Chapter 3: Cells
All living things are made of cells. Cells are microscopic; cells were first identified in 1665.
Microscopes
1) Light microscopes - focus light on the specimen.
- advantages : you can see living cells in color, microscopes are portable and cheap.
- disadvantage : magnification only up to 1000 times.
2) Electron microscopes - focus a beam of electrons on the specimen.
- advantage : high magnification ( up to 1 million times ).
- disadvantages : you can only see dead cells in black/white, not portable and expensive.
Prokaryotic cells are in bacteria. They are small, and have no nucleus or organelles.
Eukaryotic cells are in plants, fungi, animals. They are larger, and have specialized organelles.
The Cell
Cells consist of : membrane, nucleus and cytoplasm.
Membrane
The plasma membrane separates cells from their surroundings.
Membranes are made of phospholipid and protein, arranged in a fluid mosaic.
Membranes are selectively permeable : they only let some chemicals through (generally small moelcules).
Nucleus: The nucleus contains DNA arranged in chromosomes. It is surrounded by nuclear membrane which has pores to let chemicals in and out. The nucleolus, which is inside the nucleus, produces ribosomes.
Cytoplasm : the area outside the nucleus. It contains many organelles, listed below:
1). Ribosomes : contain RNA. They use this RNA to produce proteins.
2). ER (Endoplasmic reticulum) is in two types:
Rough ER : a series of membranes with ribosomes. It produces new membrane and proteins.
Smooth ER : is membranes without ribosomes. Smooth ER produces lipids.
3). Dictyosomes (called Golgi body in animals) : packages and ships off chemicals around the cell.
4). Vacuoles : typically found in plants. Storage vacuoles hold water, minerals, & poison (to deter herbivores).
5). Mitochondria : have a smooth outer membrane, and a folded inner membrane. They break down food to produce ATP (energy).
6). Plastids such as Chloroplasts : only found in plants. They contain chlorophyll. Chloroplasts consist of grana (membranes) and stroma (liquid). They carry out photosynthesis to produce carbohydrate.
7). Cytoskeleton : controls the shape, and movement, of the cell. It consists of microtubules and microfilaments ;
Microtubules : are made of the protein tubulin . They move cellulose to the cell wall.
Microfilaments : made of the protein actin. They cause acytoplasmic streaming or cyclosis in plants. Movie
8 ). Cell wall : only in plants. It is made of cellulose. It stops the cell from bursting and helps support trees.
Note: to see images of many of these organelles, and more details of their structure and function click here
Last edited August 2009, by David Byres, dbyres@fscj.edu