Photosynthesis VCE Biology 3/4

Unit 3 AOS 2 \cards include: Photosynthesis (+C3 plants), and Rubisco in C3, C4, and CAM photo sysnthesis

Photosynthesis

The conversion of light energy into chemical energy stored in glucose.

What are the main inorganic inputs of photosynthesis?

Carbon dioxide and water.

What are the main products of photosynthesis?

Glucose and oxygen.

Write the simplified balanced photosynthesis equation.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, using light and chlorophyll.

Where does photosynthesis occur in eukaryotic photosynthetic cells?

In chloroplasts.

What are grana?

Stacks of thylakoid discs containing chlorophyll.

What is the stroma?

The gel-like fluid surrounding the grana inside a chloroplast.

What is chlorophyll?

A green pigment in the grana that absorbs and traps light energy.

What is the light-dependent stage’s location?

The grana of the chloroplast.

What are the inputs of the light-dependent stage?

Water, ADP, inorganic phosphate (Pi), and NADP⁺, in the presence of light and chlorophyll.

What are the outputs of the light-dependent stage?

Oxygen, ATP and NADPH.

What happens during the light-dependent stage?

Light energy drives water splitting; oxygen is released and energy is used to form ATP and NADPH.

What is the light-independent stage also called?

The Calvin cycle.

Where does the light-independent stage occur?

In the stroma of the chloroplast.

What are the inputs of the Calvin cycle in the notes?

Carbon dioxide, ATP and NADPH.

What are the outputs of the Calvin cycle in the notes?

Glucose and water, plus ADP, Pi and NADP⁺.

What happens during the light-independent stage?

Carbon dioxide is converted into carbohydrate using hydrogen/electrons from NADPH and energy from ATP.

What is the role of ATP in photosynthesis?

It transfers energy to power reactions in the Calvin cycle.

What is the role of NADPH in photosynthesis?

It transfers electrons and hydrogen ions from the light-dependent stage to the Calvin cycle.

What happens to ATP and NADPH after use in the Calvin cycle?

They return in their unloaded forms, ADP/Pi and NADP⁺, to be reloaded in the light-dependent stage.

What are accessory pigments?

Pigments such as carotenoids and phycobilins that absorb different parts of the light spectrum.

Why can light colour affect photosynthesis efficiency?

Chlorophyll absorbs and reflects different wavelengths, so some colours provide more usable light than others.

Rubisco

An enzyme in the Calvin cycle that binds CO₂ and fixes carbon into organic molecules.

What does Rubisco bind CO₂ to?

Ribulose-1,5-bisphosphate (RuBP), producing 3-phosphoglycerate (3-PGA).

How is 3-PGA converted toward glucose?

Using ATP and NADPH, 3-PGA is converted into G3P; G3P can then be converted into glucose.

What is photorespiration?

When Rubisco binds oxygen instead of carbon dioxide.

Why does photorespiration reduce photosynthetic efficiency?

It wastes energy and reduces the rate of photosynthesis.

How does temperature affect photorespiration?

Higher temperature makes Rubisco bind O₂ more readily, increasing photorespiration.

How does the leaf’s CO₂:O₂ ratio affect photorespiration?

A higher relative O₂ concentration makes Rubisco bind O₂ more readily and increases photorespiration.

Why can closing stomata increase photorespiration?

It reduces water loss but also raises the relative O₂ concentration in the leaf and limits CO₂ entry.

What characterises C3 plants?

Rubisco fixes CO₂ in mesophyll cells, producing the three-carbon compound 3-PGA; they lack special photorespiration-reducing adaptations.

What are examples of C3 plants?

Rice, wheat, fruits, vegetables and all trees.

How do C4 plants initially fix carbon?

PEP carboxylase fixes CO₂ in mesophyll cells into the four-carbon compound malate.

What happens to malate in C4 plants?

It travels to bundle-sheath cells and releases CO₂ for Rubisco and the Calvin cycle.

How do C4 plants reduce photorespiration?

They maintain a high CO₂ concentration around Rubisco in bundle-sheath cells.

What is a cost and an advantage of C4 photosynthesis?

It uses extra ATP but is advantageous in hot, humid environments.

Name two C4 plants.

Corn and sugarcane.

How do CAM plants take in CO₂?

They open stomata at night and use PEP carboxylase to fix CO₂ into malate in mesophyll cells.

What happens to malate in CAM plants during the day?

With stomata closed, malate releases CO₂ for Rubisco and the Calvin cycle.

How do CAM plants reduce water loss and photorespiration?

They open stomata at night, then close them during the day while releasing stored CO₂ near Rubisco.

What is a cost and an advantage of CAM photosynthesis?

It uses extra ATP but is advantageous in hot, dry environments.

Name two CAM plants.

Cacti and pineapples.

How do C4 and CAM plants differ in separating carbon fixation from the Calvin cycle?

C4 plants separate the stages between different cell types; CAM plants separate them by time of day in the same mesophyll cells.