Photosynthesis

Trapping the Sun’s Energy

Photosynthesis:Life from Light and Air

Plants are energy producersLike animals, plants need energy to live

unlike animals, plants don’t need to eat food to make that energy

Plants make both FOOD & ENERGYplants are producers

animals are consumers

Using light & air to grow plants

6CO2 6H2O C6H12O6 6O2sun

energy→ + ++

→ glucose + oxygencarbondioxide

sunenergy+ water +

(ATP) = used to build the sugar

Photosynthesisusing sun’s energy to make ATPusing CO2 & water to make glucose (sugar)

occurs in chloroplastsallows plants to growmakes a waste product

oxygen (O2)

What do plants need to grow?The “factory” for making energy & sugars

chloroplast

Fuelssunlight

carbon dioxide

water

The Helpersenzymes

H2Osugars

ATP

Make ATP!Make sugar!

I can do it all…And no oneeven notices!

enzymes

CO2

sun

The chloroplast is the organelle in a plant cell where photosynthesis occurs

Chloroplasts are only in plants

animal cellsanimal cells plant cellsplant cells

What absorbs light in a plant?

Pigments are molecules that absorb specific wavelengths of sunlight

Sunlight (white light) can be separated into many different wavelengths- that appear as colors

ROYGBIV

Most common pigment is chlorophyllIt absorbs every wavelength except GREENGreen gets reflected- that’s why plants appear green to the human eye.

There are other types of plant pigmentsex. Carotene= orange

ex. Xanthophyll = yellow

Why do leaves turn colors in the fall?

Chlorophylls are more abundant than other pigments in the leaves.

As trees prepare to lose their leaves, chlorophyll molecules break down, revealing the other pigments that are also in the leaf.

Photosynthesis has 2 phases;

1. Light Dependent Reactions

2. Light Independent Reactions-aka Calvin Cycle

Let’s take a look at the structure of a chloroplast since that’s where the action is.

Calvin cycle (light independent) occur in the stroma

Light Reactions (light dependent) occur in the thylakoids

Overview of Photosynthesis

Phase 1:Light Dependent Reactions

Require Sunlight

Steps to the Light Dependent Reaction

1. Light hits the chlorophyll molecules in the thylakoid membrane of the chloroplast.

2. Causes water to split.a. H+ ions Build up in the

thylakoid spaceb. Electrons move down the

electron transport chainc. Oxygen Released into the air

as a waste product

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3. Electrons move down the electron transport chain.

4. The electron exits the electron transport chain and binds with NADP+ to make NADPH.a. NADPH is like an electron bus,

shuttling electrons to the Calvin Cycle.

5. Chemiosmosis Hydrogen ions (H+) diffuse from an area of high concentration to an area of lower concentration through ATP synthase.

ATP synthase is like an ATP turbine.

Its job is to attach a phosphate to an ADP to makeATP is transferred to the Calvin Cycle

ATP

Light Dependent Reactions Recap:

Water was split

Oxygen was released as a waste product

ATP and NADPH were transferred to the Calvin Cycle

(Calvin Cycle is aka Light Independent Reactions)

Phase 2: The Calvin Cycle

• Light independent reaction: this means it does NOT need light in order to work.

• Takes place in the stroma (fluid) of the chloroplast

Here

The Calvin Cycle

Stages of the Calvin Cycle

1. CO2 (carbon dioxide) enters the chloroplast

a. The carbon in CO2 is added to a 5-carbon (RuBP) molecule to form a 6-carbon molecule

Stages of the Calvin Cycle

2. The 6 carbon molecule is split into two 3-carbon molecules (called PGA)

a. ATP and NADPH help convert a molecule of PGA into G3P.

b. During this reaction, ATP loses a phosphate (turning it into ADP) and NADPH loses its hydrogen (turning it into NADP+).

c. These molecules return to the light dependent reaction.

Stages of the Calvin Cycle

3. After several rounds of the Calvin Cycle, two molecules of G3P leave the cycle to form glucose

Making glucose is the entire point of photosynthesis!

Stages of the Calvin Cycle

4. Some G3P molecules reform the 5-carbon sugar (RuBP) with the help of rubisco and energy from ATP

5. The cycle is ready to begin again!

The Calvin Cycle

Calvin Cycle RecapLight Independent Reaction

What is made?GlucoseADPNADP+

What goes in? Carbon DioxideATPNADPH

Remember- the point of photosynthesis is for plants to make glucose.

Why is glucose so important?Plants use it for…

Food (break it down during cellular respiration)

Making cell walls

Storing it as starch (to eat later)

Questions:

1. What is the formula for photosynthesis?

2. In what organelle does photosynthesis take place?

3. What is used by a plant during the light dependent reactions?

4. What is released by a plant during the light dependent reactions?

5. What is used by a plant during the light independent reactions?

6. What is released by a plant during the light independent reactions?

7. What two things produced by light independent reactions are used during light dependent reactions?

Questions: