Plant Physiology : NEET Biology Notes

Plant Physiology deals with the major life processes of plants, including photosynthesis, respiration, growth, and development. The following notes are designed for NEET Biology revision, with emphasis on important concepts, comparisons, examples, and high-yield facts.

1. Photosynthesis

1.1 Definition and Basic Concept

Photosynthesis is the process by which green plants synthesize organic food from CO₂ and water using light energy.
It is the major mode of autotrophic nutrition in plants.
Light energy is converted into chemical energy.
Chlorophyll and other photosynthetic pigments capture light energy.
Oxygen released during photosynthesis comes from water, not from CO₂.

Overall Reaction

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

In the detailed representation, water participates in both the formation and release processes.

Example: A green leaf uses atmospheric CO₂, water absorbed by roots, and sunlight to synthesize carbohydrates.

NEET Fact: The oxygen evolved during photosynthesis originates from H₂O.

2. Photosynthesis as Autotrophic Nutrition

2.1 Autotrophs

Autotrophs synthesize their own organic food from inorganic substances.
Green plants are mainly photoautotrophs.
They use:
- CO₂ → carbon source
- H₂O → source of electrons/hydrogen
- Light → energy source
- Chlorophyll → absorbs light

Examples: Green plants, algae, cyanobacteria.

3. Site of Photosynthesis

3.1 Chloroplast

Photosynthesis mainly occurs in the chloroplasts of mesophyll cells of leaves.

The chloroplast has two functionally important regions:

Chloroplast region	Major process
Thylakoid membrane/Grana	Light reactions
Stroma	Calvin cycle/CO₂ assimilation

3.2 Important Structural Terms

Granum: Stack of thylakoids.
Thylakoid: Flattened membrane-bound sac containing photosynthetic pigments and electron carriers.
Stroma: Fluid matrix surrounding the grana.
Stroma lamellae: Membranous connections between grana.

Easy memory:
Grana → Light reactions
Stroma → Calvin cycle

4. Photosynthetic Pigments

Photosynthetic pigments absorb light of different wavelengths and transfer the captured energy to the reaction centre.

4.1 Major Pigments

Pigment	Role
Chlorophyll-a	Primary photosynthetic pigment
Chlorophyll-b	Accessory pigment
Carotenes	Accessory pigment
Xanthophylls	Accessory pigment

Chlorophyll-a

It is the primary photosynthetic pigment.
It is directly involved in the conversion of light energy into chemical energy.
It is present in all oxygenic photosynthetic organisms.

Accessory Pigments

Chlorophyll-b and carotenoids:

Absorb additional wavelengths of light.
Transfer absorbed energy to chlorophyll-a.
Help protect the photosynthetic system from photo-oxidative damage.

5. Absorption Spectrum and Action Spectrum

5.1 Visible Light

The visible region of light is approximately:

400–700 nm

Photosynthesis is particularly effective in:

Blue light
Red light

Green light is comparatively less effective because chlorophyll reflects much of it.

5.2 Action Spectrum

An action spectrum shows the rate of photosynthesis at different wavelengths of light.

Engelmann’s experiment demonstrated that photosynthetic activity is particularly high in the blue and red regions.

NEET Point: Chlorophyll appears green because it reflects green wavelengths more than it absorbs them.

6. Photosystems

Photosynthetic pigments are organized into functional units called photosystems.

There are two major photosystems:

Photosystem I (PS-I)

Reaction centre: P700
Maximum absorption around 700 nm.
Participates in both cyclic and non-cyclic electron flow.

Photosystem II (PS-II)

Reaction centre: P680
Maximum absorption around 680 nm.
Involved in water splitting during non-cyclic photophosphorylation.

Memory trick:

PS-I → P700
PS-II → P680

7. Two Major Stages of Photosynthesis

Photosynthesis can be broadly divided into:

Light-dependent reactions
Biosynthetic reactions

7.1 Light Reactions

Location:

Thylakoid membrane

Major events:

Absorption of photons
Excitation of electrons
Splitting of water
Electron transport
ATP synthesis
NADPH formation

Main products:

ATP + NADPH + O₂

7.2 Biosynthetic Reactions

Location:

Chloroplast stroma

Major process:

Calvin cycle

Here, ATP and NADPH produced during the light reactions are used for CO₂ assimilation and carbohydrate synthesis.

Important: The term “dark reaction” does not mean that the reaction occurs only in darkness. It can proceed in light if ATP and NADPH are available.

8. Photophosphorylation

Photophosphorylation means the formation of ATP using light energy.

It occurs in two forms:

Cyclic photophosphorylation
Non-cyclic photophosphorylation

9. Cyclic Photophosphorylation

Only PS-I participates.
The excited electron eventually returns to the same photosystem.
ATP is produced.
NADPH is not produced.
Water is not split.
Oxygen is not released.

Main significance

It supplies additional ATP when the Calvin cycle requires more ATP relative to NADPH.

10. Non-Cyclic Photophosphorylation

Both photosystems participate:

PS-II → Electron carriers → PS-I

Major events:

PS-II absorbs light.
P680 becomes excited.
Water undergoes photolysis.
Oxygen is released.
Electrons pass through an electron transport chain.
ATP is generated.
PS-I absorbs another photon.
Electrons are finally transferred to NADP⁺.
NADPH is formed.

Photolysis of Water

2H₂O → 4H⁺ + 4e⁻ + O₂

Comparison

Feature	Cyclic	Non-cyclic
PS-I	Yes	Yes
PS-II	No	Yes
ATP	Yes	Yes
NADPH	No	Yes
O₂ release	No	Yes
Water splitting	No	Yes

NEET Fact: Non-cyclic photophosphorylation produces ATP, NADPH and O₂.

11. Chemiosmotic Hypothesis

The chemiosmotic hypothesis explains ATP formation through a proton gradient.

Mechanism

Electron transport causes H⁺ ions to accumulate inside the thylakoid lumen.
A proton concentration gradient develops across the thylakoid membrane.
H⁺ moves back toward the stroma through ATP synthase.
The energy released during proton movement drives ATP formation.

ADP + Pi → ATP

Key Concept

Proton gradient → ATP synthase → ATP

The same general principle of chemiosmosis also operates during oxidative phosphorylation in mitochondria.

12. Calvin Cycle / C₃ Cycle

The Calvin cycle occurs in the:

Chloroplast stroma

Major enzyme

RuBisCO — Ribulose bisphosphate carboxylase-oxygenase

CO₂ acceptor

RuBP — Ribulose-1,5-bisphosphate

Three Major Phases

12.1 Carboxylation

CO₂ combines with RuBP.
RuBisCO catalyses the reaction.
The unstable 6-carbon intermediate splits into two molecules of 3-PGA.

12.2 Reduction

ATP and NADPH are consumed.
3-PGA is converted into triose phosphate compounds.

12.3 Regeneration

RuBP is regenerated.
ATP is required.

Energy Requirement

For synthesis of one glucose molecule:

6 CO₂
18 ATP
12 NADPH

are required.

NEET Fact: The first stable product of the C₃ cycle is 3-phosphoglyceric acid (3-PGA).

13. Photorespiration

Photorespiration occurs when RuBisCO acts as an oxygenase instead of a carboxylase.

This becomes more significant when:

Temperature is high.
CO₂ concentration is low.
O₂ concentration is relatively high.
Stomata close during water stress.

Organelles Involved

Photorespiration involves:

Chloroplast
Peroxisome
Mitochondrion

Consequences

CO₂ is released.
Energy is consumed.
No useful carbohydrate is produced through this pathway.

NEET Fact: Photorespiration is a major limitation of C₃ photosynthesis.

14. C₃ and C₄ Plants

14.1 C₃ Plants

In C₃ plants, the first stable product of CO₂ fixation is a 3-carbon compound, 3-PGA.

Examples: Rice, wheat, potato.

14.2 C₄ Plants

In C₄ plants, initial CO₂ fixation produces a 4-carbon compound, oxaloacetic acid (OAA).

Examples: Maize, sugarcane, sorghum.

Comparison

Feature	C₃ plants	C₄ plants
First stable product	3-PGA	OAA
Initial CO₂ acceptor	RuBP	PEP
Initial CO₂-fixing enzyme	RuBisCO	PEP carboxylase
Kranz anatomy	Absent	Present
Photorespiration	Significant	Very low
High-temperature efficiency	Lower	Higher
Examples	Rice, wheat	Maize, sugarcane

15. C₄ Pathway / Hatch-Slack Pathway

C₄ photosynthesis involves cooperation between:

Mesophyll cells
Bundle sheath cells

15.1 In Mesophyll Cells

CO₂ is initially fixed by:

PEP + CO₂ → OAA

Enzyme:

PEP carboxylase

OAA is converted into compounds such as:

Malate
Aspartate

15.2 In Bundle Sheath Cells

The 4-carbon compound releases CO₂.

The released CO₂ enters the Calvin cycle and is fixed by RuBisCO.

Major Advantage

C₄ plants concentrate CO₂ around RuBisCO, thereby reducing oxygenase activity of RuBisCO.

Therefore:

Photorespiration is minimized.
Water-use efficiency is high.
They perform well under high temperature and strong light.

16. Kranz Anatomy

Kranz anatomy is a characteristic arrangement found in C₄ plants.

Features:

Vascular bundles are surrounded by prominent bundle sheath cells.
Mesophyll cells occur outside the bundle sheath.
C₄ fixation occurs mainly in mesophyll cells.
Calvin cycle occurs mainly in bundle sheath cells.

Examples: Maize and sugarcane.

17. Factors Affecting Photosynthesis

The major factors include:

Light intensity
Light quality
CO₂ concentration
Temperature
Water
Chlorophyll content
Internal physiological conditions

17.1 Light Intensity

At low intensity, photosynthesis is slow.
Increasing light intensity generally increases photosynthetic rate.
Beyond a certain point, the rate reaches saturation.
Excessive light can damage photosynthetic pigments.

17.2 CO₂ Concentration

CO₂ is the major carbon source for photosynthesis.
Increasing CO₂ can increase photosynthetic rate up to a saturation point.
Beyond the optimum concentration, further increase has little effect.

17.3 Temperature

Photosynthesis depends on enzyme activity.

Low temperature → slower enzymatic reactions.
Optimum temperature → maximum efficiency.
Very high temperature → enzyme damage/stomatal closure and reduced photosynthesis.

C₄ plants generally perform better than C₃ plants under high-temperature conditions.

17.4 Water

Water is a raw material for photosynthesis.

Water shortage causes:

Water stress → Stomatal closure → Reduced CO₂ entry → Reduced photosynthesis

18. Blackman’s Law of Limiting Factors

When several factors affect a process, the factor available in the least favourable amount may determine the rate of the process.

Example:

If CO₂ and water are sufficient but light intensity is very low, light becomes the limiting factor.

19. Respiration

Respiration is the metabolic process through which organic molecules are oxidized and their stored energy is released.

The released energy is conserved mainly in the form of:

ATP

Simplified Overall Reaction

Glucose + O₂ → CO₂ + H₂O + Energy

20. Exchange of Gases in Plants

Plants exchange gases mainly through:

Stomata in leaves
Lenticels in woody stems
Root surfaces

During Photosynthesis

CO₂ enters.
O₂ generally exits.

During Respiration

O₂ enters.
CO₂ exits.

The direction of gas movement depends on the balance between photosynthesis and respiration.

21. Cellular Respiration

Aerobic respiration can be divided into:

Glycolysis
Pyruvate oxidation
TCA/Krebs cycle
Electron transport system
Oxidative phosphorylation

22. Glycolysis

Glycolysis is the first stage of glucose breakdown.

It is also called the:

EMP pathway — Embden-Meyerhof-Parnas pathway

Location

Cytoplasm

Starting Material

1 Glucose (6C)

End Products

2 Pyruvate (3C each)

Net Yield

2 ATP
2 NADH

Simplified equation:

Glucose → 2 Pyruvate + 2 ATP + 2 NADH

Important Point

Glycolysis itself does not directly require oxygen.

23. Pyruvate Oxidation

In aerobic respiration, pyruvate enters the mitochondrion.

Location:

Mitochondrial matrix

Each pyruvate is converted into:

Acetyl-CoA + CO₂ + NADH

Since one glucose produces two pyruvate molecules, one glucose gives:

2 Acetyl-CoA
2 CO₂
2 NADH

during this step.

24. TCA Cycle / Krebs Cycle

Other names:

Citric acid cycle
Krebs cycle
Tricarboxylic acid cycle

Location

Mitochondrial matrix

Entry Point

Acetyl-CoA combines with oxaloacetate to form:

Citrate

Products per Acetyl-CoA

3 NADH
1 FADH₂
1 ATP/GTP
2 CO₂

Products per Glucose

Because one glucose produces two Acetyl-CoA:

6 NADH
2 FADH₂
2 ATP/GTP
4 CO₂

25. Electron Transport System

The electron transport system is located in the:

Inner mitochondrial membrane

Major Function

Electrons from:

NADH
FADH₂

are transferred through electron carriers.

The energy released is used to pump protons and create a proton gradient.

Final Electron Acceptor

Oxygen (O₂)

Oxygen accepts electrons and combines with protons to form:

H₂O

NEET Fact: Oxygen is the final electron acceptor in aerobic respiration.

26. Oxidative Phosphorylation

ATP formation associated with electron transport is called:

Oxidative phosphorylation

The proton gradient generated by ETS drives ATP synthase.

ADP + Pi → ATP

Most ATP during aerobic respiration is generated during this stage.

27. ATP Yield from One Glucose

Modern estimates generally give approximately:

30–32 ATP per glucose molecule

for aerobic respiration in eukaryotic cells.

Energy Distribution

Stage	Important products
Glycolysis	2 ATP + 2 NADH
Pyruvate oxidation	2 NADH
TCA cycle	2 ATP/GTP + NADH + FADH₂
ETS/Oxidative phosphorylation	Majority of ATP

Exam Note: Older textbooks/sources may mention 36–38 ATP. Modern accounting generally uses 30–32 ATP for eukaryotic cells.

28. Anaerobic Respiration / Fermentation

When oxygen is unavailable, glucose may undergo incomplete breakdown through fermentation.

28.1 Alcoholic Fermentation

Common in yeast.

Glucose → Pyruvate → Ethanol + CO₂

Applications include:

Bread making
Fermentation industries

28.2 Lactic Acid Fermentation

Pyruvate is converted into:

Lactic acid

This pathway occurs in certain microorganisms and under oxygen-limited conditions in some animal tissues.

Features of Fermentation

Occurs in cytoplasm.
Oxygen is not required.
Glucose is incompletely oxidized.
Net yield is only 2 ATP per glucose.

29. Aerobic Respiration vs Fermentation

Feature	Aerobic respiration	Fermentation
Oxygen	Required	Not required
Glucose oxidation	Nearly complete	Incomplete
Major products	CO₂ + H₂O	Ethanol/organic acids
ATP yield	High	2 ATP
Location	Cytoplasm + mitochondria	Cytoplasm

30. Amphibolic Nature of Respiration

Respiration is not purely a catabolic process.

Its intermediates can also be used to synthesize other molecules.

Therefore, respiration is described as an:

Amphibolic pathway

Examples

Intermediates of the TCA cycle can be used for synthesis of:

Amino acids
Fatty acids
Other cellular compounds

Acetyl-CoA also acts as an important metabolic link between carbohydrate and lipid metabolism.

NEET Fact: The TCA cycle is an important amphibolic pathway.

31. Respiratory Quotient (RQ)

Respiratory Quotient indicates the relationship between CO₂ released and O₂ consumed during respiration.

Formula

RQ = Volume of CO₂ evolved / Volume of O₂ consumed

32. RQ of Different Respiratory Substrates

32.1 Carbohydrates

For glucose:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Therefore:

RQ = 6/6 = 1

32.2 Fats

Fat oxidation requires relatively more oxygen.

Therefore:

RQ < 1

Typical value:

≈ 0.7

32.3 Proteins

Protein RQ is generally around:

0.8–0.9

32.4 Organic Acids

Some organic acids have:

RQ > 1

Quick Table

Respiratory substrate	Approximate RQ
Carbohydrate	1.0
Fat	0.7
Protein	0.8–0.9
Organic acids	>1

33. Plant Growth and Development

Plant growth refers to a permanent and generally irreversible increase in size, mass, volume, or cell number.

Growth involves:

Cell division
Cell enlargement
Cell maturation

34. Sites of Plant Growth

Growth is particularly active in meristematic regions.

Important meristems include:

Apical meristem → increase in length
Intercalary meristem → growth of internodes
Lateral meristem → increase in girth

Examples:

Root apical meristem
Shoot apical meristem
Vascular cambium
Cork cambium

35. Phases of Plant Growth

Three major phases are:

Cell division
Cell elongation
Cell maturation

35.1 Cell Division Phase

Characteristics:

Active mitosis.
Cells are small.
Dense cytoplasm.
Prominent nucleus.
Relatively small vacuoles.
Cell walls are generally thin.

35.2 Cell Elongation Phase

Characteristics:

Rapid increase in cell size.
Vacuoles enlarge.
Cell wall expands.
Cellular components increase.

35.3 Cell Maturation Phase

Cells acquire their final size and specialized structure.
Differentiation occurs.
Cells develop specific functions.

36. Growth Rates

36.1 Arithmetic Growth

Only one daughter cell continues to divide.
The other daughter cell differentiates or matures.
Increase occurs at a relatively constant rate.

36.2 Geometric Growth

Both daughter cells continue dividing.
Growth becomes rapid and exponential under ideal conditions.

37. Growth Curve

Under suitable conditions, plant growth may show a characteristic sigmoid or S-shaped curve.

Three broad phases are:

Lag Phase

Growth is initially slow.
Cells adapt and prepare for active growth.

Log/Exponential Phase

Cell division and enlargement are rapid.
Growth rate is highest.

Stationary Phase

Growth slows down.
Mature size is approached.

38. Absolute and Relative Growth Rate

Absolute Growth Rate

Increase in total size or mass per unit time.

AGR = Increase in growth / Time

Relative Growth Rate

Growth relative to the initial size of the plant or organ.

RGR = Increase in growth / Initial size × Time

Relative growth is useful when comparing plants of different initial sizes.

39. Conditions Required for Plant Growth

Major requirements include:

Water
Oxygen
Mineral nutrients
Suitable temperature
Light
Appropriate environmental conditions
Growth regulators

The exact requirement varies with plant species and developmental stage.

40. Seed Germination

Seed germination is the process by which a viable seed resumes active growth and develops into a seedling under favourable conditions.

Essential Conditions

Adequate water
Oxygen
Suitable temperature

Some seeds are also influenced by:

Light
Darkness

41. Major Events During Germination

Seed absorbs water.
Imbibition occurs.
Metabolic activity increases.
Enzymes become active.
Stored food is mobilized.
Radicle emerges.
Plumule develops into the shoot.

Remember

Radicle → Root system

Plumule → Shoot system

42. Seed Dormancy

A viable seed may remain inactive even when some external conditions appear favourable. This condition is called:

Seed dormancy

Possible causes:

Hard seed coat
Chemical inhibitors
Immature embryo
High ABA activity

Dormancy may be broken by:

Scarification
Stratification
Appropriate temperature treatment
Hormonal treatments

43. Differentiation

Differentiation is the process by which meristematic cells become structurally and functionally specialized.

Example

A meristematic cell develops into:

Xylem element
Phloem cell
Epidermal cell

Each mature cell performs a specialized function.

44. Dedifferentiation

When mature differentiated cells regain the ability to divide, the process is called:

Dedifferentiation

Examples

Formation of vascular cambium from previously differentiated tissues.
Formation of cork cambium.

45. Redifferentiation

When cells produced through dedifferentiation again become specialized mature cells, the process is called:

Redifferentiation

Sequence

Meristematic cell → Differentiation → Mature specialized cell

and:

Mature cell → Dedifferentiation → Dividing cell → Redifferentiation → Specialized cell

46. Plant Development

Plant development is the overall process involving changes in plant structure and function throughout its life cycle.

It includes:

Growth
Differentiation
Maturation
Morphogenesis
Senescence

General Developmental Sequence

Cell division → Cell enlargement → Differentiation → Maturation → Specialized function

47. Plant Growth Regulators

Plant growth regulators are chemical substances that influence plant growth and development even at very low concentrations.

The five major groups are:

Auxins
Gibberellins
Cytokinins
Ethylene
Abscisic acid

48. Auxins

A major natural auxin is:

IAA — Indole-3-acetic acid

Major Functions

Cell elongation
Apical dominance
Root initiation
Tropic responses
Fruit development
Parthenocarpy
Regulation of abscission

Apical Dominance

The shoot apical bud produces auxin, which can suppress the growth of lateral buds.

Example:

Removing the shoot tip can reduce apical dominance and promote lateral branching.

49. Agricultural Uses of Auxins

Auxins can be used for:

Root formation in stem cuttings
Production of seedless fruits
Weed control
Fruit thinning
Regulation of fruit drop

50. Gibberellins

An important gibberellin is:

GA₃ — Gibberellic acid

Major Functions

Stem elongation
Internode elongation
Bolting
Seed germination
Breaking dormancy
Fruit growth

Bolting

Rapid elongation of internodes before flowering in certain rosette plants is called:

Bolting

Examples:

Cabbage
Beet

51. Agricultural Uses of Gibberellins

Gibberellins are useful for:

Increasing stem/internode length.
Increasing stalk length in grapes.
Promoting seed germination.
Supporting malting processes in the brewing industry.

52. Cytokinins

Examples:

Kinetin
Zeatin

Major Functions

Cell division
Cell differentiation
Shoot formation
Lateral bud growth
Delay of senescence

Anti-senescence Effect

Cytokinins can delay ageing of leaves and maintain cellular activity for longer periods.

Memory clue:

Cytokinin → Cytokinesis → Cell division

53. Ethylene

Ethylene is a unique gaseous plant growth regulator.

Chemical formula:

C₂H₄

Major Functions

Fruit ripening
Senescence
Abscission
Seedling responses
Triple response

Fruit Ripening

Ethylene promotes physiological and biochemical changes associated with ripening.

Examples:

Banana
Tomato
Apple

54. Abscisic Acid (ABA)

ABA is commonly associated with:

Stress responses and dormancy

Major Functions

Stomatal closure
Seed dormancy
Bud dormancy
Growth inhibition
Response to water stress

During Water Stress

Water deficit → ABA increase → Stomatal closure → Reduced water loss

NEET Fact: ABA is often called the stress hormone of plants.

55. Comparison of Major Plant Hormones

Hormone	Important functions
Auxin	Cell elongation, apical dominance, rooting
Gibberellin	Stem elongation, bolting, germination
Cytokinin	Cell division, lateral growth, delay of senescence
Ethylene	Fruit ripening, senescence, abscission
ABA	Dormancy, stomatal closure, stress response

Easy Memory

Auxin → Elongation

Gibberellin → Growth

Cytokinin → Division

Ethylene → Ripening

ABA → Dormancy/Stress

56. Hormonal Interactions

Auxin and Cytokinin

Their relative concentrations can influence organ formation in tissue culture.

Relatively higher auxin → root formation tendency.
Relatively higher cytokinin → shoot formation tendency.

Gibberellin and ABA

They often show opposing effects in seed physiology.

Gibberellin	ABA
Promotes germination	Maintains dormancy
Promotes growth	Inhibits growth
Helps break dormancy	Helps maintain dormancy

57. Hormonal Regulation of Seed Germination

Gibberellin

In cereal seeds, gibberellin stimulates aleurone cells to produce hydrolytic enzymes.

GA → Aleurone cells → Hydrolytic enzymes → Stored food breakdown → Germination

ABA

ABA:

Promotes seed dormancy.
Suppresses germination under unfavourable conditions.

Thus, GA and ABA often act antagonistically in regulating dormancy and germination.

58. Photoperiodism

Photoperiodism is the response of plants, especially flowering, to the relative duration of light and darkness.

Short-Day Plants

Flower when the photoperiod is below a critical duration.

Long-Day Plants

Flower when the photoperiod is above a critical duration.

Day-Neutral Plants

Flowering is not strongly controlled by photoperiod.

NEET Point: In many photoperiodic responses, the duration of the uninterrupted dark period is particularly important.

59. Vernalization

Vernalization is the promotion of flowering by exposure to a period of low temperature.

Examples include:

Winter wheat
Barley
Some biennial plants

It can help plants flower after experiencing an appropriate cold period.

60. Senescence

Senescence refers to the ageing process of plant organs.

During senescence:

Photosynthetic activity decreases.
Cellular components are degraded.
Nutrients may be mobilized to younger or developing organs.

Cytokinins can delay senescence.

61. Abscission

Abscission is the natural separation of plant organs such as:

Leaves
Flowers
Fruits

from the parent plant.

Ethylene plays an important role in promoting abscission.

62. NEET Rapid Revision: Photosynthesis

Primary photosynthetic pigment → Chlorophyll-a
PS-I reaction centre → P700
PS-II reaction centre → P680
Water splitting → PS-II
Oxygen source → H₂O
Cyclic photophosphorylation → PS-I
Non-cyclic photophosphorylation → PS-I + PS-II
Cyclic → ATP
Non-cyclic → ATP + NADPH + O₂
Light reaction → Thylakoid membrane
Calvin cycle → Stroma
C₃ CO₂ acceptor → RuBP
C₃ first stable product → 3-PGA
C₄ CO₂ acceptor → PEP
C₄ first stable product → OAA
C₄ initial enzyme → PEP carboxylase
C₄ anatomy → Kranz anatomy
Photorespiration → High in C₃ plants
C₄ examples → Maize, sugarcane

63. NEET Rapid Revision: Respiration

Glycolysis → Cytoplasm
Glycolysis end product → Pyruvate
Net ATP from glycolysis → 2 ATP
Pyruvate oxidation → Mitochondrial matrix
TCA cycle → Mitochondrial matrix
ETS → Inner mitochondrial membrane
Final electron acceptor → O₂
Aerobic respiration → CO₂ + H₂O
Fermentation → Anaerobic/incomplete breakdown
Alcoholic fermentation → Ethanol + CO₂
Lactic fermentation → Lactic acid
Fermentation yield → 2 ATP
TCA cycle → Amphibolic
Carbohydrate RQ → 1
Fat RQ → ≈0.7
Protein RQ → ≈0.8–0.9
Modern ATP estimate → 30–32 ATP/glucose

64. NEET Rapid Revision: Plant Growth and Development

Growth → Generally irreversible increase in size/mass
Major growth phases → Division → Elongation → Maturation
Apical meristem → Primary growth/length
Lateral meristem → Increase in girth
Germination requirements → Water + O₂ + suitable temperature
Radicle → Root
Plumule → Shoot
Differentiation → Specialization of cells
Dedifferentiation → Regain of division capacity
Redifferentiation → Return to specialized state
Auxin → Elongation/rooting/apical dominance
Gibberellin → Stem elongation/germination/bolting
Cytokinin → Cell division/delay of senescence
Ethylene → Fruit ripening/abscission
ABA → Dormancy/stress/stomatal closure
Vernalization → Low-temperature-induced flowering
Photoperiodism → Response to light/dark duration

65. One-Table Revision of the Entire Unit

Concept	Must Remember
Light reaction	Thylakoid membrane
Calvin cycle	Stroma
PS-I	P700
PS-II	P680
Cyclic photophosphorylation	ATP; PS-I only
Non-cyclic photophosphorylation	ATP + NADPH + O₂
C₃ first product	3-PGA
C₄ first product	OAA
C₃ acceptor	RuBP
C₄ acceptor	PEP
C₃ enzyme	RuBisCO
C₄ initial enzyme	PEP carboxylase
C₄ anatomy	Kranz
Photorespiration	Significant in C₃
Glycolysis	Cytoplasm
TCA cycle	Mitochondrial matrix
ETS	Inner mitochondrial membrane
Final electron acceptor	O₂
Fermentation	2 ATP
Carbohydrate RQ	1
Fat RQ	<1
Auxin	Cell elongation
Gibberellin	Growth/bolting/germination
Cytokinin	Cell division
Ethylene	Fruit ripening
ABA	Dormancy/stress

66. High-Yield Concept Chains

Photosynthesis

Light → Pigments → Electron excitation → Electron transport → ATP/NADPH → Calvin cycle → Carbohydrate

C₄ Photosynthesis

CO₂ → PEP → OAA → 4-C compound → CO₂ release → Calvin cycle

Aerobic Respiration

Glucose → Glycolysis → Pyruvate → Acetyl-CoA → TCA → NADH/FADH₂ → ETS → ATP

Plant Growth

Cell division → Cell elongation → Cell maturation → Differentiation → Development

Hormonal Regulation

Auxin → Elongation

Gibberellin → Growth/Germination

Cytokinin → Cell division

Ethylene → Ripening

ABA → Dormancy/Stress

67. Final NEET Memory Map

Photosynthesis

Chloroplast → Thylakoid → Light reaction → ATP/NADPH → Stroma → Calvin cycle

Respiration

Cytoplasm → Glycolysis → Mitochondria → TCA → ETS → ATP

C₃

RuBP → RuBisCO → 3-PGA → Photorespiration possible

C₄

PEP → OAA → Kranz anatomy → CO₂ concentration → Low photorespiration

Growth

Division → Elongation → Maturation

Hormones

Auxin = Elongation
GA = Growth
Cytokinin = Division
Ethylene = Ripening
ABA = Dormancy/Stress