Cell Digestion - Parts of a Cell
Welcome to Quatr.us Study Guides!

Cell digestion

December 2016 - All cells have to have some way to get energy from outside themselves, or they will starve to death. The earliest, simplest cells, about 3.5 billion years ago, got their food by drifting around in the ocean until they came to a molecule of protein or another hydrocarbon, and then letting that molecule in through the cell membrane. Many cells still get their food this way today.

Plant cell

But by around 3 billion years ago some cells did different things. Sometimes the different things were not helpful, and those cells died. Some different things helped the cells get more food. These cells bent their cell walls, curving them in and out to make long arms. Then they could encircle the food with their arms and keep it from getting away. Some cells also began to make enzymes inside themselves that could react with bigger molecules or even other cells and break them down into small molecules that the cell could use. At first, the cell encircled its food with its arms and then spat out the enzymes into the ocean water to break down its food outside the cell.

But this was risky - sometimes the food floated away anyway before the cell could eat it. Successful cells began to encircle their prey completely with their arms to keep it from getting away. Then, about 2 billion years ago, a few eukaryote cells began to break off that bit of cell membrane and let it form a little bubble inside the main cell membrane, so that the food was inside the cell completely and the cell could eat it whenever it wanted to, or even store it for later. We call these bubbles vacuoles.

Once the food molecules were trapped inside the vacuoles, the cell could break the molecules apart to release the energy that held them together. Generally the part of the cell that began this process was the lysosome. Vacuoles got surrounded by the membrane of the lysosome, much the same way that the food originally got surrounded by the vacuole. Inside the lysosome there were powerful enzymes - molecules that could react with the food molecules to break them apart.

From the lysosome, these smaller molecules then moved to the mitochondria, where the mitochondria used other enzymes and oxygen to produce more chemical reactions to break up food molecules and release energy that the cell needed. This is how all eukaryote cells digest food even today, and it is how all the cells in your own body digest food. That's why you need both food and oxygen - because your cells need to combine food and oxygen to break them down and make energy to keep your cells alive.

Learn by doing: a project with lipids
More about lysosomes
More about mitochondria
More about enzymes

Bibliography and further reading:

More about mitochondria
More about Cells
More Biology
Quatr.us Home

For Presidents' Day, check out our articles about Washington in the Revolutionary War and Lincoln in the Civil War. Find out about the Constitution, the Bill of Rights and the other Amendments, and how Washington promised to include freedom of religion.
Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Quatr.us Study Guides
  • Publisher: Quatr.us
  • Date Published:
Proud of your class page, homework page, or resource page? Send it in and win a Quatr.us "Great Page!" award!
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article

Cool stuff we've been enjoying: Looking for birthday gifts? Check out these new Chromebooks - all the computer you need for only $229.00!. Then study in peace with these Beats wireless headphones - for the exact same price! When you're done, show off your presentation or watch a movie with this excellent smartphone projector for only $39.99!

Does your class page honor diversity, celebrate feminism, and support people of color, LBGTQ people, and people with disabilities? Let us know, and we'll send you a Diversity Banner you can proudly display!
Looking for more?
Quatr.us is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Quatr.us Study Guides, . Web. 22 February, 2017