Biology 2.2.4: Photosynthesis

What is photosynthesis

Photosynthesis is the production of carbohydrate (glucose) from inorganic molecules using light energy trapped by chlorophyll.

What is the role of carbon dioxide in photosynthesis?

Supplies carbon

What is the role of water in photosynthesis

Supplies protons/hydrogen and electrons

What is the function of ATP?

To trap and transfer energy

Structure of chloroplast:

*Double membrane* *Grana* - green internal membranes (draw as rectangles *Stroma* Liquid portion *Strand of DNA*

What are the green internal membranes in chloroplasts called? Give its function

*Grana* - contain chlorophyll and carry out the light stage. (think [g]rana - green for chlorophyll)

What is the liquid portion of chloroplasts called? What is its function?

*Stroma* - carries out the dark stage Think: storms are wet

Name 3 sources of carbon dioxide for photosynthesis

1. From air (main source) 2. Combustion 3. Animal respiration 4. Plant respiration (counts as separate point to animal repiration

Give the names of the first and second stages of photosynthesis 2013 14a

1. Light 2. Dark

In photosynthesis, what happens before pathway 1 or pathway 2?

1. Light is absorbed by pigments 2. The light is passed on from molecule to molecule until it reaches a *reaction centre chlorophyll molecule* 3. The chlorophyll molecule energises electrons 4. The energised electrons are passed on to the electron acceptor

Name two sources of water for photosynthesis

1. Obtained from the soil 2. Glucose is broken down to energy water and

Give two uses of glucose by the body 2015 q12

1. Respiration 2. Convert to starch

Role of photosynthesis: 4 points

1. To produce glucose for plants 2. To produce oxygen for aerobic respiration 3. To form fossil fuels 4. To remove carbon dioxide from the air

Name two ways in which rate of photosynthesis can be controlled

1. Use artificial lighting in greenhouses 2. Use artificial carbon dioxide - kerosene burners.

Describe what happens in pathway 1. 2013 q14a

1.The electrons are picked up by an electron acceptor 2. The electrons are passed along an electron carrier system. 3. Electrons lose energy and cause ADP to combine with a phosphate to form ATP 4. Electrons return directly to chorophyll (and ATP is formed?)

Describe what happens in pathway 2 2013 q14a

2 electrons are passed onto the electron carrier system Photolysis - 2e⁻ goes to chlorophyll NADP⁺ + 2e⁻ → NADP⁻ NADP⁻ + H⁺ → NADPH (H⁺ from photolysis)

What happens in photolysis?

2H₂O → O₂ + 4e⁻ + 4H⁺

Name the things required for photosynthesis

6*CO₂* + 6*H₂O* → *C₆H₁₂O₆* + 6*O₂* (*Light *+ *Chlorophyll *catalyst)

Give the balanced chemical equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (Light + Chlorophyll catalyst)

Give the details of the dark stage 2015 q12

ATP Light independent *MS:* NADPH supplies H+ and e- (or NADPH supplies hydrogen or NADPH is reducing agent) / CO2 is reduced (or converted) / to form carbohyrate (or named carbohydrate or 6C compound) / NADP (or ADP) regenerated 2 points, 3+ 6

What is the fate of the products of the light stage?

ATP supplies energy for the dark stage reactions NADPH supplies protons and energised electrons for the dark stage reactions Oxygen is used for respiration or released into the atmosphere

What does ATP stand for?

Adenosine Triphosphate

What gas is essential for dark stage reactions?

CO₂

How is glucose formed in the dark stage?

CO₂ → C₆H₁₂O₆ *CO₂ is reduced by NADPH reducing agent* *NADPH supplies protons and electrons* NADPH → NADP⁺ + H⁺ + 2e⁻ *ATP supplies energy* ATP → ADP + P

Where do the energised electrons come from? 2010 14a

Chlorophyll

What happens to the products of photolysis

Electrons replace those lost by the chlorophyll molecule Protons go to a general pool of protons Oxygen is either used for respiration or released into the atmosphere