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Cell Theory
Next Generation: MS.LS1.1 NGSS

Cell Theory

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This lesson will discuss the cell theory as it relates to all cells and will describe the basic characteristics of all cells.

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Tutorial

What's Covered

Welcome to the lesson on cell theory. In this lesson today, you are going to learn more about the cell theory, as well as basic characteristics of all cells.

  1. Cell Theory
  2. Basic Characteristics of All Cells
  3. Prokaryotic and Eukaryotic Cells

1. Cell Theory

As you know, a theory is a scientific explanation for something that has been thoroughly tested. The cell theory is actually a theory that explains characteristics of cells-- how cells behave.

Term to Know

Cell Theory

A theory that states all things are made of cells, cells are the smallest unit of life, and all cells come from preexisting cells

The cell theory is the work of several scientists who came up with three points that they believe explain characteristics of cells. They came up with these points through various types of testing and experiments and observations

1. All organisms are made up of cells.

If you'll remember, an organism is a living thing; so anything that is living is made up of cells.

Term to Know

Cell

The smallest unit of life

2. Cells are the smallest units of life.

The smallest organism is going to be made up of one cell; if it's not made up of cells, it can't be living and a cell, therefore, is the smallest unit of life. You can probably think of many unicellular organisms that are just made up of one cell, and they are the smallest living things

3. All cells arise from preexisting cells.

Cells don't just spontaneously appear. New cells are made from preexisting cells, through either meiosis or mitosis.


2. Basic Characteristics of All Cells

All cells, whether they're prokaryotic or eukaryotic-- which you’ll learn more about in just a second-- have three main characteristics in common:

1. All cells have a plasma membrane.

A plasma membrane is just something that will enclose all of the cell parts.

Term to Know

Plasma Membrane

The membrane which surrounds the outer body of the cell and controls what can enter and exit the cell

2. All cells have DNA.

DNA is genetic information and all cells contain some sort of genetic information that allows the cell to function and reproduce.

Term to Know

DNA

The macromolecule that contains all of an organism's genetic information

3. All cells have cytoplasm.

Cytoplasm is basically just like a jelly-like fluid that fills the inside of the cell. It protects the cell and kind of acts as a medium for all the organelles to the in.

Term to Know

Cytoplasm

The jelly-like substance found inside of a cell which holds all other organelles


3. Eukaryotic and Prokaryotic Cells

The two main categories of cells are prokaryotic and eukaryotic cells. To better understand the differences between prokaryotic and eukaryotic cells, refer to the image below.

Screen Shot 2015-11-28 at 10.58.42 AM.png

Terms to Know

Eukaryotic Cells

The type of cell which holds all of its genetic information inside of a membrane bound nucleus

Prokaryotic Cells

The type of cell which does not contain a nucleus

Eukaryotic Cells

Eukaryotic cells are cells where the DNA is contained in a nucleus. Our cells are all eukaryotic, because they all contain a nucleus.

Screen Shot 2015-11-28 at 10.58.42 AM.png

Another characteristic of eukaryotic cells is that they, like all cells, have a plasma membrane which is the outer layer of the cell that encloses all of the cell organelles. In other future lessons, you're going to get into more detail about characteristics of the plasma membrane.

To give you a little introduction to that, the plasma membrane of our cells is made up of a lipid bilayer which is composed of two layers of phospholipids. That lipid bilayer is what makes up the plasma membrane of your cells. And that helps to control what goes into and what can come out of the cell. It also contains DNA within the nucleus. All the free space within the cell is the cytoplasm.

Something else you might want to know about eukaryotic cells is that, generally, they are more complex than prokaryotic cells and they contain a lot more organelles.

Below you will see an image of a mitochondria, which makes energy for the cell. You will see some ribosomes, some other cell organelles you might be familiar with, endoplasmic reticulum, Golgi apparatus, et cetera. So they have several organelles contained within that plasma membrane.

Prokaryotic Cells

Prokaryotic cells do contain DNA and as we said all cells contain DNA. But the difference between a prokaryotic cell and a eukaryotic cell is that in a prokaryotic cell, the DNA is not contained within a nucleus. But it does still have the plasma membrane, which is the outer layer of the cell, and it does still have cytoplasm.

Screen Shot 2015-11-28 at 10.58.42 AM.png

You'll notice in the prokaryotic cell, there are some ribosomes in there as well, which help to make proteins for the cell.

Prokaryotic cells are a little bit less complex than eukaryotic cells and generally smaller in size. Many prokaryotic cells have something which is called flagella. Basically, that's just a means of movement for the cell, which is something eukaryotic cells don’t have.


Summary

This has been an overview of the cell theory, as well as some basic characteristics of prokaryotic and eukaryotic cells.


Keep up the learning and have a great day!

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Cell Theory

    A theory that states all things are made of cells, cells are the smallest unit of life, and all cells come from preexisting cells

  • Cell

    ​The smallest unit of life

  • ​Plasma Membrane

    ​The membrane which surrounds the outer body of the cell and controls what can enter and exit the cell

  • DNA

    The macromolecule that contains all of an organism's genetic information

  • Cytoplasm

    ​The jelly-like substance found inside of a cell which holds all other organelles

  • Prokaryotic Cells

    ​The type of cell which does not contain a nucleus

  • Eukaryotic Cells

    ​The type of cell which holds all of its genetic information inside of a membrane bound nucleus