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Excercises and solutions for class 11 anatomy of flowering plants
class 11 biology chapter 6 notes.
ANATOMY OF FLOWERING PLANTS
- State the location and function of different types of meristems.
On the basis of location, meristems are of three types, apical, intercalary and lateral.
(i) Apical: It is present at the apices of stem, root and their branches.
Functions: It helps in growth in length and formation of primary tissues.
(ii) Intercalary: It is found above or below stem nodes and leaf.
Functions: It helps in growth of internodes, growth in leaves and correction of position in lodged stems.
(a) Phellogen (Cork cambium): It develops from hypodermis in stems and pericycle in roots. Function: Formation of protective cork (phellem) and aerating lenticles on the outside and secondary cortex (phelloderm) on the inner side.
(b) Vascular Cambium: In stem it is formed from intra-fascicular cambial strips and interfascicular strips. In root it develops from conjuctive parenchyma and pericycle. Function: Formation of secondary phloem on the outer side and secondary xylem on the inner side. Vascular rays are formed at intervals for radial conduction.
2. Cork cambium forms tissues that form the cork. Do you agree with this
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.
3. Explain the process of secondary growth in the stems of woody angiosperms. What is its significance?
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.
4. 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.
One can ascertain whether the transverse section of young stem is of monocot or dicot by observing the vascular bundles. In monocot stem, vascular bundles are scattered whereas in dicot stem, they are arranged in a ring.
5. 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?
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.
6. Why are xylem and phloem called complex tissues?
Xylem and phloem are called as a complex tissue because 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 is different from the phloem as xylem conducts water from roots to leaves and phloem conducts food from leaves to different parts of plants.
7. What is stomatal apparatus? Explain the structure of stomata
Stomatal apparatus is a pair of guard cells with or without surrounding subsidiary cells which function as a value to open or close a stomatal pore for gaseous exchange and transpiration.
Each stoma is made of two bean-shaped cells called the guard cells. The guard cells are dumb-bell shaped in grasses. They contain chloroplasts and small vacuoles. They are thick-walled in the area of contact and thin-walled elsewhere. As the guard cells swell up due to endosmosis, their thin-walled sides expand. The thick walls of the two guard cells also bend outwardly and create a pore in between them.
8. Name the three basic tissue systems in the flowering plants. Give the tissue
names under each system.
The three basic tissue systems in the flowering plants include epidermal tissue system, ground tissue system and vascular tissue system.
- Epidermal tissue system- It forms the outermost covering of whole plant body. It consists of tissues like epidermis, stomata, epidermal appendages (trichomes and hairs) etc.
- 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
- Vascular tissue system- The vascular tissue system consists of complex tissues, xylem and phloem that together form vascular bundles.
9. How is the study of plant anatomy useful to us?
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.
10. What is periderm? How does periderm formation take place in the dicot stems?
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.
11. Describe the internal structure of a dorsiventral leaf .
Dorsiventral leaves are present in dicot plant and have three main parts.
Epidermis -The outermost covering of the leaf on the upper side called adaxial epidermis and on the lower side, it is known as the abaxial epidermis. A waxy thick layer cuticle is present and distinct. Stomata are higher on the abaxial epidermis and either lower or absent on adaxial epidermis.
Mesophyll-The mesophyll is present below the epidermis and is composed of parenchyma which has chlorophyll and divided into palisade parenchyma present at the upper side while spongy parenchyma present at the lower side and contains a large number of intercellular space.
Vascular bundles-These are surrounded by thick bundle sheath cells and can be seen in veins and midrib. These are distinct in size due to reticulate venation.