Origins of Cells

Question 1

What is “spontaneous generation”?

Answer 1

Until the 19th century, some biologists believed that life could appear in non-living material

Question 2

What are the reasons for which cells can only come from pre-existing cells?

Answer 2

1. A cell is a highly complex structure and no natural mechanism has been suggested for producing cells from simpler subunits
2. No example is known of increases in the number of cells without cell division
3. Viruses are produced from simpler subunits but they do not consist of cells

Question 3

What is biogenesis?

Answer 3

Describes the principle that living things only arise from other living things

Question 4

How did Pasteur falsify spontaneous generation theory?

Answer 4

1. Broths were stored in vessels that contained long tubing which blocked out dust particles
2. The broths were boiled to kill any microorganism present in the growth medium
3. Growth only occurred int he broth if the flask was broken, exposing the medium to the atmosphere
   - Thus it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur

Question 5

What are the 4 theories explaining origin of the first cells?

Answer 5

1. Production of carbon compounds by passing water vapor through ammonia, methane, and hydrogen
2. Assembly of carbon compounds into polymers in deep seas
3. Formation of membranes
4. Development of RNA

Question 6

What is symbiosis?

Answer 6

Symbiosis occurs when two different species benefit from living and working together

Question 7

What is the endosymbiotic theory?

Answer 7

States that a larger prokaryotic cell engulfed a bacterium that was capable of aerobic respiration. However, instead of killing the smaller bacterium, the larger cell allowed it to live as it benefited from the efficiency of aerobic respiration. Gradually, the aerobic bacterium evolved into mitochondria and the larger cell evolved into eukaryotes. Further on, the large cell engulfed photosynthetic bacterium in a similar fashion, and these evolved into chloroplasts.

Question 8

How do the features of chloroplast and mitochondria act as evidence for the endosymbiotic theory?

Answer 8

1. Can only be produced by pre-existing mitochondria/chloroplasts
2. They have a naked loop of DNA, like prokaryotes
3. Have 70s ribosomes
4. Have double membranes
5. Susceptible to antibiotics, indicating they might have bacterial origin