AP Bio Chap 6 Quiz

Light microscope (LM)

In a _______, visible light is passed through the specimen and then through glass lenses.

Organelles

Until recently, the resolution barrier prevented cell biologists from using standard light microscopy when studying _____, the membrane-enclosed structures within eukaryotic cells.

Electron microscope (EM)

Rather than focusing light, the ____ focuses a beam of electrons through the specimen or onto its surface.

Scanning electron microscope (SEM)

The _______ is especially useful for detailed study of the topography of a specimen.

Transmission electron microscope (TEM)

The __________ is used to study the internal structure of cells.

Cell fractionation

A useful technique for studying cell structure and function is ______, which takes cells apart and separates major organelles and other subcellular structures from one another.

Stains used for light microscopy are colored molecules that bind to cell components, affecting the light passing through, while stains used for electron microscopy involve heavy metals that affect the beams of electrons.

How do stains used for light microscopy compare with those used for electron microscopy?

(a) Light microscope, (b) scanning electron microscope.

Which type of microscope would you use to study (a) the changes in shape of a living white blood cell? (b) the details of surface texture of a hair?

Cytosol

Inside all cells is a semifluid, jellylike substance called _____, in which subcellular components are suspended.

Eukaryotic cell

In a _______, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane.

Prokaryotic cell; nucleoid

In a _______, the DNA is concentrated in a region that is not membrane-enclosed, called the ________

Cytoplasm

The interior of either type of cell is called the _______; in eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane.

Plasma membrane

At the boundary of every cell, the ________ functions as a selective barrier that allows passage of enough oxygen, nutrients, and wastes to service the entire cell.

Nucleus (structure: middle ball; function: nuclear envelope (double membrane enclosing the nucleus), nucleolus (non-membranous structure, involved in production of ribosomes, 1 nucleus has 1 or more nucleoli), chromatin (material made of DNA and proteins)), Mitochondrion (structure: pill-shaped with squiggles in the middle; function: organelle where cellular respiration occurs and most ATP is generated), Chloroplast (structure: ovals with many green columns inside; function: photosynthetic organelle, converts energy of sunlight to chemical energy stored in sugar molecules), Endoplasmic Reticulum (structure: squiggly around nucleus; function: network of membranous sacs and tubes, active in membrane synthesis and other synthetic/metabolic processes; rough ER is ribosomes-studded and smooth ER isn't)

Briefly describe the structure and function of the nucleus, the mitochondrion, the chloroplast, and the endoplasmic reticulum. (PROBABLY NOT ON QUIZ)

This cell would have the same volume as the cells in columns 2 and 3 in Figure 6.7 but proportionally more surface area than that in column 2 and less than that in column 3. Thus, the surface-to-volume ratio should be greater than 1.2 but less than 6. To obtain the surface area, you would add the area of the six sides (the top, bottom, sides, and ends): 125 + 125 + 125 + 125 + 1 + 1 = 502. The surface-to-volume ratio equals 502 divided by a volume of 125, or roughly 4.0.

Draw a simplified elongated cell that measures 125 1 1 arbitrary units. A nerve cell would be roughly this shape. Predict how its surface-to-volume ratio would compare with those in Figure 6.7. Then calculate the ratio and check your prediction. (PROBABLY NOT ON QUIZ)

Nucleus

The _________ contains most of the genes in the eukaryotic cell.

Nuclear envelope

The __________ encloses the nucleus, separating its contents from the cytoplasm.

Nuclear lamina

Except at the pores, the nuclear side of the envelope is lined by the ________, a netlike array of protein filaments (in animal cells, called intermediate filaments) that maintains the shape of the nucleus by mechanically supporting the nuclear envelope.

Chromosomes

Within the nucleus, the DNA is organized into discrete units called ________, structures that carry the genetic information.

Chromatin

The complex of DNA and proteins making up chromosomes is called __________.

Nucleolus

A prominent structure within the nondividing nucleus is the ________, which appears through the electron microscope as a mass of densely stained granules and fibers adjoining part of the chromatin.

Ribosomes

_________, which are complexes made of ribosomal RNAs and proteins, are the cellular components that carry out protein synthesis.

Ribosomes in the cytoplasm translate the genetic message, carried from the DNA in the nucleus by mRNA, into a polypeptide chain.

What role do ribosomes play in carrying out genetic instructions?

Nucleoli consist of DNA and the ribosomal RNAs (rRNAs) made according to its genes in the DNA, as well as proteins imported from the cytoplasm. Together, the rRNAs and proteins are assembled into large and small ribosomal subunits. (These are exported through nuclear pores to the cytoplasm, where they will participate in polypeptide synthesis.)

Describe the molecular composition of nucleoli and explain their function.

Each chromosome consists of one long DNA molecule attached to numerous protein molecules, a combination called chromatin. As a cell begins division, each chromosome becomes "condensed" as its diffuse mass of chromatin coils up.

As a cell begins the process of dividing, its chromosomes become shorter, thicker, and individually visible in an LM (light micrograph). Explain what is happening at the molecular level.

Endomembrane system

Many of the different membrane-bounded organelles of the eukaryotic cell are part of the ________, which includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane.

Vesicles

The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny _______ (sacs made of membrane).

Endoplasmic reticulum (ER)

The _________ is such an extensive network of membranes that it accounts for more than half the total membrane in many eukaryotic cells.

Smooth ER

________ is so named because its outer surface lacks ribosomes.

Rough ER

_________ is studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope.

Glycoproteins

Most secretory proteins are ________, proteins with carbohydrates covalently bonded to them. (PROB NOT ON QUIZ)

Transport vesicles

Vesicles in transit from one part of the cell to another are called ________; we will examine their fate shortly.

Golgi apparatus

After leaving the ER, many transport vesicles travel to the ___________.

Lysosome

A ________ is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules.

Phagocytosis

Amoebas and many other unicellular protists eat by engulfing smaller organisms or food particles, a process called ______. (PROB NOT ON QUIZ)

Vacuoles

_________ are large vesicles derived from the endoplasmic reticulum and Golgi apparatus.

Food vacuoles

_________, formed by phagocytosis, have already been mentioned. (PROB NOT ON QUIZ)

Contractile vacuoles

Many unicellular protists living in fresh water have _________ that pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell.

Central vacuole

Mature plant cells generally contain a large __________, which develops by the coalescence of smaller vacuoles.

The primary distinction between rough and smooth ER is the presence of

bound ribosomes on the rough ER. Both types of ER make phospholipids, but membrane proteins and secretory proteins are all produced by the ribosomes on the rough ER. The smooth ER also functions in detoxification, carbohydrate metabolism, and storage of calcium ions.

Describe the structural and functional distinctions between rough and smooth ER.

Transport vesicles move membranes and the substances they enclose between other components of the endomembrane system.

Describe how transport vesicles integrate the endomembrane system.

The mRNA is synthesized in the nucleus and then passes out through a nuclear pore to the cytoplasm, where it is translated on a bound ribosome, attached to the rough ER. The protein is synthesized into the lumen of the ER and may be modified there. A transport vesicle carries the protein to the Golgi apparatus. After further modification in the Golgi, another transport vesicle carries it back to the ER, where it will perform its cellular function.

Imagine a protein that functions in the ER but requires modification in the Golgi apparatus before it can achieve that function. Describe the protein's path through the cell, starting with the mRNA molecule that specifies the protein.

Mitochondria

_______ are the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels.

Chloroplasts

________, found in plants and algae, are the sites of photosynthesis.

Endosymbiont theory

Mitochondria and chloroplasts display similarities with bacteria that led to the _______. (PROB NOT ON QUIZ)

Cristae

The outer membrane is smooth, but the inner membrane is convoluted, with infoldings called _________. (PROB NOT ON QUIZ)

Mitochondrial matrix

The second compartment, the ________, is enclosed by the inner membrane. (PROB NOT ON QUIZ)

Thylakoids

Inside the chloroplast is another membranous system in the form of flattened, interconnected sacs called _________. (PROB NOT ON QUIZ)

Granum

In some regions, thylakoids are stacked like poker chips; each stack is called a _______. (PROB NOT ON QUIZ?)

Stroma

The fluid outside the thylakoids is the ______, which contains the chloroplast DNA and ribosomes as well as many enzymes. (PROB NOT ON QUIZ?)

Plastids

The chloroplast is a specialized member of a family of

closely related plant organelles called __________.

Peroxisome

The __________ is a specialized metabolic compartment

bounded by a single membrane.

Both organelles are involved in energy transformation, mitochondria in cellular respiration and chloroplasts in photosynthesis. They both have multiple membranes that separate their interiors into compartments. In both organelles, the innermost membranes—cristae, or infoldings of the inner membrane, in mitochondria and the thylakoid membranes in chloroplasts—have large surface areas with embedded enzymes that carry out their main functions.

Describe two characteristics shared by chloroplasts and

mitochondria. Consider both function and membrane

structure.

Yes. Plant cells are able to make their own sugar by photosynthesis, but mitochondria in plant cells (which are, of course, eukaryotic) are the organelles that are able to generate ATP molecules to be used for energy generation from sugars, a function required in all cells.

Do plant cells have mitochondria? Explain.

Mitochondria and chloroplasts are not derived from the ER, nor

are they connected physically or via transport vesicles to organelles of the endomembrane system. Mitochondria and chloroplasts are structurally quite different from vesicles derived from the ER, which are bounded by a single membrane.

A classmate proposes that mitochondria and chloroplasts should be classified in the endomembrane system. Argue against the proposal.

Cytoskeleton

But improvements in both light microscopy and electron microscopy have revealed the _______, a network of fibers extending throughout the cytoplasm.

Motor proteins

Cell motility generally requires interaction of the cytoskeleton with __________.

Microtubules

All eukaryotic cells have __________, hollow rods constructed from globular proteins called tubulins.

Centrosome

In animal cells, microtubules grow out from a _________, a region that is often located near the nucleus. (PROB NOT ON QUIZ?)

Centrioles

Within the centrosome is a pair of ________, each composed of nine sets of triplet microtubules arranged in a ring. (PROB NOT ON QUIZ?)

Flagella; cilia

Some eukaryotic cells have _______ and _______, cellular

extensions that contain microtubules. (PROB NOT ON QUIZ?)

Basal body

The microtubule assembly of a cilium or flagellum is anchored in the cell by a ________, which is structurally very

similar to a centriole, with microtubule triplets in a "9 + 0" pattern. (PROB NOT ON QUIZ)

Dyneins

Bending involves large motor proteins called ________ that are attached along each outer microtubule doublet. (PROB NOT ON QUIZ)

Microfilaments

_______ are thin solid rods.

Actin

They are also called actin filaments because they are built from molecules of ______, a globular protein.

Cortex

This network gives the outer cytoplasmic layer of a cell, called the ______, the semisolid consistency of a gel, in contrast with the more fluid state of the interior cytoplasm. (PROB NOT ON QUIZ)

Myosin

Thousands of actin filaments and thicker filaments made of a protein called _______ interact to cause contraction of muscle cells; (PROB NOT ON QUIZ)

Pseudopodia

The cell crawls along a surface by extending cellular extensions called ________ and moving toward them. (PROB NOT ON QUIZ)

Cytoplasmic streaming

In plant cells, actin-protein interactions contribute to _________, a circular flow of cytoplasm within cells. (PROB NOT ON QUIZ?)

Intermediate filaments

________ are named for their diameter, which is larger than the diameter of microfilaments but smaller than that of microtubules. (PROB NOT ON QUIZ)

Dynein arms, powered by ATP, move neighboring doublets of microtubules relative to each other. Because they are anchored within the flagellum or cilium and with respect to one another, the doublets bend instead of sliding past each other. Synchronized bending of the nine microtubule doublets brings about bending of both cilia and flagella.

Describe how cilia and flagella bend.

Such individuals have defects in the microtubule-based movement of cilia and flagella. Thus, the sperm can't move because of malfunctioning or nonexistent flagella, and the airways are compromised because cilia that line the trachea malfunction or don't exist, and so mucus cannot be cleared from the lungs.

Males afflicted with Kartagener's syndrome are sterile because of immotile sperm, and they tend to suffer from lung infections. This disorder has a genetic basis. Suggest what the underlying defect might be.

Cell wall

The _____ is an extracellular structure of plant cells.

Primary cell wall

A young plant cell first secretes a relatively thin and flexible wall called the _________.

Middle lamella

Between primary walls of adjacent cells is the _________, a thin layer rich in sticky polysaccharides called pectins.

Secondary cell wall

Other cells add a _______ between the plasma membrane and the primary wall.

Extracellular matrix (ECM)

Although animal cells lack walls akin to those of plant cells, they do have an elaborate ________.

Collagen

The most abundant glycoprotein in the ECM of most animal cells is ________, which forms strong fibers outside the cells.

Proteoglycans

The collagen fibers are embedded in a network woven out of __________ secreted by cells.

Fibronectin

Some cells are attached to the ECM by ECM glycoproteins such as __________.

Integrins

Fibronectin and other ECM proteins bind to cell-surface receptor proteins called _______ that are built into the plasma membrane.

Plasmodesmata

But in fact, many plant cell walls are perforated with ________, channels that connect cells.

Tight junctions

At ________, the plasma membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins.

Tight junctions

Forming continuous seals around the cells, _______ establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells

Desmosomes

_______ function like rivets, fastening cells together into strong sheets.

Desmosomes

Intermediate filaments made of sturdy keratin proteins anchor ________ in the cytoplasm.

Desmosomes

________ attach muscle cells to each other in a muscle.

Desmosomes

Some "muscle tears" involve the rupture of _________.

Gap junctions

________ provide cytoplasmic channels from one cell to an adjacent cell and in this way are similar in their function to the plasmodesmata in plants.

Gap junctions

________ consist of membrane proteins extending from the membranes of the two cells. These proteins create pores through which ions, sugars, amino acids, and other small molecules may pass

Gap junctions

________ are necessary for communication between cells in many types of tissues, such as heart muscle, and in animal embryos.

The most obvious difference is the presence of direct cytoplasmic connections between cells of plants (plasmodesmata) and animals (gap junctions). These connections result in the cytoplasm being continuous between adjacent cells.

In what way are the cells of plants and animals structurally different from single-celled eukaryotes?

The cell would not be able to function properly and would probably soon die, as the cell wall or ECM must be permeable to allow the exchange of matter between the cell and its external environment. Molecules involved in energy production and use must be allowed entry, as well as those that provide information about

the cell's environment. Other molecules, such as products synthesized by the cell for export and the by-products of cellular respiration, must be allowed to exit.

If the plant cell wall or the animal extracellular matrix were impermeable, what effect would this have on cell function?

The parts of the protein that face aqueous regions would be expected to have polar or charged (hydrophilic) amino acids, while the parts that go through the membrane would be expected to have nonpolar (hydrophobic) amino acids. You would predict polar or charged amino acids at each end (tail), in the region of the cytoplasmic loop, and in the regions of the two extracellular loops. You would predict nonpolar amino acids in the four regions that go through the membrane between the tails and loops.

The polypeptide chain that makes up a tight junction weaves back and forth through the membrane four times, with two extracellular loops and one loop plus short C-terminal and N-terminal tails in the cytoplasm. Looking at Figure 5.14, what would you predict about the amino acid sequence of the tight junction protein? (PROB NO ON QUIZ)

Colpidium colpoda moves around in freshwater using cilia, projections from

the plasma membrane that enclose microtubules in a "9 + 2" arrangement. The

interactions between motor proteins and microtubules cause the cilia to bend

synchronously, propelling the cell through the water. This is powered by ATP,

obtained via breaking down sugars from food in a process that occurs in mito-

chondria. C. colpoda obtains bacteria as their food source, maybe via the same

process (involving filopodia) the macrophage uses in Figure 6.31. This process

uses actin filaments and other elements of the cytoskeleton to ingest the bacte-

ria. Once ingested, the bacteria are broken down by enzymes in lysosomes. The

proteins involved in all of these processes are encoded by genes on DNA in the

nucleus of the C. colpoda.

Colpidium colpoda is a unicellular protist that lives in freshwater, eats bacteria, and moves by cilia (see Figure 6.23b). Describe how the parts of this cell work together in the functioning of C. colpoda, including as many organelles and other cell structures as you can. (NO WAY THIS IS ON QUIZ)