RBSE Solutions Class 11 Biology Chapter 16 Normal Secondary Growth in Stem and Root

RBSE Class 11 Biology Chapter 16 Multiple Choice Objective Questions

Question 1. Interfascicular cambium is formed from
(a) Pith
(b) Medullary rays
(c) Xylem
(d) Phloem
Answer: (b) Medullary rays
In simple words: The interfascicular cambium, which is important for a plant's width growth, actually develops from the cells found in the medullary rays. These rays are like spokes connecting the center of the stem to the outer part.

🎯 Exam Tip: Remember that vascular cambium consists of both fascicular (within bundles) and interfascicular (between bundles) cambium, each originating differently.

Question 2. Cambium ring forms
(a) inside Phloem and outer Xylem
(b) outside phloem and inside Xylem
(c)
(d) outer xylem and inside parenchyma
Answer: (b) outside phloem and inside Xylem
In simple words: The cambium ring forms in a specific spot within the plant stem. It is located just outside the primary phloem and just inside the primary xylem. This position allows it to produce new xylem and phloem cells.

🎯 Exam Tip: Visualize the layers of a stem or root to correctly place the cambium ring, which is always situated between the primary phloem and primary xylem.

RBSE Class 11 Biology Chapter 16 Very Short Answer Questions

Question 1. Intrafascicular cambium is example of which kind of meristematic tissue?
Answer: Intrafascicular cambium is an example of primary meristematic tissue. It is derived from the procambium, which is part of the shoot apical meristem. This type of cambium is responsible for the initial growth in the width of a plant stem or root.
In simple words: Intrafascicular cambium is a primary growth tissue that comes from the plant's main growing tip and helps it get wider.

🎯 Exam Tip: Differentiate between primary meristems (like apical meristem and fascicular cambium) which cause length and initial girth, and secondary meristems (like cork cambium and interfascicular cambium) which cause increased girth later on.

Question 2. Which different kinds of cells are present in cambium? Name them.
Answer: The cambium is made up of two main kinds of cells: fusiform initials and ray initials. Fusiform initials are long cells that help form tissues like xylem and phloem that run along the length of the stem. Ray initials are shorter, more square-shaped cells that form tissues that spread sideways, like rays. These specialized cells are crucial for the secondary growth that increases the girth of a plant stem or root.
In simple words: Cambium contains two kinds of cells: fusiform initials, which make long tissues, and ray initials, which make sideways tissues.

🎯 Exam Tip: Knowing the two types of initials in the cambium helps understand how secondary xylem and phloem are produced in both longitudinal and radial directions.

Question 3. Cork is formed of which kind of cells?
Answer: Cork is formed from dead cork cells, which are produced by the cork cambium. These cells are packed tightly and often contain suberin, a waxy substance that makes them waterproof. The cork cells protect the plant from water loss and infections. This layer forms the outer protective bark of woody plants, helping them withstand environmental stresses.
In simple words: Cork is made of dead cork cells that are tight and waterproof, forming a protective layer on the outside of plants.

🎯 Exam Tip: Remember that cork cells are dead at maturity, providing a robust protective barrier rather than metabolic function.

Question 4. Cork cambium is differentiated at which place of stem?
Answer: The cork cambium, also called phellogen, forms in different parts of the stem. It develops from existing permanent tissues, which can be found in the epidermis, hypodermis, cortex, or even in the outer layers of the phloem. It is a secondary lateral meristem, meaning it helps the plant grow wider. This flexible formation allows plants to adapt and produce protective bark even if the outermost layers are damaged.
In simple words: Cork cambium can form in the stem's outer layers like the epidermis, cortex, or phloem, helping the plant grow wider.

🎯 Exam Tip: Understand that cork cambium develops from existing differentiated cells, making it a secondary meristem, crucial for the formation of bark.

Question 5. Where Complementary tissue are found?
Answer: Complementary tissues are found in lenticels. Lenticels usually form under old stomata, which are small pores on the plant surface. In these areas, the cork cambium becomes very active and produces many loosely arranged cells. These cells are known as complementary or filling cells. These loosely packed cells allow for gas exchange between the plant's internal tissues and the atmosphere, even after the epidermis has been replaced by bark.
In simple words: Complementary tissues are found in lenticels, which are special openings on the plant surface that allow air to pass through.

🎯 Exam Tip: Remember that complementary cells are key to the function of lenticels, providing air passages where bark would otherwise prevent gas exchange.

Question 6. Cambium is formed from which tissue in Dicot root?
Answer: In dicot roots, the cambium ring forms from a few different tissues. Part of it develops from the conjunctive parenchyma cells, which are found between the primary xylem and primary phloem. Another part of the cambium forms from the pericycle cells that are located opposite the protoxylem. These combined parts create a complete cambium ring. This unique arrangement allows the root to increase in girth, providing better anchorage and water absorption for older plants.
In simple words: In dicot roots, the cambium forms from parenchyma cells between xylem and phloem, and also from pericycle cells.

🎯 Exam Tip: Note the difference in cambium origin between stems and roots; in roots, the pericycle plays a significant role in forming the cambial ring.

Question 7. Write the names of different layers of periderm.
Answer: The periderm is made up of three main layers. These are the cork (phellem), the cork cambium (phellogen), and the secondary cortex (phelloderm). Together, these layers form a protective outer covering for the plant. The cork cells are very strong and lignified, helping to prevent water from leaving the stem. This multi-layered structure is essential for protecting the plant's delicate inner tissues from drying out and physical damage.
In simple words: The periderm has three layers: cork, cork cambium, and secondary cortex, all working as a protective cover.

🎯 Exam Tip: Clearly list and define each component of the periderm (phellem, phellogen, phelloderm) to score full marks.

Question 8. What are the functions of lenticels?
Answer: Lenticels are mainly responsible for aeration in plants. They act as small, raised, corky spots found on the stem's periderm. These spots allow gases to pass through easily, facilitating the exchange of oxygen and carbon dioxide between the internal tissues and the atmosphere. Without lenticels, the interior cells of woody stems would not be able to respire properly due to the impermeable bark layer.
In simple words: Lenticels help the plant breathe by allowing air to pass through the bark, acting like small windows for gas exchange.

🎯 Exam Tip: Emphasize gas exchange as the primary function of lenticels, especially in mature stems where epidermal stomata are no longer functional.

Question 9. How are the lateral roots originate?
Answer: Lateral roots start to grow from a special meristematic region within the pericycle, which is a layer of cells inside the main root. As this new growth develops, it pushes its way out through the endodermis and cortex layers until it breaks through the root's outer surface. In dicot plants, these lateral roots usually begin forming opposite the protoxylem poles, looking much like the main root itself. This internal origin protects the delicate growing tip as it emerges, unlike stems where branches form from external buds.
In simple words: Lateral roots grow from the pericycle inside the main root, pushing outwards until they break through the surface, with a structure similar to the main root.

🎯 Exam Tip: Highlight the pericycle as the origin of lateral roots, which is a key anatomical distinction in root branching.

Question 3. How does the environment affects the functionality of cambium?
Answer: Environmental factors greatly influence how the cambium functions. These factors include:

• Temperature: Temperature significantly affects cambium activity. When temperatures are relatively high, the cambium is very active, leading to more growth. However, when temperatures drop low, the cambium becomes dormant and stops growing. This sensitivity ensures efficient resource use by the plant.
• Photoperiod (Daylight Length): Changes in the length of daylight, known as photoperiod, affect the type of wood There are no questions or answers located on pages 15-18 of the provided PDF. The content on these pages consists of navigational links, metadata, and a diagram whose associated question is on a page outside the specified range. Therefore, the output is empty as per the instructions to process ONLY pages 15 to 18.