ACTUAL FINAL PHOTOSYNTHESIS CARDS

What is the equation for photosynthesis?

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

What type of reaction is photosynthesis?

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

Where did photosynthesis likely originate?

It likely began in prokaryotes with chloroplasts as the main photosynthetic structure;

What is an autotroph?

An organism that makes its own organic compounds from inorganic sources using energy, usually light;

What are heterotrophs and consumers?

Organisms that depend on other organisms for food, such as animals, fungi, and decomposers like bacteria;

What are some examples of photoautotrophs?

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

What is the main photosynthetic organ in plants?

The leaf;

What is the structure of a leaf?

It is composed of the upper and lower epidermis, stomata, mesophyll, and veins;

What is the function of stomata?

They are openings (mainly on the underside of the leaf) that release oxygen and take in carbon dioxide;

Where are chloroplasts located in the leaf?

They are concentrated near the upper surface in the palisade mesophyll to maximize light absorption;

What is the function of the spongy mesophyll?

It contains loosely arranged cells with air spaces that allow gas exchange;

How many chloroplasts are typically found in a leaf cell?

About 30–40 per cell;

How are photosynthesis and respiration related?

They are complementary processes—photosynthesis produces glucose and oxygen used by respiration, while respiration produces carbon dioxide and water used by photosynthesis;

What are the two stages of photosynthesis?

The light reactions (which depend on light) and the dark reactions (the Calvin Cycle, which are light-independent);

Where do the light reactions occur?

In the thylakoid membranes of the chloroplast;

Where do the dark reactions occur?

In the stroma of the chloroplast;

What are the inputs of the light reactions?

Water, light energy, ADP, and NADP⁺;

What are the outputs of the light reactions?

Oxygen, ATP, and NADPH;

What is the purpose of the light reactions?

To convert light energy into chemical energy (ATP and NADPH) and release oxygen;

What are the inputs of the dark reactions?

Carbon dioxide, ATP, and NADPH;

What are the outputs of the dark reactions?

G3P (glyceraldehyde-3-phosphate), which is converted into glucose and sucrose;

What part of the electromagnetic spectrum is used in photosynthesis?

Visible light, which is a small portion of the spectrum (380–740 nm);

What is the dual nature of light?

It acts as both a particle (photon) and a wave (measured in nanometers);

Which colors of light are best absorbed for photosynthesis?

Red, blue, and violet;

Why do plants appear green?

Because green light is reflected, not absorbed; and they include chlorophyll

What three aspects of light do green plants respond to?

Light quality, light quantity, and light duration;

What is the quality of light?

It refers to the wavelength or color composition of light that affects photosynthesis;

What is an absorption spectrum?

A graph showing which wavelengths of light pigments absorb best—chlorophyll absorbs blue and red light most strongly;

What is an action spectrum?

A graph showing the rate of photosynthesis versus wavelength, which matches the absorption spectrum and is highest in blue and red light;

What tool measures light absorption by pigments?

A spectrophotometer, which measures absorbance at different wavelengths;

What did Engelmann’s experiment show?

That photosynthesis occurs most under blue and red light, where oxygen production is greatest;

How does green light affect plant growth?

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

What is the quantity of light?

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

What is the duration of light (photoperiod)?

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

What is the structure of chlorophyll?

A pigment molecule with magnesium at the center of a porphyrin ring; magnesium’s electrons become excited when exposed to light;

What are the types of chlorophyll?

Chlorophyll a (main pigment) and chlorophyll b (accessory pigment);

What are photosystems?

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

What happens in Photosystem II (PSII)?

It absorbs light at 680 nm, enzymatically broken down splits water (photolysis), and releases oxygen, protons (H⁺), and 2 electrons;

What happens to electrons after PSII?

They travel down an electron transport chain (ETC),

losing energy used to pump protons and generate ATP by chemiosmosis and ATP synthase;

What happens in Photosystem I (PSI)?

It absorbs light at 700 nm and re-energizes electrons that reduce NADP⁺ to NADPH using the enzyme NADP⁺ reductase;

What are the final products of the light reactions?

Oxygen (from water), ATP (from chemiosmosis), and NADPH (as an electron carrier);

What is the purpose of the Calvin Cycle (dark reactions)?

To use ATP and NADPH to convert carbon dioxide into sugars;

What happens during the first phase of the Calvin Cycle (carbon fixation)?

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

What happens during the second phase (reduction)?

3-PGA is converted into G3P using ATP and NADPH; some G3P exits to form glucose, while others remain in the cycle;

What happens during the third phase (regeneration)?

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

How much CO₂ is fixed per turn of the Calvin Cycle?

Three CO₂ molecules are fixed to produce one G3P;

What are C3 plants?

Plants that produce a 3-carbon compound (3-PGA) as the first product of carbon fixation, such as rice, wheat, soybeans, and most vegetables;

What is the disadvantage of C3 plants?

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

What is photorespiration?

A process where Rubisco binds oxygen instead of CO₂, wasting energy and reducing sugar production (up to 50% carbon loss);

What are C4 plants?

Plants such as corn, sugarcane, and grasses that minimize photorespiration by using PEP Carboxylase to fix carbon into a 4C compound;

How do C4 plants function in heat?

Their stomata partially close to conserve water while CO₂ is stored in 4C compounds and released to the Calvin Cycle later;

How much more productive are C4 plants compared to C3 plants?

About 30–40% more productive;

What are CAM plants?

Plants such as pineapple, cacti, aloe, and succulents that open their stomata at night to take in CO₂ and close them during the day;

How do CAM plants conserve water?

They store CO₂ as organic acids at night and use it in the Calvin Cycle during the day, allowing them to thrive in arid environments;

What happens to sugars produced in photosynthesis?

They are converted into cellulose, which forms plant structures;

What is cellulose?

The most abundant carbohydrate on Earth, used in plant cell walls;

How much cellulose is produced globally each year?

Around 150 billion metric tons annually.