exam 2 self assessment questions

Question 1

What are the steps necessary to synthesize mRNA from each of the following: double-stranded DNA?

Answer 1

double stranded DNA –> mRNA

Question 2

What are the steps necessary to synthesize mRNA from each of the following: single-stranded (+)DNA?

Answer 2

single-stranded (+) DNA –> double stranded DNA –> mRNA

Question 3

What are the steps necessary to synthesize mRNA from each of the following: single-stranded (-) DNA?

Answer 3

single-stranded (-) DNA –> double-stranded DNA –> mRNA

Question 4

What are the steps necessary to synthesize mRNA from each of the following: single-stranded (+) RNA?

Answer 4

single-stranded (+) RNA –> single-stranded (-) DNA –> double-stranded DNA –> mRNA
or
single-stranded (+) RNA –> single-stranded (-) DNA –> mRNA

Question 5

What are the steps necessary to synthesize mRNA from each of the following: single-stranded (-) RNA?

Answer 5

single-stranded (-) RNA –> mRNA

Question 6

How are bacterial and archaeal cells similar, and how are they different?

Answer 6

prokaryotic cells (both bacteria and archaeon’s) do not contain a nucleus or other membrane bound organelles; they rarely have introns in their genes; their DNA is in a circular form; and they are relatively small in size as compared to eukaryotic cells. Archaeal cells also possess some features that differ from those of bacteria: Archaea have different lipids present in their membrane; do not undergo photosynthesis using chlorophyll; are in some cases capable of methanogenesis; and have histones proteins in their cells. Importantly, DNA transcription in archaeon’s uses RNA polymerase and ribosomes that are more similar to those of eukaryotes than to those of bacteria. Furthermore, many of the antibiotics that target protein synthesis in bacteria are ineffective against archaeon’s, suggesting fundamental differences in translation as well.

Question 7

How do prokaryotic cells obtain nutrients, and how does this process put constraints on their size?

Answer 7

Prokaryotic cells obtain nutrients by diffusion-that is, through the random motion of molecules, with net movement from areas of higher concentration to areas of lower concentration. Nutrients diffuse from the environment across the cell membrane and need to be able to reach all areas of the cell. This requirement limits the size of cells that can obtain nutrients by diffusion.

Question 7

How does surface area and volume of a cell change with its size?

Answer 7

The surface area of a spherical cell, which represents the area available for taking up molecules from the environment, increases as the square of the radius. However, the cell’s volume, which comprises the amount of cytoplasm that is supported by diffusion, increases as the cube of the radius. Therefore, a small cell has more surface area in proportion to its volume, whereas a bigger cell has less surface area in proportion to its volume. As cell size increases, it becomes more difficult to supply the cell with the materials needed for growth using diffusion alone.

Question 7

In eukaryotes, sexual reproduction is the main process that generates new gene combinations. How do bacteria generate new gene combinations in the absence of sexual reproduction?

Answer 7

In prokaryotic organisms, genes are transferred from one organism to another by horizontal gene transfer, which facilitates the generation of new gene combinations.

Question 8

How can photosynthesis occur without the production of oxygen, and how can respiration occur without requiring oxygen?

Answer 8

Anoxygenic photosynthesis uses hydrogen sulfide, hydrogen gas, ferrous iron, or arsenite instead of H2O as the electron donor, thus, O2 is not released as a by-product. Respiration can occur without requiring oxygen, using alternative electron acceptors such as nitrogen, sulfur, manganese, iron, or arsenic oxides.

Question 8

How do photoautotrophs such as cyanobacteria differ from photoheterotrophs such as heliobacteria?

Answer 8

Cyanobacteria use much of the ATP they generate to drive the reduction of CO2 into organic molecules used for growth and reproduction. In photoheterotrophs, the organic molecules needed for growth are taken from the environment, leaving ATP available for other uses.

Question 8

How did the biological carbon cycle work on the early Earth, where oxygen gas was essentially absent from the atmosphere and oceans?

Answer 8

Carbon dioxide could have been incorporated into organic molecules by anoxygenic photosynthesis, which does not generate oxygen. Organic matter could have been oxidized to carbon dioxide by anaerobic respiration (and fermentation), which does not use oxygen.

Question 8

What are the roles of bacteria and archaeons in the sulfur and nitrogen cycles?

Answer 8

In the sulfur cycle, bacteria and archaeons reduce sulfur in a process called anaerobic respiration; they oxidize sulfur through chemosynthetic and photosynthetic processes. In the nitrogen cycle, bacteria and archaeons fix nitrogen gas to ammonia; through the processes of nitrification, denitrification, and anammox, they turn ammonia back into nitrogen gas.

Question 8

How would the nitrogen cycle operate in the absence of bacteria and archaeons?

Answer 8

It wouldn’t. Bacteria and archaeons cycle nitrogen between the atmosphere (nitrogen gas) and biologically useful forms. In the absence of these prokaryotes, only a relatively small amount of nitrogen would be fixed into a biologically useful form by lightning, greatly limiting the extent of life.

Question 8

Name and describe three major groups of Bacteria

Answer 8

Proteobacteria are the most diverse of the bacterial groups and include many organisms that participate in the expanded carbon and other biogeochemical cycles. Gram-positive bacteria include both pathogens and bacteria that produce antibiotics. Cyanobacteria are species of bacteria that can carry out oxygenic photosynthesis.

Question 9

What are three environmental extremes where Archaea thrive?

Answer 9

New Archaea are being discovered every day, so the shape and branch density of the archaeal tree of life are changing as well. Archaea include acid-loving and heat-loving organisms, as well as organisms that thrive in salt-saturated environments. Many of the physical limits to life are defined by Archaea that live in extreme environments.

Question 9

If early branches on the bacterial and archaeal trees are dominated by hyperthermophilic microorganisms, does this mean that the early oceans were very hot?

Answer 9

Not necessarily. Today, hyperthermophiles live in hot springs and hydrothermal ridges on the ocean floor. These might have been the environments in which the last common ancestors of these organisms thrived.

Question 10

Which features distinguish a eukaryotic cell from a prokaryotic cell?

Answer 10

Key features that distinguish a eukaryotic cell from a prokaryotic cell are a membrane-bound nucleus that houses DNA, creating separate cellular compartments for transcription and translation; membrane-bound organelles that further organize the cell interior and compartmentalize different cellular processes, and dynamic membranes and cytoskeleton that can be remodeled quickly, allowing cells to change shape and transport materials throughout the cell. Also, eukaryotic cells characteristically have multiple linear chromosomes, unlike the single circular chromosomes of Bacteria and Archaea

Question 11

Which forms of energy metabolism are found in eukaryotes?

Answer 11

The main forms of energy metabolism found in eukaryotes are aerobic respiration in the mitochondrion and photosynthesis in the chloroplast. A few single-celled eukaryotic organisms lack mitochondria and contain small organelles called hydrogenosomes that generate ATP by anaerobic processes.

Question 11

How did the evolutionary expansion of eukaryotic organisms change the way carbon is cycled through biological communities?

Answer 11

In general, eukaryotes employ a subset of the metabolic pathways used by bacteria. Most eukaryotes are capable of aerobic respiration; most can also gain at least some energy by fermentation; and some can perform photosynthesis. In many ways, then, carbon cycling by eukaryotes is much like carbon cycling by aerobic prokaryotes. The novel contribution of eukaryotes is the ability to capture and ingest other cells, thereby introducing predation into the carbon cycle.

Question 12

What is the origin of the chloroplast and the mitochondrion?

Answer 12

The chloroplast and mitochondrion are thought to have originated through endosymbiosis, a symbiosis in which one partner lives within the other.
Chloroplasts closely resemble cyanobacteria and are thought to be descendants of symbiotic cyanobacteria that lived within eukaryotic cells.
Mitochondria closely resemble protebacteria and are also thought to have evolved as endosymbionts.

Question 12

What are two hypotheses for the origin of the eukaryotic cell?

Answer 12

One hypothesis for the origin of eukaryotic cells is that the host for mitochondrion-producing endosymbiosis was itself a true eukaryotic cell with a nucleus, cytoskeleton, and endomembrane system; subsequent engulfment of a proteobacterium then led to the evolution of mitochondria. A second hypothesis for the origin of eukaryotic cells argues that the eukaryotic cell as a whole began as a symbiotic association between a proteobacterium and an archaeon, and subsequently evolved a nucleus and endomembrane system through the infolding of the plasma membrane

Question 12

What are the names of the seven superkingdoms of eukaryotes? Name an organism in each one.

Answer 12

The seven superkingdoms of eukaryotes are (1) Opisthokonta (example: animals); (2) Amoebozoa (example: slime molds); (3) Archaeplastida (example: land plants); (4) Stramenopila (example: brown algae), (5)
Alveolata (example: ciliates); (6) Rhizaria (example: cercozoans); and (7)
Excavata (example: euglenid algae).

Question 13

Was the common ancestor of plants and animals unicellular or multicellular?

Answer 13

Unicellular. Plants form one branch of the green algal tree, whose early nodes are all characterized by unicellular forms. Similarly, the branch containing animals has choanoflagellates and other unicellular forms in its lower part.
Thus, animals and plants evolved multicellularity independently of each other.
Note that genetic evidence further supports this phylogenetic hypothesis: plants and animals have different sets of genes that regulate multicellular development (Chapter 26)-

Question 14

How do the molecular sequences of genes in chloroplasts show how photosynthesis spread throughout the eukaryotic domain?

Answer 14

Molecular sequences for genes in red and green algae show the close evolutionary relationship of these organelles to free-living cyanobacteria. This evidence supports the hypothesis that eukaryotes initially gained the ability to photosynthesize through their incorporation of symbiotic cyanobacterial cells. Gene sequences in the chloroplasts of other photosynthetic eukaryotes (brown algae, diatoms, euglenids, and other algae) are very similar to those of red and green algal chloroplasts, indicating that photosynthesis spread throughout the eukaryotic tree by the incorporation of symbiotic green or red algal cells into other eukaryotes.

Question 15

When did the first eukaryotic cell evolve?

Answer 15

The first eukaryotic cell is thought to have evolved at least 1800 million years ago.

Question 16

What kind of evidence is used to date the timing of the first eukaryotic cell?

Answer 16

The date of the first eukaryotic cell is based on evidence in the fossil record of coastal marine environments. Microfossils found in these environments have complicated wall structures such as interlocking plates, long and branching arms, and complex internal layering. Comparison with living organisms suggests that such fossils could be formed only by organisms with a cytoskeleton and endomembrane system, the hallmarks of eukaryotic biology.

Question 17

How do simple multicellular organisms differ from complex multicellular organisms?

Answer 17

Simple multicellular organisms do not have differentiated cells and tissues, whereas complex multicellular organisms do have differentiated cells and tissues. Moreover, in simple multicellular organisms, all or nearly all cells are in direct contact with the environment. In complex multicellular organisms, most cells are completely surrounded by other cells. As a result, cells in complex multicellular organisms communicate with one another through signaling mechanisms that allow coordinated growth and cell differentiation.

Question 18

How does diffusion limit the size of organisms?

Answer 18

Diffusion-the random motion of molecules, with net movement from areas of high concentration to areas of low concentration-limits the size (thickness) of organisms because it is effective only over small distances. The distance through which molecules can diffuse quickly depends in part on how great the concentration difference is. For example, if a cell or tissue relies on diffusion of oxygen, its thickness is limited by the difference in oxygen concentration between the cell or tissue and its environment. In shallow water, organisms relying on diffusion can reach a thickness of 1 mm to 1 cm.

Question 19

How do multicellular organisms get around the size limits imposed by diffusion?

Answer 19

Plants and animals get around the size limits imposed by diffusion by actively pumping nutrients and other molecules to all parts of the organism through bulk flow. Bulk flow allows key molecules to be transported over distances much greater than those possible that can be covered by diffusion alone, making larger organisms possible. Other organisms, such as sponges or jellyfish, grow large by adopting shapes and structures that allow metabolically active cells to remain in close proximity to the environment.

Question 20

Which arose first: animals with many cells or cell adhesion molecules?

Answer 20

Evidence from the single-celled protists most closely related to animals shows that at least some of the proteins that govern cell attachment in animals were present in their unicellular ancestors. These proteins probably had distinct functions in these cells. Cell adhesion molecules continued to evolve along with complex multicellularity in animals.

Question 21

All cells in your body derive from a single fertilized egg, yet your body contains many different types of cells. How can we explain this phenomenon?

Answer 21

The differentiation of distinct cell types, tissues, and organs in animals reflects a developmental program in which cells receive molecular signals from surrounding cells and the environment. These signals alter the expression patterns of genes and the activities of proteins, thereby governing the different developmental fates of the cells in our bodies.

Question 22

How do plants and animals differ in the ways their cells adhere, communicate, and differentiate during development?

Answer 22

All multicellular organisms have molecules that promote adhesion between cells and communication between cells, but plants and animals have largely distinct sets of molecules for these functions. Plants and animals also exhibit distinct patterns of development: stem cells called meristems remain active for life in plants, whereas tissues and organs differentiate early on in animal development.

Question 23

What is a key difference in structure between the cells of multicellular plants and the cells of multicellular animals?

Answer 23

One key difference is that plants have cell walls around their cells, whereas animals do not. Cell walls restrict plant cells from moving, which in turn determines many features of plants' development and function.

Question 24

Which environmental changes) are recorded by the sedimentary rocks that contain the oldest fossils of large active animals?

Answer 24

The study of sedimentary rocks shows that abundant oxygen came to exist about 580-560 million years ago. This corresponds in time to the first fossil records of complex multicellular organisms.

Question 25

How does evo-devo research help us to understand how animals have diversified to form so many distinct species?

Answer 25

In evo-devo research, biologists compare the developmental pathways that regulate growth and differentiation of body types. By studying differences in the genetic regulation of development between species, biologists can understand how specific mutations have given rise to distinct animal morphologies. Evo-devo also helps us to understand the genetic basis of plant diversity.