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Biology Mock AS 2 > Cell Division > Flashcards

Cell Division Flashcards

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1
Q

What is the cell cycle

A

regulated sequence of events that occurs between one cell division and the next as one parent cell divides to form two genetically identical daughter cells.

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2
Q

What are the three stages

A

interphase
mitosis
cytokinesis

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3
Q

what happens to the cell in interphase

A

the cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis)

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4
Q

What are the three phases for interphase and what occurs

A

G1 phase - Cells make the RNA, enzymes and other proteins required for growth. At some point during the G1 phase a signal is received telling the cell to divide again.

S phase - The DNA in the nucleus replicates (resulting in each chromosome consisting of two identical sister chromatids)

G2 phase - the cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired

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5
Q

What generally happens in mitosis

A

Cell growth stops, the nucleus divides and chromatids separate

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6
Q

what occurs in cytokinesis

A

Once the nucleus has divided into two genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells. In animals cytoplasm constricts and in plants a new cell wall is formed

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7
Q

What is the process of mitosis

A

nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent cell nucleus

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8
Q

Explain Prophase

A

chromosomes condense and consist of two identical sister chromatids joined by centromere.
centrosomes move towards opposite side of poles which were replicated in G2.
spindle fibres form from centrosomes
nuclear envelope also breaks down into small vesicle
chromatids condense and become visible

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9
Q

Explain Metaphase

A

Centrosomes reach opposite poles

  • chromosomes line up along the equator (of the cell) (1)
    *spindle fibres (from the centrioles) attach to the {centromere / chromosome} (1)
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10
Q

Explain Anaphase

A

The sister chromatids separate at the centromere

Spindle fibres (protein microtubules) begin to shorten

The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres

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10
Q

Explain Anaphase

A

The sister chromatids separate at the centromere

Spindle fibres (protein microtubules) begin to shorten

The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres

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11
Q

Explain Telophase

A

Chromosomes arrive at opposite poles and begin to decondense

Nuclear envelopes begin to reform around each set of chromosomes

The spindle fibres break down

Cytokinesis division of cytoplasm into cell by constriction at edges. Centrosome replicate during interphase before nucleus division.

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12
Q

Significance of cell division

A

Growth. Multicellular organisms grow in size by increasing the number of cells in their bodies through mitosis.

Replacement of dead cells. Dying cells are replaced by identical cells produced through mitosis.

Repair of tissues by cell replacement. In eukaryotes, most structures which have become damaged can be replaced by new daughter cells.

Asexual reproduction. Some organisms (e.g. wasps, strawberry plants, and yeasts) reproduce asexually through mitosis (i.e. does not require the fusion of gametes). The resulting offspring will be genetically identical to its parents.

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13
Q

practical for identifying mitosis

A

Cut a small piece from the tip of a growing onion root and place it in strong acid (use this to break down middle lamella and separate layer of cells) and heat to intensify the effect

Transfer the root tip to a microscope slide.

Add a drop of stain. - toludine blue

Use a mounted needle to flatten the piece of root and place a coverslip on top and press on it to form single layer of cells

View using high power objective lens of a microscope.

Count the cells at each stage of the cell cycle.

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14
Q

How do you calculate mitotic index

A

number of cells with visible chromosomes ÷ total number of cells

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15
Q

Why do we use multiple root tips?

A

The root tips are very delicate, and can decompose. So using several increases the chances of getting good images at the end.

16
Q

Why is acid used

A

Plant cells tend to stick together due to their cellulose cell walls. The acid separates the cells, enabling the stain to enter more easily

17
Q

What does stain bind to

A

but many bind to chromatin DNA.

18
Q

why can you not see nucleus at the end of prophase in eukaryotic cell

A

because the nuclear membrane is broken down (1) because DNA is { coiled / condensed } into individual chromosomes (1)

19
Q

How do chromosomes look in metaphase

A

condensed / visible (1)
seen as pairs of chromatids (held together by a centromere) (1)
joined to the spindle (fibres) (1)
aligned on the equator of the cell (1)

20
Q

difference between anaphase and telophase

A

In anaphase, sister chromatids (now called chromosomes) are pulled toward opposite poles. In telophase, chromosomes arrive at opposite poles, and nuclear envelope material surrounds each set of chromosomes.

21
Q

advantage to reproduce both sexually and asexually

A

create genetically different cells and increase gene pool / increase genetic diversity

asexual doesn’t require mate, conserve advantageous allele and it is faster

22
Q

explain why two different values of time in anaphase is measure

A

the student may have selected a different part of the root tip
OR
different plants had different {age / rates of growth / mitotic index / rates of respiration / genes}
(1)
* it is difficult to identify the correct stage of mitosis

23
Q

2 things i tend to forget when talking about stages of mitosis

A
  • remove acid with cold water
  • tease with needle
24
Q

role of enzyme ligase in dna replication

A

joins sections of DNA together / repairs breaks in the phosphodiester backbone
(1)
* by forming phosphodiester bonds
(1)
* (forms bonds) between phosphate and {deoxyribose / sugar / pentose

25
Q

why does mitotic index increase as distance from root tip increases

A

because cells become more specialised and differentiate further from root tip

26
Q

which part of plant do you use for preparing a slide during mitosis

A

meristem

27
Q

what else can you do after adding stain to slide to show stages of mitosis

A

heat to intensify the stain (1)

{squash / tease) the tissue to separate the cells

(1)
apply a coverslip {in order to view at high magnification / stop evaporation}

28
Q

why is an appropriate stain required

A

a stain is needed to see chromosomes that would not be clearly visible
(1)

because the stain must attach to {chromosomes / DNA / histone}

29
Q

changes that can be implemented to allow mitosis to be seen clearly

A

use {5mm / shorter} piece of root tip

  • add acid and then stain separately
  • heat the root tip in { acid / stain }
  • tease the cells apart before staining
  • intensify the stain by warming (after squashing)
30
Q

explain changes during cell cycle

A
  • DNA content will double by the end of {S phase / interphase)(1)

because DNA synthesis takes place (before mitosis) (1)

  • the chromosomes will now consist of pairs of chromatidsjoined together at the centromere (1)

During mitosis the chromatids separate and chromosomes now consist of one DNA molecule (by theend of mitosis (1)

DNA content will return to normal by the end of cytokinesis(1)

  • because chromatids are separated into (two new) daughtercells
31
Q

why do cells carry out mitosis

A

growth / repair / asexual reproduction

(1)
* because this needs {genetically identical cells / clones / cells with the same number of chromosomes }

32
Q

Describe events take place during prophase in Animal cell

A

{nucleus / nuclear envelope / nucleous} breaks down

*
spindle (fibres) formed
{chromosomes / chromatids} condense
Centrioles migrate to (opposite) poles of the cell

Biology Mock AS 2 (23 decks)

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