All cells share common features including DNA, RNA, proteins, ribosomes, cytoplasm, and a cell membrane. Prokaryotes are generally smaller than eukaryotic cells. As cell size increases, surface area to volume ratio decreases, making exchanges with the environment more difficult. Prokaryotes are divided into two domains, Archaea and Bacteria. They reproduce through binary fission and can undergo horizontal gene transfer. Examples are given of how antibiotics target different cellular processes in bacteria.
2. What feature do all cells have in common?
All cells contain:
● DNA
● RNA
● proteins
● ribosomes
● cytoplasm
● cell membrane
All cells are relatively small in
size
6. Size matters…
● Surface is the primary point of exchange between the cell and its environment
(and the organism and its environment)
o Diffusion/Osmosis
o Heat balance
o Elimination of wastes
● As a cell increases in size, its volume increases at a faster rate than its surface. At
some point, a cell is too big to effectively accommodate the exchanges it makes
with its environment.
25. Classification based on oxygen requirements
obligate aerobes:
REQUIRE O2
facultative anaerobes:
live either with or
without O2
obligate
anaerobes: DIE in
O2
Habitats with oxygen Habitats without oxygen
Fig 17.8
Have students answer this question before revealing commonalities.
All cells contain DNA, RNA, proteins, ribosomes, cytoplasm, and cell membrane. [may need to define ribosomes--cell machinery that makes proteins.] All cells are relatively small in size.
As cells increase in size it is more difficult to exchange heat with the environment (which is important for thermoregulation), obtain nutrients, get rid of waste, bring in oxygen, and get rid of carbon dioxide. These items enter or leave a cell through its surface. As a cell increases in size, its volume increases more dramatically than its surface area. At some point, a cell would be too big to effectively exchange these things with its environment.
This figure shows the three domains of life and compares them according to following four criteria: 1) the absence or presence of a nucleus 2) the absence or presence of membrane bound organelles,3) differences in membrane chemistry, and 4) typical cell size.
Some organisms, obligate aerobes, require oxygen to survive. Oxygen plays a critical role in some of their metabolic pathways, specifically cell respiration which helps them obtain energy. [Note: we won’t discuss cell respiration until BIO 1482 so I am deliberately not trying to use the term here. However, it may help some students connect these terms to previous knowledge about cell respiration, fermentation, and anaerobic respiration.] They will die in the absence of oxygen. However, not all living things require oxygen to survive. Facultative anaerobes, can live with or without oxygen using either. Obligate anaerobes live in environments that lack oxygen and will die in the presence of oxygen.
