Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 4
Test Yourself Questions
1. The cell doctrine states that
a. any living organism is composed of one or more cells.
b. new cells are derived from organic molecules from the environment.
c. the smallest units of living organisms are atoms.
d. the function of cells depends on the shape of the cell.
e. all of the above.
Answer: a. The cell doctrine states that all living things are composed of cells, new cells are derived
from pre-existing cells by cell division and that the smallest unit of life is a cell.
2. When using microscopes, the resolution refers to
a. the ratio between the size of the image produced by the microscope and the actual size of
the object.
b. the degree to which a particular structure looks different from other structures around it.
c. how well a structure takes up certain dyes.
d. clarity of an image.
e. the degree to which the image is magnified.
Answer: d. Resolution is a measure of the clarity of an image.
3. A bacterial cell may possess a ___________, which may protect it from the immune system of other
multicellular organisms that it may infect.
a. cell wall
b. flagellum
c. pili
d. nucleoid
e. capsule
Answer: e. Bacterial cells with a capsule may have a lower probability of being destroyed by the immune
system of organisms that they infect.
4. Different cells of the same multicellular individual have different proteomes due to all of the following
except
a. differences in the types of proteins made in different cell types.
b. differences in the genomes of the different cell types.
c. the abundance of certain proteins may not be the same in different cell types.
d. the amino acid sequences of proteins may be different in different cell types.
e. different cell types may alter the proteins in different ways.
Answer: b. All nucleated cells of the same organism have essentially identical genomes. The differences
in proteomes are usually the result of differences in gene expression levels and modifications during
and after protein synthesis.
5. The process of polypeptide synthesis is called
a. metabolism.
b. transcription.
c. translation.
d. hydrolysis.
e. both c and d.
Answer: c. Translation is the process of polypeptide synthesis, the chemical reactions involved in linking
amino acids together.
6. Each of the following is part of the endomembrane system except
a. the nuclear envelope.
b. the endoplasmic reticulum.
c. the Golgi apparatus.
d. lysosomes.
e. peroxisomes.
Answer: e. Peroxisomes are not considered part of the endomembrane system.
7. Molecules move into and out of the nucleus by
a. diffusing through the nuclear membrane.
b. transport proteins.
c. moving through nuclear pores.
d. attaching to the nucleolus.
e. all of the above.
Answer: c. Nuclear pores provide passageways into and out of the nucleus.
8. Functions of the smooth endoplasmic reticulum include
a. detoxification of harmful organic molecules.
b. metabolism of carbohydrates.
c. protein sorting.
d. all of the above.
e. a and b only.
Answer: e. Though protein sorting does initiate in the rough endoplasmic reticulum, the smooth
endoplasmic reticulum functions in other metabolic processes including carbohydrate and lipid
metabolism, storage and detoxification.
9. The central vacuole in many plant cells is important for
a. storage.
b. photosynthesis.
c. structural support.
d. all of the above.
e. a and a only.
Answer: e. The central vacuole serves as a storage site but also provides structural support to the cell.
10. Peroxisomes
a. are vesicles similar to lysosomes that break down different classes of macromolecules.
b. play an important role in the synthesis of ATP.
c. are vesicles that contain enzymes necessary for manufacturing complex sugars.
d. are the organelles primarily involved in protein synthesis.
e. contain the enzyme catalase that breaks down hydrogen peroxide to water and oxygen.
Answer: e. Peroxisomes contain catalase, an enzyme that breaks down hydrogen peroxide producing
water and oxygen.
Conceptual Questions
1. Define organelle.
Answer: A subcellular structure or membrane-bounded compartment with its own unique structure and
function.
2. Explain how actin filaments are involved in movement.
Answer: In the case of amoeboid movement, this occurs via the dynamic rearrangement of the actin
cytoskeleton. Actin filaments are formed near the leading edge to create a projection called a
lamellipodium. The cell is pulled toward the leading edge using motor proteins, such as myosin, which
tugs on actin filaments and promotes cellular movement.
3. Explain the function of the Golgi apparatus.
Answer: The Golgi apparatus consists of a stack of flattened membrane-bound compartments. The cis
Golgi is close to the ER membrane, the trans Golgi is near the plasma membrane, and the medial Golgi
is found in the middle. The Golgi performs three overlapping functions: secretion, processing and
protein sorting. The Golgi apparatus packages different types of material into secretory vesicles that
later fuse with the plasma membrane, thereby secreting their products outside the cell. Enzymes in the
Golgi apparatus process or modify certain proteins or lipids. The third function of the Golgi apparatus is
protein sorting. After a protein enters the Golgi from the ER, it will be sorted into one of six locations,
depending on the protein’s function.
Experimental Questions
1. What hypothesis was tested in the experiment of Figure 4.14? What observations led to the proposal
of this hypothesis?
Answer: The researchers were testing the hypothesis that myosin acts as a motor protein during muscle
contraction, causing the movement of the contraction. Earlier researchers had proposed the sliding
filament model to explain muscle contraction. This suggested that actin filaments slide past myosin
filaments during contraction. This experiment proposed to demonstrate that movement was generated
by the activity of myosin.
2. What is the benefit of purifying cellular components and studying them in vitro instead of in intact
cells? What was the benefit of using Nitella axillaris to determine the function of myosin? What was the
purpose of using the fluorescent beads in the experiment? What was the purpose of NEM in the
experiment?
Answer: Cells contain a large number of different components. It is difficult to identify a single protein
and determine its function when it is combined with the thousands of other proteins and molecules
found in a cell. Obtaining a purified sample and studying it in vitro allows the researcher to determine
the function of the protein with more certainty.
Though purified samples of actin and myosin can be obtained from cells, the actin samples are not
useful for studying function. Nitella cells have actin filaments along the inside of the cell membrane that
can be used for in vitro studies. Also, the Nitella cells are very large, which makes them ideal for use in
these types of studies.
The fluorescent beads were attached to the myosin. The beads were used to track the movement of the
myosin during the experiment. In other words, the fluorescent beads acted as visual flags for the
researchers to follow during the experiment. The NEM binds to myosin and blocks its activity. If the
presence of NEM stopped myosin movement, this would indicate that myosin was the motor protein
causing the movement during muscle contraction.
3. Explain the results of the experiment of Figure 4.14.
Answer: The researchers were able to demonstrate several important features of movement due to actin
and myosin interaction. First, the researchers were able to demonstrate that ATP was necessary for
movement. In the absence of ATP no movement was observed. Also, by blocking the activity of myosin
using NEM, the researchers were able to demonstrate that myosin was responsible for movement
(which is also necessary for muscle contraction). When NEM was introduced, no movement was seen.
Collaborative Questions
1. Discuss several differences between plant and animal cells.
Answer:



Plant cells have a rigid cell wall and animal cells do not. The function of the cell wall in plants is to
provide support and stability to the plant as a whole. Unlike the cell membrane (which is found in
both plant and animal cells) the cell wall has more of a supportive role than a regulatory one.
Plant cells have a large central vacuole and animal cells do not. The term vacuole means "empty
space" although it contains fluid and sometimes contains even solid substances. In a mature plant
cell the central vacuole may occupy 80 percent or more of the cells total volume.
Plant cells contain chloroplasts and animal cells do not. The chloroplast is the site of photosynthesis
in plant cells and this is where they convert light energy into chemical energy.
2. Discuss the relationship between the nucleus, rough endoplasmic reticulum, and the Golgi
apparatus.
Answer: These three organelles are interconnected and are required in eukaryotic cells to function
properly. The nucleus is the control center of the cell and houses the DNA of the cell. DNA is the
blueprint for maintaining and building structures such as proteins inside the cell. Without the nucleus,
the cell cannot repair or maintain itself and cannot live indefinitely under this condition. The rough
endoplasmic reticulum (RER) is the place in the cell where proteins are made. It does this with the help
of structures called the ribosomes. But the RER cannot build a protein without instructions from the
nucleus. Therefore information from the nucleus must be delivered to the RER in the form of messenger
RNA. After most protein are made at the RER, they are sent to the Golgi apparatus via membrane
vesicles. From the Golgi, most proteins are then sorted to other locations such as the ER, lysosomes,
vacuoles, and plasma membrane, or they are secreted from the cell.