DE Bio -- Chapter 24 & 25

When did the Big Bang occur?

10 to 20 billion years ago.

When did Earth form?

4.6 billion years ago.

How did planets form from the post-Big-Bang universe?

Bits of matter gained enough gravity to pull nearby dust and ice particles together.

What was the thermal history of early Earth right after it formed?

It was cold at first, then heat generated by meteorite impacts, radioactive decay, and gravitational compaction turned it into a molten mass.

What three heat sources turned early Earth into a molten mass?

Meteorite impacts, radioactive decay, and compaction from gravity.

What process caused Earth's interior to separate into distinct layers of different densities?

The molten state allowed material to sort by density, with the heaviest elements sinking and the lightest rising.

What materials make up Earth's core, and why did they end up there?

Nickel and iron, because they were the densest and sank to the center.

What part of Earth formed from less dense material surrounding the core?

The mantle.

What is the outermost layer of Earth, and what is its density relative to the rest of the planet?

The crust, formed from the least dense material that settled on the surface.

What was the composition of Earth's first atmosphere, and what happened to it?

It was hydrogen gas, but it soon escaped into space.

Where did the gases of Earth's second atmosphere come from?

They were spewed from volcanoes and vents in the crust.

What six gases made up Earth's second atmosphere?

CO2, N2, H2S, water vapor, CH4, and NH3.

How did Earth's first seas form?

When the planet cooled enough to condense water vapor into rain.

What three intense environmental conditions characterized early Earth's surface?

Intense lightning, intense volcanic activity, and intense UV radiation.

Why was early Earth bombarded with UV radiation that reached the surface?

There was no ozone layer to block it.

What did Louis Pasteur prove in 1862 about the origin of cells?

That spontaneous generation no longer occurs, meaning all cells come from pre-existing cells.

Did spontaneous generation ever actually occur on Earth?

Yes, between 3.9 and 3.5 billion years ago, when there was no free oxygen in the atmosphere.

Why could spontaneous generation happen on early Earth but not today?

Because there was no free oxygen in the atmosphere at that time.

What are the four sequential steps in the origin of life?

(1) Synthesis of monomers, (2) formation of polymers, (3) formation of membranes, (4) a mechanism of polymer replication (primitive heredity).

What was the step of the origin of life that Miller and Urey's experiment modeled?

Step 1: the synthesis of monomers.

What did Miller and Urey's classic experiment demonstrate?

That amino acids and other organic molecules could have arisen by spontaneous generation under early-Earth conditions.

What type of atmosphere did Miller and Urey assume early Earth had?

A reducing atmosphere.

What four substances did Miller and Urey include in their simulated early atmosphere?

Methane, ammonia, hydrogen gas, and water vapor.

What two sources of energy were used in the Miller-Urey experiment to drive chemical reactions?

Sparks (simulating lightning) and UV radiation (made possible by the absence of an ozone layer).

In the Miller-Urey apparatus, what did the flask of warm water represent?

The primeval sea.

What did the condenser do in the Miller-Urey apparatus?

It cooled and condensed water vapor, causing rain-like precipitation back into the flask.

What four classes of organic molecules did Miller and Urey recover from their experiment?

Amino acids, simple sugars, fatty acids, and nitrogenous bases.

What type of chemical reaction would be required to form polymers from monomers in the origin of life?

Dehydration synthesis reactions.

Where on early Earth would monomers have been likely to form polymers, and why?

On hot sand, clay, or rock, because these surfaces provided heat and binding sites.

Why is clay considered a particularly plausible site for early polymer formation?

Monomers bind to electrically charged sites on clay particles, and clay contains metal atoms like iron and zinc that can catalyze the linking of monomers.

What are protobionts?

Small membrane-bound droplets that form spontaneously when lipids are added to water.

What do scientists propose were the first simple cells?

Membrane-bound droplets (protobionts) that enclosed RNA, proteins, and other macromolecules.

Why is RNA thought to have been both the first genetic material and the first enzyme?

Because RNA can replicate without enzymes and some RNAs (ribozymes) can act as enzymes themselves.

What are ribozymes?

RNA molecules that act like enzymes, catalyzing chemical reactions.

What is the key structural feature of a Gram-positive bacterial cell wall?

A thick layer of peptidoglycan, with an otherwise simple wall.

How does the Gram-negative cell wall differ from the Gram-positive cell wall?

Gram-negative walls have less peptidoglycan but are more complex, with an outer membrane containing lipids bonded to carbohydrates.

Which type of bacteria, Gram-positive or Gram-negative, is generally more threatening and more resistant to antibiotics?

Gram-negative bacteria.

What is the mechanism by which antibiotics kill bacteria at the cell wall level?

They inhibit the cross-linking of peptidoglycan in the bacterial cell wall.

What is the bacterial capsule made of, and where is it located?

A layer of polysaccharides or protein located outside the cell wall.

What are the two main functions of the bacterial capsule?

Helping bacteria stick to surfaces, and shielding them from attacks by the host's immune system.

What are the two main functions of bacterial pili?

Sticking to surfaces and swapping genes between bacterial cells.

What structures give prokaryotes motility?

Flagella.

How do prokaryotes reproduce, and why is this a key feature of their success?

By binary fission, which allows very rapid reproduction.

What are bacterial endospores?

Dormant, thick-coated protective structures that form when a bacterium dehydrates, allowing it to survive extreme heat or cold.

How long can bacterial endospores remain viable?

They can last for centuries.

Can boiling water kill bacterial endospores?

No.

What happens to a bacterial endospore when favorable conditions return?

It absorbs water and resumes normal growth.

What two metabolic processes are carried out by infoldings of the prokaryotic plasma membrane?

Cellular respiration and photosynthesis.

What are plasmids?

Small pieces of DNA in prokaryotes that exist separately from the main chromosome.

When did prokaryotes first appear on Earth, and for how long were they the only form of life?

They evolved 3.5 billion years ago and were alone on Earth for the next 1.5 billion years.

How does the prokaryote population compare to the total human population that has ever lived?

There are more prokaryotes in a handful of fertile soil than the total number of humans who have ever lived.

What is the typical size range of prokaryotic cells?

1 to 10 micrometers in diameter.

What three broad biological roles do prokaryotes play?

Pathogens, benign organisms, and beneficial organisms (including critical decomposers).

What are the two domains of prokaryotes?

Bacteria and Archaea (Archaebacteria).

What is the term for spherical bacteria?

Cocci.

What are cocci that form chains called?

Streptococci.

What are cocci that form clusters called?

Staphylococci.

What is the term for rod-shaped bacteria?

Bacilli.

What are spirilla?

Short, rigid corkscrew-shaped bacteria.

What are spirochetes, and how do they differ from spirilla?

Corkscrew-shaped bacteria that are longer and more flexible than spirilla.

What is the general name for archaebacteria that thrive in extreme environments?

Extremophiles.

What are extreme halophiles?

Archaebacteria that live in extremely salty environments.

What are extreme thermophiles, and what additional extreme condition do some tolerate?

Archaebacteria that live in extremely hot environments; some also survive extreme acidic conditions.

What are methanogens?

Archaebacteria that produce methane gas as a metabolic byproduct.

Do all archaebacteria live in extreme environments?

No, some live in moderate environments such as the oceans.

Name six notable human diseases caused by bacteria.

Tuberculosis, botulism, staph infections, E. coli O157:H7, salmonella poisoning, and Lyme disease.

Which bacterium causes anthrax, and why is it significant in modern history?

Bacillus anthracis, used as a biological weapon including in the 2001 U.S. anthrax attack.

Which bacterium causes bubonic plague and is also a potential biological weapon?

Yersinia pestis.

What three steps do researchers use to weaponize naturally-occurring pathogens?

They select highly virulent strains, make them antibiotic resistant, and develop ways to effectively disperse them.

When did the U.S. end its bioweapons program, and what happened to existing products?

In 1969, and the products were ordered destroyed.

What did the U.S. commit to by signing the Biological Weapons Convention in 1975?

Never to develop or store biological weapons.

How many nations joined the Biological Weapons Convention, and have all honored it?

103 nations joined, but not all have honored it.

Which group of photosynthetic prokaryotes can fix atmospheric nitrogen on their own?

Cyanobacteria.

Where does the nitrogen-fixing bacterium Rhizobium live?

In the root nodules of plants (legumes).

What role do bacteria play in the cycling of organic matter?

They decompose organic materials into inorganic chemicals.

What is bioremediation?

The use of organisms to remove pollutants from soil, air, or water.

Name three examples of bacterial bioremediation.

Sewage treatment facilities, oil-eating bacteria, and clean-up of old mining sites.

Whose theory is endosymbiosis?

Lynn Margulis.

What is endosymbiosis, in the context of the origin of eukaryotes?

The evolutionary process in which eukaryotic cells arose because of mutually beneficial coexistence between prokaryotes, one living inside the other.

According to endosymbiotic theory, how did the first mitochondrion arise?

One prokaryotic cell engulfed another prokaryotic cell that could perform cellular respiration, which then became the first mitochondrion.

According to endosymbiotic theory, how did the first chloroplast arise?

One prokaryotic cell engulfed another prokaryotic cell that could perform photosynthesis, which then became the first chloroplast.

What four pieces of evidence support the endosymbiotic theory?

(1) Mitochondria and chloroplasts have their own DNA and ribosomes that resemble bacterial DNA and ribosomes; (2) they divide by binary fission, like bacteria; (3) mitochondria are about the same size as bacteria; (4) both have infolded inner membranes, like bacteria.

Why is Kingdom Protista sometimes called the 'hodge-podge' or 'misfit' kingdom?

Because it contains huge diversity (unicellular, colonial, and multicellular; producers and consumers) unified only by being eukaryotic and not fitting other kingdoms.

What is the single unifying feature of all protists?

They are all eukaryotic.

What three groups are covered within the supergroup Excavata?

Diplomonads, parabasalids, and euglenozoans.

What distinguishing nuclear and flagellar features define the diplomonads?

They have two nuclei and multiple flagella.

What is unusual about diplomonad mitochondria, and how do they typically respire?

Their mitochondria have no DNA or electron transport chains, and most diplomonads are anaerobic.

What is the diplomonad intestinal parasite of mammals that spreads through feces-contaminated water?

Giardia intestinalis.

What is a key feature of parabasalid mitochondria?

They are reduced.

What is the sexually-transmitted parasitic parabasalid?

Trichomonas vaginalis.

What euglenozoan causes sleeping sickness, and how is it spread?

Trypanosoma, spread by tsetse flies.

What is a common free-living freshwater euglenozoan found in pond water?

Euglena.

What three groups make up the SAR supergroup?

Stramenopiles, alveolates, and rhizarians.

What distinguishing flagellar feature unites the stramenopiles?

Hairy flagella.

What three kinds of organisms belong to the stramenopiles?

Water molds, diatoms, and brown algae.

What are water molds, and where do they live?

Fungus-like protists that decompose dead plants and animals in freshwater habitats.

What do parasitic water molds infect, and what famous agricultural disaster did a water mold relative cause?

They sometimes grow on the skin or gills of fish; downy mildews (relatives of water molds) caused the potato blight.

What makes the diatom cell wall structurally unique?

It is glassy, containing silica, and has two halves that fit together like the top and bottom of a shoe box.

Why are diatoms ecologically important?

They are a key source of food in all aquatic environments.

In what form do diatoms store their food reserves, and what secondary function does this serve?

As an oil, which also provides buoyancy.