Plant Tissues - Olympiad Level MCQ, Class 9 Science - Class 9 MCQ

Answer:
Prosenchyma is a type of plant tissue found in higher plants. It is characterized by its elongated and tapering shape, with pointed ends. Prosenchyma cells have thick cell walls, which provide mechanical strength and support to the plant.
Here are some key points about prosenchyma:
- Location: Prosenchyma is present in various parts of the plant, such as stems, roots, and leaves.
- Function: Prosenchyma provides mechanical support and strength to the plant. It helps in maintaining the shape and structure of the plant organs.
- Cell Structure: Prosenchyma cells have thick and lignified cell walls, which provide rigidity and support. The thickening of cell walls is due to the deposition of secondary cell wall materials like lignin.
- Shape: Prosenchyma cells are long and tapering, with pointed ends. This shape allows them to provide support to the plant tissues.
- Examples: Prosenchyma cells are found in the vascular tissues of plants, such as xylem and phloem.
In conclusion, prosenchyma is a type of plant tissue that provides mechanical support and strength to the plant. It has elongated and tapering cells with thick cell walls.

Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. Tracheids, unlike vessel elements, do not have perforation plates.

The growth of plant occur in specefic region plant cell in an merisnatic tissue .In merismatic tissue are found in tips of stem , roots and base of nodes help in increasing the length and height of the plant.

Explanation:
To determine which one is not a plant fibre among the given options A, B, C, and D, we need to understand the nature and sources of these fibres.
Coir:
- Coir is a natural fibre extracted from the husk of coconuts.
- It is a plant fibre that is commonly used for making ropes, mats, and other products.
- Coir is derived from the outer shell or husk of coconut.
Flax:
- Flax is a natural fibre derived from the stem of the flax plant (Linum usitatissimum).
- It is one of the oldest known fibres and is used to make linen fabric.
- Flax fibres are long, strong, and have good moisture-wicking properties.
Hemp:
- Hemp is a natural fibre derived from the stem of the Cannabis sativa plant.
- It is a versatile plant fibre that can be used to make various products such as clothing, rope, and paper.
- Hemp fibres are known for their strength and durability.
Silk:
- Silk is not a plant fibre; it is produced by silkworms to build cocoons.
- Silkworms secrete a protein called fibroin, which is used to create silk threads.
- Silk is known for its lustrous appearance and smooth texture.
Therefore, among the given options, silk (option D) is not a plant fibre. It is a protein-based fibre produced by silkworms.

Root has a sub apical region which is divided into three zones:- zone of cell division, zone of elongation and zone of cell maturation. This region carry out the growth of root.

Cork cells are:
- Dead: Cork cells are dead at maturity. They have no cytoplasm or other living components, making them highly specialized for their function.
- Protective: Cork cells form the outermost layer of bark in woody plants, providing a protective barrier against physical damage, water loss, and pathogens.
- Cell wall: Cork cells have a thick secondary cell wall composed of suberin, a waxy substance that makes them impermeable to gases and liquids.
- Non-photosynthetic: Cork cells do not contain chloroplasts and are not involved in photosynthesis.
- Elongated: Cork cells are elongated in shape, with tapering ends, allowing them to interlock and form a tight seal.
- Low metabolic activity: Due to their dead nature, cork cells have low metabolic activity and do not participate in cellular processes like growth or movement.
- Insulating: The suberin in cork cells provides thermal and acoustic insulation, making cork a popular material for various applications, including insulation, flooring, and wine bottle stoppers.
- Meristematic role: While cork cells themselves are not meristematic, the cork cambium, a meristematic tissue, produces cork cells as part of its secondary growth process in woody plants.

Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed in order to analyze atmospheric conditions during different periods in history.

Answer:
The youngest layer of secondary phloem in a woody dicot stem is located just outside the vascular cambium. Here is a detailed explanation:
1. Introduction:
- The secondary phloem is a tissue that is produced by the vascular cambium in woody dicot stems.
- It is responsible for transporting sugars and other organic compounds from the leaves to other parts of the plant.
2. Vascular cambium:
- The vascular cambium is a meristematic tissue that is located between the primary xylem and primary phloem in the stem.
- It is responsible for the production of secondary xylem (wood) towards the inside and secondary phloem towards the outside.
3. Formation of secondary phloem:
- As the vascular cambium produces new cells, the outermost layer of the secondary phloem is the youngest layer.
- This layer is just outside the vascular cambium, adjacent to the inner side of the primary phloem.
4. Function of secondary phloem:
- The secondary phloem is responsible for conducting sugars and other organic compounds from the leaves to other parts of the plant.
- It also provides mechanical support to the stem.
Conclusion:
- In a woody dicot stem, the youngest layer of secondary phloem is located just outside the vascular cambium, adjacent to the inner side of the primary phloem.

Mesophyll tissue differentiation in plants:
The mesophyll tissue is a specialized tissue found in the leaves of plants. It is responsible for photosynthesis, gas exchange, and storage of nutrients. In some plants, the mesophyll tissue is well differentiated into spongy tissue and palisade tissue. Let's explore where this differentiation occurs.
A: Dicot leaves:
- Dicot leaves are leaves of flowering plants belonging to the class Dicotyledonae.
- The mesophyll tissue in dicot leaves is well differentiated into spongy tissue and palisade tissue.
- The palisade tissue is located in the upper layer of the mesophyll, just below the upper epidermis.
- It consists of elongated cells arranged tightly together, perpendicular to the leaf surface.
- The palisade tissue contains a high concentration of chloroplasts, making it the primary site of photosynthesis in dicot leaves.
- The spongy tissue is located below the palisade tissue, towards the lower epidermis.
- It consists of loosely arranged cells with air spaces between them, allowing for gas exchange.
- The spongy tissue also contains chloroplasts and contributes to the overall photosynthetic activity of the leaf.
B: Xerophytic stem:
- Xerophytic plants are adapted to arid or desert environments, where water availability is limited.
- Xerophytic stems may have adaptations such as reduced or absent leaves, thickened cuticles, and sunken stomata.
- However, the differentiation of mesophyll tissue into spongy and palisade tissue is not typically observed in xerophytic stems.
C: Hydrophytic stem:
- Hydrophytic plants are adapted to aquatic or water-rich environments.
- Hydrophytic stems may have adaptations such as aerenchyma tissue, which allows for buoyancy and efficient gas exchange.
- Similar to xerophytic stems, the differentiation of mesophyll tissue into spongy and palisade tissue is not typically observed in hydrophytic stems.
D: Monocot leaves:
- Monocot leaves are leaves of flowering plants belonging to the class Monocotyledonae.
- Unlike dicot leaves, monocot leaves do not show a well-defined differentiation of mesophyll tissue into spongy and palisade tissue.
- The mesophyll tissue in monocot leaves is usually more uniform, without distinct layers.
Conclusion:
Mesophyll tissue differentiation into spongy tissue and palisade tissue occurs in dicot leaves, but not in xerophytic stems, hydrophytic stems, or monocot leaves. This differentiation allows for efficient photosynthesis and gas exchange in dicot leaves, which are adapted to various environmental conditions.

The bark is composed of the periderm, the cortex, and the phloem. The periderm is the outermost layer and in turn is made up of the cork (also called phellem), the cork cambium (also called phellogen), and the phelloderm.

Cuticle are protective, hydrophobic waxy covering produced by epidermal cells of leaves, young shoots and other aerial parts. It minimises the water loss through transpiration (with the help of stomata) and also reduces pathogen entry. Lignin hardens the cell wall and provides flexibilty, tensile and compressional strength to the cell wall. Suberin is present in cork cells and makes the cell impervious to water.

Xylem vessels are very long tube-like structures formed by a row of cells placed end to end. The transverse wails between these cells are partially or completely dissolved to form continous water channels. 

Intercalary meristems are present in stems at the base of nodes and leaf blades. Cells of such meristems can divide and form new cells. 

Sugarcane is a monocot plant, which possesses intercalary meristem at the nodes. 

Hence, if the tip of the sugarcane is removed then it can still grow using the intercalary meristem present at nodes.