mitosis/ meiosis

Question 1

state what the cell cycle is and outline it stages

Answer 1

-regulated cycle of division with intermediate growth periods
-interphase
-mitosis or meiosis 9 nuclear division)
-cytokinesis (cytoplasmic division )

Question 2

outline what happens during interphase

Answer 2

-g1: cell synthesises proteins for replication & cell size doubles
-s : dna replicates
g2: organelles divide

Question 3

what is the purpose of mitosis

Answer 3

produces 2 genetically identical daughter cells for
-growth
-cell replacement / tissue repair
-asexual reproduction

Question 4

outline what happens during prophase

Answer 4

-chromosomes condense + become visible
-nucleolus disappears
-nuclear membrane starts to break down
-pair of centromeres move to opposite poles
-spindle apparatus begins to form

Question 5

outline what happens during metaphase

Answer 5

-spindle apparatus completely formed
-chromosomes lined up on equator
-spindle apparatus attached to centromere

Question 6

outline what happens during anaphase

Answer 6

-centromeres divide into 2
-spindles begin to shorten pulling sister chromatids to opposite poles
-once reached poles spindle apparatus breaks down

Question 7

outline what happens at telophase

Answer 7

-now chromosomes again
nuclear membrane reforms
-chromosomes uncoil back to chromatin state
-nucleolus reappears

Question 8

what happens during cytokinesis

Answer 8

-cell membrane cleavage furrow forms
-contractile division of cytoplasm

Question 9

how is the cell cycle regulated

Answer 9

-checkpoints regulate by cell-signalling proteins ensure damaged cells do not progress to next stage of cycle
-cyclin-dependent kinase enzymes phosphorylate proteins that initiate next phase of reactions

Question 10

describe what happens at each key checkpoint in the cell cycle

Answer 10

between G1 & S, cell checks for dna damage. after restriction point, cell enters cycle
between G2 & M,cell checks chromosome replication
at metaphase checkpoint, cell checks tat sister chromatids have attached to spindle correctly

Question 11

what are homologous chromosomes

Answer 11

pair of chromosomes with genes at the same locus. 1 maternal & 1 paternal

Question 11

what is meiosis

Answer 11

a form of cell division that produces four genetically different haploid cells with half the number of chromosomes known as gametes

Question 12

differences in plants

Answer 12

-centrioles don’t play a part in forming spindle apparatus
-cell membrane cant furrow, instead vesicles from gogli body form 2 cells

Question 13

what happens during meiosis 1

Answer 13

-homologous chromosomes pair to form bivalents
-crossing over occurs at chiasmata
-cells divide into 2, homologous chromosomes separate randomly, each cell contains either maternal or paternal

Question 14

what happens during meiosis 2

Answer 14

-independent segregation of sister chromatids
-each cell divides again, producing 4 haploid cells

Question 15

how does meiosis produce genetic variation

Answer 15

-independent assortment - when homologous chromosomes line up on equator cannot predict weather maternal or paternal will go in what gamete
-crossing over
-during fertilisation gametes fuse randomly

Question 16

how do cells become specialised

Answer 16

some genes are expressed while others are silenced due to cell differentiation mediated by transcription factors. cells produce proteins that determine their structure % function

Question 17

what is a transcription factor

Answer 17

a protein that controls the transcription of genes so that only certain parts of the DNA are expressed

Question 18

how do transcription factors work

Answer 18

1 move from the cytoplasm into nucleus
2 bind to promoter region upstream of target gene
3 makes it easier or more difficult for RNA polymerase to bind to gene. this increases or decreases rate of transcription

Question 19

what is a stem cell

Answer 19

undifferentiated cells that can divide indefinitely and turn into other specific cell types

Question 20

name and define 4 types of stem cell

Answer 20

totipotent: can develop into any cell type including the placenta and embryo
pluripotent: can develop into any cell type including embryo and placenta
multipotent: can only develop into a few different types of cell
unipotent: can only develop into one type of cell

Question 21

suggest some uses of stem cells

Answer 21

-repair of damaged tissue
-drug testing on artificially grown tissues
-treating neurological diseases e.g Parkinson’s & Alzheimer’s
-researching developmental biology

Question 22

describe the 2 groups of specialised cells in blood

Answer 22

erythrocytes: (red blood cells) - biconcave, no nucleus, lots of haemoglobin
leucocytes: (white blood cells) - lymphocytes, eosinophils, neutrophils to engulf foreign material, monocytes

Question 23

how do the specialised cells in the blood form

Answer 23

multipotent blood cells in the bone marrow differentiate into:
-erythrocytes, which have a short lifespan & cannot undergo mitosis since they have no nucleus
-leucocytes, including neutrophils

Question 24

state the relationship between a system and specialised cell

Answer 24

specialised cells ~tissues that perform specific function~ organs made of several tissue types ~ organ systems

Question 25

describe the structure of squamous and ciliated epithelium

Answer 25

simple squamous epithelium: single smooth layer of squamous cells (thin & flat with round nucleus) fixed in place by basement membrane ciliated epithelium : made of ciliated epithelial cells (Colum shaped with surface projections called cilia that move in a synchronised pattern)

Question 26

describe the structure of a spermatozoon

Answer 26

-specialised to fertilise an ovum during sexual reproduction in mammals -haploid nucleus so fertilisation restores diploid chromosome number -acrosome secretes enzymes to penetrate ovum coat -spiral shaped mitochondrion -flagellum bound by plasma membrane propels cell

Question 26

describe the structure and function of palisade cells & guard cells in plants

Answer 26

palisade cells: specialised to absorb light energy for photosynthesis, so contain many chloroplasts. pack closely together guard cells: form stoma. when turgid, stoma opens; when flaccid stoma closes. walls are thickened by spirals of cellulose

Question 27

describe the structure and function of root hair cells

Answer 27

specialised to absorb water and low-concentration minerals from soil hair like projections increase surface area for osmosis / carrier proteins for active transport many mitochondria produce ATP for active transport

Question 28

what are meristems

Answer 28

totipotent undifferentiated plant cells that can develop into various types of plant cell, including xylem vessels & phloem sieve tubes classified as apical (at root & shoot tips) intercalary (stem) or lateral (in vascular areas)

Question 29

describe the structure of phloem tissue

Answer 29

-sieve tube elements: form a tube to transport sucrose in the dissolved form of sap companion cells: involved in ATP production for active loading of sucrose into sieve tubes plasmodesmata: gaps between cell walls where the cytoplasm links, allowing substances to flow

Question 30

describe the structure of xylem tissue

Answer 30

vessel elements: lignified secondary walls for mechanical strength & waterproofing; perforated end walls for rapid water flow tracheid's: tapered ends for close packing; pits for lateral water movement; no cytoplasm or nucleus

Question 31

describe the additional cell types in xylem tissue

Answer 31

--xylem parenchyma: packing tissue with thin walls transmit turgidity -sclereids -sclerenchyma fibres: heavily lignified to withstand negative pressure

Question 32

describe the structure of cartilage

Answer 32

-avascular smooth elastic tissue made of chondrocytes, which produce extensive extracellular matrix (ECM) -ECM mainly contains collagen & proteoglycan _3 categories; hyaline, yellow elastic, wite fibrous

Question 33

name 3 types of muscle in the body and where they are located

Answer 33

cardiac- exclusively in the heart smooth- walls of blood vessels and intestines skeletal- attached to incompressible skeleton by tendons

Question 34

describe the gross structure of skeletal muscles

Answer 34

-muscle cells are fused together to form bundles of parallel muscle fibres (myofibrils) -arrangement ensures there is no point of weakness between cells -each bundle is surrounded by endomysium; loose connective tissue with many capillaries