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the C 4 -plants differ from C 3 -plants with reference to substrate that accepts carbon dioxide in carbon assimilation type of end product type of pigment involved in photosynthesis number of ATP that are consumed in preparing sugar

the C4-plants differ from C3-plants with reference to
  1. substrate that accepts carbon dioxide in carbon assimilation
  2. type of end product
  3. type of pigment involved in photosynthesis
  4. number of ATP that are consumed in preparing sugar

Grade:12th pass

1 Answers

Apoorva Arora IIT Roorkee
askIITians Faculty 181 Points
9 years ago
C4 Plants
Over 8000 species of angiosperms, scattered among 18 different families, have developed adaptations which minimize the losses to photorespiration.

They all use a supplementary method of CO2 uptake which forms a 4-carbon molecule instead of the two 3-carbon molecules of the Calvin cycle. Hence these plants are called C4 plants. (Plants that have only the Calvin cycle are thus C3 plants.)
Some C4 plants — called CAM plants — separate their C3 and C4 cycles by time.
Other C4 plants have structural changes in their leaf anatomy so that
their C4 and C3 pathways are separated in different parts of the leaf with
RUBISCO sequestered where the CO2 level is high; the O2 level low.
These adaptations are described now.
The details of the C4 cycle

After entering through stomata, CO2 diffuses into a mesophyll cell.
Being close to the leaf surface, these cells are exposed to high levels of O2, but
have no RUBISCO so cannot start photorespiration (nor the dark reactions of the Calvin cycle).
Instead the CO2 is inserted into a 3-carbon compound (C3) called phosphoenolpyruvic acid (PEP) forming
the 4-carbon compound oxaloacetic acid (C4).
Oxaloacetic acid is converted into malic acid or aspartic acid (both have 4 carbons), which is
transported (by plasmodesmata) into a bundle sheath cell. Bundle sheath cells
are deep in the leaf so atmospheric oxygen cannot diffuse easily to them;
often have thylakoids with reduced photosystem II complexes (the one that produces O2).
Both of these features keep oxygen levels low.
Here the 4-carbon compound is broken down into
carbon dioxide, which enters the Calvin cycle to form sugars and starch.
pyruvic acid (C3), which is transported back to a mesophyll cell where it is converted back into PEP.

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