Anatomy of Flowering Plants Question Answers: NCERT Class 11 Biology

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

It is present between the masses of mature tissues present at the bases of the leaves of grasses. It helps in the regeneration of grasses after they have been grazed by herbivores. Since the intercalary meristem and the apical meristem appear early in a plant’s life, they constitute the primary meristem.

Lateral meristem

It appears in the mature tissues of roots and shoots. It is called the secondary meristem as it appears later in a plant’s life. It helps in adding secondary tissues to the plant body and in increasing the girth of plants. Examples include fascicular cambium, interfascicular cambium, and cork cambium

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.

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.

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 inter cellular 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.

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.

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.

(a)Monocot root and dicot root

(b)Monocot stem and dicot stem

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.

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.

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 fibres

Tracheids 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 fibres

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 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.

Stomata are small pores present in the epidermis of leaves. They regulate the process of transpiration and gaseous exchange. The stomatal pore is enclosed between two bean-shaped guard cells. The inner walls of guard cells are thick, while the outer walls are thin. The guard cells are surrounded by subsidiary cells. These are the specialised epidermal cells present around the guard cells. The pores, the guard cells, and the subsidiary cells together constitute the stomatal apparatus.

The attachment of ovules within the ovary is known as Placentation. The placenta refers to a flattened, cushion like tissue on which one or more ovules are attached to the inner-surface of ovary wall. It provides nutrition to the embryo. Various types of placentation in the flower are:

1. Parietal: Occurs in a bi- or multicarpellary but unilocular ovary. Placenta appears as internal ridges on the ovary wall.
2. Marginal: Occurs in a monocarpellary, unilocular ovary. Placenta develops and ovules are borne along the junction of the two margins of the carpel.
3. Axile: Occurs in a bi- or multicarpellary and multilocular ovary. Placentae are formed in the center of the ovary by carpel’s margins inward folding by fusing together in the center.  
4. Free- central: Occurs in multicarpellary but unilocular ovary. Placenta develops in the center of ovary as an upgrowth from ovary base which bears ovules. It may also formed by breaking down of the septa from the initial axile placentation, like in caryophyllaceae.    
5. Basal: Occurs in a bi- or multicarpellary but unilocular ovary. The ovules are few or reduced to one and borne at the base of the ovary.
6. Superficial: Occurs in a multicarpellary and multilocular ovary. Ovules are borne on placentae which develops all around the inner surface of the partition wall.

1. Sieve tubes are present in the phloem tissue. It helps in translocation of synthesized food throughout the plant.
2. Interfascicular cambium helps in the formation of vascular cambium and also facilitates secondary growth.
3. Collenchyma provides mechanical support to young stem.
4. Aerenchyma provides buoyancy to floating plants.

The epidermal cells that surrounds the guard cells are known as Subsidiary cells.

Guard cells are kidney shaped whereas epidermal cells are barrel shaped. Guard cells are smaller but epidermal cells are bigger in size. Chloroplast is present in guard cells and is absent in epidermal cells. Stomata helps in the gaseous exchange.

Palm is a monocotyledonous plant, yet it increases in girth slowly due to secondary growth. This happens because of division and enlargement of parenchymatous cells in the ground tissue.

Anatomical mechanism that are involved in abscission of leaves are:

1. Structural: In deciduous trees, an abscission zone also known as separation zone which is formed at the base of the petiole. It is composed of top and bottom layer. The cells in the top layer have weak cell walls and the bottom layer expand in winter and break the cell walls of the top layer, which results in shedding of leaves.
2. Chlorophyll is a very important part of the plant that helps in absorption of sunlight for photosynthesis. Thus loss of chlorophyll may also results in abscission process.
3. Abscisic acid hormone is also responsible for abscission.

Yes, Pinus tree is considered as an evergreen tree, coniferous resinous trees. On the other hand, some trees always appear to be covered with leaves because they do not shed their leaves during any particular season rather keeps on doing so throughout the year. Pinus does not shed its leaves during a particular season. Thus, the Pinus tree is also considered as evergreen.  

When any plane passing through the middle axis of the plant then it divides the cell into two identical or equal halves which is known as radial symmetry. If the plant cell can be divided into equal and same left and right halves in only one vertical plane it exhibits bilateral symmetry.

1. Plasmodesmata are the microscopic channels between two cells through the cell wall.
2. Middle lamella is the layer in the cell wall and is made up of calcium pectate and magnesium pectate.
3. Secondary wall is a non- extensible layer made of hemicellulose. It provides rigidity to the cell.

a. Exarch: When the protoxylem is present towards the periphery and metaxylem is present towards the center.

Endarch: When the protoxylem is present towards the center and the metaxylem towards the periphery.

b. Stele: Stele is the central part of the root or stems.

Vascular bundle: Vascular bundle is the part of stele.

c. Protoxylem: The xylem that formed earlier is known as Protoxylem.

Metaxylem: The xylem that formed later is metaxylem.

d. Interfascicular cambium: It is present between the primary xylem and primary phloem.

Intrafascicular: It is present in between the two vascular bundles.

e. Open vascular bundles: A vascular bundle which is capable secondary growth.

Closed vascular bundles: A vascular bundle which is not capable of secondary growth.

f. Stem hair: 1. These are multicellular.

2. Function is to increase the surface for absorption.

Root hair: 1. These are unicellular.

2. Function is to prevent water loss.

Anything in excessive will create a harmful cause. When the plant watered excessively, then plant die. Because the water removes the air trapped between the soil particles. Therefore, they don’t get enough oxygen for respiration.

The growth rings in the trunk are formed by cambial rings due to secondary growth. This gives the appearance of concentric rings. Concentric rings help in making an estimate about the age of the tree.

Yes, it is an abnormality. It is an abnormal type of secondary growth, in which regular vascular cambium or cork cambium is not formed in normal position.