a. Explain that cells take in nutrients in order to grow, divide and to make needed materials. S7L2a
b. Relate cell structures (cell membrane, nucleus, cytoplasm, chloroplasts, and mitochondria) to basic cell functions. S7L2b
1. Cells are the smallest single unit that can maintain life. Within each cell are a collection of organelles that perform specific functions. In 1855 a scientist named Rudolph Virchow consolidated the published work of other scientists and drew accurate conclusions about cells. His hypothesis, which we now call the Cell Theory, was composed of the first three statements shown:
1. All living things are made up of cells.
2. The cell is structural & functional unit of all living things.
3. All cells come from pre-existing cells.
4. Cells contain inheritable information which is passed from cell to cell during cell division.
5. Cells are basically the same in chemical composition.
6. All energy flow (metabolism & biochemistry) of life occurs within cells.
Several additional facts have been added to the cell theory since then. The “Modern Cell Theory” also includes the last three statements as shown.
A unicellular organism such as an amoeba is capable of carrying out all the necessary functions to live, reproduce, and continue as a species. A single cell can also exist as part of a multicellular organism, having many cells, carrying out varying functions according to its cell type. Cells, like any living organism, must have a way to obtain and use energy as well as a way to remove wastes. A look at the organelles and their functions will illustrate how these functions are accomplished. Cells are classified into two Domains according to their specific characteristics:
A. Prokaryotic cells are very simple cells that have few organelles. These cells do not have a nucleus, but do have
DNA. This DNA contains the “blueprints” to control the cell’s growth and reproduction. There is a cell membrane surrounded by a cell wall that encloses its cytoplasm and a few other organelles. Bacteria are prokaryotic cells. Notice that some bacteria are covered with short hair-like structures known as pili as well as a long whip like flagellum that it can use to move.
The diagram of atypical bacteria.
An electomicrophotograph of actual bacteria
B. Eukaryotic cells have the organelles found in bacteria plus many more that specialize in various tasks. These different organelles function to digest food, convert food to cellular energy, break down waste products, assist with reproduction of new cells and many other activities. All cells except bacteria are eukaryotic.
Image 1 – B – 1 illustrates key differences between prokaryotes and eukaryotes http://en.wikipedia.org/wiki/Image:Celltypes.svg 2. Cell organelles vary in size and have a structure that best enables them to perform their tasks. The major organelles and their functions are listed below:
A. Nucleus: frequently the largest and most visible organelle; a covering, called a nuclear envelope, containing many tiny holes that allow some of its contents to leave and return as needed; the cell’s DNA and RNA are on chromosomes contained within the nuclear envelope; the DNA contains a complete set of the organism’s genetic information and controls all aspects of the cell’s life; sometimes called the “control center”. The image of the nucleus shows how complex an organelle it is. The nuclear pores allow its RNA to leave the nucleus as needed. DNA inside the nucleus is referred to as chromatin and is not distinctly visible until just before cell division. A dark staining area inside the nucleus is the nucleolus. The nucleolus makes ribosomes that will leave the nucleus.
Notice the dark region within this nucleus that is the nucleolus.