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homefind
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#1481
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#1481
(Original post by LiamDaly)
But I thought meiosis was the process of making gametes not the process of them fussing?
(I missed when we covered this in class)


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yes it does produce gametes, but your chromosomes are from your mother and father! Therefore your gametes will have genetics from them, you don't just use paternal chromosomes to make sperm cells etc... (if that is what your confused about) llllllllllllllllll
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zbert
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#1482
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#1482
does anyone have a clear explanation of meiosis (or a link to a place)? I read the text book but it doesn't seem to be clicking.. and I understand mitosis I think
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LiamDaly
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#1483
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#1483
(Original post by Suzanna5678)
Specifically apoplast And symplast? Don't see how it can be 6 points
Would you need to say that water along the cell wall(apoplastic) uses cohesion and water moving along water potential gradient (symplastic) in the cytoplasm is entirely because if Osmosis?


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#1484
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#1484
(Original post by Suzanna5678)
Specifically apoplast And symplast? Don't see how it can be 6 points
Ye I'm thinking that probably why it hasn't come up before.

id it does come up it will probably ask 'how can water travel to the xylem' and you talk about osmosis of water into root hair cells, WP is maintained by active transport for mineral ions into the root hair cells, talking about water travelling through cortex down a WP gradient by either Symplastic or Apoplastic pathway talk about casparian strip at the endodermis etc... Finally talk about how water moves by osmosis into the xylem (again WP gradient maintained by active transport of mineral ions into xylem) also could add how this causes root pressure.
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Suzanna5678
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#1485
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#1485
(Original post by homefind)
Ye I'm thinking that probably why it hasn't come up before.

id it does come up it will probably ask 'how can water travel to the xylem' and you talk about osmosis of water into root hair cells, WP is maintained by active transport for mineral ions into the root hair cells, talking about water travelling through cortex down a WP gradient by either Symplastic or Apoplastic pathway talk about casparian strip at the endodermis etc... Finally talk about how water moves by osmosis into the xylem (again WP gradient maintained by active transport of mineral ions into xylem) also could add how this causes root pressure.
If the question is 'explain how water enters a plant root from find soil and travels through the endodermis' do u talk about root pressure?
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LiamDaly
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#1486
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#1486
(Original post by zbert)
does anyone have a clear explanation of meiosis (or a link to a place)? I read the text book but it doesn't seem to be clicking.. and I understand mitosis I think
Same


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#1487
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(Original post by zbert)
does anyone have a clear explanation of meiosis (or a link to a place)? I read the text book but it doesn't seem to be clicking.. and I understand mitosis I think
Okay if you understand mitosis then just think about it being the whole cycle of mitosis however with two divisions

interphase - DNA is unravelled and replicates itself so there are two copies of chromatids

PROPHASE I - DNA condenses into double armed chromosomes made from two sister chromatids. (You also have nuclear envelope breaking down and centrioles move to opposite poles and produce spindle fibres) CROSSING OVER OCCURS HERE

METOPHASE I - Chromosomes arrange themselves into HOMOLOGOUS PAIRS (similar sized chromosomes, however one may have a gene for blue eyes and the other may have a dominant allele for brown eyes) they line up at the equator and are joined to the spindle fibres by their centromere. INDEPENDENT SEGREGATION OCCURS HERE

ANAPHASE I - Spindle fibres contract and pull each chromosome from the homologous pair to opposite poles of the cell (NOTE- THEY ARE STILL 'X' SHAPED, I.e each double armed chromosomes with two sister chromatids are pulled to opposite poles)

TELOPHASE I - nuclear envelope develops and cytoplasm divides, there are now TWO NUCLEI with two pairs of sister chromatids in each

PROPHASE II - this step isn't significant they just condense.

METOPHASE II - PAIRS OF SISTER CHROMATIDS LINE UP AT THE EQUATOR ATTACHED TO SPINDLE FIBRES BY CENTROMERE ETC...

ANAPHASE II - the pairs of chromatids that make up each chromosome are separated (contraction of spindle fibres)

TELOPHASE II - FOUR HAPLOID CELLS THAT ARE GENETICALLY DIFFERENT FROM EACH OTHER ARE PRODUCED (nuclear envelope forms and cytoplasm divides)

THERE ISN'T A INTERPHASE II!!!
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Suzanna5678
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#1488
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#1488
(Original post by homefind)
Okay if you understand mitosis then just think about it being the whole cycle of mitosis however with two divisions

interphase - DNA is unravelled and replicates itself so there are two copies of chromatids

PROPHASE I - DNA condenses into double armed chromosomes made for. Two sister chromatids. (You also have nuclear envelope breaking down and centrioles move to opposite poles and produce spindle fibres) CROSSING OVER OCCURS HERE

METOPHASE I - Chromosomes arrange themselves into HOMOLOGOUS PAIRS (similar sized chromosomes, however one may have a gene for blue eyes and the other may have a dominant allele for brown eyes) they line up at the equator and are joined to the spindle fibres by their centromere. INDEPENDENT SEGREGATION OCCURS HERE

ANAPHASE I - Spindle fibres contract and pull each chromosome from the homologous pair to opposite poles of the cell (NOTE- THEY ARE STILL 'X' SHAPED, I.e each double armed chromosomes with two sister chromatids are pulled to opposite poles)

TELOPHASE I - nuclear envelope develops and cytoplasm divides, there are now TWO NUCLEI with two pairs of sister chromatids in each

PROPHASE II - this step isn't significant they just condense.

METOPHASE II - PAIRS OF SISTER CHROMATIDS LINE UP AT THE EQUATOR ATTACHED TO SPINDLE FIBRES BY CENTROMERE ETC...

ANAPHASE II - the pairs of chromatids that make up each chromosome are separated (contraction of spindle fibres)

TELOPHASE II - FOUR HAPLOID CELLS THAT ARE GENETICALLY DIFFERENT FROM EACH OTHER ARE PRODUCED (nuclear envelope forms and cytoplasm divides)

THERE ISN'T A INTERPHASE II!!!
Does independent segregation happen at meiosis 2 aswell
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Suzanna5678
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#1489
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#1489
Can someone please write a 6 mark answer on how starch structure is related to its function, don't think it's come up before where as cellulose has!
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homefind
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#1490
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#1490
(Original post by Suzanna5678)
Does independent segregation happen at meiosis 2 aswell
I assume it does, yes.
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homefind
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#1491
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#1491
(Original post by Suzanna5678)
Can someone please write a 6 mark answer on how starch structure is related to its function, don't think it's come up before where as cellulose has!
Starch is the main energy storage material in plants, made from two polysaccharides of a-glucose, amylose and amylopectin. Long unbranched chains of amylose make it coiled, this cause starch to be compact and good for storage. Amylopectin is long branched chains, it has side branches which allow enzymes to readily break down the molecule (as glycosidic bonds are easier to get to and hydrolyse) so glucose can be released quicker. Starch is also good for storage because it is insoluble and so doesn't effect the net movement of water which prevent osmotic activity.
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(Original post by homefind)
Starch is the main energy storage material in plants, made from two polysaccharides of a-glucose, amylose and amylopectin. Long unbranched chains of amylose make it coiled, this cause starch to be compact and good for storage. Amylopectin is long branched chains, it has side branches which allow enzymes to readily break down the molecule (as glycosidic bonds are easier to get to and hydrolyse) so glucose can be released quicker. Starch is also good for storage because it is insoluble and so doesn't effect the net movement of water which prevent osmotic activity.
Thanks doll
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Nima123
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#1493
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#1493
I don't understand question 5dii from the june 2010 paper can someone explain it to me Name:  image.jpg
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Nima123
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#1494
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#1494
What do you guys think will be the six marker? I think something on fishes or insects?
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Son234
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#1495
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#1495
Jan 2010 can someone explain why the magnification is 2350-2500?

My answer was 1500




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Jay95
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#1496
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#1496
Can someone please rxplain the heamoglobin chapter like partial pressure, the curves and the loading/unloading

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homefind
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#1497
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#1497
(Original post by Son234)
Jan 2010 can someone explain why the magnification is 2350-2500?

My answer was 1500




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The mark scheme is for a4 paper, are you doing it on a4?
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Swords N Thorns
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#1498
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#1498
(Original post by Jay95)
Can someone please rxplain the heamoglobin chapter like partial pressure, the curves and the loading/unloading

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If the curve is shifted to the right, it means it has a lower affinity for oxygen. If it is shifted to the left, it has a higher affinity for oxygen.
Haemoglobin will associate with/load oxygen where there is a high partial pressure of oxygen, e.g. in the lungs.
It will dissociate with oxygen where there is a low partial pressure of oxygen and more carbon dioxide e.g. respiring tissues.

I think this is right, anyone feel free to add on to it. Hope it helped!
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Son234
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#1499
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#1499
(Original post by homefind)
The mark scheme is for a4 paper, are you doing it on a4?
Oh haha lol no wonder I printed it with multiple sheets

I feel a little embarrassed damm lol




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#1500
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#1500
(Original post by Son234)
Oh haha lol no wonder I printed it with multiple sheets

I feel a little embarrassed damm lol




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haha, no worries
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