Question

1. the first living organisms were most likely:

b. single-celled and prokaryotic c. plants and animals a. multicellular and complex d. aerobic eukaryotes

1. what does \anaerobic\ mean? a. needs oxygen b. produces oxygen c. does not need oxygen d. lives in water
2. what formed when molecules became enclosed in membranes?

b. atoms c. protocells a. fossils d. tissues

1. the buildup of oxygen in earths atmosphere allowed for:

b. fewer organisms c. more complex life forms a. the extinction of all life d. no change at all

1. two gases that probably existed in earths early atmosphere are

a. oxygen & hydrogen sulfide c. oxygen & carbon monoxide
b. methane & water vapor d. water vapor and oxygen

Explanation:

1. The earliest life forms were simple, single-celled organisms without a nucleus (prokaryotes), as complex life evolved much later.
2. The prefix "an-" means without, so anaerobic refers to not needing oxygen.
3. Protocells are structures where molecules are enclosed in membranes, a key step in the origin of life.
4. The rise of atmospheric oxygen allowed for aerobic respiration, which supports more energy-intensive, complex life forms.
5. Earth's early atmosphere lacked free oxygen; methane and water vapor are among the gases that are widely accepted to have been present.

Answer:

1. B. Single-celled and prokaryotic
2. C. Does not need oxygen
3. C. Protocells
4. C. More complex life forms
5. b. Methane & Water Vapor