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OCR A A-Level Biology > Unit 6 - Cell Division > Flashcards

Unit 6 - Cell Division Flashcards

1
Q

What is the cell cycle?

A

A highly ordered sequence of events which takes place in a cell, resulting in the cell’s division.

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2
Q

What are the two main phases of the cell cycle?

A
  • interphase
  • mitotic division phase
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3
Q

What is interphase?

A

The period of cell growth before cell division when the cell is working normally.

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4
Q

What are the three parts of interphase?

A

G1, S and G2.

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5
Q

What happens in G1?

A

G1 is the first growth phase - the cellular components are duplicated and cells increase in size.

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6
Q

What happens in S phase?

A

S is the synthesis phase - when DNA is replicated in the nucleus.

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7
Q

What happens in G2?

A

G2 is the second growth phase - when further growth occurs and the duplicated chromosomes are checked for errors.

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8
Q

What are the two parts of the mitotic division phase?

A

Mitosis and cytokinesis.

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9
Q

What is G0?

A

When a cell leaves the cell cycle.

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10
Q

Why can cells leave the cell cycle?

A
  • if the cell has become specialised
  • if the DNA has been damaged
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11
Q

What are senescent cells?

A

Senescent = too old to continue replicating

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12
Q

Where are the three checkpoints in the cell cycle?

A
  • G1
  • G2
  • In mitosis
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13
Q

What does the G1 checkpoint verify?

A
  • The cell is the right size
  • There are the right number of organelles
  • There is no major damage to DNA
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14
Q

What does the G2 checkpoint verify?

A

That DNA replication has occurred correctly.

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15
Q

What does the checkpoint in mitosis verify and where is it?

A

The checkpoint is during metaphase and checks that chromosomes have correctly aligned and attached to the spindles.

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16
Q

How do normal cells become cancer cells?

A

When there is a mutation in the genes controlling cell division.

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17
Q

What is an oncogene?

A

A mutated gene with the potential to cause cancer by changing normal cells into cancer cells.

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18
Q

What is a carcinogen?

A

An environmental agent which causes cancer by triggering the mutation in DNA which causes oncogene formation.

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19
Q

What is a benign tumour?

A

A growth of cancer cells which doesn’t spread from its site of origin, but can compress and displace surrounding tissues.

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20
Q

What is a malignant tumour?

A

A growth of cancer cells which can spread through the body and invade other tissues, causing tumour growth elsewhere.

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21
Q

What is metastasis?

A

When cancer cells break off from a tumour and spread through the body.

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22
Q

How many chromosomes are found in human body cells?

A

46.

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23
Q

How many chromosomes are found in human sex cells?

A

23.

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24
Q

What are sister chromatids?

A

Two chromatids which are joined at the centromere to make a chromosome.

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25
Q

What are non-sister chromatids?

A

Chromatids from two different chromosomes with different alleles of the same gene.

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26
Q

After interphase, how many chromosomes and chromatids are there?

A

92 chromatids joined to make 46 chromatids.

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26
Q

What happens in early prophase (mitosis)?

A

The chromosomes condense, becoming visible.
The centriole divides, moving to opposite sides of the cell.
The nucleolus shrinks, becoming less prominent.

27
Q

What happens in late prophase (mitosis)?

A

The chromosomes are fully visible.
The spindle fibres form from the centrioles at the poles of the cell.
The nucleolus disappears and the nuclear envelope breaks down.

28
Q

What happens in metaphase (mitosis)?

A

The nuclear membrane has broken down.
The chromosomes align on the equator of the cell.
Each chromosome attaches to a spindle fibre on each side by the centromere.

29
Q

What happens in anaphase (mitosis)?

A

The centromere of each chromosome divides.
The spindle fibres contract, pulling each chromatid to the centrioles at the poles of the cell.
There are now 46 chromosomes at each pole of the cell (46 chromatids as well).

30
Q

What happens in telophase (mitosis)?

A

The nuclear membranes reform around each set of chromosomes and the nucleolus reforms.
The spindle fibres disappear.
The chromosomes extend, becoming invisible.

31
Q

What happens in cytokinesis?

A

In animal cells, a cleavage furrow forms and the cell-surface membrane is pulled inwards by the cytoskeleton to form around each nucleus.
In plant cells, the cell-surface membrane splits due to the fusing of vesicles from the Golgi apparatus and a cell wall forms along the middle of the cell.
Two daughter cells are produced, each containing 46 chromosomes.

32
Q

What is variation?

A

Differences between individuals of the same species.

33
Q

What two processes in meiosis ensure variation?

A

Crossing over - where homologous pairs of chromosomes swap parts of their genetic material
Independent assortment - the chromosomes from each pair are randomly attached to the daughter cells

34
Q

What happens in prophase 1 (meiosis)?

A

The chromosomes condense and crossing over occurs.
The nuclear envelope disintegrates.
The spindle fibres begin to form.
Homologous chromosomes pair up, forming bivalents.

35
Q

What happens in metaphase 1 (meiosis)?

A

Bivalents align on the equator of the cell and attach to the spindle fibres by the centromeres.
Independent assortment - the position of each bivalent is independent of all the other chromosomes

36
Q

What happens in anaphase 1 (meiosis)?

A

The spindle fibres contract, pulling each chromosome to the poles of the cell. The chromatids do not divide.

37
Q

What happens in telophase 1 (meiosis)?

A

The nuclear envelopes and nucleolus reform.
The chromosomes uncoil.
After telophase 1, the cell undergoes cytokinesis to produce two daughter cells, each containing 46 chromatids joined at centromeres to make 23 chromosomes.

38
Q

Do the chromosomes replicate between mitosis 1 and mitosis 2?

A

No.

39
Q

What happens during prophase 2 (meiosis)?

A

The chromosomes re-condense.
The nuclear envelope breaks down.
The spindle fibres reform.

40
Q

What happens during metaphase 2 (meiosis)?

A

The chromosomes align on the equator of the cell and attach to the spindle fibres by the centromeres. (There is still independent assortment of chromosomes).

41
Q

What happens during anaphase 2 (meiosis)?

A

The centromeres divide and the chromatids are pulled to opposite poles of the cell by the contraction of the spindle fibres, leaving 23 chromosomes at each pole.

42
Q

What happens during telophase 2 (meiosis)?

A

The chromosomes uncoil.
The nuclear envelope reforms.
After telophase 2, the cells undergo cytokinesis to produce four daughter cells, each containing 23 chromosomes.

43
Q

What is differentiation?

A

The changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a particular function.

44
Q

What adaptations do erythrocytes have?

A
  • flattened biconcave ratio for an increased SA:V ratio
  • no nuclei and few organelles to increase space for haemoglobin
  • flexible so can squeeze through capillaries
45
Q

What adaptations do neutrophils have?

A
  • multi-lobed nucleus which makes it easier for the cell to move through small gaps
  • many lysosomes which contain enzymes used to attack pathogens
46
Q

What adaptations do sperm cells have?

A
  • flagella to help the cell move
  • many mitochondria to release enough energy to swim
  • acrosome containing enzymes which digest the protective layers around the ovum so the cell can penetrate it
47
Q

What adaptations do palisade cells have?

A
  • many chloroplasts to absorb light for photosynthesis
  • chloroplasts can move within the cytoplasm so absorb more light
  • rectangular box shape so they can be closely packed
  • thin cell walls, increasing diffusion of carbon dioxide
48
Q

What adaptations do root hair cells have?

A
  • long extensions (root hairs) which increase surface area, so there is more uptake of water and mineral ions
49
Q

What adaptations do guard cells have?

A
  • found in pairs to form stomata
  • the inner wall is thicker than the outer wall, so when the cells gain water, the shape changes to open the stomata rather than the cell expanding
50
Q

What is squamous epithelium tissue made of?

A

One layer of squamous epithelial cells - these are flat so the tissue is very thin.

51
Q

Where is squamous epithelium tissue found?

A

Where rapid diffusion is essential e.g. the lining of the lungs.

52
Q

What is ciliated epithelium tissue made of?

A
  • ciliated epithelial cells with cilia which beat rhythmically
  • goblet cells which release mucus to trap particles in the air
53
Q

Where is ciliated epithelial tissue found?

A

The lining of the trachea - the goblet cells trap particles in mucus and cilia sweep the mucus away from the lungs, preventing bacteria from reaching the alveoli.

54
Q

What is cartilage made of?

A
  • chondrocyte cells in an extracellular matrix
  • collagen and elastin fibres
55
Q

Where is cartilage found?

A
  • outer ear
  • nose
  • ends of bones
  • between bones
56
Q

Where is skeletal muscle found?

A

Attached to the skeleton.

57
Q

Where is smooth muscle found?

A

Covering the walls of internal organs.

58
Q

Where is cardiac muscle found?

A

Covering the walls of the heart.

59
Q

Where is epidermis tissue found?

A

Covering the surface of plants - covered by a waterproof waxy cuticle which prevents water loss.

60
Q

What is a totipotent stem cell?

A

A stem cell which can differentiate into any type of cell and has the potential to produce a whole organism.

61
Q

What is a pluripotent stem cell?

A

A stem cell which can form all tissue types but not a whole organism.

62
Q

What is a multipotent stem cell?

A

A stem cell which can differentiate into a range of cells within a certain type of cell.

63
Q

Where are adult stem cells found?

A
  • bone marrow
  • skin
  • other organs e.g. heart and brain
  • umbilical cord blood
64
Q

Where are plant stem cells found?

A
  • root tips
  • shoot tips (meristematic)
  • vascular cambium, between xylem and phloem
65
Q

Give three potential uses of stem cells.

A

Any three from:
- Repairing cardiac tissue after a heart attack
- Replacing insulin producing cells in type 1 diabetics
- Replacing dopamine producing cells to treat Parkinson’s
- Replacing brain cells to treat Alzheimer’s
- Treating macular degeneration
- Reversing birth defects
- Treating spinal injuries

66
Q

Give three current uses of stem cells.

A
  • providing new skin for burns patients
  • drug trials
  • research into embryo development

OCR A A-Level Biology (8 decks)

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