Cell Division,Cell Diveristy & Cellular Organsiation Flashcards by Ashwarya Magon

3 phases of cell cycle?

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

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Interphase - what happens in this stage?

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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What happens in CYTOKINESIS?

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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What are the 4 checkpoints of cell cycle?

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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What enzymes are involved in regulation of cell cycle?

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

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What is mitosis and the stages?

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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PROPHASE?

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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Metaphase?

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

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Anaphase?

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

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Telophase?

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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How to identify mitosis in plant cells?

Use garlic/onion root tips
Add suitable stain - ACETIC ORCEIN to stain chromosomes purple
Stained root tip is gently squashed on glass slide
Cells undergoing mitosis can be seen

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significance of mitosis?

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

Development of body plan
Produce gametes from haploid cells

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What is meiosis ?

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

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What is Meiosis I?

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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Process of cytokinesis in meiosis I?

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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Process of MEIOSIS II ?

SAME AS MITOSIS
- forms 4 haploid cells - genetically different

What is crossing over ?

process within meiosis that leads to genetic variation (4 genetically different haploid cells )

During meiosis I, homologous chromosomes pair up and are in very close proximity to each other
The non-sister chromatids can cross over and get entangled - crossing points are called chiasmata
The entanglement places stress on the DNA molecules
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

What is independent assortment of chromosomes ?

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

Function and adaptations of erythrocytes (RBCS)

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

Function /adaptations of neutrophils ?

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

Sperm cells function/adaptations ?

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

Function/adaptation of root hair cells ?

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

Function/adaptations of epithelial cells ?

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

Function/adaptations of palisade cells?

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

Function/adaptations of Guard cells?

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

What is a tissue?

group of cells that work together to perform a particular function

Xylem vessel tissue function/adaptations?

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

Phloem vessel cell adaptations/function?

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

Muscle cells function/adaptions

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

Function/adaptations of cartilage ?

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

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

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

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

- indentations form in nucleus —> LOBED structure - granules accumulate (lysosomes )

How are xylem/phloem formed?

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 *inner*edge of cambium differentiate into XYLEM cells Stem cells on *outer* edge of cambium differentiate into PHLOEM cells

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

XYLEM : lose cytoplasm - deposit lignin in cell walls / lose their end cells walls PHLOEM: lose some cytoplasm/organelles - develop sieve plates

3 types of potency?

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

Benefits of using stem cells?

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

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

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 ?

3 factors that leads to genetic variation from meiosis ?

**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

What are homologous pairs of chromosomes?

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