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OCR AS/A Level Biology Context > module 2.6: cell division and specialisation > Flashcards

module 2.6: cell division and specialisation Flashcards

1
Q

what happens in the G1 phase

A

cells grow and increase in size
transcription of genes (mRNA made)
protein synthesis occurs
organelles duplicate

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2
Q

what happens in the G1 checkpoints

A

G1 cyclin-CDK complexes promote the production of transcription factors needed to produce enzymes for DNA replication
G1 checkpoint ensures that the cell is ready for DNA synthesis

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3
Q

what happens in S phase

A

DNA replicates, producing pairs of identical sister chromatids

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4
Q

what happens in the S checkpoints

A

active S cyclin-CDK complexes ensure all DNA is replicated once

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5
Q

what happens in G2 phase

A

cells grow
spindle fibres begin to form
growth of organellels
short gap before mitosis

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6
Q

what happens at the G2 checkpoint

A

G2 checkpoint ensures that the cell is ready to enter M phase

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7
Q

what happens in the M phase

A

cell growth stops
nuclear divisiom consisting of stages: prophase, metaphase, anaphase and telophase

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8
Q

what are the M checkpoint

A

mitiotic cyclin-CDK complexes promote the production of the spindle and the condensation of chromosomes
metaphase checkpoint ensure that the cell is ready to complete mitosis

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9
Q

what are the reasons for mitosis

A

growth of the organism
repair of tissues
replacement of old cells
asexual reproduction

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10
Q

what happens in prophase

A

nuclear envelope breaks down
chromosomes condenses
spindle fibres attach the centromere on the chromosomes

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11
Q

what happens in metaphase

A

chromosomes are held on the spindle at the middle of the cell
each chromosome is attached to the spindle on either side of its centromere

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12
Q

what happens in anaphase

A

chromatids break apart at the centromere and are moved to opposite ends of the cell by the spindle

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13
Q

what happens in telophase

A

nuclear envelopes reform around the chromatids that have reached the 2 poles of the cell
each new nucleus has the same number of chromosomes as the original, parent cell
the nuclei are genetically identical to each other
chromosomes uncoil
cell surface membrane undergoes cytokinesis
spindle fibres break down

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14
Q

what is meiosis

A

It produces four cells that are:
not genetically identical
gametes - sex cells used for sexual reproduction
haploid (contain half the normal number of chromosomes)

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15
Q

what do these gametes contain one of

A

they contain one chromosome from each pair of homologous chromosomes

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16
Q

what is a homologous chromosomes

A

they have:
the same shape and size
the centromere in the same position
the same genes in the same positions on the chromosomes

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17
Q

what happens in prophase I

A
  • chromosomes condense — they supercoil to become shorter and thicker
  • homologous chromosomes pair to form bivalents containing four chromatids
  • the chromatids in each bivalent break and rejoin to form chiasmata or crossovers — this is where sections of the non-sister chromatids can be exchanged
  • the nuclear membrane breaks up to form small membrane sacs
  • the centriole replicates and migrates to opposite poles of the cell and forms the spindle fibres
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18
Q

what happens in metaphase I

A
  • microtubules attach from the centrioles to the centromere of each chromosome.
  • the bivalents move to the equator of the cell.
  • orientation of each bivalent on the equator is random — maternal or paternal chromosomes could be facing either pole
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19
Q

what happens in anaphase I

A
  • the microtubules shorten to separate the homologous chromosomes and pull them towards opposite poles
  • each chromosome still consists of two chromatids
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20
Q

what happens in telophase I

A
  • the chromosomes reach opposite poles
  • the nuclear membrane reforms around each set of chromosomes to produce two nuclei
  • these nuclei are haploid as they have one chromosome from each homologous pair (but there are still two sister chromatids)
  • the cell membrane pinches in to form two cells — this is cytokinesis
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21
Q

what happens in prophase II

A
  • the nuclear membranes break up again
  • the centrioles replicate again and migrate to opposite poles of the two new cells
  • chromosomes condense
  • spindle fibres develop
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22
Q

what happens in metaphase II

A
  • microtubules attach between the centrioles and the centromere of each chromosome
  • the chromosomes move to the equator and align randomly
  • nuclear envelope disappear
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23
Q

what happens in anaphase II

A
  • sister chromatids move to opposite poles
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24
Q

what happens in telophase II

A
  • the nuclear membranes reform
  • cytokinesis occurs to produce four genetically different haploid cells
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25
Q

what happens when a chromatid crosses over

A

they exchange lengths of DNA. if this occurs between non-sister chromatids, it makes new combinations of alleles

26
Q

what is independent assortment

A

the bivalents orientate on the equator during metaphase 1 is random. this means that either the maternal or the paternal chromosome of a bivalent may face either pole. therefore, the combination of maternal and paternal chromosomes migrating to either pole
happens in metaphase I and II

27
Q

what do erythrocytes do and how are they specialised

A
  • carry oxygen in the blood
  • small and flexible to fit through tiny capillaries, full of haemoglobin to bind to the oxygen, no nucleus to allow more space for haemoglobin
  • biconcave shape to provide a large surface area to take up oxygen quickly
28
Q

what do neutrophils do and how are they speciallised

A
  • engulf and digest foreign matter or old cells
  • flexible shape to enable movement through tissues
  • lobed nucleus to help movement through membranes, many ribosomes to manufacture digestive enzymes.
  • many lysosomes to hold digestive enzymes, many mitochondria to release the energy needed for activity, well-developed cytoskeleton to enable movement, membrane-bound receptors to recognise materials that needs to be destroyed
29
Q

what do sperm cells do and how are they specialised

A
  • carry the paternal chromosomes to the egg, tail (flagellum) to enable rapid movement
  • acrosome to help digest egg surface, small to make movement easier, many mitochondria to release the energy needed for rapid movement
30
Q

what do epithelial cells do and how are they specialised

A

cells act as surfaces
- often flat (squamous) to cover a large area, often thin (squamous) to provide a short diffusion distance
- may be ciliated to move mucus, may be cuboid to provide a barrier
- many glycolipids and glycoproteins in cell-surface membrane to hold cells together or for cell signalling

31
Q

what do palisade cells do and how are they specialised

A
  • photosynthesis
  • elongate to fit many chloroplasts into the space, contain many chloroplasts to absorb as much light as possible
  • show cytoplasmic streaming to move the chloroplasts around, contain starch grains to store products of photosynthesis
32
Q

what do root hair cells do and how are they specialised

A
  • absorb water and mineral ions from the soil
  • long extension (hair) to increase surface area, active pumps in cell-surface membrane to absorb mineral ions by active transport
  • thin cell wall to reduce barrier to movement of ions and water
33
Q

what do guard cell do and how are they specialised

A
  • control the stomatal opening
  • active pumps in cell-surface membrane to move mineral ions in and out of cell to alter the water potential
  • unevenly thickened wall to cause the cell to change shape as it becomes more turgid
  • large vacuole to take up water and expand to open the stoma
34
Q

what is a tissue

A

a collection of cells that work together to perform a particular function

35
Q

how is squamous epithelium a tissue

A

a layer of flattened cells bound together to produce a surface

36
Q

how is ciliated epithelium a tissue

A

contains ciliated cells that move mucus over their surface and goblet cells that produce the mucus

37
Q

how is a cartilage a tissue

A

consists of cells called chondrocytes that secrete a matrix of collagen

38
Q

what 3 types of tissues are muscles found in

A

smooth muscles, skeletal muscle and cardiac muscle

39
Q

how is a smooth muscle a tissue

A

consists of single cells that can contract

40
Q

how is a skeletal muscle a tissue

A

forms multinucleated fibres containing protein filaments that slide past one another

41
Q

how is a cardiac muscle a tissue

A

forms cross-bridges to ensure that the muscle contracts in a squeezing action

42
Q

how is the xylem a tissue

A

contains vessels that carry water and xylem fibres for support

43
Q

how is the phloem a tissue

A

it contains 2 types of cells:
sieve tube elements which form sieve tubes
companion cells

44
Q

what is an organ

A

a collection of tissues working together to perform a common function

45
Q

what is a system

A

made up of two or more organs working together to perform a life function such as excretion or transport

46
Q

what is differentiation

A

the ability of a cell to specialise to form a particular type of cell

47
Q

what are stem cells

A

a renewing source of undifferentiated cells for the growth and repair of tissues and organs. during growth and repair, stem cells divide to produce new cells, which then differentiate to become specialised to their function

48
Q

what do the stem cells in the bone marrow divide and differentiate into

A

red and white blood cells

49
Q

what is the specialisation of the xylem

A
  • lignin is deposited in their cell walls to strengthen and waterproof the wall. the cells die and the contents are removed as the end walls break down, forming continuous columns of cells
  • these form tubes with wide lumens to carry water and dissolved minerals
  • the lignification is incomplete in some places, forming bordered pits
50
Q

how is the phloem specialised

A
  • sieve tube elements lose their nucleus and most of their organelles. the end walls develop numerous sieve pores to form sieve plates between the elements
  • companion cells retain their organelles and can carry out metabolism to obtain and use ATP to actively load sugars into the sieve tubes
  • sieve tube elements and companion cells are linked by numerous plasmodesmata
51
Q

what diseases have stem cells helped with

A
  • stem cells in bone marrow are used to treat diseases of the blood, such as leukaemia
  • stem cells have been used to repair the spinal cord of rats
  • stem cells have been used to treat mice with type 1 diabetes
  • stem cells in the retina can be made to produce new light-sensitive cells
  • stem cells directed to become nerve tissue could be used to treat neurological conditions such as Alzheimer’s disease and Parkinson’s disease
  • stem cells may also be used to treat other conditions such as arthritis, stroke, burns, blindness, deafness and heart disease
51
Q

where can stem cells be sourced form

A
  • embryonic stem cells, which are present in a young embryo
  • blood from the umbilical cord
  • adult stem cells found in developed tissues such as bone marrow (but scientists are finding stem cells in almost all tissues)
  • scientists can also induce certain tissue cells to become stem cells (known as induced pluripotent stem cells or iPS cells)
52
Q

what do stem cells help scientist gain a better understanding of how multicellular organisms develop, grow and mature

A
  • they study how differentiation occurs — how cells develop to make particular cell types
  • they study what happens when differentiation goes wrong
  • they are trying to find out if they can re-enable differentiation and growth in adult cells to help tissue repair (healing) in later life or even the ability to regrow an organ or limb
53
Q

why does crossing over not happen in prophase II

A

no bivalents

54
Q

why is the root used in root tip squash

A

continuous mitosis occurs

55
Q

ROOT TIP SQUASH: why is the sample heated in acid

A

to break down the cell wall

56
Q

ROOT TIP SQUASH: why is the sample squashed w/mounted needle

A

make thin —> so light can travel through

57
Q

ROOT TIP SQUASH: why do they stain the sample

A

to provide contrast and make chromosomes more visible

58
Q

what is the mitotic index

A

total no. of cells

59
Q
A

OCR AS/A Level Biology Context (24 decks)

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