30 (2)

Question 1

Water in the liquid phase, the biogenic elements, and energy are the fundamental requirements for habitability.

Answer 1

R 2

Question 2

This provides ample incentive for evolution to fill as much of that range with life as is biochemically possible. An organism (usually a microbe) that tolerates or even thrives under conditions that most of the life around us would consider hostile, such as very high or low temperature or acidity, is known as an ………….. (where the suffix -………. means “lover of”).

Answer 2

extremophile

phile

Question 3

Both high and low temperatures can cause a problem for life. As a large organism, you are able to maintain an almost constant body temperature whether it is colder or warmer in the environment around you. But this is not possible at the tiny size of microorganisms; whatever the temperature in the outside world is also the temperature of the ……………., and its biochemistry must be able to function at that temperature.

Answer 3

microbe

Question 4

………… …………. are the enemy of complexity—………… …………… ………… tends to break apart big molecules into smaller and smaller bits, and life needs to stabilize the molecules with stronger bonds and special proteins. But this approach has its limits.

Answer 4

High temperatures / increasing thermal energy

Question 5

Nevertheless, as noted earlier, high-temperature environments like hot springs and hydrothermal vents often offer abundant sources of chemical energy and therefore drive the evolution of organisms that can tolerate high temperatures; such an organism is called a ……………

Answer 5

thermophile

Question 6

Currently, the high temperature record holder is a …………….-producing microorganism that can grow at ………. °C, where the pressure also is so high that water still does not boil.

Answer 6

methane / 122

That’s amazing when you think about it. We cook our food—meaning, we alter the chemistry and structure of its biomolecules—by boiling it at a temperature of 100 °C. In fact, food begins to cook at much lower temperatures than this. And yet, there are organisms whose biochemistry remains intact and operates just fine at temperatures 20 degrees higher.

Question 7

Cold can also be a problem, in part because it slows down ……………. to very low levels, but also because it can cause physical changes in biomolecules.

Answer 7

metabolism

Question 8

Cell membranes—the molecular envelopes that surround cells and allow their exchange of chemicals with the world outside—are basically made of fatlike molecules. And just as fat congeals when it cools, membranes …………….., changing how they function in the exchange of materials in and out of the cell.

Answer 8

crystallize

Question 9

Some cold-adapted cells (called …………..) have changed the chemical composition of their membranes in order to cope with this problem; but again, there are limits. Thus far, the coldest temperature at which any microbe has been shown to reproduce is about –………. ºC.

Answer 9

psychrophiles

25

Question 10

Conditions that are very acidic or alkaline can also be problematic for life because many of our important molecules, like …………. and ……….., are broken down under such conditions.

Answer 10

proteins and DNA

For example, household drain cleaner, which does its job by breaking down the chemical structure of things like hair clogs, is a very alkaline solution.

Question 11

The most acid-tolerant organisms (…………….) are capable of living at pH values near ………..—about ten million times more acidic than your blood.

At the other extreme, some ………… can grow at pH levels of about ………, which is comparable to the pH of household bleach and almost a million times more alkaline than your blood.

Answer 11

• acidophiles /* zero
• alkaliphiles /* 13

Question 12

High levels of salts in the environment can also cause a problem for life because the salt blocks some …………. functions.

Answer 12

cellular

Question 13

the first successful flyby of a robotic spacecraft in ………… and have led to the deployment of NASA’s Curiosity rover, which landed on Mars’ surface in ………..

Answer 13

1964

2012

Question 14

The NASA …………. landers, whose purpose was to search directly for evidence of life on Mars, arrived on Mars in 19……….

………….’s onboard instruments found no organic molecules (the stuff of which life is made), and no evidence of biological activity in the martian soils it analyzed.

Answer 14

Viking / 76

Viking

Question 15

under very low pressures, water will boil at a much lower temperature than usual and under high pressure it needs more temperature

Answer 15

R 2

Question 16

Over much of Mars, temperatures and pressures at the surface are so ………. that pure water would either freeze or boil away

Answer 16

low

Question 17

Two bold surface missions, the Mars Exploration Rovers ……….. and ……….. (2004), followed by the much larger Curiosity Rover (2012), confirmed these remote-sensing data. All three rovers found abundant evidence for a past history of liquid water, revealed not only from the mineralogy of rocks they analyzed, but also from the unique layering of rock formations.

Answer 17

Spirit / Opportunity

Question 18

The strongest evidence of an ancient habitable environment on Mars came from analyzing a very fine-grained rock called a ………… by Curiosity

Answer 18

mudstone

The mudstone can tell us a great deal about the wet environments in which they formed.

Question 19

The massive ………. and ……… giant planets of the outer solar system—Jupiter, Saturn, Uranus, and Neptune—are almost certainly not habitable for life as we know it, but some of their moons might be

Answer 19

gas / ice

Question 20

Although these worlds in the outer solar system contain abundant water, they receive so little ………… ………… in their distant orbits that it was long believed they would be “geologically dead” balls of hard-frozen ice and rock.

Answer 20

warming sunlight

Question 21

As the moon orbits Jupiter, the planet’s massive gravity creates tides on Europa—just as our own Moon’s gravity creates our ocean tides—and the ……… of all that pushing and pulling generates enough heat to keep the water in liquid form

Answer 21

friction

Question 22

Scientists now think that ………. or more of the outer solar system’s icy moons may harbor liquid water oceans for the same reason. Among these, ………… and …………, a moon of Saturn, have thus far been of greatest interest to astrobiologists.

Answer 22

six

Europa / Enceladus

Question 23

In 20………., the ……….. mission performed a close flyby of a small (500-kilometer diameter) moon of Saturn, Enceladus, and made a remarkable discovery. Plumes of gas and icy material were venting from the moon’s ………… polar region at a collective rate of about ……… kilograms of material per second.

Pulme: a tall, thin mass of smoke, dust, or similar substance that rises up into the air.

Answer 23

05 / Cassini

south / 250

Question 24

Saturn’s big moon Titan’s thick atmosphere—the only one among moons in the solar system—is composed mostly of ………… but also of about ……. ………..

Answer 24

nitrogen / 5% methane

Question 25

In the upper atmosphere of Titan, the Sun’s ultraviolet light breaks apart and recombines these molecules (Nitrogen & Methane) into more complex organic compounds that are collectively known as …………

The ………… shroud Titan in an ………… haze,

Answer 25

tholins / tholins / orange