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OCR Biology > Cell division > Flashcards

Cell division Flashcards

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1
Q

what are the two phases in the cell cycle

A

interphase and mitotic phase

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2
Q

what are three stages in interphase

A

G1
S
G2

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3
Q

explain what happens in G1

A

it is the first grow phase when proteins from which organelles are synthesised are produced and organelles replicate, the cell increases in size

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4
Q

explain what happens in S

A

this is the synthesis phase, where DNA is replicated in the nucleus

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5
Q

explain what happens during G2

A

it is the second growth phase, the cell continues to increase in size, energy stores are increased

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6
Q

how is the cell cycle regulated

A

by having checkpoints
G1checkpoint - it is at the end of G1 phase before the entry to S phase. it checks that the chemicals needed for replication are present and any damage in the DNA
G2 checkpoint - at the end of G2 phase before the entry to mitotic phase, it checks whether all the dna has been replicated without damage

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7
Q

what are the two stages in the mitotic phase

A

mitosis- the nucleus divides
cytokinesis- cytoplasms divides and two cells produced

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8
Q

what is G0

A

it is the name given to the phase when the cell leaves the cell cycle either temporarily or permanently, reasons for this could be:
- differentiation
- the dna may be damaged

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9
Q

name the stages of mitosis

A

Prophase
Metaphase
Anaphase
Telophase

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10
Q

define chromatids

A

two identical copies of DNA (a chromosome) held together by a centromere

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11
Q

why is mitosis needed

A
  • growth of multicellular organisms
    -repairing damage tissues
  • method of asexual reproduction for some plants, fungi and animals
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12
Q

what happens during prophase

A
  • chromosomes condens
  • nucleolus disappears
  • two bundles of protein called centrioles migrate to opposite poles of the cell, forming a network of protein fibres called a spindle
  • nuclear membrane disappears
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13
Q

what happens in metaphase

A
  • chromosomes become attached the spindle by their centromere and move to form a line along the centre of the cell, called the metaphase plate
  • during metaphase their is a checkpoint called spindle assembly checkpoint, this checks all chromosomes are attached to spindles and have aligned
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14
Q

what happens during anaphase

A
  • the centromeres divide, separating each pair of sister chromatids
  • the spindles shorten so each chromatid is pulled to opposite poles of the cell
  • the v shape of the chromatids moving towards the poles is a result of them being pulled by their centromeres first
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15
Q

what happens in telophase

A
  • chromatids have reached their poles, the uncoil and are now called chromosomes
  • a nuclear envelope forms around each group of chromosomes so there is two nuclei in the cell
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16
Q

describe cytokinesis in animal cells

A
  • a cleavage furrow forms around the middle of the cell
  • the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around two identical daughter cells
  • thus forming two identical daughter cells
17
Q

describe cytokinesis in plant cells

A
  • due to cell walls, cleavage furrow cannot be formed
  • vesicles from the golgi begin to assemble in the same place as where the metaphase plate was formed
  • the vesicles form with each other and the cell surface membrane, dividing the cell into two
  • new sections of cell wall then form along the new sections of membrane
18
Q

describe meiosis

A
  • type of cell division that happens in reproductive organs to produce gamete
  • involves reduction division, before meiosis cells have full 46 chromosomes (diploid cells), after meiosis cells have half the number 23 chromosomes (haploid)
19
Q

describe how crossing over of chromatids causes genetic variation

A

crossing over of chromatids,
- during prophase I, homologous pairs of chromosomes form chromatids which twist around each other and bits of chromatids swap over.
- the point at which chromosomes in the chromatids cross over is called chiasmata
-Chromatids now have a new combination of alleles

20
Q

describe how independent assortment creates genetic variation

A

independent assortment, when homologous pairs line up in metaphase I, its completely random which chromosomes are pulled to either pole during anaphase I
so four daughter cells have completely different combinations of maternal and paternal chromosomes

21
Q

describe what takes place during meiosis I

A

Prophase I- chromosomes condense, nuclear envelope disintegrates, nucleolus disappears and spindle formation begins. Homologous chromosomes pair up into bivalents. The chromatids twist around each other and bits of chromatids swap over. The chromatids still contain the same genes but now have a different combination of alleles. The points where chromatids cross, break and rejoin are called chiasmata.
metaphase I- the orientation of each homlogous pair on metaphase plate is random and independent. This is called independent assortment and can result in many different combinations of alleles facing the poles.
Anaphase I
Telophase I

22
Q

describe what happens in meiosis II

A

Prophase II
Metaphase II
Anaphase II - the chromatids of the individual chromosomes are pulled to opposite sides
Telophase II

23
Q

define differentiated

A

cells which are specialised to carry out a specific function

24
Q

describe how erythrocytes are specialised for their roles

A
  • rbcs have a flattened biconcave shape, this increases their surface area to volume ratio
    -do not have nuclei, increases space for haemoglobin
25
Q

describe how neutrophils are specialised for their role

A
  • have multilobed nucleus which makes it easier for them to squeeze through small gaps
    -granular cytoplasm contains many lysosomes that contain enzymes to break down engulfed pathogens
26
Q

describe how sperm cells are specialised for their role

A
  • has tail/flagellum so capable for movement to reach egg cell
  • have lots of mitochondria to supply energy needed to swim
    -acrosome on head of sperm contains digestive enzymes to enable the penetration of the egg cell surface.
27
Q

describe how palisade cells are specialised for their roles

A
  • contain many chloroplasts to absorb large amount of light for photosynthesis
  • have thin cell walls to increase diffusion rate of carbon dioxide
28
Q

describe how root hair cells are specialised for their roles

A
  • large surface area
  • thin permeable cell wall
  • cytoplasm contains extra mitochondria needed for active transport
29
Q

name examples of specialised animal tissues

A

squamous epithelium
ciliated epithelium
cartilage
muscle

30
Q

describe squamous epithelium

A

-made up of specialised squamous epithelial cells
- it is very thin due to the squat and flat cells, one cell thick
- it forms the lining of the lungs and allows rapid diffusion of oxygen into the blood

31
Q

describe ciliated epithelium

A

-the cells have cilia on the surface that move in a rhythmic manner
- lines trachea
- goblet cells, produce mucous, this traps pathogens and cilia allows pathogen and debris to swept away

31
Q

describe cartilage

A

it is a connective tissue
- contains elastin and collagen

32
Q

describe muscle tissue

A

needed to move bones
- skeletal muscles are attached to bones

33
Q

describe plant epidermis tissue

A

it is a single layer of closely packed cells covering the surface of plants
- usually covered by a waxy waterproof cuticle to reduce the loss of water
- stomata are present in the epidermis

34
Q

describe xylem tissue

A
  • vascular tissue responsible for transport of water and mineral throughout plants
  • the tissue composed vessel elements which are elongated dead cells
  • the walls of these cells are strengthened by lignin, providing structural support
35
Q

describe phloem tissue

A

another type of vascular tissue responsible for the transport of organic nutrients particularly sucrose from leaves and stems
- its composed of columns of sieve tube cells separated by perforated walls called sieve plates

36
Q

name the different stem cell types

A

totipotent- any type of cell
pluripotent- all tissue types but not whole organisms
multipotent- only a range of cells within a certain tissue type

37
Q

what are sources of animal stem cells

A

embryonic stem cells- present at early embryo development and are totipotent
tissue (adult) stem cells- found in bone marrow and are multipotent, stem cells can be harvested from umbilical cords of newborn babies

38
Q

what are sources of plant stem cells

A

present in meristematic tissue (meristems)
found in tips of roots and shoots
also located between phloem and xylem tissue and is called vascular cambium

OCR Biology (14 decks)

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