Secondary Growth in Plants Practice Questions
20 free Secondary Growth in Plants practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
The increase in the girth of a plant due to the activity of lateral meristems is known as:
- A Primary growth
- B Secondary growth
- C Apical growth
- D Intercalary growth
Correct answer: Secondary growth
Secondary growth refers to the increase in thickness or girth of the plant axis. it is brought about by the activity of two lateral meristems: vascular cambium and cork cambium.
The meristematic layer that is responsible for cutting off vascular tissues (xylem and phloem) is called:
- A Phellogen
- B Vascular cambium
- C Intercalary meristem
- D Phelloderm
Correct answer: Vascular cambium
Vascular cambium is the lateral meristem that produces secondary xylem toward the inner side and secondary phloem toward the outer side. In young dicot stems, it is initially present in patches between xylem and phloem.
In a dicot stem, the cambium present between primary xylem and primary phloem is called:
- A Interfascicular cambium
- B Intrafascicular cambium
- C Cork cambium
- D Phellogen
Correct answer: Intrafascicular cambium
Intrafascicular cambium is the primary lateral meristem found within the vascular bundles of a dicot stem. During secondary growth, it joins with interfascicular cambium to form a continuous ring.
The cells of medullary rays, adjoining the intrafascicular cambium, become meristematic and form the:
- A Intrafascicular cambium
- B Interfascicular cambium
- C Phellogen
- D Secondary phloem
Correct answer: Interfascicular cambium
Interfascicular cambium develops from the parenchymatous cells of the medullary rays located between adjacent vascular bundles. This completes the formation of a continuous cambial ring.
Generally, the vascular cambium is more active on the:
- A Outer side
- B Inner side
- C Both sides equally
- D Top side
Correct answer: Inner side
The vascular cambium is more active on its inner side than on the outer side. As a result, much more secondary xylem is produced compared to the amount of secondary phloem.
What happens to the primary and secondary phloem as more secondary xylem is formed?
- A They become much more active
- B They get gradually crushed
- C They transform into cork
- D They move toward the pith
Correct answer: They get gradually crushed
The continuous addition of secondary xylem exerts outward pressure, causing the primary and secondary phloem to get gradually crushed. However, the primary xylem remains more or less intact around the center.
At certain places, the cambial ring forms a narrow band of parenchyma that passes radially through the secondary xylem and the secondary phloem. This band is called:
- A Primary medullary rays (Pith rays)
- B Tracheids
- C Sieve tubes
- D Secondary medullary rays
Correct answer: Secondary medullary rays
Radial bands of parenchyma cut by the cambium through the secondary vascular tissues are the secondary medullary rays. They carry water, food and air radially between the inner and outer parts of the stem. Primary medullary rays, in contrast, are formed during primary growth and lie between the vascular bundles.
In temperate regions, the cambium is highly active early in the growing season and produces many xylary elements with wide vessels. This wood is called:
- A Autumn wood
- B Late wood
- C Heartwood
- D Spring wood
Correct answer: Spring wood
Spring wood or early wood is formed when environmental conditions are favorable and the cambium is highly active. The vessels produced during this period have larger diameters.
In winter, the cambium is less active and forms fewer xylary elements that have narrow vessels. This wood is called:
- A Spring wood
- B Early wood
- C Autumn wood
- D Sapwood
Correct answer: Autumn wood
Autumn wood or late wood is produced during the unfavorable cold season when cambial activity slows down. The resulting wood is denser and has narrower vessels.
The two kinds of wood that appear as alternate concentric rings in a transverse section of a trunk constitute an:
- A Annual ring
- B Axial ring
- C Intrafascicular ring
- D Phelloderm
Correct answer: Annual ring
An annual ring consists of one layer of spring wood and one layer of autumn wood formed in a single year. By counting these rings, the approximate age of a tree can be determined (dendrochronology).
The dark brown, non-functional central part of the secondary xylem, which is resistant to microorganisms, is known as:
- A Sapwood
- B Alburnum
- C Phelloderm
- D Heartwood
Correct answer: Heartwood
Heartwood, also known as Duramen, is the older, central secondary xylem that has become clogged with resins, tannins, and oils. It does not conduct water but provides mechanical support and durability to the tree.
The peripheral region of the secondary xylem, which is lighter in color and involved in water conduction, is called:
- A Heartwood
- B Duramen
- C Phelloderm
- D Sapwood
Correct answer: Sapwood
Sapwood, also known as Alburnum, is the younger, outer layer of secondary xylem. It remains functional and is responsible for the transport of water and minerals from the roots to the leaves.
As the stem continues to increase in girth, the outer cortical and epidermis layers get broken. They are replaced by a new meristematic tissue called:
- A Vascular cambium
- B Phelloderm
- C Periderm
- D Cork cambium
Correct answer: Cork cambium
Phellogen or cork cambium usually develops in the cortical region to provide a new protective cover for the expanding stem. It is a couple of layers thick and made of narrow, thin-walled cells.
Phellogen cuts off cells on both sides. The outer cells differentiate into _______ and the inner cells differentiate into _______.
- A Phelloderm, Cork
- B Secondary xylem, Secondary phloem
- C Epidermis, Endodermis
- D Cork, Secondary cortex
Correct answer: Cork, Secondary cortex
The activity of the phellogen produces phellem (cork) toward the outside and phelloderm (secondary cortex) toward the inside. These three layers together form the periderm.
The cork is impervious to water primarily due to the deposition of _______ in its cell wall.
- A Lignin
- B Pectin
- C Suberin
- D Cellulose
Correct answer: Suberin
Cork cells are dead at maturity and their walls are heavily impregnated with suberin. This waxy substance makes the cork waterproof and protects the inner tissues from desiccation.
Phellogen, phellem, and phelloderm are collectively known as:
- A Bark
- B Rhytidome
- C Periderm
- D Stele
Correct answer: Periderm
Periderm is the collective term for the three layers produced by the cork cambium's activity. It replaces the epidermis as the primary protective tissue during secondary growth.
Which term refers to all tissues exterior to the vascular cambium, including secondary phloem and periderm?
- A Bark
- B Wood
- C Pith
- D Heartwood
Correct answer: Bark
Bark is a non-technical term used to describe all tissues outside the vascular cambium. It includes the secondary phloem, phelloderm, phellogen, and phellem.
Lens-shaped openings formed in the bark that permit the exchange of gases between the internal tissues and the atmosphere are called:
- A Lenticels
- B Stomata
- C Hydathodes
- D Pores
Correct answer: Lenticels
Lenticels are formed when the phellogen cuts off closely arranged parenchymatous cells instead of cork cells, which eventually rupture the epidermis. They occur in most woody trees for aeration.
In a dicot root, the vascular cambium is:
- A Completely secondary in origin
- B Primary in origin
- C Partially primary and partially secondary
- D Absent
Correct answer: Completely secondary in origin
In dicot roots, the vascular cambium is entirely secondary. It originates from the tissue located just below the phloem bundles and a portion of pericycle tissue above the protoxylem.
Secondary growth does NOT occur in which of the following?
- A Dicot stems
- B Gymnosperm stems
- C Monocot stems
- D Dicot roots
Correct answer: Monocot stems
Secondary growth is absent in monocots because they lack a vascular cambium. It is a characteristic feature mainly of dicotyledons and gymnosperms.