Ch. 4: A Tour of the Cell
Conversions
1 cm = 10^-2 1 mm = 10^-3 m 1 micrometer = 10^-3 mm = 10^-6 m 1 nanometer = 10^-3 micrometer = 10^-9 m
A normal range for a typical eukaryotic cell is ____________.
10 to 100 micrometers
A certain cell has a dense nucleoid region, ribosomes, but no membrane-enclosed organelles. Based on this information, it could be _____.
an archaean archaea and other prokaryotes have no internal membrane-enclosed organelles, but have both ribosomes and a region called the nucleoid region where their DNA can be found
Where are the ribosomes that produce enzymes responsible for the first steps of sugar metabolism found?
cytoplasm first steps of sugar metabolism occur within the cytoplasm so the ribosomes in the cytoplasm are responsible for making the necessary enzymes
Where would you expect to find contractile proteins in a cell?
cytoskeleton actin, a component of the cytoskeleton, is one of the contractile proteins of the cell
Which of the following structures is NOT directly involved in cell support or movement? a. microfilament b. flagellum c. microtubule d. gap junction e. cell wall
d. gap junction
Which of the following are stored in the lysosomes of the cell?
digestive enzymes
The cell junctions in plant cells that provide channels between adjacent cells are generally _____.
plasmodesmata plasmodesmata form channels between adjacent plant cells
Of the following organelles, which group is involved in manufacturing the substances needed by the cell?
ribosome, rough endoplasmic reticulum, smooth endoplasmic reticulum each structure is capable of synthesis
Phospholipid bilayer membranes are semipermeable. Which of the following can move across the membrane without assistance?
O2 oxygen and carbon dioxide can cross the phospholipid bilayer membranes
Briefly describe the three kinds of junctions that can connect animal cells, and compare their functions.
Tight junctions form leakproof sheets of cells. Anchoring junctions link cells to each other; they form strong sheets of cells. Gap junctions are channels through which small molecules can move from cell to cell.
Mitochondria are found in ______________.
both plant cells and animal cells mitochondria are found in nearly all eukaryotic cells
The nucleolus _____________.
manufactures ribosomes nucleolus, which is composed of DNA, RNA, and protein, is the site of ribosome synthesis
In which cell would you find the most lysosomes?
white blood cell that engulfs bacteria
The cells of an ant and a horse are, on average, the same small size; a horse just has more of them. What is the main advantage of small cell size?
Small cells can better take up sufficient nutrients and oxygen to service their cell volume. Small cells have a greater ratio of surface area to volume.
Which cellular organelle is required for photosynthesis to occur in eukaryotic cells?
chloroplast chloroplasts contain the green pigment chlorophyll and enzymes and other molecules that function in the photosynthetic production of food
Under a light microscope, which substance becomes visible as the cell divides?
chromatin chromatin fibers of individual chromosomes coil and condense so that they can be distinguished
Basal bodies are most closely associated with which of the following cell components?
cilia microtubule assembly of a cilium or flagellum is anchored in the cell by a basal body, which is structurally identical to a centriole
The function of the chloroplast is to ___________________.
convert light energy to chemical energy
Which of the following is a function of the rough endoplasmic reticulum?
creating receptor proteins made by the rough ER and then processed by the Golgi apparatus before being inserted into the cell membrane
What are the inner folds of the mitochondria called?
cristae the folds within the mitochondria
In which cell would you find the most mitochondria?
muscle cell in thigh of long-distance runner
The general function of _____ is the breakdown of substances.
peroxisomes peroximsomes are involved in many processes that share the breakdown of hydrogen peroxide as a by-product
Chloroplasts are found in __________.
plant cells and some protists chloroplasts: lens-shaped organelles found in leaves and other green organs of plants and photosynthetic protists
Dye injected into a plant cell might be able to enter an adjacent cell through a(n) _____.
plasmodesma cell walls of plant cells contain numerous channels, with strands of cytoplasm passing through them and connecting one cell's cytoplasm to that of an adjacent cell
The architecture of cell surfaces can be viewed in the most detail using a __________.
scanning electron microscope uses an electron beam to provide a detailed picture of the outlines of the surface
You would expect a cell with an extensive Golgi apparatus to _____.
secrete a lot of material Golgi intercepts ER vesicles, modifies the contents for export, and repackages the material in a Golgi vesicle that can fuse with the plasma membrane
What are the limits on which maximum cell size depends?
surface-to-volume ratio limits the amount of material that can enter and exit the cell, limiting cell size
Lysosomes are derived from _____ and function in _____.
the Golgi apparatus and rough endoplasmic reticulum; digestion of worn-out organelles these are membrane-enclosed sacs of hydrolytic enzymes that are used to digest macromolecules and are produced by budding off the Golgi
Which of the following is the most likely consequence for a cell lacking functional lysosomes?
the cell becomes crowded with undigested wastes lysosome: membrane-enclosed sac of hydrolytic enzymes that the cell uses to digest macromolecule - in some cases, recycling the cell's own organic material
The term resolving power refers to _____.
the clarity of the image in showing two objects as separate resolving power: the ability to see two points or objects as separate
Your intestine is lined with individual cells. No fluids leak between these cells from the gut into your body. Why?
the intestinal cells are bound together by tight junctions membranes of neighboring cells are actually fused at a tight junction, forming a seal that prevents the leakage of extracellular fluid across a layer of epithelial cells
The ultrastructure of a chloroplast is best studied using a __________.
transmission electron microscope
Which microscope would be best suited to the measurement of the internal structures of a bacterial cell?
transmission electron microscope
Which of the following correctly matches an organelle with its function? The _______ functions in ______________.
vacuole; storage plant cells have a central vacuole while most animal cells have several smaller vacuoles located throughout the cytoplasm
Which of the following clues would tell you whether a cell is prokaryotic or eukaryotic?
whether or no the cell is partitioned by internal membranes Prokaryotic cells lack any internal membranous compartmentalization
Describe the structure of the plasma membrane of an animal cell. What would be found directly inside and outside the membrane?
The plasma membrane is a phospholipid bilayer with the hydrophilic heads facing the aqueous environment on both sides and hydrophobic fatty acid tails mingling in the center of the membrane. Proteins are embedded in and attached to this membrane. Microfilaments form a three-dimensional network just inside the plasma membrane. The extracellular matrix outside the membrane is composed largely of glycoproteins, which may be attached to membrane proteins called integrins. Integrins can transmit information from the ECM to microfilaments on the other side of the membrane.
Mitochondria and chloroplasts are similar in that they both _____; they are different in that chloroplasts, but not mitochondria, _____.
have a double membrane; carry out photosynthesis mitochondria are the sites of cellular respiration chloroplasts carry out photosynthesis
A type of cell called a lymphocyte makes proteins that are exported from the cell. Which of the following traces the path of a protein from the site where its polypeptides are made to its export?
rough ER ... Golgi ... transport vesicle ... plasma membrane
Explain how a protein inside the ER can be exported from the cell without ever crossing a membrane.
A protein inside the ER is packaged inside transport vesicles that bud off the ER and then join to the Golgi apparatus. A transport vesicle containing the finished protein product then buds off the Golgi and travels to and joins with the plasma membrane, expelling the protein from the cell.
The cells of plant seeds store oils in the form of droplets enclosed by membranes. Unlike typical biological membranes, this oil droplet membrane consists of a single layer of phospholipids rather than a bilayer. Draw a model for a membrane around such an oil droplet. Explain why this arrangement is more stable than a bilayer of phospholipids.
A single layer of phospholipids surrounding the oil droplet would have their hydrophobic fatty acid tails associated with the hydrophobic oil and their hydrophilic heads facing the aqueous environment of the cell outside the droplet.
The purpose of cellular respiration is the production of _____.
ATP cellular respiration produces ATP for use in the cell's enzyme reactions that require energy
What general function do the chloroplast and mitochondrion have in common? How are their functions different?
Both process energy. A chloroplast converts light energy to chemical energy (sugar molecules). A mitochondrion converts chemical energy (food molecules) to another form of chemical energy (ATP).
Which statement correctly describes bound ribosomes?
Bound ribosomes generally synthesize membrane proteins and secretory proteins.
Describe two different ways in which the motion of cilia can function in organisms.
Cilia may propel a cell through its environment or sweep a fluid environment past the cell.
What four cellular components are shared by prokaryotic and eukaryotic cells?
DNA as genetic material , ribosomes, plasma membrane, cytoplasm
In what ways do the internal membranes of a eukaryotic cell contribute to the functioning of the cell?
Different conditions and conflicting processes can occur simultaneously within separate, membrane-enclosed compartments. Also, there is increased area for membrane-attached enzymes that carry out metabolic processes.
A researcher made an interesting observation about a protein made by the rough endoplasmic reticulum and eventually used to build a cell's plasma membrane. The protein in the membrane was actually slightly different from the protein made in the ER. The protein was probably altered in the _____.
Golgi apparatus vesicles carrying proteins from ER fuse with Golgi, where proteins may be altered
Cilia are found on cells in almost every organ of the human body, and the malfunction of cilia is involved in several human disorders. During embryological development, for example, cilia generate a leftward flow of fluid that initiates the left-right organization of the body organs. Some individuals with primary ciliary dyskinesia exhibit situs inversus, in which internal organs such as the heart are on the wrong side of the body. Explain why this reversed arrangement may be a symptom of PCD.
Individuals with PCD have nonfunctional cilia and flagella due to a lack of dynein motor proteins. This defect would also mean that the cilia involved in left-right pattern formation in the embryo would not be able to set up the fluid flow that initiates the normal arrangement of organs.
Is this statement true or false? "Animal cells have mitochondria; plant cells have chloroplasts." Explain your answer.
Part true, part false. All animal and plant cell have mitochondria; plant cells but not animal cells have chloroplasts.
Peroxisomes are organelles that are involved in the _____.
breakdown of fatty acids break down fatty acids for fuel, and they are involved int he detoxification of alcohol and other harmful substances
In which cell would you find the most tight junctions?
cell in tissue layer lining digestive tract
Which of the following would be found in the cytoplasm of a eukaryotic cell?
centrioles
List some structures found in plant cells but not in animal cells.
chloroplast, central vacuole, cell wall
Cilia and flagella move due to energy provided by the enzymatic breakdown of ATP by _____.
dynein arms dynein arms of cilia and flagella break down ATP for energy for motility
The contractile vacuole _____.
eliminates excess water from the cytoplasm of freshwater protists keeps the freshwater protists in osmotic balance
List some structures found in animal cells but not in plant cells.
flagellum or cilia (some plant sperm cells have flagella), lysosome, centriole (involved with microtubule formation)
Which of the following structures is directly involved in the passage of electrical signals between cells as, for example, in the vertebrate heart?
gap junctions communicating junctions provide cytoplasmic channels between adjacent cells that allow ions to flow, coordinating the contractions of those cells
The maximum size of a cell is limited by ______________.
its need for enough surface area to make exchanges with its environment bc volume increases at a faster rate than surface area, large cells have proportionately less plasma membrane surface area
Bacterial cells are prokaryotic; unlike a typical eukaryotic cell, they _____.
lack a nucleus prokaryotic literally translates as "before nucleus"
Primary ciliary dyskinesia is a genetic disorder in which the cilia of the respiratory tract become immobile. As a result, these individuals suffer respiratory illnesses. This is because the cells _____.
lack dynein arms without dynein arms, cilia are unable to bend, which means they are immobilized
The rough endoplasmic reticulum is considered to be in which general functional category of organelle?
manufacturing is involved in the manufacture of proteins
Mitochondria appear in the greatest numbers in cells that are _____.
metabolically active mitochondria are the sites for cellular respiration, the catabolic process that generate ATP by extracting energy from food molecules, with the help of oxygen
The protein actin is a component of a(n) _____.
microfilament are primarily composed of actin, a globular protein
Integrins are proteins that are responsible for integrating changes that are occurring outside and inside the cell. They are able to do this because of _____.
microfilaments integrins are connected to microfilaments of the cytoskeleton
When elongated, tube-shaped cells from the lining of the intestine are treated with a certain chemical, the cells sag and become rounded. The internal structures disrupted by this chemical are probably _____.
microtubules they are cytoskeletal components, and the shape of a cell is determined by its cytoskeleton
The internal skeleton of a cell is composed of _____.
microtubules, intermediate filaments, and microfilaments make up the cytoskeleton
Which of these is a function of the endomembrane system?
molecule export
Most of the DNA in a eukaryotic cell is in the _____________.
nucleus
The genetic center of the eukaryotic cell is the ___________.
nucleus
A plant cell was grown in a test tube containing radioactive nucleotides, the monomers from which DNA is built. Later examination of the cell showed the radioactivity to be concentrated in the _____.
nucleus DNA, in association with protein, is stored as chromatin within the nucleus of a eukaryotic cell
Digestive cells produce many enzymes that break down ingested food. These cells have a large number of ribosomes _____.
on the rough endoplasmic reticulum rough ER is responsible for producing proteins that will be inserted into membranes, packaged in certain organelles, or exported from the cell
Flagella and cilia are both composed of tubular subunits. However, key differences can be observed. For example, _________________.
only cilia move as a coordinated team
In which cell would you find the most smooth ER?
ovarian cell that produces the steroid hormone estrogen
In which cell would you find the most rough ER?
pancreatic cell that secretes digestive enzymes
In plants, _________ are the cell junctions that allow the free exchange of small molecules that assist in communication. In animal cells, similar cell junctions are known as ____________.
plasmodesmata; gap junctions plant cells are interconnected by plasmodesmata, which form tubelike structures that penetrate through the cell walls gap junctions are formed by specialized channels found in animal cells both allow the free exchange of small molecules and help coordinate the activities of neighboring cells
Which of the following structures is/are found in prokaryotic cells?
ribosomes both prokaryotic and eukaryotic cells have ribosomes
Pancreatic cells secrete lots of proteins. With this in mind, which of the following organelles would be especially abundant in pancreatic cells?
rough endoplasmic reticulum ribosomes of rough ER are the sites of most protein synthesis in the cell
When isolated liver cells are combined with toxins, initial processing in the _____ increases the solubility of those compounds as an initial step in their excretion.
smooth endoplasmic reticulum most often this detoxification involves the addition of a hydroxyl group
In muscle cells, the _____ is/are specialized for the storage and release of calcium.
smooth endoplasmic reticulum when a muscle cell is stimulated by a nerve impulse, calcium is released from the smooth ER, triggering the contraction
Membrane proteins are synthesized by ribosomes that are attached to _____.
the endoplasmic reticulum ribosomes bound to ER generally make proteins destined either for inclusion into membranes, for packaging within certain organelles (e.g. lysosomes), or for export from the cell
To enter or leave any cell, substances must pass through _______________.
the plasma membrane it defines the boundary of the cell
