Longer wavelength = 700nm.
Findout which PS operates at 700 nm light.

(a) Water stress causes closure of stomata and decreases the availability of CO₂ for photosynthesis.
(b) Water stress also causes wilting of leaves, thus reducing the surface area of leaves for metabolic function.

Differences between stroma and grana of chloroplasts are

RuBP is known as Ribulose 1,5-Bisphosphate. It is the primary acceptor of carbon dioxide in Calvin cycle of C₃-plants. It forms the first stable compound of photosynthesis known as PGA.

The plants which are adapted to dry tropical regions have the C₄ pathway. However, the C₄-plants do not show any characteristic in external morphology. Therefore, it is difficult to say whether a plant is C₃ or C₄ by looking it only externally.

Cyanobacteria and some other photosynthetic bacteria have photosynthetic lamellae (membranes) suspended freely in the cytoplasm.These carry bacteriochlorophyll to conduct photosynthesis.

Lycopene pigment, which is a chromoplast.It is a non-photosynthetic pigment.

The light range between 400-700 nm of wavelength is called PAR.

Succulents (water-storing) plants such as cacti, fix CO₂ into organic compound (malic acid) using PEP carboxylase at night when the stomata are open.

The first stable compound in Calvin cycle is a 3 carbon compound namely 3 phosphoglyceric acid (PGA).

(a) Generally, light is not a limiting factor. It becomes a limiting factor for plants growing in shade or under tree canopies. In the given graph, light is a limiting factor at the point where photosynthesis is the minimum. The least value for photosynthesis is in region A. Hence, light is a limiting factor in this region.
(b) Light is a limiting factor in region A. Water, temperature, and the concentration or carbon dioxide could also be limiting factors in this region
(c) Point D represents the optimum point and gives the light intensity at which the maximum photosynthesis is recorded. The rate of photosynthesis remains constant after this point, even though the intensity of light

Carboxylation is the most crucial step of the Calvin cycle.where CO₂ is utilized for the carboxylation of RuBP.This reaction is catalyzed by the enzyme RuBP carboxylase, which results in the formation of two molecules of 3-PGA. Since this enzyme also has an oxygenation activity, it would be more correct to call it RuBP carboxylase oxygenase or RuBisCO.

comparison between the C₃ leaf anatomy and C₄ leaf anatomy

Cyclic phosphorylation occurs when 700 nm light is available and PS-I is functional. It occurs in the stroma lamellae where enzyme NADP reductase is absent and PS-II is also absent. Hence, electrons are passed on back to PS-I and not to NADP⁺. So, the cyclic flow results in the formation of ATP, but not NADPH.

Part 1:Introduction
1. The plants which use C₃ carbon fixation pathway and the first product of carbon dioxide fixation is a 3-carbon organic compound, 3-phosphoglycerate, are termed as C₃ plants.
2. The plants in which the first product of carbon dioxide fixation is a 4-carbon organic compound, oxaloacetate, are termed as C₄ plants.
Part 2 :Anatomy of leaf – C₄ plants
1. The arrangement of mesophyll and bundle sheath cells in the leaf of C₄ plants is different from C₃ plants.
2. The parenchymatous cells which are a type of ground tissue present in the leaf are called mesophyll cells. The cells surrounding the vascular bundles is called the bundle sheath cells.
3. In C₄ plant these mesophyll cells are clustered around the bundle sheath cells and forms a shape which is similar to the wreath.
This arrangement seen in the leaf of C4 plants is called Kranz anatomy.


In C₃ plants the mesophyll cells are not clustered and they do not exhibit Kranz anatomy .


Part 3:Chloroplast
1. In C₃ plants chloroplast are present only in the mesophyll cells.
2. In C4 plants chloroplasts are present in bundle sheath as well as mesophyll cells.
C₃ vs C₄ plants

C₄-plants can produce more suger than C₃-plants in condition of bright light and high tempertaure.It is because of the following reasons.
i)They have a special type of leaf anatomy
ii)They can tolerate higher temperature.
iii)They show response to high light intensities
iv)They lack a process called photorespiration.
v)They have greater productivity of biomass.
Many important crop plants are C₄-plants including maize, sorghum, sugarcane and millet.

RuBisCO has a much greater affinity for CO₂ than for O₂ under normal conditions.It is the relative concentration of O₂ and CO₂ that determines which of the two will bind to the enzyme.
In C₃-plants some O₂ does bind to RuBisCo and hence, CO₂ fixation is decreased.Here the RuBP instead of being converted to 2 molecules of PGA binds with O₂ to form one molecule and phosphoglycolate in a pathway called photorespiration.In the photorespiratory pathway, there is neither synthesis of sugars, nor of ATP, rather it results in the release of CO₂ with the utilization of ATP. In the photorespiratory pathway, there is no synthesis of ATP or NADPH. Therefore, photorespiration is a wasteful process.
In C,•plants, photorespiration does not occur. This is because they have a mechanism that increases the concentration of CO₂ at the enzyme site. This takes place when the C, acid frorn the mesophyll is brcoe down in the bundle cells to release CO₂this increasing the intracellular concentration ofCO₂ turn, thís ensures that the RuBisCO functions carboxylase minimising the oxygenase activity

Calvin cycle is a series of reactions that leads to the formation of glucose. The steps involve utilisation of 2 molecules of ATP for phosphorylation and 2 of NADPH for reduction per CO₂ molecule fixed. The fixation of six molecules of CO₂ and six turns of the cycle are required for the synthesis of one molecule of glucose through these reactions.
Hence, for every CO₂ molecule entering the Calvin cycle, 3 molecules of ATP and 2 of NADPH are required. It is probably to meet this difference in number of ATP and NADPH used in the dark reaction that the cyclic phosphorylation takes place. To make one molecule of glucose six turns of the cycle are required.

Although all cells in the green part of a plant have chloroplasts, most of the energy is captured in the leaves. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450000 and 800000 chloroplasts for every square millimetre of leaf (nearly 60-70 chloroplasts/cell).
The surface of the leaf is uniformly coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating.The transparent epidermal layer allows light to pass through to the palisade mesophyll cells, where most of the photosynthesis takes place.The green stems are also capable of performing photosynthesis.