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Ques 1: State the location and function of different types of meristem.
Ans: 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:
Ques 2: Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.
Ans: 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.
cork Ques 3: Explain the process of secondary growth in stems of woody angiosperm with help of schematic diagrams. What is the significance?
Ans: 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.
Primary and Secondary Angiosperm
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.
Ques 4: Draw illustrations to bring out anatomical difference between
(a) Monocot root and dicot root
(b) Monocot stem and dicot stem
Ans: (a) Monocot root and dicot root
(b) Monocot stem and dicot stem
Ques 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 dicot stem? Give reasons.
Ans: 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.
Ques 6: The transverse section of a plant material shows the following anatomical features,
(a) the vascular bundles are conjoint, scattered and surrounded by clerenchymatous undle sheaths
(b) phloem parenchyma is absent. What will you identify it as?
Ans: 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.
Ques 7: Why are xylem and phloem called complex tissues?
Ans: Complex tissues are those tissues that comprise more than one type of cell, varying cells that are involved in performing a dedicated function. These cells work together as a combined unit to perform a specific function. Complex tissues bring about the transportation of water, organic minerals, up and down the plants. This is the reason why they are vascular tissues. There are two common types of complex permanent tissues in plants – they are xylem and phloem.
Xylem and phloem are vascular tissues. They bring about the conduction of water, minerals and food to different plant parts. Such complex tissues, even though are made of more than one cell type have a common origin. They coordinate to perform a specific function.
Xylem and phloem are made of different cell types, who come together to perform a common function, hence they are called complex tissues. The xylem is composed of vessels, tracheids, xylem fibres and xylem parenchyma. Phloem is composed of sieve tubes, companion cells, phloem fibres and phloem parenchyma.
Ques 8: What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Ans: 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.
Ques 9: Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Epidermal tissue system
Epidermis, trichomes, hairs, stomata
Ground tissue system
Parenchyma, collenchyma, sclerenchyma, mesophyll
Vascular tissue system
Xylem, phloem, cambium
Ques 10: How is the study of plant anatomy useful to us?
Ans: 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 utilizing it to its potential. The study of various plant fibres such as jute, flax, etc., helps in their commercial exploitation.
Ques 11: What is periderm? How does periderm formation take place in dicot stem?
Ans: 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.
Ques 12: Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
Ans: Dorsiventral leaves are found in dicots. The vertical section of a dorsiventral leaf contains three distinct parts.