Biology Ch. 12 Quiz

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Roles of Cell division in unicellular organisms?
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Division of one cell reproduces the entire organism
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Roles of Cell division in Multicellular organism?
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1. Development from a fertilize cell 2. Growth 3. Repair
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Binary Fission
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Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission. In binary fission, the chromosome replicates (beginning at the ORGIN OF REPLICATION) and the two daughter chromosomes actively move apart.
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Mitosis
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Cell division
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Genome
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All the DNA in a cell constitutes the cell’s genome.
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Chromosomes
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Chromatin
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a complex of DNA and protein that condenses during cell division
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Somatic Cell (non-reproductive cells)
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have two sets of chromosomes – diploid
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Gametes (reproductive cells: sperm and eggs)
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have half as many chromosomes as somatic cell – haploid
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Chromosome during Cell division
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1. In preparation for cell division, DNA is replicated and the chromosomes condense 2. Each duplicated chromosome has two sister chromatids, which separate during cell division.
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Centromere
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where the two chromatids are most closely attached
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Eurkaryotic cell division consists of:
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1. Mitosis, the division of the nucleus 2. Cytokinesis, the division of the cytoplasm
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What are produced by variation of cell division called meiosis?
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Gametes
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Phases of the Cell Cycle
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1. Mitotic (M) phase (mitosis and cytokinesis) 2. Interphase (cell growth and copying of chromosomes in preparation for cell division)
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Interphase (about 90% of the cell cycle) can be divided into sub-phases:
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1. G₁ phase (“first gap”) 2. S phase (“synthesis”) 3. G₂ phase (“second gap”) -The cell grows during all three phases, but chromosomes are duplicated only during the S phase.
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Mitosis (5 phases)
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1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase
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Cytokinese
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is well underway by late telophase (stars in late Anaphase
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Mitotic Spindle
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an apparatus of microtubules that controls chromosome movement during mitosis
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Aster
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(a radial array of short microtubules) extends from each centrosome in animal cells
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Prometaphase
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some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes.
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Metaphase
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The chromosomes are all lined up at the METAPHASE PLATE, which is midway between the spindle’s two poles
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Anaphase
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Sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell.
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In Telophase
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genetically identical daughter nuclei form at opposite ends of the cell.
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Cytokinesis
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-in animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow. -in plant cells
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Cytochalasin B is a chemical that disrupts microfilament formation. How would this interfere with cell division?
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cleavage -In animal cells, the cleavage furrow forms when a ring of microfilaments contracts, causing the parent cell to be pinched in two.
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At which phase are centrioles beginning to move apart in animal cells?
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prophase
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Density-dependent inhibition is explained by which of the following?
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As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells and they stop dividing.
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For a chemotherapeutic drug to be useful for treating cancer cells, which of the following is most desirable?
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It interferes with rapidly dividing cells.
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Which of the following is true of benign tumors, but not malignant tumors?
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They remain confined to their original site -Benign tumors can often be surgically removed because their boundaries are well defined, whereas some malignant tumors go on to metastasize
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A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. How many chromatids does it contain?
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92 -Mitosis follows the duplication of the cell’s DNA.
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Starting with a fertilized egg (zygote), a series of five cell divisions would produce an early embryo with how many cells?
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32
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Which of the following does not occur during mitosis?
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replication of the DNA
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Mitosis
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a process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, telophase.
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Cell division consists of two processes
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1. mitosis 2. cytokinesis
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Cytokinesis
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the division of cytoplasm to form two separate daughter cells immediately after mitosis.
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Interphase
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The cytoplasm of a cell in late interphase contains two centrosomes, each of which may contain a pair of centrioles. In the nucleus, the chromosomes have been replicated during S phase, but are still dispersed in the from of chromatin. One or more nucleoli are present.
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Chromosomes
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a Threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
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Chromatin
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The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.
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During prophase
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the nucleoli disappear and chromatin fibers coil up to become discrete chromosomes. Each chromosomes consist of two identical sister chromatids, joined at the centromere. Microtubules grow out from the centrosomes, intiating formation of the mitotic spindle.
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During prometaphase,
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the nuclear envelope breaks into fragments. Some of the spindle fibers reach the chromosomes and attach to kinetochores, structures made of proteins and specific sections of DNA at the centromeres. Nonkinetochore microtubules overlap with those coming from the opposite pole.
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Kinetochore
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A specialized region on the centromere that links each sister chromatid to the miotic spindle.
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At Metaphase
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the mitotic spindle is fully formed, and the microtubules attached to kinetochores move the chromosomes to the metaphase plate, an imaginary plane equidistant from the poles.
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Anaphase
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begins when the two centromeres of each chromosome come apart, separating the sister chromatids. Once separate, each sister chromatid is considered a full-fledged daughter chromosome. Motor proteins of kinetochores “walk” the daughter chromosomes along the spindle microtubules towards opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to chromosomes lengthen, pushing the two poles farther apart.
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Interphase (own words)
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-Contains two centrosomes with centriole pairs -Chromosome are still dispersed in chromatin form. -One or more nucleoli are present.
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Prophase
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-The nucleoli disappear -Chromatin fibers coil up to become discrete chromosomes. -Each chromosomes consist of two identical sister chromatids, joined at the centromere. -Microtubules grow out from the centrosomes, initiating formation of the mitotic spindle.
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Prometaphase
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-The nuclear envelope breaks into fragments. -Some of the spindle fibers reach the chromosomes and attach to the kinetochores -Nonokinetochore microtubes overlap with those coming from the opposite pole.
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Metaphase
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The mitotic spindle is fully formed -the microtubes attached to kinetochores move the chromosomes to the metaphase plate, an imaginary plane equidistant from the poles.
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Anaphase
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-two centromeres of each chromosome come apart, separating the sister chromatids. -Once separated, each sister chromatid is considered a full-fledged daughter chromosome. -Motor proteins of the kinetochores “walk” the daugher chromosomes along the spindle microtubules towards opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to the chromosomes lengthen pushing the two poles farther apart and elongating the cell.
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Telophase
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-Nuclear envelopes form around the identical sets of chromosomes at the two poles of the cell. -the chromosomes uncoil and nucleoli appear in the two new nuclei.
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Cytokinesis (animal cell)
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In animal cells, cytokinesis begins with the formation of a cleavage furrow. At the site of the furrow, a ring of microfilaments contracts much like the pulling of drawstrings. the cell is pinched in two creating two identical daughter cells.
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Cytokinesis (plant cell)
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In plant cells, cytokinesis begins when vesicles containing cell wall material collect in the middle of the cell. The vesicle fuse forming a large sac call the CELL PLATE. the cell plate grows outwards until its membrane fuses with the plasma membrane, separating the two daughter cells. the cell plate’s contents join the parental cell wall. the result is two daughter cells, each bounded by its own continuous plasma membrane and cell wall.
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Nucleoli are present during _____.
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Interphase
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Cytokinesis often, but not always, accompanies _____.
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telophase
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Chromosomes become visible during _____.
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Prophase
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Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
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Anaphase
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Spindle fibers attach to kinetochores during _____.
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Prometaphase
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During prophase a homologous pair of chromosomes consists of _____.
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two chromosomes and four chromatids
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The Cell Cycle (18-24 hours long)
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1. G₁ phase 2. S phase 3. G₂ phase 4. Mitotic(M) Phase- Cytokinesis and Mitosis
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G₁ Phase of Interphase
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Cell carrying out its function (Number of chromosome: 4) (Number of DNA molecules: 4)
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S phase of Interphase
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DNA replication -Each (4) DNA molecules is replicated. The two copies are called sister chromatids. Each pair of chromaiteds is joined at a structure called centromere. (Number of chromosomes: 4) (Number of DNA molecules :8)
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G₂ of Interphase
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Cell growth and the duplication of organelles continue as the machinery for cell division is prepared. (Number of Chromosomes: 4) (Number of DNA molecules: 8)
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M phase
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Result in the formation of two daughter cells. For each of the two cells: (Number of Chromosomes: 4) (Number of DNA molecules: 4)
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How is the cell cycle controlled?
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By cell cycle checkpoints.
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G₁ checkpoint
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occurs late in the G1 phase. At that time the cell cycle will be arrested unless the size is adequate, nutrient availability is sufficient, and certain growth factors (in the form of sign from other cells) are presents. When growth factors stimulate a cell, they trigger the cell to increase its concentration of cyclin. The G1 cyclin activates the enzyme Cdk. Cdk, in turn, activates proteins needed for the S phase to proceed. FOR THE CELL TO PASS THROUGH THE G1 CHECKPOINT, THIS CYCLIN-CDK COMPLEX MUST BE ACTIVATED.
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G1 cyclin
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a protein that binds to and activate the enzyme cyclin-dependent kinases, or Cdk.
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G2 checkpoint
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The cell cycle will be arrested unless cell size is adequate and chromosome replication has been completed successfully. As at the G1 checkpoint involves activation of CDK by M-phase Cyclin. THIS CYCLIN-CDK COMPLEX IS NAMED MITOSIS-PROMOTING FACTOR OR MPF.
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Metaphase checkpoint
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FINAL CHECKPOINT. At this stage, the cell cycle will be arrested unless all chromosome are appropriately ATTACHED TO THE MITOTIC SPINDLES. when the metaphase checkpoint has been passed, mitosis is then completed as mitotic cyclin is degraded.
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Which of the following is a function of the S phase in the cell cycle?
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The synthesis of sister chromatids -DNA replication occurs during S phase and results in two sister chromatids for each original chromosome.
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The copying of chromosomes occurs during which of the following phases of the cell cycle?
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S phase -Chromosomes must undergo replication before mitosis can occur; this copying occurs during the S phase.
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For the first several divisions of early frog embryos, cells proceed directly from the M phase to the S phase and back to M without gaps. Which of the following is likely to be true about dividing cells in early frog embryos?
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The cells get smaller with each generation. -Without gap phases, the cells have no opportunity to grow.
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True or false? The M phase is characterized by the replication and division of a cell’s chromosomes.
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False -Correct: Cells replicate their chromosomes during the S phase and divide partition their chromosomes during the M phase.
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If an organism normally has 34 chromosomes, how many molecules of DNA should there be in the G1 phase of the cell cycle?
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34, There is one DNA molecule per chromosome.
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Ratio of Chromosome and DNA during the cell cycle?
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G1 (1:1) S (1:2) G2 (1:2) M (1:1), (1:1)
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Which of the following events would cause the cell cycle to arrest?
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Poor nutrient conditions -Poor nutrient conditions would arrest the cell cycle at the G1 checkpoint.
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Why is it difficult to observe individual chromosomes with a light microscope during interphase?
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They have uncoiled to form long, thin strands. -Except during the M phase, the DNA is extended, allowing its genes to be transcribed for protein synthesis.
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In the cells of some organisms, mitosis occurs without cytoki-nesis. This will result in
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cells with more than one nucleus
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What is a cleavage furrow?
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a groove in the plasma membrane between daughter nuclei
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An environmental substance that is known to cause cancer is called a what?
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carcinogen
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Radiation emitted from which of the following two sources are most alike?
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microwaves and cellphones
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You are trying to discover if the pesticide atrazine is a mutagen. Where are you looking for mutations?
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DNA
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Which of the following is true?
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Cancer-causing substances work in many different ways.
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Which of the following best summarizes current scientific opinion regarding cellphones and brain cancer?
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While most studies indicate that cellphones do not cause brain cancer, more research needs to be done as cellphone use increases.
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A plant-derived protein known as colchicine can be used to poison cells by blocking the formation of the spindle. Which of the following would result if colchicine is added to a sample of cells in G2?
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The chromosomes would coil and shorten but have no spindle to which to attach.
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A research team began a study of a cultured cell line. Their preliminary observations showed them that the cell line did not exhibit either density-dependent inhibition or anchorage dependence. What could they conclude right away?
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The cells show characteristics of tumors.
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S phase
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DNA synthesis and replication of chromosomes.
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Through a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. This cell is most likely
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a plant cell in the process of cytokinesis.
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In some organisms, such as certain fungi and algae, cells undergo the cell cycle repeatedly without subsequently undergoing cytokinesis. What would result from this?
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Large cells containing many nuclei
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Which of the following is true concerning cancer cells?
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When they stop dividing, they do so at random points in the cell cycle; they are not subject to cell cycle controls; and they do not exhibit density-dependent inhibition when growing in culture.
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Which of the following is found in binary fission but not in mitosis?
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Duplicated chromosomes attach to the plasma membrane.
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Measurements of the amount of DNA per nucleus were taken on a large number of cells from a growing fungus. The measured DNA levels ranged from 3 to 6 picograms per nucleus. In which stage of the cell cycle did the nucleus contain 6 picograms of DNA?
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G2
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If there are 20 centromeres in a cell at anaphase, how many chromosomes are there in each daughter cell following cytokinesis?
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10
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Which of the following correctly matches a phase of the cell cycle with its description?
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G1: follows cell division -After mitosis and cytokinesis, the newly formed daughter cells enter the G1 phase.
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One difference between cancer cells and normal cells is that cancer cells
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continue to divide even when they are tightly packed together.
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meiosis
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is a special type of cell division necessary for sexual reproduction in eukaryotes, such as animals, plants and fungi. The number of sets of chromosomes in the cell undergoing meiosis is reduced to half the original number, typically from two sets (diploid) to one set (haploid). The cells produced by meiosis are either gametes (the usual case in animals) or otherwise usually spores from which gametes are ultimately produced (the case in land plants). In many organisms, including all animals and land plants (but not some other groups such as fungi), gametes are called sperm in males and egg cells or ova in females. Since meiosis has halved the number of sets of chromosomes, when two gametes fuse during fertilization, the number of sets of chromosomes in the resulting zygote is restored to the original number.
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Why do some species employ both mitosis and meiosis, whereas other species use only mitosis?
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They need both if they are producing animal gametes. -The form of cell division that produces animal gametes is meiosis, not mitosis. The production of gametes in plants is a function of both mitosis and meiosis.
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Cell division occurs during this short phase, which generally involves two discrete processes: the contents of the nucleus (mainly the duplicated chromosomes) are evenly distributed to two daughter nuclei, and the cytoplasm divides in two.
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Mitotic Phase (M)
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DNA synthesis (or replication) occurs during this phase. At the beginning of the phase, each chromosome is single. At the end, after DNA replication, each chromosome consists of two sister chromatids.
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S phase
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Typically, this phase accounts for 90% of the cell cycle. It is a time of high metabolic activity. The cell grows by producing proteins and organelles, and chromosomes are replicated.
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Interphase
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This is when division of the nucleus occurs. The chromosomes that have been replicated are distributed to two daughter nuclei.
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Mitosis
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This third subphase of interphase is a period of metabolic activity and growth. During this phase the cell makes final preparations for division.
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G2 phase
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This is the portion of the cell cycle just after division, but before DNA synthesis. During this time the cell grows by producing proteins and organelles.
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G1
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This is the step in the cell cycle when the cytoplasm divides in two.
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Cytokinesis
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During _____ both the contents of the nucleus and the cytoplasm are divided.
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the mitotic phase -the mitotic phase encompasses both mitosis and cytokinesis
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During _____ the cell grows and replicates both its organelles and its chromosomes.
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interphase
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Carcinogens
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1. Estrogen 2. Testosterone 3. Smoking 4. Viruses 5. UV light 6. Fat
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Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of micro-tubules, its effectiveness must be related to
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Disruption of mitotic spindle formation
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Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle?
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G1, in mammalian cells, this checkpoint is termed the restriction point.
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Why do neurons and some other specialized cells divide infrequently?
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They have been shunted into G0.

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