HumbleBee_x
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I'd appreciate it if someone could explain how you got to each answer. Thankyou

a) A scientist measured the rate of removal of amino acids from a polypeptide with and without an enzyme present. With the enzyme present, 578 amino acids were released per second. Without the enzyme, 3.0 × 10–9 amino acids were released per second.
Calculate by how many times the rate of reaction is greater with the enzyme present.
Give your answer in standard form.

b) Lactulose can also be used to treat people who have too high a concentration of hydrogen ions (H+) in their blood.
The normal range for blood H+ concentration is 3.55 × 10–8 to 4.47 × 10–8 mol dm–3
A patient was found to have a blood H+ concentration of 2.82 × 10–7 mol dm–3
Calculate the minimum percentage decrease required to bring the patient’s blood H+ concentration into the normal range.
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UrbanIncentive
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Null
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HumbleBee_x
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I NEED HELP ON THIS

Some
prokaryotic cells can divide every 30 minutes. A liquid culture contained a
starting population of 1.35 × 104
cells.

Assuming each
cell divides every 30 minutes, calculate how many cells there will be after 3
hours. Assume no cells die during this time.
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HumbleBee_x
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I hate MATHS! these questions stress me out!
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ephemeral02
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(Original post by HumbleBee_x)
I NEED HELP ON THIS

Some
prokaryotic cells can divide every 30 minutes. A liquid culture contained a
starting population of 1.35 × 104
cells.

Assuming each
cell divides every 30 minutes, calculate how many cells there will be after 3
hours. Assume no cells die during this time.
I'm not 100% sure on this but if it divides every 30 mins, that means the population doubles every 30 mins. 3 hours = 6 x 30 mins, so it doubles 6 times, or 2^6. Multiply the original population by 2^6, i believe that's the answer.
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HumbleBee_x
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markscheme:

8.64
× 105;;

Accept 864 000 /
however expressed, e.g. 864 × 103 for 2 marks

Allow one mark
for

26 = 64

OR

64 / 26 × (1.35
× 104)



(Original post by ephemeral02)
I'm not 100% sure on this but if it divides every 30 mins, that means the population doubles every 30 mins. 3 hours = 6 x 30 mins, so it doubles 6 times, or 2^6. Multiply the original population by 2^6, i believe that's the answer.
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ephemeral02
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(Original post by HumbleBee_x)
markscheme:

8.64
× 105;;

Accept 864 000 /
however expressed, e.g. 864 × 103 for 2 marks

Allow one mark
for

26 = 64

OR

64 / 26 × (1.35
× 104)
yeah so 1.35x10^4 x 2^6 = 864000 = 8.64x10^5
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anonymoussse
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(1.35 × 104)*2
then do "ans*2" on ur calculator 5 times. which part of the question trips u up the most?
Last edited by anonymoussse; 2 years ago
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anonymoussse
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b) = 84.1



how much have u downgraded compared to ur original value? that's what % decrease means. use that and apply it to all % decrease questions.

if ur old value was 12 and it decreased to 3, ur % decrease is 9/12=75% because u have downgraded by 9 right? compared to what u had before, (12), what is the %? u didn't downgrade 100%, u've only downgraded 9/12=75% basically u've taken away 75% off ur original (12) value.

if ur ex was a 10, how much have u downgraded if ur new partner is a 4? u've downgraded by 6. now compare how much that is. 6/10=60%. u've downgraded a whole 60%
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anonymoussse
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a) = 578/(3.0*10^-9) then put that in standard form (2.72*10^1)
u might hate the maths in chemistry A2 , they are harder than these ones. which part do u find tricky
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HumbleBee_x
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why do you do 2^6 why isn't it just 6?

thankyou so much!!
(Original post by ephemeral02)
yeah so 1.35x10^4 x 2^6 = 864000 = 8.64x10^5
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HumbleBee_x
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where did you get 104 from?
I understand standard form, but when it comes to q's with a biological context I mess up!
(Original post by anonymoussse)
(1.35 × 104)*2
then do "ans*2" on ur calculator 5 times. which part of the question trips u up the most?
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HumbleBee_x
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yeah I understand that, but thankyou
and love the humour haha
(Original post by anonymoussse)
b) = 84.1



how much have u downgraded compared to ur original value? that's what % decrease means. use that and apply it to all % decrease questions.

if ur old value was 12 and it decreased to 3, ur % decrease is 9/12=75% because u have downgraded by 9 right? compared to what u had before, (12), what is the %? u didn't downgrade 100%, u've only downgraded 9/12=75% basically u've taken away 75% off ur original (12) value.

if ur ex was a 10, how much have u downgraded if ur new partner is a 4? u've downgraded by 6. now compare how much that is. 6/10=60%. u've downgraded a whole 60%
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ephemeral02
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(Original post by HumbleBee_x)
why do you do 2^6 why isn't it just 6?

thankyou so much!!
because whenever bacteria divides, it will double in size. say you start off with one bacteria and it divides once, that leaves you with two (1x2=2). then, the two each divide again, leaving you with four total (2x2=4). this means that every time it divides, you are multiplying the original number by two. because it will divide 6 times, you multiply it by two 6 times, which is 2x2x2x2x2x2 or 2^6. hope that makes more sense
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HumbleBee_x
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Thankyou so much!!! I understand.
(Original post by ephemeral02)
because whenever bacteria divides, it will double in size. say you start off with one bacteria and it divides once, that leaves you with two (1x2=2). then, the two each divide again, leaving you with four total (2x2=4). this means that every time it divides, you are multiplying the original number by two. because it will divide 6 times, you multiply it by two 6 times, which is 2x2x2x2x2x2 or 2^6. hope that makes more sense
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anonymoussse
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that happens a lot with a level. the actual question is easy but theyll scare u with context.
just ignore everything apart from the numbers and what u need to do with them, then treat the daunting numbers like more familiar ones....even in timed exams, u don't have enough time to understand everything. but it's okay because u don't need to. the context isn't always important. skim read everything and treat daunting questions as easy ones, because they are. theyre just disguised as hard
(Original post by HumbleBee_x)
yeah I understand that, but thankyou
and love the humour haha
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HumbleBee_x
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True indeed, the context does get me a bit stressed out
Timing is an issue for me too, I panic and just leave the maths Q's blank
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FatimaBegum844
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(Original post by HumbleBee_x)
I NEED HELP ON THIS

Some
prokaryotic cells can divide every 30 minutes. A liquid culture contained a
starting population of 1.35 × 104
cells.

Assuming each
cell divides every 30 minutes, calculate how many cells there will be after 3
hours. Assume no cells die during this time.
hii can you help me on this please
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oatesc
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(Original post by HumbleBee_x)
I NEED HELP ON THIS

Some
prokaryotic cells can divide every 30 minutes. A liquid culture contained a
starting population of 1.35 × 104
cells.

Assuming each
cell divides every 30 minutes, calculate how many cells there will be after 3
hours. Assume no cells die during this time.
so when the prokaryotic cells are dividing, they're dividing by 2 each time. If there is 6 lots of 30 minutes in an hour, the cells which be dividing 6 times, each by 2. There if you apply this to the question, (1.35 multiplied by 104) multiplied by 2 to the power of 6, which gives you the answer and then you can simplify it to 8.64.10 5
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Reality Check
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(Original post by oatesc)
so when the prokaryotic cells are dividing, they're dividing by 2 each time. If there is 6 lots of 30 minutes in an hour, the cells which be dividing 6 times, each by 2. There if you apply this to the question, (1.35 multiplied by 104) multiplied by 2 to the power of 6, which gives you the answer and then you can simplify it to 8.64.10 5
Please check the date of the original post before answering - this is over two years old, and the OP has now taken their exams and is working in Tesco.
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