Photosynthesis final

Photosynthesis equation

6H₂O + 6CO₂ → C₆H₁₂O₆ + 6O₂ in the presence of light energy;

Reaction type of photosynthesis

Redox reaction where CO₂ is reduced to glucose and H₂O is oxidized to O₂ (oxygen comes from water, not CO₂);

Origin of photosynthesis biologically

Likely began in prokaryotes with chloroplasts as the main photosynthetic structure;

Autotroph definition

Organisms that make their own organic compounds from inorganic sources using energy (usually light);

Heterotrophs and consumers

Depend on other organisms for food (ex: animals, fungi, decomposers like bacteria);

Photoautotroph examples

Green plants, algae, euglena, cyanobacteria, purple sulfur bacteria;

Main photosynthetic organ

The leaf;

Leaf structure

Composed of upper/lower epidermis, stomata, mesophyll, and veins;

Function of stomata

Openings (mainly on the underside) that release oxygen and take in CO₂;

Chloroplast location in leaf

Concentrated near upper surface in the palisade mesophyll to maximize light absorption;

Spongy mesophyll

Loosely arranged cells with air spaces that allow gas exchange;

Chloroplast count per leaf cell

About 30–40;

Relationship between photosynthesis and respiration

Complementary processes—photosynthesis produces glucose and O₂ used by respiration, while respiration produces CO₂ and H₂O used by photosynthesis;

Photosynthesis stages

Light reactions (dependent on light) and Dark reactions (Calvin Cycle, light-independent);

Light reactions location

Thylakoid membranes of chloroplasts;

Dark reactions location

Stroma of chloroplasts;

Light reaction inputs

Water, light energy, ADP, NADP⁺;

Light reaction outputs

Oxygen, ATP, NADPH;

Purpose of light reaction

Convert light energy to chemical energy (ATP and NADPH) and release O₂;

Dark reaction inputs

CO₂, ATP, NADPH;

Dark reaction outputs

adds CO2 and produces sugar; G3P (glyceraldehyde-3-phosphate) → converted to glucose and sucrose;

Electromagnetic spectrum and light

Visible light is a small part (380–740 nm) used in photosynthesis;

Light behavior

Dual nature—acts as both a particle (photon) and a wave (measured in nm);

Color absorption

Red, blue, and violet light absorbed best;

Green light

Reflected, making plants appear green;

Green plant light interest

Focus on light quality, quantity, and duration;

Quality of light definition

Describes the wavelength or color composition of light affecting photosynthesis;

Absorption spectra

Graph showing which wavelengths of light pigments absorb best (chlorophyll absorbs blue and red light strongly);

Action spectra

Graph showing photosynthetic rate versus wavelength—matches the absorption spectrum, highest in blue and red;

Spectrophotometer use

Measures absorbance of light at different wavelengths to determine pigment activity;

Engelmann’s experiment

Used algae and bacteria to show that photosynthesis occurs most under blue and red light (where oxygen production is greatest);

Green shade effect

Plants grown in green light grow poorly because green light is reflected, not absorbed;

Quantity of light

Amount of light energy available for photosynthesis, measured in foot-candles or lux;

Duration of light (Photoperiod)

Length of exposure to light; affects flowering and growth cycles (long-day, short-day, and day-neutral plants);

Chlorophyll structure

Pigment molecule with magnesium at the center of a porphyrin ring; Unique because magnesium electrons become excited and move to higher energy states;

Types of chlorophyll

Chlorophyll a (main pigment), chlorophyll b and others as accessory pigments;

Light reaction overview

Photosystems (PSII and PSI) are light-harvesting complexes that capture light and convert it into chemical energy;

PSII

Absorbs light at 680 nm; splits water molecules (photolysis) releasing O₂, protons (H⁺), and electrons;

Electron pathway

Electrons from PSII travel down an electron transport chain (ETC), losing energy that is used to pump protons and generate ATP by chemiosmosis and ATP synthase;

PSI

Absorbs light at 700 nm; re-energizes electrons that reduce NADP⁺ → NADPH using enzyme NADP⁺ reductase;

End products of light reaction

O₂ (from water), ATP (from chemiosmosis), NADPH (electron carrier);

Calvin Cycle (dark reaction) function

Uses ATP and NADPH to convert CO₂ into sugars;

Calvin Cycle phase 1 (Carbon fixation)

CO₂ enters through stomata and binds to RuBP (5-carbon sugar) via enzyme Rubisco, forming a 6C intermediate that splits into two 3C molecules (3-PGA);

Phase 2 (Reduction)

3-PGA converted to G3P using ATP and NADPH; some G3P leaves to make glucose, others stay in cycle;

Phase 3 (Regeneration)

Remaining G3P used to regenerate RuBP using ATP, allowing cycle to continue;

Each full Calvin cycle

Fixes 3 CO₂ molecules and produces one G3P;

C3 plants

Named for 3C compound (3-PGA) formed first; common agricultural plants like rice, wheat, soybeans, and vegetables;

C3 plant disadvantage

In hot, dry conditions they close stomata to conserve water, reducing CO₂ intake and causing photorespiration;

Photorespiration

Occurs when Rubisco binds O₂ instead of CO₂, wasting energy and reducing sugar production (up to 50% carbon loss);

C4 plants

Include corn, sugarcane, and grasses; Adaptation

C4 plant mechanism

Stomata partially close in heat, CO₂ stored in 4C compound, later released to Calvin Cycle;

C4 plant productivity

30–40% higher than C3 plants like rice;

CAM plants

Include pineapple, cacti, aloe, and other succulents;

CAM plant adaptation

Open stomata at night to take in CO₂ and close during day to prevent water loss; CO₂ stored as organic acids at night, used in Calvin Cycle during the day;

CAM plant advantage

Efficient water conservation in arid environments;

Sugar use

Sugars from photosynthesis converted into cellulose for plant structure;

Cellulose

Most abundant carbohydrate on Earth;

Global cellulose production

About 150 billion metric tons produced annually.