Question
Select the correct pair. [NEET 2021]
(a) Large colourless empty cells in the epidermis of grass leaves Subsidiary cells
(b) In dicot leaves, vascular bundles are surrounded by large thick-walled cells – Conjunctive tissue
(c) Cells of medullary rays that form part of cambial ring Interfascicular cambium
(d) Loose parenchyma cells rupturing the epidermis and forming a lens-shaped opening in bark Spongy parenchyma
Answer/Explanation
Ans. (c)
Medullary rays (pith rays or wood rays) are sheets or ribbons of cells running from the inside of the plant to the outside. That is, they run at right angles to the xylem and phloem, which run vertically. While the plant is alive, these medullary cells are alive. In dicot stems, the cambium which is present between primary xylem and primary phloem is called intrafascicular cambium. The cells of medullary rays near these intrafascicular cambium become meristematic and form interfascicular cambium. This leads to the formation of a continuous ring of cambium. Other options can be corrected as : Few epidermal cells in the vicinity of guard cells become specialised in their shape and size and are called subsidiary cells.
The parenchymatous cells which lie between xylem and the phloem are called conjunctive tissue.
A spongy layer of irregular chlorophyll bearing cells interspersed with air spaces that fills the interior part of leaf below the palisade layer is called spongy parenchyma.
Question
Match the List -I with List – II.
Choose the correct answer from the options given below. [NEET 2021]
A B C D
(a) 4 1 3 2
(b) 3 1 4 2
(c) 2 3 4 1
(d) 4 2 1 3
Answer/Explanation
Ans. (b)
(A)-(3), (B) (1), (C)-(4), (D)-(2)
Lenticels permit the exchange of gases between the environment and the internal tissue spaces of the organs (stems and some fruits). They permit the entrance of oxygen and simultaneously the output of carbon dioxide and water vapour. Thus, they are responsible for gaseous exchange.
Cambium, called the phellogen or cork cambium, is the source of the periderm, a protective tissue that replaces the epidermis when the secondary growth displaces, and ultimately destroys, the epidermis of the primary plant body.
Phelloderm is the parenchymatous tissue which originates from the phellogen towards its inner side known as the secondary cortex. It is a living tissue having a cellulosic cell wall.
Cork tissue, consisting of dead cells surrounded by alternating layers of suberin and wax, has a particularly high suberin content. Cork cells are found in a secondary protective layer (periderm) in the bark of trees.
Question
Which of the following statements about cork cambium is incorrect? [NEET (Oct.) 2020]
(a) It forms secondary cortex on its outerside
(b) It forms a part of periderm
(c) It is responsible for the formation of lenticels
(d) It is a couple of layers thick
Answer/Explanation
Ans. (a)
Cork cambium is a meristematic tissue involved in secondary growth. It is also called phellogen. It is few layer thick and it cut off cells into an outer layer and an inner layer. The former differentiates into cork or phellem while the latter differentiate into secondary cortex or phelloderm. The phellogen, phellem and phelloderm are collectively known as periderm. In woody trees, phellogen cuts off closely arranged parenchymatous cells which ruptures the epidermis and form lenticels. Thus, statement 1 is incorrect while other are correct.
Question
Which of the statements given below is not true about formation of annual rings in trees? [NEET (National) 2019]
(a) Differential activity of cambium causes light and dark bands of tissue early and late wood, respectively
(b) Activity of cambium depends upon variation in climate
(c) Annual rings are not prominent in trees of temperate region
(d) Annual ring is a combination of springwood and autumnwood produced in a year
Answer/Explanation
Ans. (c)
The statement “annual rings are not prominent in trees of temperate region” is incorrect. Correct information about the statement is as follows: Annual rings are formed due to the seasonal activity of cambium. In the plants of temperate region, cambium is highly active in spring and less active in autumn season. Hence, prominent rings are formed in these plants having light and dark bands of tissue. Rest statements are correct about the formation of annual rings in trees.
Question
Plants having little or no secondary growth are [NEET 2018]
(a) conifers
(b) deciduous angiosperms
(c) grasses
(d) cycads
Answer/Explanation
Ans. (c)
Secondary growth occurs due to the presence of vascular cambium. Grasses are monocot and lacks vascular cambium. Therefore, they do not show secondary growth.
Deciduous angiosperms are usually woody dicot plants and show secondary growth. Conifers and cycads are gymnosperms and usually show anomalous secondary growth.
Question
Secondary xylem and phloem in dicot stem are produced by [NEET 2018]
(a) phellogen
(b) vascular cambium
(c) apical meristems
(d) axillary meristems
Answer/Explanation
Ans. (b)
Secondary vascular tissues, i.e., secondary xylem and pholem are formed by the vascular cambium. It is produced by two types of meristems; fascicular or intrafascicular and interfascicular cambium.
Intrafascicular cambium is a primary meristem which occurs as strips in vascular bundles.
It divides to form secondary phloem on outer side and secondary xylem on the inner side. Interfascicular cambium arises secondarily from the cells of medullary rays.
Phellogen or cork cambium is produced in the outer cortical cells of dicot stems. It is helpful in increasing the girth. Apical meristems are present at the tips of stem, root and their branches. They are responsible for increase in length of the plant. Axillary meristem is found in axillary buds. These cells are left behind from shoot apical meristem during the formation of leaves and elongation of stems.
Question
Plants having little or no secondary growth are [NEET 2018]
(a) conifers
(b) deciduous angiosperms
(c) grasses
(d) cycads
Answer/Explanation
Ans. (c)
Secondary growth occurs due to the presence of vascular cambium. Grasses are monocot and lacks vascular cambium. Therefore, they do not show secondary growth.
Deciduous angiosperms are usually woody dicot plants and show secondary growth. Conifers and cycads are gymnosperms and usually show anomalous secondary growth.
Question
Identify the wrong statement in context of heartwood. [NEET 2017]
(a) Organic compounds are deposited in it
(b) It is highly durable
(c) It conducts water and minerals efficiently
(d) It comprises dead elements with highly lignified walls
Answer/Explanation
Ans. (c)
Heartwood also called duramen is the central dead wood of trees. It comprises of dead, lignified cells containing organic compounds, e.g. tannins or other substances. These substances make it darker in colour and aromatic. Heartwood is strong durable and resistant to decay. It does not conduct water and minerals because of the presence of dead elements. Thinking Process The conduction of water and minerals is carried out by sapwood, because it contains living cells.
Question
The vascular cambium normal gives rise to [NEET 2017]
(a) phelloderm
(b) primary phloem
(c) secondary xylem
(d) periderm
Answer/Explanation
Ans. (c)
Vascular cambium located between xylem and phloem in the stems and roots of vascular plants. It produces secondary xylem towards the pith and secondary phloem towards the bark. Phellogen is made of narrow thin-walled and nearly rectangular cells. phellogen cuts off cells on both sides. The outer cells differentiate into cork or phellem while inner cells differentiate into secondary cortex or phelloderm. The phellogen, phellem and phelloderm are collectively known as periderm.
Question
Read the different components from I-IV in the list given helnw and tell the correct order of the components with reference to their arrangement from outer side to inner side in a woody dicot stem. [CBSE AIPMT 2015]
I. Secondary cortex
II. Wood
III. Secondary phloem
IV. Phellem
The correct order is
(a) III, IV, II, I
(b) I, II, IV, III
(c) IV, I, III, II
(d) IV, III, I, II
Answer/Explanation
Ans. (c)
The correct order of arrangement of the given components from outside to inside in a woody dicot stem is as follows
Phellem $\longrightarrow$ Secondary cortex $\longrightarrow$
Secondary phloem $\longrightarrow$ Wood
Question
You are given a fairly old piece of dicot stem and a dicot root. Which of the following anatomical structures will you use to distinguish between the two? [CBSE AIPMT 2014]
(a) Secondary xylem
(b) Secondary phloem
(c) Protoxylem
(d) Cortical cells
Answer/Explanation
Ans. (c)
We will observe the protoxylem of the dicot stem and dicot root to distinguish between them. In dicot stem the protoxylem is present towards center (pith) and metaxylem is present towards the periphery of the organ. This type of xylem is known as endarch.
In root protoxylem is present towards periphery and metaxylem is present towards center that is called exarch.
Question
Interfascicular cambium develops from the cells of [NEET 2013]
(a) medullary rays
(b) xylem parenchyma
(c) endodermis
(d) pericycle
Answer/Explanation
Ans. (a)
In dicot stems, the cells of cambium present between primary xylem and primary phloem is the intrafascicular cambium. The cells of medullary rays, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium.
Xylem parenchyma are living and thin-walled and their cell walls are made up of cellulose. In dicot roots the innermost layer of the cortex is called endodermis. Next to endodermis lies a few layers of thick walled parenchymatous cells called as pericycle.
Question
Age of a tree can be estimated by [NEET 2013]
(a) its height and girth
(b) biomass
(c) number of annual rings
(d) diameter of its heartwood
Answer/Explanation
Ans. (c)
Age of a tree can be estimated by counting the number of annual rings. This study is known as dendrocronology. The two kinds of woods that appear as alternate concentric rings, constitute an annual ring heartwood comprises dead elements with highly lignified walls that give mechanical support to the stem. The height and girth of a tree increases due to the activity of vascular cambium.
Question
The cork cambium, cork and secondary cortex are collectively called [CBSE AIPMT 2011]
(a) phellogen
(b) periderm
(c) phellem
(d) phelloderm
Answer/Explanation
Ans. (b)
The periderm is a secondary protective structure and is made up of cork cambium(phellogen), cork (phellem) and secondary cortex (phelloderm).
Question
Heartwood differs from sapwood in [CBSE AIPMT 2010]
(a) presence of rays and fibres
(b) absence of vessels and parenchyma
(c) having dead and non-conducting elements
(d) being susceptible to pests and pathogens
Answer/Explanation
Ans. (c)
As a result of continued secondary growth in subsequent years, the older part of secondary xylem or wood becomes non-functional (dead) as it loses the power of conduction. The cells of this wood are filled with resins or tannins produced by adjacent functional cells. The activities of vessels become blocked by tyloses. Due to these activities, non-functional, secondary xylem becomes hard, durable and blackish in colour, called heartwood. Now, the function of secondary xylem (water and mineral conduction from roots) is performed by outer younger-rings of xylem which is called sapwood.
Question
For a critical study of secondary growth in plants which one of the following pairs is suitable? [CBSE AIPMT 2007]
(a)Sugarcane and sunflower
(b) Teak and pine
(c) Deodar and fern
(d) Wheat and maiden hair fern
Answer/Explanation
Ans. (b)
The increase in diameter or thickness is due to the formation of secondary tissues as a result of the activities of vascular cambium and cork cambium. This secondary growth is characteristic of dicot stem and root. Thus, sugarcane, pine, ferns, wheat, etc. cannot be used to study secondary growth.
Question
Main function of lenticel is [CBSE AIPMT 2002]
(a) transpiration
(b) guttation
(c) gaseous exchange
(d) bleeding
Answer/Explanation
Ans. (c)
The primary function of lenticels is gaseous exchange. Lenticel respiration generally seen in stem of dicotyledons plants. Transpiration takes place mostly through stomata. Guttation and bleeding takes place through hydathodes.
Question
As the secondary growth takes place (proceeds) in a tree, thickness of [CBSE AIPMT 1994]
(a) heartwood increases
(b) sapwood increases
(c) both increase
(d) both remain the same
Answer/Explanation
Ans. (a)
As a result of continous secondary growth in subsequent year, the older part of secondary xylem becomes non-functional. Due to this activities of vessels become blocked by bladder like ingrowths which are called tyloses. Due to this non-functional xylem becomes hard and blackish in colour called duramen or heartwood.
Now, the function of secondary xylem is continoued by younger rings called sapwood or alburnum with the passage of time and addition of new outer rings of secondary xylem more rings of sapwood changes into heartwood. This is why the heartwood increases in diameter year after year but the sapwood remains almost in the same thickness.
Question
Procambium forms [CBSE AIPMT 1994]
(a) only primary vascular bundles
(b) only vascular cambium
(c) only cork cambium
(d) primary vascular bundles and vascular cambium
Answer/Explanation
Ans. (d)
The meristematic tissue which forms the primary xylem and phloem is known as procambium. The term procambium is used to indicate the meristematic tissue that give rise to the morphological vascular units.
Question
Abnormal/anomalous secondary growth occurs in[CBSE AIPMT 1993]
(a) Dracaena
(b) ginger
(c) wheat
(d) sunflower
Answer/Explanation
Ans. (a)
Secondary growth in monocotyledons is rather rare, it is commonly seen in woody monocotyledons such as Dracaena, Aloe, Agave, etc. In Dracaena sp exceptionally large secondary growth in thickness occurs that begins with the formation of secondary meristematic tissue-the cambium, in the parenchyma outside the primary bundles. Moreover, cork in Dracaena appears in seriated bands without the formation of cork cambium (phellogen) and is known as storied cork.
Question
A narrow layer of thin walled cells found between phloem/bark and wood of a dicot is [CBSE AIPMT 1993]
(a) cork cambium
(b) vascular cambium
(c) endodermis
(d) pericycle
Answer/Explanation
Ans. (b)
Vascular cambium is formed by strips of fascicular cambium and interfascicular cambium. It consists of narrow layer of thin walled cells found between phloem and xylem tissues.
Vascular cambium helps in secondary growth in dicot root and stem.
Question
Periderm is produced by [CBSE AIPMT 1993]
(a) vascular cambium
(b) fascicular cambium
(c) phellogen
(d) intrafascicular cambium
Answer/Explanation
Ans. (c)
Phellogen or cork cambium which develops secondarily from some outer layer of cortex (or pericycle)divides on the outside as well a inside to form respectively cork or phellem and secondary cortex or phelloderm. Cork, cork cambium and secondary cortex are together called periderm.
Question
Which exposed wood will decay faster? [CBSE AIPMT 1993]
(a) Sapwood
(b) Softwood
(c) Wood with lot of fibres
(d) Heartwood
Answer/Explanation
Ans. (a)
In old trees, secondary xylem or wood gets differentiated into outer light coloured functional sapwood or alburnum and inner dark coloured non-functional heartwood or duramen. Heartwood is stronger and highly durable because of presence of oils, resins, gums, tannins and tyloses which are plugged into the tracheids and vessel elements.
As the secondary growth takes place size of heart wood increases because of conversion of inner alburnum (sapwood) into it.
Question
Commercial cork is obtained from [CBSE AIPMT 1991]
(a) Berberis/Barberry
(b) Salix/Willow
(c) Quercus/Oak
(d) Betula/Birch
Answer/Explanation
Ans. (c)
Cork or phellem develops from cark cambium and is made up of dead suberised and rectangular cells which are filled with air and tannins. Cork is protective and is obtained commercially from Quercus suber (cork oak, bottle cork).
Question
Cork cambium and vascular cambium are [CBSE AIPMT 1990]
(a) parts of secondary xylem and phloem
(b) parts of pericycle
(c) lateral meristems
(d) apical meristems
Answer/Explanation
Ans. (c)
Lateral meristems are present along the lateral sides of stem and root. They divide only in radial direction. The cambium of vascular bundles (fascicular, intrafascicular) and the cork cambium or phellogen belongs to this category and are found in dicotyledons and gymnosperms.
Question
For union between stock and scion in grafting which one is the first to occur? [CBSE AIPMT 1990]
(a) Formation of callus
(b) Production of plasmodesmata
(c) Differentiation of new vascular tissues
(d) Regeneration of cortex and epidermis
Answer/Explanation
Ans. (a)
In grafting, cambium bearing shoot (scion) of one plant is joined to cambium bearing stump(root system = stock) of related plant through different union like tongue grafting, wedge grafting, etc. The union of scion and stock leads to irregular, unorganised and undifferentiated mass of actively dividing cells known as callus.
Question
Vascular cambium produces [CBSE AIPMT 1990, 92]
(a) primary xylem and primary phloem
(b) secondary xylem and secondary phloem
(c) primary xylem and secondary phloem
(d) secondary xylem and primary phioem
Answer/Explanation
Ans. (b)
Vascular cambium is formed by fascicular and interfascicular cambium. It leads to secondary growth in dicot roots and dicot stems. Cells of vascular cambium, known as fusiform initially produce secondary phloem on the out side and secondary xylem on the inner side.
Youngest xylem layer occur inner to vascular cambium while oldest layer of secondary xylem is found outside the primary xylem or towards pith. In case of phloem, youngest layer of secondary phloem lies just outside the vascular cambium while oldest layer is towards outside, inner to primary phloem.
Question
Cork is formed from [CBSE AIPMT 1988]
(a) cork cambium (phellogen)
(b) vascular cambium
(c) phloem
(d) xylem
Answer/Explanation
Ans. (a)
Cells of cork cambium (phellogen) divide on the outside as well as inside to form