Photosynthesis:� Life from Light and Air�General Biology A

Energy needs of life

• All life needs a constant input of energy
• Heterotrophs (Animals)
• get their energy from “eating others”
• eat food = other organisms = organic molecules
• make energy through respiration
• Autotrophs (Plants)
• produce their own energy (from “self”)
• convert energy of sunlight
• build organic molecules (CHO) from CO₂
• make energy & synthesize sugars through photosynthesis

consumers

producers

How are they connected?

Heterotrophs

Autotrophs

making energy & organic molecules from light energy

making energy & organic molecules from ingesting organic molecules

Where’s �the ATP?

oxidation = exergonic

reduction = endergonic

What does it mean to be a plant

• Need to…
• collect light energy
• transform it into chemical energy
• store light energy
• in a stable form to be moved around �the plant or stored
• need to get building block atoms �from the environment
• C,H,O,N,P,K,S,Mg
• produce all organic molecules �needed for growth
• carbohydrates, proteins, lipids, nucleic acids

ATP

Objective 1: Explain the Function and Purpose of ATP

• The function of ATP is to be a chemical energy storage molecule by storing energy in the bonds between phosphate groups.
• The purpose of ATP is to be a molecule which can be used by cells to provide a source of chemical energy so the cell can complete cellular tasks/activities.

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• What is ATP?

ATP

ATP

Adenosine Triphosphate

• Adenosine is made of:
• a nitrogen base (Adenine) Adenine + Ribose = Adenosine
• a sugar (Ribose)
• 3 phosphate groups

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Where is the chemical energy stored in ATP?

• Chemical Energy is stored in the bonds between the 2^nd and 3rd phosphate groups.

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How Energy in ATP is Used?

• ATP is unstable and exergonic when a phosphate group is broken off.
• ADP (adenosine diphosphate) is created.
• ADP can again add a phosphate group and recreate ATP. Energy is stored in the bonds between the phosphate groups. The most energy is stored between the 2^nd + 3^rd phosphate groups.

Objective 2: Describe the Process of Photosynthesis

• The purpose of photosynthesis is to make sugar using solar energy.
• The function of photosynthesis is to use light (solar energy), carbon dioxide, and water to make sugar and oxygen gas.

Where does photosynthesis occur?

Light Reactions and Light Independent Reactions

• Light Reactions (Rx) occur in the thylakoid membranes in chloroplasts

Light Dependent Rx (Photosystem II and Photosystem I)

• Photosystem II (PSII) -Located in the membrane of the thylakoid in a chloroplast
• Light strikes the chlorophyll a pigments which transfer energy to existing electrons this raises the electrons to a higher energy level (excites electrons) or state (not ground state).

Light Dependent Rx (Photosystem II)

• Energized electrons move from one protein to the next protein in the thylakoid membrane. As energized electrons move, electrons “lose” energy. That ”lost” energy is used to pump protons (H+) ions across the membrane.

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Light Dependent Rx (Photosystem II)

• Water is broken down to produce protons (H⁺) x 2 and electrons (e-) x 2. H₂0 has 2 hydrogen atoms. Each hydrogen is made of 1 proton and 1 electron. The protons are pumped through the membrane. The 2 electrons replace the 2 electrons used at the beginning of photosystem II (PSII). Oxygen binds with another oxygen and is released (O₂).
• The protons move through a

protein called ATP synthase,

which makes ATP.

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PSII makes ATP.

Light Dependent Rx (Photosystem I)

• Photosystem I (PSI)-Located in the membrane of a thylakoid in a chloroplast.

• Electrons from PSII are again energized by sunlight. Chlorophyll b transfers energy to the 2 electrons, again raising their energy state.
• NADPH is an electron carrier (in the Hydrogen atom)
• Photosystem I makes NADPH molecules
• 18 ATP and 12 NADPH are used in the Calvin cycle (Light Independent Rx)

Light Independent Reaction (Calvin Cycle)

• The Calvin Cycle:
• Uses:
• CO₂
• ATP
• NADPH
• Makes G3P x 2 = glucose

G3P-glyceraldehyde-3-Phosphate

• G3P is a building block to make a sugar.
• 2 G3P molecules combine to form a sugar called glucose.
• G3P can also be used as a building block to make proteins (amino acids), lipids (fats, waxes), nucleic acids (DNA or RNA), and other carbohydrates (fructose).

Objective 3: Molecules Used and Produced in Photosynthesis with the equation

Reactants Products

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• 6 CO2 + 6 H20 + Sunlight 🡪 C6H12O6 + 6O2

Calvin Cycle + Light Dep + Light Dep 🡪 Glucose + Calvin Cycle/PSII

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Objective 4: Explain what molecules are used and produced in the process of photosynthesis

• Summary:
• Light Dependent Rx: PSII and PSI
• Make: ATP, NADPH, O2-Oxygen Gas
• Uses: H20
• Light Independent Rx – Calvin Cycle
• Make: G3P (Sugar) X 2 = Glucose
• Uses: ATP, NADPH, CO2
• The products of photosynthesis are ATP, NADPH, O2, and G3P (1/2 glucose). ATP and NADPH are used in the Calvin cycle. Extra ATP are used by cells for cellular activities. O2 (oxygen gas) is used for cellular respiration in our cells. G3P can be used to make sugar (glucose).