Question 1

State the location and function of different types of meristematic tissues in plants.

Accepted Answer

Meristems are specialised 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:It is present at the root apex and the shoot apex. The shoot apical meristem is present at the tip of the shoots and its active division results in the elongation of the stem and formation of new leaves. The root apical meristem helps in root elongation.Intercalary meristem:The intercalary meristems are located at the internodes or the base of the leaves. The intercalary meristems help in increasing the length of the internode. This is usually seen in monocotyledonous plants.Lateral meristem:The lateral meristems are present on the lateral side of the stem and root of a plant. These meristems help in increasing the thickness of the plants.

Question 2

Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.

Accepted Answer

When secondary growth occurs in the dicot stem and root, the epidermal layer gets broken. There is a need to replace the outer epidermal cells for providing protection to the stem and root from infections. Therefore, the cork cambium develops from the cortical region. It is also known as phellogen and is composed of thin-walled rectangular cells. It cuts off cells toward both sides. The cells on the outer side get differentiated into the cork or phellem, while the cells on the inside give rise to the secondary cortex or phelloderm. The cork is impervious to water but allows gaseous exchange through the lenticels. Phellogen, phellem, and phelloderm together constitute the periderm.

Question 3

Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance?

Accepted Answer

In woody dicots, the strip of cambium present between the primary xylem and phloem is called the interfascicular cambium. The interfascicular cambium is formed from the cells of the medullary rays adjoining the interfascicular cambium. This results in the formation of a continuous cambium ring. The cambium cuts off new cells toward its either sides. The cells present toward the outside differentiate into the secondary phloem, while the cells cut off toward the pith give rise to the secondary xylem. The amount of the secondary xylem produced is more than that of the secondary phloem.The secondary growth in plants increases the girth of plants, increases the amount of water and nutrients to support the growing number of leaves, and also provides support to plants.

Question 4

Draw illustrations to bring out the anatomical difference between(a) Monocot root and dicot root (b) Monocot stem and dicot stem

Accepted Answer

(a) Differences between monocot and dicot root-(b) Difference between monocot and dicot stem-

Question 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.

Accepted Answer

The dicot stem is characterised by the presence of conjoint, collateral and open vascular bundles, with a strip of cambium between the xylem and phloem. The vascular bundles are arranged in the form of a ring, around the centrally-located pith. The ground tissue is differentiated into the collenchyma, parenchyma, endodermis, pericycle and pith. Medullary rays are present between the vascular bundles. The monocot stem is characterised by conjoint, collateral and closed vascular bundles, scattered in the ground tissue containing the parenchyma. Each vascular bundle is surrounded by sclerenchymatous bundle-sheath cells. Phloem parenchyma is absent and water-containing cavities are present.

Question 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 sheaths. (b) Phloem parenchyma is absent. What will you identify it as?

Accepted Answer

The monocot stem is characterised by conjoint, collateral, and closed vascular bundles, scattered in the ground tissue containing the parenchyma. Each vascular bundle is surrounded by sclerenchymatous bundle-sheath cells. Phloem parenchyma and medullary rays are absent in monocot stems.

Question 7

Why are xylem and phloem called as complex tissues?

Accepted Answer

Xylem and phloem are known as complex tissues as they are made up of more than one type of cells. These cells work in a coordinated manner, as a unit, to perform the various functions of the xylem and phloem.Xylem helps in conducting water and minerals. It also provides mechanical support to plants. It is made up of the following components:• Tracheids (xylem vessels and xylem tracheids)• Xylem parenchyma• Xylem fibresTracheids are elongated, thick-walled dead cells with tapering ends. Vessels are long, tubular, and cylindrical structures formed from the vessel members, with each having lignified walls and large central cavities. Both, tracheids and vessels lack protoplasm. Xylem fibres consist of thick walls with an almost insignificant lumen. They help in providing 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 helps in conducting food materials. It is composed of:• Sieve tube elements• Companion cells• Phloem parenchyma• Phloem fibresSieve 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 are parenchymatous in nature. They help in maintaining the pressure gradient in the sieve tube elements. Phloem parenchyma helps in the storage of food and is made up of long tapering cells, with a dense cytoplasm. Phloem fibres are made up of elongated sclerenchymatous cells with thick cell walls.

Question 8

What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.

Accepted Answer

Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed*of two bean shaped cells known as guard cells which enclose stomatal pore. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.

Question 9

Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.

Accepted Answer

Sr. No Tissue system  Tissues present  1 Epidermal tissue systemEpidermis, trichomes, hairs, stomata 2 Ground tissue system Parenchyma, collenchyma, sclerenchyma,mesophyll 3 Vascular tissue system Xylem, phloem, cambium

Question 10

How is the study of plant anatomy useful to us?

Accepted Answer

The study of plant anatomy helps us to understand the structural adaptations of plants with respect to diverse environmental conditions. It also helps us to distinguish between monocots, dicots, and gymnosperms. Such, a study is linked to plant physiology. Hence, it helps in the improvement of food crops. 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 various plant fibres such as jute, flax, etc., helps in their commercial exploitation.

Question 11

What is a periderm? How does periderm formation take place in the dicot stems?

Accepted Answer

Periderm is composed of the phellogen, phellem and phelloderm.During secondary growth, the outer epidermal layer and the cortical layer are broken because of the cambium. To replace them, the cells of the cortex turn meristematic, giving rise to cork cambium or phellogen. It is composed of thin-walled, narrow and rectangular cells.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.

Question 12

Describe the internal structure of a dorsi-ventral leaf with the help of labelled diagram.

Accepted Answer

Dorsiventral leaves are found in dicots. The vertical section of a dorsiventral leaf contains three distinct parts:[1] Epidermis:Epidermis is present on both the upper surface (adaxial epidermis) and the lower surface (abaxial epidermis). The epidermis on the outside is covered with a thick cuticle. Abaxial epidermis bears more stomata than the adaxial epidermis.[2] Mesophyll:Mesophyll is a tissue of the leaf present between the adaxial and abaxial epidermises. It is differentiated into the palisade parenchyma (composed of tall, compactly-placed cells) and the spongy parenchyma (comprising oval or round, loosely-arranged cells with intercellular spaces). Mesophyll contains the chloroplasts which perform the function of photosynthesis.[3] Vascular system:The vascular bundles present in leaves are conjoint and closed. They are surrounded by thick layers of bundle-sheath cells.

Chapter 6 : Anatomy of Flowering Plants