1. Life: Chemical, Cellular, and Evolutionary Foundations
Chapter 1

2. THE SCIENTIFIC METHOD
In the previous slide, you made observations of the hummingbird and the flower. By making these observations, you can propose tentative explanations (hypotheses).
A good hypothesis makes predictions about observations not yet made or experiments not yet run. These predictions can be tested.
Once a hypothesis has been supported by a large body of experiments and observations, it can become a theory.
Note that, in general conversation, the term theory is often synonymous with hypothesis.
But in science, a theory is fact.

3. COMPOSITION OF EARTH AND HUMAN BODY
Living and nonliving worlds share the same chemical foundations and obey the same physical laws. There is nothing special about our chemical components when taken individually.
However, the relative abundances of elements differ greatly.
The Earth’s crust consists of mainly oxygen and silicon with significant amounts of aluminum, iron, and calcium.
Organisms mainly consist of oxygen, carbon, and hydrogen.

4. 1st LAW OF THERMODYNAMICS
The first law of thermodynamics states that energy can neither be created nor destroyed, it can only be transformed from one form into another.
All organisms obtain energy from the sun or from chemical compounds.
As this energy is harnessed, some is used to do work (moving, reproducing, and building cellular components) while the rest is dissipated as heat.

5. 2nd LAW OF THERMODYNAMICS
The second law of thermodynamics states that the degree of disorder in the universe tends to increase.
The amount of disorder in a system is the entropy of the system.

6. ESSENTIAL FEATURES OF A CELL
It can store and transmit information.
It has a plasma membrane.
It can harness energy from the environment.
It has the ability to store and transmit information.
It has a plasma membrane that separates the living material within the cell from the nonliving environment around it.
It has the ability to harness energy from the environment. Cells can break down sugar, releasing energy in the process and converting it into a usable form (ATP).

7. THE CENTRAL DOGMA
DNA is transcribed into RNA, which is then translated into protein. This is the basic flow of information in a cell.
A gene is the DNA sequence that corresponds to a specific protein product.

8. PLASMA MEMBRANE
The plasma membrane separates the living material within the cell from the nonliving environment around it. It controls the exchange of material between the cell and the environment.
Some cells have internal membranes that divide the cell into compartments. Highlight the nucleus in this image and show its separation from the cytoplasm.
Not all cells have a nucleus. Some cells have a nucleus (eukaryotes) and others do not (prokaryotes).

9. TREE OF LIFE Today, three domains of life are recognized.
Both the bacteria and archaea lack a nucleus and are therefore prokaryotes, while the eukaryotes have a nucleus.
However, in spite of the similar cellular structure of the bacteria and the archaea, the eukarya and archaea are closely related.
Biologists call this full set of evolutionary relationships among organisms the Tree of Life.

10. Elena and Lenski demonstrate evolution through experimentation
Elena and Lenski grew E. coli in liquid medium containing a poor food source, succinate.
They hypothesized that, if a mutation occurred that increased the bacteria’s ability to utilize the succinate, then those particular mutated bacteria would be able to reproduce at a faster rate than those that did not have the mutation.
In the beginning of the experiment, the researchers froze some of the ancestral (starting bacterial) population
Over 20,000 generations, they grew what was believed to be the evolving population on succinate.
As the experiment progressed, they took samples of the evolving bacterial population at periodic intervals and grew them together with samples of the ancestral population.
They compared the rate of growth of the two different populations.
The bacteria over time did evolve an improved ability to use succinate as their food source.