General Q&A for Class 12 · Page 72
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is the cavity found in vascular bundles of monocot stems?
The cavity found in vascular bundles of monocot stems is called a lysigenous cavity or protoxylem lacuna. This cavity forms in the position where the first-formed xylem elements (protoxylem) were located. As the stem matures, these early xylem vessels, which developed when the stem was still elongating, become stretched, crushed, and eventually disintegrate, leaving behind an air-filled space. This lysigenous cavity is created by the breakdown and dissolution of protoxylem cells rather than b
- GeneralClass 12All
What is the endodermis of the root and what is its function?
The endodermis is a specialized single layer of cells that forms the innermost boundary of the cortex in roots, surrounding the vascular cylinder (stele). These barrel-shaped cells are characterized by the presence of Casparian strips—bands of suberin and lignin deposited in the radial and transverse walls. The endodermis functions as a selective barrier, controlling the movement of water and dissolved minerals from the cortex into the vascular tissue. The Casparian strips force all sub
- GeneralClass 12All
Which layer is the most active in dicot roots?
The pericycle is the most active layer in dicot roots. This single layer of parenchymatous cells lies just inside the endodermis and surrounds the vascular tissue. The pericycle retains its meristematic potential throughout the life of the root, making it highly active. Its primary functions include: initiating lateral root formation (branch roots originate from pericycle cells), contributing to secondary growth by forming part of the vascular cambium in roots that undergo secondary thickenin
- GeneralClass 12All
How do you predict future population size using r?
Predicting future population size requires the exponential growth equation: Nt = N0 × e^(rt), where Nt is the population at time t, N0 is the initial population, e is Euler's number (approximately 2.718), r is the intrinsic rate of increase, and t is the time period. For instance, with June beetles starting at 3,000 individuals, 400 births and 150 deaths per month (giving r = 250/3000 = 0.083 per month), the population after 6 months would be: N6 = 3,000 ×
- GeneralClass 12All
How do you calculate the intrinsic rate of increase (r) from population data?
Calculating r depends on the type of data you have available. When you know births and deaths over a specific period, use: r = (births - deaths) / (population size × time period). This gives you the per capita growth rate. When you have population counts at two time points, use the exponential growth formula: r = ln(final population / initial population) / time elapsed. For example, if marine algae increase from 100,000 cells to 500,000 cells in
- GeneralClass 12All
What is spring wood and what is its other name?
Spring wood, also called early wood, is the wood formed during the beginning of the growing season, typically in spring. This wood is characterized by larger xylem vessels with wider cavities and thinner walls, produced when conditions favor rapid growth and abundant water is available. The larger vessels allow for efficient water transport to support the burst of growth in spring. Spring wood appears lighter in color compared to summer wood (late wood) and is less dense. The alternation of s
- GeneralClass 12All
What is the difference between exponential and logistic growth?
Exponential growth and logistic growth represent two fundamental patterns of population change. Exponential growth occurs when a population increases at a constant percentage rate without environmental constraints, following the formula dN/dt = rN. This creates a J-shaped curve where growth accelerates continuously. In nature, exponential growth typically occurs when populations are small, resources are abundant, or species colonize new habitats. Logistic grow
- GeneralClass 12All
How do you calculate doubling time for a population?
Doubling time is the period required for a population to double in size, and it's directly related to the intrinsic rate of increase (r). The formula is remarkably simple: doubling time = ln(2) / r, which equals approximately 0.693 / r. For instance, if an annual plant population like Nicotiana increases by 12% per year (r = 0.12), the doubling time would be 0.693 / 0.12 = approximately 5.78 years. This means the population will double roughly every 5
- GeneralClass 12All
What is the intrinsic rate of increase (r) in population ecology?
The intrinsic rate of increase (r) is a fundamental measure in population ecology that represents how quickly a population grows under ideal conditions. It indicates the per capita rate of change in population size, accounting for both births and deaths. When r is positive, the population is growing; when negative, it's declining; and when zero, the population remains stable. To calculate r, you can use the formula: r = (births - deaths) / population size for a given
- GeneralClass 12All
What is porous wood and what are its characteristics?
Porous wood is wood that contains vessels (characteristic of angiosperms/hardwoods) with relatively large diameters, creating a porous appearance when viewed in cross-section. Porous wood is further classified into ring-porous wood and diffuse-porous wood. Ring-porous wood (found in oak, ash, and elm) has large vessels concentrated in the early wood, forming distinct rings, while diffuse-porous wood (found in maple, birch, and poplar) has vessels of relatively uniform size distributed fairly
- GeneralClass 12All
What alkaloid is found in the latex of poppy (Papaver somniferum)?
The latex of poppy (Papaver somniferum) contains morphine and other related alkaloids belonging to the phenanthrene class of alkaloids. These alkaloids also include codeine, thebaine, and papaverine. Morphine is the principal alkaloid and is one of the most potent naturally occurring analgesics (pain relievers). The latex, obtained by making incisions in the unripe seed capsules, dries to form opium, which has been used medicinally and recreationally for thousands of years. These alk
- GeneralClass 12All
What is a tylosoid and where is it found?
A tylosoid is an intrusion of a parenchyma cell into the cavity of a vessel or tracheid in xylem tissue. The statement should actually read "tylosis" (not "tylosoid"). Tyloses (plural) are bladder-like outgrowths from adjacent parenchyma cells that protrude through pit cavities into the lumens of vessels or tracheids. They form when parenchyma cells adjacent to vessels grow through pit pairs and expand into the vessel cavity. Tyloses serve several functions: they can block water movement thro
- GeneralClass 12All
Does the root of Trapa contain diarch xylem?
False. The root of Trapa (water chestnut) does not contain diarch xylem (two strands of protoxylem). Instead, Trapa roots are typically tetrarch or polyarch, meaning they have four or more protoxylem groups. Aquatic and semi-aquatic plants like Trapa often show polyarch conditions to facilitate efficient water and nutrient absorption from their aquatic environment. The number of protoxylem groups (xylem ridges) in a root is an important diagnostic feature used in pl
- GeneralClass 12All
Do monocot stems show secondary growth?
False (generally). The vast majority of monocot stems do not exhibit secondary growth because they lack vascular cambium, the lateral meristem responsible for producing secondary xylem and phloem. However, a few exceptional monocots do show secondary growth, making the statement "few monocot stems show secondary growth" true. Examples include certain palms (like Dracaena and Yucca), bamboos, and some members of the Agave family. These exceptional monocots have evolved altern
- GeneralClass 12All
Does Ficus leaf contain a multilayered epidermis?
True. Ficus (fig) leaves contain a multilayered epidermis, also called multiple epidermis or hypodermis. This specialized adaptation consists of several layers of cells beneath the outer epidermis, providing additional protection and support. The multilayered epidermis in Ficus serves multiple functions: it offers extra mechanical strength to the leaf, provides protection against excessive water loss in dry conditions, offers defense against pathogen invasion, and may help in light reflection
- GeneralClass 12All
Do isobilateral leaves have well-differentiated mesophyll tissue?
False. Isobilateral leaves do not have well-differentiated mesophyll tissue into distinct palisade and spongy layers. In isobilateral leaves (found in many monocots and some xerophytes), the mesophyll is uniform in structure, with palisade-like cells arranged on both the upper and lower surfaces of the leaf, or with spongy mesophyll throughout. This contrasts with dorsiventral (bifacial) leaves, which have distinct palisade mesophyll on the upper surface and spongy mesophyll on the lower surf
- GeneralClass 12All
When a ball is thrown up, the magnitude of its momentum first decreases and then increases. Does this violate the conservation of momentum principle?
No, here momentum of the ball is not conserved as weight of the ball is acting on it.
- GeneralClass 12All
Which type of alkaloid is found in the latex of poppy (Papaver somniferum)?
The latex of poppy (Papaver somniferum) contains morphine and related opiate alkaloids including codeine, thebaine, and papaverine. Morphine is the most abundant and medically significant alkaloid, comprising about 10-15% of the opium latex by dry weight. These alkaloids are stored in specialized latex-producing cells called laticifers found throughout the plant's tissues. When the unripe seed capsules are incised, a milky latex (opium) oozes out and dries into a bro
- GeneralClass 12All
What is the most active layer of a dicot root?
The pericycle is considered the most active layer in a dicot root. This single layer of parenchyma cells is located just inside the endodermis and surrounds the vascular tissue. The pericycle is remarkable for retaining its meristematic capability and performs several crucial functions: Lateral root formation: Initiates and produces lateral (branch) roots through periclinal divisions Vascular cambium formation: Contri
- GeneralClass 12All
In a thermodynamic process, 400 J of heat is given to a gas and 100 J of work is also done on it. What is the change in the internal energy of the gas?
ΔU = 400 – (–100) J = 500 J