Biology Unit 2 Topic 3

what is mitosis

a type of nuclear cell division that results in new biological material → diploid cells

what are needs for mitosis

• a- mitosis… for genetically identical offspring as parent

• s- meiosis then mitosisi to produce new cells after gametes have fused

• growth

define karyotype and the use of it

a display of all the chromosomes of all a cell arranged in pairs it is used to detect abnormalities

what are chromosomes made of and the need for them?

Dna is very long

dna + histones

why do chromosomes condense during mitosis but then uncondense

they condense because DNA is extremely long and can get tangled, to allow accurate seperation during metaphase and to prevent damage.

they uncoil in telophase because tightly condense DNA does not allow RNA polymerase to bind so the gene is unavaliable to be transcriped to make proteins

what are nucleosomes and explain their importance

single DNA wrapped around histone proteins held by electrostatic attraction (DNA is negatively charged and hsitones are positively charged)

they can control gene expression as they can tightly compact DNA to not allow transcription but loosen them to then allow transcription

describe the visibility of chromosomes

not visisble during interphase because they are incondensed chromatins but when they condense during mitosis they can hold stain better

what are homologous pairs

matching pairs of chromosomes with the same loci and genes (but may have different alleles) from each parent… determines phenotype

what are the 3 main phases of the cell cycle and the average length

interphase → mitosis → cytokinesis

can vary between 24 hours (in developing tissues) to years in mature tissues

what factors can control cell cycle

• chemical signals

• gene activity

• check points

• Cyclin- dependent kinases (CDKs)

what are CDKs

enzymes that control the progression of the cell cycle taht work only when bound to cyclins (proteins)…. they can bid to the enxymes to create complxes that add phosphate groups and trigger the next stage of mitosis…

e.g. can help break down memebrane proteins in cell division

describe the different phases of interphase (where cells spend most of their life)

G1 → cell grows, material taken in for cell developemny and ATP production increases for enhanced metabolic activity

S → DNA replicates, chromosoes double with two sister chromatids joined by a centromere

G2 → organelles synthesised and duplicated, proteins made (e.g. spindles) , cell check DNA for errors

what are the different phases of mitosis (PMAT)

prophase- chromsomes condense, nuclear membrane breaks down, centrioles form spindles

metaphase- nuclear membrane fully broek down chomrosomes line up at centre and centromeere attach to spindle fibre

anaphase- centromere divide, spindle fibers shortern and chromosomes begin to get pulled to opposite poles

telophase- poles reached, spindles break down, nuclear membrane reforms, and chromosomes uncoil

explain the last stage of cell cycle in plants and animals

animals- central membrane is pulled inwards to create a grove that fuses to form two independent cells

plants- cell membrane cannot create furrows so vesicles from golgi (carrying cell wall components- cellulose) form structures down centre (cell plates) of cell to divide cytoplasm into two and from there the middle lamella forms and remaining gaps become plasmodesmatas

what is the mitotic index and the use

proportion of cells undergoing mitosis

cells in mutosis/tital cells

identifies cancer + moniters effectiveness of cancer treatemnts

what are the pros and cons of asse reprocution

• rapid, no mate needed, large yield, creates clones (genetically identical to parent)

• no genetic variation (ex. through mutation) , if environment changes every population is at risk, disease can wipe out whole population

define sse reproduction and pros

fusion of two specialised haploid cells to form a genetically different offspring —- genetical variation so greater chance of survival in a changing environment

what are gomads and examples

places where gametes are formed e.g. testes, ovaries, anthers

what is meiosis

a type of cell division that occurs in sex organs and produces gametes

what occurs in prophase I of meiosis

• nuclear membrane break down, spindle fibers form

• recombination —> homologous chromosomes pair up and cross over to form a bivalent. chromosomes can vreak off at chiasmata and exchange between homologous chromosomes

what occurs in metaphase I, anaphase I, and telophase I in meiosis?

m- pairs of homologous chromosomes line up in equatior (independent assortment, maternal and paternal chromoeoms go to opposite poles)

a- spindle fibers shortern, centromere breaks and chromosomes go to opposite poles

t- nuclear membranes reform, uncoil, cytokinesis

what occurs in prophase II, metaphase II, anaphase II, and telophase II in meiosis?

p2- chromosomes condense, nuclear membrane break down and spindle fibers develope

m- line up equator

a- spindle shorten, chromatids move to opposite poles

t- chromatides reach poes and nuclear membrane reform, uncoil + cytokinesis

what is gametogensis

the formation of gametes by meiosis in the gonads

explain gametogenesis in males and females in mammals

males- millions of sperm created every day after puberty

females - primary oocytes formed before birth and new ones are made later

what is the structrues of a ovum

• nucleus (haploid)

• large cytoplasm which contains nutrients for growing emrbyo

• zona pellucide (glycoprotein layer around egg that binds sperm and prevent more than one sperm entering - polyspermy)

• cortical granuales release enzymes after fertilisation that harden zona pellucide

what is the structures of sperm

• head contains haploid nucleus and acrosome that contains digestive enzymes to digest zona pellucida

• mid piece contain many mitachondira for moving

• tail (flagellum- made of microtubules) that allows sperm to swim

• cell membrane receptors to recognise eggs

what is fertilisation

the fusion of male and female nuclei

describe fertilisation in humans

1. gametes meet (sperm swims towards egg that is released during ovulation)

2. acrosome reaction - digestive enzymes released on zona pellucida

3. one sperm reaches oocyte membrane, membranes fuse and sperm nucleus enters egg

4. cortical reaction- as soon as sperm fuses, cortical granuales release enzymes that harden the zona pellucida and destroy sperm binding sites

5. ovum copletes M2, and becomes haploid nucleus

6. zygote formed

what is polyspermy and why is it bad

when more than one sperm fertilisies egg, too many chromosomes and embryo wouldn’t develope properly

describe the structure of a pollen gamete

• contains two nuclei

  • tube contains digestive enzymes to digest style

  • generative that divides to form two male nuclei for double fertilisation

describe fertilisation in plants

1. pollination- pollen from anther reaches stigma through self or cross pollintaion

2. fertilisation- pollen grow tube, genertaive nuclei split into two and target an ovule…

3. double fertilisation- egg and one male gamete fuse to form zygote and second male gamete fuses with two polar nuclei for form endosperm

4. seed + fruit… fertilised ovule bomes seed and ovary bcomes fruit to protect

5. seeed dispersal to reduce competition with parent — wind, animals or water

6. germination- seed germinates abd embryo grows