Why is carbon an ideal element to be the backbone for the chemical processes of life on Earth? Select all that apply.
Responses
Carbon can build complex molecules.
Carbon can build complex molecules.
Carbon is the most abundant element on Earth.
Carbon is the most abundant element on Earth.
Carbon is not very reactive.
Carbon is not very reactive.
Carbon can form double and triple bonds easily
Carbon can form double and triple bonds easily
Carbon has 4 valence electrons, which means that it can bond with up to 4 other atoms at one time.
**Correct choices:**
– Carbon can build complex molecules.
– Carbon can form double and triple bonds easily.
– Carbon has 4 valence electrons, which means that it can bond with up to 4 other atoms at one time.
**Not correct:**
– Carbon is the most abundant element on Earth. (It isn’t.)
– Carbon is not very reactive. (Too absolute—carbon’s reactivity varies; life benefits from its versatile, stable-yet-reactive covalent bonding.)
It is 2045, and we discover microbial communities surrounding deep ocean hydrothermal vents beneath the ice sheets of Saturn’s moon Enceladus. What metabolic classification would this new organism be?
Responses
chemoautotroph
chemoautotroph
photoheterotroph
photoheterotroph
chemoheterotroph
chemoheterotroph
photoautotroph
**chemoautotroph**
No sunlight under the ice; energy comes from inorganic chemicals (e.g., H₂, H₂S) at vents, and carbon is fixed from CO₂—classic chemolithoautotrophy.
We form many of our guesses about extraterrestrial life from Earth life – It’s the only form of life we can study right now!
Based on our understanding of Earth life,
is likely to be a critical requirement for any extraterrestrial life.
**liquid water**
The oldest evidence that strongly suggests that life was already present on Earth comes from ________.
Responses
rocks dating to more than 3.95 billion years ago that have a ratio of carbon-13 to carbon-12 indicative of life
rocks dating to more than 3.95 billion years ago that have a ratio of carbon-13 to carbon-12 indicative of life
the oldest known microstructures that appear to be individual, fossilized organisms
the oldest known microstructures that appear to be individual, fossilized organisms
the oldest known stromatolites
the oldest known stromatolites
4.3-to 4.4-billion-year-old zircons that show evidence of ancient life in oceans on Earth
**rocks dating to more than 3.95 billion years ago that have a ratio of carbon-13 to carbon-12 indicative of life**
In the 1950s, Stanley Miller and Harold Urey undertook an experiment to simulate the environmental conditions of early Earth. On the diagram below, label the major components of the experiment.
The Miller–Urey experiment setup has **four main labeled components**:
1. **Gas chamber (atmosphere flask):**
Contained gases thought to be present in early Earth’s atmosphere (CH₄, NH₃, H₂, and H₂O vapor).
2. **Electrodes (spark discharge):**
Produced electric sparks to simulate lightning as an energy source driving chemical reactions.
3. **Condenser (cooling system):**
Cooled the water vapor so that it condensed back into liquid, allowing molecules to dissolve.
4. **Collection trap (liquid chamber):**
Gathered the cooled liquid “ocean,” which eventually contained amino acids and other organic molecules.
Would you like me to sketch a **labeled diagram** of the setup for clarity?
How do RNA and DNA compare? The difference between these hereditary molecules led to our understanding of an ‘RNA World’ for early life on Earth. Sort the characteristics below based on whether they describe RNA and/or DNA. Some characteristics may apply to both RNA and DNA.
Put responses in the correct input to answer the question. Select a response, navigate to the desired input and insert the response. Responses can be selected and inserted using the space bar, enter key, left mouse button or touchpad. Responses can also be moved by dragging with a mouse.
RNA DNA
Here’s the correct sorting of characteristics for **RNA vs DNA**:
**RNA**
– Single-stranded
– Contains ribose sugar
– Uses uracil (U) instead of thymine
– Can act as both information storage **and** a catalyst (ribozymes)
– Thought to have come first in the “RNA World” hypothesis
**DNA**
– Double-stranded (double helix)
– Contains deoxyribose sugar
– Uses thymine (T) instead of uracil
– More chemically stable, good for long-term information storage
**Both RNA and DNA**
– Made of nucleotide building blocks
– Store genetic information through base sequences
– Use complementary base pairing (A–U/T, G–C)
Would you like me to make this into a **table format** for easy drop-in to your assignment interface?
wnhich serves as a tekmplate for making copies of self
That would be **DNA** (in modern life).
But in the **RNA World hypothesis**, **RNA** also served as a template for making copies of itself — both storing information *and* catalyzing replication.
So:
– **Today:** DNA is the main self-copying template.
– **Early life:** RNA likely served this role before DNA evolved.
Which of the following is a key piece of evidence suggesting that the mitochondria in our cells evolved from free-living bacteria?
Responses
They are much smaller than an entire human cell.
They are much smaller than an entire human cell.
They can process oxygen and make ATP.
They can process oxygen and make ATP.
They contain their own DNA.
They contain their own DNA.
We have discovered bacteria with genomes that are a near-exact match to the genomes of mitochondria.
**They contain their own DNA.**
That’s the strongest evidence supporting the **endosymbiotic theory** — mitochondria (and chloroplasts) originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.
You study two regions of the Moon. Region 1 is densely cratered. Region 2 is mostly smooth, with just a few craters. What can you conclude?
Responses
Region 2 suffered a much larger impact than Region 1 ever did.
Region 2 suffered a much larger impact than Region 1 ever did.
Region 1 has an older surface age than Region 2.
Region 1 has an older surface age than Region 2.
Region 1 was hit by a lot more impacts than Region 2.
Region 1 was hit by a lot more impacts than Region 2.
Region 2 has an older surface age than Region 1.
**Region 1 has an older surface age than Region 2.**
(More craters = exposed longer, so it’s older. Smooth surfaces mean resurfacing events, like lava flows, erased older craters.)
Defining what life is can be very challenging. Most characteristics that we can come up with to define life do not apply exclusively to living organisms. Sort the properties below based on whether or not they are key properties of life.
Here’s how to sort them:
**Key properties of life**
– Order (organized structure)
– Energy utilization (metabolism)
– Growth and development
– Response to environment (stimuli)
– Reproduction
– Evolutionary adaptation
**Not exclusive to life / Not key defining properties**
– Movement (nonliving things can move)
– Complexity alone (crystals, machines)
– Death (only applies after life exists)
Want me to make a **clean two-column list** so you can drag/drop easily in your assignment tool?
cells with organells, growth and dev, response to env, eveolution adapt, carbon base, energy util, order, respiration, left-hand prtoeiend, reproduction
Here’s the correct sort of your list into **key properties of life** vs. **not universally required/defining**:
**Key properties of life**
– Cells with organelles (cellular organization)
– Growth and development
– Response to environment
– Evolutionary adaptation
– Energy utilization
– Order (organized structure)
– Reproduction
**Not universally defining properties**
– Carbon-based (life elsewhere might not be)
– Respiration (only one type of energy metabolism; not all life uses it)
– Left-hand proteins (chirality is a feature of Earth life, but not a universal requirement)
How do RNA and DNA compare? The difference between these hereditary molecules led to our understanding of an ‘RNA World’ for early life on Earth. Sort the characteristics below based on whether they describe RNA and/or DNA. Some characteristics may apply to both RNA and DNA.
Here’s a clean **sorting of characteristics** between RNA and DNA, with shared traits listed under both:
**RNA**
– Usually single-stranded
– Contains **ribose** sugar
– Uses **uracil (U)** instead of thymine
– Can fold into shapes that act as **catalysts (ribozymes)**
– Likely the first hereditary molecule (“RNA World”)
**DNA**
– Usually double-stranded (double helix)
– Contains **deoxyribose** sugar
– Uses **thymine (T)** instead of uracil
– More chemically stable (better for long-term info storage)
**Both RNA and DNA**
– Made of nucleotides (sugar + phosphate + base)
– Use bases adenine (A), guanine (G), and cytosine (C)
– Store genetic information in base sequences
– Replicate using complementary base pairing
Do you want me to put this into a **drag-and-drop style table** so it matches how your quiz sorts answers?
Which of the following provides key evidence that 3.5-billion-year-old stromatolites indicate the presence of life onEarth at that time?
Responses
The similarity in structure between the stromatolites and bacterial mats that still live today
The similarity in structure between the stromatolites and bacterial mats that still live today
The layered structure of the stromatolites, because layering can be produced only by life
The layered structure of the stromatolites, because layering can be produced only by life
The presence of living bacteria in stromatolites
The presence of living bacteria in stromatolites
Microfossils found within stromatolites that appear to be individual fossilized microbes
**The similarity in structure between the stromatolites and bacterial mats that still live today**
That resemblance is the key evidence scientists use to argue that ancient stromatolites were formed by microbial communities.
Which statements accurately describe the Miller-Urey experiment? Select all that apply.
Responses
The gases used in the original experiment were a near-perfect representation of Earth’s early atmosphere.
The gases used in the original experiment were a near-perfect representation of Earth’s early atmosphere.
The gases used in the original experiment are no longer thought to have been a good representation of Earth’s early atmosphere.
The gases used in the original experiment are no longer thought to have been a good representation of Earth’s early atmosphere.
The experiment was unsuccessful, because no organic molecules were found.
The experiment was unsuccessful, because no organic molecules were found.
The experiment was designed to investigate whether organic molecules could have formed on the early Earth.
The experiment was designed to investigate whether organic molecules could have formed on the early Earth.
The experiment was designed to investigate whether organic molecules could have come to Earth on meteorites.
The experiment was designed to investigate whether organic molecules could have come to Earth on meteorites.
The experiment suggested that many of the building blocks of life can be formed spontaneously and naturally.
**Correct statements:**
– The gases used in the original experiment are no longer thought to have been a good representation of Earth’s early atmosphere.
– The experiment was designed to investigate whether organic molecules could have formed on the early Earth.
– The experiment suggested that many of the building blocks of life can be formed spontaneously and naturally.
“RNA world” refers to the idea that ________.
Responses
there is a separate branch of life on Earth that uses RNA, rather than DNA, as its genetic material
there is a separate branch of life on Earth that uses RNA, rather than DNA, as its genetic material
life migrated to Earth from Venus or Mars
life migrated to Earth from Venus or Mars
RNA was life’s first genetic material
RNA was life’s first genetic material
the early oceans were filled with free-floating RNA molecules
**RNA was life’s first genetic material**
Assuming life began with an “RNA world,” what advantage did it gain by later evolving to use DNA as its hereditary molecule?
Responses
Individual strands of DNA are more stable than strands of RNA.
Individual strands of DNA are more stable than strands of RNA.
Less energy is required forDNA replication than for RNA replication.
Less energy is required forDNA replication than for RNA replication.
The bases that make up DNA are much more common in nature
The bases that make up DNA are much more common in nature
DNA is less prone to errors during replication than RNA.
**DNA is less prone to errors during replication than RNA.**
(Also, DNA’s double-stranded structure makes it more stable than RNA — a key reason it replaced RNA as the main hereditary molecule.)
Which statement best describes current scientific thought concerning the possibility that life migrated to Earth from elsewhere?
Responses
The idea of life migrating to Earth has been explored and discarded, and no one takes it seriously today.
The idea of life migrating to Earth has been explored and discarded, and no one takes it seriously today.
It is possible that life migrated to Earth from one of the other planets in our solar system or from a planet around another star.
It is possible that life migrated to Earth from one of the other planets in our solar system or from a planet around another star.
No other planets in our solar system are likely to have had life at early times, but life could have reached Earth from another star.
No other planets in our solar system are likely to have had life at early times, but life could have reached Earth from another star.
It is possible that life migrated to Earth from Venus or Mars, but unlikely that it migrated from a planet around another star.
**It is possible that life migrated to Earth from one of the other planets in our solar system or from a planet around another star.**
Meteorites might be blasted from Venus or Mars and land on Earth in a time as short as about . However, a meteorite would require to travel from an exoplanet to Earth.
Meteorites might be blasted from Venus or Mars and land on Earth in a time as short as about **a few months to a few years**.
However, a meteorite would require **many thousands to millions of years** to travel from an exoplanet to Earth.