Anatomy of Flowering Plants

The correct answer is Option B: Aleurone layer.

• The aleurone layer is a protein-rich tissue that surrounds the starchy endosperm in cereal seeds.

• It lies just beneath the seed coat and separates the endosperm from the embryo.

• In contrast:

– Integuments are the tissues surrounding the ovule.

– Coleoptile is the sheath covering the emerging shoot.

– Coleorhiza is the sheath covering the emerging root.

The statement that is NOT correct for a typical monocot stem is:

Option C: Hypodermis is parenchymatous.

Explanation:

• In monocot stems

– Vascular bundles are indeed conjoint (xylem + phloem together), closed (no cambium) and scattered throughout the ground tissue.

– Phloem parenchyma is absent.

– The hypodermis, however, is usually sclerenchymatous (providing mechanical support), not parenchymatous.

The correct answer is Option A: Sclereids. Here's why:

Sclereids are a type of sclerenchyma tissue, characterized by their thick, lignified cell walls. These rigid cells provide structural support and protection. They are commonly found in the hard, protective layers of nuts and the gritty texture of pear pulp. Let's break down why the other options are incorrect:

• Fibres are another type of sclerenchyma tissue, but they are long and slender, providing tensile strength. While they are present in some plant structures, they are not the primary component of nut shells or pear pulp.
• Parenchyma cells are thin-walled and loosely packed, making them suitable for storage and photosynthesis. They are found throughout plants but don't provide the same level of rigidity as sclereids.
• Collenchyma cells have thickened cell walls at the corners, offering flexibility and support to young, growing tissues. They are not typically found in mature fruit structures.

In summary, the presence of sclereids with their thick, lignified walls explains the hardness of nut shells and the gritty texture of pear pulp.

To evaluate the given statements about dicotyledonous leaves, let's break down each statement and understand its validity.

Statement I: In a dicotyledonous leaf, the adaxial epidermis generally bears more stomata than the abaxial epidermis.

This statement is generally false. In most dicotyledonous leaves, the abaxial (lower) epidermis typically has more stomata than the adaxial (upper) epidermis. This adaptation helps in efficient gas exchange while minimizing water loss as the lower surface is less exposed to direct sunlight.

Statement II: In a dicotyledonous leaf, the adaxially placed palisade parenchyma is made up of elongated cells, which are arranged vertically and parallel to each other.

This statement is true. The palisade parenchyma in dicotyledonous leaves is located on the adaxial (upper) side and consists of elongated cells aligned vertically and parallel to each other. This arrangement is crucial for maximizing light absorption for photosynthesis.

Based on the explanation above, the correct evaluation of the given statements is:

Option B: Statement I is false but Statement II is true.

Guard cells to stomata have thin outer wall and highly thickened inner walls.

Let's analyze each statement separately to determine the correct answer:

Statement I: Parenchyma is living but collenchyma is dead tissue.

This statement is incorrect. Parenchyma and collenchyma are both types of simple tissues found in plants. Parenchyma is indeed a living tissue comprised of cells that are often involved in metabolic processes, storage, and photosynthesis. Collenchyma, similarly, is also a living tissue. It is known for providing support and mechanical strength to growing parts of a plant such as leaves and stems, particularly in areas where growth is active. The cells of collenchyma are elongated and have thicker primary walls compared to parenchyma, but they are definitely living.

Statement II: Gymnosperms lack xylem vessels but the presence of xylem vessels is the characteristic of angiosperms.

This statement is true. Gymnosperms are a group of seed-producing plants that include conifers, cycads, Ginkgo, and Gnetales. One of the distinguishing features of gymnosperms is that their xylem consists of tracheids but lacks vessels. Tracheids are elongated cells in the xylem of vascular plants that facilitate the transport of water and mineral salts. On the other hand, angiosperms, or flowering plants, have a more advanced xylem that contains both tracheids and vessels. Vessels are more efficient at transporting water than tracheids, which is one of the evolutionary advantages of angiosperms over gymnosperms.

Therefore, considering the above explanations:

• Statement I is false as both parenchyma and collenchyma are living tissues.
• Statement II is true regarding the absence of xylem vessels in gymnosperms and their presence in angiosperms.

Based on the analysis, the correct answer is:

Option D: Statement I is false but Statement II is true

Option B : (B), (C) and (D) only

Explanation : Lateral meristems are the meristems that add to the width or girth in a process known as secondary growth. They are responsible for the secondary growth in plants and are found parallel to the sides of the plants.

1. 1. Axillary buds (A) are not lateral meristems; they are capable of forming branches or flowers.


2. 2. Fascicular vascular cambium (B) is a type of lateral meristem. It contributes to secondary growth and produces secondary vascular tissues.


3. 3. Interfascicular cambium (C) is also a type of lateral meristem. It also contributes to secondary growth in the stem.


4. 4. Cork cambium (D), also called phellogen, is a lateral meristem and it produces the cork, a part of the protective outer layer (periderm) in stems and roots.


5. 5. Intercalary meristem (E) is not a type of lateral meristem but rather a type of apical meristem located at the base of leaves or internodes on a plant stem, which is involved in primary growth and elongation of the plant.

Therefore, the correct answer is option B : Fascicular vascular cambium (B), Interfascicular cambium (C) and Cork cambium (D) only.

Late wood, formed in the latter part of the growing season, indeed has fewer xylary elements with narrower vessels. This is because the cambium, the layer of cells in plants that gives rise to secondary xylem (wood), is less active in colder temperatures, which are typically associated with the later parts of the growing season, such as autumn and winter.

So, both Assertion A and Reason R are true. Moreover, Reason R correctly explains why Assertion A is the case: the decreased activity of the cambium in colder temperatures results in the formation of late wood with fewer, narrower vessels.

Therefore, the correct answer is :

Option D : Both A and R are true and R is the correct explanation of A.

Statement I : Endarch and exarch are the terms often used for describing the position of secondary xylem in the plant body.

• This statement is incorrect. Endarch and exarch are used to describe the developmental sequence of primary xylem, not secondary xylem. In endarch condition, the first formed xylem is towards the centre (protoxylem) and the last formed xylem is towards the periphery (metaxylem), which is typical of stems. In the exarch condition, the first formed xylem is towards the periphery and the last formed xylem is towards the centre, which is typical of roots.

Statement II : Exarch condition is the most common feature of the root system.

• This statement is true. The exarch condition, where the first-formed xylem is towards the periphery and the last-formed xylem is towards the centre, is indeed the most common feature of the root system.

So, the correct answer is :

Option C : Statement I is incorrect but Statement II is true.

Initiation of lateral roots and vascular cambium during secondary growth takes place in pericycle cells of dicot roots. Epiblema, endodermis and cortex do not dedifferentiate.

The girdling experiment shows that phloem is the tissue responsible for translocation of food; and that transport takes place in one direction i.e. towards the root.

All the statements are correct regarding vascular bundles but none of the options with such combination is given.

In old trees, the greater part of secondary xylem is dark brown due to deposition of organic compounds like tannins, resins, oils, gums, aromatic substances and essential oils in the central or innermost layers of the stem. These substances make it hard, durable and resistant to the attacks of micro-organisms and insects.

The large cells around the vascular bundles of C₄ plants form bundle sheath. These cells have large number of chloroplasts to perform calvin cycle.

Spring wood is also called early wood. It is lighter in colour and has a lower density. The vessels are produced with the wider lumens to transport more water to meet the requirement by increased transpiring surface in spring season.

The spring and autumn wood appear as alternate concentric rings of light and dark colour forming annual rings.

In botanical terms, the cortex of a plant is the region found between the epidermis and the stele. Therefore, the correct answer is:

Option C: Epidermis and stele.

To clarify:

• Epidermis: This is the outermost layer of cells in the plant stem and root. It serves as a protective barrier against the external environment.




• Stele: This is the central part of the root or stem, containing the vascular tissue (xylem and phloem), pith, and often a pericycle. The stele is located inside the endodermis.

The cortex lies between these two layers, functioning mainly in storage and transport of nutrients and water. It is composed primarily of parenchyma cells and is a significant part of the root and stem where it often stores starch.

The other options refer to different parts of the plant anatomy:

• Option A: "Endodermis and pith" - The pith is located in the center of the stem, surrounded by the vascular tissue, which is inside the endodermis. The cortex is not between these two.




• Option B: "Endodermis and vascular bundle" - The endodermis is a single layer of cells forming a boundary between the cortex and the stele; it doesn't define the boundaries of the cortex.




• Option D: "Pericycle and endodermis" - The pericycle is a layer of cells found just inside the endodermis, and it is part of the stele. This option does not correctly describe the position of the cortex.

Thus, Option C is the most accurate in describing the location of the cortex in a plant.

Vascular bundles in monocotyledons (plants with a single seed leaf, like grasses and grains) are considered "closed" primarily due to Option D: Cambium is absent.

In botany, vascular bundles are the part of the plant that transport nutrients and water. In monocotyledons, these bundles are typically scattered throughout the stem and do not have a cambium layer. The cambium is a layer of actively dividing cells found in most dicotyledons (plants with two seed leaves) and is responsible for secondary growth, which includes the widening of the stems and roots. This secondary growth is possible because the cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem.

In monocotyledons, the absence of cambium means there's no secondary growth, and thus, the vascular bundles are termed "closed." This is different from "open" vascular bundles found in dicotyledons, where the presence of cambium allows for continuous growth and change in the arrangement of the xylem and phloem.

Options A, B, and C describe other aspects of vascular bundles but are not the reasons why monocotyledonous vascular bundles are considered closed. For instance:

• Option A: The presence or absence of vessels with perforations is more about the type of vessels in the xylem and not directly related to the concept of open or closed vascular bundles.


• Option B: While xylem surrounded by phloem is a characteristic of some vascular bundles, it doesn't define them as open or closed.


• Option C: A bundle sheath may be present in both monocotyledons and dicotyledons and is not a defining factor for open or closed vascular bundles.

Therefore, Option D, "Cambium is absent," is the correct reason for vascular bundles in monocotyledons being considered closed.