What's the same between a bacterial cell and one of your cells?
There are many different types of cells, but they all have certain parts in common. As this image of human blood shows, cells come in different shapes and sizes. The shapes and sizes directly influence the function of the cell. Yet, all cells - cells from the smallest bacteria to those in the largest whale - do some similar functions, so they do have parts in common.
Common Parts of Cells
Cells with different functions often have different shapes. The cells pictured in Figure below are just a few examples of the many different shapes that cells may have. Each type of cell in the figure has a shape that helps it do its job. For example, the job of the nerve cell is to carry messages to other cells. The nerve cell has many long extensions that reach out in all directions, allowing it to pass messages to many other cells at once. Do you see the tail-like projections on the algae cells? Algae live in water, and their tails help them swim. Pollen grains have spikes that help them stick to insects such as bees. How do you think the spikes help the pollen grains do their job? (Hint: Insects pollinate flowers.)
As these pictures show, cells come in many different shapes. How are the shapes of these cells related to their functions?
Four Common Parts of a Cell
Although cells are diverse, all cells have certain parts in common. The parts include a plasma membrane, cytoplasm, ribosomes, and DNA.
- The plasma membrane (also called the cell membrane) is a thin coat of lipids that surrounds a cell. It forms the physical boundary between the cell and its environment, so you can think of it as the “skin” of the cell.
Cytoplasm refers to all of the cellular material inside the plasma membrane, other than the nucleus. Cytoplasm is made up of a watery substance called cytosol, and contains other cell structures such as ribosomes.
Ribosomes are structures in the cytoplasm where proteins are made.
DNA is a nucleic acid found in cells. It contains the genetic instructions that cells need to make proteins.
These parts are common to all cells, from organisms as different as bacteria and human beings. How did all known organisms come to have such similar cells? The similarities show that all life on Earth has a common evolutionary history.
A nice introduction to the cell is available at http://www.youtube.com/user/khanacademy#p/c/7A9646BC5110CF64/33/Hmwvj9X4GNY (21:03).
- Cells come in many different shapes. Cells with different functions often have different shapes.
- Although cells comes in diverse shapes, all cells have certain parts in common. These parts include the plasma membrane, cytoplasm, ribosomes, and DNA.
Use this resource to answer the questions that follow.
- What is included in a cell's cytoplasm? What is in the cytosol?
- How much cytosol is in a cell, compared to the total cell volume?
- Where are ribosomes made? What are ribosomes made from?
- How many ribosomes are in a typical liver cell?
- What are the two general locations ribosomes are located in the cell?
1. List and describe the four parts common to all cells.