Science

Cell Structure

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A cell is the smallest unit in a living organism that is capable of carrying out all of the activities of life. It would stand to reason, then, that a cell could survive by itself. Indeed, there are many single-celled organisms that can be found all around us, such as an amoeba (a single-celled organism found in water); however, most of the living things we see are made of billions of cells that all work together. In the 17th century, after the invention of the microscope, Robert Hooke was able to see cells for the first time. Since then scientists have learned much about cells and have developed the Cell Theory, which says…

• A cell is the basic unit of life.
• All organisms are made of one or more cells.
• All cells come from existing cells.

There are two basic types of cells: plant and animal. All cells can be classified as one or the other. For the most part, they are very similar; however, there are a few important differences. Let's look at what they have in common first.

Plant and animal cells both have the following:

• A cell membrane (plasma membrane).
• A nucleus.
• Cytoplasm (a jellylike substance that fills the inside of a cell.
• Organelles (special structures inside a cell that each perform a necessary activity).

Plant cells have the following:

• A cell wall.
• Chloroplasts (one type of organelle).

Look at the following diagram. A plant cell cross-section is shown on the left and an animal cell cross-section is shown on the right.

Cell Membrane

Protects the cell, controls what goes in and out of the cell, and maintains the cell's shape. Both animal and plant cells have cell membranes.

Mitochondrion

Produces energy for the cell. Both animal and plant cells have mitochondrion.

Endoplasmic Reticulum

Transports protein throughout the cell and produces and stores lipids. Both animal and plant cells have endoplasmic reticulum.

Nucleus

Controls all activity of the cell. Contains DNA, the cell's genetic material. Regulates the production of proteins required by each cell to carry out its function. Both animal and plant cells have a nucleus.

Ribosomes

Manufactures protein and may be found in the cytoplasm or attached to the endoplasmic reticulum. Both animal and plant cells have ribosomes.

Golgi Apparatus

Modifies proteins so they are in usable form, packages proteins in membrane-bound sacs, releases them and sends them to other parts of the cell or releases them from the cell to be used elsewhere. Both animal and plant cells have Golgi Apparatus.

Chloroplast

Carries out photosynthesis, the reaction necessary to make food.

Central Vacuole

Stores materials for the cell such as food, water, enzymes, and waste products.

Cell Wall

Provides the physical support for the plant cell, much like the cell membrane does in an animal cell.

Both plant and animal cells are very complex, yet they are very similar when compared to each other.

Now look at the Venn diagram that compares and contrasts plant and animal cells. Think about the cross-sectional cell diagram above. Both are explanations of the same concepts but use different approaches to visually explain the information.

Isn't it interesting that there is so much diversity among living things, yet if you look at their cells, they are similar? The only real difference between a human cell, a horse cell, and a chicken cell is the kind of genetic information found inside the cell's nuclei.