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Science 9: Chapter 5 Review Questions
What are the 3 stages of the cell cycle?
Interphase, mitosis, cytokinesis
What happens during interphase?
Growth and preparation, DNA replication and continued growth and
preparation
List the steps in DNA replication.
1. Unzipping of the DNA to separate the base pairs
2. New bases pair with those on the parent DNA strands
3. 2 identical DNA molecules are produced
What happens during mitosis?
Sister chromatids become separated to produce daughter chromosomes,
which will split into 2 separate cells in cytokinesis
What are the 5 phases of mitosis and what happens at each stage?
Prophase: nucleolus and nuclear membrane disintegrate, centrioles move
to opposite ends of the cell, spindle fibres begin to form and chromatin
condenses into chromosomes
Metaphase: spindle fibres attach to each centromere and sister chromatids
(chromosomes) line up on the metaphase plate (equator of cell)
Anaphase: sister chromatids are pulled apart to opposite ends of the cell
Telophase: nuclear membrane begins to form around each new set of
daughter chromosomes, nucleolus re-forms and cell begins to pinch (animal
cell) or form a cell plate (plant cell)
Why is it necessary for the nucleus to dissolve during prophase?
DNA cannot leave the nucleus so if the nuclear membrane did not dissolve
the spindle fibres would not be able to access the centromeres on the
chromosomes
What happens during cytokinesis?
The cells actually split into 2 new cells.
What are 2 reasons why cells need to divide?
- growth
- healing and repair
There are checkpoints in the cell cycle. What situations in the cell
would make these checkpoint proteins send a message to the nucleus
saying “stop dividing!”?
- not enough nutrients to support cell division
- not enough growth of the cell
- DNA has not replicated properly
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What are spindle fibres? What would happen if the cell was
unable to create spindle fibres?
Spindle fibres are proteins strands found within the cell that allow for the
sister chromatids to split (anaphase). If the fibres did not form proper cell
division would not occur.
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What is cancer and how does cancer develop?
Cancer is uncontrolled cell division (they ignore the checkpoints). Cancer
can be caused by mutagens (environmental “things” that cause mutations or
it can be genetic.
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What is reproductive cloning?
Producing offspring that are genetically identical to the parent for the
purpose of duplicating desirable characteristics.
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What is therapeutic cloning?
Using stem cells to correct health problems
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Explain what is meant by asexual reproduction.
Asexual reproduction is the means of producing offspring (entire organisms)
from only ONE parent (does not require the mixing of DNA and therefore,
offspring are clones)
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What are the advantages and disadvantages of asexual
reproduction?
Advantages: quick, produces many offspring, increased chance of survival
of at least some of the offspring, no energy needed to find a mate
Disadvantages: no genetic diversity (no individuals, all clones of parent),
competition for resources with so many offspring, mutation or bad conditions
can wipe out entire colony/species
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List the 5 types of asexual reproduction.
Binary Fission, Budding, Fragmentation, Vegetative Reproduction, Spore
Formation
What is the difference between budding and binary fission?
Binary Fission: involves the splitting of parent organism into two so parent
no longer exists whereas Budding involves a section of the organism to
grown off of the parent which then falls off and begins developing into its
own organism.
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Explain what happens in fragmentation.
An organism is separated (usually due to trauma or predation) and then
each separated part grows into its own organism.
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Explain what happens in vegetative reproduction.
Stems and roots of plants divide repeatedly to form structures that develop
into an identical plant.
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What is a spore?
A specialized, single cell that can develop into a new individual.