GSEB Class 11 Biology Solutions Chapter 6 Anatomy of Flowering Plants

Question 1. State the location and function of different types of meristems.
Answer: Plant growth is largely limited to specific areas of active cell division known as Meristems. Without meristems, normal plant development is not possible. Plants have various kinds of meristems. The meristems found at the tips of roots and shoots, which produce primary tissues, are called apical meristems. Root apical meristem is located at the very end of a root, while shoot apical meristem is found in the farthest region of the stem axis. During leaf formation and stem lengthening, some "left behind" cells of the shoot apical meristem develop into the axillary bud. Buds are present in the axils of leaves and have the capacity to form a branch or a flower. The initial apical meristems occur during the embryo's formation. The meristem that exists between mature tissues is known as intercalary meristem. These appear in grasses and help repair parts removed by grazing herbivores. Both apical meristems and intercalary meristem are also known as primary meristem because they appear early in a plant's life and contribute to the formation of the primary plant body. The meristem that appears in the mature parts of shoots and roots of many plants, especially those that produce a woody axis, and develops later than the primary meristem, is called the lateral meristem. Generally, these are cylindrical meristems. Examples of lateral meristems include fascicular vascular cambium, interfascicular cambium, and cork-cambium.
In simple words: Meristems are special growth areas in plants where cells divide actively. They are found at root and shoot tips (apical meristems) and between mature tissues (intercalary meristems), helping plants grow longer and replace lost parts. Lateral meristems cause plants to grow wider.

Exam Tip: Remember to clearly state both the location and the specific role (function) of each meristem type for a complete answer.

Question 2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Answer: Yes, I agree with this statement. As the stem continues to get wider because of the vascular cambium's activity, the outer cortical and epidermis layers break and need replacement to offer new protective cell layers. For this reason, another meristematic tissue, called cork cambium or phellogen, develops, typically in the cortex region. Phellogen is a few layers thick. It consists of narrow, thin-walled, and almost rectangular cells. The outer cells become cork, while inner cells change into the cortex. This clearly shows how cork cambium produces tissues that form the cork.
In simple words: Yes, cork cambium makes cork. When a stem grows thicker, its outer layers break, so the cork cambium steps in to create new, protective cork tissue.

Exam Tip: When explaining processes like cork formation, it's vital to describe the sequence of events and the tissues involved. Mentioning phellogen and its cell types is key.

Question 3. Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?
Answer: Roots and stems grow in length with the help of apical meristem, which is called primary growth. Besides this, most dicotyledonous plants show an increase in width. This increase is called secondary growth. It does not happen in monocot roots and stems. The tissues involved in secondary growth are the two lateral meristems: vascular cambium and cork cambium. The following describes secondary growth in a dicotyledonous stem: Vascular cambium: This meristematic layer, responsible for producing vascular tissues-xylem and phloem-is called vascular cambium. In a young stem, it exists in patches as a single layer between the xylem and phloem. Later, it forms a complete ring. Formation of cambial ring: In dicot stems, the cambium cells present between the primary xylem and primary phloem are called intrafascicular cambium. The cells of the medullary rays, next to this intrafascicular cambium, become meristematic and form the interfascicular cambium. This creates a continuous ring of cambium. The cambial ring becomes active and starts to produce new cells, both towards the inside and the outside. The cells produced towards the pith mature into secondary xylem, and the cells produced towards the periphery mature into secondary phloem. The cambium is generally more active on the inner side than the outer. As a result, much more secondary xylem is produced than secondary phloem, quickly forming a dense mass. The primary and secondary elements gradually get crushed due to the continuous formation and buildup of secondary xylem. However, the primary xylem stays mostly intact, in or near the center. In some places, the cambium forms a narrow band of parenchyma, which goes through the secondary xylem and secondary phloem in radial directions. These are the secondary medullary rays.
In simple words: Secondary growth makes woody plants wider. It uses vascular and cork cambiums. The vascular cambium forms a ring that makes new xylem (wood) and phloem, mostly adding wood to the inside. This process adds girth to the stem, helping the plant grow stronger and last longer.

Exam Tip: When explaining secondary growth, remember to differentiate between primary and secondary growth, identify the two types of cambium involved, and clearly describe the formation and activity of the cambial ring. Mentioning the terms 'intrafascicular' and 'interfascicular' cambium is important.

Question 4. Draw illustrations to bring out the anatomical difference between 1. Monocot root and Dicot root 2. Monocot stem and Dicot stem
Answer:Anatomical differences between Monocot root and Dicot root 1. Monocot root: * The cortex is quite wide. * Casparian bands are visible only in young roots. The endodermal cells later show more thickening. * Pericycle produces lateral roots only. * Xylem and phloem bundles are 8 or more in number. * Xylem elements are usually rounded or oval. * Conjunctive tissue may be parenchymatous or sclerenchymatous. * It does not produce cambium. * A well-developed pith is present in the center of the root. * It does not show secondary growth. 2. Dicot root: * Cortex is relatively narrow. * Endodermal cells are less thick, and Casparian bands are more noticeable. * Pericycle produces lateral roots, cork, cambium, and part of the vascular cambium. * The number of xylem and phloem bundles varies from 2-6 or sometimes 8. * Xylem elements (vessels and tracheids) are polygonal. * Conjunctive tissue is parenchymatous. * Conjunctive parenchyma forms from vascular cambium. * Pith is either missing or very small. * It shows secondary growth through the activity of vascular cambium and cork cambium.
In simple words: Monocot and dicot roots have different internal structures. Monocot roots have a wide cortex, many xylem bundles, and a large pith, but no secondary growth. Dicot roots have a narrower cortex, fewer xylem bundles, a small or absent pith, and can show secondary growth.

Exam Tip: When comparing monocot and dicot structures, focus on key distinguishing features like the number of vascular bundles, pith presence/size, cortex width, and the presence or absence of secondary growth. Use clear, concise points for each comparison.

Question 5. Cut a transverse section of the young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Given reasons.
Answer: The transverse section of a typical young dicotyledonous stem shows the following characteristics, which help to distinguish it from a monocot stem: (1) The epidermis, which is the outermost protective layer, is covered with a thin layer of cuticle and may have trichomes and a few stomata. (2) The cortex is made up of multiple layers of cells arranged between the epidermis and pericycle. It consists of three sub-zones: 1. The outer hypodermis includes a few layers of collenchymatous cells directly beneath the epidermis, which offers mechanical support to the young stem. 2. Cortical layers below the hypodermis are composed of rounded, thin-walled parenchymatous cells with clear intercellular spaces. 3. The innermost layer of the cortex is called the endodermis. The cells of the endodermis are rich in starch grains, and this layer is also known as the 'starch sheath'. (3) The pericycle is present on the inner side of the endodermis and above the phloem, in the form of crescent-shaped patches of sclerenchyma. (4) Between the vascular bundles, there are a few layers of radially arranged parenchymatous cells, which form medullary rays. A large number of vascular bundles are arranged in a ring. This 'ring' arrangement of vascular bundles is a key feature of the dicot stem. Each vascular bundle is conjoint, open, and includes protoxylem. A large number of rounded, parenchymatous cells with large intercellular spaces that fill the central part of the stem make up the pith.
In simple words: To tell if a young stem is monocot or dicot, observe its cross-section. Dicot stems have vascular bundles arranged in a ring, an outer protective epidermis with a cuticle, distinct cortex layers (including hypodermis and endodermis), and a clear pith in the center. Monocot stems have scattered vascular bundles.

Exam Tip: When identifying monocot versus dicot stems, the most important characteristic to look for under a microscope is the arrangement of vascular bundles (scattered in monocot, ring in dicot). Also, check for the presence of pith and clearly defined cortex layers.

Question 6. The transverse section of plant material shows the following anatomical features 1. The vascular bundles are conjoint, scattered, and surrounded by a sclerenchymatous bundle sheath, 2. Phloem parenchyma is absent. What will you identify it as?
Answer: It is clear from the above transverse section of the plant material that the plant has a monocot stem. This is because vascular bundles are scattered in monocot stems, and phloem parenchyma is absent in them.
In simple words: Based on the description, where vascular bundles are scattered and phloem parenchyma is missing, the plant material is identified as a monocot stem.

Exam Tip: Key features for identifying a monocot stem include scattered vascular bundles and the absence of phloem parenchyma. Dicot stems, in contrast, have vascular bundles arranged in a ring and typically include phloem parenchyma.

Question 7. Why are xylem and phloem called complex tissues?
Answer: Permanent tissues that consist of many different types of cells are called complex tissues. Xylem and phloem are termed complex tissues because they are made up of more than one kind of cell, and these cells work together as a single unit. Xylem functions as a conducting tissue for water and minerals from the roots to the stem and leaves. It also offers mechanical strength to the plant parts. Xylem is composed of four different types of elements: tracheids, vessels, xylem fibers, and xylem parenchyma. Gymnosperms do not have vessels in their xylem. Tracheids are elongated or tube-like cells with thick and lignified walls and tapering ends. In flowering plants, tracheids and vessels are the main water-transporting elements. Xylem fibers have highly thickened walls and small central lumens. Xylem parenchyma cells store food materials such as starch, fat, and other substances like tannins. The radial movement of water happens through the ray parenchymatous cells. Phloem moves food materials, usually from leaves to other parts of the plant. Phloem in angiosperms is composed of sieve tube elements, companion cells, phloem parenchyma, and phloem fibers. Gymnosperms possess albuminous cells and sieve cells but lack sieve tubes and companion cells. The activities of sieve tubes are managed by the nucleus of companion cells. The companion cells are specialized parenchymatous cells, and they help maintain the pressure gradient in the sieve tubes.
In simple words: Xylem and phloem are called complex tissues because they have several different cell types that all work together to perform a specific function. Xylem moves water and minerals, while phloem transports food.

Exam Tip: To answer why xylem and phloem are complex, mention that they are made of multiple cell types that work cohesively. List the main components of each (e.g., tracheids, vessels for xylem; sieve tubes, companion cells for phloem) and their primary functions.

Question 8. What is the stomatal apparatus? Explain the structure of stomata with a labeled diagram.
Answer: The stomatal aperture, guard cells, and the surrounding subsidiary cells are together called the stomatal apparatus. Stomata are tiny openings found in the epidermis of leaves. Stomata control the process of transpiration (water loss) and gaseous exchange (CO2 and O2). Each stoma consists of two bean-shaped cells known as guard cells. In grasses, these guard cells are dumbbell-shaped. The outer walls of guard cells are thin, while the inner walls are highly thickened. Guard cells contain chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells near the guard cells become specialized in their shape and size and are known as subsidiary cells.
In simple words: The stomatal apparatus includes the stomatal opening, guard cells, and nearby subsidiary cells. Stomata are tiny pores on leaves that manage water loss and gas exchange. Each stoma has two guard cells that open and close it, often with special surrounding cells.

Exam Tip: When describing the stomatal apparatus, ensure you name all three components: the stomatal aperture, guard cells, and subsidiary cells. Clearly explain the role of guard cells in regulating opening and closing and mention their unique structure.

Question 9. Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Answer: Based on their structure and location, there are three types of tissue systems: * Epidermal Tissue system: Epidermis, stomata * Ground or Fundamental Tissue system: Parenchyma, sclerenchyma, and collenchyma. * Vascular or conducting Tissue system: Phloem and Xylem.
In simple words: Flowering plants have three main tissue systems: Epidermal (outer covering like epidermis and stomata), Ground (bulk tissues like parenchyma and collenchyma), and Vascular (transport tissues like phloem and xylem).

Exam Tip: For this question, naming the three main tissue systems and then listing 2-3 key tissues under each is sufficient for full marks.

Question 10. How is the study of plant anatomy useful to us?
Answer: The study of the internal structure of plants is called anatomy. Plant cells are the basic unit, and cells are organized into tissues, which in turn are organized into organs. Different organs in a plant show variations in their internal structure. Within angiosperms, monocots and dicots are also known to be anatomically different. Internal structures also show adaptations to various environments. We can easily observe the structural similarities and differences in the external morphology of plants and find several common features as well as distinctions.
In simple words: Studying plant anatomy helps us understand how plants are built inside, from cells to organs. It reveals differences between plant types like monocots and dicots, and how plants adapt to their surroundings, which is useful for agriculture and understanding plant life.

Exam Tip: Highlight how plant anatomy helps in understanding classification, adaptation to environment, and the basic organization from cells to organs. This shows a broader understanding of its utility.

Question 11. What is periderm? How does periderm formation take place in the dicot stems?
Answer: As the stem continues to increase in width due to the activity of vascular cambium, the outer cortical and epidermis layers get broken and need to be replaced to offer new protective cell layers. Consequently, sooner or later, another meristematic tissue called cork cambium or phellogen develops, typically in the cortex region. Phellogen consists of a few layers of narrow, thin-walled, and almost rectangular cells. Phellogen cuts off cells on both sides. The outer cells change into cork or phellem, while the inner cells change into secondary cortex or phelloderm. The cork is impermeable to water due to suberin being deposited in the cell wall. The cells of the secondary cortex are parenchymatous. Phellogen, phellem, and phelloderm are collectively known as periderm. Because of the cork cambium's activity, pressure builds up on the remaining layers outside the phellogen, and eventually, these layers die and peel off.
In simple words: Periderm is a protective outer layer that forms in dicot stems when they grow thicker. It's made by the cork cambium, which produces cork cells on the outside and secondary cortex cells on the inside, replacing old, broken layers.

Exam Tip: Define periderm as the collective term for phellogen, phellem, and phelloderm. Clearly explain the role of cork cambium (phellogen) in producing the phellem (cork) and phelloderm (secondary cortex), emphasizing its protective function as the stem expands.

Question 12. Describe the internal structure of a dorsiventral leaf with the help of labeled diagrams.
Answer: Mesophyll, which has chloroplasts and performs photosynthesis, is made up of parenchyma. It consists of two types of cells: the palisade parenchyma and the spongy parenchyma. The palisade parenchyma, located on the adaxial side, is made of elongated cells arranged vertically and parallel to each other. The oval or round, loosely arranged spongy parenchyma is located below the palisade cells and extends to the lower epidermis. There are many large spaces and air cavities between these cells. The vascular system includes vascular bundles, which can be seen in the veins and the midrib. The size of the vascular bundles depends on the size of the veins. The veins vary in thickness in the reticulate venation of dicot leaves. Vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.
In simple words: A dorsiventral leaf has an internal structure with a mesophyll layer divided into two types of parenchyma: palisade (tightly packed, for photosynthesis) and spongy (loose, for gas exchange). Vascular bundles, which carry water and food, are found in the veins and are covered by thick-walled cells.

Exam Tip: When describing the internal structure of a dorsiventral leaf, focus on the distinct layers: epidermis, mesophyll (palisade and spongy), and vascular bundles. Emphasize the cell arrangements and their functions, particularly for photosynthesis and gas exchange.