Chapter 1 Flashcards
Genetic changes followed by selection are best described as the fundamentals of what process?
- regeneration
- reproduction
- evolution
- genetic drift
- DNA replication
Evolution
(Genetic changes followed by selection are the fundamentals of evolution, and this process is responsible for the stunning variety of organisms on this planet. With a deeper understanding of cells, we can begin to tackle the grand historical problems of life on Earth: its mysterious origins, its stunning diversity produced by billions of years of evolution. All living things on Earth share a common cell ancestor that lived on Earth at least 3.5 billion years ago. Over the course of time, driven by evolution, this ancestral cell gave rise to the great diversity of life we see around us today, yet it also explains why all living things are united by the cell as the fundamental unit of life.)
When comparing liver cells and kidney cells within an organism, many differences can be observed and documented. Which of following is not a difference between liver cells and kidney cells in the same animal?
- The different cells are generated during the animal’s development.
- The different cells express different genes.
- The different cells produce different proteins.
- The different cells have different DNA.
- The different cells have different roles in the body.
The different cells have different DNA.
(The statement that these different cells have different DNA is NOT true about liver cells and kidney cells in the same animal. Liver cells and kidney cells have the same genome, but they use the encoded information differently, expressing different genes and producing different proteins. The different cells have different roles in the body and are generated during the animal’s embryological development.)
Which structure could not be seen using an electron microscope?
- plasma membrane
- electron
- Individual cell
- DNA
- ribosomes
Electron.
(An electron microscope uses a beam of electrons to “illuminate” a sample, and it is the sample that is visualized. However, no one has ever “seen” an individual electron. The electron microscope allows biologists to visualize very small structures, including DNA, ribosomes, and the plasma membrane. This represents the highest magnification and resolution capacity at the biologist’s disposal when observing cells.)
What is a drawback to using light microscopy?
- It cannot be used to view living cells.
- It can be used only to view samples that are sliced very thinly.
- It requires the use of fluorescent probes.
- It cannot be used to view structures smaller than a bacterium.
- It cannot be used to view a whole cell or organism.
It cannot be used to view structures smaller than a bacterium.
(One drawback of light microscopy is that it cannot be used to view structures smaller than a bacterium. Although the limit of resolution for light microscopy is about 0.2 µm, in practice structures smaller than bacteria or mitochondria (which are about 0.5 µm wide) are difficult to resolve without the use of special stains or fluorescent dyes. Unlike electron microscopy, light microscopy can be used to view living specimens. For example, in an introductory biology class, students commonly watch amoebas, paramecia, and other unicellular organisms swim in a sample of pond water. Light microscopy is ideal for viewing individual cells and single-celled organisms like these on slides that are called a “wet mount.” Although samples viewed with a light microscope must be thin enough for light to pass through them, many unicellular organisms can be viewed without any more advanced preparation. Techniques such as confocal microscopy can be used to view the three-dimensional architecture of a cell or tissue that is too thick for light microscopy. )
Which is the smallest object that can be seen using an electron microscope?
- Individual nanometer
- Individual large organelle
- Individual molecule
- Individual hydrogen atom
- Individual electron
Individual molecule.
(An electron microscope allows visualization of structures that are as small as a few nanometers and provides the greatest magnification and resolution currently possible. An individual molecule that is only a few nanometers is therefore the smallest object that can be seen using an electron microscope. An example would be a phospholipid that makes up the plasma membrane or even nucleotides that make up DNA. An electron microscope uses a beam of electrons rather than a beam of light to “illuminate” a sample. Because electrons have a much shorter wavelength than light, electron microscopes greatly extend our ability to see the fine details of cells and even render some of the larger molecules visible individually. Their resolving power is therefore much better than that of the compound light microscope. Only larger cell organelles can be observed with a compound light microscope.)
Is the following statement true, false, or impossible to determine?
An individual ribosome can be seen with a fluorescence microscope.
True.
(Fluorescence microscopes use sophisticated methods of illumination and electronic image processing to see fluorescently labeled cell components in much finer detail. Some modern, super-resolution fluorescence microscopes can push the limits of resolution to about 20 nanometers (nm). That is the size of a single ribosome, a large macromolecular complex in which RNAs are translated into proteins. These microscopes rely on cells incubated with a fluorescently labeled molecule that will bind to the intracellular target.)
What do eukaryotic cells have that prokaryotes lack?
- a nucleus and membrane-bound organelles
- ribosomes
- a cell wall
- nucleic acids
- a means of using chemical energy
A nucleus and membrane-bound organelles.
(All cells have a means of converting energy from one form to another, whether from food, inorganic minerals, or directly from sunlight. Additionally, all cells contain nucleic acids (DNA as their genome) and ribosomes (for creating protein), and some eukaryotic cells like plants and fungi have cell walls. However, only eukaryotic cells have cell nuclei and other membrane-bound organelles; these features are not observed in prokaryotic cells. DNA is contained in the eukaryotic cell nucleus and each membrane-bound organelle carries out a specific cellular function.)
Is the following statement true, false, or impossible to determine?
One thing all cells have in common is an ability to colonize any environment on Earth.
False.
(This statement is false. No cell is capable of colonizing any environment on Earth. Although living cells have expanded to fill every conceivable habitat on Earth, most cells are capable of thriving only in a single, specific environment. A bacterium adapted for life in the human gut, for example, would not survive in a hot spring or an Antarctic lake.)
What organisms commonly colonize the hot acid of volcanic springs, the airless depths of marine sediments, the sludge of sewage treatment plants, the pools beneath the frozen surface of Antarctica, as well as the acidic, oxygen-free environment of a cow’s stomach where they break down ingested cellulose and generate methane gas?
- eukaryotes
- bacteria
- archaea
- all of these
Archaea
(Archaea are prokaryotic cells that can survive in these rather “extreme” environmental conditions. Archaea are found not only in these habitats but also in environments that are too hostile for most other cells. Many of these extreme environments resemble the harsh conditions that must have existed on the primitive Earth, a time when living things first evolved before the atmosphere became rich in oxygen.)
Is the following statement true, false, or impossible to determine?
Like the differentiated cells in an individual plant or animal, all bacteria have the same DNA.
False.
(Unlike the differentiated cells in an individual plant or animal, all bacteria do not have the same DNA. Each bacterial species has its own characteristic nucleotide sequence. The specialized cells within a multicellular organism develop from a single fertilized egg and thus share the same DNA. Bacteria belong to different species, each of which has evolved independently, becoming gradually modified and adapted to suit specific environments. )
Is the following statement true, false, or impossible to determine?
At a molecular level, the members of the two domains of prokaryotes—the archaea and bacteria—differ as much from each other as either does from the eukaryotes.
True.
(Currently, biologists classify all living organisms into three domains: eukaryotes, bacteria, and archaea. Eukaryotic cells, which are bigger and more complex than bacteria and archaea, have long been recognized as a distinct cell type. However, because bacteria and archaea are similar in appearance, they were previously grouped together as prokaryotes. Recent discoveries achieved through DNA sequencing have revealed that bacteria and archaea are actually quite evolutionarily distinct, and diverged from a common prokaryotic ancestor approximately 3.5 billion years ago. Thus, bacteria and archaea are just as distinct from each other as either is from eukaryotic cells.)
Which organelle’s ancestor was likely engulfed by primitive eukaryotes to help the cell survive in an oxygen-rich atmosphere?
- endoplasmic reticulum
- lysosome
- Golgi apparatus
- peroxisome
- mitochondrion
Mitochondrion
(The mitochondrion is an organelle that contains a double membrane—that is, two lipid bilayers that surround it. This organelle’s ancestor was likely engulfed by primitive eukaryotes to help the cell survive in an oxygen-rich atmosphere. Thus, the inner mitochondrial membrane derived from the plasma membrane of the engulfed cell, and the outer mitochondrial membrane derived from the evolving eukaryotic cell’s plasma membrane. The Golgi apparatus, endoplasmic reticulum, lysosome, and peroxisome are not surrounded by a double membrane.)
What is the name of the process by which eukaryotic cells engulf material captured from an external medium?
- endocytosis
- exocytosis
- endosymbiosis
- cytokinesis
- endomitosis
Endocytosis
(Endocytosis is the name of the process by which eukaryotic cells engulf material captured from an external medium. This is accomplished when a portion of the plasma membrane invaginates and then pinches off, forming a transport vesicle. In the reverse process, termed exocytosis, a transport vesicle fuses with the plasma membrane and in so doing, releases its contents outside the cell. Together, endocytosis and exocytosis represent an important import and export mechanism for the cell, especially for large sized or large quantities of materials.)
Which of the following is a stack of flattened membrane-enclosed sacs that receives molecules made in the endoplasmic reticulum, often chemically modifies them, and then directs them to the exterior of the cell or to various locations inside the cell?
- endoplasmic reticulum
- ribosome
- Golgi apparatus
- lysosome
- peroxisome
Golgi apparatus
(The Golgi apparatus functions to modify and package molecules and appears like a stack of large, flattened vesicles with smaller vesicles that have budded from the Golgi stack nearby. These vesicles contain molecules that are being transported to other parts of the cell or are destined to be excreted. The Golgi apparatus is one of a group of membrane-bound organelles including the endoplasmic reticulum, lysosomes, and peroxisomes, which all work together in a dynamic fashion to synthesize, break down, modify, and transport molecules within the cell.)
Which cellular component separates the DNA of eukaryotic cells from the cytoplasm?
- nuclear membrane
- smooth endoplasmic reticiulum
- plasma membrane
- cell wall
Nuclear membrane
(The DNA of eukaryotic cells is contained within the cell nucleus, and the nucleus is separated from the cytoplasm by the nuclear envelope. The nucleus is enclosed within two concentric membranes that form the nuclear envelope, and it contains molecules of DNA: extremely long polymers that encode the genetic information of the organism. All eukaryotic cells contain an endoplasmic reticulum and plasma membrane, but these are not the barriers between eukaryotic DNA and the cytoplasm.)
Which of the following is a model plant used by scientists?
- Saccharoymeces cerevisiae
- Homo sapiens
- Caenorhabditis elegans
- Homo floresiensis
- Arabidopsis thaliana
Arabidopsis thaliana
(Arabidopsis thaliana, the common wall cress, is a model plant that is favored by plant biologists for a number of reasons: it can be grown indoors and reproduces quickly, with one plant giving rise to thousands of offspring in just 8–10 weeks, and it is related to plants of agricultural value, making research with it relevant to the production of crops that feed humans. A. thaliana, like S. cerevisiae, C. elegans, and other model organisms, has its strengths and limitations, but all are indispensable in helping researchers understand the cellular and molecular processes that govern life.)
Which is not a function of proteins?
- acting as molecular motors
- encasing certain viruses
- providing cells with structural support
- encoding genetic information
- catalyzing biochemical reactions
Encoding genetic information
(Encoding genetic information is not a cellular function of proteins; rather, nucleic acids perform this function. A cell’s genome—that is, the entire sequence of nucleotides in an organism’s DNA—provides the information that instructs a cell how to produce all of the proteins needed to function. However, DNA codes for proteins indirectly, with messenger RNA molecules serving as the link between the DNA sequence of a gene and the amino acid sequence of the protein. Proteins carry out a wide range of tasks and the function of a cell is determined, in large part, by which proteins it produces.)
Is the following statement true or false, and why?
Within a developed multicellular organism, all cells possess the ability to divide and do so regularly.
- It is false, because some cells lose the ability to replicate their DNA and divide.
- It is true, because all cells can always split into two cells in the same manner.
- It is true, because all cells can always replicate their DNA in the same manner.
- It is false, because most multicellular organisms cannot reproduce at all.
It is false, because some cells lose the ability to replicate their DNA and divide.
(The ability to reproduce themselves is the hallmark of a living organism. However, in a multicellular organism, this does not necessarily mean that all cells in that organism undergo continual cell division. Multicellular organisms have many different types of specialized cells, each performing a specific function. In certain cases, such as epithelial cells that line body cavities, that function requires continual cell division and replacement. However, in other cases—including red blood cells, nerve cells, skeletal muscle cells, and gametes—the cells are no longer capable of further cell division. Such cells are said to be “terminally differentiated.”)
What is a drawback to using electron microscopy?
- It cannot be used to view a whole cell or organism.
- It can be used only to view atomic details in structures larger than a ribosome.
- It cannot be used to view living cells
- It can be used only to view samples that are sliced very thinly.
- It requires the use of fluorescent probes.
It cannot be used to view living cells.
(Electron microscopy can reveal details down to a few nanometers, but it cannot be used to view living cells. Electron microscopy is carried out in a vacuum and bombards samples with electrons, conditions that would destroy living cells. Transmission electron microscopy requires samples to be thinly sliced, but scanning electron microscopy can be used to view the surface details of whole samples. For both types of electron microscopy, the sample must be incubated and heated with heavy metals. These conditions would be far too harsh for living cells.)
Which of these cannot be resolved with a conventional light microscope?
- bacterium
- cell nucleus
- ribosome
- embryonic cell
- mitochondrion
Ribosome
(A conventional light microscope has a resolution of about 0.2 µm. A ribosome is approximately 20 nanometers (nm) in size, which is 0.02 µm, and below the resolution of a light microscope. If an object is below the limit of resolution, then that object cannot be individually seen with that instrument. Mitochondria, bacterial cells, cell nuclei, and embryonic cells are all larger than the limit of resolution (about 0.2 µm) of the conventional light microscope and therefore these structures can be observed.)
In 1970, Frye and Edidin published research describing the mobility of plasma membrane proteins. They fused mouse and human cells together, creating a hybrid cell, and then examined the localization of mouse and human proteins over time. Initially mouse and human proteins were each restricted to one-half of the heterokaryon, but over time the mouse and human proteins mixed, with each being present over the entire cell surface. What technique did Frye and Edidin likely use to examine the mouse and human proteins?
- transmission electron microscopy
- Interference contrast light microscopy
- scanning electron microscopy
- fluorescence microscopy
Fluorescence microscopy
(Frye and Edidin tagged antibodies that recognized mouse proteins with the fluorescent protein rhodamine and antibodies that recognized human proteins with fluorescein. The location of mouse and human proteins could then be observed over time with a fluorescent microscope, as shown in the schematic below.)
Which statement represents the cell theory?
- All cells resemble square or rectangular chambers
- All cells contain DNA
- All cells require a continual input of energy to sustain life.
- All cells can be seen using a microscope.
- All cells are formed by the growth and division of existing cells.
All cells are formed by the growth and division of existing cells.
(Observations made with the light microscope in the nineteenth century by biologists, including the seminal work by Matthias Schleiden and Theodor Schwann, documented that all plant and animal tissues were composed of cells. With repeated examination, a concept slowly emerged that all living organisms are composed of cells and that new cells are formed by the division of existing cells. Later experiments by Louis Pasteur helped confirm the cell theory and dispel the competing idea of spontaneous generation.)
Which statement represents the cell theory?
- All cells resemble square or rectangular chambers
- All cells contain DNA
- All cells require a continual input of energy to sustain life.
- All cells can be seen using a microscope.
- All cells are formed by the growth and division of existing cells.
All cells are formed by the growth and division of existing cells.
(Observations made with the light microscope in the nineteenth century by biologists, including the seminal work by Matthias Schleiden and Theodor Schwann, documented that all plant and animal tissues were composed of cells. With repeated examination, a concept slowly emerged that all living organisms are composed of cells and that new cells are formed by the division of existing cells. Later experiments by Louis Pasteur helped confirm the cell theory and dispel the competing idea of spontaneous generation.)
Which is not evidence for the endosymbiotic origins of mitochondria and chloroplasts?
- Mitochondria and chloroplasts reproduce by dividing in two.
- Mitochondria and chloroplasts resemble bacteria.
- Mitochondria and chloroplasts are each surrounded by a double membrane.
- Mitochondria and chloroplasts contain their own DNA.
- Mitochondria and chloroplasts have similar DNA.
Mitochondria and chloroplasts have similar DNA.
(Mitochondria and chloroplasts do not have similar DNA. The endosymbiotic origins of mitochondria and chloroplasts suggest that these organelles arose from separate instances of the developing/evolving primitive eukaryotic cell engulfing a smaller bacterial cell. The inner membrane would be derived from the engulfed cell membrane and the outer membrane would be derived from the primitive eukaryotic cell membrane. Because these are separate instances of endosymbiosis, there would be no expectation that the mitochondria and the chloroplast would have similar DNA. Mitochondria and chloroplasts resemble bacteria and have DNA that has evolved from those very different forms of bacteria—thus, they have unique DNA.)
