What You Need to Know

Key Concept Diagram

Overall equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ — carbon dioxide and water are converted into glucose and oxygen

Photosynthesis occurs in chloroplasts, where the green pigment chlorophyll absorbs light energy (mainly red and blue wavelengths)

The light-dependent reactions occur in the thylakoid membranes, converting light to ATP; the light-independent (Calvin) cycle occurs in the stroma

Rate of photosynthesis is affected by light intensity, CO₂ concentration, temperature, and water availability (limiting factors)

Key Vocabulary

Chlorophyll

The green pigment found in chloroplasts that absorbs light energy (mainly red and blue) to power photosynthesis

Chloroplast

The organelle in plant cells where photosynthesis occurs, containing thylakoid membranes and stroma

Glucose

The sugar produced by photosynthesis (C₆H₁₂O₆), which stores chemical energy and is used in cellular respiration

Limiting factor

The variable (light, CO₂, temperature, water) that is in the shortest supply and therefore controls the rate of photosynthesis

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

What are the raw materials (reactants) required for photosynthesis?

Glucose and oxygen Carbon dioxide, water, and light energy Oxygen and carbon dioxide ATP and glucose

Question 2

Why do leaves appear green?

Green is the colour of glucose being produced Chlorophyll absorbs all light including green Chlorophyll reflects green light and absorbs red and blue wavelengths Leaves absorb green light most efficiently

Question 3

A plant in a sealed chamber is given extra CO₂. Initially, the photosynthesis rate increases. What would eventually limit further increase?

Too much glucose building up CO₂ becomes toxic to chloroplasts The plant runs out of chlorophyll Another factor such as light intensity or temperature becoming limiting

Photosynthesis: Energy Transformation