CHAPTER 10 - Photosynthesis

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CHAPTER 10 - PHOTOSYNTHESIS

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

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

Add-on to Leaf Structure Sheet

Stoma (plural = stomata) The pore \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

Chloroplasts

• Chloroplasts are the organelles where photosynthesis takes place!

Know the following structures:

• Stroma – inside of the chloroplast; clear liquid surrounding the thylakoids; Calvin Cycle happens here

• Thylakoid – individual sacs inside chloroplast, light reactions happen here

• Grana – stacks of thylakoids• Lumen - inside thylakoid

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

CHLOROPLAST

Occurs in the chloroplast Divided into 2 sets of reactions:

- Light Dependent Reaction- Calvin Cycle (Dark Reaction)

Photosynthesis

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

6CO2 + 6 H2O 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)

Photosynthesis

SunlightREDUCED

OXIDIZED

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!

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

- Often appear orange and yellow - Can give flower petals their color!

Chlorophyll and

Accessory Pigments

Part 1 – Light Reactions

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

111/117)

Photosystem IIPhotosystem I

H2O Splits

During the “light reaction,” ETC makes ATP and NADPH 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

Reaction Center Chlorophyll & Photosystems

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+• Electrons get replaced by e- from

Photosystems • Located on the thylakoid membranes• Clusters of light-absorbing pigments

trap energy from the sun energize e-

• This energy is passed from molecule to molecule until it reaches the rxn center

Reaction Center → • Surrounded by photosystems• Made up of the special chlorophyll

a molecule and a primary e- acceptor

• Primary e- acceptor passes the e- to the electron transport chain (ETC)

When a chlorophyll molecule absorbs a photon of light, some of the electrons are excited and raised to a higher energy level

The primary electron acceptor catches them & they enter the ETC (on the thylakoid membrane)

CHEMIOSMOSIS

• As e- go down the ETC, they lose energy

• That energy is used to power proton pumps that pump H+ from the stroma INTO the lumen (aka - thylakoid space)

• This creates a concentration gradient

B/c of that concentration gradient, the H+ ions want to get back OUT of the lumen and into the stroma

These ions can only do this by using the enzyme ATP Synthase

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

Summary : ATP Synthase creates ATP as H+ pass through it

ATP Synthase

Summary: Chemiosmosis The process that uses the proton gradient

and ATP synthase to make ATP Both ATP (via ATP Synthase) and NADPH (by reducing

NADP+) are produced during the light reaction these then enter the Calvin Cycle

e- travel from PSII PSI NADP+ NADP+ is the final e- acceptor in photosynthesis

CHEMIOSMOSIS…

Calvin Cycle!- Second part of PS- AKA – “The Dark Reaction”- Occurs in the stroma of the chloroplast- Can occur with or without light

Main job: Incorporate CO2 and rearrange C’s to form sugar using the energy (ATP/NADPH) from the Light Rxn

- The CC “fixes” CO2

- Carbon enters as CO2 and leaves as sugar

-Goal is to produce a sugar (G3P)

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

INPUT: Each Turn needs:

- 3 ATP- 2 NADPH- 1 CO2

Three turns shown above

Calvin Cycle Steps:1) Enzyme

Rubisco attaches CO2 to RuBP creates 6 x 3-PGA

2) 6 x PGA are reduced to = 6 x G3P (sugar) via ATP/NADPH

3) 1 x G3P exits as glucose

4) 5 x G3P remain in the cycle . ATP rearranges the atoms 3 x RuBP

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!

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 Photorespiration adds oxygen to the Calvin

Cycle instead of carbon dioxide- This makes NO sugar or ATP- This wastes all of the plants resources!

C4 Plants- Fixes 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

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

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

Calvin Cycle Light Reactions Leaf Structure

All these can be found on the wiki/book!!

CHAPTER 10 - Photosynthesis

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