Photosynthesis_lab_results_info.pdf

8/10/2019 Photosynthesis_lab_results_info.pdf

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PHOTOSYNTHESIS

Pre-assessment

Test your knowledge before you begin this module on "Photosynthesis."

There are five multiple-choice questions in this assessment section.

1. Which pigment captures the sunlight during photosynthesis?

A. ChlorophyllB. MelaninC. Phycocyanine

2. Which is the chemical equation for photosynthesis in plants?light

A. 6H2O+6CO2 C6H12O6+6O2B. C6H12O6+6O2+ATP 6CO2+6H2OC. C6H12O6+6O2 6CO2+6H2O+energy

3. Which of the following prepare their food through photosynthesis?

A. Plants and algaeB. Human beings and birdsC. Plants and human beings

4. Where does photosynthesis take place in a plant?

A. RootB. LeavesC. Fruits

5.Which of the following gases is produced at the end of photosynthesis?

A. OxygenB. Carbon dioxideC. Carbon monoxide

Objectives

Following this module on "Photosynthesis," you should be able to:

Define Photosynthesis

Describe the structure of chloroplast and chlorophyll

Describe the pigments found in the plants

Define light energy

Differentiate the stages of photosynthesis

Demonstrate the role of light, carbon dioxide, and chlorophyll in photosynthesis


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Definition and Photosynthesis Process

Definition:Photosynthesis is the conversion of unusable sunlight energy intousable chemical energy.

Overall reaction:light6H2O + 6CO2 C6H12O6+ 6O2Water Carbon Glucose Oxygen

dioxide

Role of Plants in Photosynthesis

Photosynthesis takes place in the leaves and green stems.Within the leaves and green stems are specialized organelles calledchloroplasts. The chloroplasts play an important role in photosynthesis.


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Chloroplast

Structure: Double membrane organelle

The outer membrane is more permeable than the inner membrane.

Stroma: Fluid filled area in the chloroplasts

Thylakoids

Tiny sacs that float in the stroma. They contain the pigments(chlorophyll and carotenoids) that capture light energy.

The sacs are stacked in groups known as grana. Many grana togetherare called Granum.

Function: The thylakoid membranes are the sites for photosyntheticlight reactions.

Chlorophyll

The thylakoid membrane contains light-absorbing molecules calledpigments such as chlorophyll a, chlorophyll b, and carotenoids.

Other Name:Photoreceptor

Structure:Porphyrin ring, coordinated to a central atom calledmagnesium.

Both the chlorophylls a and b differ in the composition of one of theirside chains. In 'Chlorophyll a' it is CH3, In 'Chlorophyll b' it is CHO.

Function: Chlorophyll a and b absorb sunlight for the light reactionof photosynthesis.

Both chlorophyll a and b absorb the light most strongly in the redand violet portions of the spectrum.

Green light is poorly absorbed.


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Mesophyll

The photosynthetic tissue of a leaf located between the two outer leaftissues.

In many tree species, there are two distinct layers of mesophyll cells:

Palisade mesophyll Spongy mesophyll

Function: Play a major role in C4 pathway (a type of photosyntheticpathway).

Stomata

Stomata are microscopic pores found on the under side of leaves.The stomata are surrounded by two half moon shaped guard cells.Guard cells regulate the opening and closing of the stoma. It isregulated primarily by water pressure.

Function: Play a major role in all types of photosynthesis.


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Activity

Light and Photosynthesis

Inner membrane Stoma Thylakoid Granum Outer membrane


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Definition

Light: Light is a form of electromagnetic radiation from the sun, whichis composed of different wavelengths.

The entire range of electromagnetic radiation, from shortest to longestwavelength is known as the electromagnetic spectrum.

Photosynthesis is mainly dependent on visible light.

Chlorophyll absorbs all visible light except the color green. Since thechlorophyll reflects green light, a plant containing a lot of chlorophyllappears green to the observer.

Different Stages of PhotosynthesisBased on the presence or absence of light, the photosynthesis processis divided into:

Light dependent reactions

Light independent reactions (sometimes called dark reaction)


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Light Dependent Photosynthesis

Steps involved in light dependent reaction:

Step 1:Chlorophyll in photosystem II absorbs sunlight.This excites an electron. The electron moves through an electron transport chain.To replace the electrons that were lost, a water molecule is split. The water molecule is split into two electrons, 2H

+

ions, and one oxygen atom.

Step 2:The electrons move from photosystem II to photosystem I via the electron transport chain.Energy produced by this electron is used to transport H

+ions.

Step 3:

The pigments in photosystem I absorb light and re-excite the electrons.The electron carrier NADP+picks up the high energy electrons and H

+ions.

At this point NADP+becomes NADPH.

Step 4:ATP synthase allows the H

+ions to pass through the membrane.

At this time, the ATP synthase binds a phosphate group to ADP and results in ATP molecule formation.


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Light Independent Photosynthesis

Other name: Dark reaction or light independent reaction

Steps involved in Calvin cycle:

Step 1:Six molecules of CO2combine with six 5-carbon molecules and form twelve 3-carbon molecules.

Step 2:The twelve 3-carbon molecules are converted to a higher energy form with the input of ATP and NADPH.

Step 3:Two of the twelve 3-carbon molecules are removed and used to produce sugars for the plant.

Step 4:The remaining ten 3-carbon molecules are converted back into six 5-carbon molecules with the help of ATP.

The six 5-carbon molecules will combine with six new CO2molecules to begin the cycle again.

Diversity in the Photosynthetic PathwayThere are a total of three pathways.

Calvin cycle-Light independent reaction (dark reaction)

C4 pathway-Light dependent reaction

CAM (Crassulacean Acid Metabolism) pathway-Light dependent reaction

C4 Pathway

In the C4 plant an alternate mode of carbon fixation is utilized. The C4 method is used by sugarcane, corn, and some members of the grass family.


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Crassulacean Acid Metabolism or CAM


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Activity

You have the images and their labels on screen.

Laboratory Experiments

To prove:

Role of light in photosynthesisRole of carbon dioxide in photosynthesisRole of photosynthetic pigments in photosynthesis

Role of Light in Photosynthesis

Plants use the energy that is present in the sunlight to synthesize food material from carbon dioxide and water. In theprocess, light energy is used to split water. The splitting of water produces oxygen gas as a waste product.

Reaction:light

2H2O 2H2+ O2

Principle:Oxygen, being lighter than water, displaces the water contained in the calibrated jar. The volume of liberated oxygenis measured in mL.


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Conclusion: Standardisation oxygen produciton is more in the jars containing Sodium bicarbonate than the jars

without Sodium bicarbonate. This concludes that Carbon-di-oxide is necessary for Oxygen production duringPhotosynthesis.

Role of Carbon Dioxide in PhotosynthesisCO2+H2O H2CO3

Carbonic acid

During photosynthesis, the plants consume carbon dioxide. This leads to a decrease in the level of carbonic acid andan increase in pH.

pH Indicator: Bromothymol Blue (BTB)

Uses of BTB: Based on the pH level in the solution, the BTB will turn into different colors.

pH Color of the solution

Less than 6.0 Yellow6.0 to 7.6 Green

Above 7.6 Blue

Conclusion: Blue Color change indicates the decrease in carbonic acid level and then increase in the pH above 7.6,this is due to the uilisation of Carbon dioxide in the presence of sunlight.


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Photosynthetic Pigments

A variety of pigments found in plants provide the brilliant colors.The best example for this plant is a common houseplant called Coleus.The leaves of this plant are green and red.Green color is due to chlorophyll a and b and the red color is due to anthocyanins.

Conclusion: Change of light blue color indicates the presence of Starch and light brown in color indicates theabsence of starch.

Summary

This concludes the module on "Photosynthesis." In this module, you:

Defined Photosynthesis

Described the structure of chloroplast and chlorophyll

Described the pigments found in plants

Defined light energy

Differentiated the stages of photosynthesis


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Demonstrated the role of light, carbon dioxide, and chlorophyll in photosynthesis

Congratulations! You have completed the module on Photosynthesis.

Post-assessment

Welcome to the test on "Photosynthesis."

1. This organelle plays a major role in photosynthesis ___________.2. For photosynthesis, most of the carbon dioxide is derived from here ___________.3. This is the chemical element used to test the presence of starch ___________.4. This is the part of the chloroplast in which the light reaction takes place ___________.5. In the Calvin cycle, carbon dioxide is converted into this product ___________.

Photosynthesis_lab_results_info.pdf

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