Cell Division in Eukaryotic & Prokaryotic Cells (AQA A Level Biology): Flashcards
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Define cell cycle.
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Define cell cycle.
The cell cycle is the regulated sequence of events that occurs between one cell division and the next.
What are the three main phases of the cell cycle?
The three main phases of the cell cycle are interphase, nuclear division (mitosis), and cell division (cytokinesis).
The transition from one phase of the cell cycle to another is triggered by .
The transition from one phase of the cell cycle to another is triggered by chemical signals called cyclins.
True or False?
The length of the cell cycle is always the same, regardless of the organism or cell type.
False.
The length of the cell cycle is variable depending on environmental conditions, cell type, and organism.
Define interphase.
Interphase is the phase of the cell cycle during which the cell grows, carries out normal functions, and replicates its DNA in preparation for mitosis.
What happens during the S phase of interphase?
During the S phase, DNA in the nucleus is replicated, resulting in each chromosome having two identical sister chromatids.
During phase, the cell continues to grow and the new DNA is checked for errors.
During G2 phase, the cell continues to grow and the new DNA is checked for errors.
What main event occurs during the G1 phase of interphase?
During G1 phase, the cell grows and synthesises proteins needed for growth. It also receives a signal to divide before entering S phase.
Define mitosis.
Mitosis is a type of nuclear division that produces two genetically identical daughter nuclei from one parent nucleus.
List the four stages of mitosis in order.
The four stages of mitosis are: prophase, metaphase, anaphase, telophase.
During , chromosomes align at the of the cell.
During metaphase, chromosomes align at the equator of the cell.
What happens to the nuclear envelope during prophase?
During prophase, the nuclear envelope breaks down.
In , spindle fibres shorten and are pulled to opposite poles.
In anaphase, spindle fibres shorten and chromatids are pulled to opposite poles.
What key event distinguishes telophase from other stages of mitosis?
During telophase, nuclear envelopes reform around each set of chromosomes, and the chromosomes begin to decondense.
Define photomicrograph.
A photomicrograph is an image taken using a microscope to show details of cells or tissues.
True or False?
In prophase, chromosomes are not visible under a microscope.
False.
In prophase, chromosomes condense and become visible under a microscope.
Cells at have chromosomes lined up along the middle of the cell.
Cells at metaphase have chromosomes lined up along the middle of the cell.
Define asexual reproduction.
Asexual reproduction is a form of reproduction that involves one parent and produces genetically identical offspring.
How does mitosis allow a zygote to develop into a multicellular organism?
Mitosis produces genetically identical daughter cells that allow a zygote to develop into a multicellular organism by increasing cell number.
Mitosis is essential for the and repair of damaged tissues in multicellular organisms.
Mitosis is essential for the replacement and repair of damaged tissues in multicellular organisms.
Define cytokinesis.
Cytokinesis is the division of the cytoplasm that occurs after telophase, producing two genetically identical daughter cells. It is not a part of mitosis.
True or False?
Cytokinesis is a stage of mitosis.
False.
Cytokinesis occurs after telophase and is not considered a part of mitosis.
What is formed in animal cells during cytokinesis to separate the two new cells?
A cleavage furrow forms in animal cells during cytokinesis, allowing the membrane to pinch inwards and separate the cells.
How does cytokinesis differ between animal and plant cells?
In animal cells, a cleavage furrow forms and the membrane pinches inwards. In plant cells, a cell plate forms at the metaphase plate and new cell walls are built to separate the cells.
During cytokinesis in plant cells, a forms at the metaphase plate, and new are built from it to separate the cells.
During cytokinesis in plant cells, a cell plate forms at the metaphase plate, and new cell walls are built from it to separate the cells.
Cytokinesis produces genetically identical .
Cytokinesis produces two genetically identical daughter cells.
What must reform at each pole before cytokinesis occurs?
The nuclear envelope, which reforms at each pole after telophase.
Cytokinesis follows the reformation of the envelope at each pole.
Cytokinesis follows the reformation of the nuclear envelope at each pole.
In an animal cell, how does the cleavage furrow separate the two cells?
The membrane pinches inwards to separate the two cells.
True or False?
Cytokinesis produces two genetically different daughter cells.
False.
Cytokinesis produces two genetically identical daughter cells.
Cytokinesis involves the division of the to form two daughter cells.
Cytokinesis involves the division of the cytoplasm to form two daughter cells.
Define meristem.
A meristem is a region in plants where cells actively divide by mitosis, enabling growth.
What part of a plant is commonly used to study mitosis?
The root tip meristem is commonly used to study mitosis because it contains many dividing cells.
The root tip meristem is found just behind the of the root.
The root tip meristem is found just behind the protective root cap of the root.
True or False?
The zone of cell division in a root tip contains cells undergoing mitosis.
True.
The zone of cell division in the root tip meristem is where cells are actively dividing by mitosis.
What is the squash technique and why is it used when preparing root tip slides?
The squash technique involves gently pressing a stained root tip to spread its cells into a thin layer, making it easier to see individual cells undergoing mitosis under the microscope.
After cutting the root tips, they are placed in ethanoic alcohol to the tissue and prevent mitosis from continuing.
After cutting the root tips, they are placed in ethanoic alcohol to fix the tissue and prevent mitosis from continuing.
Define acetic orcein stain.
Acetic orcein stain is a dye that stains chromosomes a deep purple colour to make them visible under a microscope.
What is one potential limitation when preparing root tip tissue for microscopy?
Preparing tissue can damage cells or create artefacts, which may alter their appearance and affect observations.
Define mitotic index.
The mitotic index is the proportion of cells in a sample that are undergoing mitosis.
How do you calculate the mitotic index?
The mitotic index is calculated as the number of cells with visible chromosomes divided by the total number of cells.
To express the mitotic index as a percentage, multiply your answer by .
To express the mitotic index as a percentage, multiply your answer by 100.
True or False?
The mitotic index can be greater than 1.
False.
The mitotic index is a proportion so it cannot be greater than 1.
In the formula for mitotic index, you divide the number of cells with chromosomes by the number of cells.
In the formula for mitotic index, you divide the number of cells with visible chromosomes by the total number of cells.
Define magnification.
Magnification is the ratio of the size of an image to the actual size of the object, with no units.
Which equation is used to calculate the actual size of a root tip cell from a micrograph?
The equation is: actual size = size of image ÷ magnification.
When using the magnification equation, all measurements must be in the units.
When using the magnification equation, all measurements must be in the same units.
True or False?
There are 1000 micrometres (µm) in a millimetre (mm).
True.
There are 1000 micrometres in a millimetre.
To convert from micrometres (µm) to nanometres (nm), by 1000.
To convert from micrometres (µm) to nanometres (nm), multiply by 1000.
What is the best unit of measurement to use when working with very small cellular structures?
The best unit to use is the smallest unit shown in the question, typically micrometres (µm) or nanometres (nm).
Define visible chromosomes.
Visible chromosomes are chromosomes that can be seen under a microscope during mitosis, indicating cells are actively dividing.
Define mitosis.
Mitosis is a controlled process of cell division that produces genetically identical daughter cells.
What can result from uncontrolled mitosis in the body?
Uncontrolled mitosis can result in the formation of a tumour, which is an abnormal mass of cells and can lead to cancer.
Define oncogene.
An oncogene is a mutated gene that can cause continuous cell division and contribute to the development of cancer.
Mutations in controlling the cell cycle can lead to uncontrolled cell division.
Mutations in genes controlling the cell cycle can lead to uncontrolled cell division.
How do mutations in tumour suppressor genes contribute to cancer development?
Mutations in tumour suppressor genes can prevent programmed cell death (apoptosis) or allow continuous cell division, leading to cancer.
Most cancer treatments aim to or stop mitosis in rapidly dividing cells.
Most cancer treatments aim to slow or stop mitosis in rapidly dividing cells.
True or False?
Cancer treatments often work by targeting processes involved in mitosis.
True.
Many cancer treatments slow or stop mitosis to prevent the uncontrolled division of cancer cells.
Define apoptosis.
Apoptosis is programmed cell death.
How does the drug Methotrexate act as a cancer treatment?
It inhibits DNA nucleotide synthesis, preventing cells from dividing.
How does the drug Taxol act as a cancer treatment?
It prevents the disassembly of spindle fibres, freezing mitosis.
State two ways in which mutations in cell-cycle genes can lead to cancer.
They can cause continuous cell division.
They can prevent programmed cell death (apoptosis).
Define binary fission.
Binary fission is a type of cell division in prokaryotes that is simpler than mitosis and involves the replication and division of a single circular DNA molecule and plasmids.
Which type of cell division occurs in prokaryotes?
Cell division in prokaryotes is called binary fission.
During binary fission, prokaryotic cells replicate their DNA molecule and their .
During binary fission, prokaryotic cells replicate their single, circular DNA molecule and their plasmids.
True or False?
Prokaryotic cells divide by mitosis.
False.
Prokaryotic cells divide by binary fission, not mitosis.
What happens to the cytoplasm during binary fission in prokaryotes?
During binary fission, the cytoplasm divides roughly equally between the two daughter cells.
Each daughter cell from binary fission receives copy of circular DNA and a number of plasmids.
Each daughter cell from binary fission receives one copy of circular DNA and a variable number of plasmids.
Why is it important for each daughter cell to inherit a copy of the circular DNA molecule during binary fission?
If a daughter cell does not receive a copy of the circular DNA molecule, it will die, because this carries the genes essential for survival.
Plasmids are not essential — they carry only additional genes (e.g. antibiotic resistance), so the number inherited is variable.
Why is binary fission simpler than mitosis?
Binary fission is simpler because prokaryotic cells have no nucleus, no chromosomes, no spindle fibres, and no membrane-bound organelles.
Define plasmids.
Plasmids are small, circular DNA molecules found in prokaryotic cells.
How does the ability to reproduce rapidly by binary fission benefit bacteria?
Rapid binary fission allows bacteria to:
Colonise new environments quickly
Outcompete other microbes
Accumulate mutations faster, increasing genetic variation.
Rapid binary fission allows bacteria to accumulate faster, contributing to antibiotic .
Rapid binary fission allows bacteria to accumulate mutations faster, contributing to antibiotic resistance.
Define virus.
A virus is an acellular infectious particle that is non-living and capable of replicating only inside host cells.
A virus consists of a core and a protein coat called a .
A virus consists of a nucleic acid core and a protein coat called a capsid.
What is the function of the envelope in some viruses?
The envelope in some viruses is an outer layer formed from the membrane-phospholipids of the host cell, which can help the virus evade the host's immune system or assist in entry into new host cells.
True or False?
Viruses undergo cell division to reproduce.
False.
Viruses are non-living and do not undergo cell division; instead, they replicate only inside host cells by hijacking the host's cellular machinery.
Define capsid.
A capsid is the protein coat that surrounds and protects the nucleic acid core of a virus.
How do viruses attach to specific host cells?
Viruses attach to specific host cells using attachment proteins that bind to complementary receptors on the host cell surface.
Viruses can only replicate host cells because they are .
Viruses can only replicate inside host cells because they are parasitic.
What are two ways viruses are released from host cells?
Viruses are released from host cells by cell lysis (bursting the cell) or by budding (taking host membrane to form an envelope).
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