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Question 12 pts

All of this week's Essay Questions will be based on the following scenario:

Imagine that you are a marine biologist.
On an expedition, you find a reddish brown organism floating in one of your nets (pictured below). It has structures resembling leaves and stems.



You hypothesize that this is a photosynthetic organism.
Describe how you could test this hypothesis using a pH indicator solution.
Carefully describe the steps you would take, the reactants required, and what result would indicate that the organism was undergoing photosynthesis.
(Hint: See Lab 3 Part 1)

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Question 22 pts

After testing your hypothesis, you determine that the organism is photosynthetic.
Because the organism is a reddish brown color, you are curious what color (wavelength) of light it absorbs for photosynthesis.

Describe an experiment in which you will use volumeters to test the relative rate of photosynthesis in different colors of light.
What are your dependent and independent variables? What result will indicate a high absorbance of a certain color?

(Hint: See Lab 3 Part 3)

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Question 31 pts

You carry out the experiment from Part 2, and determine the rate of photosynthesis for several colors of light.
You conclude that the organism can most efficiently absorb blue-green light (wavelength 500-550nm), and does a poor job absorbing red light (700-750nm).

You originally found the organism floating in a net at the ocean's surface. The seafloor at this site was approximately 150 meters deep.
It is possible that the organism did not originate from the surface. You suspect that this is a small piece of a larger organism which could have floated up from the sea floor.

The figure below shows how far different colors/wavelengths of the visible spectrum penetrate through water. Does this graph support the conclusion that this organism originated from the sea floor? Why or why not?

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Answer 1

Answer 1 :- reddish brown organism floating in one of your nets . It has structures resembling leaves and stems. :-

this organism is no doubt a thalloid structure of red algae. Red algae, or Rhodophyta, are one of the oldest groups of eukaryotic algae. Red algae are red because of the presence of the pigment phycoerythrin; this pigment reflects red light and absorbs blue light. Because blue light penetrates water to a greater depth than light of longer wavelengths, these pigments allow red algae to photosynthesize and live at somewhat greater depths than most other "algae". Some rhodophytes have very little phycoerythrin, and may appear green or bluish from the chlorophyll and other pigments present in them.

experiment to prove photosynthesis performed in by red algae:-

Hydrogencarbonate indicator is very sensitive to changes in carbon dioxide level.

The indicator is orange/red in colour when equilibrated with atmospheric air.

It changes to yellow when more carbon dioxide is added .

changes through red to a deep purple colour when carbon dioxide is removed. [see photo]

When you place the alga in hydrogencarbonate indicator solution, the colour of the indicator changes from orange / red to purple. This is because the algae are taking carbon dioxide out of the indicator thereby lowering the concentration in the indicator as they use carbon dioxide in photosynthesis.

Answer 2 :- Because the organism is a reddish brown color, you are curious what color (wavelength) of light it absorbs for photosynthesis.:-

-In red algae containing chiefly phycoerythrin, the action spectrum with peaks corresponding to its absorption maxima (495, 540, and 565 mµ). Such algae include Delesseria, Schizymenia, and Porphyrella.

In the genus Porphyra, there is a series P. nereocystis, P. naiadum, and P. perforata, with increasingly more phycocyanin and less phycoerythrin: the action spectra reflect this, with increasing activity in the orange-red region (600 to 640 mµ) where phycocyanin absorbs.

In all these red algae, photosynthesis is almost minimal at 435 mµ and 675 mµ, where chlorophyll shows maximum absorption. Although the chlorophylls (and carotenoids) are present in quantities comparable to the green algae, their function is apparently not that of a primary light absorber; this role is taken over by the phycobilins. In this respect the red algae (Rhodophyta) appear unique among photosynthetic plants.

in short we can say that the red algae absorb the wave length as -

Absorption spectrum from 1 April 1999 the true wavelengths for green start at about 1.5 Optical Density Units at 400nm and sink to .30odu at 600nm and thin rise from there to about .65oduover 700nm and fall to 0 at about 720nm.

Red pigments (incl. phycoerethryn) started at .6 odu at 400nm rise to 1.0 odu at 440nm and fall to .1 at 480, rise to .3 over 500nm and taper at .1 odu until a short rise over 700nm to .3 odu.[optical density unit]

Phycoerethryn absorbs best between 500nm and 600nm.

Chlorophyll a best at 420nm and 700nm

Chlorophyll b at 450nm and 650nm

Fucoxanthin at 500nm

Phycocyanobilin between 600nm and 700nm

experiment :- by using volumetric meter we can obser the rate of photosynthesis on the basis of evolution of Oxygen molecule. The more the Oxygene evolve the more is the rate of photosynthesis.

Answer 3:- different colors/wavelengths of the visible spectrum penetrate through water. :-

Red wavelengths are absorbed in the first few metres of water.

Blue wavelengths are more readily absorbed if the water contains average or abundant amounts of organic material.

Thus, green wavelengths are often the most common light in deep water.

Chlorophylls absorb red and blue wavelengths much more strongly than they absorb green wavelengths, which is why chlorophyll-bearing plants appear green. The carotenoids and phycobiliproteins, on the other hand, strongly absorb green wavelengths. Algae with large amounts of carotenoid appear yellow to brown, those with large amounts of phycocyanin appear blue, and those with large amounts of phycoerythrin appear red.

the cell structure of the deepwater algae is designed to capture virtually all light, green or otherwise. Thus, while green-absorbing pigments are advantageous in deeper waters.

note :- you have given me incomplete information to give you complete answer of this question.

I hope the above information will help you to solve your problem.