The chapter 'Anatomy of Flowering Plants' deals with higher plants' functional organization and internal structure. In simple words, the analysis of the internal structure of plants is referred to as Anatomy. Here, it is explained that plants are composed of cells as their primary unit, which is further organized into tissues that are arranged into various parts of the plant.
The monocots and dicots inside an angiosperm are said to be anatomically different. Even the internal structures of a plant easily adapt to diverse environments. Other topics introduced in this chapter are the Tissues, The Tissue System, Secondary Growth, Anatomy of Monocotyledonous and Dicotyledonous Plants, and a few more. A gist of all the above topics is given below.
In biological terms, a detailed study of a living entity's internal structure is called anatomy. And, in this chapter, the internal structure of the flowering plant will be studied. To study the anatomy of plants, the study of histology is a prerequisite. The study of the tissue structure and the organization structure is called histology. From this chapter, the students are enriched with knowledge about different types of tissues plants have.
Plant tissues are broadly classified into permanent and meristematic tissues. Transportation of minerals & water, offering mechanical support, photosynthesis, assimilation of food materials, and proper storage are essential operations of plants carried out by the tissues. Each part of the flowering plant's anatomical characteristics has been thoroughly explained in this chapter that includes the seeds, various parts of a dicot and monocot seeds, how they are different from each other, and their different zones, and more.
Q1. State the location and function of different types of meristems.
Meristem refers to the simple tissue composed of a group of similar and immature cells that can divide and form new cells. On the basis of position, there can be three types of meristem including apical meristem, intercalary meristem, and lateral meristem. The location and function of these meristems are as follows:
Q2. Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
-Cork cambium or phellogen is the secondary meristem that develops in the region of the cortex to replace the outer epidermal cells that will provide protection to the stem and root from infections.
- Cork cambium is composed of thin-walled rectangular cells and it cuts off cells on both sides.
- The outer cells differentiate to form cork or phellem while the inner cells differentiate into secondary cortex or phelloderm. Together, the phellogen, phellem, and phelloderm constitute the periderm.
-The cork is impervious to water but allows gaseous exchange through the lenticels.
Hence, cork cambium forms tissues that form the cork.
Q3. Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?
-The increase in girth of a plant’s body is called secondary growth.
-The tissues involved in secondary growth are vascular cambium and cork cambium.
-In a young stem, vascular cambium is found in the form of patches as a single layer between the xylem and phloem.
-During the later stage, it forms a complete ring. Soon, the cambial ring becomes active and begins to cut off new cells towards the inner and the outer sides.
-The cells which are cut off towards the pith mature into secondary xylem while those which are cut off towards the periphery after maturation develops into secondary phloem.
-The cambium is most of the time more active on the inner side than on the outer.
-This is the reason, the amount of secondary xylem produced is more than secondary phloem.
-The primary and secondary phloems get gradually crushed due to the continued formation and accumulation of secondary xylem.
-Then at some places, the cambium forms a narrow band of parenchyma, which passes through the secondary xylem and the secondary phloem in the radial directions.
-These are the secondary medullary rays.
The secondary growth in plants increases the girtth of plants, increases the amount of water and nutrients to support the growing number of leaves, and also provides support to plants.
Q4. Draw illustrations to bring out the anatomical difference between
(i)Monocot root and (ii)Dicot root
Q5. 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? Give reasons.
An unknown sample can be identified to be either dicot stem or monocot stem based on the following characteristics-
Characteristics of a dicot stem-
1.The vascular bundles are conjoint, collateral, and open, with a strip of cambium between the xylem and phloem.
2.The vascular bundles are arranged to form a ring, around the centrally-located pith.
3.The ground tissue is differentiated into the collenchyma, parenchyma, endodermis, pericycle, and pith.
4.In between the vascular bundles, medullary rays are present.
Characteristics of monocot stem-
1.The hypodermis is made up of sclerenchyma.
2.The vascular bundles are conjoint, closed, and scattered.
3.Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.
4.Phloem parenchyma is absent.
5.Water-containing cavities are present within the vascular bundles.
Q6. The transverse section of a plant material shows the following anatomical features -
a) the vascular bundles are conjoint, scattered, and surrounded by a sclerenchymatous bundle sheath.What will you identify it as?
-The vascular bundles are conjoint, scattered, and surrounded by a sclerenchymatous bundle sheath in monocot stem.
b) phloem parenchyma is absent.What will you identify it as?
-Phloem parenchyma is absent in the monocot stem.
Q7. Why are xylem and phloem called complex tissues?
-Complex tissues are tissues made up of more than one type of cell. Since xylem and phloem are consists of different kinds of elements, they are called complex tissues.
-Xylem is consists of vessels, tracheid, xylem fiber, and xylem parenchyma.
-Tracheids- These are elongated, thick-walled dead cells having pointed ends. These lack protoplasm.
-Vessels- These are long, tubular, and cylindrical structures that are formed from the vessel members, with each having lignified walls and large central cavities. Vessels being dead lack protoplasm.
-Xylem fibers consist of thick walls with an almost insignificant lumen. These provide mechanical support to the plant.
-Xylem parenchyma is made up of thin-walled parenchymatous cells that help in the storage of food materials and in the radial conduction of water.
-Phloem is made up of a sieve tube, companion cells, phloem parenchyma, and phloem fibers.
-Sieve tube- The sieve tube elements are tube-like elongated structures associated with companion cells. The end walls of sieve tube elements are perforated to form the sieve plate. Sieve tube elements are living cells containing cytoplasm and nucleus.
-Companion cells- These cells are parenchymatous in nature and they help in maintaining the pressure gradient in the sieve tube elements.
-Phloem parenchyma- These cells help in the storage of food and they are made up of long tapering cells, with dense cytoplasm.
-Phloem fibers- These are made up of elongated sclerenchymatous cells with thickened walls.
Q8. What is the stomatal apparatus? Explain the structure of stomata with a labeled diagram.
-Stomata are tiny pores or holes found to be present in the epidermis of leaves. The major function of these stomata is to regulate the process of transpiration and gaseous exchange.
-The stomatal pore remains surrounded by specialized cells called guard cells which in turn are surrounded by subsidiary cells.
-The stomatal pore, guard cells, and the surrounding subsidiary cells together constitute the stomatal apparatus.
-The gaseous exchange is maintained by guard cells. In dicots, guard cells are bean-shaped while in monocots, guard cells are dumbbell-shaped.
Q9. Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
The three basic tissue systems in flowering plants include the epidermal tissue system, ground tissue system, and vascular tissue system.
1.Epidermal tissue system- It forms the outermost covering of the whole plant body. It consists of tissues like the epidermis, stomata, epidermal appendages (trichomes and hairs), etc.
2.Ground tissue system- All the tissue between the epidermis and vascular bundle forms the ground tissues. It consists of simple permanent tissues like parenchyma, sclerenchyma, collenchyma, mesophyll, etc. It includes pericycle, cortex, pith, and medullary rays
3.Vascular tissue system- The vascular tissue system consists of complex tissues, xylem, and phloem that together form vascular bundles.
Q10. How is the study of plant anatomy useful to us?
The study of plant anatomy is useful to us in the following ways -
-The study of anatomy helps to know the structures of plants that can be of commercial value. For example, jute, flax, etc.
-Study of anatomy can help in knowing the age of trees.
-By knowing the anatomical details, we can identify the unknown plant samples.
-Anatomy may also help in understanding the structural adaptations of plants with respect to diverse environmental conditions.
Q12. Describe the internal structure of a dorsiventral leaf with the help of labeled diagrams.
The internal structure of a dorsiventral leaf-
-The leaf lamina of a dorsiventral leaf has three parts: epidermis, mesophyll, and vascular system.
(a)Epidermis- The epidermis is two-layered. The upper epidermis is called the adaxial epidermis and the lower one is called the abaxial epidermis. More number stomata are present on the abaxial epidermis.
(b)Mesophyll- Inner to epidermis, mesophyll tissue is present. There are two types of cells in the mesophyll i.e. palisade parenchyma and spongy parenchyma. The palisade parenchyma is placed adaxially while the spongy parenchyma is situated below the palisade parenchyma and extends to the lower epidermis. There are numerous large spaces and air cavities between the cells of spongy parenchyma.
(c)Vascular system- The vascular bundles are surrounded by a layer of thick-walled bundle sheath cells. They are conjoint and closed.
Q13. What is periderm? How does periderm formation take place in the dicot stems?
-The periderm refers to the collective term used to signify phellogen, phellem, and phelloderm in a plant stem.
-Periderm formation in plants mainly occurs to replace the existing epidermis.
Formation of periderm:-
-The formation of periderm occurs during secondary growth.
-During this process, to replace the broken outer epidermal layer and the cortical layer, the cells of the cortex turn meristematic.
-As a result of this, cork cambium or phellogen is formed.
-The phellogen is composed of thin-walled, narrow, and rectangular cells.
-Later on, the phellogen cuts off cells on either side.
-The cells of the outer side give rise to the phellem or cork which due to the deposition of suberin in its cell wall is impervious to water.
-Similarly, the inner side forms the secondary cortex or phelloderm which is mainly parenchymatous in nature.
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