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Anatomy of Flowering Plants Test - 29

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Anatomy of Flowering Plants Test - 29
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  • Question 1
    1 / -0
    Which of the following provide maximum mechanical strength to a tree trunk?
    Solution
    Heartwood, also called as duramen, dead, central wood of trees. Its cells usually contain tannins or other substances that make it dark in colour and sometimes aromatic. Heartwood is mechanically strong, resistant to decay, and less easily penetrated by wood preservative chemicals than other types of wood. One or more layers of living and functional sapwood cells are periodically converted to heartwood. Heart wood provide maximum mechanical strength to a tree trunk than sapwood, cork or late wood (autumn wood). 
  • Question 2
    1 / -0
    In dicot root, vascular cambium originates from
    Solution
    Dicot roots have little or no pith and thus pith rays are not the source of interfascicular cambium. The parenchyma cells present between xylem and phloem elements in the vascular bundles constitute conjunctive tissue. The parenchymatous cells present beneath phloem take on meristematic activity and form cambial strands. Similarly, the cells of pericycle present against protoxylem divide and form multiple layers of cells, which are joined by cambial cells derived from conjunctive tissues and together they make a complete cambium ring. Thus, the correct answer is option D.
  • Question 3
    1 / -0
    How many types of cells are present in vascular cambium?
    Solution
    The vascular cambium is located between the xylem and the phloem in the stem and root of a vascular plant and is the source of both the secondary xylem growth inwards, towards the pith and the secondary phloem growth outwards. It is a cylinder of unspecialized meristem cells that divide to give new cells, which then specialize to form secondary vascular tissues. The vascular cambium usually consists of two types of cells - fusiform initials and ray initials. The fusiform initial cells are tall cells and axially oriented. The ray initials are small and round. Sometimes, they are angular in shape.

  • Question 4
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    In dicot root, which tissue becomes dead due to activity of phellogen?
    Solution
    • The pericycle is the outermost covering of stele, lying just beneath the endodermis. During secondary growth, the cells of pericycle present against protoxylem divide and form multiple layers of cells which are joined by cambial cells derived from conjunctive tissues and together they make a complete cambium ring. Cambial activity produces secondary tissues that push and rupture epidermal cells and the outer cortex; a new protective layer, the periderm is formed. 
    • Periderm divides to form cork cambium or phellogen. The cork cambium exhibits meristematic activity and produces cork or phellem towards the periphery and phelloderm on the inside, i.e., extra stellar growth. These secondary tissues cause pressure and rupture the cells layers present outside the pericycle (endodermis and cortex).
    • A dicot root has tissues layers in the following order: epidermis, cortex, endodermis, pericycle, and vascular tissues, cork cambium activity ruptures the cells layers present outside the pericycle. The hypodermis is the thickest layer of the epidermis but is present in leaves not in roots.
    So, the correct answer is 'Tissue outside pericycle'.
  • Question 5
    1 / -0
    In dicot stem, cork cambium first derived from
    Solution
    Cork cambium is the extrastelar lateral meristem that produces extrasteler secondary tissue system. Cortex is the ground tissue which surrounds the central stele and is derived from ground meristem. Hypodermis refers to 5-7 layers of cortical cells present just beneath the epidermis which resume the meristematic activity and produce phellogen or cork cambium just beneath the epidermis. The outer most covering of stele forms pericycle, it is an intrasteler tissues present in a stele which means that phellogen (extrastelar lateral meristem) cannot be produced by pericycle. The phellogen or cork cambium produces cork or phellem towards the periphery and phelloderm towards inner side. As phellem and phelloderm are the product of cork cambium, not its progenitor. 
    Thus, the correct answer is option A.
  • Question 6
    1 / -0
    Four radial vascular bundles are found in
    Solution
    Dicot root vascular bundles are described as radial and tetrarch. There are four bundles each of xylem and phloem occurring alternately. Xylem is described as exarch. 
    Monocot root vascular bundles are radial in arrangement. There are eight bundles each of xylem and phloem. Hence, the condition is described as polyarch. Xylem is described as exarch. 
    Dicot stem vascular bundles are eight in number, arranged in form of a broken ring. The vascular bundles are conjoint, collateral and open. Xylem is on the inner surface and phloem on the outer surface. Xylem is described as endarch. 
    Monocot stem vascular bundles are described as conjoint, collateral and closed. Presence of numerous vascular bundles irregularly scattered with cerifugal arrangement. Thus, option A is correct.
  • Question 7
    1 / -0
    Which of the following tissues originate from ray initials of cambium?
    Solution
    Phloem is a complex tissue and is composed of four elements namely, sieve elements, companion cell, phloem fibres and phloem parenchyma. 
    Xylem is composed of tracheids, vessels, fibres and parenchyma. The primary xylem and phloem are derived from procambium, which is an embryonic tissue, while secondary xylem and secondary phloem are derived from vascular cambium, which is a lateral cambium. The ray initials of the vascular cambium divide tangentially and produce parenchymatous cells on both sides, which differentiate as parenchymatous vascular rays. These rays traverse from pith to cortex through secondary xylem and phloem. Thus, the correct answer is option D.
  • Question 8
    1 / -0
    Annual rings are distinct in plants growing in
    Solution
    Solution :
    The correct answer is option D.
    The solution for the correct option is ,
    • Annual ring of the trees are usually seen in temperate region due to the different weather conditions throughout the year.
    • Cambium is most active in the spring but in winter the activity decreases.
    • The vascular cambium contains xylem and phloem primarily forms the cambium ring in the stem and performs the function of cutting new cells both toward the outer and inner sides.
    • The function of the Cambial ring is under the control of many physiological and environmental factors. In temperate (cooler) regions, climates vary throughout the year and vary from time to time.
    • In the spring, cambium is very active and produces a large number of xylary elements with vessels with wide holes. The wood produced at this time is therefore called the wood of the spring or the original wood.
  • Question 9
    1 / -0
    An example of monocots showing secondary growth in stem is
    Solution
    Secondary growth is increase in the circumference / girth of the plant organs due to the formation of secondary tissues in stelar and extra stelar regions. Normally secondary growth takes place in roots and stem of dicotyledons and gymnosperms. Due to lack of cambium in monocotyledons, secondary growth is absent. But exceptionally, secondary growth takes place in some monocotyledons, such as palm, Yucca, Dracaena etc. 
  • Question 10
    1 / -0
    The cells of the quiescent centre are characterized
    Solution
    According to quiescent centre theory, root apical meristem is present as the tip of main root and has a biconvex quiescent centre in its centre which is characterized by presence of inactive cells with less number of cell organelles, light cytoplasm, small nuclei and low synthesis of DNA, RNA and protein caused by low frequency of cell division, mitosis. The corpus-tunica theory is applicable to shoot apex, while the quiescent centre is present in root apex.
    Thus, the correct answer is option B.
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