Biology 1B Chapter 1, 2, & 3
Which best summarizes the conditions of early Earth at the time that life first evolved?
Early Earth had a very different atmosphere, was subject to extreme radiation, and had a lot of geologic upheaval and volcanic activity.
Why do scientists believe that the first organisms on Earth were extremophiles?
Earth's early environment was full of extreme places with little oxygen in the atmosphere, no ozone to shield Earth's surface from mutagenic radiation, much geologic upheaval and volcanic activity. Extremophiles are bacteria and archaea that are adapted to grow in extreme environments.
Soil bacteria that form endospores to resist drought and heat are not considered extremophiles. Why?
Endospore formation allows organisms to resist heat and drought until conditions become favorable again while extremophiles are adapted not to merely survive, but to live and grow in extreme environments.
A paleontologist claims that most extant animal phyla appeared during the Cambrian. Is the claim correct?
Yes, massive extinction did not kill all species. The survivors in each phylum continued to evolve and occupy niches vacated by the species that disappeared.
How many neutrons do carbon-12 and carbon-13 have, respectively?
carbon-12 contains 6 neutrons while carbon-13 contains 7 neutrons.
Which of the following is not a theory currently proposed to explain the cause of the Cambrian explosion?
decreased oceanic calcium concentrations preceded the Cambrian period
Which of the following represents the earliest forms of life on Earth?
microbial bat
Define microbial mat in your own words.
multi-layered sheet of prokaryotes that may include bacteria and archaea
Isotopes
one or more forms of an element that have different numbers of neutrons
Define halophile in your own words.
organism that require a salt concentration of at least 0.2 M
Based on our current understanding about the composition of the ancient atmosphere, order the following types of prokaryotes from those that arose the earliest to those that arose more recently. 1. aerobic prokaryotes that used photosynthesis 2. anaerobic prokaryotes that fed on organic materials 3. anaerobic prokaryotes that used photosynthesis
2,3,1
Carbon dating is one method scientists use to date fossils to determine their ages. This protocol works because many of the elements used have a known decay rate called a half-life. Basically, this means that half of a sample will decay after a given amount of time. The half-life of thorium-227 is 18.72 days. How long is needed for ¾ of a sample to decay?
37.44 days
Approximately how many mass extinction events occurred throughout the evolutionary history of animals?
5
The time between 542-488 million years ago marks which period?
Cambrian period
Laboratory experiments have demonstrated that the abiotic synthesis of organic molecules in condition similar to those of early Earth is possible. Which of the following provides additional support for the idea of abiotic synthesis of organic compounds?
Analysis of the chemical composition of meteorites sometimes yields amino acids.
Explain the relationship between Earth's ancient atmosphere and the evolution of some of the first life forms on Earth. Use the terms anaerobic and phototrophic, and explain the effect of cyanobacteria on the atmosphere.
For the first two billion years of Earth's existence, the atmosphere had no molecular oxygen. Thus, the first organisms were anaerobic. Phototrophic organisms appeared within one billion years of Earth's formation. From these organisms evolved the cyanobacteria, which produce oxygen as a by-product of photosynthesis, leading to the oxygenation of the atmosphere.
Which of the following pieces of evidence is the BEST support for the alternative scenario of early life formation, in which organic compounds on early Earth formed near submerged volcanoes?
Fossilized stromatolites that are 3.5 billion years old are found near deep-sea vents.
What makes ionic bonds different from covalent bonds?
Ionic bond involves the transfer of electrons whereas covalent bond involves the sharing of electrons.
What are atoms that vary in the number of neutrons found in their nuclei called?
Isotopes
Stanley Miller and Harold Urey conducted experiments which demonstrated that several organic compounds could be formed spontaneously by simulating the conditions of Earth's early atmosphere. When Miller and Urey repeated their experiment without the electrical discharge, no organic compounds were found. Hypothesize what might explain this result. Consider your answer in the context of the conditions of early Earth.
Lightning, or some form of energy, is needed for the inorganic molecules in the atmosphere to interact with each other. This indicates that a similar energy source was present on early Earth which stimulates the interaction and development.
Which of the following explanations is not correct regarding the Cambrian explosion?
Massive glaciation changed the climate of the Earth.
Why is it difficult for scientists to assess the development of animals before the Cambrian Era?
Most animals were soft-bodied, limiting the fossil record.
Massive glaciation changed the climate of the Earth.
New niches are available to be colonized by surviving animals.
Which of the following geological boundaries would have shown the greatest loss of diversity in animal species?
Ordovician - Permian
Based on carbon dating, scientists estimate this pygmy mammoth died 11,000 years ago. How would the ratio of 14 C 14C to 12 C 12C in a living elephant compare to the 14 C 14C to 12 C 12C ratio found in the mammoth?
The ratio would be higher in the elephant than the mammoth. In living organisms, the ratio of 14 C 14C to 12 C 12C is in equilibrium with the ratio in the atmosphere. After death, no new 14 C 14C is taken in, and as this radioisotope decays, the ratio of 14 C 14C to 12 C 12C decreases
Which is the best evidence that prokaryotes evolved about 3 billion years ago?
There is fossil evidence of microbial mats—large multi-layered sheets of prokaryotes—starting about 3.5 billion years ago.
Which statement describing the environment of early Earth is false?
There was little to no geologic activity.
Define anaerobic in your own words.
refers to organisms that grow without oxygen
Halophiles prefer conditions in which there is a _____.
salt concentration of at least 0.2 M
