- Information
- AI Chat
Pteridophytes gymnosperm angiosperms
Bsc botony (Botony)
University of Calicut
Recommended for you
Preview text
Photosynthesis
Notes
Forms and Functions of Plants and animals
11
PHOTOSYNTHESIS
Photosynthesis (Photo = light; synthesis = to join) is the single most important process on earth on which depends the existence of human beings and almost all other living organisms. It is a process by which green plants, algae and chlorophyll containing bacteria utilize the energy of sunlight to synthesize their own food (organic matter) from simple inorganic molecules. Innumerable number of organic molecules which compose the living world are derived directly or indirectly from the photosynthetic organic matter. The oxidation of organic compounds releases stored energy to be utilized by the living organisms to carry out essential metabolic processes. It is important to note that photosynthesis is the only natural process which liberates oxygen to be used by all living forms for the process of aerobic respiration. You have studied in lesson 4, that chloroplasts are the organelles that carry out photosynthesis or in other words they act as solar cells producing carbohydrates. In this lesson you will learn how green plants carry out photosynthesis.
OBJECTIVES
After completing this lesson, you will be able to : z define photosynthesis; z name the different pigments found in chloroplasts; z explain the main aspects of the process of photosynthesis; z enumerate the steps involved in the light and dark reactions of photosynthesis; z define the terms absorption spectrum, action spectrum, electron acceptor and photophosphorylation; z distinguish between, absorption spectrum and action spectrum; light and dark reactions, cyclic and non-cyclic photo-phosphorylation, C 3 and C 4 photosynthesis; z list the environmental variables and internal factors affecting photosynthesis; z describe the principle of limiting factor giving suitable graphs.
Photosynthesis
Notes
Forms and Functions of 11 PHOTOSYNTHESIS Plants and animals
11 Let us look into the significance of the process
Significance
Green plants possess the green pigment, chlorophyll which can capture, transform, translocate and store energy which is readily available for all forms of life on this planet.
Photosynthesis is a process in which light energy is converted into chemical energy.
Except green plants, no other organism can directly utilise solar energy to synthesize food, hence they are dependent on green plants for their survival.
Green plants which can prepare organic food from simple inorganic elements are called autotrophic while all other organisms which cannot prepare their own food are called heterotrophic.
During photosynthesis, oxygen liberated into the atmosphere makes the environment livable for all aerobic organisms.
Simple carbohydrates produced in photosynthesis are transformed into lipids, proteins, nucleic acids and other organic molecules.
Plants and plant products are the major food sources of almost all organisms on the earth.
Fossil fuels like coal, gas, and oil represent the photosynthetic products of the plants belonging to early geological periods.
11.1 What is photosynthesis? Photosynthesis is the process by which green plants, in the presence of light combine water and carbon dioxide to form carbohydrates. Oxygen is released as a by product of photosynthesis. Current knowledge of photosynthesis has resulted from discoveries made over 300 years of work. Some landmark experiments are given in the box below.
z Joseph Priestley (1772) and later Jan Ingenhousz (1779) showed that plants have the ability to take up CO 2 from the atmosphere and release O 2. z Ingenhousz also discovered that release of O 2 by plants was possible only in presence of sunlight and by the green parts of the plant. z Robert Hill (1939) demonstrated that isolated chloroplasts evolve O 2 when they are illuminated in the presence of electron acceptor which gets reduced. This reaction called Hill reaction accounts for the use of water as a source of electrons and protons for CO 2 fixation and release of O 2 as bye-product.
Photosynthesis is represented by the following overall chemical equation:
6CO 2 + 12H 2 O →ChlorophyllSunlight C 6 H 12 O 6 + 6H 2 O + 6O 2
Photosynthesis
Notes
Forms and Functions of Chlorophyll-a (a special type of chlorophyll) is the main pigment that traps solar Plants and animals energy and converts it into chemical energy. Chlorophyll-a is present in all autotrophic plants except photosynthetic bacteria. Thus Chl-a is called the essential photosynthetic pigment responsible for representing the reaction centre.
All other pigments such as chlorophyll b and carotenoids are collectively called accessory pigments since they pass on the absorbed light energy to chlorophyll a (Chl-a) molecule to be utilized for photosynthesis. These pigments, that is the reaction centres (Chl-a) and the accessory pigments ( harvesting centre ) are packed into functional clusters called photosystems. Photosystems are of two types PSI and PSII.
About 250-400 Chl-a molecules constitute a single photosystem. Two different photosystems contain different forms of chlorophyll a in their reaction centres. In photosystem I (PSI), chlorophyll– a with maximum absorption at 700 nm (P 700 ) and in photosystem II (PSII), chlorophyll– a with peak absorption at 680 nm (P 680 ), act as reaction centres. (P stands for pigment). The primary function of the two photosystems, which interact with each other is to trap the solar energy and convert it into the chemical energy also called assimilatory power (ATP and NADPH 2 ). The differences between them are given in the following Table 11.
Table 11 Differences between Photosystem I and Photosystem II
Photosystem I Photosystem II z PS I has a reaction centre of z PS II has a reaction centre of chlorophyll ‘a’ molecule with chlorophyll ‘a’ molecule with maximum maximum light absorption at 700 nm light absorption at 680 nm. This wavelength. This reaction centre is reaction centre is also referred to referred to as P 700. to as P 680. z Primary electron acceptor is an iron z Primary electron acceptor, pheophytin, protein (Fe-S-protein) is a modified chlorophyll-a molecule with 2 hydrogen atoms in place of magnesium ion. z A set of electron carriers are z A set of electron carriers are pheophytin plastocyanin, ferredoxin and plastoquinone, cytochromes. cytochrome
11 ROLE OF SUNLIGHT IN PHOTOSYNTHESIS
Light consists of small particles or packages of energy called “photons”. A single photon is also called quantum. What does the chlorophyll do? It absorbs light energy.
Chlorophyll molecules absorb light energy and get into an excited state and lose an electron to the outer orbit. No substance can remain in an excited state for long, so the energised and excited chlorophyll molecule comes down to a low energy state known as ground state and releases the extra amount of energy. This energy can be lost as heat, or as light (fluorescence) or can do some work. In photosynthesis, it works by splitting water moelcule to produce H+ and OH– ions.
Photosynthesis
Notes
Forms and Functions of Plants and animals Carotene is orange-yellow pigment present along with chlorophylls in the thylakoid membrane. A carotene molecule breaks down into the vitamin A molecules. It is this pigment which gives carrot its colour.
Absorption and Action Spectra For investigating a process such as photosynthesis that is activated by light, it is important to establish the action spectrum for the process and to use this to identify the pigments involved. An action spectrum is a graph showing the effectiveness of different wavelengths (VIBGYOR) of light in stimulating the process of photosynthesis, where the response could be measured in terms of oxygen produced at different wavelengths of light. An absorption spectrum is a graph representing the relative absorbance of different wavelengths of light by a pigment. An action spectrum for photosynthesis is shown in Fig. 11 together with an absorption spectrum for the combined photosynthetic pigments. Note the close similarity, which indicates that the pigments, chlorophyll-a in particular, are responsible for absorption of light used in photosynthesis. All wavelengths of light are not equally effective in photosynthesis i. the rate of photosynthesis is more in some and less in others.
Fig. 11 Absorption Spectra of electromagnetic radiation B. Action Spectrum Photosynthesis occurs maximum in blue and red region of spectra. Photosynthesis is very little in green and yellow light, because these rays are reflected back from the leaf.
INTEXT QUESTIONS 11.
- (i) Define photosynthesis ..................................................................................................................
Action spectrum
Absorption spectrum
Chlorophyll b Absorption Chlorophyll a
Rate of photosynthesis
Photosynthesis
Notes
Forms and Functions of Plants and animals 11.4 Electron transport chain in photosynthesis After receiving light PSII absorbs light energy and passes it on to its reaction centre, P 680. When P 680 absorbs light, it is excited and its electrons are transferred to an electron acceptor molecule (Primary electron acceptor i. pheophytin) and it itself comes to the ground state. However by losing an electron P 680 is oxidised and in turn it splits water molecule to release O 2. This light dependent spliting of water is called photolysis. With the breakdown of water electrons are generated, which are then passed on to the electron deficient P 680 (which had transferred its electrons earlier). Thus the oxidised P 680 regains its lost electrons from water molecules. The reduced primary acceptor now donates electrons to the down stream components of the electron transport chain. The electrons are finally passed onto the reaction centre P 700 or PSI. During this process, energy is released and stored in the form of ATP. Similarly, PSI also gets excited when it absorbs light and P 700 (Reaction centre of PSI) gets oxidised as it transfers its electrons to another primary acceptor molecule. While the oxidised P 700 draws its electrons from PSII, the reduced primary acceptors molecule of PSI transfers its electrons via other electron carrier to NADP (Nicotinamide Adenine Dinucleotide Phosphate) to produce NADPH 2 a strong reducing agent. Thus we see that there is a continuous flow of electrons from the H 2 O molecules to PSII to PSI, and finally to the NADP molecule which is reduced to NADPH 2. NADPH 2 is then utilised in reduction of CO 2 to carbohydrates in the biosynthetic pathway.
Fig. 11 Non-cyclic (z-scheme) photophosphorylation PQ = Plastoquinine, PC-Plastocyanin Fd = Ferredoxin z Reduction of CO 2 to carbohydrate also requires ATP, which too are generated via electron transport chain. As the energy rich electrons pass down the electron transport system, it releases energy which is sufficient to bind inorganic phosphate (Pi) with ADP to form ATP. This process is called photo-
Primary acceptor
Primary acceptor
Cytochrome complex
= PS-I
= PS-II
Photons
Photosynthesis
Notes
Forms and Functions of phosphorylation. Since this takes place in presence of light it is called Photo- Plants and animals phosphorylation. It occurs in chloroplast in two ways: (a) Non-cyclic photophosphorylation where electrons flow from water molecule to PSII and then to PSI and ultimately reduce NADP to NADPH 2. Since the electron flow is unidirectional and the electrons released from one molecule do not return to the same molecule, it is called non-cyclic photosphorylation (Fig. 11). (b) Cyclic photophosphorylation occurs in photosynthetic bacteria which lack PS-II, and it involves PSI only. During this process electrons from PSI are not passed on to NADP. Instead the same electrons are returned to the oxidised P 700 molecule. During this downhill movement of electrons ATP formation takes place. Thus this is termed as cyclic photophosphorylation (Fig. 11).
Fig. 11 Cyclic photophosphorylation Table 11 Differences between cyclic and non-cyclic photophosphorylation
Cyclic photophosphorylation Non-cyclic photophosphorylation
- Only PSI is functional. 1. Both PSI and PSII are functional.
- Electron comes from the chlorophyll P 700 2. Water is the primary source of the electorns molecule and returns to the same and H+. It gets photolysed through the chlorophyll P 700 process called Photolysis; NADP is the final acceptor of the electrons and H+ ions.
- Oxygen is not evolved because there is 4. Oxygen is evolved as a bye product. no photolysis of water
- This process is found mainly in 5. This mainly takes place in all green plants, photosynthetic eubacteria e. purple and cyanobacteria except photosynthetic sulphur bacteria. eubacteria.
2 Photons
Cytochrome Complex
Primary Acceptor
Photosynthesis
Notes
Forms and Functions of z In the next step, PGA is reduced to 3-carbon carbohydrate called triose Plants and animals phosphate using NADPH 2 and ATP (from light reaction). Much of these molecules are then diverted from the C 3 cycle and used for synthesis of other carbohydrates such as glucose and sucrose. z To complete the cycle, the initial 5-carbon acceptor molecule, RuBP is regenerated from the triose phosphates using ATP molecule thus the C 3 cycle continues to regenerate the CO 2 -acceptor (RuBP).
11.5 C 4 Cycle (or Hatch Slack Cycle) z The C 4 cycle seems to be an adaptation for plants growing under dry hot environment. Such plants can photosynthesise even in the conditions of very low CO 2 concentration and under partial closure of stomata.
z Such plants can thus grow at low water content, high temperature and high light intensity. Sugarcane, and maize are some examples.
z Photorespiration (oxidation of RuBP in presence of O 2 ) is absent in these plants. So the photosynthetic rate is high. (For detail of photorespiration refer to lesson-12 Plant Respiration Section No. 12)
z The leaves of C 4 plants show presence of dimorphic chloroplasts, called Kranz anatomy. (a) In these plants, the vascular bundles have a sheath of large parenchyma cells around them in the form of a wreath, thus the name Kranz anatomy (Kranz : wreath) (b) Leaves possess two types of chloroplasts (dimorphic chloroplasts) (c) Chloroplasts in the mesophyll cells are smaller and have well developed grana (granal chloroplasts) but do not accumulate starch. (d) Chloroplasts in the bundle sheath cells are larger and lack grana ( agranal chloroplasts ) but contain numerous starch grains. (See Fig. 11).
Fig. 11 Transverse section of maize leaf showing Kranz’ anatomy
z In C 4 plants, the initial acceptor of CO 2 is phosphoenol pyruvic acid or PEP , a 3-carbon compound. It combines with CO 2 in presence of an enzyme Phosphoenol pyruvate carboxylase (PEP carboxylase) and forms a C 4 acid, oxaloacetic acid (OAA). This fixation of CO 2 occurs in the cytosol of the mesophyll cells of the leaf. OAA is the first stable product of this cycle which is 4 carbon compound and hence the name C 4 pathway is given.
Photosynthesis
Notes
Forms and Functions of Plants and animals z OAA then travels from mesophyll cells to the chloroplasts of bundle sheath cell where it releases the fixed CO 2. C 3 cycle operates within these cells and this CO 2 immediately combines with RuBP in C 3 cycle producing sugars. (See Fig. 11).
Fig. 11 The C4 photosynthetic carbon cycle z Thus in C 4 pathway of dark reaction, there are two carboxylase enzymes that take part. PEP carboxylase (PEPCo) in the mesophyll cells and RUBP carboxylase (Rubisco) in the bundle sheath cells.
z The differences between C 3 and C 4 plants are tabulated below. Table 11 Difference between C 3 and C 4 Plants
C 3 Plants C 4 Plants Carbon dioxide Occurs once Occurs twice, first in mesophyll fixation cells, then in bundle sheath cells. Carbon dioxide Only one acceptor, RuBP which In Mesophyll cells, PEP (Phosphoenol acceptor occurs in all green cells of the Pyruvic acid), 3-C, compound is CO 2 plant acceptor, but in the bundle sheath cells- RuBP, 5C, compound, is the CO 2 – acceptor Carbon dioxide RuBP carboxylase, which is not PEP caboxylase which is very fixing enzymes efficient when CO 2 conc is low efficient, even if CO 2 conc. is low RuBP carboxylase, works efficiently because carbon dioxide concentration is high. First product of The first stable product is 3-C The first product is 4-C compound photosynthesis compound phosphoglyceric acid oxaloacetic acid
Atmospheric CO 2
Plasma membrane
Cell wall
Mesophyll cell
Bundle sheath cell
Fixation Regeneration
Phosphoenol pyruvate
Plasmodesmate
Transport Transport
HCO 2 –
Cacid 4 Fixation byCalvin cycle
CO 2 C 3 acid Decarboxylation
C 4 acid C 3 acid
Photosynthesis
Notes
Forms and Functions of Plants and animals (i) Internal Factors 1. Chlorophyll : The amount of chlorophyll present has a direct relationship with the rate of photosynthesis because this pigment is directly involved in trapping light energy responsible for the light reactions. 2. Leaf age and anatomy : Newly expanding leaves show gradual increase in rate of photosynthesis and the maximum is reached when the leaves achieve full size. Chloroplast functions decline as the leaves age. Rate of photosynthesis is influenced by variation in (i) number, structure and distribution of stomata, (ii) size and distribution of intercellular spaces (iii) relative proportion of palisade and spongy tissues and (iv) thickness of cuticle.
3. Demand for photosynthate : Rapidly growing plants show increased rate of photosynthesis in comparison to mature plants. When demand for photosynthesis is lowered due to poor meristematic activity, the photosynthetic rate declines.
(ii) External Factors The major external factors which affect the rate of photosynthesis are temperature, light, carbondioxide, water, and mineral elements.
Concept of limiting factors : When a process is affected by various factors, the rate of the process depends upon the pace of the slowest factor. Let us consider three factors like light, carbon dioxide and temperature. It is seen that when all three factors are optimum, the rate of photosynthesis is maximum. However, of the three factors even if one of the factors becomes suboptimal and the other factors remain optimal, the rate of the photosynthetic process declines substantially. This is known as law of limiting factors shown by Blackman in 1905. It is defined as when a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the slowest factor which is known as the limiting factor. Light : The rate of photosynthesis increases with increase of intensity of light within physiological limits or rate of photosynthesis is directly proportional to light intensity. Except on a cloudy day and at nights, light is never a limiting factor in photosynthesis in nature. At a certain light intensity the amount of CO 2 used in photosynthesis and the amount of CO 2 produced in respiration are the same. This point of light intensity is known as compensation point. Wavelength of light absorbed by photosynthetic pigments affects rate of photosynthesis. Red light and to some extent blue light has an enhancing influence on photosynthesis (See action spectrum). The proportion of the total incident sunlight on earth, absorbed by green plants is generally a limiting factor. As per the estimates of the total incident light reaching the green plants, only about 1-2% is actually absorbed, because 70% is transmitted, and 28-29% is reflected back into the atmosphere.
Photosynthesis
Notes
Forms and Functions of Temperature : Very high and very low temperature affect the rate of photosynthesis Plants and animals adversely. Rate of photosynthesis will rise with temperature from 5°-37°C beyond which there is a rapid fall, as the enzymes involved in the process of the dark reaction are denatured at high temperature. Between 5°-35°C, with every 10°C rise in temperature rate of photosynthesis doubles or Q 10 is 2 (Q = quotient), or slightly less than two.
Carbon dioxide : Since carbon dioxide being one of the raw materials for photosynthesis, its concentration affects the rate of photosynthesis markedly. Because of its very low concentration (0%) in the atmosphere, it acts as limiting factor in natural photosynthesis. At optimum temperature and light intensity, if carbon dioxide supply is increased the rate of photosynthesis increases markedly until CO 2 conc. is as high as 3%. Thus, CO 2 conc. in the atmosphere is always a limiting factor for photosynthesis.
Water : Water has an indirect effect on the rate of photosynthesis. Loss of water in the soil is immediately felt by the leaves, which get wilted and their stomata close down thus hampering the absorption of CO 2 from the atmosphere. This causes decline in photosynthesis.
Oxygen : Concentration of oxygen as an external factor, is never a limiting factor for photosynthesis because it is a by-product of photosynthesis, and it easily diffuses into the atmosphere from the photosynthesizng organ, the leaf. However, excesss of O 2 surrounding a green plant, reduces photosynthetic rate by promoting the rate of aerobic respiraiton.
Mineral elements : Some mineral elements like magnesium, copper, manganese and chloride ions, which are components of photosynthetic enzymes, and magnesium as a component of chlorophylls are important, and their deficiency would affect the rate of photosynthesis indirectly by affecting the synthesis of photosynthetic enzymes and chlorophyll, respectively.
11 CHEMOSYNTHESIS
Chemosynthesis
When plants utilise light energy to reduce carbon dioxide to carbohydrates, they are called photosynthetic autotrophs. There are some bacteria which can utilise chemical energy released during biological oxidation of certain inorganic substances to reduce carbon dioxide to carbohydrate. These bacteria are called chemosynthetic autotrophs.
This is found in many colourless bacteria and because they use chemical energy to reduce carbon dioxide, this process of carbohydrate synthesis is known as chemosynthesis.
Photosynthesis
Notes
Forms and Functions of Plants and animals
INTEXT QUESTIONS 11.
- List the internal factors that influence the rate of photosynthesis?
............................................................................................................................
- State the principle of limiting factor.
............................................................................................................................
- Give an example of chemosynthetic bacteria.
............................................................................................................................
- Why are prokaryotes not able to produce ATP by chemiosmosis?
............................................................................................................................
WHAT YOU HAVE LEARNT
z Green plants are capable of synthesizing carbohydrates from CO 2 and H 2 O in the presence of light, by the process of photosynthesis.
z During photosynthesis ‘light energy’, which is captured by the photosynthetic pigments (chlorophyll, carotenoids and xanthophylls) present in the chloroplasts, is converted into chemical energy.
z Photosynthesis in general is expressed by the following equation:
6CO 2 + 12H 2 O ChlorophyllLight →C 6 H 12 O 6 + 6H 2 O + 6O 2
z Photosynthesis comprises two sets of reactions:
z Light reactions: which take place in grana or thylakoids of chloroplasts only in the presence of light.
z Dark reactions: Which occur in the stroma of chloroplast and are independent of light, if products of light reaction are provided.
z Light energy is used for splitting of water, and production of ATP and NADPH 2 and actual reduction of CO 2 takes place in the dark reaction.
z Light reaction occurs with the help of two functional units, photosystem-I and photosystem-II.
z During light reaction phosphorylation of ADP to ATP may occur in two ways, cyclic and non-cyclic.
z During dark reactions CO 2 is accepted by Ribulose biphosphate (RuBP) and the first stable product. 3-PGA (3 phosphoglyceric acid) is formed, which by further cyclic reactions (Calvin Cycle) leads to the formation of carbohydrates as well as in regeneration of RuBP.
Photosynthesis
Notes
Forms and Functions of Plants and animals z In C 4 plants like maize, jawar, bajra , the primary acceptor of CO 2 is in mesophyll cells and the first detectable product of dark reaction is oxaloacetic acid (OAA), whereas in the bundle sheath cells CO 2 fixation occurs through. Calvin cycle. z Occurrence of dimorphic chloroplasts in C 4 plants is known as “Kranz anatomy” and is characterized by the presence of a sheath of parenchyma cells around a vascular bundle (bundle sheath). Cells of this sheath have larger chloroplasts which lack grana and are filled with starch grains. In contrast mesophyll cells contain chloroplasts which are smaller but have well developed grana. z Rate of photosynthesis is influenced by (i) environmental factors such as light, temperature, carbon dioxide concentration and water, and (ii) internal factors which include age of leaf, chlorophyll content and leaf anatomy.
A SUMMARY OF PHOTOSYNTHESIS
Photosynthesis
Light dependent stage Light-independet stage
grana
CO 2
O 2 CO 2 reduced (CH O)carbohydrate 2
Stroma
Water split
HO 2
1 2
NADPH 2
in in
out
Light-dependent stage Light independent stage z occurs in the thylakoid membranes z occurs in the stroma of the grana z largely a photochemical change, z a series of biochemical changes, each requiring light energy reaction catalysed by an enzyme z light energy is converted to chemical z carbon dioxide is converted to compounds energy in the form of ATP and NADPH 2 ; such as carbohydrates (with the help of chemical water is split into hydrogen and oxygen; energy of ATP and NADPH 2 ); the reactions hydrogen is combined in NADPH 2 ; of the light-independent stage are known oxygen gas is released as a byproduct as the Calvin cycle and C 4 -pathway z chlorophylls are grouped together in z carbon dioxide is combined with ribulose units of about 300 molecules (known as bisphosphate (the acceptor substance) and photosystems); two types exist, the product splits instantly into two photosystems I and II molecules of glycerate 3-phosphate (GP, the first product of photosynthesis) in C 3 -plants z light energy absorbed by the photo- z CO 2 is reduced with the help of RuBP and systems causes electrons from chlorophyll Rubisco to a three-carbon sugar, triose phosphate; to be raised to a high energy level and then, in a series of reactions, the acceptor to pass to NADPH 2 ; ATP is generated; molecule is regenerated and sugars, starch and water is split and provides the electrons other substances are formed from
Photosynthesis
Notes
Forms and Functions of Plants and animals 11. Why is cyclic photophosphorylation called so?
What is Kranz anatomy?
Name the two carboxylase enzymes in C 4 cycle.
What are chemosynthetic autotrophs?
How does CO 2 concentration affect the rate of photosynthesis?
What is the effect of excess of oxyygen on the rate of photosynthesis?
Whether light absorbed by green plants, on global basis is limiting factor for photosynthesis or not! Explain
ANSWERS TO INTEXT QUESTIONS
11 1. (i) It is the process by which green plants produce food (carbohydrates) from simple substances like CO 2 and water in presence of sun light and chlorophyll.
(ii) 6CO 2 + 12H 2 O
Chlorophyll Sunlight → C 6 H 12 O 6 + 6H 2 O + 6O 2
- (i) Chlorophylls and carotenoids.
(ii) Carotenoids and chlorophyll b
- (i) Absorb it and then convert it into chemical energy.
(ii) Chlorophyll a and b 4. (i) Minimum in green and yellow light and maximum in blue and red light.
(ii) light energy; chemical energy
From photolysis of water in PSII 11 1. NADP acts as an electron acceptor and H+ acceptor and finally, it gets reduced to NADPH 2.
It is called dark reaction because it can occur independent of light i. can occur both in light and in dark.
(i) Rubisco is a part of C 3 cycle and combines with CO 2 to produce a C 3 compound called PGA.
(ii) PEPCo is a part of C 4 path way and combines with CO 2 to form a C 4 compound called OAA.
Photosynthesis
Notes
Forms and Functions of Rubisco is present in the mesophyll cells of C 3 plants and in the Plants and animals bundle sheath cells of C 4 plants. PEPCo is found only in mesophyll cells of C 4 plants. 4. See text 5. See text 6. C 4 plants have no photorespiration and thus there is no loss of additional carbon dioxide, due to breakdown of RuBP to Glycolate and CO 2. 7. (i) Photolysis of water
11 1. leaf age, chlorophyll content, leaf anatomy (size, internal structure, stomatal distribution) 2. See text 3. Nitrosomonass and Nitrobacter. 4. Because they are not able to maintain H+ gradient across a membrane in the absence of membrane bound organelles in their cytoplasm.
Pteridophytes gymnosperm angiosperms
Course: Bsc botony (Botony)
University: University of Calicut
- Discover more from:
