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Two main phases of cell cycle
interphase and mitotic phase
First stage of interphase: G1
cell grows, organelles duplicate, proteins are synthesis
G1 Checkpoint
cells are checked for size, nutrients and damage; centrioles also start to replicate in animal cells
First stage outside interphase: G0
where specialised/differentiated cells, senescent/old cells and damaged cells go
Re-entering interphase from G0
lymphocytes and hepatocytes can be stimulated to re-enter the cell cycle from G0
Second stage of interphase: S
DNA is replicated
Third stage of interphase: G2
cell grows, ATP is saved up and stored, nutrients are built up
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
First stage of mitotic phase: mitosis
nucleus divides
Second stage of mitotic phase: cytokinesis
cell divides to form two genetically identical daughter cells which are identical to the parent cell
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
Metaphase checkpoint
check if spindle assembly has correctly formed
Stages of mitosis in order
prophase, metaphase, anaphase, telophase
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
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
Third stage of mitotic stage: anaphase
spindle fibres contract; centromeres divide and sister chromatids separate to become daughter chromosomes which migrate to the poles
Fourth stage of mitotic stage: telophase
cell elongates; new nuclear envelopes form and chromosomes decondense into chromatin and nucleoli form
Fifth stage of mitotic stage: cytokinesis
contractile ring forms between the two nucleoli, the cleavage furrows to form two genetically identical daughter cells
homologous chromosomes
same genes in the same loci but not necessarily the same allele
Stages of meiosis in order
Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II
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
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
Third stage of meiosis I: anaphase I
spindle fibres contract, bivalents seperate
Fourth stage of meiosis I: telophase I + cytokinesis
chromosomes decondense, nuclear envelope and nucleoli reform
cytokinesis occurs, producing two daughter cells
First stage of meiosis II: prophase II
chromatin condenses into chromosomes; nuclear envelope disintegrates and nucleoli disappear
centrioles move to poles
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)
Third stage of meiosis II: anaphase II
spindle fibres contract, centrosomes divide
sister chromatids separate to become daughter chromosomes
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
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
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
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
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
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
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
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
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
Biosphere
all living things on earth and the regions that living things affect and are affected by
Biome
a large and distinct area that encompasses living and non-living components
Ecosystem
a distinct community of organism and their environment
Community
all the living things in one area
Population
all the living things of one species in an area
individual
a single organism
Cell
smallest unit of life
tissue
a group of specialised cells with a particular function
organ
a collection of tissues with a particular function
organ system
a collection of organs with related function or carrying out a major function
stem cells
unspecialised and undifferentiated cells
The four main types of tissue
epithelial, connective, muscle, nervous
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)
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
Muscular tissue
skeletal, cardiac, smooth
contractile and very active
skeletal muscle striated due to aligned contractile proteins/myofibrils
Two types of epithelial tissue
Squamous and ciliated
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
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.
Meristem
undifferentiated plant stem cells which can conduct mitosis
Permanent tissues within plants
vascular, epidermis, ground tissues
Features of the plant epidermis
only one single layer
cells packed very closely together
waxy cuticle covers epidermis
contains stomatal pores
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.
Features of the phloem
living cells
transport photosynthetic assimilates bidirectionally
contain sieve tubes and companion cells
vascular tissue
List of organ systems in the human body
digestive/excretary, endocrine, integumentary, immune/lymphatic, muscular, skeletal, nervous, reproductive, circulatory
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).
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)
Source of haemotopoietic stem cells
bone marrow, where blood cells are produced.
Two types of cells that haematopoietic stem cells can differentiate into
myeloid progenitor and lymphoid progenitor cells
Three types of cells that lymphoid progenitor cells can differentiate into
T cells, B cells, and natural killer cells.
Four types of cells that myeloid progenitor cells can differentiate into
erythrocytes, megakaryocytes (produce platelets), macrophage and neutrophils