Bromothymol blue (BTB) is a chemical that can be used as an indicator of the pH of a solution. Because CO2 produces an acid in water, BTB can indirectly measure how much CO2 is present in a solution. When placed in solutions with neutral pH (little CO2), the solution appears green. In solutions with low pH (high CO2), the solution appears yellow. A teacher performed a demonstration to investigate how photosynthesis and respiration cycle carbon and oxygen. She placed a few drops of BTB in a test tube containing distilled water. Because distilled water has a neutral pH, the solution appeared green. The teacher used a straw to blow into the solution, and the solution turned yellow. She then placed an aquatic plant into the test tube, covered it to keep it air tight, and placed it under a light for 24 hours.

What color would the solution in the test tube be after being in the light, and what would it be if it were then placed in the dark for 24 hours, and why?
A
Green after being placed in the light because the plant would remove CO2 by photosynthesis; yellow after being placed in the dark because the plant would release CO2 by respiration.

B
Yellow after being placed in the light because the plant would release CO2 by photosynthesis; green after being placed in the dark because the plant could not photosynthesize in the dark.

C
Green after being placed in the light because the plant would remove CO2 by photosynthesis; green after being placed in the dark because no CO2 would enter the tube since it is air tight.

D
Yellow after being placed in the light because the plant would release CO2 by photosynthesis; yellow after being placed in the dark because no CO2 could leave the tube since it is air tight.

A. Green after being placed in the light because the plant would remove CO2 by photosynthesis; yellow after being placed in the dark because the plant would release CO2 by respiration.

Explanation:

According to this question, Bromothymol blue (BTB) is a chemical that can be used as an indicator of the pH of a solution. The presence or absence of CO2 in a solution decreases or increases the pH of the solution respectively.

- BTB appears green in a neutral pH i.e. little CO2

- BTB turns yellow in a low pH i.e. high CO2

Plants, in the presence of light, will perform photosynthesis and use CO3 as a reactant while in the dark, will perform cellular respiration and release CO2 as a waste product. Hence, in this case where an aquatic plant was placed into a test tube and covered it to keep it air tight.

- When placed under light for 24 hours, the aquatic plant will undergo photosynthesis and remove CO2 from the solution to make the solution appear GREEN due to neutral pH.

- When placed in the dark for 24 hours, the aquatic plant will undergo cellular respiration and release CO2 into the solution making the solution appear YELLOW due to low pH.

from almost the creation of the first true maps of the earth, people started seeing how continents would be able to fit together.   in particular, people noticed that south america fits almost exactly into africa.

you should be aware that while world maps were around early in the 1600’s and better defined by the end of the 1700’s, those maps were not ‘public’ but were treated as state secrets.   and so it was not till much later that the broader ‘science’ community had access to good quality and accurate world maps.

get the whole story here…

it is now known that most of the major continental masses can be fit together in a jigsaw process.   in fact we now know that the continents were indeed once all joined together as one land mass – the supercontinent of pangaea.

if you look at most world maps you will ponder how this is evidence, as the continents really don’t appear to ‘fit’ together very well.   what you need to understand is that the vast majority of maps are drawn using a map projection that has the north and south poles (which are points) are a line the width of the map at the top and bottom.   this means that the map distorts the true shape of the earth’s land and oceans as you love closer to the poles.     some other map projections distort less, but have the map shape looking like segments of an orange.   see here for a range of map projections.   check out the way greenland changes size in each!

what is more remarkable, is the next piece of evidence when added to the shape of continents.

location of mountains and fossils

what is remarkable, when you reassemble all the continents together, the ancient mountain ranges (many now eroded to their cores) and the location of rock types and fossils all match up.