22964 questions

When do I use the passato prossimo versus l'imperfetto?

The passato prossimo is used in the majority of cases and is used to describe finished actions that happened once. For example: ho mangiato instead of mangiavo. However, l'imperfetto is used for actions that are either continuous or repeated. For example: when I was younger would be 'quando ero piccolo/a' as you were young for a period of time. A simple way to remember the difference is to think if in English we would say 'I was eating' then we would use l'imperfetto as it is an incomplete or continuous action. For example, we might say 'mentre mangiavo, ho guardato la TV' (whilst I was eating, I watched the TV).
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Phoebe C.

Answered by Phoebe, Italian GCSE tutor with MyTutor

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Explain the process of DNA replication, including the names of vital enzymes

DNA replication is used to copy DNA. This process is semi-conservative, meaning the new double helix contains both a parent and a new strand. The process begins during S phase, where helicase unwinds the DNA helix in a 5' to 3' direction. This breaks the hydrogen bonds between bases. On the leading strand, RNA primase adds primers complementary to the bases on the parent strand. DNA polymerase III then adds dNTPs to complete the strand, which lose two phosphate groups to ensure a continuous formation of the leading strand strand. The primer is removed by DNA polymerase I. On the lagging strand, RNA primase again adds primers, followed by DNA polymerase III adding dNTPs in a 5' to 3' direction. However, this movement is away from the replication fork and does not allow for continuous assembly. Okazaki fragments are therefore left when DNA polymerase I removes the primer. These fragments are joined together by DNA ligase, which makes sugar/phosphate bonds allowing a full strand to be synthesised.
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Farrah V.

Answered by Farrah, Biology IB tutor with MyTutor

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Explain the process of DNA replication, including the names of vital enzymes

DNA replication is used to copy DNA. This process is semi-conservative, meaning the new double helix contains both a parent and a new strand. The process begins during S phase, where helicase unwinds the DNA helix in a 5' to 3' direction. This breaks the hydrogen bonds between bases. On the leading strand, RNA primase adds primers complementary to the bases on the parent strand. DNA polymerase III then adds dNTPs to complete the strand, which lose two phosphate groups to ensure a continuous formation of the leading strand strand. The primer is removed by DNA polymerase I. On the lagging strand, RNA primase again adds primers, followed by DNA polymerase III adding dNTPs in a 5' to 3' direction. However, this movement is away from the replication fork and does not allow for continuous assembly. Okazaki fragments are therefore left when DNA polymerase I removes the primer. These fragments are joined together by DNA ligase, which makes sugar/phosphate bonds allowing a full strand to be synthesised.
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Farrah V.

Answered by Farrah, Biology IB tutor with MyTutor

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What does it mean for an argument to be valid?

An argument is valid if and only if the following is impossible: all of the premises are true and the conclusion is false. E.g. the argument below is valid:
(1) All men are mortal
(2) Socrates is a man
(3) So, Socrates is mortal
The argument is valid because it cannot be the case that (1) and (2) are both true while (3) is false. The following argument, by contrast, is invalid:
(1) Some men have beards
(2) Socrates is a man
(3) So, Socrates has a beard
This argument is invalid because it could be the case that (1) and (2) are both true while (3) is false. After all, it could be the case that Socrates is one of those men who don't have a beard.
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Oliver H.

Answered by Oliver, Philosophy A Level tutor with MyTutor

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What is an action potential, and what steps are involved?

Action potentials are changes of electrical potential in a cell. The normal resting membrane potential inside cells is around -70mV. This membrane potential is maintained through the action of the Na+K+ATPase pump (which moves 3Na+ out and 2 K+ in), leaky Na channels (that allow influx of Na+) and leaky K+ channels (that allow efflux of K+). The net movement of Na+ and K+ is balanced at this point.
An action potential starts when Na+ channels open and Na+ starts moving into the cell. This starts depolarisation of the cell, where the membrane potential starts increasing. At around -30mV a threshold is met. This is an all or nothing response, if enough stimulus is present all the voltage-gated Na+ channels open causing a rapid depolarisation of the cell. When the membrane potential reaches around +30/40mV the Na+ channels close, and the voltage-gated K+ channels open at the same time. As K+ starts moving into the cell, it starts repolarisation of the cell - the membrane potential starts moving down. The K+ channel remain open past -70mV and eventually close when the potential reaches -90mV - this is known as hyperpolarisation. The action of the Na+K+ATPase pump then brings the cell back to its resting membrane potential (-70mV). At this point a second action potential can occur.
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Claudia L.

Answered by Claudia, Human Biology GCSE tutor with MyTutor

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Define Populism. Can populism ever be democratic?

Populism separates societies into two homogenous and antagonistic groups: the corrupt elites and the pure people. Populists claim that they alone represent the will of the people, implying that opponents are illegitimate political actors. This anti-elitism and anti-pluralism often goes hand in hand with oversimplifications of the political processes.
By channeling the will of the people into political action, populists claim that they are the purest democratic actors. But modern democracy - or liberal democracy - is defined by the checks and balances to majority rule such as minority rights, separation of powers, and the rule of law. Populists oppose these features because they mediate the will of the people. The inherent anti-pluralism of populism also makes it incompatible with political party-based representative democracy.
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Leonard S.

Answered by Leonard, Politics University tutor with MyTutor

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Solve x^2 + 7x + 10 = 0

First factorise the quadratic into the form (x + a)(x + b) = 0.This will make x^2 + ax + bx + ab = 0.Work out a and b so that a + b = 7 and a*b = 10.a = 5 b = 25+2 = 7 5*2 = 10.
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Simone K.

Answered by Simone, Maths GCSE tutor with MyTutor

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A guitar string 0.65m long vibrates with a first harmonic frequency of 280Hz. Mary measures 1m of the string and discovers that it weighs 8.0x10^-4 kg. What is the tension in the guitar string?

f = 280 Hz, l = 0.65 m, μ = 8x10^-4 kgm^-1
Therefore use the equation f=(1/2l)(T/μ)^1/2
Rearrange it to get it in the form T= by multiplying f by 2l, squaring both sides and then multiplying by μ to getT = μ*(2lf)^2(This can also be simplified to T = 4μ*l^2*f^2 )
Then simply plug in the numbers that we gathered from the questionT = 4*8x10^-4*0.65^2*280^2T = 4*8x10^-4*0.4225*78400T = 105.9968 N
The numbers in the question were to two significant figures, so round to two significant figuresT = 110 N
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Evie S.

Answered by Evie, Physics A Level tutor with MyTutor

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