Photosynthesis + Cellular Respiration

Photosynthesis chemical equation

6CO2+6H2O→C6H12O6+6O2.

Cellular Respiration chemical equation

C₆H₁₂O₆ +6 O₂ ——>6 CO₂+ 6 H₂O + 30 ATP

Light dependent reaction

Location: Thylakoids

Requires: Light energy + Water (H20)

Produces: Oxygen (O2) ATP (energy) NADPH (electron carrier)

Main Steps:

1. Photons excite electrons in chlorophyll (Photosystem II).

2. Water is split (photolysis) → releases O₂, H⁺, and electrons.

3. Electron Transport Chain (ETC): electrons move through proteins, pumping H⁺ into thylakoid space.

4. Photosystem I: electrons are re-energized and transferred to NADP⁺ → NADPH.

5. ATP Synthase: H⁺ flows back out through ATP synthase → ATP is made (chemiosmosis).

Purpose:

• To convert solar energy into chemical energy (ATP & NADPH) for the Calvin Cycle.

Photostem

What is a Photosystem?

• A protein-pigment complex in the thylakoid membrane that absorbs light and transfers excited electrons.

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Photosystem II (PSII):

• First in the chain (but discovered second).

• Absorbs light → excites electrons.

• Splits water (photolysis) → O₂, H⁺, and e⁻.

• Passes electrons to the Electron Transport Chain (ETC).

Photosystem I (PSI):

• Second in the chain (discovered first).

• Re-energizes electrons from the ETC.

• Electrons are used to form NADPH from NADP⁺.

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Key Points:

• Contain chlorophyll (main pigment).

• Work together to capture solar energy and power ATP & NADPH production.

Photolysis

Definition:

• The splitting of water molecules using light energy during the light-dependent reactions of photosynthesis.

Where it happens:

• In Photosystem II (thylakoid membrane)

Equation:

• 2H₂O → 4H⁺ + 4e⁻ + O₂

Produces:

• Electrons (e⁻) – replace those lost by chlorophyll in PSII

• Hydrogen ions (H⁺) – used to make ATP

• Oxygen (O₂) – released as a byproduct into the atmosphere

Purpose:

• Supplies electrons for the Electron Transport Chain

• Contributes H⁺ for the proton gradient

• Releases oxygen gas we breathe

Light Independent Reaction (Calvin cycle)

Location:

• Stroma of the chloroplast

Requires:

• ATP and NADPH (from light-dependent reactions)

• Carbon dioxide (CO₂)

Produces:

• Glucose (C₆H₁₂O₆) or other sugars

Main Steps:

1. Carbon Fixation: CO₂ is attached to a 5-carbon molecule (RuBP) using the enzyme RuBisCO.

2. Reduction: ATP and NADPH are used to convert the fixed carbon into G3P (a 3-carbon sugar).

3. Regeneration of RuBP: Some G3P is recycled using ATP to regenerate RuBP, so the cycle can continue.

Purpose:

• To use chemical energy (ATP & NADPH) to build sugars from CO₂.

Krebs cycle

Location:

• Mitochondrial matrix

Requires:

• Acetyl-CoA (from glucose)

• Oxygen (indirectly)

Produces (per 1 glucose):

• 2 ATP

• 6 NADH

• 2 FADH₂

• 4 CO₂

Main Steps:

1. Acetyl-CoA combines with a 4-carbon molecule to make citric acid (6 carbons).

2. Citric acid is broken down, releasing CO₂.

3. NADH and FADH₂ are made, and ATP is produced.

Purpose:

• Make NADH, FADH₂, and ATP to power the Electron Transport Chain.

Electron support chain

Location:

• Inner mitochondrial membrane

Requires:

• NADH and FADH₂

• Oxygen (final electron acceptor)

Produces:

• ATP

• Water (H₂O)

Main Steps:

1. Electrons from NADH and FADH₂ pass through proteins.

2. Protons (H⁺) are pumped across the membrane, creating a gradient.

3. ATP Synthase uses the proton flow to make ATP.

4. Oxygen combines with electrons and H⁺ to form water.

Purpose:

• Make lots of ATP and water using oxygen.

glycolysis

Location:

• Cytoplasm

Requires:

• 1 Glucose

• 2 ATP (to start)

Produces:

• 2 Pyruvate

• 2 NADH

• 4 ATP (net gain of 2)

Main Steps:

1. Energy Investment: Use 2 ATP to break glucose into two 3-carbon molecules (G3P).

2. Energy Payoff: Each G3P makes 2 ATP and 1 NADH, ending with 2 pyruvate.

Purpose:

• Break down glucose for energy and produce ATP and NADH.

Glycolosis aerobic vs anaerobic

Location:

• Cytoplasm (for both anaerobic and aerobic)

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Anaerobic Glycolysis(No Oxygen):

• Ends with: Lactate (in animals) or Ethanol (in yeast)

• ATP Produced: 2 ATP (net gain)

• NADH: Recycled to NAD⁺ so glycolysis can continue without oxygen.

When it occurs:

• When oxygen is not available (like in intense exercise).

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Aerobic Glycolysis(With Oxygen):

• Ends with: Pyruvate, which enters the Krebs Cycle

• ATP Produced: 2 ATP (net gain)

• NADH: Goes to the Electron Transport Chain to produce more ATP.

When it occurs:

• When oxygen is available.

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Main Difference:

• Anaerobic: No oxygen, produces lactate or ethanol, less ATP.

• Aerobic: Oxygen available, produces pyruvate for more ATP production in mitochondria.

Autotroph

organism that makes its own fo

Heterotroph

organism that relies on other organisms for food

ATP

adenosine triphosphate

Three parts of ATP

adenine, ribose + 3 phosphate

Where is energy scored in the ATP molecule

covalent bonds between the phosphate groups

Reactants of photosynthesis

CO2, H2O & sunlight

Products of photosynthesis

C6H12O6 (glucose) & O2

What is chlorophyll

light absorbing pigment

What colors of light does chlorophyll absorb

red, blue and violet

What colors of light does chlorophyll reflect

green + yellow

The name for the group of orange and yellow accessory pigments

Carotenoids

Where does the whole process of photosynthesis take place

Chloroplast

The name of the first biochemical pathway in photosynthesis

light dependent reaction

The name of the structure within the chloroplast where the light dependent reaction occurs

Thylakoids

What gas is released from the thylakoids into the atmosphere

O2

The subatomic particle released from water responsible for the production of NADPH

Electrons

The combination of photosystems and electron carries is called the….

Electron transport chain

The subatomic particle released from water is responsible for the production of ATP

protons

the diffusion of these H+ ions is called

chemiosmosis

where in the chloroplast do NADPH and ATP end up

in the stroma

What molecules serve as activation energy for the Calvin cycle

carbohydrates (glucose)

What is the purpose of carbohydrates

energy storage and fuel + energy production

The process by which a glucose molecules is broken into pyretic acid molecules

glycolysis (occurring in the cytoplasm)

what is the net gain of ATP from glycolysis2

2

Another name for anaerobic respiration

fermentation

product of anaerobic respiration in animals and plants

animals: Lactic acid Plants: ethanol and carbon dioxide

does anaerobic respiration produce any additional ATP

no

Where does aerobic respiration occur

mitochondria

name of the central biochemical pathway in aerobic respiration

Krebs cycle

how many carbon dioxide molecules are lost in each cycle of the Krebs cycle

3

How many times does the Krebs cycle have to turn for one molecule pf glucose

twice

net loss of carbon dioxide for one molecule of glucose

6

net gain ATP from Krebs cycle

2

how many ATP molecules are produced from each NADH molecule

3

How many ATP molecules are produced from each FADH2 molecule

2

total ATP production from one molecule of glucose is…

38