anaerobic respiration/fermentation

when does fermentation occur

oxygen is unavailable

fermentation — what does it begin and end with

begin → glycolysis, end → when NAD+ generated

where does fermentation and aerobic respiration mainly differ

ETC because no oxygen available → can’t pass down to final electron receptor and causes NADH buildup → NAD+ shortage

2 main types of fermentation

alcohol & lactic acid

alcohol fermentation steps

conversion of pyruvate → 2-carbon acetaldehyde molecules → converted to ethanol, regeneration 2 NAD+ molecules in the process

3 things produce ethanol

yeast, fungi, bacteria

lactic acid steps

pyruvate directly reduced to lactate by NADH to regen NAD+ needed for resumption of glycolysis

where does the 1st stage of photosynthesis occur

stroma → thylakoid membrane system

bundle sheath cells

cells that are tightly wrapped around the veins of a leaf. Site for Calvin cycle in C₄ plants

C₄ plant

plant has adapted its photosynthetic process to more efficiently handle hot & dry condition

mesophyll

interior tissue of a leaf

photolysis

water is broken up by an enzyme into hydrogen ions and oxygen atoms → occurs during light-dependent reactions of photosynthesis

photophosphorylation

ATP is produced during the light-dependent reaction of photosynthesis. Chloroplast equivalent of oxidative phosphorylation

photorespiration

oxygen competes with CO2 and attached to RuBP

photosystem

cluster of light-trapped pigment involved in the process of photosynthesis. Photosystems vary tremendously in their organization and can possess hundreds of pigments. 2 most important systems = I & II of light reactions

pigment

a molecule that absorbs light of a particular wavelength. Pigments are vital to the process of photosynthesis and include chlorophyll, carotenoids, phycobilins

rubisco

enzyme that catalyzes the first step of the Calvin cycle in C₃ plants

stomata

structure through which CO2 enters a plant and water vapor and O₂ leave

transpiration

natural process by which plants lose water via evaporation through their leaves

photosynthesis 2 sets of reactions

light-dependent & light-INDEPENDENT reaction

light-dependent reactions (noncyclic)

• starts in thylakoid system

• pigments of thylakoid sys. organize themselves into photosystems (varying combos of chlorophyll a&b, phycobilins, carotenoids)

• light excites photosystem, absorbing the photon and transmits energy (losing E with each step) eventually reaching chloro a → 1st step of photosynthesis

  • TL;DR passing electron to primary electron receptor aka chloro a

• As light strikes photosystem 2, energy is absorbed and passed along until it reaches P680 chlorophyll. When it’s excited it passes electrons to primary electron acceptor

2 chlorophylls

chlorophyll a - major pigment of photosynthesis

chlorophyll b - accessory pigment → help pick up light when chloro a can’t do it effectively

light-dependent reactions pt 2. (noncyclic)

• photolysis in thylakoid space takes electrons from H2O and passes them to P680 to replace the electrons given to the primary acceptor

• this reaction causes lone oxygen atom and pair of hydrogen ions. Lone oxygen atom quickly finds another oxygen buddy & pairs with it, creating O₂ → FIRST PRODUCT OF THE LIGHT REACTIONS

light-dependent reactions pt 3 (noncyclic)

• as electrons are passed from P680 to P700, lost energy is used to create ATP (chemiosmosis) → 2nd product of light reactions via photophosphorylation

• after P700 electrons are excited, it passes the energy to its own primary electron acceptor, which are sent down to another chain to ferridoxin, donating the electrons to NADP+ to make NADPH → 3rd and final product of light reaction

inputs to light reactions

water and light

light reactions produce 3 products

ATP, NADPH, O₂

oxygen produced in light reactions comes from…

WATER NOT CO2

the 2 reaction centers

photosystem I & II (P700, P680 respectively)

cyclic pathway only uses photosystem I or II

photosystem I

why is cyclic pathway cyclic

electrons pass down the electron chain and eventually back to P700. Energy given off is used to make ATP. O₂ and NADPH is not produced

important for Calvin cycle

how is ATP formed in this process

• as electrons are passing form the primary electron acceptor to the next photosystem, H ions are picked up from outside the membrane and brought back to the thylakoid

  • creates H+ gradient similar to ox-phos

• when H ions are taken from water during photolysis, the proton gradient grows larger, causing some protons to leave → forms ATP

inputs into Calvin cycle

• NADPH (provides hydrogen and electrons)

• ATP (provide energy)

• CO2

where calvin cycle occurs

stroma of chloroplast (fluid around thylakoid aka poker chips)

beginnng of calvin cycle

• carbon fixation — binding of carbon from CO2 to a molecule that can enter the Calvin cycle (usually RuBP)

• reaction is assisted by the rubisco enzyme

• 6-carbon molecule breaks into 2 3-carbon molecules, 3PG

• ATP & NADPH donate phosphate group & hydrogen electrons to 3PG, making G3P

  • most G3P converted into RuBP

  • remaining G3P is used to make carbs for plant

in calvin cycle, which is used more, ATP or NADPH

ATP → creates need for cyclic photophosphorylation

the carbon of the sugar produced in photosynthesis comes from the [__] of the calvin cycle

the carbon of the sugar produced in photosynthesis comes from the CO2 of the calvin cycle

transpiration

natural process by which plants lose water by evaporation from their leaves → close stomata to conserve water during high temps

photorespiration

excess oxygen competes with CO2 & attached to RuBP → formation of 1 molecule of PGA & 1 phosphoglycolate

what happens to plants that experience photorespiration?

lowered capacity for growth → sugar formed in photosynthesis comes from PGA, not phosphoglycolate

C4 photosynthesis

• converts CO2 into 4-carbon molecule (oxaloacetate) in the mesophyll cells

• converts that product to malate

• takes the malate into the bundle sheath cells

  • malate releases CO2, which reacts w/ rubisco to make carbohydrate

CAM photosynthesis

plants close their stomata during the day, collect CO2 at night, and store CO2 in the form of acids until needed during the day for photosynthesis