GK: Class 12 General Q&A · Page 163
3,658 free answers on GK (General) for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Name the two factors on which water potential depends? Also give its relationship with them.
Water potential (Ψ<sub>w</sub>) depends on two components: Factor Symbol Nature Effect on Ψ<sub>w</sub> Solute Potential (Osmotic Potential) <td
- GeneralClass 12All
What is turgor pressure? Give its one significance to plants.
Turgor pressure (Ψ<sub>p</sub>) is the hydrostatic pressure exerted by the cell contents (protoplast) against the rigid cell wall when water enters the cell through osmosis. Mechanism: Cell placed in hypotonic solution Water enters by osmosis Vacuole swells, protoplast pushes against cell wall Cell wall resists, creating wall pressure (equal
- GeneralClass 12All
What are the two conditions for imbibition to occur?
Imbibition is the passive absorption of water by hydrophilic colloids, causing them to swell. Two essential conditions are: Condition Explanation 1. Water Potential Gradient There must exist a water potential gradient between the
- GeneralClass 12All
What is cytoplasmic streaming? Give an example of a plant where cytoplasmic streaming can be observed.
Cytoplasmic streaming (also called cyclosis) is the continuous, automatic movement of cytoplasm within living cells. This vital process: Facilitates distribution of nutrients, organelles, and metabolites Enhances intracellular transport Requires energy from ATP and involves motor proteins (myosin) interacting with actin filaments
- GeneralClass 12All
Give shape of guard cells in dicotyledonous plants.
Guard cells in dicotyledonous plants are kidney-shaped (or bean-shaped). Their unique structure, with: Thicker inner (ventral) walls Thinner outer (dorsal) walls Radial arrangement of cellulose microfibrils ...enables the opening and closing of stomatal pores through changes in turgor pressure. Contrast: In monocots (
- GeneralClass 12All
Which means of transport occurs when sugar is loaded in phloem at the source?
Active transport is the mechanism by which sugars (primarily sucrose) are loaded into phloem sieve tube elements at the source. This process: Requires metabolic energy (ATP) Moves sugars against their concentration gradient Involves proton pumps and sucrose-H⁺ cotransporters in companion cells Evidence: Metab
- GeneralClass 12All
State the direction of movement of food in the phloem.
The direction of food movement in phloem is bidirectional, meaning it can move: Upwards (from roots to shoots during early spring when stored food is mobilized) Downwards (from leaves to roots, stems, fruits during active photosynthesis) Key Concept: Movement is from source (site of synthesis or storage) to sink (site of utilization or
- GeneralClass 12All
What happens to the water potential of a solution when more solute is added to it?
When more solute is added to a solution, its water potential decreases (becomes more negative). This occurs because: Solute particles reduce the free energy of water molecules The solute potential (Ψ<sub>s</sub>) becomes more negative Since Ψ<sub>w</sub> = Ψ<sub>s</sub> + Ψ<sub>p</sub>, a decrease in Ψ<sub>s</sub> decreases Ψ
- GeneralClass 12All
Give net direction of water movement in a plant cell in flaccid state.
In a flaccid cell, there is no net movement of water. The cell is in equilibrium with its surroundings, meaning: Water potential inside the cell (Ψ<sub>w</sub>) = Water potential outside the cell Ψ<sub>w</sub> = 0 Endosmosis (water entering) = Exosmosis (water leaving) Condition: Flaccid cells are neither turgid nor plasmolyzed
- GeneralClass 12All
Give an example of region in plants where negative pressure potential is found.
Xylem vessels exhibit negative pressure potential (also called tension) during transpiration. This negative pressure, generated by water loss from leaves, creates a transpiration pull that draws water upward from roots through the xylem. Numerical Context: During active transpiration, xylem pressure can reach values as low as -2 MPa or lower.
- GeneralClass 12All
Define antiport.
In facilitated diffusion, when two different molecules or ions move across a membrane in opposite directions simultaneously through a transport protein, the mechanism is called antiport. Example: The Na⁺/H⁺ antiporter exchanges sodium ions for hydrogen ions across the plasma membrane. Transport Type </
- GeneralClass 12All
What is the membrane of vacuole called?
The membrane surrounding the vacuole is called the tonoplast. This selectively permeable membrane regulates the movement of ions and molecules between the cytoplasm and the vacuolar sap, maintaining turgor pressure and cellular homeostasis.
- GeneralClass 12All
Explain plasmodesmata.
Plasmodesmata (singular: plasmodesma) are microscopic protoplasmic connections that traverse the cell walls of adjacent plant cells. These channels facilitate intercellular communication and transport by creating a continuous cytoplasmic network called the symplast. Plasmodesmata allow the passage of: Water Ions Small molecules Regulatory proteins and RNA </u
- GeneralClass 12All
What is mycorrhiza?
A mycorrhiza is a symbiotic association between a fungus and the root system of a higher plant. This mutualistic relationship benefits both organisms: the fungus receives organic nutrients (sugars) from the plant, while the plant gains enhanced absorption of water and minerals (especially phosphorus) through the extensive fungal hyphae network. Mycorrhizae are classified into ectomycorrhizae and endomycorrhizae</stron
- GeneralClass 12All
What happens to the somatic cell if its surface area to volume ratio decreases?
When the surface area-to-volume ratio decreases (cell becomes too large), the cell undergoes mitosis to restore optimal size and maintain efficient nutrient/waste exchange. Explanation: Larger cells have insufficient surface area for diffusion Cell division maintains nucleocytoplasmic ratio Critical for cellular homeostasis
- GeneralClass 12All
Define cell plate.
The cell plate is a precursor structure formed during plant cytokinesis that develops into the middle lamella separating two daughter cells. Explanation: Composed of pectin and cellulose Delivered by Golgi vesicles Grows centrifugally to meet parental cell walls
- GeneralClass 12All
What are the four major stages of karyokinesis?
Prophase, Metaphase, Anaphase, Telophase Explanation: Stage Key Events Prophase Chromatin condensation, nuclear envelope breakdown Metaphase
- GeneralClass 12All
What is M phase? Which two processes are involved during M phase?
M phase (Mitotic phase) is the stage where actual cell division occurs. It consists of: Karyokinesis – Division of the nucleus Cytokinesis – Division of the cytoplasm Explanation: Karyokinesis includes prophase, metaphase, anaphase, telophase Cytokinesis physically separates two daughter cells M phase acco
- GeneralClass 12All
What is meant by metaphasic plate?
The metaphase plate (also called the equatorial plate) is the imaginary plane at the cell's equator where chromosomes align during metaphase. Explanation: Chromosomes attach to spindle fibres via kinetochores Ensures equal segregation of sister chromatids/chromosomes Critical checkpoint: spindle assembly checkpoint v
- GeneralClass 12All
Write the names of two cells which do not divide after attaining fully differentiated state.
Red blood cells (RBCs) and nerve cells (neurons) Explanation: RBCs (erythrocytes): Lack a nucleus in mammals; cannot undergo mitosis Neurons: Enter G₀ phase (quiescent state) after differentiation; remain in non-dividing state These cells are considered terminally differentiated.