Question

The net photosynthetic production rate (NPP) is the difference between the rate of carbon fixation by photosynthesis (P) and the respiration rate (R). Each of these rates can be expressed in units of grams of carbon per day (gC/d). Vascular plants convert fixed carbon that is not released as carbon dioxide into biomass with a growth rate (G). A. Draw areas within the box to represent the rates of growth (G) and respiration (R) to show the limit of each on the overall growth rate. The area of the box represents the rate of photosynthesis (P). When the dependences on temperature of photosynthetic and respiration rates of a vascular plant are measured, the results depend on the species but have the general form shown in the figure. In these measurements, the temperature is maintained for several hours. The plant is then returned to 25 °C for several hours before the next set of measurements is made at a slightly higher temperature. B. Evaluate these data to approximately predict the quantitative effect on the NPP and free energy availability in a deciduous forest ecosystem with a $3-5-^{circ} mathrm{C}$ increase in temperature. This is the expected temperature increase by the year 2100. Assume the current average summer temperature of the forest ecosystem is $25^{circ} mathrm{C}$ In other experiments, rather than returning the plants to $25^{circ} mathrm{C}$ the plant is grown for several days at a constant higher temperature. Under these conditions, the maximum photosynthetic rate shifts towards the temperature of the new growing conditions. However, there is little change in the temperature dependence of respiration rate. This is referred to as temperature acclimation, an effect of great importance to predictions of future climate change. C. Pose two scientific questions whose pursuit could lead to either an improved understanding of the mechanisms of temperature acclimation or improvements in models of atmospheric carbon dioxide concentrations that control temperature. According to the graph, growth is predicted to increase when acclimation is taken into account and the average temperature increases of Earth’s surface increases by the expected $3-5^{circ} mathrm{C}$ . Growth enhancement may be reduced, however, if respiration increases more rapidly than photosynthesis, particularly under periods of drought and stress. Thus, climate warming may result in positive, negative, or potentially no effect on the free energy availability in forest ecosystems. D. In the figure below, the response to temperate change in terms of the rates of photosynthesis and respiration are sketched as a function of time from the very short-term (seconds) to the longer-term (decades) changes. Acclimation in the laboratory occurs in days. Analyze the graphs; in the box bounded by a dashed line, sketch curves for responses of both processes beyond the acclimation observed in the laboratory that are consistent with a neutral effect on free energy availability and provide your reasoning. E. Analyze the long-term effect of a rate of respiration that exceeds the rate of photosynthesis in terms of dynamic homeostasis.

The net photosynthetic production rate (NPP) is the difference between the rate of carbon fixation by
photosynthesis (P) and the respiration rate (R). Each of these rates can be expressed in units of grams of carbon per day (gC/d). Vascular plants convert fixed carbon that is not released as carbon dioxide into biomass with a growth rate (G).
A. Draw areas within the box to represent the rates of growth (G) and respiration (R) to show the limit of each on the overall growth rate. The area of the box represents the rate of photosynthesis (P).
When the dependences on temperature of photosynthetic and respiration rates of a vascular plant are measured, the results depend on the species but have the general form shown in the figure. In these measurements, the temperature is maintained for several hours. The plant is then returned to 25 °C for several hours before the next set of measurements is made at a slightly higher temperature.
B. Evaluate these data to approximately predict the quantitative effect on the NPP and free energy availability in a deciduous forest ecosystem with a $3-5-^{circ} mathrm{C}$ increase in temperature. This is the expected temperature increase by the year 2100. Assume the current average summer temperature of the forest ecosystem is $25^{circ} mathrm{C}$ In other experiments, rather than returning the plants to $25^{circ} mathrm{C}$ the plant is grown for several days at a constant higher temperature. Under these conditions, the maximum
photosynthetic rate shifts towards the temperature of the new growing conditions. However, there is little change in the temperature dependence of respiration rate. This is referred to as temperature acclimation, an effect of great importance to predictions of future climate change.
C. Pose two scientific questions whose pursuit could lead to either an improved understanding of the mechanisms of temperature acclimation or improvements in models of atmospheric carbon dioxide concentrations that control temperature. According to the graph, growth is predicted to increase when acclimation is taken into account and the average temperature increases of Earth’s surface increases by the expected $3-5^{circ} mathrm{C}$ . Growth enhancement may be reduced,
however, if respiration increases more rapidly than photosynthesis, particularly under periods of drought and stress. Thus, climate warming may result in positive, negative, or potentially no effect on the free energy availability in forest ecosystems.
D. In the figure below, the response to temperate change in terms of the rates of photosynthesis and respiration are sketched as a function of time from the very short-term (seconds) to the longer-term (decades) changes. Acclimation in the laboratory occurs in days. Analyze the graphs; in the box bounded by a dashed line, sketch curves for responses of both processes beyond the acclimation observed in the laboratory that are consistent with a neutral effect on free energy availability and provide your reasoning.
E. Analyze the long-term effect of a rate of respiration that exceeds the rate of photosynthesis in terms of dynamic homeostasis.

Added by Ashley S.

Biology for AP Courses

Julianne Zedalis, John Eggebrecht

Instant Answer

Solved by Expert Bryan Lynn

07/30/2019

Step 1

To draw the areas within the box, we need to consider the limit of each rate on the overall growth rate. The growth rate (G) will increase as long as the photosynthetic rate (P) is greater than the respiration rate (R). Therefore, we can draw an area for growth Show more…

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The net photosynthetic production rate (NPP) is the difference between the rate of carbon fixation by photosynthesis (P) and the respiration rate (R). Each of these rates can be expressed in units of grams of carbon per day (gC/d). Vascular plants convert fixed carbon that is not released as carbon dioxide into biomass with a growth rate (G). A. Draw areas within the box to represent the rates of growth (G) and respiration (R) to show the limit of each on the overall growth rate. The area of the box represents the rate of photosynthesis (P). When the dependences on temperature of photosynthetic and respiration rates of a vascular plant are measured, the results depend on the species but have the general form shown in the figure. In these measurements, the temperature is maintained for several hours. The plant is then returned to 25 °C for several hours before the next set of measurements is made at a slightly higher temperature. B. Evaluate these data to approximately predict the quantitative effect on the NPP and free energy availability in a deciduous forest ecosystem with a $3-5-^{circ} mathrm{C}$ increase in temperature. This is the expected temperature increase by the year 2100. Assume the current average summer temperature of the forest ecosystem is $25^{circ} mathrm{C}$ In other experiments, rather than returning the plants to $25^{circ} mathrm{C}$ the plant is grown for several days at a constant higher temperature. Under these conditions, the maximum photosynthetic rate shifts towards the temperature of the new growing conditions. However, there is little change in the temperature dependence of respiration rate. This is referred to as temperature acclimation, an effect of great importance to predictions of future climate change. C. Pose two scientific questions whose pursuit could lead to either an improved understanding of the mechanisms of temperature acclimation or improvements in models of atmospheric carbon dioxide concentrations that control temperature. According to the graph, growth is predicted to increase when acclimation is taken into account and the average temperature increases of Earth’s surface increases by the expected $3-5^{circ} mathrm{C}$ . Growth enhancement may be reduced, however, if respiration increases more rapidly than photosynthesis, particularly under periods of drought and stress. Thus, climate warming may result in positive, negative, or potentially no effect on the free energy availability in forest ecosystems. D. In the figure below, the response to temperate change in terms of the rates of photosynthesis and respiration are sketched as a function of time from the very short-term (seconds) to the longer-term (decades) changes. Acclimation in the laboratory occurs in days. Analyze the graphs; in the box bounded by a dashed line, sketch curves for responses of both processes beyond the acclimation observed in the laboratory that are consistent with a neutral effect on free energy availability and provide your reasoning. E. Analyze the long-term effect of a rate of respiration that exceeds the rate of photosynthesis in terms of dynamic homeostasis.

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Transcript

00:01 Okay, so this problem, 110 has a lot of parts to it.

00:05 So this is a, it would be a longer video, but bear with.

00:09 And part a gives us this sort of big black square, and it says, well, this is our photosynthesis.

00:19 Okay.

00:21 And then it asks us, well, how do, you know, the rates of respiration compare with, with this and the rates of growth.

00:35 Okay, so respiration, respiration rate should be less than the rate of photosynthesis rate.

00:44 So this can be our respiration.

00:48 And the thing is respiration, some of it goes towards metabolism, but then another portion of it, the portion of the respiration goes to growth.

00:58 And the point of this is not to have the precise portion is exactly correct, is that's going to vary depending on some external factors, which we'll see in later parts, but just sort of knowing how they're nested.

01:13 Right, so this was part a, and then we can kind of move on then to part b here.

01:19 And b gives us this nice graph on how these respiration rates vary with temperature, and it says, okay, so we're in a forest whose typical temperature is 25, okay? so that puts us sort of in this portion of the graph.

01:41 This is where we're at.

01:43 And then it says, well, the temperature is increased, has increased three to five degrees.

01:48 That sort of moves us to this next data point.

01:51 So that's where our focus is.

01:54 Okay.

01:55 I'm just going to get rid of those lines to, so we don't sort of put too much on that graph, make it hard to read.

02:03 And then what it asks, us is, well, what would you expect to happen in that increase of temperature? well, if we look at what happens between those data points, we see that the respiration increases and the photosynthesis rate decreases.

02:18 So maybe that's what i would expect to happen if the temperature goes up by five degrees.

02:25 And so that's sort of what b is getting on.

02:30 Okay, but then it goes on to tell us, well, it turns out that when the temperature is, increases, so instead of the photosynthesis decreasing and the respiration rate increasing, you'll see that this whole arc that sort of peaks, peaks above our ideal temperature will move to the right.

02:58 And so instead, it would peak above our new temperature, right? however, the respiration rate does not do the same thing.

03:11 So the respiration rate is just kind of stay where it is for that increased temperature.

03:20 And so this is called acclamation.

03:25 And so part c wants us to pose a couple of questions.

03:28 And there's no right answer then to this.

03:32 This is sort of just a, it's just thinking scientifically.

03:37 And so if then the photosynthesis rate, so if our photosynthesis rate is able to stay at its sort of max, max, but the peak with the respiration rate has increased from where it was before the difference, the difference between the photosynthesis rate and the respiration rate is now higher.

04:03 Right? so that means this difference between our max up here and the photosynthesis rate is higher than it was here.

04:17 Okay, and so that means we're respiring more.

04:21 And so why i would ask, why doesn't the plant dry out? okay, because we lose water during respiration...

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