MLB photosynthesis (copy)

What is the difference between autotrophic and heterotrophic organisms? Provide examples.

Autotrophic organisms make their own food (e.g., plants, algae), while heterotrophic organisms rely on consuming other organisms for food (e.g., animals, fungi).

Autotrophs

Able to use only H2O and CO2 to make their own carbohydrates

Heterotroph

Cannot make own carbohydrates must consume other organisms to obtain molecules for their activities

Photosynthesis formula

sunlight + 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What is the chemical equation for photosynthesis, and how does it relate to aerobic respiration

Photosynthesis equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O2. Aerobic respiration equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Both are opposite processes; photosynthesis stores energy, while aerobic respiration releases energy

Describe the experiment of Ruben et al. and how it showed that oxygen during photosynthesis comes from H2O and not CO2.

Ruben et al. used isotopic labeling (oxygen-18) to track oxygen atoms. They found that the oxygen released during photosynthesis came from water (H2O), not carbon dioxide (CO2), proving that water is split during photosynthesis.

What are the two stages of photosynthesis, and how do they support its endergonic/anabolic nature?

Light-dependent reaction: Produces ATP and NADPH. Light-independent reaction (Calvin cycle): Uses ATP and NADPH to fix carbon into glucose. Photosynthesis is anabolic and endergonic, as both stages involve energy input.

Light-dependent reactions

Prooduce ATP and NAPH

Carbon-fixation (calvin cycle) Light independent

Use ATP and NAPDH made from light reactions and CO₂ → Carbohydrates

Anabolic building

When a photon meets a molecule.

1. photon bounces off/ scattered or reflected

2. pass through the molecule / transmitted

3. Photon is absorbed by the molecule, adding energy

Where do the light-dependent and light-independent reactions of photosynthesis take place?

Light-dependent reactions occur in the thylakoid membranes. Light-independent reactions (Calvin cycle) occur in the stroma.

What is the relationship between wavelength and energy in the electromagnetic spectrum?

Shorter wavelengths (e.g., violet light) have higher energy, while longer wavelengths (e.g., red light) have lower energy.

How do photosynthetic pigments determine the action spectrum of photosynthesis?

Photosynthetic pigments absorb light at specific wavelengths. The action spectrum shows the range of light that drives photosynthesis, corresponding to the absorption spectrum of chlorophyll and other pigments.

Explain how components of chlorophyll and the photosystem work together to excite electrons.

Chlorophyll a absorbs light and excites electrons, while accessory pigments capture additional wavelengths. The antenna complex gathers light and transfers energy to the reaction center, where electrons are excited and passed to the electron transport chain.

Electron transport path (2e^-)

H₂O → photosystem II → Plastoquinone → Cytochrome → plastocyanin → Photosystem I → Ferrodoxin → NADP+ reductase → NADP+

What are the four processes of the thylakoid reaction, and how do they contribute to ATP and NADPH production?

1. Light capture: Absorption of photons. 2. Energy transfer: Excited electrons move to the reaction center. 3. Electron transport: Electrons are passed along the transport chain. 4. ATP synthesis: Protons flow through ATP synthase, generating ATP. These steps produce ATP and NADPH for the light-independent reactions.

How do the two photosystems function, and what are their products?

Photosystem II absorbs light, splits water, and produces oxygen. Photosystem I excites electrons, which produce NADPH. Together, they power the light-dependent reactions, producing ATP and NADPH.

Photophosphorylation/ATP synthesis

Maintenance of H+ conc gradient across thylakoid membrane

1. Electron Carriers actively transport H+ from stroma to thylakoid lumen

2. Water oxidation creates more H+ in the thylakoid lumen

3. NADP+ reduction removes H+ in the stroma

What is cyclic electron transport, and why does it occur?

Cyclic electron transport occurs in Photosystem I, where electrons cycle back instead of moving to NADP+, generating additional ATP without producing NADPH.

cyclic transport (e-)

Photosystem I → Ferrodoxin → cytochrome → Plastocyanin → Photosystem I → light energy gives excited e-

How do the products of Photosystems I and II drive the light-independent reactions?

The products of Photosystems I and II (ATP and NADPH) provide the energy and reducing power necessary for the Calvin cycle to fix carbon into glucose.

Describe carbon fixation via the Calvin cycle, including the inputs and outputs.

Inputs: CO2, ATP, and NADPH. Outputs: Triose phosphates (which are used to form glucose). The cycle fixes carbon from CO2 into organic molecules, using energy from ATP and NADPH.

main enzyme for Calvin cycle

Rubisco ( ribulose biphosphate carboxylase/oxygenase)

Calvin cycle

1. Fixation of CO₂

2. reduction of 3PG → forms glyceraldehyde 3-phosphate

3. regeneration of RuBP

What is photorespiration, and how does it affect photosynthesis efficiency?

Photorespiration occurs when oxygen is used instead of carbon dioxide in the Calvin cycle, reducing efficiency and wasting energy. CO₂ wastage which in necessary in the calvin cycle

Compare and contrast photosynthesis and aerobic respiration of glucose.

Photosynthesis uses light energy to convert CO2 and H2O into glucose and oxygen (endergonic). Aerobic respiration breaks down glucose and oxygen into CO2, H2O, and energy (exergonic). Both processes are involved in energy transformations but occur in opposite directions.

Factors affecting CO₂ levels

• during hot days stomata close to preserve H₂O

• gas exchange stops

  • CO₂ is used up in calvin cycle

  • O₂ being used by Photosystem II

• photorespiration

  • occurs in light

  • consumes O₂

  • releases CO₂

Photosyntheis vs respiration

chloroplast vs mitochondrion

NAD+ vs NADP+

reversible vs non-reversible

Creates net ATP vs Photosynthesis that uses ATP it creates

Similarities of Photosynthesis vs respiration

• Involve energy

• G3P is a intermediate moleculule

• Electron transport chains

• crrate and use ATP

• priducts that enter other metabolic pathways