Many biological graphs are curves, for example the volume of product formed by an enzyme over time. On a curve the rate is changing, so it cannot be found from a single gradient for the whole line.The rate at a particular moment is found by drawing a tangent. A tangent is a straight line that touches the curve at one point and has the same gradient as the curve at that point.The gradient of the tangent (change in y ÷ change in x) gives the rate at that time.
The initial rate is found by drawing a tangent to the curve at time zero. Initial rates are used to compare enzyme reactions because at the start the substrate concentration is known and has not yet been reduced.As an enzyme reaction continues, the curve levels off because the substrate is being used up, so the gradient and the rate decrease. When the curve is flat, the reaction has stopped.Draw the tangent with a ruler and make it long, so that the changes in x and y can be read accurately.
The initial rate is found by drawing a tangent to the curve at time zero. Initial rates are used to compare enzyme reactions because at the start the substrate concentration is known and has not yet been reduced.As an enzyme reaction continues, the curve levels off because the substrate is being used up, so the gradient and the rate decrease. When the curve is flat, the reaction has stopped.Draw the tangent with a ruler and make it long, so that the changes in x and y can be read accurately.