23278 questions

Why does deforestation occur and what are its effects?

Deforestation occurs for a variety of reasons. These are some of the main causes of deforestation. Countries require food and in order for food to be grown farms are necessary. In order to create space hundreds of acres of forest are cut down for each farm.  Logging is another reason for deforestation. Logging can be very profitable and therefore hundreds of thousands of trees are cut down every year to be sold. Rarer trees fetch a higher market value and therefore they are targeted by loggers, which is reducing biodiversity and causing some species to become endangered. Extraction of minerals is also another cause of deforestation. Quarries require a huge amount of area and due to the complete destruction of the land regrowth once the quarry has stopped being used is almost impossible.  Hydropower requires large dams, which require a large amount of land to be flooded. Although this isn't directly cutting down the trees they are unable to survive whilst being flooded and therefore thousands die. The pollution that sometimes occurs in rivers can also poison the forest and cause the trees to die. Finally, population pressure can cause deforestation, especially in areas where space is limited.    The impacts of deforestation can be serious and wide reaching. The effects of deforestation vary with location and extent of deforestation. Deforestation has a significant impact on the environment, the most dramatic of which is the loss of habitat for millions of species. Forests also play a vital role in the hydrological cycle. They protect the soil from drying out by protecting it from the sun and ensure water returns back to the atmosphere. Forests also absorb thousands of tons of CO2 every year and without them greenhouse gases in the atmosphere will increase, leading to increased global warming. Forests also reduce the impact of floods. Without them the impact of floods will increase significantly, as seen in Bangladesh. Those that rely on forests for their livelihood and survival are finding it increasingly difficult to do so as more and more of their home is destroyed. This includes indigenous populations who use the forests for most aspect of their lives and people who rely on the tourist industry brought in by the forests such as the rainforests of Brazil. Deforestation reduces the natural beauty and therefore could threaten the tourism industry. If the tourism industry is affected it can affect the economy of the country which can further impact any measures to reduce/ recover forests, further increasing the problem (a positive feedback loop). Increasing impacts of floods will also cost more to repair, and protection from floods doesn't come cheap. 
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Sarah M.

Answered by Sarah, Geography GCSE tutor with MyTutor


What is cross bridge cycling and why is it important in muscle contraction?

In order to understand cross bridge cycling and its importance in muscle contraction, you need to be familiar with the ‘contractile machinery’ that causes muscle contraction and the sliding filament theory. To briefly recap, muscle contraction occurs when the thin filament, actin, slides past the thick filament, myosin - This is essentially the sliding filament theory.   The mechanism that causes the actin filaments to slide past myosin in skeletal muscle in brief is as follows:  remembering that a sarcomere is the stretch of myofibril between two z lines where myosin in central and an actin filament is both above and below the myofibril on each side of it, with its medial side slightly overlapping myosin and its lateral side attached firmly to the z line . Nerve impulse arrives at muscle, causing release of calcium from the sarcoplasmic reticulum of muscle fibre Troponin is bound to tropomyosin which is bound to actin. When the muscle is at rest, tropomyosin is sitting in such a position, that it is covering the binding sites for myosin heads on actin. Calcium bind to troponin. This causes it to undergo a conformational change which pulls the tropomyosin it is attached to out of its resting position, exposing binding sites for myosin heads on actin. Myosin heads covalently bind to the exposed binding sites.  The myosin head undergoes a conformational change which pulls the actin along. It then releases the actin, returns to its original conformation, extending out laterally again and forms a bind with another actin binding site that is further along the actin and closer to the z line. This repeated motion is what causes the sliding of the actin filament past myosin. Cross bridge cycling refers specifically to the action of the cross bridge, that being the head and hinge region of the myosin filament. It is essentially acting like a bridge when the head is covalently bonded to actin, and this bridge is continuously being formed and broken during muscle contraction-the cross bridges are being cycled, and it is this action which is allowing for the filaments to slide the way they do. The cross bridge cycle can be broken down as follows: Hydrolysis of ATP to ADP and Pi, with products still covalently bonded to myosin, cause it to enter an energised state. Cross bridge binds to actin. It undergoes a conformational change. ADP and Pi are released. You then get a power stroke (ie cross bridge moves, pulling actin along which causes the power stroke (ie the cross bridge moves pulling the actin along) ATP binds to myosin, causing cross bridge to detach. The process starts again.
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Moonisah S.

Answered by Moonisah, Biology A Level tutor with MyTutor


How should I cross-reference sources well in an exam?

It can be daunting to have to use sources in an exam situation, as it provides another unknown: as well as not knowing what topic the question will be on, you also don't know what the sources will be. But this can also be an advantage, as even if you don't know the topic that well, you can use information from the sources to help you answer the question.  As with all exam questions, the first thing is to read the question and the sources carefully. Think about how the sources can be used to answer the question - do they support what it says, or do they oppose it, and how do they do this? You of course also need to think about the origins of the source - who was it written by, when, and with what likely intention? Another of the key things is to think about how they work together. This is cross-referencing, and a really key A Level skill. You need to compare and contrast the sources to see how they work as a group in answering the question. For example, you might write that sources A and C support the question, as they have similar ideas, but source B is opposed to them and comes from a very different perspective. Or, that while source A discusses x as the main reason, the author of source B suggests it is y, which source C also supports. It can be helpful to talk about the sources in a different order from how they are presented in order to make these connections, so you might talk about source B first, link it to source C, and then talk about source A at the end, or however this works best to make the links between them.  Then you also need include a conclusion, as with all your exam answers. In this, you should aim to answer the question given. If this is in the form of 'How far do these sources suggest...' then think about to what extent they do suggest this. So this could be: sources B and C both suggest that x was true, but source A does not, so in conclsion, these sources support the idea of x. But if you have cross-referenced successfully throughout the essay, then you will just be summarising your ideas in the conclusion, not making the connections for the first time. 
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Poppy C.

Answered by Poppy, who tutored History A Level with MyTutor


How do I form the present subjective in French?

French Present Subjunctive First thing to know – the subjunctive is not a tense but a mood. So if you’re getting a bit moody struggling through the subjunctive, keep reading… Regular verbs The present tense subjunctive is formed by conjugating –ER, -IR, and –RE verbs into the present third person plural (‘they’ or ils), removing the ‘ent’ ending and then adding the endings (-e, -es, -e, -ions, -iez, -ent) to the stem. ·     For example:To say “it is necessary that the government understand the importance of secondary education” you take the infinitive of the verb ‘understand’ (comprendre), conjugate it (compredent), make it into a subjunctive stem (comprend-) and then add the first person singular ending, ‘e’. So…Il est necessaire que* le gouvernement comprende l’importance de l’education scholaire. *Remember – if you’re stuck on when to the use the subjunctive, it is always placed after ‘que’. ·     Another example: It is important that the girls finish their homework tomorrow.Il est important que les filles finissent leurs devoirs demain.  Nasty Irregulars Of course, life is never that simple. You’ve got to tackle the irregular verbs too, especially as there are many commonly used ones in the subjunctive. The most important ones are être, avoir, faire, and aller. Although there is a slight pattern in the subjunctive endings, as with all irregulars you just have to learn them, as the stems look quite different from the original infinitive. Être: je sois, tu sois, il soit, nous soyons, vous soyez, ils soient.Avoir: j’aie, tu aies, il ait, nous ayons, vous ayez, ils aient.Faire: je fasse, tu fasses, il fasse, nous fassions, vous fassiez, ils fassent.Aller: j’aille, tu ailles, il aille, nous allions, vous allies, ils aillent. 
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Florianne H.

Answered by Florianne, French GCSE tutor with MyTutor


How can I stop 'feature spotting' in an exam?

'Feature spotting' is a term that teachers often throw around in classrooms, and sometimes never fully explain. This can lead students feeling confused and frustrated. This was a problem that I used to have, before I established what  'feature spotting' actually was. Basically, 'feature spotting' is when you simply name the different techniques used by an author in a piece of text. So in a question such as 'Compare how Marvell uses language to present ideas and feelings in 'To His Coy Mistress'', instead of analysing the way that the features work you will simply state what Marvell uses. Feature spotting - 'The structure of To His Coy Mistress is split up into 3 stanzas. Marvell uses exaggeration here. He then uses explicit imagery here, to back up the exaggeration. He then uses alliteration here.'   Answering the question - 'Marvell structures To His Coy Mistress as a three pronged attack upon the female addressee, starting in the first stanza by using flattery and extremely exaggerated imagery. 'I would / Love you ten years before the flood, / And you should, if you please, refuse / Till the conversion of the Jews.' The images that Marvell conjures up - the notion of the speaker's love existing before the Flood, and for it to last until the conversion of the Jews - is farsical as the whole idea is that the Flood happened an impossibly long time ago, and Jews do not convert. This imagery helps to present the idea that the speaker in To His Coy Mistress loves the addressee for a particularly long time, due to the farsical, unimaginable comparisons that Marvell is alluding to. 
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Annie D.

Answered by Annie, English Literature A Level tutor with MyTutor


How can I write a good introduction?

To write a good introduction, first re-read the question and underline any key phrases - try to really understand what the question is asking. In your introduction you need to outline what your argument will be. This argument should be maintained throughout the whole essay by using your main body paragaphs to give analysis and evidence to back it up. For the first line you can use it to provide a context or background to your argument. Then provide your main thesis, or argument. This shows how you are choosing to answer the question and what your argument is. You should then set out what your essay will look like in order that the marker can have a clear view of what is to come. To do this give a mini introduction into each of your body paragraphs, they only need to be a sentance each. 
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Anna G.

Answered by Anna, English IB tutor with MyTutor


How do I write a personal statement for English Literature?

For your personal statement, you should show off your academic ability by using practical examples. For example, if you enjoyed studying Frankenstein for AS Level, you could talk about how this sparked your interest in Feminist Literary theory. This could link to activities such as involvement in groups like Amnesty International, and thus you are placing your passion for your subject in a real world context. 
Using quotes may be relevant, but don't be cliche, it won't impress the University you are applying to. Equally, keep your extra-curricular activities relevant- if you love unicycling, great, but how is that relevant? It probably isn't. Nevertheless, if you are head of your school's unicycling club, then this could be used as an example of leadership.
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Lettie B.

Answered by Lettie, Personal Statements University tutor with MyTutor


How do I find the nth term of a sequence?

For any sequence where there is a common difference (it increases or decreases with the same amount, n, each time) you can find the nth term using the formula: dn+(a-d)"a" is the value of the first term in the sequence"d" is the common difference between the termsTo find the nth term you find the values of "a" and "d" and stick them in the formula, dn+(a-d)For example: Find the nth term of this sequence: 3,7,11,15The first term is 3, so a=3The common difference is 4 (as it increases by 4 each time), so d=4By using the formula we get, 4n+(3-4), which is equal to 4n-1We can check this works by subbing in values of n into the formula and you will see that it is correct. 
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Laura M.

Answered by Laura, Maths GCSE tutor with MyTutor

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