Internal Structures of Organisms: Lesson for Kids

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  • 0:04 Structures
  • 0:36 Animals
  • 1:44 Plants
  • 2:55 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

The external structures of organisms are easy to identify. They are what you can see when you look at a living thing. But do you know what's inside plants and animals that helps them survive and grow? Come find out!


All organisms, or living things, have external structures. 'External' means 'outer.' A plant's external structures include roots, stems, leaves, and flowers. Meanwhile, most animals have a body, arms, legs, and a head. External structures are what you see on the outside. But, do you know what's inside?

The internal structures are the inner pieces and parts that keep organisms alive, help them grow, and help them reproduce. Here, we will learn about some basic internal structures of both plants and animals and the functions of those internal structures.


The internal structures of an animal are essential to its survival. For example, inside their bodies, a lot of animals (including you!) have a heart. The heart works as a pump to move blood through the animal's blood vessels.

Blood vessels are like highways that travel to every inch of your body. The blood inside the vessels contains important chemicals that your body uses to grow and work, like nutrients (including vitamins and minerals), gases (including oxygen and carbon dioxide), and hormones.

The stomach is an important internal structure because it's where an animal gets nutrients. First, the animal eats food, and then the stomach breaks that food down, sending the good nutrients to the blood and getting rid of everything else.

A lot of animals, such as humans, also have lungs that are used for breathing. When you breathe in, your lungs pull in oxygen, which is a gas from the environment that your cells need to function. Then when you breathe out, the lungs release carbon dioxide, which is a waste gas that your body must remove to stay healthy.

The brain is one of the most important internal structures of any animal! The brain takes all the sensory information an organism receives, like from your eyes, ears, and nose, and tells the body what to do with it. Much of your body would not function without your brain.


Did you ever pick a flower for someone? When you snipped the stem, you might have noticed a gooey substance dripping from the cut end. That goo found on the inside of a plant might not look very impressive, but it contains important internal structures that transport substances around the plant, much like the blood vessels inside of you transport things around your body.

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