Search our library of homework questions

Top answers

All subjects

All levels

Guard cells open and close stoma in different conditions. When light intensity is high, potassium ions move into guard cells. Describe how this movement of potassium ions causes the stoma to open.

When the potassium ions move into the guard cells they increase the concentration. This causes water to move into the guard cells from more dilute areas by osmosis. The additional water leads to the guard...

Answered by Emily W. • Biology tutor

30003 Views

P is a point on a circle with the equation x^2 + y^2 = 45. P has x-coordinate 3 and is above the x axis. Work out the equation of the tangent to the circle at point P.

First insert x = 3 into the equation of the circle3^2 + y^2 = 459 + y^2 = 45 take 9 away from both sidesy^2 = 36 take the square root of both sidesy = 6 (not -6 as P is above the x-axis)Next find the grad...

Answered by Emily W. • Maths tutor

3219 Views

Calculate the pH of a 0.0131 mol dm^-3 solution of calcium hydroxide at 10 degrees centigrade.

Multiply by 2 because calcium hydroxide = Ca(OH)2 so 2 x [OH-] per molecule.[OH-] = 0.0131 x 2 = 0.0262
Insert [OH-] value into the equilibrium equation along with the value of Kw at 10 degrees centi...

Answered by Emily W. • Chemistry tutor

8036 Views

Explain why adding small amounts of acid or base hardly changes the pH of an acidic buffer solution.

An acidic buffer solution is made up of a weak acid (e.g. ethanoic acid) and a salt containing its conjugate base (e.g. sodium ethanoate). It resists pH change via two mechanisms: The fact that the acid i...

Answered by • Chemistry tutor

6540 Views

The genetic code is described as degenerate, universal and overlapping. Explain these terms.

The genetic code is universal because all species use the same four bases A,T,C and G, and each base sequence codes for the same amino acid in all species. despite the 64 possible codons (sequence of thre...

Answered by Emily W. • Biology tutor

43809 Views