Chapters
- How is Rice Adapted for Anaerobic Respiration?
- Adaptations of Rice Plant for Aerobic Respiration
- Adaptations of Rice Plant for Anaerobic Respiration
- Effects of Temperature and Substrate Concentration
- Mechanism
- Investigating How Temperature and Substrate Concentration Affect the Respiration Rate in Yeast
- Effect of Temperature: Respirometer
In this article, we will discuss how rice is adapted to grow with its roots submerged in water, limited to the development of aerenchyma in roots, ethanol fermentation in roots, and faster growth of stems. Furthermore, we will describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast. In the end, we will elucidate and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration. So, let us get started.
How is Rice Adapted for Anaerobic Respiration?
One of the major problems faced while growing crops is flooding. When the level of water rises and it covers various parts of the plant, it can prevent the plant from getting the oxygen needed for aerobic respiration. Moreover, the plants' leaves do not get the required carbon dioxide for photosynthesis.
Both oxygen and carbon dioxide are less available in water because they diffuse slowly in liquid than in air. Rice plants are adapted to grow and survive in waterlogged conditions.
Adaptations of Rice Plant for Aerobic Respiration
- Few types of rice plants exhibit an enhanced rate of upward growth away from the waterline. It implies that the leaves always remain above the water line so that they can have access to the required gases, i.e. oxygen and carbon dioxide through stomata.
- Rice plants contain aerenchyma tissue in their stems and roots.
- This specialized tissue has important air spaces that enable gases that enter the stomata to diffuse to the other parts of the plants that are present above and under the waterline.
- This tissue can therefore hold oxygen and carbon dioxide even when it is underwater. These gases can be moved from plants parts that can access air.
Adaptations of Rice Plant for Anaerobic Respiration
- When sufficient energy is not supplied to the cells through aerobic respiration, then the plants turn to anaerobic respiration as a source of ATP
- Plants employ ethanol fermentation during anaerobic respiration. Harmful ethanol is generated which can accumulate in plant tissue and cause damage
- Rice plants can bear higher levels of toxic ethanol as compared to other plants.
- Moreover, they also produce more ethanol dehydrogenase which is an enzyme that breaks down ethanol.
- Rice plants are resistant to ethanol which enables them to carry out anaerobic respiration for long enough so that sufficient ATP is produced for the plant which allows it to survive and actively grow.
In the next section of the article, we will describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast.
Effects of Temperature and Substrate Concentration
- A redox indicator refers to a substance that alters colour when it is reduced or oxidized.
- Examples of redox indicators include DCPIP and methylene which are employed to investigate the effects of temperature and concentration of substrate on the respiration rate in yeast
- We can add these indicators to a suspension of living yeast cells because they do not damage the cells
- Yeast can respire aerobically as well as anaerobically. In this particular experiment, we will just investigate their anaerobic respiration rate.
Mechanism
- Dehydrogenation occurs regularly throughout various stages of aerobic respiration
- The hydrogens that are removed from the substrate molecules are moved to the last stage of aerobic respiration, oxidative phosphorylation through the hydrogen carriers like NAD and FAD.
- In the presence of DCPIP and methylene blue, they can also take up hydrogens and get reduced
- Both of these redox indicators DCPIP and methylene blue undergo the same change in colour when they get reduced, i.e. from blue to colourless
- If the rate of respiration is rapid, then the rate of release of hydrogen is also faster. Moreover, the dyes get reduced and change colour faster. It implies that the rate of colour change is related to the rate of respiration in yeast.
- There is an inverse relationship between the respiration rate and time taken.
Rate of Respiration (
) = 
Investigating How Temperature and Substrate Concentration Affect the Respiration Rate in Yeast
- We can investigate the effect of temperature by adding the test tubes that have the yeast suspension to a temperature-controlled water bath. After the addition of the dye, we can record the time it takes to change the colour.
- This step should be repeated across the range of temperatures, for instance, 30oC, 35oC, 40oC, 45oC
- Investigate the effect of substrate concentration by adding varying concentrations of a substrate to the yeast cells suspension. After that, record the time it takes to change the colour after the addition of the dye. For instance, 1% glucose, 0.5% glucose, 1.0% glucose.
How can we control other variables?
- When investigating a single variable, it is critical to ensure that other variables in the experiment are being controlled. These variables include:
- The volume of dye added: In the presence of more dye molecules, more time will be taken to change the colour
- The volume of yeast suspension: The rate of respiration will be increased in the presence of more yeast cells
- Substrate type: Yeast cells will respire various substrates at varying rates
- Substrate concentration: Respiration in yeast cells will be limited when there is a limited substrate in one tube.
- Temperature: An increase or decrease in temperature can influence the respiration rate because of changes in kinetic energy and energy demands. We should also consider the temperature of the dye that is being added.
In the next section, we will elucidate and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration.
Effect of Temperature: Respirometer
- The purpose of respirometers is to measure and investigate the oxygen consumption rate during aerobic respiration in organisms.
- When we add the apparatus to a water bath that is controlled thermostatically, we can investigate the effect of temperature on respiration rate.
Procedure
- Step 1: Measure the consumption of oxygen by setting up the respirometer and running the experiment with both the tubes in a controlled water bath. A manometer reading is used to compute the change in volume of gas within a given time.
- Step 2: Reset the apparatus by allowing the air to enter the tubes again through a screw cap and reset the manometer fluid using a syringe. After that, change the water bath temperature and allow the tubes to acclimate. In the end, close the screw clip to start the experiment.
- Step 3: Run the experiment again by employing the manometer reading to compute the change in volume of gas in a given time.
Repeat the experiment many times at different temperatures.
Calculations
The oxygen volume consumed can be calculated using the diameter of the capillary tube and the distance covered by the manometer fluid in a minute using the following formula:
How to Analyze Results?
- The rate of oxygen consumption is usually taken as the rate of respiration for organisms.
- The various volumes of oxygen consumed obtained for various temperatures can be shown in the form of a table or a graph.
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