Interaction and Interdependence — Free Biology SL Practice Questions

A researcher investigates an enzyme-catalysed reaction. The graph below shows reaction rate against substrate concentration under two conditions: no inhibitor (control) and with an inhibitor present. Graph description: Michaelis–Menten curves. Control curve: hyperbolic, $V_{max} = 100\,\mu\text{mol}\,\text{min}^{-1}$, $K_m = 2\,\text{mM}$. Inhibitor curve: hyperbolic, $V_{max} = 60\,\mu\text{mol}\,\text{min}^{-1}$, $K_m = 2\,\text{mM}$.

The enzyme lactate dehydrogenase (LDH) catalyses the reduction of pyruvate to lactate in human muscle cells during anaerobic respiration. A student investigates the effect of an inhibitor on the rate of this reaction. The student measures the initial reaction rate at various substrate (pyruvate) concentrations, both without the inhibitor and with a fixed concentration of the inhibitor. The results are shown in the graph below.

A student investigates the effect of an inhibitor on the enzyme catalase, which breaks down hydrogen peroxide ($\text{H}_2\text{O}_2$) into water and oxygen. The initial rate of oxygen production is measured at different $\text{H}_2\text{O}_2$ concentrations. The results are shown in the table below. $[\text{H}_2\text{O}_2]$ / mM — Rate without inhibitor / $\text{mL O}_2\,\text{min}^{-1}$ — Rate with inhibitor / $\text{mL O}_2\,\text{min}^{-1}$ 5 — 1.2 — 0.6 10 — 2.0 — 1.0 20 — 3.8 — 1.5 40 — 4.2 — 1.9 80 — 4.5 — 2.1 The Michaelis–Menten equation is: $v = \dfrac{V_{\max}[\text{S}]}{K_m + [\text{S}]}$

The graph below shows antibody concentration in the blood of a patient following two doses of a vaccine. The first dose was given on day $0$, and the second dose (booster) was given on day $28$.

A student investigates the effect of temperature on the activity of lysozyme, an enzyme found in tears and saliva. The student measures the rate of bacterial cell wall breakdown at different temperatures. The results are shown in the table below. Temperature ($^\circ\text{C}$) — Rate (arbitrary units) $10$ — $2$ $20$ — $5$ $37$ — $9$ $45$ — $12$ $55$ — $1$

In a clinical trial for a novel mRNA-based vaccine against a newly emerged viral pathogen, researchers measured the concentration of neutralising antibodies (IgG) in the blood of 50 volunteers over a 12-month period. The vaccine was administered in two doses: the first dose at day 0 and a booster dose at day 28. The mean antibody titres (in arbitrary units, AU) are shown below: Day — Mean antibody titre (AU) | 0 | 14 — 120 28 — 480 42 — 3200 90 — 2800 180 — 1500 360 — 600 A separate group of 50 volunteers who had previously recovered from natural infection with the same virus showed a mean antibody titre of $900\,\text{AU}$ at day 360 post-infection.

A researcher cultures yeast (Saccharomyces cerevisiae) in a chemostat and records the following data. Time / hours — Population / cells $\text{mL}^{-1}$ 0 — 50 2 — 100 4 — 200 6 — 400 | 800 | 10 — 1600 The exponential growth equation is $N_t = N_0 e^{rt}$, where $r$ is the intrinsic rate of increase and $t$ is time in hours. The doubling time is given by $t_d = \dfrac{\ln 2}{r}$.

A population of Escherichia coli is grown in a nutrient-rich broth in a closed flask. The initial population is $1000$ cells. The population doubles every hour during the first $6$ hours, reaching $64\,000$ cells at $t = 6\,\text{h}$. After $12$ hours the population stabilises at approximately $1 \times 10^{9}$ cells. $$N_t = N_0\,e^{rt} \qquad t_d = \frac{\ln 2}{r}$$

A population of Paramecium caudatum was cultured in a closed flask with a constant volume of nutrient medium. The population size was recorded every 24 hours. The culture medium was not replenished and waste products accumulated over time. Time (hours) — 0 — 24 — 48 — 72 — 96 — 120 — 144 — 168 — 192 — 216 — 240 Population (cells $\text{mL}^{-1}$) — 10 — 20 — 40 — 80 — 155 — 280 — 420 — 510 — 550 — 560 The following equations are provided: $$\frac{dN}{dt} = rN \quad \text{(exponential growth)}$$ $$\frac{dN}{dt} = rN\!\left(1 - \frac{N}{K}\right) \quad \text{(logistic growth)}$$

The graph below shows the rate of oxygen consumption by isolated mitochondria when different substrates are added to the medium.

A of a mitochondrion is shown below.

In a study of metabolic adaptation, scientists compare the efficiency of ATP production in two types of human muscle cells: slow-twitch (Type I, oxidative) and fast-twitch (Type IIb, glycolytic). They isolate mitochondria from both cell types and measure oxygen consumption and ATP synthesis under identical conditions (excess pyruvate, ADP, and oxygen).

A simplified food web from a lake ecosystem in Sweden is shown below.

A coral reef ecosystem contains the following food web: - Algae $\rightarrow$ Parrotfish $\rightarrow$ Moray eel $\rightarrow$ Reef shark - Algae $\rightarrow$ Zooplankton $\rightarrow$ Damselfish $\rightarrow$ Moray eel $\rightarrow$ Reef shark The moray eel assimilates $800\,\text{kJ}$ from damselfish and $200\,\text{kJ}$ from parrotfish. The reef shark assimilates $15\%$ of the moray eel's total assimilated energy.

A simplified food web for a freshwater lake ecosystem in temperate North America is shown below. Arrows indicate the direction of energy flow. The following data apply to this ecosystem: - Net primary productivity (NPP) of phytoplankton: $20{,}000\,\text{kJ}\,\text{m}^{-2}\,\text{year}^{-1}$ - Respiration rate of phytoplankton: $8{,}000\,\text{kJ}\,\text{m}^{-2}\,\text{year}^{-1}$ - Mean ecological efficiency between each trophic level: $12\%$ - Biomass of Largemouth Bass: $2.5\,\text{kg}\,\text{m}^{-2}$; energy content: $4{,}500\,\text{kJ}\,\text{kg}^{-1}$

A student investigated the rate of photosynthesis in pondweed (Elodea) by counting the number of oxygen bubbles produced per minute at different light intensities. The results are shown below. Light intensity (arbitrary units) — 0 — 20 — 40 — 60 — 80 — 100 Oxygen bubbles per minute — 0 — 8 — 15 — 20 — 22 — 23

In the light-dependent reactions of photosynthesis, electrons pass along an electron transport chain embedded in the thylakoid membrane. This generates a proton gradient across the membrane, which drives ATP synthesis. During active photosynthesis: - pH of the thylakoid lumen $\approx 4.5$ - pH of the stroma $\approx 8.0$

Isolated chloroplasts from spinach (Spinacia oleracea) were illuminated with saturating white light in the presence of $^{14}\text{C}$-labelled carbon dioxide ($^{14}\text{CO}_2$). The light was then switched off, and the concentrations of $^{14}\text{C}$-labelled 3-phosphoglycerate (3-PGA) and ribulose-1,5-bisphosphate (RuBP) were measured over the following 120 seconds. Time after light off — $[\text{3-PGA}]\ /\ \mu\text{mol}\,\text{mg}^{-1}$ chlorophyll — $[\text{RuBP}]\ /\ \mu\text{mol}\,\text{mg}^{-1}$ chlorophyll $0\,\text{s}$ — $12.0$ — $4.0$ $30\,\text{s}$ — $15.0$ — $1.5$ $120\,\text{s}$ — $18.0$ — $0.5$

A patient with multiple sclerosis (MS) has damage to the myelin sheaths of their neurons, slowing signal transmission. A researcher measures the speed of an action potential along a myelinated neuron from a healthy individual and finds it travels at $120\,\text{m s}^{-1}$. The distance between two adjacent Nodes of Ranvier is $1.2\,\text{mm}$.

A biologist stains two neurons from a rat: a sensory neuron from the skin and a motor neuron from the spinal cord. The sensory neuron has a long dendrite and a short axon; the motor neuron has a short dendrite and a long axon.

A researcher investigates how neuron structure affects the speed of nerve impulse conduction in the sciatic nerve of the frog Rana temporaria. She records the diameter and myelination status of three neuron types. Neuron — Myelination — Axon diameter A — Unmyelinated — $2.5\,\mu\text{m}$ B — Myelinated — $2.5\,\mu\text{m}$ C — Myelinated — $10\,\mu\text{m}$ For unmyelinated neurons, conduction speed $v \propto \sqrt{d}$, where $d$ is axon diameter. For myelinated neurons, $v \propto d$.

A medical researcher investigates autonomic dysreflexia in a patient with a complete spinal cord transection at the T6 level. The researcher stimulates the patient's skin below the injury site and records the following

A patient is admitted to hospital with severe dehydration following prolonged vomiting and diarrhoea. Blood analysis reveals that the sodium ion concentration in the plasma has risen from the normal range of $135$–$145\,\text{mmol dm}^{-3}$ to $158\,\text{mmol dm}^{-3}$. The patient's urine output is very low and has a high osmolality.

A researcher investigates the regulation of blood glucose concentration during moderate-intensity exercise. A healthy volunteer cycles at $70\%$ of maximal oxygen uptake for 30 minutes. Blood samples are taken at rest ($0\,\text{min}$), during exercise ($15\,\text{min}$), and after recovery ($45\,\text{min}$). Variable — $0\,\text{min}$ — $15\,\text{min}$ — $45\,\text{min}$ Plasma glucose $(\text{mmol}\,\text{L}^{-1})$ — $5.0$ — $5.8$ — $5.2$ Plasma insulin $(\mu\text{U}\,\text{mL}^{-1})$ — $12$ — $6$ — $10$ Plasma glucagon $(\text{pg}\,\text{mL}^{-1})$ — $80$ — $140$ — $90$ Plasma adrenaline $(\text{nmol}\,\text{L}^{-1})$ — $0.3$ — $2.5$ — $0.4$ The pancreas contains alpha cells (secrete glucagon) and beta cells (secrete insulin). The sympathetic nervous system innervates the pancreas via splanchnic nerves.