mitosis

Question 2

What is the cell cycle and outline its stages

Answer 2

Regulated cycle of division with intermediate growth periods

-Interphase
-Mitosis
-Cytokinesis

Question 3

What happens during interphase

Answer 3

DNA is replicated and checked for errors
Protein synthesis
Mitochondria and chloroplasts grow and divide
Normal metabolic reactions occur

Three stages of interphase:
G1-the first growth phase, the proteins from which organelles are synthesised are produced and organelles replicate.The cell increases in its size
S-synthesis phase.DNAs replicated in nucleus
G2-The second growth phase,cell continues to increase its size,energy stores are increased and the duplicated dna is checked for errors

Question 4

What happens in g0 and why does it occur

Answer 4

Where the cell moves out of the cell cycle

When it goes through differentiation-a cell becomes specialised to carry out a particular function.this can make it unable to divide,it will carry out this function indefinitely.

DNA becoming damaged-cell division may no longer be viable. It enters a state of permanent cell arrest. Most cells will do this as they only divide a set number of times

Question 5

When the no of cells that goes through differentiation o r gets damaged increase in the body what could happen

Answer 5

Diseases could occur

Question 6

What is the purpose of mitosis

Answer 6

Produces 2 genetically identical daughter cells for :
Growth
Cell replacement/tissue repair
Asexual reproduction

Question 7

What’s the purpose of checkpoints
What does the spindle assembly checkpoint check for
What does g1 check for
What does G2 check for

Answer 7

Control the mechanisms of cell cycle
They Verify if the processes that each stage have been completed correctly before the cell is allowed to move onto the next phase .

Chromosome attachment to spindle
G1- cell size, nutrients,growth factors,dna damage
G2-cell size,dna replication,dna damage

Question 8

What’s the duration of the cell cycle

Answer 8

If a cycle lasts 24 hrs
Interphase generally last 18-20 hrs as cells spend most of the time there as G1 lasts for about 10 hours
S phase lasts according to the dna that the cell contains,the rate of synthesis is fairly constant between cells and species.Usually cells will take between 5 and 6 hours to complete S phase
G2 is shorter, lasting only 3-4 hours in most cells
Mitosis takes 2 hours

Question 9

Structure of chromosomes in mitosis

Answer 9

Chromosomes are made of two strands joined in middle by a centromere. The separated strands are chromatids , two strands on the same chromosome are called sister chromatids
Two strands-chromosomes already made a copy of itself during interphase
After mitosis chromosomes end up as one strand chromosomes in new daughter cells

Question 10

What happens during early prophase and late prophase

Answer 10

Early- during prophase the chrosmomes becomes more distinct.
-They coil up
-shorten
-thicken
-take up stain more intensely
The centriole divides
Nucleolus becomes less prominent.
Nuclear membrane begins to break down
Late prophase-
chromosomes have becomes more distinct and seen to consist of two chromatids joined by centromere
Protein microtubules form spindle shaped structures linking the poles of the cell. Fibres forming the spindle are necessary to move chromosomes into correct positions before division.
2 Centrioles migrate to opposite poles of the cell
Spindle fibres form and attach to specific areas on the centromeres and to move the chromosomes to centre .
Nucleolus continues to shrink and disappear
Nucelear envelope disintegrates

Question 11

What happens in metaphase

Answer 11

The Chromosomes(w two chromatids) are moved by spindle fibres and they attach to centromere to form a plane in the centre of the cell,called metaphase plate and then held in position.at metaphase checkpoint cell checks all the chrosomes are attached to the spindle before mitosis can continue

Question 12

What happens in anaphase

Answer 12

Centromeres holding the pairs of chromatids in each chromosome divide during anaphase . Chromatids are seperated and pulled to opposite poles of the cell by shortening spindle fibres(when they contract).

Question 13

The v shape of the chromatids moving towards the pole is due to….

Answer 13

Them being dragged by their centromeres through the liquid cystosol.

Question 14

What happens in telophase

Answer 14

The chromatids have reached the poles and are called chromosomes. The two new sets of chromosomes assemble at each pole and nuclear envelope forms around em.Chromosomes start to uncoil and nucleolus formed. Cell didvsuon begins to

Question 15

What happens in cytokinesis in animals cells and plants cells

Answer 15

Cell divides and Daughter cells have same chrome number and genetic makeup as each other and the parent cell

In animal, constriction from edges of cell where cytoskeleton pulls membrane inwards forming a cleavage furrow
In plant,no cleaver furrow due to cell walls
Vesicles produced by Golgi assemble where metaphase plate was fusing with each other and membrane splitting the cell
And new sections of cell wall then forms

Question 16

Difference between mitosis and cytokinesis

Answer 16

Mitosis is nuclear division where as cytokinesis cytoplasm splits to make daughter cells so its cell division

Question 17

Explain with reference to structure and function of proteins importance of g2 checkpoints

Answer 17

If there’s an error in chromosomes it could affect amino acid sequence in protein and change in amino acid sequence could affect the shape and function of the progeny and proteins may not fold properly affecting primary secondary and tertiary structures

Question 18

What are telomeres

Answer 18

Repetitive sequences of dna at end of chromosomes that protect genes at end of chrosomes and stop ends of C from fusing.
DNAs not replicated all the way to the end so everytime replication occurs telomeres shorten
Limiting no of times a cell can shorten

Question 19

How is cell cycle regulated

Answer 19

Checkpoints are regulated by cell signalling proteins who ensure damaged cells don’t progress to next stage of cell cycle

Question 20

What happens at each key checkpoint between cell cycle my

Answer 20

Between g1 and S cell checks for dna damage. After restriction point cell enters cycle.Between g2 and M cell checks chrosoome replication
At metaphase checkpoint cell checks of sister chromatids have been attached to spindle correctly

Question 21

How to do carry out mitosis

Answer 21

1)using a scalpel cut off 4 root tips each 1-2cm long.
2)put tips on watch glass and cover w ethanoic acid.Leave for 10 mins in fume cupboard
3)pour 10cm3 Of HCL into test tube and place in water batch at 60c for 5 mins
4)remove tips with forceps and place in a 100ml beaker with cold water. Wash the tips for 5 mins dry it on filter paper and take water out.
5)transfer root tips into HCL in water bath for 5 mins
6)place two root tips into a clean microscope slide cut and keep last two mm of tip break them up w forceps till flat
7)add small drop of toluidene stain and leave for 2 mins
8) remove slide from fume cupboard and place on paper towel before covering with coverslip. Firmly press it down covered without twisting

Question 23

Why do we use ethanoic acid
Why do we use HCL
Why do we use toiludine blue
why do we not twist

Answer 23

Break down cell walls,make it easier to get stain in
Breaks down cell contents especially nuclear envelope
Toludine blue- affinity for acids esp nucleic acids.makes chromosomes visible
to not break chrom0somes

Question 24

How does cancer occur

Answer 24

Cancer cells form from uncontrollable cell division and continue to replicate rapidly without control systems normal cells have.
They form lumps/tumours dangling strong tissues and cancer cells can break off from tumour and go to other parts of the body.
When it goes to another party of body it’s meta sized. They continue to replicate and make secondary tumours.

Question 25

How could medicines stop cancer

Answer 25

Inhibit growth signals for that type of cell Or chemo where they inhibit synthesis and function of DNA and aimed at killing cells that rapidly divide by mitosis

Question 26

For a cell to divide successfully what two things must it undergo and what’s the order of checkpoints and what’s the order of the cell cycle

Answer 26

Mitosis and cytokinesis G1,g1 checkpoint,g0,S,g2,g2 checkpoint, resting state and spindle assembly point

Question 28

What are p53 levels and what happens to p53 levels when dna damaged and when damage is repaired

Answer 28

Protein and Tumour suppressor to imitate repair mechanisms and regulate cell division. Increase rapidly-allows cell cycle to arrest to allow DNA to repair or apoptosis where it removes irreparably damaged cells. They decrease when damage is repaired if they’re too low it shows they failed to respond to damage leading to cancer dev

Question 29

Diff between normal cell and cancer cell

Answer 29

Normal- large cytoplasm,one nucleus,single nucleons,fine chromatic Cancer-small cytoplasm,multiple nuclei, multiple and large nucleoli,coarse chromatin

Question 31

Where’s the p53 protein found

Answer 31

In nucleus of cells throughout body where it binds directly to dna

Question 32

What is meiosis

Answer 32

A form of cell division that produces 4 genetically different haploid cells (half the no of chromospmes found in parent) known as gametes

Question 33

Significance of meiosis

Answer 33

Gamete cells only need half the no of Chromosones and their haploid

Question 34

Why does meiosis cause genetic variation

Answer 34

Through two processes that make up the unique makeup of the 4 daughter cells Crossing over-homologous pairs of chromosomes swap over parts of their genetic material in meiosis1 Independent assortment-chromosomes from each pair easily allotted to daughter cells Resulting in new combination of alleles

Question 35

What are homologous chromosomes

Answer 35

Pair of chromosomes with genes at the same locus They code for the same characters Each pair contains one chromosome from each parent 1 mat and 1 pat Some alleles might be same whilst others are diff

Question 36

What are the different stages of mitosis

Answer 36

Mitosis 1 -first division where two haploid cells are created and mitosis 2 second division where 4 haploid daughter cells created.

Question 37

What happens in prophase 1

Answer 37

Chromosomes condense Nuclear envelope disintegrates (losing nucleolus) Spindle fibres begin to form Homologous chromosomes pair up forming bivalents Crossing over occurs as they’re moved through cytoplasm

Question 38

What happens in crossing over

Answer 38

Chromatids of homologous chromosomes twist around one another, crossing over many times. Equivalent portions of chromatid has been exchanged by breaking off and rejoining at chiasmata there’s an exchange of dna And due to exchange chromatids are now recombinant Causing genetic variation

Question 39

What happens in metaphase 1

Answer 39

Chromosomes align on cell equator and spindle fibres attach to the centromere . Independent assortment occurs where position of each bivalent is independent of all the other chromosomes The maternal and paternal chromosomes can be on either side of the equator which can effect which daughter cell it finishes in.

Question 41

What does independent assortment lead to

Answer 41

Different combinations of alleles on either side of metaphase plate

Question 42

What happens in anaphase 1

Answer 42

Homologous chromosomes are pulled by the spindle fibres to the poles They’re not pulled apart (chromatids stay joined at centromere)

Question 43

What happens in telophase 1

Answer 43

Nuclear envelopes reform Chromosomes uncoil Cells undergo cytokinesis These cells are now haploid cells

Question 44

What happens at prophase 11

Answer 44

Beginning of second division Chromosomes recondenses Nuclear envelope breaks down again Spindle fibres reform

Question 45

What happens at metaphase 11

Answer 45

Chromosomes are lined on equator by the spindle fibres Independent assortment happens again More genetic variation caused

Question 46

What happens at anaphase 11

Answer 46

Chromatids are split apart by the spindle fibres (unlike in anaphase 1) and centrosome division doesn’t happen in Meiosis 1 Chromatids move to the poles of the cells Which is same as anaphase in mitosis.

Question 47

What happens in Telophase

Answer 47

Chromatids uncoil Nuclear envelope reforms Cell then undergoes cytokinesis 4 haploid daughter cells are produced

Question 48

Cells of intestinal lining divide rapidly how is this different to cells that divide more slowly

Answer 48

Their interphase is shorter so less time for growth stages but duration of mitosis and cytokinesis remains unchanged.

Question 49

Compare meiosis and mitosis

Answer 49

Mitosis has 2 genetically identical diploid cells Meiosis has 4 genetically unique haploid cells Mitosis has 1 division meiosis has two divisions In mitosis chromatids are pulled apart to opposite poles in anaphase. Dividing centromere In meiosis Chromatids aren’t pulled apart and stay joined for genetic variation with whole chromosome being taken

Question 50

What’s a tissue

Answer 50

A group of cells ( w any extracellular material secreted by them) that are specialised to wirk tg to carry out a particular function A tissue can contain more than one cell type

Question 51

What are the different animal tissues

Answer 51

Sqaumous epithelium tissue cell- Ciliated epithelium Cartilage- Muscle

Question 52

What is squamous epithelium tissue

Answer 52

Sqaumous epithelium tissue cell-single layer of flat cells lining a surface. It’s very thin due to the squat or flat cells that make it to and also because it is one cell thick. It’s present when rapid diffusion across a cell is essential. It forms the lining of the lungs and allow rapid diffusion of oxygen into blood

Question 53

What is ciliated epithelium cells

Answer 53

Ciliated epithelium is a layer of cells covered in cilia that move in a rhythmic manner Ciliated epithelium lines the trachea causing mucus to be swept away from lungs.goblet cells are also present releasing mucus to trap unwanted particles like bacteria from reaching alveoli once inside lungs.

Question 54

What is cartilage n muscle

Answer 54

Cartilage- connective tissue found in outer ear nose and ends of bones.contains fibres of elastin n collagen.firm n flexible composed of chondrocyte cells embedded in a extracellular matrix. It prevents ends of bones rubbing tg n causing damage.many fish have whole skeletons made of cartilage not bone Muscle is a tissue that needs to contract to move bones n move diff parts of body. Diff types of muscle fibres eg skeletal (muscles attached to bone) containing microfibrils

Question 56

What are the different typws of animal cells that can group together to form a tissue

Answer 56

Erythrocytes-red blood cells that have a flattened bioconvave shape increasing SA:V. Essential to transposed O2 around body. In mammals they don’t have a nuclei or many organelles which increases space for haemoglobin to carry O2. They’re flexible so they can squeeze through narrow capillaries. Neutrophils- ( type of wbc) play role in immune system. They have a multilobed nucleus making it easier to squeeze through small gaps to get site of infections.Granular cytoplasm contains many lysosomes that contain enzymes used to attack pathogens. Sperm cells- male gametes. Function is to deliver genetic info to the female gamete the ovum. Sperm has a tail of flagellum so they’re capable of movement and contain many mitochondria to supply the energy. Acrosome on head of sperm has digestive ended which digest the protective layers around ovum and allow sperm to penetrate leading to fertilisation.

Question 57

What are the different typws of plant cells that can group together to form a tissue

Answer 57

Palisade cells - present in mesophyll w chloroplasts to absorb alot of light for photosynthesis.Cells are rectangular box shapes which can be closely packed to form a continuous layer. They have thin cell walls increasing ROD of CO2. It has large vacuole to maintain turgid pressure. Chloroplasts can move within the cytoplasm in order absorb more light. Root hair cells - present at surface of roots near growing tips, have long extensions called root hairs increasing SA of cell. It maximised the uptake of water and minerals from the soil. Pairs of guard cells- on surface of leaves form small openings called stomata. These are necessary for CO2 to enter plants for photosynthesis. When guard cells lose water n become less swollen (osmotic forces) they change shape n stoma closes to prevent further water loss from plant. Cell wall of guard cell is thicker on one side so cell doesn’t change shape symmetrically as vol changes.

Question 58

What are the plant tissues

Answer 58

The epidermis- a single layer of closely packed cells covering the surfaces of plants. It is usually covered by a waxy, waterproof cuticle to reduce the loss of H20. Stomata-formed by a pair of guard cells that can open and close are present in the epidermis. They allow CO2 in and out, and water vapour and O2 in and out. Xylem tissue- a type of vascular tissue responsible for transport of H20 and minerals throughout plants. The tissue is composed of vessel elements, which are elongated dead cells. The walls of these cells are strengthened with a waterproof material called lignin which provides structural support for plants. Phioem tissue - another type of vascular tissue in plants, responsible for the transport of organic nutrients, particularly sucrose, from leaves and stems where it is made by photosynthesis to all parts of the plant where needed. It is made of columns of sieve tube cells separated by perforated walls called sieve plates.

Question 59

What’s an organ

Answer 59

A group of difference theses that work tg to perform a particular function. Eg lungs animal organ that carries out gas exchange. They contain squamous epithelium tissue (alveoli)and epithelial tissue (bronchi)and have elastic connective tissue band vascular tissue in blood vessels. Leaf is a plant organ carrying out gas exchange n photosynthesis. Contains palisade tissue and epidermal tissue( preventing water loss from leaf and xylem n phloem tissues in veins)

Question 60

What do organs work tg to do

Answer 60

Form an organ system with a different function. Eg respiratory system is made up all organs involved in gaseous change eg larynx nose mouth lungs trachea diaphragm Circulatory stem made up of organs involved in blood supply. Heart arteries veins n capillaries.

Question 61

Sequence of structure of chromosomes in mitosis

Answer 61

After interphase -46 two strand chromosomes In anaphase - split into 92 sister chromatids After mitosis -46 1 strand chromosomes.

Question 63

Structure of sequence of chromsosomes in meiosis

Answer 63

After interphase - 46 2 strand chromosomes In anaphase 1- pull into 2 sets of 23 2 strand After meiosis 1-23 2 stand chrosomes Anaphase 2-chromatids, centromere split After meiosis -23 1 strand chrosomes

Question 64

How to calculate rate of reaction over first min Rate of reaction at one minute Initial rate of reaction

Answer 64

Gas after 1 min- gas at 0 min / 1 min Rate of reaction at one minute Initial=draw a tangent and calculate gradient Initial rate of reaction- at time 0 draw tangent and calc gradient change in y over change in x