GCE BIOLOGY - Chapter 6: Cell Division

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66 Terms

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Two main phases of cell cycle

interphase and mitotic phase

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First stage of interphase: G1

cell grows, organelles duplicate, proteins are synthesis

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G1 Checkpoint

cells are checked for size, nutrients and damage; centrioles also start to replicate in animal cells

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First stage outside interphase: G0

where specialised/differentiated cells, senescent/old cells and damaged cells go

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Re-entering interphase from G0

lymphocytes and hepatocytes can be stimulated to re-enter the cell cycle from G0

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Second stage of interphase: S

DNA is replicated

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Third stage of interphase: G2

cell grows, ATP is saved up and stored, nutrients are built up

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G2 Checkpoint

cell is checked for size and nutrients and whether DNA replication has been successful or not (if it has not, the cell self-destructs to prevent cancer); cell division begins after this

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First stage of mitotic phase: mitosis

nucleus divides

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Second stage of mitotic phase: cytokinesis

cell divides to form two genetically identical daughter cells which are identical to the parent cell

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Controlling the progression of the cell cycle

when a cell should progress through the cell cycle, a cyclin is activated, which binds to kinase to form a CDK complex, which activates the kinase; the kinase also phosphorylates various proteins in the cell cycle to allow the cell cycle to proceed

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Metaphase checkpoint

check if spindle assembly has correctly formed

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Stages of mitosis in order

prophase, metaphase, anaphase, telophase

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First stage of mitotic stage: prophase

  • chromatin condenses into visible chromosomes, nuclear envelope disintegrates, nucleolus disappears, transcription of DNA ceases

  • centrioles move in pairs to poles of the cell and microtubules associate with centrioles, forming spindle fibres, which bind to centromeres

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Second stage of mitotic stage: metaphase

  • spindle fibres apply tension to chromosomes to align them on the metaphase plate at the equator

  • centrioles + spindle fibres + chromosomes = spindle assembly

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Third stage of mitotic stage: anaphase

spindle fibres contract; centromeres divide and sister chromatids separate to become daughter chromosomes which migrate to the poles

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Fourth stage of mitotic stage: telophase

cell elongates; new nuclear envelopes form and chromosomes decondense into chromatin and nucleoli form

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Fifth stage of mitotic stage: cytokinesis

contractile ring forms between the two nucleoli, the cleavage furrows to form two genetically identical daughter cells

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homologous chromosomes

same genes in the same loci but not necessarily the same allele

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Stages of meiosis in order

Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

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First stage of meiosis I: prophase I

  • nuclear envelope disintegrates, nucleolus disappears, spindle assembly formation begins, chromosomes condense

  • homologous chromosomes pairs come together to form bivalents

  • as bivalents form, they cross over in multiple places called the chiosmata; here, sections of DNA break off and rejoin so sections of DNA are exchanged between non-sister chromatids, creating new combo of alleles

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Second stage of meiosis I: metaphase I

  • bivalents are aligned along equator by spindle fibres

  • the pole each chromosome in a bivalent faces is random; this is the independent assortment of chromosomes

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Third stage of meiosis I: anaphase I

  • spindle fibres contract, bivalents seperate

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Fourth stage of meiosis I: telophase I + cytokinesis

  • chromosomes decondense, nuclear envelope and nucleoli reform

  • cytokinesis occurs, producing two daughter cells

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First stage of meiosis II: prophase II

  • chromatin condenses into chromosomes; nuclear envelope disintegrates and nucleoli disappear

  • centrioles move to poles

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Second stage of meiosis II: metaphase II

  • spindle fibres align chromosomes on the equator at the metaphase plate

  • independent assortment of chromosomes occur (makes a difference because sister chromatids are no longer genetically identical due to crossing over)

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Third stage of meiosis II: anaphase II

  • spindle fibres contract, centrosomes divide

  • sister chromatids separate to become daughter chromosomes

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Fourth stage of meiosis II: telophase II + cytokinesis

  • new nuclear envelope and nucleoli form, chromosomes decondense, cytokinesis occurs; in total, four daughter gametes are formed

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Genetic variation within meiosis

  • through the crossing over in prophase I

  • independent assortment of chromosomes in metaphase I and II

  • random fusion of gametes, mate selection and genetic mutation

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Specialisation of erythrocytes

  • no nuclei or other organelles to make space for more haemoglobin

  • flattened biconcave disc shape which increase SA:V

  • flexible so can squeeze through narrow capillaries

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Specialisation of neutrophils

  • granular cytoplasm contains lysosomes with hydrolytic enzymes to kill pathogens

  • multi-lobed nucleus makes it easier to squeeze through small gaps to get to the site of infections

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Specialisation of sperm cells

  • acrosome contains digestive enzymes to break down outer layers of the egg

  • tail which moves side to side for movement, powered by lots of mitochondria which release energy in the form of ATP

  • tail contains proteins fibres which strengthen it

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Specialisation of palisade mesophyll cells

  • rectangular and box shaped so they can be closely packed together to form a rigid and continuous layer

  • vacuole contains cell sap to maintain turgidity

  • thin cellulose cell wall maintains short diffusion pathway to speed up diffusion

  • contains chloroplasts which trap light energy for photosynthesis and can move around

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Specialisation of plant root hair cells

  • have long extensions called root hairs which increase surface area of the cell so increase rate of osmosis

  • contain lots of mitochondria to release energy in the form of ATP for active transport of minerals

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Specialisation of guard cells

  • form small openings on leaves to form gaps called stomata which allow water to enter and leave the plant

  • stoma closes when too much water has been lost to prevent water loss

  • thin outer walls so osmosis is faster

  • cell wall of guard cell thicker on one side of the cell so the cell does not change shape symmetrically as volume changes

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Cytokinesis in plants

  • golgi vesicles assemble along the equator, forming a cell plate

  • vesicles fuse, forming two seperate cells and the endoplasmic reticulum creates a connection between the two cells called the plasmodesmata

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Biosphere

all living things on earth and the regions that living things affect and are affected by

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Biome

a large and distinct area that encompasses living and non-living components

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Ecosystem

a distinct community of organism and their environment

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Community

all the living things in one area

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Population

all the living things of one species in an area

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individual

a single organism

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Cell

smallest unit of life

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tissue

a group of specialised cells with a particular function

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organ

a collection of tissues with a particular function

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organ system

a collection of organs with related function or carrying out a major function

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stem cells

unspecialised and undifferentiated cells

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The four main types of tissue

epithelial, connective, muscle, nervous

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Connective tissue

A body tissue that provides support for the body and connects all of its parts e.g. cartillage. Can be hyaline (bone ends) or elastic (ears)

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Nervous tissue

makes up the nervous system which is made up of multiple types of neurones: motor, sensory, relay; supported by other cells such as glial cells

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Muscular tissue

  • skeletal, cardiac, smooth

  • contractile and very active

  • skeletal muscle striated due to aligned contractile proteins/myofibrils

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Two types of epithelial tissue

Squamous and ciliated

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Squamous epithelial tissue

  • exchange surface, can be one cell thick or multiple cells thick

  • found in alveoli and capillaries

  • cell adhesion to extracellular basement membrane - collagen and other proteins

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Cilliated epithelial tissue

  • have cillia (microtubules which extend and shorten to waft)

  • found in the trachea and oviduct

  • contains goblet cells that produce mucus to trap particles.

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Meristem

undifferentiated plant stem cells which can conduct mitosis

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Permanent tissues within plants

vascular, epidermis, ground tissues

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Features of the plant epidermis

  • only one single layer

  • cells packed very closely together

  • waxy cuticle covers epidermis

  • contains stomatal pores

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Features of the xylem

  • plant vascular tissue

  • dead, lignified cells; form hollow tubes

  • transport water up the cell (unidirectional)

  • vessel elements and tracheids are key components.

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Features of the phloem

  • living cells

  • transport photosynthetic assimilates bidirectionally

  • contain sieve tubes and companion cells

  • vascular tissue

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List of organ systems in the human body

digestive/excretary, endocrine, integumentary, immune/lymphatic, muscular, skeletal, nervous, reproductive, circulatory

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Differentiation

the process by which unspecialized cells develop into specialized cells with distinct functions (involves loss of potency, genes being switched on/off, irreversible changes in cell structure and function).

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Process of differentiation from an embryo

  • fusion of egg and sperm form a zygote (totipotent)

  • differentiates into a blastocyst, which contains the trophoblast (develops into the placenta) and the inner cell mass (pluripotent, source of embryonic stem cells)

  • inner cell mass differentiates into endoderm (lungs, gut), mesoderm (muscles, bones, genitourinary) and ectoderm (epidermis, nerves)

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Source of haemotopoietic stem cells

bone marrow, where blood cells are produced.

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Two types of cells that haematopoietic stem cells can differentiate into

myeloid progenitor and lymphoid progenitor cells

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Three types of cells that lymphoid progenitor cells can differentiate into

T cells, B cells, and natural killer cells.

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Four types of cells that myeloid progenitor cells can differentiate into

erythrocytes, megakaryocytes (produce platelets), macrophage and neutrophils