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The three-part experiment performed by Mizokami et al. to analyze the relationship of mesophyll conductance and change in the CO2 levels enabled them to explain the characteristic of mesophyll conductance in plants (2017). As said in the beginning, there are many studies done for the stomatal conductance, but not many for mesophyll conductance. This report has given four key discoveries to understand about the mesophyll conductance behavior. Starting on 1) decrease in mesophyll conductance to increase in CO2 is independent from the stomatal conductance. 2) The different reactions observed in mesophyll conductance for CO2 levels, and ABA application concluded how mesophyll conductance uses different mechanisms to decrease depending on the external factor. 3) Mesophyll conductance reacts better in 1% O2 than 21% O2.  4) Mesophyll conductance do not react spontaneously, rather gradually to the external environment (Mizokami et al., 2017). There were experimental error such as overestimation in the intercellular concentration, how aquaporins behave, and nitrogen balance. So, to have a better result Mizokami concludes how these factors should be considered in further studies (Mizokami et al., 2017).

The second experiment was carried out to examine the mesophyll conductance responding to ABA application (Mizokami et al., 2017). This experiment was done in a similar setting to the first experiment with the investigation of the change in the CO2 levels. Mizokami et al. grew each plant, Col-0, ost1, and slac1-2 in a pot that were placed in a chamber that provided a photoperiod of eight hours, 23 degrees Celsius for day temperature, 21 degrees Celsius for night temperature, humidity of 60%, ambient CO2  of 390μmol and a Hoagland solution twice a week (Mizokami et al., 2017). In this ABA application experiment, the CO2 level in the chamber was not manipulated and stayed constant for two weeks. Mizokami et al. first made a tiny slit with a razor in the Arabidopsis thaliana’s petiole to make a space to inject the ABA solution so that the plants will not wilt (2017). They kept these plants in the dark for about 15 minutes before turning on the fluorescent lamp again to prevent the slit from embolism. After the plant is adjusted to the slit, an artificial xylem sap called AXS was injected and the fluorescent lamp in the chamber was turned on shining a 600μmol light on the plants. Then the initial photosynthetic rate was measured (Mizokami et al., 2017). When the initial photosynthetic rate and the atmospheric conditions were recorded, Mizokami et al. applied 100μl of ABA solution gradually into the same slit where they injected the AXS solution (2017). It took an hour and a half to complete this injection, and they measured the photosynthetic gas exchange parameter to compare the results from the initial data. Not only the measurements, but also ABA contents in the leaf was observed (Mizokami et al., 2017). By using liquid nitrogen to freeze the leaf and removing the veins from it, the contents were determined by using a liquid chromatograph and a mass spectrometer. Finally, to evaluate the mesophyll conductance, Mizokami et al. created an equation (Figure 1) to analyze how sensitive the mesophyll is to both ABA and CO2 levels (2017).

There are various reports that mentions the response of stomatal conductance to CO2 levels but not many for mesophyll conductance. Since there are limited understanding for mesophyll conductance, Mizokami has been studying this subject from different prospective. From his past case study, he has found that mesophyll conductance is independent from stomatal conductance however, this did not support the influence of ABA and intercellular CO2 levels on the mesophyll conductances (Mizokami et al., 2017). Therefore, to answer the question whether or not decrease in the intercellular CO2 concentration decreases the mesophyll conductance, the first experiment was done (Mizokami et al., 2017). It was examined by comparing the mesophyll conductance responding to instant increase in the intercellular CO2.  Three pots of A. thaliana plant, the wildtype Col-0, mutant ost1, and mutant slac1-2 were placed into a chamber that has an ambient CO2 of 390μmol  . After the plant adjusts to this condition, then the ambient CO2  was switched to 780μmol . The measurements for mesophyll conductance was taken every thirty minutes for two hours and plotted on a graph (Mizokami et al., 2017).

A plant called Arabidopsis thaliana was used to conduct three different experiments to explain how mesophyll conductance respond to the environment (Mizokami et al., 2017). One wildtype control called Col-0, two mutations, ost1 and slac1-2, were examined to eliminate factors that may influence the data not to represent an accurate display (Mizokami et al., 2017). Both of these mutants are insensitive to increase in the ABA and external CO2 levels because the stomata do not close properly. These mutations allowed Mizokami et al. to factor out the relationship between the stomatal conductance and the intercellular CO2 (2017). The data were collected and presented in multiple graphs and panels for different scenarios so that the readers could follow along the descriptions.

The article, “Effects of instantaneous and growth CO2 levels and abscisic acid on stomatal and mesophyll conductance” by Yusuke Mizokami, Ko Noguchi, Mikiko Kojima, Hitoshi Sakakibara, and Ichiro Terashima (2017) was a research specific to analyze the trend of the mesophyll conductance changing with different CO2 levels and abscisic acid, abbreviated as ABA. The research was based on the results obtained in 2015 by Mizokami et al. that dealt with mesophyll conductance in drought environments. To understand further about the mesophyll conductance and the stomatal conductance in plants, the new case study was developed. To obtain a more accurate data than from the previous experiment, they included additional factors to consider; such as the relationship between stomatal conductance and the intercellular CO2 concentration (Mizokami et al., 2017). In the past, Mizokami et al. have concluded two points. First, if ABA level increases in a leaf, both mesophyll and stomatal conductance decreases. Secondly, ABA is not responsible for decreasing both conductance because the ABA-deficient plants also decreased both conductance in response to high CO2 levels (Mizokami et al., 2017). With these two points in mind, the new study was carried out to understand the function of mesophyll conductance (Mizokami et al., 2017)

Bird songs can be represented visually. With modern technology, sonograms can be created from the song recordings. However, before being able to read a sonogram, there are some teminology that must be used reviewed. In order to be familiar to birds’ vocalization, terms such as:  Amplitude (maximum energy), Fundamental tone, Frequency (number of complete cycles per unit of time), Glissando (bleeding of one tone into the next), Harmonic (a tone in the series of overtones produced by a fundamental tone), Hertz (one cycle per second), Modulation (form of a sound: carrier wave), Oscillograph (a device that records oscillations as a continuous graph), Overtone , Pitch (relative position of a tone in a scale, as determined by its frequency), Resonance (intensification and prolongation of a sound), Sinusoidal waveform (y=sin x), Sonogram (display of the frequency of a sound related to time), and Tone (distinct pitch and quality) are necessary for a better understanding of birds.

Birds have a special organ called the syrinx, that allow them to sing the way they sound. It is located on the trachea to produce sound. It is similar to the mammalian larynx but the way air is used is different. In the syrinx 100% of the air is converted to sound where the larynx only uses 2%. The vibrated air passes through the syringeal passageway to project on the tympaniform membrane. This vibration is the result of how birds can vocalizes. The syrinx is a complex organ itself but the muscle attached around it is also complex. There are layers of muscle structures to create fine adjustment of vibration. Sound produced by the syrinx can be filtered to change the loudness and the pitch. The experiment done to prove that sound travel faster than helium atmosphere showed sound produced in such atmosphere had different pitch and frequency than the sound produced in our normal atmosphere. The understanding of syrinx and physics of sound helped scientists to learn more about vocalization.

In order to be familiar to birds’ vocalization, there are terms that one's needs to study such as:  Amplitude (maximum energy), Fundamental tone, Frequency (number of complete cycles per unit of time), Glissando (bleeding of one tone into the next), Harmonic (a tone in the series of overtones produced by a fundamental tone), Hertz (one cycle per second), Modulation (form of a sound: carrier wave), Oscillograph (a device that records oscillations as a continuous graph), Overtone , Pitch (relative position of a tone in a scale, as determined by its frequency), Resonance (intensification and prolongation of a sound), Sinusoidal waveform (y=sin x), Sonogram (display of the frequency of a sound related to time), and Tone (distinct pitch and quality).

    Most birds use 5 to 14 different vocal structures to produce a song. The experiment was done with the Chaffinch of Europe and was found that there was 12 different sounds all used for different purposes: territorial, mate, predator, etc. In songbirds, it is not unique if a bird species have individualized songs, 100 call patterns, or a very complex song that characterises that bird specie. Syntax, phase, pitch are all calculated by these birds and the combination of them turns into a song to communicate with one another. For example Black-Capped Chickadees have a distinctive alarm call that yells “dee-dee-dee.” The number of times Chickadee calls “dee” correlates with how dangerous the predator is. So the more alarm you hear, it is more likely the predator is an owl or a hawk.

The songs produced by each birds are diverse. Some can be short and high note, other can be long note. Frequency and amplitudes can be studied by creating a graph to visually study the sound of the birds. The higher amplitude it is, the louder song is produced by the bird.  The difference between a song and a call is that songs have patterns, syllables and phrases where a call is a short simple sound. Calls are used for multiple situations for defense, conversation and other uses where calls are mostly used to attract mates. Most songs are similar to human songs. Each bird has their very own type of call and vocalization to attract mates. Based on the tempo and frequency is what attracts neighbors and predators. Sound travels much farther distance so using that physical property, birds can communicate with a larger range of birds. Not only the vocalization produced by the bird itself, but also the environment can affect how the bird is heard by others. Some birds like Great Tits that live in the urban area adapted a vocalization that will not be erased from the traffic noise caused by human activities and other loudness.