Get detailed analysis on Photosynthesis in Higher Plants class 11 NCERT notes in pdf. Understand the process of photosynthesis how to plants make their food

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Introduction :
A close analysis of Botany Chapter ‘Photosynthesis’ based on previous 22 years exam
questions (between 2000-2021) suggests that overall weightage of this chapter in the NEET
Exam is 4 % which means on an average 2-3 questions are asked from this chapter each year.
The high priority topics of the chapter ‘Photosynthesis’ from which there is greater chance of
occurrence in the NEET Exam are listed below.
1. C4 Pathway (Hatch and Slack)
2. What is Light Reaction
3. Photorespiration
4. Photosythesis Pigments
The students are advised to practice at least 200-300 questions from the high priority topics
mentioned above.

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Noteworthy Points of the Chapter :
1. Joseph Priestley in 1770 performed a series of experiments that revealed the essential role
of air in the growth of green plants.
2. Jan Ingenhousz showed that only the green part of plants could release oxygen.
3. T.W. Engelmann has prepared first action spectra of photosynthesis, using aerobic bacteria
and Cladophora.
4. Cornelius van Niel demonstrated the requirement of H-donor or oxidisable compounds in
photosynthesis.
5. Radioisotope techniques confirmed that the O2 released in photosynthesis is coming from
water.
6. The mesophyll cells in the leaves have a large numbers of chloroplasts and chloroplast is
the site of photosynthesis.
7. The membrane system is responsible for trapping the light energy and also for the synthesis
of ATP and NADPH in the chloroplast.
8. The wavelength at which there is maximum absorption by chlorophyll-a , i.e. in the blue and
red region shows higher rate of photosynthesis.
9. Chlorophyll a, chief pigment of photosynthesis absorbs maximally at the blue and red
wavelengths of light.
10. Pigments like chlorophyll b, xanthophylls and carotenoids are accessory pigments that
absorb light of other wavelengths and transfer the energy to chlorophyll-a.
11. Chlorophyll a molecule forms the reaction centre.

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12. In PS-I, the reaction centre chlorophyll-a has an absorption peak at 700 nm, hence is called
P700 , while in PS-II, it has absorption maxima at 680 nm, and is called P680.
13. The membrane of the thylakoids of grana has both PS-I and PS-II whereas stroma
lamellae membrane lacks PS-II as well as NADP reductase enzyme.
14. The splitting of water is associated with the PS-II.
15. The process through which ATP is synthesized is named as phosphorylation.
16. When the two photosystems work in a series, first PS-II and then PS-I, a process called
non-cyclic photo -phosphorylation occurs. When only PSI is functional, the electron is
circulated within the photosystem, called cyclic photophosphorylation.
17. Non-cyclic photophosphorylation results in synthesis of ATP and NADPH + H+
whereas
cyclic photophosphorylation results in ATP synthesis only.
18. Cyclic photophosphorylation occurs when light of wavelength beyond 680 nm is available for
excitation.
19. ATP synthesis is linked to development of a proton gradient across a membrane.
20. Chemiosmosis requires a membrane, a proton pump, a proton gradient and
ATPsynthase enzyme.
21. Splitting of water molecules, movement of electrons through photosystems and reduction of
NADP+
are responsible for accumulation of protons in lumen.
22. The enzyme NADPH reductase is located on the stroma side of the membrane in the
chloroplast.

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23. The ATP synthase enzyme consists of two parts: one is CF0 which is embedded in the
thylakoid membrane and forms a transmembrane channel that carries out facilitated
diffusion of protons across the membrane and the other portion is called CF1 and
protrudes on the outer surface of the thylakoid membrane on the side that faces the
stroma.
24. The products of light reaction are ATP, NADPH and O2.
25. Dark reaction or CO2 fixation occurs through C3 pathway or C4 pathway.
26. The acceptor molecule of CO2 in Calvin cycle (C3 pathway) is a 5-C ketose sugar i.e.,
RuBP.
27. RuBP carboxylase also has an oxygenation activity, so it would be more correct to call it
RuBisCO.
28. Calvin cycle have three important stages carboxylation, reduction and regeneration.
29. The fixation of 6 molecules of CO2 and 6 turns of the cycle are required for the removal of on
molecule of glucose from the Calvin cycle.
30. For every CO2 molecule entering the Calvin cycle, 3 molecules of ATP and 2 of NADPH are
required.
31. C4 plants have a special type of leaf anatomy, tolerate higher temperatures, lack
photorespiration and have greater productivity of biomass.
32. Large cells around the vascular bundles of the C4 pathway plants are called bundle sheath
cells and it is called Kranz anatomy.
33. ‘Kranz’ means wreath and is a reflection of the arrangement of cells.

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34. C4 pathway has been named as Hatch and Slack pathway.
35. In C4 plants, the primary CO2 acceptor is a 3-C molecule that is PEP and is present in the
mesophyll cells.
36. In C4 plants, mesophyll cells lack RuBisCO enzymes. The C4 acid OAA is formed in
mesophyll cells
37. 4-C compounds like malic acid or aspartic acid are formed in mesophyll cells of C4 plants
are transported to the bundle sheath.
38. C4 acid from the mesophyll is broken down in the bundle sheath cells to release CO2 this
results in increasing the concentration of CO2.
39. The bundle sheath cells are rich in an enzyme RuBisCO but lacks PEPcase.
40. Calvin pathway of CO2 fixation is common to both C3 and C4 plants.
41. The active site of RuBisCO has both O2 and CO2 binding sites. It has greater affinity for CO2
than O2.
42. In C3 plants RuBisCO shows its oxygenase activity when O2 concentration is higher than
CO2.
43. C3 plants show photorespiration phenomenon which involves chloroplast, mitochondria
and peroxisomes.
44. PGA binds with O2 to form one molecule of phosphoglycerate and phosphoglycolate in
photorespiration. There is neither synthesis of sugars nor of ATP and therefore it is called
a wasteful process.

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45. Blackman’s law of limiting factors defines that rate of photosynthesis is determined by the
factor. Which is nearest to minimum value.
46. CO2 is the major limiting factor for photosynthesis.
47. Increase in concentration upto 0.05% can cause an increase in CO2 fixation rates; beyond
this level it can become damaging over longer periods.
48. C4 plants show saturation at about 360 μlL–1
while C3 responds to increased CO2
concentration and saturation is seen only beyond 450 μlL–1
.
49. Photosynthesis rate increases at high light intensity and light saturation occurs at 10% of
full sunlight.
50. Water is rarely a limiting factor.