Internal structure of leaf Questions in English

(N/A) $\Rightarrow$ In a maize leaf,a group of $5$ to $7$ large,thin-walled cells without chloroplasts and cuticle are located at certain intervals in the upper epidermis.
$\Rightarrow$ When atmospheric moisture decreases and dryness increases,these cells lose water and become flaccid. As a result,the leaf lamina curls inward. This reduction in the exposed surface area of the leaf helps in preventing excessive transpiration.
$\Rightarrow$ In a humid atmosphere,these cells absorb water and regain their turgidity,causing the leaf to unroll and become exposed again. Due to this water-absorbing property,they are also known as water-absorbent cells.
$\Rightarrow$ Because these cells facilitate the rolling and unrolling movements of the leaf,they are also referred to as motor cells or mechanical cells.

(N/A) $(i)$ In a dicot leaf,the mesophyll tissue is differentiated into palisade parenchyma and spongy parenchyma,which are located towards the upper and lower epidermis,respectively. Due to this differentiation,it is called a dorsiventral leaf.
$(ii)$ The phellogen (cork cambium),phellem (cork),and phelloderm (secondary cortex) are collectively known as the periderm.

(N/A) The leaf of peepal $(Ficus \text{ } religiosa)$ is a dicot leaf, while the leaf of maize $(Zea \text{ } mays)$ is a monocot leaf. The key differences are as follows:
$1$. Stomata: In dicot leaves (peepal), stomata are generally present more on the abaxial surface. In monocot leaves (maize), stomata are present on both the adaxial and abaxial surfaces.
$2$. Mesophyll: In dicot leaves, the mesophyll is differentiated into palisade parenchyma and spongy parenchyma. In monocot leaves, the mesophyll is not differentiated and consists of similar cells.
$3$. Bulliform cells: These are absent in dicot leaves but are present in the adaxial epidermis of monocot leaves (maize) to help in leaf rolling during water stress.
$4$. Vascular bundles: Dicot leaves show reticulate venation, resulting in vascular bundles of different sizes. Monocot leaves show parallel venation, resulting in vascular bundles of similar sizes.

(A) In grasses (monocots),certain adaxial epidermal cells along the veins modify themselves into large,empty,colourless cells. These are known as $Bulliform$ cells. When these cells absorb water and become turgid,they make the leaf surface exposed. When they become flaccid due to water stress,they make the leaves curl inwards to minimize water loss.

(B) Bulliform cells,also known as motor cells,are large,bubble-shaped epidermal cells found in groups on the upper surface of leaves in many monocotyledonous plants,such as wheat,maize,and grasses.
These cells are characterized by their large vacuoles and thin walls.
When water availability is low,these cells lose turgor pressure,causing the leaves to roll inwards to minimize water loss through transpiration.

(B) In grasses,certain adaxial epidermal cells along the veins modify themselves into large,empty,colourless cells. These are called bulliform cells.
When the bulliform cells in the leaves have absorbed water and are turgid,the leaf surface is exposed.
When they are flaccid due to water stress,they make the leaves curl inwards to minimise water loss.

(A) The photosynthetic cells in leaves are located in the mesophyll tissue.
These cells are specialized for photosynthesis and are parenchymatous in nature,containing numerous chloroplasts.

(D) Bulliform cells are specialized large,empty,colorless epidermal cells found in the upper epidermis of leaves of many monocotyledonous plants.
These cells are responsible for the rolling and unrolling of leaves to minimize water loss during dry conditions.
Among the given options,wheat $(II)$ and grass $(IV)$ are monocots,which possess bulliform cells.
Sunflower and pea plants are dicots and do not possess bulliform cells.

(A) The vertical section of a dorsoventral (dicot) leaf through the lamina reveals three primary components: the epidermis,the mesophyll,and the vascular system.
$1$. The epidermis covers both surfaces of the leaf.
$2$. The upper surface is known as the adaxial epidermis.
$3$. The lower surface is known as the abaxial epidermis.
$4$. Therefore,$A$ is mesophyll,$B$ is adaxial epidermis,and $C$ is abaxial epidermis.

(C) dorsiventral leaf (typically a dicot leaf) has an epidermis that covers both the adaxial (upper) and abaxial (lower) surfaces. This epidermis is covered by a waxy layer called the cuticle to prevent water loss. In dorsiventral leaves,stomata are more abundant on the abaxial surface compared to the adaxial surface,and in many cases,the adaxial surface may completely lack stomata. Therefore,statements $(a)$ and $(d)$ are correct.

(A) In a dicot leaf,the mesophyll is differentiated into palisade and spongy parenchyma.
$1$. Palisade parenchyma is present on the adaxial (upper) surface,consists of vertically and parallelly arranged cells,and contains a large number of chloroplasts.
$2$. Spongy parenchyma is present on the abaxial (lower) surface and is characterized by the presence of numerous large spaces and air cavities between its cells to facilitate gas exchange.
Therefore,the correct option is $A$.

(B) In a dorsiventral leaf,the vascular bundles are found within the veins. The size of the vascular bundle is directly proportional to the size of the vein it supports. Larger veins contain larger vascular bundles to facilitate the transport of water,minerals,and food throughout the leaf lamina,while smaller veins contain smaller vascular bundles.

(D) An isobilateral leaf is typically found in monocotyledonous plants. In these leaves,the mesophyll is not differentiated into palisade and spongy parenchyma. Since the leaf is exposed to similar light conditions on both sides,the stomata are present on both the adaxial (upper) and abaxial (lower) surfaces of the epidermis to facilitate efficient gas exchange.

(D) Bulliform cells are large,empty,colorless epidermal cells present in the leaves of many grasses.
When there is sufficient water,these cells are turgid,making the leaf surface flat and exposed.
During water stress,these cells lose water and become flaccid.
This loss of turgidity causes the leaves to curl inwards to minimize the exposed surface area,thereby reducing transpiration and water loss.

(B) In dicot leaves,the vascular bundles are scattered within the mesophyll tissue. They are described as conjoint (xylem and phloem present together in the same bundle),collateral (phloem lies towards the outer side and xylem towards the inner side),and closed (cambium is absent,as secondary growth does not occur in leaves).

(C) Generally,stomata are responsible for water loss through transpiration. However,plants that grow in xeric (dry) habitats have sunken stomata located in the lower epidermis of their leaves to minimize water loss. An example of such a plant is $Nerium$.

(D) In many monocotyledonous leaves,the adaxial (upper) epidermis contains specialized large,thin-walled,and empty cells known as $Bulliform$ cells.
These cells are responsible for the rolling and unrolling of the leaf.
When the water content is high,these cells become turgid,causing the leaf to open.
Conversely,under dry conditions,these cells lose water and become flaccid,which causes the leaf to curl inward to minimize the surface area exposed to the atmosphere,thereby reducing water loss through transpiration.

(B) The inner wall of the guard cell (facing the stomatal aperture) is thick and inelastic,while the outer wall (away from the aperture) is thin and elastic. This structural difference is crucial for the opening and closing of stomata. Therefore,the statement that the inner wall is thin and elastic is incorrect.

(B) The correct answer is Bulliform cells.
Bulliform cells are large,bubble-shaped epidermal cells present in the upper epidermis of leaves in many grasses.
When water is available,these cells are turgid and keep the leaf blade expanded.
During water stress,these cells lose water and become flaccid (lose turgidity).
This loss of turgidity causes the leaves to curl inwards,which reduces the surface area exposed to the atmosphere,thereby minimizing water loss through transpiration.

(C) In a dorsiventral leaf (typically a dicot leaf),the leaf is differentiated into two surfaces:
$1$. The upper surface is known as the adaxial surface,and its epidermis is called the adaxial epidermis.
$2$. The lower surface is known as the abaxial surface,and its epidermis is called the abaxial epidermis.
Therefore,$P$ corresponds to the adaxial epidermis and $Q$ corresponds to the abaxial epidermis.

(A) In $isobilateral$ leaves,which are typically found in monocotyledonous plants (like grasses),the stomata are present in equal numbers on both the $abaxial$ (lower) and $adaxial$ (upper) surfaces. In contrast,$dorsiventral$ leaves,which are characteristic of dicotyledonous plants,have more stomata on the $abaxial$ surface compared to the $adaxial$ surface. Therefore,the correct answer is $A$.

(D) In a dorsiventral leaf (typical of dicots),the vascular bundles are found in the veins.
In these bundles,the xylem is located towards the adaxial (upper) surface of the leaf.
The phloem is located towards the abaxial (lower) surface of the leaf.
Therefore,the correct arrangement is xylem towards the adaxial epidermis and phloem towards the abaxial epidermis.

(A) In the provided image,structure $P$ represents a Dicot leaf (Dorsiventral leaf),which is characterized by the presence of distinct palisade parenchyma (columnar cells) and spongy parenchyma.
Structure $Q$ represents a Monocot leaf (Isobilateral leaf),which is characterized by the absence of differentiation into palisade and spongy parenchyma,and the presence of bulliform cells.
Therefore,$P$ is a Dicot leaf and $Q$ is a Monocot leaf.

(C) Bulliform cells,also known as motor cells,are large,bubble-shaped epidermal cells found in groups on the adaxial surface of leaves in many monocots,particularly grasses (isobilateral leaves).
These cells are responsible for the rolling and unrolling of leaves in response to water stress to minimize transpiration.
Therefore,they are located in the adaxial epidermis of isobilateral leaves.

(C) In the anatomy of a flowering plant leaf,the vascular bundles are primarily found within the veins.
These veins are the continuation of the vascular system of the stem and are embedded within the mesophyll tissue.
They provide structural support and facilitate the transport of water,minerals,and photosynthetic products.
Therefore,the correct location for vascular bundles in a leaf is the veins.

(B) Mesophyll cells are specialized plant cells found in the leaves.
These cells are primarily responsible for photosynthesis.
According to the $NCERT$ textbook,mesophyll cells are typically round and oval in shape to facilitate efficient gas exchange and light absorption.

(A) In a $Dorsiventral$ leaf (typically found in dicotyledonous plants),the two surfaces are differentiated into the adaxial (upper) and abaxial (lower) surfaces.
Stomata are generally more abundant on the abaxial surface to reduce water loss through transpiration.
In contrast,an $Isobilateral$ leaf (typically found in monocotyledonous plants) has an equal distribution of stomata on both surfaces.

(B) In the provided cross-section of a leaf:
$P$ points to the larger,thick-walled vessels located in the vascular bundle,which represent the Xylem.
$Q$ points to the smaller,thin-walled cells located in the vascular bundle,which represent the Phloem.
$R$ points to the specialized cells surrounding the stomatal pore,which are the Guard cells.
Therefore,the correct identification is $P$: Xylem,$Q$: Phloem,$R$: Guard cell.

(D) In grasses,certain adaxial epidermal cells along the veins modify themselves into large,empty,colourless cells. These are called bulliform cells.
When the bulliform cells in the leaves have absorbed water and are turgid,the leaf surface is exposed.
When they are flaccid due to water stress,they make the leaves curl inwards to minimise water loss.

(D) In grasses,certain adaxial epidermal cells along the veins modify themselves into large,empty,colourless cells. These are called $Bulliform$ cells. When these cells in the leaves have absorbed water and are turgid,the leaf surface is exposed. When they become flaccid due to water stress,they make the leaves curl inwards to minimize water loss. Therefore,the correct option is $D$.

(D) In grasses,certain adaxial epidermal cells along the veins modify themselves into large,empty,colourless cells. These are called $Bulliform$ cells.
When these cells in the leaves have absorbed water and are turgid,they make the leaf surface exposed.
When they become flaccid due to water stress,they make the leaves curl inwards to minimize water loss.
Therefore,the correct option is $D$.

(A) In dorsiventral leaves (typical of dicots),the vascular bundles are present in the veins and the midrib.
The size of the vascular bundles is dependent on the size of the veins.
Since the veins in a leaf vary in thickness (the midrib is the thickest,followed by primary,secondary,and tertiary veins),the vascular bundles associated with them also vary in size.
Therefore,the vascular bundles are dissimilar in size because of the variation in vein thickness.
Thus,both Assertion and Reason are true,and the Reason is the correct explanation of the Assertion.

(B) Guard cells are specialized cells that surround the stomata and regulate the opening and closing of the stomatal pore.
In dicotyledonous plants,guard cells are typically bean-shaped or kidney-shaped.
In monocotyledonous plants,such as grasses (e.g.,wheat,maize,rice),the guard cells are dumb-bell shaped.
Among the given options,Wheat is a monocotyledonous plant,while Mango,Gram,and Potato are dicotyledonous plants.
Therefore,Wheat contains dumb-bell shaped guard cells.

(B) Bulliform cells are large,bubble-shaped epidermal cells present in the leaves of many grasses.
When water is abundant,they become turgid,causing the leaf to expand.
During water stress,they lose turgidity,causing the leaf to roll inward to minimize the surface area exposed to the atmosphere,thereby reducing transpiration and water loss.