Interaction of Major Systems & Processes in Animals

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  • 0:04 Animal Structure
  • 0:45 Organelles
  • 1:24 Cells & Tissues
  • 2:42 Organs & Organ Systems
  • 4:10 Organisms
  • 4:46 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, you'll learn about interactions at all levels of animals: organelles, cells, tissues, organs, organ systems, and organisms themselves. You'll also gain a better understanding of the complexity of the organization of living things.

Animal Structure

Living things are all around us, including ourselves and other people. When you zoom in on the microscopic level, all living things are made of cells, the basic units of life. Animal cells are composed of tiny compartments called organelles that do different jobs inside the cell.

Cells in different parts of our body contain different organelles. Even though these parts are microscopic, they all play a role in regulating the processes in our bodies that work to maintain homeostasis, or balance within the body. Today, we're going to learn how different parts of animals work together, from the smallest compartments, organelles, to large-scale interactions between entire organisms.


Organelles regulate all processes inside cells. For example, cellular signals let the nucleus, the brain of the cell, know that more proteins are needed. The DNA is copied into another form, called RNA, that can leave the nucleus. The RNA is transported to another organelle, called a ribosome. The ribosomes read the RNA and make proteins needed for the cell.

Sometimes, two organelles, called the endoplasmic reticulum and the Golgi, assist in shipping proteins where they need to go in the cell. When enough of the protein has been made, the cell sends signals to the nucleus to let it know to stop making the protein.

Cells & Tissues

Cells not only have processes going on inside them, but they also interact with each other. For example, cells in the brain, called neurons, talk to other parts of the body to control our actions. Special neurons, called motor neurons, control movement. When you decide to move your body, for example to open your computer and log in to, your brain sends an electrical impulse through the neurons in your spine. These neurons connect to muscle cells (myocytes) in your arm. The neurons send a chemical signal to the myocytes, which causes your muscles to contract and take the actions necessary to open your computer.

A collection of cells is called a tissue. There are many types of tissue in your body, like the muscle tissue that helps you move, connective tissue which makes up your bones, blood, fat and cartilage, and epithelial tissue that lines your digestive system and blood vessels.

Tissues need to work together to make your organs function. For example, during exercise your muscle tissues require oxygen to keep making energy to power your actions. Your blood vessels are lined with epithelial tissue that creates the tubes needed to bring blood to your muscle. Inside the blood vessels, a liquid called plasma suspends red blood cells, a type of connective tissue that binds to oxygen, allowing it to be delivered to muscle tissue.

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