lab 6 student

8/8/2019 Lab 6 Student

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Photosynthesis

Photosynthesis

____________ is defined as a complex chemicalprocess that converts radiant energy (light) to chemicalenergy (sugar).

_______ is released to the environment, and sugar isused to fuel growth or is stored as starch, apolysaccharide.

Virtually all organisms are dependent uponphotosynthesis for food and oxygen.

Photosynthesis

A Summary equation for photosynthesis is demonstratedbelow:

Equation:

light 6 C O2 + 12 H2O C6H 1206 + 6 H20 + 6 0 2 c a r bo n d i o xi d e w a t er

ch orophyll Sugar water oxygen

Therefore, another way to define photosynthesis is thelight-dependent and chlorophyll-dependent conversion ofcarbon dioxide and water to sugar, water, and oxygen.

Photosynthesis

Photosynthesis occurs in the following 3 stages: 1.) capturingenergy from sunlight 2.) using the energy to make ATP nadreducing power in the form of NADPH 3.) using ATP &NADPH to power synthesis of organic molecules from CO2 inthe air.

A.) The first two stages can only take place in the presence oflight which are referred to as the photochemical rxns or thelight-dependent rxns.

B.) The 3rd stage occurs via the Calvin Cycle. As long as ATP &NADPH are available, The Calvin Cycle can occur with orwithout light; therefore, these rxns are referred to asBiochemical Rxns or the light-independent rxns.

Photosynthesis

light 6 CO2 + 12 H2O C6H1206 + 6 H20 + 6 02 carbon dioxide water chorophyll Sugar water oxygen

** The water molecules seen on both sides of theequationARE NOT THE SAM E!!!

~_______ H2O molecules split and release electronsduring photochemical rxns.

~_______ H2O molecules are formed from Hydrogen& O2 release during photochemical & biochemical rxns.


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Photosynthesis

Photochemica l Biochemica l

Light Rxns Dark Rxns

Fa s t (p r a ct ica lly S lo w er , b u t s t i ll

i n s t a n t a n e ou s ) e x t r em e ly f a s t

L ig h t d ep en d en t L ig h t - in d ep en d en t

S p li t s w a te r t o r ele as e C on v er ts (f ix es ) c ar bo n

Oxy gen , e lect r o n s , & d iox id e t o s u g a r

p r o t o n s

Photosynthesis

All organisms (including plants) carry out

respiration in one form or another.

________-containing organisms (plants) canalso carry out photosynthesis.

We will start our study of photosynthesis byexplaining the pigments observed inphotosynthesis.

Photosynthesis

Pigment:___________________

Primary pigments for photosynthesis:

chlorophyll a ( blue-green)

chlorophyll b (yellow-green)

Accessory pigments:

________ (yellow) Change to this color on your sheet!

________ (yellow-orange) Change to this color too!

* The accessory pigments absorb light and transfer energy tochlorophyll a.

Uptake of CO2 during photosynthesis

Carbon dioxide will _ _ _ _ _ _ _ the pH of a plant duringthe light-independent reactions of photosynthesis.(acid)

As the plant fixes or uses the carbon dioxide, the pH will_ _ _ _ _ _ _ back up toward neutral. (base)

Equation:

H2O + CO2 H2CO3 H+ + HCO3

-

Water Carbon Carbonic Hydrogen Bicarbon-

Dioxide Acid Ion ate Ion

Use of Light and Chlorophyll toProduce Starch During Photosynthesis

- The light-dependent reactions of photosynthesisoccur on photosynthetic membranes.

- In plants and algae, these membranes are called_________, which are located within a specialorganelle called a________ (see Fig. 12.8).

- Thylakoids are stacked to form columns called_____, which are held in place by______.

- A semiliquid called_____bathes the interior ofthe chloroplast and contains the enzymes thatcatalyze the light-independent reactions.

Chloroplast

1 = cell wall, 3 = vacuole, 4 = chloroplast envelope (2membranes), 5 = tonoplast, 7 = grana, 8 = stromathylakoids, 9 = starch grains, 2 = cytoplasm, 6 = plasma

membrane and 10 = stroma


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Use of Light and Chlorophyll to ProduceStarch During Photosynthesis

- Sugars produced by photosynthesis are oftenstored as ______.

- To produce starch, photosynthesis requires light asan energy source. In the absence of light, sugarsand starch are not produced.

- Photosynthesis also requires chlorophyll tocapture light energy. Without chlorophyll, sugarsand starches will not be produced.

- You will be able to detect the presence of starch bystaining it with a solution of iodine.

Lab Experiments

Paper Chromatography

Paper chromatography: a technique forseparating dissolved compounds such aschlorophyll, carotene, and xanthophyll


Technique: A solution of pigments is applied to theend of a strip of chromatography paper and the endis dipped into a solvent. The solvent is absorbed andas it moves up the paper, the pigments dissolve inthe moving solvent. Some pigments can keep upwith the solvent, some are slower. This differentialmovement is due to each pigments solubility andcharacteristic tendency to stick (adsorb) to thefibers of the paper. A pigments molecular size,polarity, and solubility determine the tendency tostick.

*Pigments that adsorb strongly move the slowest.


Separation ofPhotosyntheticpigments using

PaperChromatography


Each pigment will move a different distance upthe chromatography paper due to its ownsolubility, adsorbance, polarity, size, and

molecular density Absorption spectrum- range of absorption for

each pigment

Action spectrum- range of light used by plant;combination of all pigments together so it isbigger


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RfValue

The relationship of the distance moved by

a pigment to the distance moved by thesolvent front is specific for a given set ofconditions. We call this the Rfnumber.

The Rfnumber for a pigment is constant ina particular solvent-matrix system

Calculating the Rfvalue

Rf= Distance moved by a pigment

Distance from pigment origin to solvent front

We will use paper chromatography to identify eachpigment by its characteristic Rf.

The four pigments we should see are:

1.) Carotenes an orange band

2.)Xanthophylls - a yellow-orange band

3.) Chlorophyll a - a blue-green band

4.) Chlorophyllb - a yellow-green band

Procedure 12.1

You will work in PAIRS.

Each pair will need: collard green, a quarter, a piece ofchromatography paper, a test tube, and a cork stopper.)

Do not put your fingers all over the paper! Hold it bythe edges so you do n ot get the oils from yourhands on the face of it .

Procedure 12.1

Use a pencil to mark a line across the paperabout 2 cm up from the ANGLED TIP of thepaper.

Place the spinach leaf across the paper and rollthe quarter edge across the leaf in line with yourmark on the paper. You may want to repositionthe spinach leaf several times and roll across it inorder to get enough pigment on the paper.

Procedure 12.1 Place the chromatography paper (ANGLED TIP

DOWN) in the test tube. Make sure it is straight andis touching the solvent.

With a few centimeters of paper sticking out of the

tube, wedge the cork stopper into the tube. This willhold the paper upright in the tube. Place the tube ina test tube rack.

After the solvent front reaches the top of the paper(about 20 minutes), we will remove our strips andallow them to dry. Be sure to put a pencil mark onyour solvent front at the top. It will disappear whenit dries.

Procedure 12.1

~ Mark the distance thesolvent moved

~ Mark the distanceeach pigment moved

~Calculate Rf for eachpigment (distance thepigment moved/distance the solventmoved)


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Procedure 12.1

After we observe the dried paper and the

pigments:

1.) Label Fig. 12.5 (chromatogram)

2.) Calculate the Rffor each pigment and recordit in Table 12.1

Procedure 12.4

Phenol red is a pH-indicator that turns yellow in thepresence of an acidic solution (pH < 7) and red in aneutral or basic solution (pH > 7).

In this experiment we will use phenol red to detect theuptake of CO2by a photosynthesizing aquatic plant,Elodea.

We will put the Elodea in a slightly acidic solution madeby your breath and phenol red.

Procedure 12.4

We will follow the directions in the lab book onp.131 exactly.

We will allow the Elodea to be exposed to lightfor 30-60 minutes.

After the light exposure, we will use pH papers todetect differences in the control and Elodea,especially if color differences are not obvious.

Absorption Spectrum of Chlorophyll

Collard greens have been ground and filtered in 80%acetone. The filtrate (our filtered solution of spinach andacetone) is a light green color.

We will use this filtrate to determine the absorptionspectrum of chlorophyll using the spectrophotometer.

The spectrophotometers will be blanked with a cuvettecontaining 80% acetone.

Absorption Spectrum of Chlorophyll

After blanking the spectrophotometer, set thewavelength at 350nm in absorbance mode.

The filter lever (a small lever on the front left of themachine) should be set in the lower range.

This lever will need to be moved over to the higher rangewhen you reach wavelength measurements of 600nm.

Use the 8 wavelength readings in Table 7.5 on p.74 andread the absorbance of chlorophyll from the spinach foreach wavelength.

Dont forget to blank the spectrophotometer before eachnew wavelength reading!!

* Refer to Procedure 7.4 on pg. 72

roce ure 12. p.132; roce ure12.7p.134

Procedure 12.8p.134 We will do this procedure and the rest as 3

demos done by trustworthy and willingstudents!

We will follow the directions exactly for

each procedure.

When we are finished, record your results(sketches) in Fig. 12.9a on p.133.

Answer questions for all procedures onp.134.

lab 6 student

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