The VIDYANKER team has thoughtfully prepared the NCERT Solutions for Class 11 Biology Chapter 6, "Anatomy of Flowering Plants" These solutions are designed to help you tackle the NCERT textbook questions with ease. We recommend going through the chapter's theory before diving into the solutions for a deeper understanding. Feel free to share these NCERT Solutions for Class 11 Biology with others—learning is always better when shared!
NCERT TEXTBOOK QUESTIONS SOLVED
1.State the location and function of different types of meristems.
Ans. Meristems are specialized regions of plant growth. The meristems mark the regions where active cell division and rapid division of cells take place. Meristems are of three types depending on their location.
→ Apical meristem: These are located at the tips of the roots and shoots. Shoot apical meristem is at the shoot tip, and their active division causes elongation in the stem and production of leaves. Root apical meristem allows for root elongation.
→ Intercalary meristem: These take place between the mature tissues that exist at the bases of the leaves of grasses. It aids in the re-growth of grasses after they have been grazed by herbivores.
Both, apical meristems and intercalary meristems are primary meristems because they occur early in life of a plant and contribute to the formation of the primary plant body.
→ Lateral meristem: These appear in the mature regions of roots and shoots of most of the plants and it assists them to add secondary tissues in plant body and also in increasing girth of the plants. Hence, it is called as the secondary meristem since it develops in later age of the plant life.
2.Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Ans. Yes, I concur with this statement. Cork cambium cuts cells on both its outer as well as inner side. The cells cut off from the outer side form cork whereas those cut off from inner side form secondary cortex. While the cells of cork are dead, those of the secondary cortex are alive.
3.Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?
Ans. Secondary growth is the development of secondary tissues from lateral meristems. It occurs in dicots alone. It increases the diameter of the stem. Two types of lateral meristems form secondary tissues, namely, vascular cambium and cork cambium. Vascular cambium develops secondary vascular tissues whereas cork cambium forms periderm. The vascular bundles in dicot stem are conjoint, collateral, open and are arranged in a ring. The cambium present between xylem and phloem in vascular bundles is called fascicular or intrafascicular cambium. Besides this, some cells of medullary rays also become meristematic and this is called interfascicular cambium. Both these cambia collectively constitute complete ring of vascular cambium. This ring of vascular cambium divides periclinally to cut off cells both on inner side and outer side. The cells cuts off on outer side are secondary phloem and inner side are secondary xylem. The amount of secondary xylem cut off is more than secondary phloem, thus increase in girth or diameter takes place with the formation of secondary tissue. Secondary xylem as well as secondary phloem structurally similar to the primary xylem and primary phloem. With the increase in secondary tissue, the primary xylem and primary phloem get crushed. The ray initials of vascular cambium ring divide by tangential divisions and add new cells. These new cells produced on both the sides of ray initials remain meristematic for sometime and then differentiate into parenchymatous cells of rays. Secondary medullary rays are those rays which are produced by vascular cambium in between the secondary xylem and secondary phloem. They are usually one to few layers in thickness and one to several layers in height. Medullary rays form the radial systejn responsible for radial conduction of solutes. They maintain connection between pith and cortex There is a marked difference in activity of cambium with change in season. In spring, the activity of cambium is more and hence the wood elements are larger in size with wide lumen. The activity of cambium is less during autumn and the wood elements are smaller in size with narrow lumen. Spring wood and autumn wood of a year constitute annual ring.
In order to increase in girth and prevent harm on the rupturing of the outer ground tissues due to the formation of secondary vascular tissues, dicot stems produce a cork cambium or phellogen in the outer cortical cells. Phellogen cells divide on both the outer side as well as the inner side to form secondary tissues. The tissue developed on the inner side is known as secondary cortex while the tissue developed on the outer side is known as cork.
Importance of secondary growth is as follows:
(i) It increases the girth of the plant and therefore supports increase in weight due to growth of aerial parts.
(ii)It produces a corky bark around the tree trunk protecting the inside from abrasion, heat, cold and infection.
(iii)It brings in new vascular tissues to replace the old non-functioning one as well as to fulfill increasing demand for long distance transport of sap and organic nutrients.
4.Draw illustrations to bring out the anatomical difference between
(a) Monocot root and dicot root
(b) Monocot stem and dicot stem
Ans. (a) Monocot root and dicot root
5.Cut a transverse section of 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.
Ans. The transverse section of monocot and dicot stem are:
We can determine whether it is a monocot stem or dicot stem with the help of vascular bundles. In dicot system, they are arranged in a ring while in monocot system, they are in a scattered arrangement.
6.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, (b) phloem parenchyma is absent. What will you identify it as?
Ans. The monocot stem is differentiated by conjoint, collateral, and closed vascular bundles scattered in the ground tissue with the parenchyma. Each bundle is bordered by sclerenchymatous bundle-sheath cells. The phloem parenchyma and medullary rays are absent in the monocot stems.
7.Why are xylem and phloem called complex tissues?
Ans. Complex tissue is a group of different kinds of cells which perform common functions. Xylem and phloem are called complex tissues as all cells which work together as a unit for a common function have different structural organisation. Xylem contains four types of cells -tracheids, vessels, xylem parenchyma and xylem fibres. Phloem comprises sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Xylem is related to conduction of water and minerals from roots to top of plants and phloem is responsible for the transport of organic food.
8.What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Ans. Stomata are structures that occur in the epidermis of leaves. They control the process of transpiration and gaseous exchange. Each stoma consists of two bean-shaped cells known as guard cells which enclose stomatal pore. The inner walls of guard cells are thick whereas the outer walls are thin. The guard cells are surrounded by subsidiary cells. These are the specialized epidermal cells present around the guard cells. The pores, the guard cells and subsidiary cells together form the stomatal apparatus.
9.Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Ans. The three basic tissue systems in flowering plants are epidermal tissue system, ground tissue system, and vascular tissue system.
Epidermal tissue system consists of epidermal cells, stomata, trichomes and hairs.
Ground tissue system comprises of cortex, endodermis, pericycle, pith and medullary rays, in primary roots and stems. In leaves, the ground tissue constitutes of thin walled chloroplast containing cells and it is known as mesophyll.
The vascular tissue system contains complex tissues, the xylem and the phloem.
10.How is the study of plant anatomy useful to us?
Ans. The study of plant anatomy is useful in many ways. It helps us understand the way a plant functions carrying out its routine activities like transpiration, photosynthesis and growth and repair. It also helps botanists and agriculture scientists to understand the disease and cure for plants. The study of plant-structure allows us to predict the strength of wood. This is useful in utilising it to its potential. The study of different plant fibres like jute, flax, etc, is helpful to exploit them commercially.
11 .What is periderm? How does periderm formation take place in the dicot stems?
Ans. Periderm is mainly comprised of the phellogen, phellem, and phelloderm.
In secondary growth, the outer epidermal layer and the cortical layer break due to the presence of cambium. They have to be replaced with meristematic cells derived from the cortex that forms the cork cambium or phellogen. This consists of small and narrow cells that are almost rectangular and with thin walls.
Phellogen cuts off cells on its either side. The cells cut off toward the outside give rise to the phellem or cork. The suberin deposits in its cell wall make it impervious to water. The inner cells give rise to the secondary cortex or phelloderm. The secondary cortex is parenchymatous.
12. Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
Ans.
Dicots possess dorsiventral leaves. The three different parts present in the vertical section of a dorsiventral leaf are
→ Epidermis: The epidermis on both upper surface (adaxial epidermis) and lower surface (abaxial epidermis) of the leaf bears a well-marked cuticle. It is made up of elongated, compactly arranged cells which forms a continuous layer. Epidermis on outside is covered by a thick cuticle. Abaxial epidermis bears more stomata than the adaxial epidermis.
Mesophyll: It is the tissue of the leaf placed between adaxial and abaxial epidermises. It consists of differentiated palisade parenchyma comprising of tall, compactly placed cells and spongy parenchyma with oval or round loosely-arranged cells with intercellular spaces. Mesophyll comprises chloroplasts, and these chloroplasts function through photosynthesis.
→ Vascular system: It includes vascular bundles, visible in the veins and midrib. The size of the vascular bundles depends upon the size of the veins. The veins vary
in thickness in the reticulate venation of the dicot leaves. The vascular bundles are surrounded by a layer of thick walled bundle sheath cells.