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AQA AS (A-level) Biology > 3.2.2 All cells arise from other cells > Flashcards

3.2.2 All cells arise from other cells Flashcards

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1
Q

Definition of the cell cycle

A

A regulated sequence of events that occurs between one cell division and the next

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2
Q

Is interphase part of mitosis?

A

No

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3
Q

Role of cyclins

A

Trigger the movement of one phase to the next through chemical signals

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4
Q

A cell spends most of its time in which phase?

A

Interphase

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5
Q

3 stages of interphase

A
  1. G1
  2. S
  3. G2
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6
Q

G1 phase

A

Makes RNA, enzymes and proteins required for growth

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7
Q

S phase

A

DNA in nucleus replicates (through semi conservative replication), each chromosome consists of 2 identical sister chromatids

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8
Q

G2 phase

A

Cells continued to grow, newly synthesised DNA is checked and any errors are repaired

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9
Q

Role of centrioles

A

Produce spindle fibres

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10
Q

During G2, what is the function of centrioles?

A

Duplicate and move to opposite poles of the cell

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11
Q

How do cancer drugs generally treat cancer?

A

Killing dividing cells by blocking parts of the cell cycle, cell division ceases, hence growth of cancer

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12
Q

How do cancer drugs disrupt the cell cycle?

A
  • Preventing DNA replication
  • Inhibiting the metaphase stage affecting spindle formation
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13
Q

Explain what occurs during prophase (3)

A

Mark in pairs
1. Chromosomes thicken/condense/become visible
AND
2. Chromosomes consist of 2 identical chromatids (called sister centromere)

  1. Two centrioles move towards opposite poles of the cell
    AND
  2. Spindle fibres emerge from centrioles
  3. Nuclear envelope breaks down into vesicles
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14
Q

Explain what occurs during metaphase (2)

A
  1. Chromosomes line in the middle of the cell
  2. They attach to spindle fibres by their centromeres
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15
Q

Describe what occurs during anaphase (1)

A

Spindle fibres contract and pull sister chromatids to opposite poles of the cell

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16
Q

Explain what occurs during telophase (3)

A
  1. Chromosomes arrive at opposite poles and uncoil
  2. Spindle fibres break down
  3. Nuclear envelope reforms around chromosomes
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17
Q

When does cytokinesis occur?

A

After telophase - final step of cell cycle

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18
Q

Describe what occurs during cytokinesis (2)

A
  1. Cytoplasm divides
  2. Forms 2 genetically identical daughter cells
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19
Q

Mitotic index definition?

A

The proportion of cell tissue undergoing mitosis

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20
Q

Equation for mitotic index

A

Number of cells with visible chromosomes/Total number of cells

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21
Q

How do you calculate the length/duration of mitosis

A

Number of cells in specific stage of mitosis/Total number of cells x Time taken for whole cycle in minutes

22
Q

When preparing onion root on a slide, why is only the first 5mm of the tip of the root used?

A

This is were mitosis occurs

23
Q

When preparing an onion root tip slide, why would a student press down firmly on the cover slip?

A

To ensure the specimen is a thin layer of cells

24
Q

Cancer

A

Uncontrolled mitosis, leading to a tumour

25
Q

Tumour

A

Abnormal mass of cells

26
Q

When does uncontrollable mitosis begin?

A

When changes occur in genes controlling cell division, the change in base sequence is a mutation

27
Q

Which gene is cancerous?

A

Oncogene

28
Q

Most mutations result in…

A
  1. Cell death
  2. OR cell being destroyed by immune system
29
Q

Why don’t dead cells have an impact on the body?

A

They’re easily replaced

30
Q

Which mutations don’t result in early cell death or being destroyed by the lymphatic system?

A

Generations of cancerous cells

31
Q

Carcinogens

A

Agents that may cause cancer

32
Q

Examples of carcinogens

A
  1. UV light
  2. Tobacco tar
  3. Asbestos
  4. X-rays
33
Q

Benign tumours

A

Bound by membrane so don’t spread

34
Q

Malignant tumours

A

Gain a blood supply, break off, invade healthy tissue, form secondary tumours

35
Q

What is the main role of drugs involved in cancer treatment?

A

Killing dividing cells by blocking parts of the cell cycle ceasing growth of a tumour

36
Q

How do cancer drugs disrupt the cell cycle?

A
  • Preventing DNA replication
  • Inhibiting the metaphase stage of mitosis affecting spindle formation
37
Q

The main issue with cancer treatments

A

They disrupt the cell cycle for normal cells, e.g., hair cell leading to hair loss

38
Q

How do bacterial cells divide?

A

Binary fission

39
Q

Bacterial cells do not contain nuclei, instead, what do they contain?

A

Circular DNA and plasmids

40
Q

True or False: Bacterial cells contain spindle fibres

A

False - they do not contain spindle fibres

41
Q

Because of no spindle fibres in binary fission, what doesn’t break down?

A

The nuclear envelope

42
Q

Explain how bacterial cells divide to form new cells (4)

A
  1. Binary fission
  2. Single, circular DNA (and plasmids) undergo DNA replication (through semi-conservative replication)
  3. Cell membrane grows (between 2 DNA molecules and) pinches inwards, dividing the cytoplasm
  4. 2 daughter cells (each) containing a single copy of the circular DNA and a variable number of plasmids
43
Q

If in a cell, there is only one spindle fibre, instead of two, how would this affect division?

A
  • There would be no separation of chromatids
  • Chromosomes all go to one pole of the cell
  • Twice the amount of chromosomes in one daughter cells
44
Q

Suggest and explain two environmental variables that could be changed to increase the growth rate of cells in mitosis (4)

A

Principle of marking pairs: Named environmental variable; Correct effect on growth rate;

Examples

  1. Increased (concentration of) glucose;
  2. Increased respiration;
  3. Increased (concentration of) oxygen;
  4. Increased respiration;
  5. Increased temperature;
  6. Increased enzyme activity;
  7. Increased (concentration of) phosphate;
  8. Increased ATP/DNA/RNA;
  9. Increased (concentration of) nucleotides;
  10. Increased DNA synthesis;
45
Q

Describe and explain the arrangement of genetic material in prophase (2)

A
  1. Chromosomes (are) becoming visible/distinct;
  2. Because (still) condensing;

OR

          *Accept ‘chromosomes are condensed’ for 2 marks.*
         *Accept shorten or thicken for ‘condensed’*
  1. Chromosomes (arranged) at random/not lined up;
  2. Because no spindle (activity);

OR

Because not attached to spindle fibres;
Link marking points-
1 and 2
3 and 4

46
Q

When preparing a root tip squash, explain why only the first 5mm of the tip is used and why it is importantly to press firmly on the cover slip (2)

A
  • Because this is where most mitosis occurs
  • To ensure a thin layer of cells for light to pass through
47
Q

A scientist treated growing tips of onion roots with a chemical that stops root tips growing.

During anaphase, he found that only some of the sister chromatids were pulled to opposite poles of the cell.

Use this information to suggest how the chemical stops the growth of roots (3)

A
  1. Stopping / disrupting / spindle fibres forming / attaching / pulling;
          *Ignore affects anaphase*
  2. Preventing separation of (sister) chromatids;
                 *Ignore chromosomes separate / split*

             *Accept chromatids split*
  3. (So) no new cells added (to root tip);
48
Q

A scientist viewed chromosomes under a microscope. These cells were undergoing mitosis.

Explain why 2 identical sister chromatids could be seen (1)

A

Because DNA has replicated

49
Q

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.

Suggest how this procedure moved the chromosomes apart (2)

A
  1. Water moves into the cells/cytoplasm by osmosis;
             *Reject water moving into chromosomes/nucleus.*
  2. Cell/cytoplasm gets bigger;
            *Accept idea of cell/cytoplasm has greater volume/swells/expands*

        *Ignore references to pressure changes, turgidity and chromosomes being more dilute*

        *Ignore references to changing water/fluid contents of the cell*

        *Allow ECF for ‘nucleus expands’ but not for ‘chromosomes expand’*
50
Q

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.

Suggest how this procedure moved the chromosomes apart (2)

A
  1. Water moves into the cells/cytoplasm by osmosis;
             *Reject water moving into chromosomes/nucleus.*
  2. Cell/cytoplasm gets bigger;
            *Accept idea of cell/cytoplasm has greater volume/swells/expands*

        *Ignore references to pressure changes, turgidity and chromosomes being more dilute*

        *Ignore references to changing water/fluid contents of the cell*

        *Allow ECF for ‘nucleus expands’ but not for ‘chromosomes expand’*
51
Q

Suggest why a student, when preparing a temporary mount of an onion root tip, was instructed to ’push down hard on the cover slip, but do not push the cover slip sideways’ (2)

A
  1. Push hard – spread / squash tissue;
  2. Not push sideways – avoid rolling cells together / breaking chromosomes.
                *Neutral – to see cells clearly*
52
Q

A student viewed chromosomes under an optical microscope.

He concluded that the cell was in anaphase.

Give two reasons why the student was able to conclude this (2)

A
  1. Chromosomes / chromatids are (in two groups) at poles of spindle / at ends of spindle;
       *Do not accept ‘ends of cell’*
  2. V-shape shows that (sister) chromatids have been pulled apart at their centromeres / that centromeres of (sister) chromatids have been pulled apart.

AQA AS (A-level) Biology (13 decks)

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