IB Biology – Theme C: Interaction and Interdependence

(a) Using the induced-fit model, describe how an enzyme’s active site interacts with its substrate.(b) Explain why enzyme activity decreases sharply above the optimum temperature.

(a) Write the overall balanced chemical equation for aerobic cell respiration of glucose.(b) State the location in the cell where the majority of ATP is produced during aerobic respiration.

Yeast can respire anaerobically, producing ethanol, while human muscle cells can respire anaerobically, producing lactate.(a) Write a word equation for anaerobic respiration in yeast.(b) State one similarity and one difference between anaerobic respiration in yeast and in human muscle cells.

Germinating seeds were placed in a respirometer. Over a fixed time, they consumed $17.1\,\text{cm}^3$ of oxygen and produced $12.0\,\text{cm}^3$ of carbon dioxide.(a) Calculate the respiratory quotient (RQ), given $\text{RQ} = \dfrac{\text{volume of CO}_2\text{ produced}}{\text{volume of O}_2\text{ consumed}}$.(b) Suggest, with a reason, the main respiratory substrate being used.

(a) Write the overall balanced equation for photosynthesis.(b) State the region of the chloroplast where the light-dependent reactions occur and the region where the light-independent reactions (Calvin cycle) occur.

In an experiment, the rate of photosynthesis of an aquatic plant was measured (as bubbles of oxygen produced per minute) at increasing light intensity, with $\text{CO}_2$ concentration and temperature kept constant. The rate increased steadily at low light intensities but then levelled off at high light intensity.Explain, in terms of limiting factors, why the rate of photosynthesis levels off at high light intensity even though more light is available.

The hormone insulin binds to a receptor protein on the surface of liver cells, triggering a series of intracellular events that result in glucose uptake and glycogen synthesis.Outline the three general stages of a cell-signalling pathway (reception, transduction, response), using insulin as your example.

Explain how an enzyme cascade during signal transduction can amplify a single signalling event into a much larger cellular response.

(a) Distinguish between the innate and adaptive (specific) immune response.(b) Explain why the secondary immune response to a pathogen is faster and stronger than the primary response.

HIV (human immunodeficiency virus) infects and destroys helper T-cells, eventually leading to AIDS (acquired immunodeficiency syndrome).Explain why the destruction of helper T-cells severely weakens the overall immune response.

In a grassland ecosystem, producers have a gross energy content of $20\,000\,\text{kJ m}^{-2}\,\text{yr}^{-1}$, and the energy available to the primary consumer trophic level is $1800\,\text{kJ m}^{-2}\,\text{yr}^{-1}$.(a) Calculate the percentage efficiency of energy transfer between these two trophic levels.(b) State two reasons why energy transfer between trophic levels is never 100% efficient.

A student estimates the population size of snails in a field using the mark–release–recapture (Lincoln index) method. She marks and releases $50$ snails. Later, she catches $60$ snails, of which $12$ are already marked.(a) Use the Lincoln index, $N = \dfrac{(\text{number marked}) \times (\text{total caught second time})}{\text{number of marked individuals recaptured}}$, to estimate the total population size.(b) State one assumption of this method.