Eukaryotic and Prokaryotic Cells

• Biology is about living organisms, which all contain cells.

Eukaryotes vs Prokaryotes

• Eukaryotes include all animals and plants, which are made of complex cells called eukaryotic cells.
• Prokaryotes include bacteria, which are smaller and simpler cells called prokaryotic cells.
• Both types of cells contain sub-cellular structures, which are parts of cells that each have a specific function.

Structures Within Eukaryotic Cells

• Animal cells include the following:
• Nucleus: contains DNA in the form of chromosomes, controlling the cell's activities.
• Cytoplasm: a gel-like substance where most chemical reactions happen.
• Mitochondria: the site of cellular respiration, containing necessary enzymes.
• Ribosomes: where proteins are made.
• Cell Membrane: holds the cell together, controls what goes in and out via a selective barrier, and contains receptor molecules for cell communication (e.g., by hormones).
• Plant cells include everything animal cells have as well as these extras:
• Rigid Cell Wall: made of cellulose, providing support.
• Chloroplasts: where photosynthesis occurs, containing chlorophyll (a green substance).

Structures Within Prokaryotic Cells

• Chromosomal DNA: a long, circular chromosome that controls cell activities and replication, located in the cytoplasm (not in a nucleus).
• Plasmids: small loops of extra DNA that aren't part of the chromosome, contain genes (e.g., for drug resistance), and can be passed between bacteria.
• Cell Membrane: controls what goes in and out and is supported by a cell wall.

Studying Cells Using Microscopes

• Microscopes use lenses to magnify images, making them look bigger.
• Microscopes increase the resolution of an image, increasing the detail you can see.
• Resolution describes how well a microscope distinguishes between two close points.
• Light microscopes were invented in the 1590s, enabling the observation of nuclei and chloroplasts.
• Electron microscopes were invented in the 1930s, enabling the observation of smaller structures in more detail such as the internal structure of mitochondria.
• Electron microscopes have allowed a greater understanding of sub-cellular structures, enabling observation of things as tiny as plasmids or viruses.
• Transmission Electron Microscopes (TEMs) offer higher magnification and resolution than light microscopes.
• TEMs aren't portable, are expensive, and require complicated processes to prepare specimens, meaning that they cannot be used to look at living tissue as opposed to light microscopes that can.

Cell Structures

• The number of sub-cellular structures depends on the cell's function such as muscle cells, which respire a lot, will have more mitochondria, and plant cells that don't get any light won't have chloroplasts.