Name: ______________________
Animals
Directions: Read, highlight, and answer the questions on schoology.com.
What is an animal? It's a simple enough question, but the answer is kind of difficult (isn’t everything in cell
biology?). Below, we'll walk through the characteristics that make a living thing an animal and attempt to
figure out what exactly an animal is.
So what is an animal? It's easy to say that a giraffe, a whale, or a dog is an animal. But when it
comes to making a list of animal characteristics—identifying things shared by all animals—it’s
kind of difficult (but we are still going to try ).
The list that follows describes characteristics shared by all animals, from snails and zebras to mongooses
and sea stars. These characteristics help us to say that coral is an animal but not a plant. That seems kind
of weird saying that coral is an animal, but it meets the characteristics below.
All animals are eukaryotes.
If you recall, all living organisms can be sorted into two groups depending on one organelle, the
nucleus. These two groups are called prokaryotes and eukaryotes.
Prokaryotes have no nucleus while eukaryotes have a nucleus. In eukaryotes, the nucleus holds
the cell's genetic material in an organelle called the chromosome (DNA). In prokaryotes, the
chromosomes are located in the middle of the cell and just float around inside that area.
Since animal cells have a nucleus, that makes them eukaryotes. Their DNA is organized into chromosomes
which are located inside the nucleus.
All animals are heterotrophs.
All living things need energy in the form of an element called carbon to help them grow, develop, and
reproduce. There are two ways an organism can get the food they need:


An organism can get food from the air they breathe (carbon dioxide) and combine it with sunlight to
make energy. They can also get the food chemically from the ground absorbing it into their bodies.
The term autotroph describes these organisms. We’ve talked about autotrophs before being
chemoautotrophs (chemical) and photoautotrophs (sun).
An organism can get the food they need by getting it from other living organisms that are made up of
carbon. They get it this way by scavenging and eating other organisms. The term heterotroph
describes this type of organism.
Remember from our discussion of plants that green plants are photoautotrophs. They take energy from
the sun and use it along with carbon dioxide in the air to produce sugar. In contrast, all animals are
heterotrophs. They eat plants and other organisms as a way to get their carbon, the energy they need to
live.
Animals are multicellular. Most animals (with the exception of sponges) have bodies that are
differentiated into tissues.
Animals' bodies are made up of many cells (which is why we are multi-cellular). In most animals, those
cells are organized into different tissues that perform different functions. During the development of an
animal (the very early part of reproduction), cells differentiate so they can perform different jobs.
Groups of cells with similar jobs that perform a common function are referred to as a tissue. One
exception to this is sponges which do not possess tissues (they don't have muscles or nerves). Plants also
have cells that form tissues and perform special jobs.
Most animals are capable of movement.
Unlike plants, which are fixed to where they grow, most animals are able to move. One exception is again
sponges and coral, which are fixed in one place. Animals that do move can move quickly which is of great
benefit when compared to other organisms.
Most animals undergo sexual reproduction although a small number are capable of asexual
reproduction.
Most animals reproduce sexually (egg and sperm). This means genetic information is combined between
parents and the offspring has an equal blend of chromosomes from both parents. Remember from our
reproduction discussion that this is a benefit since the offspring are now slightly different.
There are a few animals that are capable of asexual reproduction. These include sharks, frogs, and snakes
to name a few. Keep in mind though that this type of event only happens during extreme moments. It’s
not a normal/typical way of reproducing.
When you are done, go to schoology.com and answer the questions under “animals.”