Botany - Paper I - For Class XI (Science Group) - Model papers with Solved MCQs 2020 -2021

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Botany - Paper I
For Class XI (Science Group)
Model papers 2020 -2021

Time: 01 hour     Total Marks: 23

SECTION 'B' (SHORT-ANSWER QUESTIONS) (Marks: 14)

Q.2: Attempt any Six-part questions. Each question carries one mark. Give answer not more than two lines.
(i) Give two difference between Prokaryotes and Eukaryotes.
Ans: DIFFERENCE BETWEEN PROKARYOTES AND EUKARYOTES

	PROKARYOTES	EUKARYOTES
Type of Cell	Always unicellular	Unicellular and multicellular
Cell size	Ranges in size from 0.2 μm 2.0 μm in diameter.	Size ranges from 10 μm 100 μm in diameter.
Cell wall	Usually present chemically complex in nature.	When present chemically simple in nature.
Nucleus	Absent. Instead they have a nucleoid region in the cell.	Present
Ribosomes	Present. Smaller in size and spherical in shape.	Present. Comparatively larger in size and linear in shape.
DNA arrangement	Circular	Linear
Mitochondria	Absent	Present
Cytoplasm	Present. But cell organelles absent.	Present, cell organelles Present.

(Note: write two two differences as mentioned in question)

(ii) Why lysosomes are called suicide sacs?
Ans: Lysosomes are known as suicide bags of the cell because they contain lytic enzymes capable of digesting cells and unwanted materials. Autolysis and burst open, when the cell is damaged. This causes the hydrolytic enzyme to be released. The released enzymes then digest their own cell, causing the cell to die. As a result, they are known as cell suicide bags.

OR

(ii) Name any two diseases caused by Virus.
Ans: Name of plant diseases caused by Virus

• Tobacco mosaic -Virus (TMV)
• Cucumber mosaic -Virus (CMV)
• Tomato spotted wilt-Virus (TSWV)

Name of Animal diseases caused by Virus

• Poliomyelitis
• Colds, Flu
• Dengue and yellow fever
• Aids
• Rabies
• Measles
• Mumps
• Hepatitis

(Note: Any two disease name, better to select plant's viral disease as it is botany section.)

(iii) Define any two of the followings:
♦ Double Fertilization
♦ Homosporous
♦ Diffusion
♦ Pili
Ans: DEFINITION:
a) Double Fertilization:
Double fertilization is a special type of fertilization which occurs only in angiospermic plants. During this process a sperm fuses with the ovum to form oospore. The other sperm fuses with secondary nucleus to form triploid endosperm nucleus.

OR

Double Fertilization is a chief trait of flowering plants. In the phenomena, one female gamete unites with two male gametes. One of the male gametes fertilizes the egg resulting in the formation of a zygote and the other unites with a polar nuclei for the formation of an endosperm.

b) Homosporous:
Plants like Lycopodium, Pteridophytes that produce only one kind of spore, and hence have only one kind of gametophyte that bears both male and female organs (i.e not separated by sex) are said to be homosporous.

OR

(iii) Diffusion:
The movement of molecules from the region of higher concentration to the region of lower concentration is called diffusion. Example: One of the most common example of diffusion is, if a bottle of perfume is opened in a comer of a room, it can be smelt in the entire room after some time.

(iv) Pili:
Pili is found in the bacterial cell. They are generally referred to as the hollow, filamentous appendages, which are involved in the conjugation. They help in conjugation and not in locomotion. They are also known as long conjugative pili. They are smaller than flagella and longer than fimbriae and involved in the cell to cell attachment during conjugation for DNA transfer.

(iv) On what basis Fungi are classified?
Ans: BASIS OF CLASSIFICATION OF FUNGI:
Fungi are usually classified in four divisions:

1. Zygomycota (bread molds)
2. Ascomycota (yeast and sac fungi)
3. Basidiomycota (club fungi)
4. Deuteromycota or Chytridiomycota (chytrids)

These major groups of fungi are distinguishable on the basis of sexual reproduction.

OR

(iv) Write the molecular formula of chlorophyll a and b.
Ans: MOLECULAR FORMULA OF CHLOROPHYLL A and B:
The molecular formula of chlorophyll a is: C₅₅ H₇₂ O₅ N₄ Mg
The molecular formula of chlorophyll Is b is: C₅₅ H₇₀ O₆ N₄ Mg

(v) Why protoctista considered as polyphyletic kingdom?
Ans: Kingdom Protista is considered as polyphyletic group because they have many characters of their ancestors. The word polyphyletic means they do not share a single common ancestor and as protoctists have characters of animals, plants and fungi so that they are regarded as polyphyletic group of organism.

(vi) Why yeast is placed in fungi, while it is unicellular?
Ans: The yeast is placed in fungi because

1. Yeast reproduces sexually with the production of ascospores.
2. The have cell wall made of chitin.
3. They have haploid nuclei.
4. Most of their reproduction is asexual and takes place by cell fission or budding (the formation of a smaller cell from a larger one).

(vii) Name three methods of genetic recombination in Bacteria.
Ans: In bacteria the process of genetic recombination takes place through three process which are following:

1. Conjugation
2. Transduction
3. Transformation (Transforming Principle)

CONJUGATION:
In this process of recombination bacteria attached with each other through pili. Pili of two bacteria after fusion form a tube like structure called conjugation tube (or cytoplasmic bridge) through this tube DNA of one bacteria transfer to another bacteria. This process was carried out experimentally by Laderberg and Tatum in 1946.

TRANSDUCTION:
It is a mode of genetic recombination in which genetic material is transferred from one bacterium to another by a third party which is a bacteriophage. This process was carried out experimentally by Laderberg and Zinder in 1952.

TRANSFORMATION (Transforming Principle):
It is a process of transmitting genetic information from one bacterium to another bacterium through environment causing it to transform (undergo change). This principle was first notified by Fred Griffth in 1928.
(Note: As in question names are asked so do not write description)

(viii) What is the role of potassium in transpiration?
Ans: ROLE OF POTASSIUM IN TRANSPIRATION:
In clay time K⁺ is actively transported by guard cells. Turgor pressure increases because of a negative water potential due to an inflow of potassium ions (K⁺) the cell becomes hypertonic to its environment. Then water comes inside the epidermal cells by osmosis. Reversible uptake of K⁺ ions takes place because of the membrane potential created when H⁺ are actively pumped out of the cell consuming ATP. The cells interior becomes negative compared to the surroundings. Water flows out of guard cells causing them to become flaccid which result the closure of stomata.

OR

(viii) Why do insectivorous plant use insects as food?
Ans: Insectivorous plants are plants which have insects and small birds as their prey. They are found in areas where the soil is poor in nutrients and nitrogen is deficient. They are poor in nitrogen which is very important for the growth of the plants, such as rock outcrops and acidic bogs. They have to depend on insects for their nitrogen and protein requirements. Thus This nitrogen is obtained by digesting the insects.

(ix) Why ATP called as energy currency?
Ans: ATP is known as adenosine triphosphate, and it is a molecule containing carbon, hydrogen, nitrogen, oxygen and phosphorus. ATP is the energy currency of the cell because, it is the most preferred energy molecule in the cell. Its preference is due to the following factors:

1. It donates its phosphoryl groups to release energy.
2. On hydrolysis, it releases a high negative Gibbs free energy which can be drive many important biosynthetic reactions in metabolic pathways.
3. The presence of adenine and ribosyl groups provide additional features for attachment to enzymes so it is able to to regulate enzymatic activities.

Q.3: Attempt any Four part questions. Each question carries two marks. Answer should not be exceed 5 to 6 lines.
(i) Write four important events takes place during light reaction of photosynthesis.
Ans: EVENTS OF LIGHT REACTION:
Following four important event take place during photosynthesis:

1. Photolysis of water.
2. Electron transport chain i.e. PS II and PS I.
3. Reduction of NADP⁺ to NADPH + H⁺
4. Synthesis of ATP by photophosphorylation.

OR

(i) Write note on Diversity among protoctista.
Ans: DIVERSITY AMONG PROTOCTISTA:
The Kingdom Protista consists of eukaryotic protists. Members of this kingdom are very diverse, typically unicellular and less complex in structures and have similarities with other eukaryotes. Due to this diversification, biologists regard protist kingdom as a polyphyletic group of organisms. It means they do not share a single common ancestor.
Here we have divided them into three groups:

1. Plant-like Protoctists-Algae (Chlorella and Ulva)}
2. Fungi-like Protoctists-Primitive fungi (Slime molds and Water molds)
3. Animal-like Protoctists-Protozoa (Trypanosoma, Amoebae, Paramecium)

(ii) Briefly describe the fluid mosaic plasma membrane.
Ans: FLUID MOSAIC MODEL:

• This model was presented by Singer and Nicolson in 1972.
• In the fluid mosaic model, the lipid bilayer is retained as the core of the membrane.
• These lipid molecules are present in a fluid state capable of rotating and moving laterally within the membrane.
• The structure and arrangement of membrane, proteins in the fluid-mosaic model are like icebergs sea.
• Some protein molecules penetrate deeply into and even completely through the lipid sheet.
• The components of plasma membrane are mobile and capable of coming together to engage in various types of transient or semi permanent interaction.
• The protein associated with lipid bilayer can be divided into two groups:
  (i) Integral proteins (intrinsic proteins)
  (ii) Peripheral proteins (extrinsic proteins)

(iii) Describe the concept of species and taxonomic hierarchy of biological classification?
Ans: TAXONOMIC HIERARCHY:
"Taxonomic hierarchy is the process of arranging various organisms into successive levels of the biological classification, either in a decreasing or an increasing order from kingdom to species and vice versa."
UNIT OF BIOLOGICAL CLASSIFICATION:
Following are the units of classification or taxonomic categories:

1. Species:
   The group of living organisms which are not only similar in morphological characteristics but they can also sexually inter breed with each other to give fertile offspring.
2.  Genra: 
   The basic unit of the biological classification is specie. Closely related species are grouped together into Genra.
3. Families:
   Genera are grouped into Families.
4. Order:
   Families are grouped into order.
5. Classes:
   Orders are grouped into classes.
6. Phyla (Division):
   Classes are grouped into phyla (For animals), Division (for plants).
7. Kingdom (Largest unit):
   Phyla or divisions are grouped into kingdoms.

OR

(iii) Point out two problems with having two kingdom system.
Ans: OBJECTIONS OF TWO KINGDOMS SYSTEMS:
There are some problems with two kingdom system of classification which are following:

• First is Euglena which has both animals and plants like characters, have no cell wall like animals and have chlorophyll like plants. They are autotrophic as well as heterotrophic.
• It cannot explain the difference between prokaryotic and eukaryotic.
• Fungi which are totally different from plants also included in kingdom plantae.

(iv) Write postulates of cell theory?
Ans: POSTULATES OF CELL THEORY:
Cell theory is the contribution of Schieiden 1839, Schwann 1839 and Virchow 1855. Cell theory has following points.

1. Cells are the structural and functional unit of living organisms.
2. Cells arise from preexisting cells.
3. Cells contain nucleic acid through which specific characters are passed to the next generation of cells

OR

(iv) Salient features of Cyanobacteria
Ans: FEATURES OF CYANOBACTERIA:

• Blue-Green Algae are a type of photosynthetic bacteria consisting either of single cells or colonies which is also known as the Cyanobacteria. Cyanobacteria contain only one type of chlorophyll, Chlorophyll a, a green pigment in addition , they also contain pigments such as carotenoids, phycobilln.
• These bacteria grow naturally in marine and fresh water systems. They thrive in dams, rivers, reservoir lakes and even in hot springs. These bacteria normally look green and sometimes turns blue when scum are dying. Almost all specie of these bacteria are buoyant and float on the water surface and forms floating mats.
• The accumulation of these algae is termed as blooms. These blooms discolour the water and produce unpleasant taste and odour. They effect the fish population and reduces water quality. The decomposition of these blooms deplete the oxygen and triggers the killing of fish.
• Examples of cyanobacteria: Nostoc, Oscillatoria, Spirulina, Microcystis, Anabaena

v. Write structure and functions of the following: (any one)
Mitochondria
Nucleus
Ans: (I) NUCLEUS:
The nucleus was discovered by a scientist Robert Brown in 1831. It is spherical or oval in shape and is located in the center in a young cell while in a mature cell it comes to lie on one side.
STRUCTURE OF NUCLEUS:
1) NUCLEAR-MEMBRANE:
The nucleus is surrounded by a thin, transparent membrane separates the cytoplasm from the nucleus. The nuclear membrane has numerous large pores which help in direct communication between cytoplasm and the nucleoplasm.
2) NUCLEOPLASM:
In the nucleus there is a dense but clear mass of protoplasm, called nucleoplasm. It contains enzymes and other complex substances which take part in the formation of DNA and RNA.
3) CHROMATIN NETWORK:
In the neoplasm a network of fine loosely connected threads is present called chromatin network. The chromatin is the hereditary material. In division of nucleus the chromatin forms a definite number of thread like structures, called chromosomes, which contain hereditary units on their surface, called genes. Chemically chromatin consists of ribonucleic acid and Deoxyribonucleic acid (DNA).
4) NUCLEOLUS:
In each nucleus one or more globular bodies present, called nucleolus. They consists of proteins and RNA. The nucleolus produce ribosomes, which take part in protein synthesis.

FUNCTION OF NUCLEUS:

• The nucleus controls all the vital activity of a cell, so it is consider the brain of the cell.
• It produces chromosomes during cell division.
• The chromosomes transfer hereditary characters from parent cell to daughter cell.
• It directly takes part in cell division and reproduction.
• It produces DNA and RNA. DNA is a generic material and RNA takes part in protein synthesis.
• In the nucleolus of nucleus ribosomes are produced, which help In protein synthesis.

MITOCHONDRIA OR CHROMOSOMES:
They are small spherical or plate like bodies present in the cytoplasm. Mitochondria are transferred from mother to the new generation. These are present in eggs and not in sperms, so mother transfer them into new generation.
Mitochondria consists of three parts:
1) AN OUTER MEMBRANE:
It is smooth and consists of proteins and lipids.
2) INNER MEMBRANE:
It forms numerous folds, called cristae. On these cristae enzymes and co-enzymes are present which help in oxidation of starch, fatty acids and amino acids. These compounds are converted into CO₂ and water. In this process energy is released in the form of ATP. This energy is stored in the mitochondria.
3) MATRIX:
It is central granular part. It contains many organic compounds.

FUNCTIONS:
Mitochondria are the main centers of the intercellular energy production, they are called power house of the cell. Almost all the respiratory activities take place in mitochondria and they contain a number of enzymes.

(vi) Draw a well labelled diagram of the followings (any one):
♦ Bacteriophage virus
♦ Bacterium
♦ Fern prothallus

BACTERIOPHAGE VIRUS

BACTERIUM

FERN PROTHALLUS

SECTION "C" (DETAILED-ANSWER QUESTIONS)
(Max Marks: 09)

Note: Attempt any two question from this section all question carries equal marks.

Q.4: Explain the life cycle of Moss (No diagram required)
Ans: LIFE CYCLE OF MOSS ( Funaria hygrometrica - Bryophyte):
The life cycle is completed into two stages called alternation of generations.

1. Gametophytic stage
2. Sporophytic stage

It shows heteromorphic alternation of generations.

1. Gametophytic Stage:

• It is the first and dominant phase of life cycle.
• The gametophyte stage is haploid (n), and consisting of rhizoids, pseudo stem and leaves.
• In this phase. the sex organs antheridia (male) and archegania (female) are produced at the tips of stem.
  (i) The Antheridia:
  - The antheridia are club-shaped.
  - Each antheridiurn is surrounded by an outer jacket layer.
  - Inside the anthendium antherozoid mother cells or androcytes are produced.
  - They divide and redivide to form biflagellate male gametes called antherozoids.
  - There is protoandry because antheridia mature earlier and liberate their anthrozoids, which start swimming with the help of their flagella in dew or rainwater.
  
  The Archegonia:
  - Each archigonium is flack-shaped.
  - It consists of three parts stalk, venter and neck .
  - The stalk helps in the attachement of archegonium.
  - Venter is the middle swollen part.
  - It contains a large egg cell (ovum) and a small, venter canal cell.
  - Neck is the upper elongated tube-like part. It contains neck canal cells.

Fertilization:-
The motile anthrozoids move towards the archeeonium in the presence of water. They enter the archegonium through its open mouth and one antherozoid fuses with egg cell (ovum) to form diploid (2n) oospore (zygote). This is retained within archegonium and form an embryo (2n).

2. Sporophytic Stage:

• This embryo undergo repeated mitoticdivisions to form sporogonium (a sporophyte) which is diploid.
• The saprophyte grows upon gametophyte.
• It depends partially or completely for its nourishment upon the tissues of gametophyte.
• The sporophyte consists of three parts, foot seta and capsule.
  (i) Foot:
  Foot helps in the attachment of sporophyte and in the absorption of food from the tissues of gametophyte.
  (ii) Seta:
  The seta is the stalk of capsule.
  (iii) Capsule:
   The capsule produces spore-mother cells. They are diploid (2n).
• They divide by meiosis and form four haploid (n) spores.
• Each spore can germinate into filamentous body called protonema.
• Later on gametophyte (haploid) develops from protonema during favourable conditions to complete life cycle .

(Note : No diagram is required, as mentioned in question.)

OR

(4) Describe adaptive characteristics of Bryophytes to land habitat.
Ans: Adaptive Characteristics Of Bryophytes To Land habitat
The land plants and animals evolved from aquatic living organism. On land, they developed certain characteristics according to the environment.
ln water, the life is easy, because water is essential for all processes of life. The aquatic organisms do nor face dry conditions. The temperature of sea water does not change rapidly in dry land. In this way, the life of aquatic living organism remains continuous in a normal way.
When the plants migrated on land, they faced certain problems. The most important ones are as follows:

• To obtain and conserve water.
• To absorb CO₂ from the atmosphere for photosynthesis.

To solve these problems, the plants changed their body structure according to the environment. First of all, they shifted from aquatic to the amphibians habitat, then they started their life on dry land. Amphibians are the plants which grow on moist places or live body in dry and wet habitat For example. Mosses and Liverworts.
The characteristics cf plants which they adaptive from wet to dry conditions an as follows:

1. Rhizoids for water absorption
2. Conservation of water
3. Absorption of CO₂
4. Heterogamy
5. Protection of reproductive cells
6. Formation of embryos

1. Rhizoid for water absorption:

• These are long, filamentous extensions of the cells of the lower surface of the thallus.
• They greatly increase the surface for absorption of water from the soil.

2. Conservation of water:

• The plant-body called thallus of all bryophytes is multilayered.
• The outer and uppermost layer of cells is covered with cuticle. It is non-cellular layer of wax-like substance called cutin.
• Cuticle is also found in the stem and leaves of highly evolved land plants and is very efficient in reducing the rate of evaporation so water should stay in their body.

3. Absorption of CO₂:

• Land plants need an efficient means for the exchange of gases with the environment in contrast to aquatic plants which exchange gases dissolved in water.
• The upper surface of the thallus is provided with a number of aerating pores, which leads inside into an air-chamber, partially filled with branching filaments of photosynthetic cells.
• These cells absorb CO₂ for photosynthesis i.e manufacture of food.

4. Heterogamy:

• Heterogamy is the most successful kind of reproduction that has evolved in bryophytes.
•  It is defined as production of two different types of gametes, one is male (motile) and the other is female (non-motile) full of stored food.

5. Protection of reproductive cells:

• The land environment requires special protection for the reproductive cells. They are protected by outer covering.
• Moreover, together with these organs, hair like structures called paraphyses are also present which help to prevent drying of the sex organs.

6. Formation of embryos:

• Embryo developed into new amphibious plants is of universal occurrence..
• Egg called oospore (zygote) is formed inside the archegonium.
• An embryo develops from the oospore as it divides, remain inside the protective coverings of the archegonia.
• Thus The coverings formed by the female organ during development, protect the growing embryo from drying out and from mechanical injury.

Q.5: Describe in detail the process of Glycolysis.
Ans: Glycolysis: (Glyco = sugar, Lysis = splitting):
Glycolysis is the initial stage of aerobic respiration. This process starts with glucose. Glucose, a six-carbon molecule is degraded through sequential enzyme dependent reactions into two molecules of pyruvic acid (a three carbon compound).

ATP Provide Energy To The Process

A small amount of energy must be invested by the cell to initiate glycolysis. It is adenosine tri phosphate (ATP) that provides the energy for initiating glycolysis.

Process of glycolysis consists of following steps:
Phosphorylation Reactions:

• The first step in glycolysis is the transfer of phosphate group from ATP to 6-carbon of glucose. Adenosine di phosphate and glucose 6-phosphate are formed.
• After an enzyme catalyses, the conversion of glucose 6-phosphate to its isomer fructose-6-phosphate (F-6-P).
• Another molecule of ATP is invested which transfers its phosphate group this time to 1-carbon of F-6-P forming fructose-1, 6-di phosphate and ADP.
• These reactions are known as phosphorylation reactions because phosphate groups are added to glucose and fructose molecules.

Energy Investment Phase:

• Since two molecules of ATP are used this part of glycolysis is considered as the energy investment phase.
• The next step in glycolysis is enzymatic splitting of fructose 1, 6-di phosphate into two fragments. Each of these two molecules contain three carbon atoms. One is called 3-phosphoglycer aldehyde (PGAL) and other is Dihydroxy acetone phosphate (DHAP).
• These two sugar molecules are isomers to each other and are interconvertible. This is the reaction from which glycolysis derives its name.
• Normally both these molecules are converted into pyruvic acid through subsequent enzyme controlled reactions.

Energy Yielding Phase:

• In the remaining part of glycolysis ATP molecules are synthesized hence it is called energy yielding phase.
• In the following reaction, an enzyme dehydrogenase and a co-enzyme nicotinamide dinucleonde NAD+ work together.
• The enzyme strips off two hydrogen atoms from PGAL. These electrons are captured by NAD+. This is a redox reaction where PGAL is oxidized by removal of electrons and NAD is reduced by the addition of electrons.
• With the loss of two hydrogen atoms PGAL is converted into 1- 3 phosphoglyceric acid (PGA).
• Now PGA picks up phosphate group (Pi) present in cytoplasm and becomes 1-3 di phosphoglyceric acid (DPGA).
• In the very next step DPGA loses its phosphate group to ADP forming ATP and 3-phosphoglycerate. The phosphate group attached with carbon-3 atom of PGA changes its position to carbon-2 atom forming an isomer 2-phosphoglycerate.
• With removal of water molecule 2 PGA is converted into phosphoenol pyruvic acid (PEPA).
• Finally phosphate group is transferred to ADP forming ATP and pyruvic acid.
• Synthesis of ATP during glycolysis is known as substrate level phosphorylation because phosphate group is transferred directly to ADP from another molecule.

OR

Q.5: Light independent reaction (C3 cycle) of photosynthesis.
Ans: Light independent reaction (Dark reaction) or Calvin-Benson Cycle Or (C3 cycle):
Dark reaction:
This is the second phase of photosynthesis, which results in the fixation of atmospheric CO₂ into sugar phosphates. This part of photosynthesis does not require light energy directly, therefore it is generally termed as the 'dark reaction'.
Calvin-Benson Cycle:
This process was explained by Calvin and Benson in the form of a cycle. These reactions require chemical energy in the form of ATP and NADPH2, are collectively known as the Calvin-Benson Cycle (reductive pentose phosphate cycle).
C3 Cycle:
During this cycle CO₂ is reduced to triose-phosphate (phosphoglyceraldehyde and dihydroxyacetone phosphate) and subsequently via other metabolic pathways to carbohydrates. Type of plants in which first stable product is glycerate, 3 phosphate (PGA) contains 3 carbon atom are called C3 plants and the cycle called C3 cycle.

Phases Of Cycle:
This cycle consists of 3 main reactions catalysed by 11 enzymes, and is divide into three distinct phases, which are:

1. Carboxylation or carbon fixation - during which CO₂ is fixed into organic molecules.
2. Reduction of synthesis of phosphoglyceraldehyde (PGAL) by the reduction of organic molecules.
3. Regeneration where the reduced carbon can be utilized either to regenerate the carbon acceptor molecules or for metabolism.

i) Carboxylation:

• This is the first and key reaction of Calvin cycle where ribulose-1, 5-bisphosphate (RuBP) is combined with atmospheric CO₂ to produce a short lived, six carbon (Keto acid) intermediate, which breaks into two molecules of glycerate-3-phosphate (G3P).
• This reaction is catalysed by the enzyme ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco).

ii) Reduction:

• This phase of the calvin cycle comprises a series of freely reversible reactions.
• During this phase G3P is reduced to lycerate-1, 3- biphosphate (G1, 3P) and then triose phosphate [ 3 Phosphoglyceraldehyde (GA3P) and Dihydroxyacetonephosphate (DHAP) ] at the cost of ATP and NADPH produced during light reaction.

iii) Regeneration:

• Many carbon rearrangement takes place during this phase.
• Three carbon compounds are rearranged to form 5 carbon units including the primary acceptor molecule, RuBP. This stage involves enzymes 5-11.
• During this cycle 3 molecules of CO₂ fix by 3 molecule of RuBP (3 x C5), which produces 6 molecules of 3-carbon compounds i.e. triose (6 x C3).
• From these 6 molecules five are required to regenerate RuBP:
• (5 x C3 ⟶ 3 x C5).
• Therefore, only one molecule of 3C is produced (generally called triose-phosphate) which can
• (a) re-enter the cycle, or
• (b) be used for starch synthesis within the chloroplast or
• (c) be exported via a phosphate translocator to cytosol for sucrose synthesis.
• For the net synthesis of one G3P molecule, the Calvin cycle consumes a total of nine molecules of ATP and six molecules of NADPH+H+. The G3P spunoff from the Calvin cycle becomes the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates.

Special Thanks To:

By: SIR. DR. M. SAAD BAIG (M. Sc (Microbloiogy), A.D (Counselling Psychology]

GMAIL AND CONTACT: dr.balg267@gmail.com, 0345-2442224-/-0334-2552299-(Whatsapp)

SOURCE: Board Of Intermediate Education Karachi