Cells

 

 

OverviewDiscovered by Robert Hooke in his study of cork, cells are the basic unit of life.  All living things are composed of cells, from the tiniest of organisms to the largest.  Cells show diversity; differing in shape, size and function.  Such diversity can be seen between species as well as within species.

 

Each cell in turn has 3 basic components; the cell or plasma membrane, the cytoplasm and the nucleus.

 

Suspended in the cytoplasm are different organelles that help the cell to perform its basic function.

 

Animalcules Although these organisms are singled celled, they look very different. 

 

Some such as the euglena are green and have tail like structures called flagella that they use to propel them through their watery environment. 

 

Paramecium are slipper shaped and have cilia or hair like extensions that they too use for locomotion. 

 

The amoeba however doesn’t have a specific shape.  It changes shape by extending pseudo pods which it uses for locomotion as well as to engulf its food. 

 

The amoeba in fact feeds on other unicellular organisms such as bacteria and paramecium.

Click on the picture above to see!

 

 

History

Just as we have an external boundary to our body called the skin, cells too have an external boundary called the cell membrane or the plasma membrane.  This membrane is made up of phospholipids or fat- like substances, proteins, carbohydrates and even cholesterol. 

 

Although we absorb certain substances through our skin, it is impermeable to others.  The cell membrane too allows some substances to pass through it while others cannot.  It is thus said to be selectively permeable. 

 

Cell membrane

Robert Hooke observed dead cells of cork, carrot and leaves.  The box like pattern of cells he saw was intricate.  Although beautiful, they did not show signs of life. 

 

Using a microscope that he built Anton van Leeuwenhoek however saw cells that were alive. He heard about a lake that had become cloudy and green and set out to discover the reason.  He took a sample from the lake and examined it under one of his microscopes.  He was amazed at what he saw!  He saw “little animalcules” of various shapes and colors.  No one had ever seen life under the microscope.  He took some tarter from his teeth and mixed it with water and again he saw living organisms.  How exciting!

 

Today, we know some of these animalcules or unicellular organisms as bacteria, amoeba, paramecium and euglena. Far more of them exist than we could ever dream of. 

 

Nucleus & Organelles

Plant and animal cells share many similarities. They have external boundaries, a nucleus and organelles suspended in the cytoplasm.  They also have differences.

 

Where To Go

 

Do you know what the similarities and differences are?

 

Cellsalive

 

Click on this interactive website to find out!

What To Do

Once you have arrived at the website,

*      Click on Animal Cells to see picture

*      Move the mouse to identify each part of the cell

*      Click on list of organelles to find out more about each one.

*      Do the same for the Plant Cells.

 

On the paper provided, label the following parts:

  • Cell membrane
  • Cell Wall
  • Nucleus
  • Vacuole
  • Endoplasmic reticulum
  • Ribosomes
  • Golgi apparatus
  • Chloroplasts
  • Mitochondria
  • Lysosomes

 

The cytoskeleton is the supporting structure for the cell as our bones are to our body!

 

Now that you are familiar with each, list 3  similarities and  3 differences?

 

 

 

 

References:

http://www.aichi-gakuin.ac.jp/~jeffreyb/dental/micro.html

http://www.cellsalive.com/toc.htm

http://www.ucmp.berkeley.edu/history/hooke.html

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.html

http://staff.jccc.net/aalarabi/memb_related_mov.htm