General Q&A for Class 12 · Page 75
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is lateral meristem and how does it differ from apical meristem?
Lateral meristem is a type of meristematic tissue located along the sides of stems and roots, responsible for increasing the girth or thickness of plant organs (secondary growth). The two main types are vascular cambium (produces secondary xylem and phloem) and cork cambium (produces protective cork tissue). Unlike apical meristems that enable vertical growth at shoot and root tips, lateral meristems facilitate horizontal expansion. This secondary growth is characteristic of
- GeneralClass 12All
How many types of cells constitute phloem and what are they?
Phloem consists of four main types of cells: Sieve tube elements: The primary conducting cells that transport sugars and organic nutrients. They are elongated, living cells arranged end-to-end with perforated end walls called sieve plates. Companion cells: Specialized parenchyma cells closely associated with sieve tube elements, providing metabolic support and controlling their function. They have den
- GeneralClass 12All
What is the cavity found in vascular bundles of monocot stems called?
The cavity found in vascular bundles of monocot stems is called a lysigenous cavity or protoxylem lacuna. This cavity forms through the breakdown and dissolution of the first-formed xylem vessels (protoxylem) as the stem matures. As the plant grows and secondary xylem develops, these early-formed vessels become stretched and eventually disintegrate, leaving behind an empty space. This characteristic feature is commonly observed in monocot stems like maize, wh
- GeneralClass 12All
Name two modified types of parenchyma and their functions
Two important modified types of parenchyma are: Chlorenchyma (Chloroplast-containing parenchyma): Contains abundant chloroplasts for photosynthesis Found in leaves (mesophyll), young stems, and other green plant parts Responsible for producing sugars and oxygen through photosynthesis Essential for the plant's energy production and food manufacturing Well-developed intercellular spaces for gas exchange </u
- GeneralClass 12All
Who is considered the father of plant anatomy?
Nehemiah Grew is widely recognized as the "father of plant anatomy." This English physician and botanist made groundbreaking contributions to plant science in the 17th century through his detailed microscopic observations of plant structures. His pioneering work, published in "The Anatomy of Plants" (1682), provided the first comprehensive descriptions of plant tissues, cells, and their arrangements. Grew's meticulous illustrations and observations laid the foundation for modern plant anatomy
- GeneralClass 12All
What is lateral meristem and what type of growth does it produce?
Lateral meristem is a type of secondary meristematic tissue located parallel to the sides of organs where it occurs, typically forming cylindrical layers in stems and roots. The two main types are vascular cambium (producing secondary xylem and phloem) and cork cambium or phellogen (producing cork tissue). Unlike apical meristems that cause primary growth (elongation), lateral meristems are responsible for secondary growth, which increases the girth or diameter of stems and roots. This growth
- GeneralClass 12All
What are modified types of parenchyma tissue?
Two important modified types of parenchyma include chlorenchyma and aerenchyma. Chlorenchyma consists of parenchyma cells containing numerous chloroplasts, specializing in photosynthesis. These cells are abundant in leaves and green stems, where they capture light energy and convert it into chemical energy. Aerenchyma is parenchyma tissue with large air spaces or lacunae between cells, facilitating gas exchange and providing buoyancy. This tissue is particularly well-developed in aquatic and
- GeneralClass 12All
What are the three most common types of collenchyma?
The three most common types of collenchyma, classified based on the pattern of cell wall thickening, are: (1) Angular collenchyma, where thickening occurs at the corners where cells meet, commonly found in stems of many herbaceous plants; (2) Lamellar (plate) collenchyma, characterized by thickening on tangential walls (walls parallel to the surface), often seen in stems of some dicots; and (3) Lacunar collenchyma, which has thickening around intercellular spaces, providing flexibility while
- GeneralClass 12All
How many types of cells constitute phloem tissue?
Phloem tissue is composed of four main types of cells, each serving distinct functions. Sieve tube elements are the primary conducting cells that transport organic nutrients throughout the plant. Companion cells are closely associated with sieve tube elements, providing metabolic support and helping regulate transport. Phloem parenchyma cells store nutrients and assist in lateral transport of materials. Phloem fibers provide mechanical strength and support to the phloem tissue. Together, thes
- GeneralClass 12All
What are sclereids and what functions do they serve?
Sclereids are a type of sclerenchyma cell characterized by thick, heavily lignified cell walls and a relatively short, irregular shape. Unlike fibers (the other type of sclerenchyma), sclereids are typically isodiametric or branched and occur in various forms including stone cells, astrosclereids, and macrosclereids. These dead cells at maturity provide mechanical support and protection to plant tissues. Sclereids are responsible for the gritty texture in pears, the hardness of seed coats, an
- GeneralClass 12All
What are the conducting tissues in plants and what do they transport?
Plants have two main conducting tissues: xylem and phloem. Xylem is responsible for transporting water and dissolved minerals from the roots upward to all parts of the plant. It consists of specialized cells including tracheids and vessel elements that form continuous tubes for efficient water conduction. Phloem, on the other hand, transports organic nutrients, particularly sugars produced during photosynthesis, from leaves to other plant parts where they're needed for growth and storage. The
- GeneralClass 12All
What is promeristem and what role does it play in plant growth?
Promeristem is the earliest, most primitive form of meristematic tissue found at the extreme tips of roots and shoots. It consists of actively dividing, self-perpetuating initial cells that give rise to all other meristematic tissues. The promeristem maintains a constant supply of undifferentiated cells while simultaneously producing derivatives that develop into primary meristems (protoderm, ground meristem, and procambium). This tissue is characterized by small, isodiametric cells with thin
- GeneralClass 12All
What does the term "meristem" mean and who coined it?
The term "meristem" refers to regions of plant tissue containing undifferentiated cells capable of continuous division and growth. These specialized tissues are responsible for plant growth throughout the plant's lifetime. The term was coined by Carl Wilhelm von Nägeli, a Swiss botanist, in 1858. Meristems are essential for both primary growth (increase in length) and secondary growth (increase in girth) in plants. They remain perpetually embryonic, producing new cells that differentiate
- GeneralClass 12All
What is plant anatomy and why is it important to study?
Plant anatomy is the study of the internal structure of plants, including their tissues, cells, and organs. This scientific field examines how different plant parts are organized at the microscopic and macroscopic levels. Studying plant anatomy is crucial for understanding how plants function, grow, and adapt to their environments. It helps botanists, agriculturalists, and researchers identify plant species, improve crop yields, develop disease-resistant varieties, and understand evolutionary
- GeneralClass 12All
What is porous wood and how does it differ from non-porous wood?
Porous wood refers to wood containing vessels (pores) visible to the naked eye or under low magnification, characteristic of dicotyledonous (hardwood) trees. These woods can be further classified as: Ring-porous wood: Large vessels concentrated in spring wood, forming distinct rings (e.g., oak, ash, elm). This arrangement provides excellent water conduction during peak growing seasons. Diffuse-porous wood: Ves
- GeneralClass 12All
What is spring wood and why is it called that?
Spring wood, also known as early wood, is the wood formed during the spring and early summer growing season when environmental conditions are optimal for growth. This type of wood is characterized by: Large vessel diameter: Cells are wider with larger lumens for efficient water conduction Thin cell walls: Less lignification compared to late wood Light color: Appears lighter
- GeneralClass 12All
In which plant is there no distinction between tunica and corpus?
The distinction between tunica and corpus is absent in gymnosperms and certain lower vascular plants. In most angiosperms (flowering plants), the shoot apical meristem shows a clear zonation into outer tunica layers (where cells divide anticlinally) and inner corpus (where cells divide in all planes). However, in gymnosperms like pine, spruce, and other conifers, the apical meristem is organized differently and doesn't show this distinct tunica-corpus arrange
- GeneralClass 12All
How many meiotic divisions are needed to produce 60 ova and 60 spermatozoa?
To produce 60 ova, 60 meiotic divisions are required because one meiotic division in females (oogenesis) produces only one functional ovum along with three polar bodies that degenerate. In contrast, to produce 60 spermatozoa, only 15 meiotic divisions are needed because one meiotic division in males (spermatogenesis) produces four functional sperm cells. Therefore, the total number of meiotic divisions required would be 75 (60 for ova + 15 for spermatozoa). This difference reflects the fundam
- GeneralClass 12All
What is the foetal ejection reflex and which hormones does the placenta produce?
The foetal ejection reflex, also known as the Ferguson reflex, is a neuroendocrine positive feedback mechanism that occurs during childbirth. When the fully developed fetus is ready for delivery, its head pushes against the cervix, triggering stretch receptors in the cervical walls. These receptors send signals to the mother's hypothalamus, which stimulates the posterior pituitary to release oxytocin. This hormone causes strong uterine contractions, which further push the fetus against the ce
- GeneralClass 12All
What are ammensalism, protocooperation, pseudocopulation, transformation, and cistron?
(a) Ammensalism: This is a biological interaction between two species where one organism is harmed or inhibited while the other remains unaffected. A classic example is when Penicillium fungus secretes antibiotics that kill bacteria while the fungus itself experiences no benefit or harm from this interaction. Another example is when large animals inadvertently trample smaller organisms without any impact on themselves. (b) Protocooperation: This is a