Question

Why do plants tend to absorb the wavelengths 500-625 nm less than other wavelengths of light?

(5 pts):

If we conducted an experiment to cut Chlorophyll in half where we cleaved the hydrophobic tail from the porphyrin ring how would either part behave on the chromatography sheet when separated? (5pts):

Now isolated on the sheet how would the individual subunits of Chlorophyll behave when we analyze their optic densities? Make sure to provide comments on both subunits. (5 pts):

If we conducted the same experiment with Beta- Carotene where would the products travel and how would they behave optically? (10 ps):

What is the function of having two Chlorophylls that have slightly different properties? What advantages does each property provide? (5 pts):

What is the purpose of applying acetone to the leaf pulp? Why did we not apply dH₂O?

(5 pts):

What factors impact why different plants utilize Chlorophyll and carotenes in different combinations? (5 pts):

Answer 1

1.Photosynthetic organisms such as plants and algae use electromagnetic radiation from the visible spectrum to drive the synthesis of sugar molecules. Special pigments in chloroplasts of plant cells absorb the energy of certain wavelengths of light, causing a molecular chain reaction known as the light-dependent reactions of photosynthesis. The best wavelengths of visible light for photosynthesis fall within the blue range (425–450 nm) and red range (600–700 nm). Therefore, the best light sources for photosynthesis should ideally emit light in the blue and red ranges.

2.Chlorophyll molecules embedded in the thylakoid membrane absorb light energy. These molecules are the most important pigments for absorbing the light energy used in photosynthesis. A chlorophyll molecule has a hydrophobic "tail" that embeds the molecule into the thylakoid membrane. The "head" of a chlorophyll molecule is a ring called a porphyrin. The porphyrin ring of chlorophyll, which has a magnesium atom at its center, is the part of a chlorophyll molecule that absorbs light energy. Examine the illustration to view the chlorophyll molecule and to learn which wavelengths of light are absorbed by this pigment. Compare the absorption spectrum of chlorophyll with the action spectrum of photosynthesis that Engelmann found.

3.Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum, which it reflects, producing the green color of chlorophyll-containing tissues.Chlorophyll fluorescence is not utilization of light energy at all. Energy lost as chlorophyll a fluorescence is completely wasted. But this does not mean that chlorophyll fluorescence is useless! In fact, current plant biology uses chlorophyll fluorescence as a signal that can tell a lot about photosynthesis.

4.

i. Chlorophyll content

Dunaliella cells were taken into a graduated tube and centrifuged at 5000 rpm for 15

minutes. The pellet was extracted in acetone by homogenizing using pestle and mortar and

extract was kept in dark for 1 hour. This was subjected to vortexing for few minutes

followed by centrifugation under low light at 3000 rpm for 10 minutes. The absorbance of

supernatant was measured spectrophotometrically (Shimadzu-160A, Japan) at 645 nm and

661.5 nm against acetone blank. Concentration of chlorophyll a, b and total content were

calculated by the equation of Lichtenhaler (1987) and expressed as (mg/mL).

ii. Carotenoids content

Carotenoids were extracted in acetone as mentioned above and analyzed

spectrophotometrically by measuring the absorbance at 470nm. Content of carotenoids

was calculated according to method of Davis (1976) using extinction co-efficient 2500.

Content of carotenoids were also expressed as pico gram cell –1.

Carotenoids content (mg/vol.) = (OD 450 × volume of the sample taken)/ 2500

Chl a =11.24 × OD 661.5 - 2.04 × OD 645.0

Chl b =20.13 × OD 645.0 - 4.19 × OD 661.5

Total chlorophyll = Chl a + Chl b =7.05 X OD 645.0 + 18.09 × OD 645.0"

5.Chlorophyll's role is to absorb light for photosynthesis. There are two main types of chlorophyll: A and B. Chlorophyll A's central role is as an electron donor in the electron transport chain. Chlorophyll B's role is to give organisms the ability to absorb higher frequency blue light for use in photosynthesis.There are actually several types of chlorophyll, but all land plants contain chlorophyll a and b. These 2 types of chlorophyll are identical in composition apart from one side chain, composed of a -CH3 in chlorophyll a, while in chlorophyll b it is -CHO.In addition to giving plants their green color, chlorophyll is vital for photosynthesis as it helps to channel the energy of sunlight into chemical energy. With photosynthesis, chlorophyll absorbs energy and then transforms water and carbon dioxide into oxygen and carbohydrates.The chlorophyll molecule consists of a central magnesium atom surrounded by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon–hydrogen side chain, known as a phytol chain. Variations are due to minor modifications of certain side groups.

6.if you want to identify and isolate secondary plant compounds you should use methanol (lower boiling point) or ethanol (somewhat higher boiling point), pure acetone or acetone/warer mixtures. This is for most of the polar and semipolar constituents. However, for lipophilic compounds you should use lipophilic solvents such as petrol or (bit mor polar) chloroform. for some of these solvents you should take care; acetone is highly fire sensitive and liver toxic; chloroform shows liver toxicity; thus take care for a well working hood. Don't use diethylether because of its high tendency for explosion.

7.chlorophyll (Chl) is an important photosynthetic pigment to the plant, largely determining photosynthetic capacity and hence plant growth. However, this concept has not been verified in natural forests, especially at a large scale. Furthermore, how Chl varies in natural forests remains unclear. In this study, the leaves of 823 plant species were collected from nine typical forest communities, extending from cold-temperate to tropical zones in China, to determine the main factors influencing leaf chlorophyll content in different regions and at different scales. We measured chlorophyll a (Chl a), chlorophyll b (Chl b), Chl (Chl a+Chl b), and the ratio of Chl a and Chl b (Chl a/b). The results showed that Chl a, Chl b, and Chl a/b values were in the range of 0.87–15.92 mg g−1 (mean: 4.18 mg g−1), 0.32–6.42 mg g−1 (mean 1.72 mg g−1), and 1.43–7.07 (mean: 2.47). The values of these three Chl parameters significantly differed among plant functional groups (trees < shrubs < herbs, coniferous trees < broadleaved trees, and evergreens < deciduous trees). Unexpectedly, Chl a, Chl b, and Chl a+b increased slightly with increasing latitude. Climate, soil, and phylogeny exert only a small effect on the spatial variation of Chl in natural forests, with large variation in the Chl of coexisting species masking the spatial patterns.