General Q&A for Class 12 · Page 66
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What are the two main types of sclerenchyma cells?
The two types of sclerenchyma cells are fibers and sclereids (stone cells). Fibers are long, slender cells typically found in bundles, providing tensile strength and commonly used in making ropes, textiles, and paper. Sclereids are shorter, variably shaped cells with extremely thick walls that create hardness in structures like seed coats, nutshells, and the gritty texture in fruits like pears. Both types are dead at maturity with lignified walls, but they di
- GeneralClass 12All
Which tissue transports water and minerals in plants?
Xylem tissue is responsible for transporting water and dissolved minerals from the roots upward through the plant to the stems and leaves. This complex tissue acts as the plant's plumbing system, conducting water absorbed by root hairs throughout the entire plant body. The transport occurs through specialized dead cells (tracheids and vessels) that form continuous tubes. This upward movement of water and nutrients is essential for photosynthesis, cooling the plant through tra
- GeneralClass 12All
What are the four types of cells found in xylem tissue?
Xylem consists of four distinct cell types: tracheids, vessels (tracheae), xylem parenchyma, and xylem fibers. Tracheids and vessels are dead, hollow cells that form the actual water-conducting tubes, with vessels being more efficient due to their wider diameter and perforated end walls. Xylem parenchyma cells are living cells that store food and assist in lateral transport of water. Xylem fibers are dead, thick-walled cells that provide mechanical support to the tissue. Toge
- GeneralClass 12All
In which regions of a plant is parenchyma tissue present?
Parenchyma tissue is the most widely distributed plant tissue, present in roots, stems, leaves, flowers, and fruits. It forms the bulk of ground tissue in these organs and fills spaces between specialized tissues. In leaves, parenchyma cells (especially chlorenchyma) are abundant in the mesophyll layer where photosynthesis occurs. In roots and stems, parenchyma stores nutrients and water. It's also found in the pith and cortex regions, forming packing tissue around vascular b
- GeneralClass 12All
Which plant tissue remains in an active metabolic state always?
Meristematic tissue remains in a perpetually active metabolic state. Unlike permanent tissues that differentiate and often become metabolically less active or die, meristematic cells continuously divide and maintain high metabolic activity throughout the plant's life. These cells have dense cytoplasm, prominent nuclei, and lack vacuoles, all indicating their constant readiness for division and growth. This continuous activity enables plants to grow indefinitely, produce new o
- GeneralClass 12All
Which plant cells are dead and have no intercellular spaces?
Sclerenchyma cells are dead at maturity and are tightly packed with no intercellular spaces. This compact arrangement maximizes structural support and creates a solid, impenetrable barrier. The absence of air spaces between cells, combined with their thick, lignified walls, makes sclerenchyma extremely dense and strong. This characteristic is essential for tissues that must withstand mechanical stress, provide protection, or maintain rigid structural integrity in mature plant
- GeneralClass 12All
What are the functions of phloem tissue?
Phloem performs the critical function of transporting organic nutrients, particularly sugars produced during photosynthesis, from leaves to all other parts of the plant. This process, called translocation, moves food bidirectionally—both upward and downward—depending on where nutrients are needed for growth, storage, or metabolic activities. Phloem also transports amino acids, hormones, and other organic compounds. Unlike xylem's one-way water transport, phloem's
- GeneralClass 12All
What are the dead elements of phloem?
The dead elements of phloem are phloem fibers (also called bast fibers). These thick-walled, lignified cells provide mechanical support and strength to the phloem tissue but do not participate in food transport. Unlike sieve tubes and companion cells which must remain living to transport nutrients, phloem fibers die at maturity after developing their supportive cell walls. Commercially, these fibers are valuable—jute, hemp, and flax fibers used in rope and textile produ
- GeneralClass 12All
Which cell is attached to the lateral sides of sieve tubes?
Companion cells are specialized parenchyma cells attached to the lateral sides of sieve tubes. These living, nucleated cells have dense cytoplasm and maintain a close physiological connection with sieve tube elements through numerous plasmodesmata (cytoplasmic connections). Since sieve tubes lose their nuclei at maturity, companion cells provide essential metabolic support, controlling the loading and unloading of nutrients and maintaining the functionality of the sieve tubes
- GeneralClass 12All
Give two examples of complex tissues that constitute vascular bundles in plants.
The two complex tissues forming vascular bundles are xylem and phloem. These tissues work together as an integrated transport system within plants. Xylem transports water and minerals upward from roots, while phloem distributes organic nutrients throughout the plant. In vascular bundles, these tissues are typically arranged together, often with cambium tissue between them in dicots, creating an efficient two-way transport network. This vascular system is anal
- GeneralClass 12All
What is lignin and what is its function?
Lignin is a complex organic polymer that is deposited in cell walls, making them thick, hard, and impermeable to water. This natural substance is primarily found in sclerenchyma and xylem tissues, providing rigidity and strength to plant structures. Lignification transforms flexible cellulose walls into rigid, waterproof barriers that can withstand compression and provide structural support. Lignin is crucial for allowing plants to grow tall, transport water efficiently throu
- GeneralClass 12All
What are the common names for xylem and phloem?
Xylem is commonly called wood, while phloem is referred to as bast or inner bark. These traditional names reflect the tissues' practical uses and physical locations. Xylem constitutes the hard, woody portion of stems and roots, especially in trees, providing both structural support and water transport. Phloem, located in the inner bark region, is the living tissue that transports food materials. These common
- GeneralClass 12All
What are cristae in mitochondria?
Cristae are the folded inner membranes of mitochondria that extend into the interior space (matrix). These fold-like structures significantly increase the surface area available for chemical reactions, particularly for the enzymes and proteins involved in ATP production through oxidative phosphorylation. The presence of cristae enhances the mitochondrion's efficiency in energy production by providing more space for the electron transport chain components.
- GeneralClass 12All
What are the functions of the Golgi body?
The Golgi body (Golgi apparatus) serves two primary functions: (1) Modification and packaging – it receives proteins and lipids from the endoplasmic reticulum, modifies them by adding carbohydrate groups or other molecules, and packages them into vesicles for transport, and (2) Secretion – it sorts and directs modified molecules to their correct destinations, either within the cell or for secretion outside the cell. The Golgi apparatus acts as the
- GeneralClass 12All
Which organelle controls osmotic pressure in a cell?
The vacuole controls osmotic pressure in a cell, particularly in plant cells. By regulating the concentration of dissolved substances (solutes) and water content within the vacuole, the cell can maintain appropriate osmotic pressure (turgor pressure) that keeps plant cells firm and rigid. This pressure is essential for maintaining cell structure and supporting non-woody plant tissues.
- GeneralClass 12All
Write four differences between Algae and Fungi. Four key differences between Algae and Fungi: Feature Algae Fungi 1. Nutrition Autotrophic (photosynthetic); produce their own food using chlorophyll and sunlight Heterotrophic (saprophytic or parasitic); absorb nutrients from dead organic matter or living hosts 2. Pigmentation Contain chlorophyll and other photosynthetic pigments (green, brown, or red) Lack chlorophyll; non-photosynthetic; typically white, brown, or black 3. Cell Wall Composition Cell walls primarily made of cellulose Cell walls primarily made of chitin (same material as arthropod exoskeletons) 4. Habitat & Storage Primarily aquatic (marine and freshwater); store food as starch Primarily terrestrial; prefer moist, shaded environments; store food as glycogen
Additional difference: Algae are important primary producers in aquatic ecosystems, while fungi serve primarily as decomposers in terrestrial ecosystems, playing crucial roles in nutrient cycling.
- GeneralClass 12All
In mitochondria, which portion contains specific proteins?
The cristae (inner membrane folds) of mitochondria contain specific proteins essential for ATP synthesis. These include enzymes of the electron transport chain and ATP synthase complexes. Additionally, the mitochondrial matrix contains proteins involved in the Krebs cycle and other metabolic pathways.
- GeneralClass 12All
Which cell organelle is called the digestive bag?
Lysosomes are called the digestive bags of the cell. These membrane-bound organelles contain powerful digestive enzymes (hydrolytic enzymes) that break down various cellular materials, including proteins, lipids, carbohydrates, and nucleic acids. Lysosomes digest worn-out organelles, food particles, and foreign substances that enter the cell.
- GeneralClass 12All
Why are lysosomes known as suicidal bags?
Lysosomes are known as suicidal bags because they can cause cell death (autolysis) under certain conditions. When a cell is damaged, infected, or no longer needed, lysosomal membranes may rupture, releasing digestive enzymes into the cytoplasm. These enzymes then digest the cell's own components, leading to programmed cell death. This self-destructive capability is important during development, tissue remodeling, and removing damaged cells.
- GeneralClass 12All
What are the main functions of lysosomes?
Lysosomes perform several critical functions: (1) Intracellular digestion – breaking down food particles and foreign materials engulfed by the cell, (2) Autophagy – removing and recycling damaged or worn-out cell organelles, (3) Defense mechanism – destroying bacteria and viruses that invade the cell, and (4) Cellular waste removal – digesting and eliminating metabolic waste products. These functions m