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Biology Alevel > Cell Division,Cell Diveristy & Cellular Organsiation > Flashcards

Cell Division,Cell Diveristy & Cellular Organsiation Flashcards

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1
Q

3 phases of cell cycle?

A

INTERPHASE (consist of 3 phases - G1, S and G2)
NUCLEAR DIVISION (MITOSIS)
CELL DIVISION (CYTOKINESIS)

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2
Q

Interphase - what happens in this stage?

A

G1 (GROWTH) PHASE: a signal is received telling the cell to divide
- cells make RNA/enzymes/proteins to grow
S (SYNTHESIS) phase : DNA in nucleus replicates
G2 PHASE: cell continues to grow/synthesised DNA is checked
- protein synthesis

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3
Q

What happens in CYTOKINESIS?

A

Cytoplasm divides
In animal cells , cleavage furrow forms to divide cell surface membrane
FORMS 2 GENETICALLY IDENTICAL DAUGHTER CELLS , which are also identical to parent cells

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4
Q

What are the 4 checkpoints of cell cycle?

A

G1 phase : Chromosomes checked for damage - repaired if damaged before S phase
S phase : composers checked to ensure they have REPLICATED
G2 phase: check DNA damage after replication
METAPHASE : check whether the chromosomes are correctly attached to the spindle fibres prior to anaphase

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5
Q

What enzymes are involved in regulation of cell cycle?

A

Proof reading enzymes /repair enzymes
- sometimes cell may destroy itself to prevent passing on harmful mutations

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6
Q

What is mitosis and the stages?

A

process of nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent cell nucleus

PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

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7
Q

PROPHASE?

A

Chromosomes condense
- centrioles move to opposite ends of cell , forming network of protein fibres across it called the SPINDLE
- nuclear envelope breaks down/chromosomes lie free in cytoplasm

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8
Q

Metaphase?

A

Chromosomes line up along middle of cell/become attached to spindle by their CENTROMERE (where 2 chromatids are joined up)

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9
Q

Anaphase?

A

Centromeres DIVIDE ,separating each pair of sister chromatids
- spindles contract, pulling chromatids to opposite ends of cell

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10
Q

Telophase?

A

Chromosomes are at opposite poles on spindle
- chromosomes start to decondense / SPINDLE FIBRES BREAK DOWN
-nuclear envelopes REFORM around each set of CHROMOSOMES —> new nuclei form in nucleus

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11
Q

How to identify mitosis in plant cells?

A
  1. Use garlic/onion root tips
  2. Add suitable stain - ACETIC ORCEIN to stain chromosomes purple
  3. Stained root tip is gently squashed on glass slide
  4. Cells undergoing mitosis can be seen
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12
Q

significance of mitosis?

A

Growth of multicellular organisms:
- daughter cells are genetically identical /have same no. Chromosomes as parent cell
- enables unicellular zygotes to grow into multicellular organisms

Replacement of cells/repair
- cells always dying, so constantly replaced

Asexual reproduction
- for Amoeba, cell division results in reproduction of clones

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13
Q

What is meiosis ?

A

Form of nuclear divide that results in the production of HAPLOID (single chromosomes) cells from diploid cells

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14
Q

What is Meiosis I?

A

PROPHASE I : chromosomes condense - getting shorter/fatter
- chromosomes arranged into HOMOLOGOUS PAIRS / CROSSING over can occur
- centrioles move to opposite ends of cell/spindle fibres formed / NUCLEAR ENVELOPE BREAKS DOWN

METAPHASE I : homologous pairs line up across centre of cell/attach to spindle by their CENTROMERES
- maternal and paternal chromosomes in each pair position themselves independently of the others - independent assortment

ANAPHASE I : spindles contract, separating homologous pairs

TELOPHASE I : nuclear envelopes forms around each group of chromosomes
- spindle fibres break down

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15
Q

Process of cytokinesis in meiosis I?

A

IN ANIMAL CELLS : the cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half

IN PLANT CELLS : vesicles form from GOLGI APPARATUS /gather along equator of spindle
- vesicles merge/form new cell surface membrane

BOTH FORM 2 HAPLOID CELLS

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16
Q

Process of MEIOSIS II ?

A

SAME AS MITOSIS
- forms 4 haploid cells - genetically different

17
Q

What is crossing over ?

A
  • process within meiosis that leads to genetic variation (4 genetically different haploid cells )
  1. During meiosis I, homologous chromosomes pair up and are in very close proximity to each other
  2. The non-sister chromatids can cross over and get entangled - crossing points are called chiasmata
  3. The entanglement places stress on the DNA molecules
  4. As a result of this a section of chromatid from one chromosome may break and rejoin with the chromatid from the other chromosome- ALLELES SWAPPED
    - base sequence of chromosomes ALTERED
18
Q

What is independent assortment of chromosomes ?

A

the random alignment of homologous pairs along the equator during metaphase I
- it is random which chromosome from each pair ends up in which cell
Maternal and paternal chromosomes can end up facing either pole

  • leads to 4 daughter cells having different combination of alleles
19
Q

Function and adaptations of erythrocytes (RBCS)

A

Function : transport of oxygen around body /carbon dioxide to lungs

ADAPTATIONS :
biconcave- increase SA over which oxygen can be absorbed
NO nucleus : more space for haemoglobin for max oxygen-carrying capacity
Elastic membrane : allows cell to be flexible/change shape to squeeze in capillaries

20
Q

Function /adaptations of neutrophils ?

A

Function : destroy pathogens by phagocytosis /secretion of enzymes

Adaptations :
Flexible : squeeze through cell junctions in capillary walls
- also enables them to form pseudopodia that engulf microorganisms
Many lysosomes : contain digestive enzymes to digest/destroy cells

21
Q

Sperm cells function/adaptations ?

A

Function: reproduction - to fuse with an egg, initiate the development of an embryo and pass on fathers genes

Adaptations :
Acrosome : contains digestive enzymes to break outer layer of egg / so nucleus can fuse with egg nucleus
Many mitochondria : release energy for tail movement
- tail rotates to propel sperm forwards

22
Q

Function/adaptation of root hair cells ?

A

Function: absorption of water and mineral ions from soil

Adaptations :
root hair increase SA: rate of osmosis/absorption of minerals is greater
Thinner walls- shorter diff distance - quicker rate of diffusion
Mitochondria - active transport of mineral ion

23
Q

Function/adaptations of epithelial cells ?

A

CILIATED:
Function: moving substances across the surface of a tissue
Adaptations:
Have cilia - shift material along the surface of the epithelium tissue

SQUAMOUS :
Function : provide a surface covering or outer layer.
Adaptations :
Thin/permeable - quicker rate of diffusion

24
Q

Function/adaptations of palisade cells?

A

Function: carry out photosynthesis to produce glucose and oxygen

Adaptations:
A large number of chloroplasts- maximise the absorption of light for photosynthesis
The tall/thin shape of the cells - allows light to penetrate deeper
- CO2 can diffuse into cell easily

25
Q

Function/adaptations of Guard cells?

A

Function: control the opening of the stomata to regulate water loss and gas exchange

Adaptations:
Inner cell walls are thicker, outer cell walls are thinner - difference in the thickness allows the cell to bend when turgid
Many chloroplasts and mitochondria

26
Q

What is a tissue?

A

group of cells that work together to perform a particular function

27
Q

Xylem vessel tissue function/adaptations?

A

Transport tissue for water/dissolved ions
ADAPTATIONS:

No top and bottom walls between cells - to form continuous hollow tubes through which water is drawn upwards
dead cells - without organelles or cytoplasm, to allow free movement of water
lignin thickens outer walls - strengthening the tubes, which helps support the plant

28
Q

Phloem vessel cell adaptations/function?

A

Function: transport of dissolved sugars and amino acids
Adaptations:
living cells- supported by companion cells
Cells joined end-to-end - contain holes in the end cell walls (sieve plates) - forms tubes that allow translocation

29
Q

Muscle cells function/adaptions

A

Function: contraction for movement
Adaptations:
There are three different types of muscle in animals: skeletal, smooth and cardiac (heart)
- have layers of protein filaments in them - layers can slide over each other causing muscle contraction
Many mitochondria- provide sufficient energy for muscle contraction

30
Q

Function/adaptations of cartilage ?

A

Function: to provide support
- strong and flexible tissue - Tracheal rings
These rings help to support the trachea and ensure it stays open while allowing it to move and flex while we breathe

31
Q

Production of erythrocytes (RBCS) from bone marrow stem cells?

A
  1. Cell is multi potent - divides to form proerythrocytes
  2. Haemoglobin builds up in cytoplasm
  3. Nucleus ejected
32
Q

What changes occur when stem cells differentiate into neutrophils from bone marrow stem cells?

A
  • indentations form in nucleus —> LOBED structure
  • granules accumulate (lysosomes )
33
Q

How are xylem/phloem formed?

A

From stem cells that are found in tissue called CAMBIUM, between xylem/phloem
- it is a meristem (undifferentiated tissue) located at tips of shoots/roots

Stem cells in the inneredge of cambium differentiate into XYLEM cells
Stem cells on outer edge of cambium differentiate into PHLOEM cells

34
Q

What changes are made when cambium cells differentiate into xylem/phloem ?

A

XYLEM : lose cytoplasm
- deposit lignin in cell walls / lose their end cells walls

PHLOEM: lose some cytoplasm/organelles
- develop sieve plates

35
Q

3 types of potency?

A

Totipotency : STEM CELLS that can differentiate into any cell type found in embryo/extra embryonic cells

Pluripotent: embryonic stem cells that can differentiate into any type of cell found in embryo, but not int extra embryonic cells

Multipotency : adult stem cells that have lost some potency

36
Q

Benefits of using stem cells?

A
  • treat wide variety of diseases
    (Embryonic : differentiate into many cell types , adult stem cell are limited )
  • adult stem cells are used successfully
37
Q

Issues (health, ethical and social ) of stem cell use?

A

Issues :
- stem cells could transfer viruses
- cause mutations - cancer
- low no. Stem cell donors
- can’t give permission for use/ do we have right to use them?
- destroying living thing ?

38
Q

3 factors that leads to genetic variation from meiosis ?

A

Crossing over
Independent assortment
Random fusion of gametes- gametes have different alleles due to crossing over/independent assortment
- random fusion of gametes in fertilisation creates genetic variation in zygotes

39
Q

What are homologous pairs of chromosomes?

A

Pairs of Chromosomes with the same genes/same size but different alleles

Biology Alevel (24 decks)

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