Lesson 13: Pair-of WHAT??!?

The last protozoan we will look at in detail is the paramecium, which is a member of phylum Ciliophora. 

Like the others we have studied, paramecia are unicellular heterotrophs that like to live in still water.  They are large compared to other protozoans and can often be seen without the aid of a microscope.   You can barely see them in this picture, but paramecia are covered with tiny hair like projections called cilia that enable the paramecium to move.   Look very closely at this video around the edges of the paramecium and you can see the cilia wiggling:

 

  Print the diagram below and color the cilia black, and then follow along as we discuss the organelles and other structures found in a typical paramecium.

 

 

As you may have noticed in the video, the paramecium, unlike the amoeba and the euglena, does not change its shape when it moves.  This is due to the very stiff outer pellicle that surrounds the cell membrane and holds the organism’s shape.  Color the pellicle light blue.

Paramecia are heterotrophic.  This means that they cannot make their own food and must obtain their nutrition from algae and other tiny microorganisms.  How does the food get inside the cell?  Well, each paramecium has an opening in its pellicle called an oral groove that is lined with cilia.  The cilia sweep bits of food through a hole called a mouth pore into a gullet, where food vacuoles are formed.  The vacuoles break away from the gullet and are suspended in the cytoplasm until the food is digested.  Find the large oral groove on the top of the diagram and color it orange.  The thin tunnel at the bottom of it is the gullet – color it dark blue.  Color all of the food vacuoles, including the one still attached to the gullet, light brown. Then watch this short video of a paramecium eating. Watch how the food vacuole gets larger and then eventually breaks off into the cytoplasm:

Waste is eliminated through an opening called the anal pore.  In the diagram, the anal pore looks like a small sunburst ( do not get it confused with the large contractile vacuole).  Color the anal pore dark brown.

On the left side you can see the large nucleus.  But because paramecium are so large, a smaller nucleus, called the micronucleus, is also necessary.  The micronucleus, above the large nucleus, is involved in reproduction.  The large nucleus, called the macronucleus, is in charge of making proteins, digesting food, and other processes that help the paremecium use energy.  Color the macronucleus red and the micronucleus pink. 

Contractile vacuoles, as you know, regulate the amount of water allowed in the cell and get rid of the excess.  The one in the diagram looks like a large sunburst.  Color it dark green.

Do you see the raindrop-shaped trichocysts all around the paramecium, right inside the pellicle?  These are sort of like protist armor – the paramecium can shoot tiny threads out of the trichocysts to trap  predators or to make themselves look larger in order to scare them away.  Color the trichcysts purple.

That leaves the cytoplasm.  Like amoeba, paramecium have two types: thicker endoplasm near the center, and thinner ectoplasm near the outer edges.  Color the endoplasm yellow and leave the ectoplasm clear.

If you have a prepared slide of a paramecium, take a few minutes to check it out now.  Draw and label what you see on a sheet of microscope paper.  Try to find as many of these structures as you can: Macronucleus, micronucleus, food vacuole, contractile vacuole, oral groove, gullet, pellicle, cilia.

Can you guess why paramecium are placed in phylum ciliophora? It is the phylum for all protozoans that move using cilia.  Here is a video of another member of this family: the Stentor.  Watch for the cilia moving near the tops of the organisms.

 

How many of these questions can you answer without looking back? Don’t forget to send me your answers!

• To what kingdom and phylum do paramecia belong?
• Are paramecia heterotrophic or autotrophic?  Are they unicellular or multicellular?
• How do paramecia move?
• Where do paramecia live?
• What keeps a paramecium from changing its shape like amoeba do?
• Why does a paramecium have two nuclei?
• What does a contractile vacuole do?
• How does a paramecium get rid of waste?
• What do the trichocysts do?

 

Then   TAKE THIS QUIZ to see how much you’ve learned so far about protozoa!