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Biology SL/HL help


Mahuta ♥

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hey!

help is much appreciated considering i'm about to go berserk over this:

heres my dilemma

its about meiosis~

first of all, do BOTH homologous pairs cross over or only the uhh larger one?

one of my textbooks only shows the larger one, the powerpoint that my teacher showed us shows both, my OTHER textbook shows NONE and my OTHER OTHER textbook starts off with 2 chromosomes for meiosis @_______________@

secondly!

do the cells split in two after telophase 1? or do they remained joined? and then fully split after telophase II into 4 different cells

IF they do split into two, why is it called telophase and why is the cell beginning to divide in anaphase (according to one of the diagrams anyway)? shouldn't it be called cytokinesis? @-@ or is there cytokinesis I & II

argh i'm so confused D:

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*TOPIC 4 (4.2)---MEIOSIS*

Alrighty Alrighty calm down. :)

OK, so, you have 2 homologous pairs in the parent cell. The cross over is in Prophase 1.

a homologous pair has 2 sister chromatids.

In crossing over, one sister chromatid from the 1st pair and another from the second pair form chiasmata, which means that a DNA of one if connected to the other.

The other other two(one from each) remain as they are.

Cell splits in two after Telophase 1 and then each one splits into two in telopahse 2/cytokinesis.

The cell doesnt split in neither of the anaphases. Anaphase 1 is the stage where the cell is getting ready to split into two. Anaphase 2 is the same thing, but its where the two divided parts are getting ready to divide again.

Telophase vs. cytokinesis:

Cytokinesis is the process where the cell literally splits into two by the membrane being split into two. It is put within telophase, its not a phase on its own.

Telophase is where : 1)nuclear membrane forms 2)chromosome going to normale size 3)cytokinesis happens.

Anything else?

Edited by Mahuta ♥
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Hows that? Please explain.

Because cytokinesis is a process not a phase. Just like endocytosis and exocytosis.

What is a fact is that cytokinesis is not really a phase as much as its a process.

As for the IB Bio Syllabus, doesnt make much of a difference as long as you know what it means and mention it in your answer.

I personally was told what I said. But Im interested in knowing about your comment. Please <3

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Alrighty Alrighty calm down. :wtf:

OK, so, you have 2 homologous pairs in the parent cell. The cross over is in Prophase 1.

a homologous pair has 2 sister chromatids.

In crossing over, one sister chromatid from the 1st pair and another from the second pair form chiasmata, which means that a DNA of one if connected to the other.

The other other two(one from each) remain as they are.

Cell splits in two after Telophase 1 and then each one splits into two in telopahse 2/cytokinesis.

The cell doesnt split in neither of the anaphases. Anaphase 1 is the stage where the cell is getting ready to split into two. Anaphase 2 is the same thing, but its where the two divided parts are getting ready to divide again.

Telophase vs. cytokinesis:

Cytokinesis is the process where the cell literally splits into two by the membrane being split into two. It is put within telophase, its not a phase on its own.

Telophase is where : 1)nuclear membrane forms 2)chromosome going to normale size 3)cytokinesis happens.

Anything else?

oh wow, it's beginning to make sense now.

i'd always assumed cytokinesis was a stage of its own because of the way we learnt it: inter, pro, meta, ana, telo, CYTOKINESIS

and it always had its own little label and everything >____> well at least now i've got that clarified!

thank you soo much, if i get full marks for meiosis on the mock exams this term, you'll definitely get majority of the credit xP

EDIT:

ok i'm back with another question on meiosis, prophase is the phase when the DNA duplicates correct? so why do they call it "prophase II - after the first division (telophase I) -" even though technically the chromosomes don't duplicate?!

this naming is getting on my nerves as well as the major differences between my textbooks.

thanks again *sigh~

Edited by Chelleee
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Cytokinesis is not a phase of mitosis or meosis but it is part of the cell cycle which is divided into interphase, mitosis/meosis, cytokinesis. In telophase, the last thing that happens is the constriction of the cell membrane for an animal cell. Cytokinesis happens just after mitosis when the two cells divide completely. It is indeed a process just like mitosis is a process by which the nucleus divides to form two identical nuclei. Our teacher told us that there has been a lot of debate about this and some say that cytokinesis happens in late telophase but as you said, in doesn't really make a diffenrence for IB as long as you know what it means. :(

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I also need help! I hate doing labs but we have to design a lab and it has to be on behavior of invertebrates. i already thought of a research question: Can the woodlice remember the way out of a maze when a reward is given to them at the end? but i dont know what my variables are. my dependent variable is how many errors the woodlice make until they find the reward, but what's my independent variable? because i just let the woodlouse enter the maze and count the error it makes without giving it the reward. and then í'm gonna count the errors it makes when it gets a reward. I hope somebody can help me, because i really suck at biology.

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  • 2 weeks later...

*TOPIC 7 (7.6)---Enzymes and enzyme inhibition*

Enzyme inhibition:

1) Competitive inhibition:

Competitive inhibition is the type of inhibition where the inhibitor inhibits/takes over the active site. It is competing for the active site.

To be able to compete for the active site, the inhibitor has to be similar, chemically, to the substrate.

Since the inhibition is due to the competition over active site, the higher the concentration of the substrate, the lower the effect of the inhibitor. Because there is less chance of the inhibitor taking over the active site.

2)Incompetitive inhibition:

Incompetitive inhibition as the name suggests, is the type of inhibition where the inhibitor is not competing for the active site.

The only thing that this inhibitor does is that it binds to another site, not the active site but the allosteric site. Binding to the allosteric site causes a change in the shape of the active site. A change in shape of the active site stops the substrate from binding to the active site.

The problem with this is, that even if you increase the concentration of the substrate, the inhibitor will still have the effect as its not a matter of 'competition'.

Since this inhibitor is not competing for the active site, it doesn't have to have a similar structure, thus, the incompetitve inhibitor is not chemically similar to the substrate.

3) End product inhibition:

This could be put under incompetitve inhibition.

When you have a metabolic pathway, whether cyclical or non-cyclical.

This is when the last product inhibits the enzyme that catalyzes the first reaction at the allosteric site.

The significance of this inhibition is to stop the build-up of the products if there is too much of it. This is an example of negative feedback.

Anything else? I'm not sure I explained the last one properly, so if there's anything unclear, please tell me. smile.gif

Edited by Mahuta ♥
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  • 1 month later...

You mean +/- 0.1g type of thing?

It's an error marker and tells you how accurate the reading is. So like if you had measured out 33.05 grams, +/-0.01g would tell you that the machine you measured it with is accurate to within plus or minus an extra 0.01g. i.e. your measurement could either be correct, plus one 0.01g (33.06) or minus 0.01g (33.04). The machine isn't 100% sure, so it's giving you an idea of the sort of range it could be out by.

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LOL, no Alice, thats something in bacteria.

*OPTION F (F.1.7)---GRAM +VE and GRAM -VE eubacterial cell wall*

HJ, gram positive and gram negative are one way you could distinguish between eubacteria.

Gram +ve and gram -ve are two different types of cells walls.

Gram +ve:

The reason its called this, is that its structure allows it to be stained with purple by the Gram stain. The thing that stains is the peptidoglycan. So this type of eubacteria has a thick peptidoglycan layer.

Gram -ve:

This means that it is stained less by the gram stain, so the color red is visible instead. Therefore, this eubacteria has a gram -ve cell wall because it has a thin peptidoglycan layer.

Thats all you have to know about Gram +ve and -ve.

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