IB HL Photosynthesis - light independent reactions

Which of the following protein structures does rubisco have?

• Primary

• Secondary

• Tertiary

• Quaternary

Answer explanation

It consists of 8 polypeptide subunits!

The 5C molecule that CO₂ is fixed to by rubisco

(a)  

How does carbon dioxide enter the stroma?

• Simple diffusion

• Facilitated diffusion

• Active transport

• Osmosis

The process of carbon dioxide combining with RuBP is known as what kind of reaction?

• Reduction

• Decarboxylation

• Carboxylation

• Oxidation

Answer explanation

Decarboxylation occurs as CO₂ is removed from substrates in the Krebs cycle. Reduction and oxidation involve electrons and protons rather than carbon dioxide.

Rubisco shows affinity for which molecule(s)?

• CO₂

• O₂

• RuBP

• Glucose

Answer explanation

CO₂ and RuBP are the substrates for the first step of the Calvin cycle. Rubisco also shows affinity for O₂ which means that O₂ is a competitive inhibitor.

Which are true of the Calvin cycle?

I - Rubisco fixes RuBP and CO₂ into a 6C molecule that immediately splits into two 3C molecules

II - ATP from the light-dependent reactions is required as an energy source

III - hydrogen from NADH is used to reduced glycerate 3-phosphate to produce triose phosphate molecules

• I and II only

• I and III only

• II and III only

• I, II and III

Answer explanation

NADH is the coenzyme used for respiration. Remember that NADPH is used in photosynthesis.

P - photosynthesis!

How much of the triose phosphates that are produced from the Calvin cycle are used to produce glucose?

• 1/6

• 4/6

• 3/6

• 5/6

Answer explanation

The remaining 5/6 are recycled and used for fixing CO₂

Check the molecules that are common to both photosynthesis AND aerobic respiration.

• ADP

• Triose phosphate

• NADH

• ATP synthase

Answer explanation

Triose phosphate is oxidised and dephosphorylated to pyruvate during glycolysis

Glucose produced from the light-independent reactions can be synthesised into larger polymers by the plant cells. Which one is shown?

(a)  

Answer explanation

Glycogen is synthesised by animals. Amylose is coiled and mostly of a single strand.

In which part of a chloroplast do the light independent reactions occur?

• Stroma

• Thylakoid

• Matrix

• Intermembrane space