Download 1 - Cells.notebook

1 ­ Cells.notebook
February 02, 2017
Characteristics of Life
1
1 ­ Cells.notebook
February 02, 2017
Cells
STUDYING LIFE
• No single characteristic is enough to confirm life, but most organisms have the following in common:
Made of cells
o
Exhibit order
o
Respond to the environment
o
Exchange energy and materials with the environment
o
Maintain homeostasis (a stable internal environment)
o
Grow and develop
o
Able to reproduce o
Evolve
o
Venus Flytrap in Action
Pygmy Sea Horse
Characteristics of Life
2
1 ­ Cells.notebook
February 02, 2017
• Life can be studied at different levels, the smallest level being at the cellular level.
• There are ten levels of biological organization:
Biosphere
o
Biome
o
Ecosystem
o
Community
o
Population
o
Organism
o
Organs and organ systems
o
Tissue
o
Cell
o
Organelle
o
Molecule
o
Atom/ion
o
Biological Organization
3
1 ­ Cells.notebook
February 02, 2017
• No one scientist is individually responsible for the development of cell theory; it was formed as a result of many years of experimentation and collaboration.
There are three key principles to cell theory:
o
All organisms are made up of one or more cells.
§
The cell is the smallest living organizational unit.
§
All cells are produced from previously existing cells.
§
*Be sure to review the document posed on edline on cell organelles and their purposes.
o
Analyze and describe how
scientific understanding was
enhanced/revised by the
microscope.
Cell Theory
4
1 ­ Cells.notebook
February 02, 2017
PROKARYOTES AND EUKARYOTES
• Cells are classified within two broad categories:
Prokaryotes are…
o
Considered to be more primitive; they are very simple and §
small.
Lacking a nucleus and extensive system of organelles. They §
have a rigid cell wall.
Able to grow and divide rapidly because of their size (they §
have a small surface area to volume ratio).
Are divided into eubacteria, which can be found almost §
anywhere, and archaebacteria, which live in extremely harsh environments.
o
Eukaryotes are…
More advanced and larger; all species, other than bacteria, are §
eukaryotes.
Consisting of a nucleus and organelles.
§
­
Organelles allow many activities to take place in the cell at once. Many reactions take place within or on the membrane of organelles, therefore eukaryotic cells are found to have much more internal membrane surface than prokaryotic cells.
Pro/Eukaryotes
5
1 ­ Cells.notebook
February 02, 2017
http://www.youtube.com/watch?v=bBjD4A7R2xU
Endosymbiont Theory
It is believed that eukaryotic cells arose from groups of prokaryotic cells living together ­
smaller ones inside larger ones. These cooperative arrangements provided advantages to the cells
in them.
Evidence comes from:
Some eukaryotic organelles resemble bacteria.
Mitochondria and chloroplasts surrounded by a double membrane.
Mitochondria and bacteria have similar size.
Mitochondrial ribosomes resemble bacterial ribosomes.
Mitochondria and chloroplasts have their own DNA and it s circular like bacterial DNA.
Mitochondria divide as bacteria do.
Endosymbiont Theory
6
1 ­ Cells.notebook
February 02, 2017
WHY ARE CELLS SO SMALL?
• Cells exchange all materials with their environment through the cell membrane. Exchange is faster in a smaller cell.
• In order to efficiently exchange materials with the environment, cells need a certain surface area that is proportional to their volume. • The rate at which they can exchange materials is proportional to their surface area. • Many cells are roughly spherical in shape and, as a result, the volume of the cell increases faster than the surface area. In other words, the surface area:volume ratio of cells decreases as they get larger. This indicates a poor rate of exchange.
• Cells that are specialized for absorption (ex. intestinal cells) have folds in the plasma membrane that increase the surface area.
• Due to the rate of exchange of materials, organisms add more cells to grow larger rather than have larger cells.
Why so small?
7