Summary of Section 8.2 :)

-=Light Reactions convert light energy into chemical energy=-

Light Energy + Pigments

-sunlight is a type of electromagnetic energy

-electromagnetic energy travels in waves

-distance between two adjecent waves is called a wavelength

-electromagnetic spectrum: the different ranges of wavelengths

-shorter wavelengths have more energy than longer ones

-wavelengths shorter than visible light can damage organic molecules

Pigments + Color

-a substance's color is cause by chemical compounds called pigments

-when light shines on material with pigments, the wavelengths can be absorbed, transmitted or reflected 

-pigments in chloroplasts absorb blue-violet and red-orange light well

-chloroplasts convert the absorbed light energy into chemical energy

-but they cannot absorb green light well

-most of green light is transmitted through leaf or is reflected

-leaves look green because green light is not absorbed

Identifying Chloroplast Pigments

-using paper chromatography, you can observe pigments in a leaf

 

Procedure

1. Press leaf on filter paper

2. Seal paper in a cylinder containing solvents

-solvents will move up the paper

-different pigments will travel at different rates depending on how easily they dissolve and how much they are attracted to the paper 

-chlorophyll a mainly absorbs blue and red light, and reflects green light

-plays big role in light reactions of photosynthesis

-there are "helper pigments" which absorb mainly blue and orange light reflects yellow-green light

 

Harvesting Light Energy

-in the thylakoid membrane, chlorophyll and other molecules are arranges in the groups calles photosystems

-each photosystem contains a few hundred pigment molecules (including chlorophyll a, and b)

-act like light gathering panel

-each time pigment molecule absorbs energy, one of the pigments electrons gains energy

-becomes at an "excited stage"

~unstable

~almost immediately goes back to normal (ground stage) and transfers energy to a molecule next to it

~when at ground state, it "excites" another pigment molecule and that keeps going down the line 

~energy jumps from molecule to molecule until it arrives at the reaction center of photosytem

-reaction center: contains chlorophyll a molecute next to a primary acceptor molecule 

-primary acceptor molecule traps the excited electron from the chlorophyll a molecule

-other molecules can then use energy to create ATP and NADPH 

Chemical Products of Light Reactions

-two photosystems are involved in light reactions

-first photosystem:

traps light energy and transfers the excited electrons to an electron transport chain

electrons are replaces by a splitting molecule of water

release oxygen and hydrogen ions as waste products

-the electron transport chain releases energy for the chloroplast to make ATP 

~connects the two photosystems

-is similar to cellular respiration

-electron transport chain pumps hydrogen ions across membrane

-light-excited electrons travel down the chain

-second photosystem: 

produces NADPH by transferring excited electrons and hydrogen ions to a carrier molecule called NADP+

-input of light energy is shown by the large yellow mallets

-light energy makes electrons excited at the top of the platform in each photosystem

-energy released as the electrons move down the electron transport chain 

-photosystems is used to pump hydrogen ions across a membrane and produce ATP

-light reactions convert chemical energy to NADPH and ATP

Concept Check 8.2

1. Explain why a leaf appears green.

A leaf looks green because the chloroplast pigments don't absorb the green light good, so the green light relflects back on the leaf.

2. Describe what happens when a molecule chlorophyll a absorbs light. 

When it molecule chlorophyll a absorbs light, one of its pigments gains energy and become "excited". The "excited" stage is very unstable, so it almost instantly falls back down to the "ground stage" and transfers its energy to a neighboring molecule. This keeps going down the chain until the energy reaches the reaction center of the photosystem, which will capture the "excited" electron from the chlorophyll a molecule. 

3. Besides oxygen, what two molecules are produced by light reactions?

ATP and NADPH are produces besides oxygen

4. Where in the chloroplast do the light reactions take place?

Light reactions take place in the in thylakoid membranes of the chloroplast.

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Vocabulary for 8.1 + 8.2

chloroplast- cellular organism found in plant cells where photosynthesis occurs

chlorophyll- pigment that gives chloroplast its green color and uses light energy to split water molecules during photosynthesis

thylakoid- disk-shaped sac in the stroma, where light reactions take place

stroma- thick fluid inside the inner membrane of chloroplast

light reactions- chemical reaction that converts sun's energy to chemical energy

Calvin Cycle- cycle in plants that makes sugar from carbon dioxide, high-energy electrons carried by NADPH

wavelength- the distance between two waves that are next to each other 

electromagnetic spectrum- range of electromagnetic waves

pigment- chemical compound that determines substance's color

paper chromotography-technique used to observe different pigments in material

photosystem- cluster of chlorophyll and other molecules in the thylakoid 

Summary of Section 8.1 :)

-=Photosynthesis Uses Light Energy to Make Food=-

The Structure of Chloroplasts

-photosynthesis occurs in a cellular organ called called a chloroplast

-chloroplasts contain chemical contain chlorophylls that give the organelle its green color

-in most plants, the leaves contain the most chloroplasts and that is where photosynthesis occurs the most

-chloroplasts are mostly in the inner layer of the tissue called the mesophyll 

-carbon dioxide goes in and oxygen leaves through tiny pores on the surface of the leaf called stomata 

-the veins carry the nutrients, water and organic molecules to other parts of the plant

-the structure of the chloroplast is the key to its function

~has an inner and other membrane

~inner membrane has fluid called stroma

~in the stroma, there are thylakoids which are disks-shapes sacs

~each thylakoid has a membrane around it

~thylakoids are in stacks called grana

-the structure in the chloroplasts organize chemical reactions that take place during photosynthesis

Photosynthesis 

-opposite of cellular respiration

-electrons from water are lifted by the sunlight energy 

-chloroplast uses those electrons, hydrogen ions and carbon dioxide to produce sugar molecules

this is the equation for photosynthesis

-photosynthesis occur in 2 stages: Light Reactions + Calvin Cycle 

The Light Reactions

-convert sunlight energy -----> chemical energy

-reactions depend on molecules built in the membranes in the thylakoids

Procedure:

1. Chlorophyll molecules in the membranes capture sunlight energy 

2. Chloroplasts use energy to remove the electrons from water

-splits oxygen and hydrogen ions resulting in oxygen becoming a waste product (escapes throught the stomata)

3. Chloroplasts use water's electrons + hydrogen ions = electron carries NADPH

4. Chloroplasts also use the energy to create ATP

Light energy ----> chemical energy in ATP and NADPH

The Calvin Cycle 

-makes sugar from carbon dioxide + hydrogen ions + electrons from NADPH

-enzymes for Calvin Cycle are outside thylakoids and are dissolved in the stroma

-ATP made by light reactions provides energy to make sugar

-does not require light to begin

-requires to inputs supplied by ATP and NADPH

Concept Check 8.1

1. Draw and label a simple diagram of a chloroplast that includes the following structures: outer and inner membranes, stroma, thylakoids. 

2. What are the reactants for photosynthesis? What are the products

Carbon dioxide + Water = reactants

Glucose + Oxygen =products 

3. Name the two main stages of photosynthesis. How are the two stages related?

The two main stages of photosynthesis are: Light Reactions and the Calvin Cycle. The Light Reactions stage produces chemical energy from light energy in ATP and NADPH while the Calvin Cycle makes sugar from them.