Cells – An Introduction
All living things are made up of tiny structures called cells.
A cell is the smallest unit that can perform all the things we need to be able to live – like taking in energy, etc.
Because of their small size, however, cells were not discovered until microscopes were invented in the 1600s. A scientist and inventor named Robert Hooke was the first person to describe plant cells by looking at corks, plants and fungus under a high-powered magnifier (kind of like a primitive microscope).
Later, Anton Van Leeuwenhook (pronounced: Lay-vun-hook) invented the microscope we think of today (much more powerful than Hooke’s) and observed animal blood cells, which were different in different types of animals. He was also the first person to see protozoa.
After about another 200 years of observations based on the discoveries of Hooke and Leeuwenhook, scientists were able to conclude that cells existed in all living things, and eventually came up with something called the Cell Theory.
The Cell Theory
- all organisms are made of cells
- the cell is the basic unit of all living things
- all cells come from other cells
So that’s the history of the cell in a very, very brief amount of info.
Now, on to the specifics of cells:
All cells, regardless of type – be they human, plant or bacterial cells – have a few parts in common:
- Cell Membrane:a protective layer that separates the cell’s inner contents from the world around it. Covers and protects the cell. It also controls the flow of objects into and out of the cell.
- Cytoplasm: fluid that exists inside the cell and helps support the cell.
- DNA: genetic information that is used to make new cells and organisms.
In some cells, DNA is kept inside of the nucleus.
There are two basic kinds of cells: prokaryotic cells and eukaryotic cells. Within each category, there are even more subcategories of cells – but in general, they are separated by one thing; prokaryotes have no nucleus, eukaryotes have a nucleus.
Prokaryotes
Prokaryotes are single celled organisms with no nucleus or membrane-bound organelles.
Prokaryotes are bacteria.
They can be classified as archaebacteria or eubacteria.
Archaebacteria live in extremely hostile environments like swamps, volcanic pools and very salty areas.
Eubacteria are common bacteria. They exist EVERYWHERE!
Eukaryotic cells
Eukaryotes are every other type of cell.
They have all the most basic parts of a cell, plus a few more:
- Nucleus: an organelle that contains the cell’s DNA and that has a role in growth, metabolism, and reproduction
- Membrane-bound Organelles: Small “organs” in a cell’s cytoplasm that are specialized to perform specific functions
Eukaryotes can also be single-celled or multicellular.
When they are single-celled, they are called eukaryotic cells; when they are multi-cellular, they are called eukaryotes.
Plants, animals, fungi, etc are all eukaryotes.
Tags: Cells, eukaryotic cells, prokaryotic cells
Posted in Biological Science, Cells
