Pigments involved in photo synthesis Questions in English

(C) Chlorophyll pigments appear green in white light because they reflect green wavelengths and absorb red and blue wavelengths. When chlorophyll is illuminated only by red light,it absorbs the red light efficiently for photosynthesis. Since there is no green light to be reflected to the observer's eye,the chlorophyll appears black.

(A) Grana are the sites for the light reaction of photosynthesis and consist of photosynthetic units called "quantasomes".
Park and Biggins $(1964)$ introduced the term "quantasome" for these photosynthetic units.
Each quantasome is equivalent to approximately $230$ chlorophyll molecules.

(B) The chemical composition and structure of photosynthetic pigments such as chlorophyll,carotene,and xanthophyll were extensively studied and revealed by the scientists $Willstatter$ and $Stoll$ in the early $20^{th}$ century. Their work provided the fundamental understanding of the molecular structure of these pigments.

(B) Plastocyanin is a copper-containing protein that acts as an electron carrier in the photosynthetic electron transport chain.
It facilitates the transfer of electrons from the cytochrome $b_6f$ complex to Photosystem $I$ $(PSI)$.
Unlike cytochromes which contain iron $(Fe)$,or ferredoxin which is an iron-sulfur protein,plastocyanin specifically contains a copper atom at its active site.

(C) Chlorophyll $a$ and $b$ are the primary photosynthetic pigments in plants.
These pigments exhibit maximum absorption in the blue and red regions of the visible light spectrum.
The blue region corresponds to wavelengths between $400$ $nm$ and $500$ $nm$.
The red region corresponds to wavelengths between $600$ $nm$ and $700$ $nm$.
Therefore,chlorophylls absorb light effectively in these two specific ranges.

(D) The photosynthetic unit is called a $Quantasome$.
$Quantasomes$ are granular structures found in the thylakoid membranes of chloroplasts.
They contain the pigments and proteins necessary for the light-dependent reactions of photosynthesis,specifically acting as the site for light energy harvesting.

(A) Photosynthesis occurs most efficiently in the blue and red regions of the visible light spectrum.
Chlorophyll $a$ and $b$ show peak absorption in the blue region (around $430-450 \, nm$) and the red region (around $640-680 \, nm$).
Among the given options,$440 \, nm$ falls directly within the blue light absorption peak,which is highly effective for driving the light-dependent reactions of photosynthesis.

(A) Chlorophyll-$a$ is the primary photosynthetic pigment found in all green plants.
It is considered the universal photosynthetic pigment because it is essential for the light-dependent reactions of photosynthesis.
Therefore,the correct option is $A$.

(A) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain during photosynthesis and respiration.
They facilitate the transfer of electrons through redox reactions,which is essential for the generation of $ATP$ and $NADPH$.
Phytochrome is a photoreceptor pigment involved in light-mediated plant development and signaling,not in electron transport.
Therefore,the correct answer is Cytochrome.

(C) The reaction center of Photosystem $I$ $(PS-I)$ is known as $P_{700}$.
It consists of a special form of Chlorophyll $a$ molecule that absorbs light at a wavelength of $700 \ nm$.
Therefore,$P_{700}$ is a special form of Chlorophyll $a$.

(A) Carotenoids are accessory photosynthetic pigments that absorb light energy and transfer it to chlorophyll $a$.
They primarily absorb light in the violet and blue regions of the visible spectrum.
By absorbing these wavelengths,they protect the chlorophyll molecules from photo-oxidation and expand the range of light wavelengths that can be utilized for photosynthesis.

(A) In the light-harvesting complex $(LHC)$ of photosynthesis,hundreds of pigment molecules (chlorophyll $a$,chlorophyll $b$,and carotenoids) are bound to proteins.
These pigments form light-harvesting systems also called antennae.
These pigments help to make photosynthesis more efficient by absorbing different wavelengths of light.
Each photosystem has a single reaction centre (chlorophyll $a$) surrounded by hundreds of pigment molecules,which typically number around $200$ to $400$ molecules per reaction centre.

(D) Chlorophyll pigments,specifically chlorophyll $a$ and $b$,show maximum absorption peaks in the blue and red regions of the visible spectrum.
Chlorophyll $a$ has a primary absorption peak near $430$ $nm$ (blue) and another near $662$ $nm$ (red).
Among the given options,$660$ $nm$ falls within the red region of the spectrum,which is highly effective for photosynthesis.
Therefore,$660$ $nm$ is the correct wavelength absorbed by chlorophyll.

(C) The chlorophyll molecule consists of a porphyrin head and a long hydrocarbon tail known as the phytol chain.
This phytol chain is a hydrophobic tail that helps anchor the chlorophyll molecule into the thylakoid membrane of the chloroplast.
Therefore,the phytol chain is a characteristic component of chlorophyll.

(D) In photosynthesis,the reaction centre is a complex of proteins and pigments that performs the primary photochemistry of photosynthesis.
It consists of a special pair of chlorophyll '$a$' molecules that absorb light energy and initiate the electron transport chain.
Therefore,the reaction centre is located in chlorophyll '$a$'.

(C) Chloroplasts are the sites of photosynthesis in eukaryotic plants.
They contain various pigments,proteins,and lipids.
Chlorophyll is the primary photosynthetic pigment responsible for capturing light energy.
In a typical,healthy chloroplast,the chlorophyll content constitutes approximately $5-10\%$ of the total dry weight of the chloroplast.
The remaining dry weight is primarily composed of proteins and lipids that form the thylakoid membranes and stroma.

(B) Chlorophyll $a$ is the primary photosynthetic pigment found in all oxygenic photosynthetic organisms,including algae,bryophytes,pteridophytes,gymnosperms,and angiosperms.
Photosynthetic bacteria (such as purple and green sulfur bacteria) perform anoxygenic photosynthesis and contain bacteriochlorophyll instead of chlorophyll $a$.

(D) Photosynthetic bacteria are prokaryotic organisms and do not possess membrane-bound organelles like chloroplasts.
Instead,they contain photosynthetic pigments within specialized membranous structures called chromatophores.
These structures are extensions of the plasma membrane that house the pigments required for photosynthesis.

(D) The correct answer is $D$. Photosynthetic bacteria,such as purple and green sulfur bacteria,perform anoxygenic photosynthesis. They utilize inorganic electron donors like $H_2S$ or $H_2$ instead of water. These organisms contain bacteriochlorophyll as their primary photosynthetic pigment,but they lack chlorophyll $a$,which is the primary pigment found in oxygenic photosynthetic organisms like cyanobacteria,algae,and higher plants.

(A) Bacteria are prokaryotic organisms,meaning they lack membrane-bound organelles such as chloroplasts or complex thylakoid systems found in eukaryotes.
In photosynthetic bacteria,the photosynthetic pigments are located in the invaginations of the plasma membrane,which are often referred to as chromatophores or lamellae.
Since the options provided do not explicitly list plasma membrane or chromatophores,the most appropriate answer in the context of prokaryotic cellular organization is that these pigments are associated with the cell membrane or distributed within the cytoplasm/membrane-associated structures.
However,among the given choices,the question is often framed to test the understanding that they are not in chloroplasts. Given the options,if we consider the membrane-bound nature of these pigments,they are associated with the plasma membrane,which is often functionally analogous to the thylakoid membrane in these organisms.

(B) The absorption spectrum of chlorophyll $a$ and $b$ shows two major peaks.
One peak is in the blue region $(430-450 \ nm)$ and the other is in the red region $(640-680 \ nm)$.
Among these,the absorption of light is maximum in the blue region of the spectrum,which leads to a higher rate of photosynthesis compared to other wavelengths.

(B) Chlorophyll $a$ is the primary photosynthetic pigment.
According to the absorption spectrum of chlorophyll $a$,it shows two major absorption peaks.
The first peak is in the blue-violet region (approximately $430-450 \ nm$) and the second peak is in the red region (approximately $640-680 \ nm$).
Among the given options,both blue and red are absorption peaks,but the absorption in the blue region is generally higher than in the red region.
However,in many standard biology contexts,blue light is considered the primary peak for maximum absorption.

(C) The $fret$ membranes,also known as $stroma$ $lamellae$,are the tubular membrane structures that connect the $grana$ (stacks of $thylakoids$) within the chloroplast.
These structures facilitate the connection between different $grana$ stacks,allowing for the transport of materials and maintaining the structural integrity of the internal chloroplast system.

(A) Chlorophyll $a$ is the primary photosynthetic pigment present in all oxygenic photoautotrophs.
Oxygenic photosynthesis is performed by plants,algae,and cyanobacteria.
Non-oxygenic photosynthetic bacteria (such as green and purple sulfur bacteria) use bacteriochlorophyll instead of chlorophyll $a$.
Therefore,chlorophyll $a$ is found in all oxygen-releasing photosynthetic organisms.

(C) Chlorophyll $a$ is the primary photosynthetic pigment found in plants,algae,and cyanobacteria.
Its molecular structure consists of a porphyrin ring with a central magnesium $(Mg)$ atom and a long phytol tail.
The empirical formula for chlorophyll $a$ is $C_{55}H_{72}O_5N_4Mg$.

(B) Chlorophyll $a$ is a pigment molecule consisting of a porphyrin ring with a central magnesium atom.
In the structure of chlorophyll $a$,the pyrrole ring $II$ contains a methyl group $(-CH_3)$ attached to its carbon atom $3$.
In contrast,chlorophyll $b$ has an aldehyde group $(-CHO)$ at the same position.

(D) In the light-harvesting complex of photosynthesis,accessory pigments absorb light energy of different wavelengths and transfer it to the reaction center (Chlorophyll $a$).
Energy transfer generally occurs from pigments with higher energy (shorter wavelengths) to pigments with lower energy (longer wavelengths).
The sequence of energy transfer is: Accessory pigments (like Phycobilins and Carotenoids) $\to$ Chlorophyll $b$ $\to$ Chlorophyll $a$ (Reaction Center).
Among the given options,the most accurate pathway for accessory pigment energy transfer towards the reaction center is represented by the flow from accessory pigments to the primary pigment.

(B) Bacteriochlorophyll is the primary photosynthetic pigment found in purple sulfur and non-sulfur bacteria.
It differs from chlorophyll $a$ structurally because one of its pyrrole rings is reduced,meaning it contains two additional hydrogen atoms compared to chlorophyll $a$.
This structural modification allows bacteriochlorophyll to absorb light in the infra-red region,typically between $850-950 \, nm$.

(B) Fluorescence is the physical process in which a substance absorbs light or other electromagnetic radiation at a specific wavelength and emits it at a longer wavelength.
During this process,the absorbed energy excites electrons to a higher energy state,and as they return to the ground state,the excess energy is released as light waves (photons) of lower energy.
Therefore,the process in which excess energy is lost by light waves is known as Fluorescence.

(C) The chlorophyll molecule consists of a porphyrin ring,which is a tetrapyrrole structure.
At the center of this porphyrin ring,a single atom of $Magnesium$ $(Mg^{2+})$ is coordinated.
This $Mg$ atom is held in place by the nitrogen atoms of the four pyrrole rings,which is essential for the light-harvesting function of chlorophyll.

(B) The chlorophyll molecule consists of a porphyrin ring with a central magnesium $(Mg)$ atom.
This magnesium atom is coordinated with four nitrogen atoms of the pyrrole rings.
It plays a crucial role in the structure and function of chlorophyll,which is essential for photosynthesis.

(B) Chlorophyll is a magnesium-porphyrin complex.
In the structure of the chlorophyll molecule,a single $Mg^{2+}$ ion is coordinated at the center of the porphyrin ring system.
This magnesium ion is held by four nitrogen atoms from the four pyrrole rings of the porphyrin structure.

(A) The chlorophyll molecule consists of a tetrapyrrole porphyrin ring head,which measures approximately $15 \times 15 \, \mathring A$,and a long hydrocarbon tail known as phytol,which measures approximately $25 \, \mathring A$.
The tail is attached to the ring structure and helps anchor the chlorophyll molecule in the thylakoid membrane.

(A) In a typical green leaf,the photosynthetic pigments are present in specific proportions.
Chlorophyll $a$ and chlorophyll $b$ are the primary pigments,while carotenoids (which include xanthophylls and carotenes) act as accessory pigments.
The molar ratio of total chlorophyll to xanthophyll is generally observed to be $4:1$ in many plant species.
This ratio is essential for the efficient absorption of light energy and the protection of the photosynthetic apparatus from photo-oxidation.

(A) quantasome is a physical unit of photosynthesis found in the thylakoid membranes of chloroplasts. It was proposed by Park and Biggins in $1964$. Each quantasome contains approximately $230$ to $400$ pigment molecules,which include chlorophyll $a$,chlorophyll $b$,and carotenoids,organized into light-harvesting complexes to capture solar energy.

(B) Leaves contain pigments like chlorophyll $a$ and chlorophyll $b$,which are primarily responsible for photosynthesis. These pigments absorb light most efficiently in the blue and red regions of the visible spectrum. They reflect green light,which is why leaves appear green to the human eye.

(A) Photosynthetic units are known as quantasomes. These are clusters of chlorophyll and other pigment molecules located in the thylakoid membranes of chloroplasts,which are responsible for capturing light energy during photosynthesis. Oxysomes are associated with mitochondria,and $F_1$ particles are part of the $ATP$ synthase complex.

(A) Chlorophyll '$a$' is the primary photosynthetic pigment found in all oxygenic photosynthetic organisms. This includes higher plants,algae,and cyanobacteria. Since all these organisms release $O_2$ as a byproduct of photosynthesis,the correct answer is all $O_2$ releasing photosynthetic organisms.

(A) Chlorophyll '$a$' is the primary photosynthetic pigment.
According to the absorption spectrum of chlorophyll '$a$',it shows two major peaks of absorption.
The first peak is in the blue region (approximately $430-450 \ nm$) and the second peak is in the red region (approximately $640-680 \ nm$).
Among the options provided,while both blue and red are absorbed,the peak in the blue region is generally higher in intensity compared to the red region.
Therefore,blue light shows the maximum absorption capacity.

(C) Pigments like chlorophyll,carotene,and xanthophyll are fat-soluble (lipophilic) and are found in the thylakoid membranes of chloroplasts.
Anthocyanins are water-soluble vacuolar pigments that belong to the flavonoid group.
They are responsible for the red,purple,or blue colors in many fruits,flowers,and leaves.

(A) In the chloroplast,chlorophyll pigments are embedded within the thylakoid membranes.
These thylakoid membranes are stacked to form structures known as $Grana$.
Therefore,the primary location of chlorophyll is the $Grana$ of the chloroplast,where the light-dependent reactions of photosynthesis occur.

(C) The chlorophyll molecule is a complex organic compound. Its structure consists of a central porphyrin ring (also known as the head) and a long hydrocarbon tail (phytol tail). The porphyrin ring is a tetrapyrrole structure with a central magnesium $(Mg^{2+})$ atom. Therefore,the general structure of every chlorophyll molecule is based on the porphyrin system.

(D) Chloroplasts contain photosynthetic pigments such as Chlorophyll $a$,Chlorophyll $b$,Carotenoids (which include Carotenes and Xanthophylls).
Anthocyanins are water-soluble vacuolar pigments that appear red,purple,or blue depending on the $pH$. They are typically found in the cell vacuole,not in the chloroplasts.
Therefore,Anthocyanin is the pigment not found in the chloroplast.

(D) Chloroplasts are the sites of photosynthesis in plants.
Inside the chloroplast,there is a system of flattened,sac-like structures called $Thylakoids$.
The membranes of the $Thylakoids$ contain the light-harvesting pigments,including $Chlorophyll$ $a$ and $Chlorophyll$ $b$.
These pigments are essential for capturing light energy during the light-dependent reactions of photosynthesis.
Therefore,the correct location for chlorophyll is the $Thylakoids$.

(A) Chlorophyll $a$ is known as the universal photosynthetic pigment because it is present in all oxygen-evolving photosynthetic organisms,including plants,algae,and cyanobacteria.
It acts as the primary pigment that directly participates in the light reactions of photosynthesis by converting light energy into chemical energy.
Other pigments like chlorophyll $b$,xanthophylls,and carotenoids are called accessory pigments because they absorb light and transfer the energy to chlorophyll $a$.

(A) Chlorophyll is a porphyrin derivative with a central metal ion. The molecular structure of chlorophyll consists of a porphyrin ring with a central $Mg^{2+}$ ion. When chlorophyll is burned or incinerated,the organic components (carbon,hydrogen,oxygen,nitrogen) are oxidized and released as gases,leaving behind the inorganic mineral residue,which is magnesium $(Mg)$.

(B) Chlorophyll is a green pigment found in the chloroplasts of plants,algae,and cyanobacteria.
The molecular structure of chlorophyll consists of a porphyrin ring with a central magnesium $(Mg^{2+})$ ion coordinated to four nitrogen atoms.
Therefore,the correct element present in the center of the chlorophyll molecule is magnesium $(Mg)$.

(D) Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. This process primarily takes place in the chloroplasts,which contain the green pigment chlorophyll. Therefore,photosynthesis can only occur in cells that contain chlorophyll.

(C) Chlorophyll '$a$' and chlorophyll '$b$' are the primary photosynthetic pigments.
Chlorophyll '$a$' has the molecular formula $C_{55}H_{72}O_5N_4Mg$ and contains a methyl group $(-CH_3)$ at the third carbon position of the porphyrin ring.
Chlorophyll '$b$' has the molecular formula $C_{55}H_{70}O_6N_4Mg$ and contains an aldehyde group $(-CHO)$ at the same position.
Therefore,the presence of a $-CH_3$ group in chlorophyll '$a$' and a $-CHO$ group in chlorophyll '$b$' is the key structural difference.