11. Photosynthesis

Question 1

Where does the LID take place?

Answer 1

The stroma of the chloroplasts

Question 2

How are the chloroplasts adapted to carry out LID?

Answer 2

Fluid of stroma contains enzymes needed to carry out the reduction of CO2
Stroma fluid surrounds grana so products of LD reaction can diffuse easily into the stroma
Contains DNA and ribosomes so it can make proteins needed for LID reaction

Question 3

describe the process of the Light independent reaction.

Answer 3

• co2 diffuses into the leaf through the stomata
• it then diffuses through plasma membranes, cytoplasm and chloroplast membranes into stroma of the chloroplast
• In the stroma the co2 combines with the 5c compound RUBP
• The enzyme rubisco catalyses this reaction
• the combination of RUBP and co2 produces 2 molecules of glycerate-3-phosphate (GP)
• ATP and reduced NADP from the LD reaction are used to reduce GP to triose phosphate (TP)
• NADP is re-formed and goes back to the LD reaction to be reduced again
• Some TP molecules are converted to useful molecules such as glucose
• Most TP molecules are used to regenerate RUBP using ATP from the LD reaction

Question 4

What name is also commonly used instead of the Light Independent Reaction?

Answer 4

Calvin Cycle

Question 5

Can you explain how the plant leaf is adapted to carry out photosynthesis?

Answer 5

Large surface area to absorb as much sunlight as possible
Thin, as most light is absorbed in the first few micrometers of the leaf and the diffusion distance for gases is kept short
A transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells beneath
Long, narrow upper mesophyll cells packed with chloroplasts that collect sunlight
Numerous stomata for gaseous exchange so that all mesophyll cells are only a short diffusion pathway from one
Stomata that open and close in response to changes in light intensity
Many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen
A network of xylem that brings water to the leaf cells, and phloem that carries away the sugars produced during photosynthesis