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A Level Biology OCR A > cell division > Flashcards

cell division Flashcards

chap 6

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1
Q

What is G0? Why might a cell enter G0?

A

The resting phase, in which the cell leaves the cycle temporarily or permanently
When a cell is specialized it no longer needs to divide, hence entering G0

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2
Q

Which cells DON’T divide?

A

DNA damaged cells and senescent cells

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3
Q

What happens at each checkpoint of the cell cycle? (4, 3, 2)

A

G1 checkpoint checks for:
cell size, nutrients, growth factors, DNA damage

G2 checkpoint checks for:
cell size, DNA replication, DNA error

Spindle assembly checkpoint checks for:
all chromosomes attached to spindles and being aligned

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4
Q

What happens at G1 phase? (3)

A
  • proteins synthesised
  • organelles replicated
  • cell enlarges
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5
Q

What happens at synthesis phase?

A

DNA replicated

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6
Q

What happens at G2 phase? (3)

A
  • energy stores are increased
  • DNA checked for errors
  • cell enlarges
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7
Q

True or false- chromatids are singular structures of DNA and chromosomes are the X ones

A

False- chromatids and chromosomes are the same thing! X pairs are typically called sister chromatids and when they split into singular structures they are then chromosomes

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8
Q

What is the role of the centromere in mitosis? (3)

A
  • holds chromatids together
  • attaches chromatids to spindle fibres
  • allows chromatids to be separated
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9
Q

MITOSIS: Prophase (3)

A
  • chromatins condense to form chromosomes/chromatids
  • nuclear envelope breaks down
  • spindle fibres form at poles
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10
Q

MITOSIS: Metaphase

A

chromosomes lined up at metaphase plate (equator)

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11
Q

MITOSIS: Anaphase (2)

A
  • centromeres divide
  • spindle fibres contract to separate sister chromatids
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12
Q

MITOSIS: Telophase (3)

A

-chromatids/chromosomes reach poles and coil
- nuclear envelope reforms
- nucleolus formed

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13
Q

MEIOSIS I: Prophase I

A

Chromosomes pair up into BIVALENTS + CROSS OVER

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14
Q

MEIOSIS I: Metaphase I

A

Homologous pairs (4 chromatids) line up via INDEPENDENT ASSORTMENT

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15
Q

MEIOSIS I: Anaphase I

A

Chromosomes are pulled to poles + chromatids become RECOMBINANT (as DNA breaks off and rejoins at CHIASMATA)

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16
Q

How is MEIOSIS II different to mitosis? (2)

A
  • results in 4 genetically different, haploid cells
  • recombinant chromatids don’t need to pair up and can line up as is
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17
Q

Functions of 4 types of tissues

A
  • Connective: holds tissues together + transport medium
  • Muscular: contracts
  • Nerve: transmits electrical impulses
  • Epithelial: covers internal and external body surfaces
18
Q

True or false- all cells have a different part of the human genome

A

False- all cells share an identical genome but it is the activation of genes that cause differentiation

19
Q

3 adaptations of erythrocytes

A
  • flattened biconcave shape
  • no nuclei
  • flexible (to squeeze thru capillaries)
20
Q

4 adaptations of sperm

A
  • acrosome (contains lysozymes)
  • flagellum
  • many mitochondria
  • streamlined
21
Q

2 adaptations of neutrophil

A
  • multi-lobed nucleus (move around quicker, change shape, extend cytoplasm to engulf)
  • granular cytoplasm (contains many lysosomes)
22
Q

4 adaptations of palisade

A
  • many chloroplasts
  • rectangular
  • thin walls
  • large vacuole
23
Q

2 adaptations of root hair

A
  • long extensions
  • concentrated vacuole sap
24
Q

2 adaptations of guard cell

A
  • thicker inner wall (on one side, so stoma can actually shut properly as shape isn’t symmetrical)
  • ring of cellulose
25
Q

2 adaptations of squamous epithelium

A
  • flattened cells
  • permeable (for selective diffusion)
26
Q

2 adaptations of ciliated epithelium

A
  • cilia
  • goblet cells
27
Q

Stem cells (what are they able to do?)

A

undifferentiated cells w the potential to differentiate into any one of the range of specialised cell types of an organism (can renew themselves constantly)

28
Q

3 tiers of stem cell potency and explain what this means (and give examples)

A

Totipotent eg zygotes
- differentiate into all tissue types, AND extra-embryonic tissues, SO whole organism

Pluripotent eg embryonic stem cells
- differentiate into all tissue types (not extra-embryonic or whole organism)

Multipotent eg adult stem cells
- differentiates into a limited range of cell types

29
Q

2 types of plant stem cells? where are they in the plant? how does the one of them help the other?

A

Meristematic tissue
- wherever growth occurs (eg roots and shoots)
Vascular cambium
- between xylem and phloem
- stay pluripotent throughout life cycle so provide secondary growth for meristems

30
Q

2 uses of stem cells (and 2 sub-uses for each)

A

Medicine (for treatment of damaged tissues and neurological diseases)

Research (developmental biology and drug trials)

31
Q

2 advantages and 1 disadvantage of embryonic stem cells

A
  • makes use of discarded embryos from IVF
  • plentiful, easy to harvest
  • EMBRYO RIGHTS
32
Q

1 advantage and 1 disadvantage of umbilical stem cells

A
  • avoids ethical issues
  • only multipotent (so limited)
33
Q

What are induced pluripotent stem cells (iPSCs) and give 1 advantage?

A

Adult stem cells that have been genetically modified to be pluripotent
- less chance of rejection

34
Q

2 adaptations of epidermis tissue

A
  • single layer of many, closely packed chloroplasts
  • waxy and waterproof
35
Q

How does differentiation occur?

A

Stem cells can use all their genes, and switch certain ones on or off to specialise

36
Q

Why is it important for neutrophils and erythrocytes to be constantly produced? Why for erythrocytes?

A
  • both have very short lifespans
  • erythrocytes have no nucleus + organelles so can’t undergo mitosis
37
Q

How are erythrocytes and neutrophils produced?

A

colonies of hematopoietic stem cells in the bone marrow specialize them

38
Q

How are xylem vessels produced from meristems? (3)

A
  • lignin deposited in cell walls (so waterproof)
  • cells die
  • end walls break down, forming a continuous, wide tube to carry H20
39
Q

How are phloem sieve tubes produced from meristems? (4)

A
  • sieve tube elements lose their nuclei
  • end walls develop sieve plates
  • companion cells retain organelles
  • carry out metabolism to obtain ATP to load sugars into sieve tubes
40
Q

How does cytokinesis produce 2 daughter ANIMAL cells? (3)

A
  • cleavage furrow forms around the middle
  • plasma membrane is pinched inwards by cytoskeleton
  • fuses in the middle
41
Q

How does cytokinesis produce 2 daughter PLANT cells? (3)

A
  • cell walls = no cleavage furrow
  • SO vesicles assemble at equator and fuse with each other + plasma membrane
  • new cell wall forms from new membrane

A Level Biology OCR A (9 decks)

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