Cell Division,Cell Diveristy & Cellular Organsiation Flashcards
3 phases of cell cycle?
INTERPHASE (consist of 3 phases - G1, S and G2)
NUCLEAR DIVISION (MITOSIS)
CELL DIVISION (CYTOKINESIS)
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
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
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
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
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
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
Metaphase?
Chromosomes line up along middle of cell/become attached to spindle by their CENTROMERE (where 2 chromatids are joined up)
Anaphase?
Centromeres DIVIDE ,separating each pair of sister chromatids
- spindles contract, pulling chromatids to opposite ends of cell
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
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
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
What is meiosis ?
Form of nuclear divide that results in the production of HAPLOID (single chromosomes) cells from diploid cells
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
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
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?
- Cell is multi potent - divides to form proerythrocytes
- Haemoglobin builds up in cytoplasm
- 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 inneredge 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
