username3835832
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Positive and negative control?

Also, what are serial dilutions? I have watched some youtube videos but still don't get it!
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westcw13
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Serial dilutions is when you start with say 1moldm^-3 of a solution, and then you take a sample of it and top it up with water to make another concentration (e.g. take half of it and top it up = 0.5moldm^-3). Repeat this with your new solution and so on (to, for example, keep on halving the concentration). It's basically an easier way of making different concentrations of a solution for an experiment.

As for positive and negative control, I'm assuming you mean positive and negative feedback in homeostasis?

Negative = brings about a change to return the system to its original state. E.g. if blood glucose increased too much, there is a mechanism to decrease it again back to normal.

Positive is the opposite, so if there is a change, there will be a mechanism to cause more of the change. E.g. when oxytocin in released, the uterus contracts - but these contractions cause more oxytocin to be released, so more contractions and so on.

Sorry if any of that was unclear, but I hope that helps!
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(Original post by westcw13)
Serial dilutions is when you start with say 1moldm^-3 of a solution, and then you take a sample of it and top it up with water to make another concentration (e.g. take half of it and top it up = 0.5moldm^-3). Repeat this with your new solution and so on (to, for example, keep on halving the concentration). It's basically an easier way of making different concentrations of a solution for an experiment.

As for positive and negative control, I'm assuming you mean positive and negative feedback in homeostasis?

Negative = brings about a change to return the system to its original state. E.g. if blood glucose increased too much, there is a mechanism to decrease it again back to normal.

Positive is the opposite, so if there is a change, there will be a mechanism to cause more of the change. E.g. when oxytocin in released, the uterus contracts - but these contractions cause more oxytocin to be released, so more contractions and so on.

Sorry if any of that was unclear, but I hope that helps!

So serial dilutions is used to make different concentrations of a solution for an experiment?

And with positive and negative control I mean in an experiment...
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westcw13
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(Original post by chemquestion)
So serial dilutions is used to make different concentrations of a solution for an experiment?

And with positive and negative control I mean in an experiment...
Yep!

Sorry, not sure about positive and negative control lol
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(Original post by westcw13)
Yep!

Sorry, not sure about positive and negative control lol
From my text book:
''Cytoplams of adjecent cells are connected through the holes in the sieve plates''

Do you know what this means?

Are the sieve plates the end walls with holes in them allowing solutes to pass through?
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westcw13
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(Original post by chemquestion)
From my text book:
''Cytoplams of adjecent cells are connected through the holes in the sieve plates''

Do you know what this means?

Are the sieve plates the end walls with holes in them allowing solutes to pass through?
Yep, exactly that
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(Original post by westcw13)
Yep, exactly that
Oh and do you know what endothermis and cortex means?
In a plant root
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(Original post by chemquestion)
Oh and do you know what endothermis and cortex means?
In a plant root
Cortex is the big layer between the epidermis (outer layer) and the endodermis. The endodermis is one of the layers around the centre that has the xylem and phloem in (the other one being the pericycle, the endodermis is on the outside).

So from outside to inside, it goes epidermis, cortex (big layer), endodermis, pericycle and then the phloem and xylem in the centre.
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(Original post by chemquestion)
Oh and do you know what endothermis and cortex means?
In a plant root
You're just rude.

You're getting help yet not even a thank you, just firing ridiculous questions which can easily be found online with a quick search or in your textbook. You can literally just search "plant endothermis" / "plant cortex" into google and you'd get a great definition and thousands of pictures. Stop being lazy and get some manners.

Good luck with anything that requires thinking (eg A level Biology, I would know) if you can't use such simple initiative. Ridiculous
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(Original post by westcw13)
Cortex is the big layer between the epidermis (outer layer) and the endodermis. The endodermis is one of the layers around the centre that has the xylem and phloem in (the other one being the pericycle, the endodermis is on the outside).

So from outside to inside, it goes epidermis, cortex (big layer), endodermis, pericycle and then the phloem and xylem in the centre.
Thank you for your help
Much appreciated

Sorry for asking so many questions
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