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When Does Respiration Occur in Plants? | Hunker
A higher photosynthetic capacity in sun plants does, however, incur some costs. The sun leaves tend to have higher respiration rates which increases the light-compensation point relative to shade plants (Figure 12.7). Higher respiration rates probably result from (1) increased carbohydrate processing in high light, (2) increased costs of constructing sun leaves and (3) a higher cost of maintaining sun leaves. Further details on maintenance costs are given in Chapter 5, Section 6.5.
In low light, plants need to absorb maximum light for photosynthesis if they are to survive. In high light the problem is reversed. Plants need to maximise their capacity for utilising their abundant light energy. At the same time, the plants have to deal with excess sunlight when their photosynthetic capacity is exceeded. As a consequence of such unrelenting selection pressures, plants have evolved a variety of features that optimise light interception, absorption and processing, according to the light environment in which they had evolved and adapted (Figure 12.2). Adaptation implies a genetically determined capability to adjust attributes, i.e., acclimate to either sun or shade. Such acclimation calls for adjustment in one or more attributes concerned with interception and utilisation of sunlight. Common features of either sun or shade plants are outlined below, and the advantage to plants growing in different light environments is discussed. Field applications are illustrated with examples of sun/shade acclimation and sunfleck utilisation in rainforest plants.
When Does Respiration Occur in Plants
As a rule, the major chemical transformations that occur in plants proceed by exactly the same series of steps in all species. For instance, take the process of respiration where sugars and starch are broken down to CO2 and H2O, yielding energy for living cells. It is almost certain that this proceeds by exactly the same 20 or so steps in species right across the Plant Kingdom. In fact, the same process also operates in yeast, mice and man.
Regardless of photosynthetic capacity, the ability of a plant to use sunflecks is also affected by the induction requirement of photosynthesis. When a leaf that has been in low light for some time is exposed to an increase in photon irradiance, the rate of photosynthesis does not increase instantaneously to the new level. Instead, there is a gradual increase in assimilation which can take from 10–60 min for completion. This ‘induction period’ varies according to species as well as the induction state of the leaf concerned. Three different processes are involved; namely (1) buildup of PCR cycle intermediates and in particular ribulose-1,5-bisphosphate (RuBP), (2) light-dependent activation of Rubisco, and (3) light-dependent opening of stomata. Each of these processes follows a different time-course. Buildup of a metabolite pool is fastest (1–2 min), followed by Rubisco activation (2–5min) and ﬁnally stomatal opening (up to 60 min). Relaxation in low light is more protracted but generally occurs in the same sequence, leading to a decline in the induction state.
Photosynthesis in Plants; Photosynthesis and ..
As we can see, there is a close relationship between the action spectrum and absorption spectrum of photosynthesis. There are many different types of photosynthetic pigments which will absorb light best at different wavelengths. However the most abundant photosynthetic pigment in plants is chlorophyll and therefore the rate of photosynthesis will be the greatest at wavelengths of light best absorbed by chlorophyll (400nm-525nm corresponding to violet-blue light). Very little light is absorbed by chlorophyll at wavelengths of light between 525nm and 625 (green-yellow light) so the rate of photosynthesis will be the least within this range. However, there are other pigments that are able to absorb green-yellow light such as carotene. Even though these are present in small amounts they allow a low rate of photosynthesis to occur at wavelengths of light that chlorophyll cannot absorb.
In addition to differences in leaf anatomy and chloroplast ﬁne structure, energy derived from absorbed sunlight is processed in ways that differ subtly between shade-grown and sun-grown plants. In high light, there is a requirement for greater capacity in both the light and CO2 fixation reactions of photosynthesis. Photosynthesis–light response curves for shade and sun plants (Figure 12.7) illustrate such differences. The initial slope of each light response curve represents the quantum or photon efﬁciency of photosynthesis. This is the same for sun and shade plants. The reason it does not change is that the efﬁciency of the light reactions is the same irrespective of how much light has been received during growth (i.e. eight photons are required for the evolution of one molecule of O2 and ﬁxation of one molecule of CO2 in all plants).
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The cycle of photosynthesis and respiration ..
Nevertheless, more experimental trials under the same conditions would be necessary to derive more accurate rates of photosynthesis and respiration. These results are collaborated by those found on the cable web-page, specifically Beer, et al. 2001 who reported significant changes in respiration rates similar to those in this experiment. Also, t-tests for both this study and the Fink et al. 2001 study showed there are no significant differences in photosynthesis rates between germinating and non-germinating peas.
If A Plant Carried Out Photosynthesis And Cellular ..
It appears that the dominant process occurring in germinating peas is respiration. Nonetheless, the data would suggest that seeds, in general, contain enough material to sustain respiration, during germination, without a significant contribution from photosynthesis until the plant matures enough to begin large-scale photosynthetic processes.
Can Photosynthesis and Respiration occur at the same …
Each experimental trial was performed at room temperature (21 - 24 degrees Celsius). This was important so that changes in photosynthesis or respiration were isolated to the peas biological processes and not due to a change in temperature. Ten non-germinating peas were weighed, then placed in a sealed bottle and the concentration of CO2 was monitored for a period of ten to twenty minutes. This time was equally divided between light and darkness and was long enough to derive an accurate slope, and consequently photosynthesis and respiration rates, from changes in CO2 concentration. Then ten germinating peas were measured, using the same procedure. A total of two runs for germinating peas and a total of two runs for non-germinating peas were completed for this experiment. The rates derived from these procedures were then divided by its groups corresponding mass. This standardized results so that quantitatively the data was equivalent among trials and not skewed by differences in mass.
Photosynthesis occurs in chlroplast ..
Measured photosynthetic capacities of understorey plants are often low. When a leaf experiences a sunfleck, carbon ﬁxation will increase to the point of light saturation. If an understorey plant could increase Pmax, it could utilise more light. But there are trade-offs. For example, higher respiration rates would increase the light-compensation point, and increase carbon losses during the low light periods separating sunflecks.
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