2.6 Cell Division, Cell Diversity and Cell Differentiation

  • Created by: elbungay1
  • Created on: 29-04-19 18:56
What is the role of G1/S and G2/M checkpoints in the regulation of the eukaryotic cell cycle?
Prevent any uncontrolled division that would lead to tumours. Detect and repair damage to DNA (e.g. caused by UV light). Also ensures cycle cannot be reversed and that DNA is only replicated once.
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What is M phase?
Checkpoint that triggers condensation of chromatin, Metaphase checkpoint ensures cell is ready to complete mitosis. Cell growth stops, Mitosis occurs and then Cytokinesis
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What is G0 (gap 0) phase?
Resting phase triggered during early G1 at the restriction point. Cells may undergo apoptosis (programmed cell death), differentiation or senescence. Cells may be in this period for a long time
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What is the G1 (growth) phase?
Ensures cell is ready to enter S phase and begin DNA synthesis. Cells grow and increase in size, transcription of genes to make RNA. Organelles duplicate. Biosynthesis (production of enzymes for Mitosis), p53 (tumour suppressor) controls phase
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What is the S phase of interphase?
Chromosomes are unwound and DNA is diffuse, it all replicates. Once cell is committed, it is committed to whole cycle. DNA replicates. When chromosomes duplicated they are now sister chromatids. Phase is rapid to reduce chance of mutation
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What is G2 phase of interphase?
Chemicals ensure cell is ready for Mitosis by stimulating proteins involved in making chromosomes condense and in formation of spindle. Cells grow
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What is Mitosis?
Type of nuclear division that maintains the chromosome number; each daughter cell contains the same genetic information as the parent cell. They are also genetically identical to each other
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What is the significance of Mitosis in the life cycle?
Asexual reproduction (single-celled protoctists, strawberry runners). Growth (multicellular organisms grow by producing more cells that are genetically identical). Tissue Repair (wounds heal by stimulation of proliferation of endothelial and smooth)
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What occurs at Prophase?
Chromosomes that have replicated in S, consisting of two identical chromatids, condense. Nuclear envelope breaks down. Centriole divides and moves to either end of cell. Cytoskeleton tubulin threads form between centrioles.
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What events occur during Metaphase?
The pairs of chromatids attach to the spindle threads at the equator region. They attach by their centromeres.
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What are Chromatids?
Replicates of Chromosomes
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What events occur at Anaphase?
Centromere of each pair of chromatids splits. Motor proteins, walking along tubulin threads, pull each sister chromatid towards opposite poles. Chromatids are know chromosomes, in a V shape
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What happens at Telophase?
The separated chromosomes reach the poles. A new nuclear envelope forms around each set of chromosomes. The cell now contains two nuclei each genetically identical to each other and to the parent cell from which they arose
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What is Cytokinesis?
Once mitosis has occurred, the cell splits in two, each new cell contains a nucleus. In animal cells, plasma membrane folds inwards and pinches off cytoplasm
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What is the significance of meiosis in life cycle?
Sexual reproduction increases genetic variation, meiosis forms haploid gametes, which have half the number of chromosomes of the parent cell.
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What are homologous chromosomes?
Matching chromosomes containing the same genes at the same loci. They may contain different alleles for some of the genes.
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What occurs at Prophase 1 of Meiosis?
Chromatin condenses and nuclear envelope breaks down. Chromosomes come together in homologous pairs. Crossing over occurs where non-sister chromatids wrap around each other and may swap sections so alleles are shuffled
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What occurs at Metaphase 1 of Meiosis?
Pairs of homologous chromosomes, still in crossed state, align along equator. Each attaches to a spindle at centromere. Homologous pairs are arranged randomly in independent assortment. They way they align dictates how they will segregate in Anaphase
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What occurs in Anaphase 1 of Meiosis?
Members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along tubulin threads. Centromeres do not divide and each chromosomes consist of two chromosomes. Crossed-over areas segregate resulting in swapped areas
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What occurs in Telophase 1 of Meiosis?
Two nuclear envelopes form around each set of chromosomes and cell divides by cytokinesis, short interphase where chromosomes uncoil. Each new nucleus contains half the original number of chromosomes but each chromosomes consist of two chromatids.
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What occurs in second stage of Meiosis?
Same as Mitosis but two cells divide to give 4 haploid cells.
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How does Meiosis produce genetic variation?
Crossing over during prophase 1 shuffles alleles. Independent assortment of chromosomes in anaphase 1 leads to random distribution of maternal and paternal chromosomes. Independent assortment in anaphase 2. Random fusion of gametes in fertilisation.
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What is the need for cell differentiation and specialisation?
Multicellular organisms have a small SA/V ratio meaning cells are not in direct contact with external environment, they need specialised cells to carry out particular functions.
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What is cell differentiation?
Process by which stem cells become specialised into different types of cells. Genes are switched off so that: proportions of organelles differs from other cells, shape of cell changes, some of cell contents change.
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How are erythrocytes adapted to carry out their function?
Large SA/V ratio, oxygen can easily diffuse and reach all regions in cell, biconcave shape increases ratio. Flexible, well developed cytoskeleton fitting in capillaries. No nucleus, mitochondria or ER, more space of haemoglobin
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How are Neutrophils adapted to their function?
Twice the size of erythrocytes and contain multilobed nucleus. Attracted to infection sites by chemotaxis. Ingest bacteria and fungi by phagocytosis. Large amount of lysosomes for digestion
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How are Spermatozoa adapted to their function?
Many mitochondria for aerobic respiration, providing ATP to propel cell to Ovum. Small, long, thin they can move easily. Specialised lysosomes (acrosome) digest outer covering of ovum allowing head to enter. Head contains haploid male gamete nucleus
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What are Epithelial cells and in what ways are they specialised?
Epithelium is lining tissue, making up walls of alveoli and capillaries. Squamos epithelial cells are flattened in shape. Many of the cells have cilia.
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What are Palisade cells and how are they specialised?
Closely-packed photsynthetic cells within leaves. Pack together closely for a short diffusion distance. large vacuole so chloroplasts positioned at periphery of cell. Cotain many chloroplasts. Cytoskeleton moves chloloplasts on different lux
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What are Guard cells and how are they specialised?
Light energy used to make ATP. Actively pump K+ ions into cell, lowering ψ. Water enters by osmosis and cells swell, becoming turgid and stoma enlarges, allowing gaseous exchange to occur. CO2 in and O2 out
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What are Root Hair Cells and how are they specialised?
Epidermal cells on outer layer of young plant roots. Hair-like prjections increase SA for water absoprtion and mineral ions (nitrates). Ions actively pumped in, lowering ψ, allowing water to enter by osmosis. Special carrier proteins and ATP product
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What is a tissue?
Group of cells that work together to perform a specific function/set of functions
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What are the 4 main tissue types in the body?
Epethelial or lining tissue, connective tissue - hold structure together or provide strength (blood, bone, cartilage). Muscle tissue - contract and cause movement. Nervous Tissue - conduct electrical impulses
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What is the function of epithelial tissue?
Covers and lines free surfaces in the body such as the skin, cavities of the digestive system and respiratory systems, blood vessels, heart chambers and walls of organs. Made entirely of cells, forming continuous sheets, some have projections
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What is the function of connective tissue?
Consists of non-living extracellular matrix containing proteins (collagen and elastin). Separates living cells and enables it to withstand forces such as weight. Blood, bone, cartilage, tendons and ligaments.
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What is the function of muscle tissue?
Skeletal muscles are joined to bones by tendons and contraction causes bones to move. Cardiac muscle makes up wall of the heart and allow heart to beat and pump blood. Smooth muscle occurs in walls of intestine, blood vessels, propels substances
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What is epidermal tissue?
Plant equivalent to epithelial tissue. Consists of flattened cells that form protective covering over leaves, stems and roots.
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What is vascular tissue?
Concerned with transport. Xylem vessels carry water and minerals from roots to all parts of plants. Phloem sieve tubes transfer the products of photosynthesis (sucrose) in solution from leaves to parts of plants that do not photosynthesise (sinks)
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What is Meristematic tissue?
Contains stem cells, found in Meristems (root, shoots and cambium of vascular bundles). Cells have thin cellulose walls, do not have chloroplasts,do not have a large vacuole, can divide by mitosis and differentiate into other types of cells
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How do cambium cells differentiate into xylem vessels?
Lignin is deposited into cell walls to reinforce and waterproof them; this kills the cell. Ends of cells breaks down so xylem forms continuous columns with wide lumens to carry water and dissolved minerals
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How do cambium cells differentiate into phloem sieve tubes or companion cells?
Sieve tubes lose most of their organelles and sieve plates develop between them. Companion cells retain organelles and continue metabolic fucntions to provide ATP for active loading of sugars into the sieve tubes.
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Identify plant organs and their fucntions
Leaf- photosynthesis. Root- anchorage, absoprtion of mineral ions and water, storage of starch. Stem- support, hold leaves up, transpiration, mass flow, storage of assimilates. Flower- sexual reproduction
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What are stem cells?
Undifferentiated cells capable of being any type of cell in an organism. Pluripotent, able to express all of their genes. Can divide by mitosis and provide more cells that can then differentiate into specialised cells, for growth and tissue repair.
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What are the sources of stem cells?
Embryonic stem cells present when zygote forms. Stem cells in umbilical cord blood. Adult stem cells for repair found in developed tissues such as blood, brain, muscle, bone, tissue and skin. Induced pluripotent cells (iPS) developed in laboratories
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What are the potential uses in research and medicine?
Bone marrow transport to treat blood diseases such as sickle-cell anaemia and leukaemia. Drug research. Developmental biology- see how cell differentiate and potential uses. Repair of damaged tissues or replacement of lost tissues- β cells for diabet
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Card 2


What is M phase?


Checkpoint that triggers condensation of chromatin, Metaphase checkpoint ensures cell is ready to complete mitosis. Cell growth stops, Mitosis occurs and then Cytokinesis

Card 3


What is G0 (gap 0) phase?


Preview of the front of card 3

Card 4


What is the G1 (growth) phase?


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Card 5


What is the S phase of interphase?


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