Photosynthesis

Question 1

Fill in the blanks (1):

Photosynthesis occurs in ___trophic organisms, such as plants, algae and cyanobacteria.

Answer 1

Auto (1)

Question 2

Outline the process of photosynthesis (3)

Answer 2

Light energy is trapped (1) and used to convert simple inorganic compounds into complex organic molecules (1) where energy is stored. (1)

Question 3

How does respiration link to photosynthesis. (1)

Where does photosynthesis occur? (1)

Answer 3

In respiration, the energy stored in the complex organic molecules produced in photosynthesis is released. (1)

Chloroplasts (1)

Question 4

Describe the structure of chloroplasts. (4)

Answer 4

• Surrounded by double-membrane envelope. (1)
• Outer membrane permeable to certain ions and molecules. (1)
• Partially permeable inner membrane only allows certain molecules and ions to enter/leave the chloroplast. (1)
• Filled with stroma. (1)
• Network of membranes in stroma; thylakoids (flattened, fluid filled sacs). (1)
• Thylakoids stack to form grana. (1)
• Grana are connected by lamellae. (1)
• Membranes of grana make a large surface area. (1)
• Stroma contains a loop of DNA. (1)

Question 5

The membranes of the grana contain photosynthetic pigments. What is the main importance of them? (2)

Answer 5

They form photosystems/light harvesting systems (1), which transfer energy to the reaction centre. (1)

Question 6

Fill in the blanks about the two stages of photosynthesis () :

Light ___ stage - Occurs in the membranes of ___. Energy from ___ is absorbed and used to form ATP. Hydrogen from water is used to reduce the coenzyme ___.

Light ___ stage - Occurs in the ___. Reduced NADP and ___ ___ are used to build complex, organic molecules (mainly ___).

Answer 6

• Dependent (1)
• Grana/thylakoids (1)
• Sunlight (1)
• NADP (1)
• Independent (1)
• Stroma (1)
• Carbon dioxide (1)
• Glucose (1)

Question 7

Describe non-cyclic phosphorylation. (5)

Answer 7

• The reaction centre of photosystem 2 (PSII) absorbs light. (1)
• The light absorbed excites the electrons at the reaction centre. (1)
• The excited electrons are released from the reaction centre, passed onto the electron transport chain (ETC). (1)
• As the electrons pass through the electron carriers (ECs), they release energy which is used to produce ATP (in chemiosmosis). (1)
• At the end of the ETC, the electrons pass into photosystem 1 (PSI). (1)
• Excited electrons from PS1 are released into another ETC. (1)
• The coenzyme NADP accepts electrons leaving the ETC and one hydrogen, producing reduced NADP. (1)

Question 8

In photolysis, energy from the sun is used to split water molecules into hydrogen, oxygen and electrons. What is the purpose of this?

Answer 8

• ## The electrons replace the electrons released at PSII. (1)

Question 9

Describe cyclic phosphorylation and when it occurs. (4)

Answer 9

• Light energy is absorbed by PSI, causing a pair of electrons to become excited. (1)
• These electrons pass through an ETC, producing ATP. (1)
• Electrons return back to PSI. (1)
• Occurs when the chloroplast requires an increased amount of ATP. (1)

Question 10

How is ATP generated in photophosphorylation? (5)

Answer 10

• The energy released by electrons while they are in ECTs is used to pump protons/hydrogen ions from the stroma into the thylakoid. (1)
• The thylakoid membrane is impermeable to protons, preventing diffusion back into the stroma. (1)
• This produces an electrochemical/proton gradient. (1)
• Protons diffuse through ATP synthase in the thylakoid membrane into the stroma. (1)
• The ATP synthase uses the movement of protons to generate ATP (by adding an inorganic phosphate onto ADP). (1)

Question 11

How is oxygen a product of photosynthesis? (1)

Answer 11

The photolysis of water. (1)

Question 12

What is the other name for the light-independent reactions of photosynthesis? (1)

Answer 12

The Calvin cycle (1)

Question 13

Fill in the blanks about the Calvin cycle (7) :

The first stage is ___, where the five carbon molecule ___ reacts with carbon dioxide. This reaction is catalysed by the enzyme ___. This ___ intermediate is broken down into two molecules of GP. The GP is converted to ___ (using a ___ from reduced NADP and energy from ATP), the starting material for glucose, lipids and amino acids. The final stage is ___, where RuBP is regenerated using ATP.

Answer 13

• Fixation (1)
• RuBP (1)
• RuBisCO (1)
• Unstable (1)
• TP (1)
• Hydrogen (1)
• Regeneration (1)