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How are the alveoli adapted for gas exchange?

The alveoli are covered by a rich blood supply of capillaries- this provides a diffusion gradient for oxygen to move into the blood and carbon dioxide to move into the lungs.The alveoli are also highly folde...
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Answered by Fergus L. • Biology tutor
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Ella has just finished running a half marathon. She hasn't been drinking enough water so is dehydrated and is feeling incredibly hot. Describe how her body responds to these changes. (6)

She is dehydrated so osmoreceptors in the hypothalamus shrink, this causes ADH to be secreted by the pituitary gland. The ADH travels in the blood stream and acts on the collecting ducts of the kidney nephro...
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Answered by Natasha H. • Biology tutor
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Edexcel 2017, Q8) A square, with sides of length x cm, is inside a circle. Each vertex of the square is on the circumference of the circle. The area of the circle is 49cm. Work out x.

First we should draw what the question tells us. Draws circle with square inside it We want to find out some extra information about the circle based on what we have been told. How can we do this?Well we kno...
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Answered by Alex B. • Maths tutor
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Why does differentiation work like it does.

Differentiation is about the tangent at a point, from GCSE we have a formula to work out the gradient between two points, in other words, the gradient of the tangent. This means that as the two points get in...
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Answered by Lucas F. • Maths tutor
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(a) Express (1+4*sqrt(7))/(5+2*sqrt(7)) in the form a+b*sqrt(7), where a and b are integers. (b) Then solve the equation x*(9*sqrt(5)-2*sqrt(45))=sqrt(80).

(a) We can ‘get rid of’ a square root in the denominator simply by multiplying by 1 (value of the fraction stays unchanged) in a suitable form. We will take advantage of this formula: (a+b) (a-b)=a^2-b^2. So...
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Answered by Kristina B. • Maths tutor
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