Lesson 5 – CELL-ebration

Now we are ready to begin a detailed study of living things, and we will start by looking at cells.  All living organisms on earth are made up of very tiny compartments that hold the equipment and information necessary to keep the organism alive.  In order to fully understand life we must understand how cells are organized and how they work.  Cells can be divided into two major divisions:

EUKARYOTIC cells are surrounded by a membrane and contain special structures called organelles that perform important functions.  All the cells that make up animals, humans, plants are eukaryotic.

PROKARYOTIC cells do not have organelles.  Bacteria are prokaryotic cells.

We will spend some more time looking further at prokaryotic cells in the next lesson.  For now, let’s focus on eukaryotic cells.  Click here to print diagrams of a typical animal cell and a typical plant cell.  Then color the parts as we discuss them: 

As I said, eukaryotic cells contain many different organelles which are resonsible for performing many different jobs within the cell.  Let’s look at the outside covering of a typical cell and work our way in.

Each eukaryotic cell is surrounded by a thin membrane which holds the cell together and keeps its contents contained.  In the pictures, the CELL MEMBRANE is a thin covering over the  entire outside of the cell.  In the plant cell it is the innermost of the two layers.   Color the cell membranes of both cells YELLOW.  Plant cells have an additional, thicker covering over the cell membrane, called the CELL WALL,  which helps the cell hold its shape.  Color the cell wall on the plant cell dark green.

Inside the cell are many smaller structures, called organelles, which are each responsible for a different function. They are suspended in place by a jelly-like fluid called CYTOPLASM. In the diagrams, the cytoplasm is all of the empty space within the cell membrane.   Leave the cyptoplasm white..

The NUCLEUS is the control center of a cell. It contains the DNA, which is the code which tells the cell what traits the organism will have.  Find the large nucleus near the center of each diagram and color it gray.  Inside the nucleus is a dark NUCLEOLUS, which is involved in the manufacture of protein. Color it BLACK.

The nucleus is surrounded by a thin NUCLEAR MEMBRANE that holds its contents together and regulates what goes in and out of the nucleus.  Color the nuclear membrane BROWN.

The MITOCHONDRIA are oblong organelles that produce energy for the cell. In the animal cell diagram there are three mitochondria near the top. In the plant cell there are four, and they have wiggly lines inside them.  Color them RED.

The GOLGI BODIES, which are sometimes called golgi apparatus, look like a stack of curved pancakes. They are on the right hand side of the animal cell diagram and in each bottom corner of the plant cell.  They package fats and proteins the cell needs and either deliver them to other parts of the cell or store them until they are needed later. Color both the plant and animal golgi apparati DARK BLUE.

RIBOSOMES, which look like tiny circles in the pictures, are responsible for making proteins. Color the ribosomes PURPLE.  Ribosomes are usually not considered true organelles because they are not bound by membranes and are very simple, but almost all cells – including prokaryotic cells – have them.

The ENDOPLAMSIC RETICULUM, or ER,  looks like fingers or tentacles reaching through the cytoplasm. There are two types:  ROUGH and SMOOTH.   SMOOTH ER makes important chemicals such as fats.  ROUGH ER, which is dotted on the surface with ribosomes, makes protein. Color the rough ER PINK, dotted with PURLPLE ribosomes, and the smooth ER PINK

LYSOSOMES are like the garbage trucks of a cell – they break down the cell’s waste and arrange for it to be carried to the outside of the cell. The lysosomes in the animal cell diagram are large circles. Color them ORANGE.  Plant cells do not have lysosomes.

MICROTUBULES, which are mostly found in animal cells, are strands of proteins that help the cytoplasm hold its shape.  Microtubules also make up organelles called CENTRIOLES.  Cells reproduce by dividing in half, and centrioles are  responsible for this division.  The microtubules in the animal cell drawing are thin x-shaped structures.  Color them BROWN. 

Plants use a green pigment called chlorophyll in the process of photosynthesis, by which they make their own food.  This pigment is stored in organelles called CHLOROPLASTS.  Color the two large chloroplasts near the top corners of the plant cell GREEN.

Lastly we’ll take a look at the FLAGELLUM, which looks like a tail near the upper left of the animal cell.  Not all cells have flagella, but those who do can swim about because flagella are responsible for movement.  Color the flagellum GRAY.

Now remember: not all cells contain all organelles.  Prokaryotic cells contain no membrane-bound organelles. Smaller eukaryotic cells have fewer organelles.  Some  organelles are specific to animal cells.  Plant cells, which we will discuss in more detail later, contain some organelles that you will not find in animal cells.  But it is important to understand and recognize common organelles  and understand their functions, so let’s spend some time reviewing what we have read. As we work through the next few lessons, refer often to your colored cell for reference.

Before we go on, practice these flashcards over and over until you can identify the organelle quickly and easily.  From the flashcard page, hit the “start study session” link in the top left. Make sure to switch the sequence to “definition then term” before you click on the “begin” button.