Plastids Questions in English

(D) Plastids are organelles found in plant cells and algae. They are classified into three types based on the type of pigments they contain: chloroplasts,chromoplasts,and leucoplasts.
All these plastids originate from proplastids and possess the ability to multiply by a fission-like process.
Chloroplasts contain chlorophyll and carotenoid pigments which are responsible for trapping light energy essential for photosynthesis.
Chromoplasts contain fat-soluble carotenoid pigments like carotene,xanthophylls,and others,which give plants their yellow,orange,or red color.
Leucoplasts are the colourless plastids of varied shapes and sizes with stored nutrients: amyloplasts store carbohydrates (starch),elaioplasts store oils and fats,and aleuroplasts store proteins.
Therefore,the common feature among all these plastids is their origin from proplastids and their ability to divide by fission.

(D) Many cells,such as animal cells,function properly and undergo mitotic division even in the absence of plastids. Plastids are organelles found primarily in plant cells and algae,responsible for photosynthesis and storage,but they are not essential for the basic cellular processes of metabolism or mitosis in all cell types.

(N/A) $\Rightarrow$ Plastids are found in all plant cells and in euglenoids.
$\Rightarrow$ These are easily observed under the microscope as they are large. They bear some specific pigments,thus imparting specific colours to the plants.
$\Rightarrow$ Based on the type of pigments,plastids can be classified into three types:
$(a)$ Chloroplasts,$(b)$ Chromoplasts,and $(c)$ Leucoplasts.
$(a)$ Chloroplasts: These contain chlorophyll and carotenoid pigments,which are responsible for trapping light energy essential for photosynthesis.
$(b)$ Chromoplasts: In these,fat-soluble carotenoid pigments like carotene,xanthophylls,and others are present. This gives the plant parts a yellow,orange,or red colour.
$(c)$ Leucoplasts: These are colourless plastids of varied shapes and sizes with stored nutrients:
$(i)$ Amyloplasts: Store carbohydrates (e.g.,potato).
$(ii)$ Elaioplasts: Store oils and fats.
$(iii)$ Aleuroplasts: Store proteins.

(N/A) $ \Rightarrow $ The majority of the chloroplasts of green plants are found in the mesophyll cells of the leaves.
$ \Rightarrow $ These are lens-shaped, oval, spherical, discoid, or even ribbon-like organelles.
$ \Rightarrow $ They have a variable length $(5-10 \mu m)$ and width $(2-4 \mu m)$.
$ \Rightarrow $ Their number varies from $1$ per cell in Chlamydomonas, a green alga, to $20-40$ per cell in the mesophyll.
$ \Rightarrow $ Chloroplasts are double-membrane bound. Of the two, the inner chloroplast membrane is relatively less permeable.
$ \Rightarrow $ The space limited by the inner membrane of the chloroplast is called the stroma. A number of organized flattened membranous sacs called thylakoids are present in the stroma.
$ \Rightarrow $ Thylakoids are arranged in stacks like piles of coins called grana (singular: granum) or the intergranal thylakoids.
$ \Rightarrow $ There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
$ \Rightarrow $ The membrane of the thylakoids encloses a space called a lumen.
$ \Rightarrow $ The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.
$ \Rightarrow $ It also contains small, double-stranded circular $DNA$ molecules and ribosomes.
$ \Rightarrow $ The ribosomes of the chloroplasts are smaller $(70S)$ than the cytoplasmic ribosomes $(80S)$.

(A) Leucoplasts are colorless plastids of varied shapes and sizes with stored nutrients.
$(i)$ $Amyloplasts$: Store carbohydrates (starch),e.g.,potato.
$(ii)$ $Elaioplasts$: Store oils and fats.
$(iii)$ $Aleuroplasts$: Store proteins.

(N/A) The chloroplast is a double-membrane-bound organelle. Its structure consists of the following components:
$1$. Membrane System: It consists of grana,stroma lamellae,and the fluid stroma. The membrane system is responsible for trapping light energy and for the synthesis of $ATP$ and $NADPH$.
$2$. Stroma: The stroma is the fluid-filled matrix where enzymatic reactions occur. These reactions incorporate $CO_{2}$ into the plant,leading to the synthesis of sugar,which is subsequently stored as starch.
$3$. Functional Division: There is a clear division of labour within the chloroplast.
- Light Reactions: The reactions occurring in the membrane system are directly light-driven and are called light reactions.
- Dark Reactions: The reactions occurring in the stroma are not directly light-driven but depend on the products of light reactions ($ATP$ and $NADPH$). By convention,these are called dark reactions,though this does not mean they occur in darkness or are independent of light.

(A) $\therefore$ Plastids are found in all plant cells and in euglenoids.
$\Rightarrow$ These are easily observed under the microscope as they are large.
$\Rightarrow$ They contain specific pigments,thus imparting specific colours to the plants.
$\Rightarrow$ Based on the type of pigments,plastids are classified into three types: $(a)$ Chloroplasts,$(b)$ Chromoplasts,and $(c)$ Leucoplasts.
$(a)$ Chloroplasts: These contain chlorophyll and carotenoid pigments,which are responsible for trapping light energy essential for photosynthesis.
$(b)$ Chromoplasts: These contain fat-soluble carotenoid pigments like carotene,xanthophylls,and others. This gives the plant parts a yellow,orange,or red colour.
$(c)$ Leucoplasts: These are colourless plastids of varied shapes and sizes that store nutrients.
$(i)$ Amyloplasts: Store carbohydrates,e.g.,potato.
$(ii)$ Elaioplasts: Store oils and fats.
$(iii)$ Aleuroplasts: Store proteins.

(N/A) Yes,plastids are interchangeable and can be converted from one form to another based on the physiological requirements of the plant cell.
$(i)$ In $Capsicum$ (chilli),the ovary is initially green (containing chloroplasts),but as the fruit ripens,the chloroplasts are converted into chromoplasts,giving the fruit its red color.
$(ii)$ In potato tubers,leucoplasts (colourless plastids) are present underground. When these tubers are exposed to sunlight,they develop chlorophyll and are converted into chloroplasts,turning the skin green.
$(iii)$ During the ripening of fruits like tomatoes,chloroplasts (green) are converted into chromoplasts (red/orange) due to the synthesis of carotenoids and the breakdown of chlorophyll.

(B) The red colour in tomatoes,carrots,and chillies is primarily due to the presence of the pigment $Lycopene$.
$Lycopene$ belongs to the group of pigments known as $Chromoplasts$.
$Chromoplasts$ are plastids that contain carotenoids and are responsible for the yellow,orange,or red colours in various plant parts.
$Lycopene$ is not a photosynthetic pigment because it does not participate in the light-dependent reactions of photosynthesis; it primarily serves as an accessory pigment or for coloration to attract pollinators/seed dispersers.
Photosynthetic pigments are primarily $Chlorophylls$ ($a$ and $b$) and certain accessory pigments like $Carotenoids$ (which include $Xanthophylls$ and $Carotenes$ that aid in light harvesting).

(N/A) The figure shows a chloroplast,which is a characteristic organelle of plant cells. It contains thylakoids arranged in grana,which are the sites of photosynthesis.
$(b)$ Yes,chloroplasts can be passed on to the progeny. During cell division,chloroplasts are distributed into daughter cells through the cytoplasm. Furthermore,because they contain their own circular $DNA$,they are capable of semi-autonomous replication.
$(c)$ $(A)$ represents the stroma,which is the site of the dark reaction (Calvin cycle or biosynthetic phase) of photosynthesis.
$(B)$ represents the chloroplast $DNA$ (cp$DNA$),which carries genetic information necessary for the synthesis of some chloroplast proteins and is responsible for the semi-autonomous nature of the organelle.

(D) The correct matching is as follows:
$(i)$ Elaioplast: These are leucoplasts specialized for the storage of fats or oils.
$(ii)$ Aleuroplast: These are leucoplasts specialized for the storage of proteins.
$(iii)$ Amyloplast: These are leucoplasts specialized for the storage of starch (carbohydrates).
$(iv)$ Chromoplast: These contain fat-soluble carotenoid pigments like carotene,xanthophylls,etc.,which provide yellow,orange,or red colors to plant parts.
Therefore,the correct sequence is $(i-b, ii-c, iii-a, iv-d)$.
The correct option is $(D)$.

(B) The bright colors of petals are primarily due to the presence of pigments like anthocyanins,which are water-soluble pigments found in the vacuoles of plant cells. While chromoplasts also contain pigments like carotenoids that provide yellow,orange,or red colors,anthocyanins are specifically responsible for many of the vibrant red,purple,and blue hues observed in flowers.

(B) In the given diagram of a chloroplast,the parts marked as $A, B, C,$ and $D$ are respectively Granum,Thylakoid,Stromal lamella,and Stroma.
$1$. $A$ represents the Granum,which is a stack of thylakoids.
$2$. $B$ represents the Thylakoid,which is a single flattened sac-like membrane.
$3$. $C$ represents the Stromal lamella,which connects the grana of different thylakoid stacks.
$4$. $D$ represents the Stroma,which is the fluid-filled space containing enzymes,$DNA$,and ribosomes.

(C) In the given diagram of a chloroplast,the structures are labelled as follows:
$A$ represents the Thylakoid,which is a flattened sac-like structure.
$B$ represents the Granum,which is a stack of thylakoids.
$C$ represents the Stroma lamella,which connects the grana of different thylakoids.
$D$ represents the Stroma,which is the fluid-filled space surrounding the thylakoids.
Therefore,the correct identification is $A -$ Thylakoid,$B -$ Granum,$C -$ Stroma lamella,$D -$ Stroma.

(D) Plastids are organelles found in the cells of plants and algae. They are responsible for manufacturing and storing food. Plastids are present in all plant cells and in euglenoids (e.g.,Euglena). They are absent in animal cells.

(A) Elaioplasts are a type of leucoplast that is specialized for the storage of lipids in plants.
Elaioplasts house oil body deposits as rounded plastoglobuli,which are essentially fat droplets.

(B) Elaioplasts are colourless plastids that store oils and fats (lipids).
Amyloplasts are plastids that store carbohydrates like starch.
Chromoplasts contain fat-soluble carotenoid pigments like carotene and xanthophylls,which give yellow,orange,or red colours to plant parts.
Chloroplasts contain chlorophyll and carotenoid pigments,which are responsible for trapping light energy for photosynthesis.
Therefore,the pair $Elaioplasts - Starch$ is wrongly matched because Elaioplasts store lipids,while Amyloplasts store starch.

(C) Centrioles serve as basal bodies for cilia and flagella and are involved in spindle formation during cell division.
Lysosomes are membrane-bound organelles containing hydrolytic enzymes,which are optimally active at an acidic $pH$ (near $pH$ $5$).
Thylakoids are flattened,sac-like membranous structures found within the stroma of chloroplasts. These thylakoids are stacked like coins to form structures called grana.
Ribosomes in the cytoplasm of eukaryotic cells are $80S$,while those in chloroplasts and mitochondria are $70S$.

(A) Aleuroplasts are specialized leucoplasts that store proteins.
Elaioplasts are plastids that store oils and fats.
Amyloplasts are plastids that store starch.
Chromoplasts contain pigments like carotene and xanthophylls,providing color to plant parts.

(D) Chromoplasts are coloured plastids that contain fat-soluble carotenoid pigments like carotene and xanthophylls.
These pigments provide yellow,orange,or red colours to various plant parts.
Aleuroplasts store proteins,elaioplasts store oils and fats,and amyloplasts store carbohydrates like starch.

(C) Plastids are classified based on the type of pigments they contain.
$1$. $Chromoplasts$ contain fat-soluble carotenoid pigments like carotene and xanthophylls, which provide yellow, orange, or red colours to plant parts like carrot roots and flowers.
$2$. $Aleuroplasts$ store proteins.
$3$. $Elaioplasts$ store oils and fats.
$4$. $Amyloplasts$ store carbohydrates like starch.
Therefore, the orange colour of carrot root is due to the presence of $Chromoplasts$.

(C) Thylakoids are flattened,sac-like membranous structures found within the stroma of chloroplasts.
They contain chlorophyll and other photosynthetic pigments,which are essential for the light-dependent reactions of photosynthesis.

(B) . False: The outer membrane of the chloroplast is permeable to small molecules and ions due to the presence of porins.
$B$. True: The inner membrane is selectively permeable and contains specific carrier proteins for transport.
$C$. True: Grana are stacks of thylakoids where the light-dependent reactions occur,producing assimilatory power ($ATP$ and $NADPH$).
$D$. False: $D$ represents the stroma lamellae (or fret channels),which connect grana. They contain $PSI$ and $ATP$ synthase,but the enzymes for the dark reaction (Calvin cycle) are located in the stroma $(E)$.
$E$. True: The stroma contains enzymes required for the synthesis of sugars (Calvin cycle) and proteins (due to the presence of chloroplast $DNA$ and ribosomes).

(C) Chromoplasts are indeed plastids that contain fat-soluble carotenoids and are responsible for the yellow,orange,or red colours in flowers and fruits. This makes the Assertion correct.
However,the Reason is incorrect because chlorophyll and carotenoid pigments are fat-soluble (lipophilic),not water-soluble. Therefore,the statement in the Reason is false.

(B) Chloroplasts are considered semi-autonomous organelles because they contain their own circular $DNA$ and $70S$ ribosomes,which allow them to synthesize some of their own proteins.
The ribosomes found in chloroplasts are $70S$ type,whereas the ribosomes found in the cytoplasm of eukaryotic cells are $80S$ type.
Since $70S$ ribosomes are smaller than $80S$ ribosomes,the Reason is correct.
However,the fact that chloroplast ribosomes are smaller is not the reason why the chloroplast is semi-autonomous; rather,the presence of its own genetic material $(DNA)$ and protein-synthesizing machinery makes it semi-autonomous.
Therefore,both statements are correct,but the Reason is not the correct explanation of the Assertion.

(C) Chloroplasts are the organelles responsible for photosynthesis. Since leaves are the primary photosynthetic organs of a plant,they contain the highest density of chloroplasts,particularly within the mesophyll cells.

(C) Inside the chloroplast,there is a system of flattened,sac-like structures called thylakoids.
These thylakoids are arranged in piles or stacks,which are known as grana (singular: granum).
Therefore,grana are defined as the stacks of thylakoids where the light-dependent reactions of photosynthesis occur.

(N/A) $\Rightarrow$ Thylakoids are arranged in stacks like piles of coins,which are called grana (singular: granum).
$\Rightarrow$ These stacks are interconnected by flat membranous tubules known as stroma lamellae.
$\Rightarrow$ The membrane of the thylakoids encloses a space called the lumen.
$\Rightarrow$ The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.
$\Rightarrow$ It also contains small,double-stranded circular $DNA$ molecules and ribosomes.
$\Rightarrow$ The ribosomes of the chloroplasts are smaller $(70S)$ than the cytoplasmic ribosomes $(80S)$.

(A) The given organelle is a chloroplast.
In the diagram,$P$ points to the fluid-filled space inside the chloroplast,which is known as the $Stroma$.
$Q$ points to the membrane channels that connect the thylakoids of different grana,which are known as the $Stroma$ $lamellae$ or $Intergrana$ $lamellae$.

(C) Plastids are found in all plant cells and in euglenoids. Based on the type of pigments,plastids are classified into three types:
$1$. Chloroplasts: Contain chlorophyll and carotenoid pigments which are responsible for trapping light energy essential for photosynthesis.
$2$. Chromoplasts: Contain fat-soluble carotenoid pigments like carotene,xanthophylls,and others. This gives the part of the plant a yellow,orange,or red color.
$3$. Leucoplasts: These are colorless plastids of varied shapes and sizes with stored nutrients. Amyloplasts store carbohydrates (starch),elaioplasts store oils and fats,and aleuroplasts store proteins. Since they are colorless,they lack pigments.

(A) The color of flowers is primarily due to the presence of $Chromoplasts$.
$Chromoplasts$ contain fat-soluble carotenoid pigments like carotene,xanthophylls,and others,which provide yellow,orange,or red colors to various plant parts including flowers and fruits.
$Leucoplasts$ are colorless plastids that store nutrients.
$Chloroplasts$ contain chlorophyll and are responsible for photosynthesis.
$Mitochondria$ are the powerhouses of the cell and are not responsible for pigmentation.

(B) Plastids are organelles found in plant cells that store various nutrients.
They are classified based on the type of pigment or storage material they contain:
$1$. Amyloplasts $(P)$ are leucoplasts that store carbohydrates like starch $(II)$.
$2$. Elaioplasts $(Q)$ are leucoplasts that store oils and fats $(I)$.
$3$. Aleuroplasts $(R)$ are leucoplasts that store proteins $(III)$.
Therefore,the correct matching is $P-II, Q-I, R-III$.

(B) The $Mesophyll$ cells of leaves are specialized for photosynthesis and contain a large number of chloroplasts,typically ranging from $20$ to $100$ per cell.
$Chlamydomonas$ and $Euglena$ are unicellular organisms that contain only one or a few large chloroplasts.
$Epidermal$ cells generally lack chloroplasts as their primary function is protection.

(B) The stroma of the chloroplast contains enzymes required for the synthesis of carbohydrates and proteins. It also contains small,double-stranded circular $DNA$ molecules and ribosomes. However,the ribosomes present in the chloroplast stroma are $70S$ type,not $80S$. Therefore,the statement '$80S$ ribosomes' is incorrect regarding the stroma of the chloroplast.

(A) Chloroplasts are double-membrane-bound organelles found in plant cells and algae.
According to the $NCERT$ textbook,the size of chloroplasts varies significantly.
Their length typically ranges from $5$ to $10 \mu m$ and their width ranges from $2$ to $4 \mu m$.
Therefore,option $A$ is the correct description of the dimensions of a chloroplast.

(A) The $DNA$ present in chloroplast is circular and double-stranded. This is similar to the $DNA$ found in prokaryotes and mitochondria,which supports the endosymbiotic theory of the origin of these organelles.

(B) Statement $- I$ is incorrect because plastids are found only in plant cells and euglenoids,not in animal cells.
Statement $- II$ is incorrect because aleuroplasts store proteins,whereas amyloplasts store carbohydrates (starch).
Therefore,both statements are incorrect.

(C) The endomembrane system includes organelles whose functions are coordinated. These include the endoplasmic reticulum,Golgi complex,lysosomes,and vacuoles. Since the functions of the mitochondria and chloroplasts are not coordinated with the above components,they are not considered part of the endomembrane system. Therefore,the chloroplast is the correct answer.

$(D)$ Statement $(A)$ is correct: The number of chloroplasts varies significantly; for example, $Chlamydomonas$ has $1$ chloroplast per cell, while mesophyll cells contain $20-40$ chloroplasts per cell.
Statement $(B)$ is correct: Both chloroplasts and mitochondria are double-membrane organelles. In both, the inner membrane is less permeable than the outer membrane, which contains porins.
Statement $(C)$ is correct: Thylakoids are flattened sac-like structures arranged in stacks known as grana (singular: granum). These stacks are connected by stroma lamellae or intergranal thylakoids.
Statement $(D)$ is correct: The stroma is the fluid-filled space within the chloroplast that contains enzymes necessary for the Calvin cycle (carbohydrate synthesis) and also contains small circular $DNA$ and ribosomes for protein synthesis.
Therefore, all statements $(A, B, C, D)$ are correct.