Photosynthesis DAT Ch 4

DAT Ch 4

Heterotrophs

must get energy from the food they eat

Autotrophs

make their own food

Photoautotrophs

use light energy to convert it to chemical energy using photosynthesis

Photosynthesis

process originally developed in cyanobacteria and reduces atmospheric carbon dioxide, releases oxygen, and creates chemical energy that can be transferred through food chains

Photons

light energy used to synthesize sugars in photosynthesis

Carbon Fixation

process by which inorganic carbon is converted into an organic molecule of glucose

Photolysis

releases electrons to be used in photosynthesis, process of splitting water molecules, excites them by using solar energy

Photosynthesis Spontaneity

non spontaneous and endergonic

Cellular Respiration Spontaneity

spontaneous and exergonic

Mesophyll Cells

between upper and lower epidermis of leaves, facilitate gas movement within the leaf, contain chloroplasts

Chloroplasts

organelle that carries out photosynthesis, found in plants and photosynthetic bacteria but not in cyanobacteria

Outer Membrane

Outer plasma membrane made of phospholipid bilayer

Intermembrane Space

Space between the outer and inner membranes

Inner membrane space

Inner membrane plasma made of phospholipid bilayer

Stroma

Fluid material that fills the area inside the inner membrane. Calvin cycle occurs here

Thylakoids

A membrane structure within the stroma. Multiple stack up to form a granum. They are the site of light dependent reactions

Thylakoid Lumen

Interior of the thylakoid, H+ ions accumulate here, making it acidic

Light dependent reactions

thylakoid membrane, harness light energy to produce ATP and NADPH, this ATP is NOT used to power the cell it is used to power the Calvin Cycle

NADPH

an electron carrier from Light dependent reaction to Calvin Cycle

Photosystems

special pigments such as chlorophyll, that absorb photons

Chlorophyll

absorbs red and blue light, reflects green light

Reaction Center

special pair of chlorophyll molecules in the center of these proteins

Chlorophyll Structure

porphyrin rings structure with a magnesium atom bound in its center, containing Photosystem II and Photosystem I that are used in photosynthesis

Non cyclic photophosphorylation

carried out by the light dependent reactions, with six steps

Step 1 of Non cyclic photophosphorylation

water is split (photolysis), passing electrons to Photosystem II and releasing protons into the the thylakoid lumen

Step 2 of Non cyclic photophosphorylation

Photons excite electrons in the reaction center of PS II, passing electrons to the primary electron accepter (NADPH)

Step 3 of Non cyclic photophosphorylation

Primary electron accepter sends the excited electrons to the electron transport chain during redox reactions, protons pump into the thylakoid lumen. Electrons deposited into the PS I

Step 4 of Non cyclic photophosphorylation

Photons excite pigments in PS I, energizing electrons int he reaction center to be passed to another primary electron acceptor

Step 5 of Non cyclic photophosphorylation

The electrons are sent to a short electron transport chain that terminates with NADP+ reductase

NADP+ reductase

enzyme that reduces NADP+ into NADPH using electrons and protons during step five of the non cyclic photophosphorylation

Step 6 of Non cyclic photophosphorylation

accumulation of protons in the thylakoid lumen generates an electrochemical gradient that is used to produce ATP using an ATP synthase, moving H+ into the stroma

Cyclic Photophosphorylation

Electrons from PS I are cycled back into the first ETC, increasing the amount of protons pumped into the Thylakoid lumen. Bypass NAD+ reductase so no NADPH is produced

Calvin Cycle

light independent reactions in the chloroplast stroma of plant mesophyll cells , use ATP and NADPH from light dependent reactions, fixes carbon dioxide that enters the leaves through the stomata

Stomata

pores in the epidermis of the leaves of a plant, closed in hot environments to minimize water loss and accumulate oxygen (photorespiration)

Carbon fixation (step 1)

carbon dioxide combines with five carbon (RuBP) to form six carbon molecules, which quickly break down into three carbon PGA, catalyzed by RuBisCo

Reduction (step 2)

PGA is phosphorylated by APT, then NADPH to form G3P

Regeneration (Step 3)

Most of G3P is converted back into RuBP

Carbohydrate Synthesis (Step 4)

Some of the G3P is used to make glucose

Calvin Cycle Reaction Formula

6Co2 +18ATP +12 NADPH +H+ → 18ADP + 18pi + 12 NADP+ + 1 Glucose

Photorespiration

produces two carbon phosphoglycerate and eventually converts it to PGA, there is a net loss of fixed carbon in the process and no new glucose is produced

RuBISCO

in addition to fixing carbon dioxide into RuBP, can also cause oxygen to bind to RuBP in a process called photorespiration

Alternate name for photorespiration

C2 Photosynthesis, since a two carbon molecule is produced (PGA)

Alternative Photosynthetic Pathways

C3 Photosynthesis, C4 Photosynthesis, and Crassulacean Acid Metabolism (CAM) Photosynthesis

C3 Photosynthesis

Normal photosynthesis, where three carbon PGA is produced

C4 Photosynthesis

produce a four carbon intermediate , uses spacial isolation of carbon dioxide to prevent photorespiration in plants living in hot environments

C4 Step 1

Co2 is fixed and produces a four carbon intermediate, oxaloacetate which is then converted into a second intermediate, malate in the mesophyll cells

C4 Step 2

Malate is transferred into the bundle sheath cells which have less oxygen

C4 Step 3

Malate is decarboxylated, spatially isolating Co2. It is then fixed by rubisco and enters the calvin cycle

CAM

Uses temporal isolation of carbon dioxide to prevent photorespiration in hot and dry environments

CAM Step 1

During the day the stomata are closed to prevent transpiration

Transpiration

evaporation of water from plants

CAM Step 2

During the night stomata open to let Co2 in, just as in C4, photosynthesis, Co2 is fixed, producing oxaloacetate. however malate is not shuttled to bundle sheaths

CAM Step 3

During the next day, the stomata are closed again and malate is decarboxylated. Co2 is temporally isolated from O2 which cannot enter during the day. Co2 is fixed by RuBIsCo and enter the Calvin Cycle

C3 Plants

C4 Plants

CAM plants