Internal structure of monocot leaf - class-XI

• The leaves of monocots have a large bubble-shaped epidermal cell called bulliform cells.
• They are also known as motor cells.
• They are present in the adaxial surface of the leaves.
• They play an important role in the unfolding of the developing leaves and in the rolling and unrolling of mature leaves in response to the alternating wet and dry conditions.
• So, the correct answer is 'Motor cells'.

Monocot leaves are called isobilateral leaves since both the sides of monocot leaves are more or less similar. Isobilateral leaves orient themselves parallel to the main axis and parallel to the direction of sunlight. Epidermis is single layered, present on both surfaces and has cuticles (cuticularized) and stomata on both surfaces (amphistomatic). It  is composed of compactly arranged oval or barrel shaped thin walled parenchymatous cells. Mesophyll is the ground tissue that is present between the two epidermal layers. Vascular bundles are of two types- small bundles are abundant and larger bundles are found in between them.

The upper surface of the leaf is known as the adaxial surface. The type of cells presents in the adaxial epidermis of grasses is bulliform cells (only one type). These are large bubble-shaped cells present in the adaxial or upper surface of the leaves in monocots. So, the correct answer is '1'.

Generally, the patterns of the leaf veins, or vascular bundles are pinnate and the veins are free; that is, they all diverge and never coalesce, either along their sides or at the ends. So, the incorrect statement is all vascular bundles have different size in leaf showing parallel venation.

In dorsiventral leaf, epidermis is in two layers, one on each surface of the leaf. Both the layers are composed of compactly arranged, barrel-shaped cells. Intercellular spaces are absent. A cuticle surrounds both the layers. Multicellular hairs called as trichomes are present on both the layers. Stomata occur only in the lower epidermis. This condition is described as hypostomatic. 

Bulliform cells or motor cells are large, bubble shaped epidermal cells that occur in groups on the upper surface of the leaves of many grasses. Loss of turgor pressure in these cells causes leaves to roll up during water stress. During drought, the loss of moisture through vacuoles induces bulliform cells to cause the leaves of many grass species to close as the two edges of the grass blade fold up toward each other. Once, adequate water is available, these cells enlarge and the leaves open again. Bulliform cells are absent in dicot leaves. 
Thus, the correct answer is option B.

Leaves, in which both sides appear in equally green color are called isobilateral leaves. It is due to the presence of spongy parenchyma.

So, the correct option is ‘both the surface are equally green’.

Many grass leaves, folds during drought conditions and unfolds during moisturized conditions. It is due to the presence of large, thin-walled cells present on the adaxial side of the upper epidermis, called Bulliform cells.

So, the correct option is ‘Bulliform cells’.

The ligule is a part of the leaf that is found at the junction of the leaf blade and sheath of the leaf. It may take several forms. But commonly, it is a translucent membrane or a fringe of hairs. It is seen in plants belonging to the family Poaceae. Hence, ligule occurs on the leaf of Barley, Oat and Rice.

Grasses have monocot leaves. Leaves of grasses have specialized bulliform cells on the upper epidermis. These bulliform cells are capable of folding and unfolding of leaves to help in the process of transpiration. 

A ligule is a thin outgrowth which is found at the junction of sheathing leaf base (leaf base is broad and surrounds the stem as an envelope) and leaf blade. It is commonly a form of a translucent membrane or a fringe of hairs. The ligule appears to be a continuation of the leaf sheath and encircles the stem as done by the leaf sheath.

Leaf having stomata equally distributed on both surfaces is called amphistomatic (isobilateral) leaf, e.g., most monocot leaves.

The large sized, thin-walled, water containing colourless epidermal cells present on the adaxial epidermis of an isobilateral leaf or monocot leaf are called bulliform cells.

So, the correct option is ‘Isobilateral leaf’.

The large sized, thin-walled, vacuolated, water containing colourless epidermal cells present on the adaxial epidermis of an isobilateral leaf or monocot leaf are called Bulliform cells. They differ from other cells in being size, structure and function.

So, the correct option is ‘large, thin-walled, vacuolated containing water’

In the monocot leaf, mesophyll is undifferentiated, shows spongy parenchyma with oval-shaped cells.

So, the correct option is ‘Mesophyll not differentiated into palisade and spongy tissues'.

A.Isobilateral leaves – Mesophyll is undifferentiated, contains spongy parenchyma only.

B.Dorsiventral mesophytic leaves – Mesophyll is differentiated into upper palisade parenchyma and lower spongy parenchyma.

C.Dorsiventral xerophytic leaves – Mesophyll is differentiated into upper and lower palisade parenchyma and middle spongy parenchyma.

D.Vertical leaves - Mesophyll is differentiated into upper and lower palisade parenchyma and middle spongy parenchyma.

So,
the correct option is ‘isobilateral leaves’.

In isobilateral leaves or monocot leaves, stomata are present on both upper or adaxial epidermis as well as lower epidermis or abaxial epidermis.

So,
the correct option is ‘Both upper and lower surfaces’.

Dicot leaf differs from monocot leaf anatomically in terms of presence of more number of stomata in the lower epidermis, presence of differentiated mesophyll,  and vascular bundle.

Leaf, in which both surfaces are similar in appearance are called isobilateral leaves. These are found in monocotyledons. It is due to the presence of spongy parenchyma.

So, the correct option is ‘Similarly two green surfaces’.    

• Leaves have a layer of waxy cuticle on their surface as it helps in preventing water loss due to excess transpiration. The leaves may also have hair on the lower surface which act as trichomes and protect the surface of the leaves.
• The epidermis of the leaves has minute pores called stomata through which gaseous exchange takes place.
• Endodermis and Casparian strips are present in the roots of the plants.

Bulliform cells or the motor cells are the modified epidermal cells present on the upper surface or the adaxial surface of the monocot leaf (the grasses). They are colourless, large-sized and vacuolated cells. They regulate the rolling of leaves to prevent the loss of water. When water is adequately present, they become turgid and keep the leaf open and exposed. When there is scarcity of water, the become flaccid and roll-up the leaf to prevent the loss of water.