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CHAPTER 10 - PHOTOSYNTHESIS

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Autotrophs vs. Heterotrophs

Autotrophs can make their own food (by doing photosynthesis or chemosynthesis)

Ex: Plants, algae, and some bacteria

Heterotrophs organisms that can NOT make their own food; they have to eat to get chemical energy Ex: Animals, humans

Oxidation when you give an electron away; become more positive

Reduction when you gain an electron; become more negative

Redox processes ALWAYS happen together! Example: Photosynthesis

Oxidation vs. Reduction

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Leaf StructurePlant cells have chloroplasts. The structure of a leaf is to the left.

Structures to note:- Stoma (stomata)- Cuticle- Veins (xylem/ phloem)- Guard Cells- Epidermis- Palisades vs. Spongy Mesophyll

***YOU WILL HAVE A SEPARATE SHEET FOR NOTES ON LEAF STRUCTURE

Xylem = carry water

Phloem = carry food

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Add-on Leaf Structure Sheet

Stoma (plural = stomata) The pore or pores surrounded by guard cells in

the epidermis of a leaf. When the stoma open, CO2 enters the leaf and

H20 and O2 exit the leaf. This is how plants conserve water.

Xylem (upper portion) – involved in H20 transport

Phloem (lower portion) – involved in sugar (food) transport

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ChloroplastsChloroplasts are the organelles where photosynthesis takes place. Know the following structures: Stroma – inside of the chloroplast; clear liquid surrounding the thylakoids; Calvin cycle happens hereThylakoid – individual circles, light reactions happen hereGrana – stacks of thylakoidsLumen - inside thylakoid

***Note the difference between stroma and stoma (stomata)

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Definition: Process that converts sunlight (light energy) into food (chemical energy)

6CO2 + 6 H2O + Light → C6H12O6 + 6O2

Photosynthesis utilizes biochemical pathways, which is when the product of one pathway is the reactant of the next; a series of linked chemical reactions (pg. 110)

Background of Photosynthesi

s

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Light

Light can be transmitted, reflected, or absorbed. Whatever color wavelength is reflected is the color that the pigment appears to be. For Example: CHLOROPHYLL IS GREEN because it reflects GREEN light!

Best colors for Photosynthesis = red/blueWorst color = green

PHOTONS = packets of radiant energy (light energy) that are absorbed by pigments to energize electrons

The ultimate source of energy for all living things is the SUN!

For the visible light spectrum, the shorter the wavelength, the more energy it contains!

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Chlorophyll A - MAIN light absorbing pigment for PS - Absorbs light energy - Reflects green light (so we see it as green)

Accessory Pigments help Chlorophyll A absorb light - Ex: Chlorophyll B and carotenoids (appear orange and yellow usually; can give flower petals their color!)

Chlorophyll and

Accessory Pigments

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Part 1 – Light Reactions

You need to be able to draw this picture! (pg

111/117)

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Light Reaction makes ATP and NADPH and sends it to the Calvin Cycle

It occurs in the thylakoid (in chloroplast) Makes ATP by chemiosmosis Energy carrier = NADPH (reduced from NADP+) Gets electrons from H2O and gives off O2 (the oxygen released is

from water, not CO2) Requires Light!!

Light Reaction

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Reaction Center Chlorophyll and

Photosystems

Reaction Center → made up of the special chlorophyll a molecule and a primary e- acceptor

Photosystems clusters of light-absorbing pigments that energize e- by trapping energy from the sun; located on the thylakoid membranes

Photosystem II → comes first in the ETC, but was discovered second; e- come from water splitting (more on this later)

Photosystem I → comes second in the ETC, but was discovered first; gives e- to NADP+, the e- get replaced by e- from PSII

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When a chlorophyll molecule absorbs a photon of light, some of the electrons are excited and raised to a higher energy level…where they are caught by a primary electron acceptor and enter the ETC (which is on the thylakoid membrane)

As e- go down the ETC, they lose energy. That energy is used to power proton pumps to pump H+ from the stroma INTO the lumen (also called thylakoid space)…this creates a concentration gradient

B/c of that concentration gradient, the H+ want to get back OUT of the lumen back into the stroma, and they can only do this by using the enzyme ATP Synthase

This enzyme creates ATP as H+ pass through it This entire process is called CHEMIOSMOSIS.

ATP Synthase

ATP Synthase is an enzyme that is powered by the H+ gradient and converts ADP to ATP.

This is how ATP is produced = CHEMIOSMOSIS

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Chemiosmosis

Makes both ATP (via ATP Synthase) and NADPH (via NADP+ reductase)

Chemiosmosis The process that uses the proton gradient and ATP synthase to make ATP

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Calvin Cycle

- Second part of PS- The CC “fixes” CO2

-Occurs in the stroma of the chloroplast

-Carbon enters as CO2 and leaves as sugar

-Produces a sugar (G3P)

-Each turn “fixes” one molecule of carbon, so one G3P takes 3 turns of the Calvin Cycle

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Calvin Cycle:

The enzyme that adds CO2 to RUBP is RUBISCO

The “dark reaction” can occur with or without light

Each Turn needs:

3 ATP2 NADPH

1 CO2

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Rate of Photosynthesis

The rate of PS is affected by 3 things: Light intensity Amount of CO2

Temperature

Why wouldn’t roots need chloroplasts?

Root cells don't have chloroplasts, because chloroplasts catch sunlight! Since roots are underground, they are not exposed to the sun!

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Alternate Pathways

Sometimes if it is too hot out, the plant will close the stomata so that it doesn’t lose too much water and become dehydrated… however, this eliminates the gas exchange!!

SO the levels of CO2 drop and the levels of O2 increase…which results in…. PHOTORESPIRATION

- Adds oxygen to the Calvin Cycle instead of carbon dioxide

- This makes NO sugar or ATP- This process wastes all of the plants

resources!

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C4 Plants- Fix the carbons into a 4C molecule instead of a 3C molecule- Uses a different enzyme that makes sure to

add CO2 instead of O2

- Ex: Corn & Sugarcane

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CAM Plants - Open their stomata at night and store the CO2 in organic acids

- During the day they break those acids down to use the CO2

- Ex: Pineapples, cacti

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For the test, you will need to know these pictures:

Calvin Cycle Light Reactions Leaf Structure

All these can be found on the wiki!!