1.5 (Topic 1)

Question 1

Discuss implications of all cells being formed from preexisting cells.​​

Answer 1

Implication #1: We can trace the origin of all the cells in our body back to the first cell; the zygote produced by the fertilization of a sperm and egg.

Implication #2: The origins of all cells can be traced back through billions of years of evolution to “LUCA” the last universal common ancestor of all life on Earth.

Implication #3: There must have been a first cell that arose from non-living material.

Question 2

Outline the four processes needed for the spontaneous origin of cells on Earth.

Answer 2

1. The synthesis of simple organic molecules from inorganic compounds.
2. The assembly of these organic molecules into polymers.
3. The formation of a polymer that can self replicate (enabling inheritance).
4. Packaging of molecules into membranes with an internal chemistry different from the surroundings.

Question 3

Outline the experiments of Miller and Urey into the origin of organic compounds.

Answer 3

• Boiled water evaporates and moves into the larger flask, where it combines with methane, ammonia and hydrogen gases in a large flask.
• Sparks are fired between electrodes to simulate lightning.
• A cooling condenser turns steam back into liquid water, which drips down into the trap, where organic molecules produced in the reactions also settle.

Question 4

Define polymerization, monomer and polymer.

Answer 4

• Polymerization: The process in which relatively small molecules, called monomers, combine chemically to produce a large chainlike molecule, called a polymer.
• Monomer: “one part.” The single building block unit of a polymer.
• Polymer: “many parts.” A large molecule composed of many monomer subunits.

Question 5

State the endosymbiosis theory.

Answer 5

• Theory that mitochondria and chloroplasts evolved from free living prokaryotic cells that were engulfed (but not digested) by early eukaryotic cells.
• The mitochondria and chloroplasts evolved as “symbiotic” (together, both benefiting) “endobionts” (inside living).

Question 6

Outline the major events in the origin of eukaryotic cells.

Answer 6

An endosymbiont is a cell which lives inside another cell with mutual benefit. Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis. The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis). Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle

Question 7

Describe the evidence for the endosymbiotic theory.​

Answer 7

• Mitochondria and chloroplasts share the following with prokaryotic cells:
  
  • shape
  • size
  • 70s ribosomes
  • circular, naked DNA
  • genetic sequences
  • movement
  • division by binary fission
  • inhibited by antibiotics
• Additionally, mitochondria and chloroplasts have a double layer membrane.
  
  • Membranes (double membrane bound)
  • Antibiotics (susceptibility)
  • Division (mode of replication)
  • DNA (presence and structural composition)
  • Ribosomes (size)

Question 8

Define spontaneous generation.

Answer 8

The theory, now discredited, that living organisms can routinely emerge from nonliving matter independently of other living matter.

Question 9

Describe Pasteur’s experiments about spontaneous generation.

Answer 9

• Pasteur’s experiments (1859) provided evidence that spontaneous generation of cells and organisms does not now occur on Earth.
• Pasteur’s experiment consisted of three parts. In the first part, the broth in the flask was boiled to sterilize it. When this broth was cooled, it remained free of microbial contamination.
• In the second part of the experiment, the flask was boiled and then the neck was broken off. The broth in this flask became cloudy as it became contaminated with microbes from the air.
• In the third part of the experiment, Pasteur created a flask with a curved neck. The curve allowed indirect exposure to air but prevented entry of microbes. The broth remained free of microbial contamination.

Question 10

​Explain why Pasteur’s experiments did not support the idea of spontaneous generation.

Answer 10

• If a life force was responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not.
• However, because the broth in the flask remained clear, Pasteur’s experiment showed that air does not contain a “vital force” that creates life. Life could not spontaneously generate.