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Biology AS > 2.2 Cell Cycle, Mitosis and Meiosis > Flashcards

2.2 Cell Cycle, Mitosis and Meiosis Flashcards

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1
Q

What is the cell cycle?

A

Cells that don’t divide continuously but undergo a regular cycle of division separated by periods of cell growth are said to have a cell cycle

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2
Q

What are the three stages of the cell cycle?

A
  • interphase
  • nuclear division
  • cytokinesis
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3
Q

What is interphase? (Cell cycle)

A

It occupies most of the cell cycle and is sometimes known as the resting phase because no division takes place

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4
Q

What is nuclear division?

A

When the nucleus divides either into two during mitosis or four during meiosis

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5
Q

What is cytokinesis?

A

Division of cytoplasm which follows nuclear division

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6
Q

What is the length of the cell cycle?

A
  • complete cycle length varies greatly between organisms
  • typically, a mammalian cell takes about 24 hours to complete a whole cycle (90% of this time the cell is in interphase)
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7
Q

What are the 5 stages of mitosis?

A
  • interphase
  • prophase
  • metaphase
  • anaphase
  • telophase
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8
Q

Describe interphase.

A
  • occupies most of the cell cycle, and is sometimes known as the resting phase because no division takes place
  • lots of cellular activity which includes the replication of DNA
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9
Q

Describe prophase.

A
  • the chromosomes condense (shorten and thicken) so that they can be seen
  • centrioles move to opposite ends of the cell and spindle fibres develop from them. Together spindle fibres are known as spindle apparatus
  • nucleolus disappears and nuclear envelope breaks down
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10
Q

Describe metaphase.

A
  • the chromosomes are pulled along the spindle apparatus by their centromeres and arrange themselves along the equator of the cell
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11
Q

Describe anaphase.

A
  • the centromeres divide in two and the spindle fibres pull the chromatids apart
  • the chromatids move to their respective poles and we now refer to them as chromosomes again
  • the energy for this process is provided by the mitochondria
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12
Q

Describe telophase.

A
  • chromosomes reach their respective poles and become longer and thinner, finally disappearing completely (leaving widespread chromatin)
  • spindle fibres disintegrate and the nuclear envelope and nucleolus reform
  • cytoplasm divides in a process called cytokinesis
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13
Q

What is mitosis?

A

Division of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell (except for mutations which are rare)

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14
Q

What is the importance of mitosis?

A
  • growth
  • repair
  • reproduction (single cells organisms)
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15
Q

How can cell division take place?

A

Either by mitosis or meiosis

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16
Q

Factors of mitosis (x11)

A
  • DNA is copied exactly (if there are no mutations)
  • the daughter (new) cells are copies of the parent cell
  • daughter cells have the same number of chromosomes as the parent cell
  • chromosomes of the parent cell are duplicated in the daughter cells
  • enables a species to colonise an area quickly using asexual reproduction
  • important for the growth of plants and animals
  • produces clones
  • important for the repair of damaged tissue where new cells must be identical to damaged cells
  • the original (parent cells) become 2 daughter cells
  • when out of control, a cancerous tumour may result
  • produces cells with the diploid number of chromosomes
17
Q

Factors of meiosis (x11)

A
  • 4 daughter cells are made
  • cell division by reduction
  • forms gametes (sex cells)
  • increases the variety of offspring - provides a varied stock of individuals
  • happens only in gamete producing organs (testes, ovaries, pollen, sacs, ovules)
  • the daughter cells contain half the number of chromosomes as the parent cell
  • produces new genetic combinations in individuals
  • ensures that the number of chromosomes remains the same in sexually reproducing organisms
  • enables a species to adapt to a changing environment or to colonise new environments
  • halves the number of chromosomes in cells
  • produces cells with the haploid number of chromosomes
18
Q

Describe stem cells

A
  • the first group of cells in an embryo are initially identical
  • all cells are produced through mitosis division and contain the same genes
  • only some genes are switched on
  • different genes are switched on depending on the cells specialism
19
Q

Why does the cell cycle not occur in some cells?

A

After differentiation, some types of cell in multicellular organisms no longer have the ability to divide

20
Q

What is the difference between the cell cycle and mitosis?

A

Cell cycle includes growth period between divisions; mitosis is only 10% of the cycle and refers only to nuclear division

21
Q

Explain the procedure for a root tip squash experiment.

A
  1. prepare a temporary mount of root tissue
  2. focus an optical microscope on the slide. Count total number of cells in the field of view and number of cells in a stage of mitosis
  3. calculate mitotic index
22
Q

How do you prepare a temporary root tip mount?

A
  1. place root in hydrochloric acid to halt cell division and hydrolyse middle lamella
  2. stain root tip with a dye that binds to chromosomes
  3. macerate tissue in water using mounted needle
  4. use mounted needle at 45° to press down coverslip and obtain a single layer of cells. Avoid trapping air bubbles
23
Q

Name 2 dyes that bind to chromosomes

A
  • toluidine blue
  • acetic orcein
24
Q

Why is only the root tip used when calculating a mitotic index?

A

• meristematic cells at root tip are actively undergoing mitosis
• cells further from root tip are elongating rather than dividing

25
Q

How do prokaryotic cells replicate?

A

Binary Fission:
1. DNA loop replicates. Both copies stay attached to cell membrane. Plasmids replicate in cytoplasm
2. Cell elongates, separating the 2 DNA loops
3. Cell membrane contracts and septum forms
4. Cell splits into 2 identical progeny cells, each with 1 copy of the DNA loop but a variable number of plasmids

26
Q

Why are viruses classified as non-living?

A

they are acellular; no cytoplasm, no metabolism and cannot self-replicate

27
Q

Outline how viruses replicate.

A
  1. attachment proteins attach to receptors on host cell membrane
  2. enveloped viruses fuse with cell membrane or move in via endocytosis and release DNA/RNA into cytoplasm or viruses inject DNA/RNA
  3. Host cell uses viral genetic information to synthesise new viral proteins/nucleic acid
  4. Components of new viral particle assemble
28
Q

How do new viral particles leave the host cell?

A

a) bud off and use cell membrane to form envelope
b) cause lysis of host cell

29
Q

Why is it so difficult to develop effective treatments against viruses?

A

replicate inside living cells = difficult to kill them without killing host cells

Biology AS (36 decks)

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