycle of a Reptile
Sea turtles spend most of their time
underwater, where they swim, sleep, and eat.
Like all reptiles, they have to come to the
surface to breathe air with their lungs. If they
are swimming, they need to come up for air
about every five or ten minutes. However, if they
are asleep, they can stay underwater for hours.
Male sea turtles rarely come on land, but female
sea turtles come on land about six times each
nesting year to lay their eggs.
Scientists are not sure how old female sea
turtles are when they nest for the first time. But
they do know that they swim back to the same
area where they were hatched as babies—even if
that place is miles and miles away. A female sea
turtle lays her eggs on land. Baby turtles hatch
from the eggs between forty-five and seventy
days later, and they make their way to water.
The turtles grow to be adults who will reproduce.
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Animals Without a Backbone
Animals without a backbone are called
invertebrates. You might be surprised to learn
that most animals in the world are invertebrates.
Arthropods are the largest group of
invertebrates. This group includes ticks, spiders,
bees, shrimp, scorpions, and centipedes. At
first, these animals seem very different because
some swim, some fly, and some crawl. However,
they have two common characteristics that
cause scientists to group them together. The first
characteristic is that all arthropods have legs
and a body that are divided into sections. The
second is that all arthropods are covered with a
lightweight, hard skin that protects them. This
hard skin is called an exoskeleton.
The second largest group of invertebrates is
mollusks. This group includes scallops, oysters,
squid, and snails. Mollusks have soft bodies.
Some have a hard shell and some don’t. Most
mollusks live in water, but some live on land
in damp places. Most mollusks are only a few
inches long, but a few kinds are huge!
Giant clams, for example, can grow to more
than four feet long and weigh more than five
hundred pounds!
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The Life Cycle of a Mollusk
When octopuses are ready to mate, the male
fertilizes the female’s eggs. The female attaches
the fertilized eggs to a rock or places them in a
hole. Over the course of several days, a female
may lay more than 100,000 eggs! If the female
has laid her eggs in a hole, she will often seal
up the hole to protect the eggs and ensure that
they are not harmed. Females guard the eggs
constantly.
Depending on temperature, the eggs hatch
anytime between four weeks and seven months
later. A short time after the baby octopuses
emerge from their eggs, the female octopus dies.
When the baby octopuses emerge from their
eggs, they float to the top of the water. They stay
there until they grow larger and can return to
the bottom of their water habitat.
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Animal Adaptations
Adaptations are physical features or behaviors
passed on from parents. Adaptations help
animals get food, protect themselves, move, and
reproduce. Animals with the best adaptations
have a better chance at getting the resources
they need, so they have a better chance of
reproducing.
Adaptations That Help and Protect
Many animals have physical adaptations
that help them move. Did you know that birds
have hollow bones to make them lighter? Did
you know that fish have bags of air in them that
help them float? Or that flamingoes have long
necks so they can submerge their heads in water
and find food in the muddy bottom? What about
snails? They have a flat foot that oozes a sticky
liquid. They move by sliding along paths of their
own slime.
Shapes and colors can provide protection by
making animals nearly invisible. When the long,
thin razor fish holds itself straight up and down
in the water, it looks like a piece of floating grass.
Features such as claws, tusks, and horns protect
some animals.
Chemicals are another kind of adaptation.
Some chemicals give animals a nasty smell or
taste so other animals won’t eat them. Others
poison their victims.
An octopus can use its sharp teeth to drill
a hole in a clamshell. It then injects poison
through the hole. After the clam is poisoned, its
shell can be opened easily.
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Animal Instincts
Instincts are behaviors that are inherited from
parents. These natural behaviors tell young
animals how to move, how to hide, and how to
catch food. They will remember these things all
their life. Remember the baby turtles that find
their way to the sea? That is an instinct.
Migration and Hibernation
Migration is an instinct. Many animals
migrate to find food as seasons change. Arctic
terns leave the Arctic Ocean in the fall, when the
ocean begins to freeze and fish are scarce. They
fly to Antarctica, where fish are plentiful. In the
spring, when the ice in the Arctic Ocean begins
to melt, the terns fly home to nest.
Another natural behavior that does not need
to be learned is hibernation. Some kinds of
mammals, reptiles, and amphibians hibernate,
or become inactive, when the weather is very
cold and food is hard to find. Chipmunks, for
example, eat a lot in the fall. The food is stored
as body fat that gives them energy during winter,
when they hibernate. They don’t sleep straight
through the winter but wake for short periods to
move around and snack on saved food.
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Animals Learn
Not all animal behaviors are instincts.
Many animals learn behavior from their
parents. Mother bears teach their cubs to fish.
And wolves have a way of teaching their young
to avoid traps!
All living things, from the smallest cell to the
largest organism, can be classified. Knowing
the classification of living things gives us
information about what they are made of and
how they adapt.
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Glossary
cell
t he smallest unit of a living
thing that can carry out all
life functions
chloroplast
t he part of a plant cell that
traps energy from sunlight
so the plant can make its
own food
cytoplasm
t he substance in a cell that
contains what the cell needs to
carry out its life processes
genus
group of closely related
a
animals
invertebrates animals without a backbone
nucleus
the control center of a cell
species
group of animals whose
a
members can mate and
produce offspring that can also
produce offspring
vertebrates
animals with a backbone
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