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AS Human Biology > Chapter 8 - Cell Division > Flashcards

Chapter 8 - Cell Division Flashcards

1
Q

What is the name of the process by which cells divide to make exact copies of themselves?

A

Mitosis

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2
Q

How is DNA organised in eukaryotic cells?

A

Into chromosomes

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3
Q

How many chromosomes do human cells have?

A

46

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4
Q

Why can’t you see chromosomes when a cell isn’t dividing?

A

The DNA is ‘unwound’ and spread out in the nucleus

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5
Q

What phase is a cell in if it isn’t dividing?

A

Interphase

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6
Q

What is chromatin?

A

DNA molecule wrapped around histones (proteins)

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7
Q

When does DNA replicate?

A

In interphase

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8
Q

What happens to chromatin when a cell starts to divide?

A

It coils up and folds to form chromosomes

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9
Q

What does a chromosome look like in prophase?

A

It has two sister chromatids, held together by a centromere

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10
Q

Why are there two chromatids?

A

The DNA replicated in interphase

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11
Q

What does the cell do in interphase?

A

Protein synthesis
Cell organelle replication
Respiration

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12
Q

What is interphase divided into?

A

G1, S and G2

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13
Q

What happens in growth phase 1 (G1)?

A

Cell organelle synthesis

Biochemicals produced

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14
Q

What happens in synthesis (S) phase?

A

DNA is replicated

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15
Q

What happens in growth phase 2 (G2)?

A

Energy stores are increased

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16
Q

What are the four phase of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase

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17
Q

What happens in prophase?

A

Chromosomes shorten and thicken
Spindle fibres form
Nuclear envelope disintegrates

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18
Q

What happens in metaphase?

A

Chromosomes are arranged on the equator

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19
Q

What happens in anaphase?

A

Chromosomes migrate to opposite poles

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20
Q

What happens in telophase?

A

Spindle fibres disintegrate

Nuclear envelope develops

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21
Q

What is mitosis important for?

A

Growth
Repair
Asexual reproduction

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22
Q

Explain the importance of mitosis in growth

A

Zygotes are diploid
The chromosomes contain all the information needed to make a whole new organism
The zygote divides by mitosis to ensure every cell has the exact same alleles

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23
Q

Explain the importance of mitosis in repair

A

If cells die or are damaged, they need to be replaced by cells with exact same genetic information as them

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24
Q

Explain the importance of mitosis in

A

All the offspring are identical to the one parent
This is advantageous if environmental conditions aren’t changing
It enables one organism to produce offspring very quickly

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25
Q

Explain what happens in prophase in detail

A

Chromosomes become visible
Centrioles (organelle) move to the poles of the cell
They send out microtubules (fibres) which form a system called the spindle

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26
Q

Explain what happens in metaphase in detail

A

The centromeres of the chromosomes attach to the equator of the spindle
Centromeres divide
The chromatids can be called daughter chromosomes

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27
Q

Explain what happens in anaphase in detail

A

Microtubules attached to the centromeres contract

Daughter chromosomes are pulled to the opposite poles

28
Q

Explain what happens in telophase in detail

A

Daughter chromosomes reach their poles
They unwind to become longer and thinner
Spindle fibres break down
Nuclear membrane reforms
The centrioles divide so each daughter cell can have two
The cytoplasm constricts, separating the cell in two

29
Q

What is a tumour?

A

A mass of cells that have divided too many times

30
Q

What types of tumour are there?

A

Benign and malignant

31
Q

Describe benign tumours

A 
Slow-growing
Stay in one tissue
Do not spread to other parts of the body
Not usually life-threatening
When removed, they do not grow back
32
Q

Describe malignant tumours

A

Grow rapidly
Invade surrounding tissues
Cells can break off from the main tumour
Life-threatening unless treated early

33
Q

What are proto-oncogenes?

A

Genes that stop cells dividing by mitosis too often

34
Q

What is one way a proto-oncogene can work?

A

Coding for receptor proteins
These are then activated by growth factor
This switches the genes on to stimulate DNA replication (hence cell division)

35
Q

How else can proto-oncogenes work?

A

They produce the growth factor needed to stimulate cell division

36
Q

When do proto-oncogenes become oncogenes?

A

When the base sequence changes; a mutation occurs

37
Q

Describe one way how oncogenes cause uncontrolled cell division

A

They can produce a different form of receptor protein that stimulates cell division even without growth factor

38
Q

How else can oncogenes cause uncontrolled cell division?

A

They can produce uncontrolled amount of growth factor

39
Q

What are tumour suppressor genes?

A

Genes that code for proteins that stop cells dividing

Also, they cause cells with damaged DNA to die

40
Q

What would happen if a tumour suppressor gene mutated?

A

The cell might carry on dividing uncontrollably, passing on damaged DNA

41
Q

What is a primary tumour?

A

A mass of cells that has become large enough to develop its own blood and lymph vessels in one place

42
Q

What is a secondary tumour?

A

When cells from the primary tumour break off and spread into blood and lymph vessels
They travel around the body and cause new tumours in other parts of the body - secondary tumours

43
Q

What is the name for the spreading of tumour cells?

A

Metastatis

44
Q

What are secondary tumours also known as?

A

A metastatis

45
Q

What are the causes of cancer?

A 
Genetic factors
Age
Ionising radiation
UV radiation
Chemicals
Viruses
46
Q

How can genetic factors cause cancer?

A

Some people have proto-oncogenes which are more likely to mutate
This is why it can run in families

47
Q

How does age affect getting cancer?

A

They have been exposed to environmental factors, such as radiation and chemicals, for longer
They have had more of a chance to damage their DNA

48
Q

How does ionising radiation cause cancer?

A

Includes X-rays, alpha and beta radiation

Has a lot of energy so can penetrate body cells and break bonds in DNA molecules

49
Q

How does UV radiation cause cancer?

A

Has enough energy to penetrate skin cells

Breaks bonds in DNA and can cause skin cancer

50
Q

How can chemicals cause cancer?

A

Cancer causing chemicals are called carcinogens

Cigarette smoke, asbestos, some pesticides and diesel exhaust can cause cancer

51
Q

How can viruses cause cancer?

A

HPV is the best known example

It carries the code for a protein that interferes with a tumour suppressor gene

52
Q

What is the process by which gametes are formed called?

A

Meiosis

53
Q

What is the diploid number in humans?

A

2n = 46

54
Q

What is a cell with a homologous pair of chromosomes called?

A

Diploid

55
Q

Why do gametes have to be haploid (n = 23)?

A

Because each individual develops from a zygote that divides by mitosis

56
Q

What happens in the first stage of meiosis?

A

Two cells are formed

Each chromosome still has two chromatids

57
Q

What happens in the second stage of meiosis?

A

The chromatids divide, making four haploid cells

58
Q

What can go wrong in meiosis?

A

A gamete can end up with one less or one more chromosome

59
Q

What problems will arise if one of these gametes fuses with a normal gamete?

A

The zygote will have one extra or one missing chromosome

60
Q

What is this called?

A

Non-disjunction

61
Q

What causes Down’s syndrome?

A

When someone has 3 copies of chromosome 21 (trisomy 21)

62
Q

How is trisomy 21 formed?

A

When a gamete with two copies of chromosome 21 fuses with a normal gamete, which has one copy, to get 3 copies

63
Q

When does the risk of having a Down’s syndrome increase?

A

As the woman gets older

64
Q

What are some characteristics of a person with Down’s syndrome?

A 
Flatter head than normal
Smaller ears
Protruding ears
Shorter than average
Single crease along the palm
65
Q

What do all Down’s syndrome people suffer with?

A

Learning difficulties

66
Q

Describe the personality and lifestyle of a Down’s syndrome person

A

Very happy
Very affectionate
Some can enter employment and lead independent lives
Some may need lifelong care

67
Q

What is the average life expectancy for someone with Down’s syndrome?

A

60 years

AS Human Biology (4 decks)

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