Which plant hormone actively stimulates the closure of stomata during severe water stress?
- Cytokinin
- Abscisic acid
- Gibberellic acid
- Indole acetic acid
Explanation: Abscisic acid (ABA) acts as a stress hormone, signaling guard cells to lose turgor and close stomatal pores during drought conditions.
The system of interconnected protoplasts linked by plasmodesmata throughout the plant is the:
- Apoplast pathway
- Vacuolar pathway
- Transmembrane pathway
- Symplast pathway
Explanation: The symplastic system is the continuous network of living cell cytoplasm that is connected from cell to cell via plasmodesmata.
Facilitated diffusion requires the presence of highly specific membrane:
- Cholesterol molecules
- Lipid bilayers
- Transport proteins
- Carbohydrate chains
Explanation: Facilitated diffusion relies on specific transmembrane proteins (channels or carriers) to help hydrophilic molecules cross the lipid bilayer.
The widely accepted mechanism explaining the translocation of sugars from source to sink is:
- Active transport theory
- Root pressure theory
- Cohesion tension theory
- Pressure flow hypothesis
Explanation: The mass flow or pressure flow hypothesis is the accepted mechanism for the translocation of sugars from source to sink via phloem.
Many minerals are actively transported into root epidermal cells against their established:
- Concentration gradient
- Pressure gradient
- Temperature gradient
- Gravity vector
Explanation: Because soil mineral concentrations are often lower than inside the root, minerals must be actively absorbed against the concentration gradient.
The specialized water channels present in plant cell membranes are primarily made of:
- Sterols
- Aquaporins
- Lipids
- Carbohydrates
Explanation: Aquaporins are highly specific integral membrane proteins that serve as channels to rapidly facilitate the transport of water across cell membranes.
At standard atmospheric pressure, the water potential of a solution is exactly equal to its:
- Solute potential
- Osmotic pressure
- Matric potential
- Pressure potential
Explanation: If a solution is at atmospheric pressure (zero pressure potential), its overall water potential is dictated entirely by its solute potential.
The water potential of pure water at standard temperature and pressure is strictly:
- Always positive
- Always infinite
- Always negative
- Always zero
Explanation: By convention, the water potential of pure water at standard temperature, which is not under any pressure, is taken to be zero.
Before leaf fall, highly mobile elements like nitrogen and phosphorus are salvaged and exported to:
- Root caps
- Bark tissues
- Dead heartwood
- Growing regions
Explanation: Plants salvage mobile nutrients from senescing (aging) leaves and transport them to younger, growing regions or storage organs.
Seeds of which plant fail to germinate and establish without a mycorrhizal association?
Explanation: Pinus seeds have an obligate association with mycorrhizae and cannot germinate or establish themselves without the presence of the symbiotic fungus.
Guttation typically occurs through specialized pores at the leaf margins known as:
- Trichomes
- Stomata
- Hydathodes
- Lenticels
Explanation: Hydathodes are specialized pore structures located at the tips and margins of leaves through which guttation exudate is released.
Plasmolysis is physically characterized by the shrinking of the plant protoplast away from the:
- Tonoplast
- Plasma membrane
- Cell wall
- Nuclear envelope
Explanation: When placed in a hypertonic solution, water exits the cell, causing the cell membrane and protoplast to physically shrink away from the rigid cell wall.
Phloem sap primarily consists of water and which translocated organic sugar?
- Glucose
- Maltose
- Fructose
- Sucrose
Explanation: Sucrose is a non-reducing, chemically stable disaccharide, making it the ideal form for carbohydrate transport through the phloem.
The swelling of dry wooden doors during the rainy season is a classic example of:
- Plasmolysis
- Imbibition
- Osmosis
- Active transport
Explanation: Imbibition is a special type of diffusion where water is absorbed by solid colloids (like wood or seeds), causing them to swell enormously in volume.
The classic botanical experiment used to identify the tissue responsible for downward food transport is the:
- Girdling experiment
- Plasmolysis experiment
- Potometer experiment
- Bell jar experiment
Explanation: Removing a ring of bark (containing phloem) stops downward sugar transport, causing swelling above the cut, proving phloem translocates food.
Transpiration actively cools the leaf surfaces, sometimes lowering the temperature by:
- Twenty to thirty
- Fifty degrees
- One to two
- Ten to fifteen
Explanation: The evaporative cooling effect of transpiration can lower the temperature of leaf surfaces by 10 to 15 degrees Celsius.
The phenomenon of guttation is most prominently observed during the:
- Hot dry afternoon
- Midday bright sunlight
- Early morning hours
- Windy evening hours
Explanation: Guttation occurs under conditions of high root pressure and low evaporation rates, which are typically found at night or during early morning hours.
The water-impermeable waxy material deposited in the Casparian strip is called:
- Cellulose
- Pectin
- Suberin
- Lignin
Explanation: Suberin is a highly hydrophobic, waxy polymer deposited in the Casparian strips of the endodermis, preventing the apoplastic flow of water.
Symbiotic association of a fungus with a root system aiding in water absorption is:
- Rhizobium
- Lichen
- Nodules
- Mycorrhiza
Explanation: A mycorrhiza is a mutualistic symbiotic association between a fungus and the roots of a higher plant, vastly expanding the surface area for water and mineral absorption.
The physical process by which water is absorbed by solid colloids causing them to swell is:
- Active transport
- Imbibition
- Osmosis
- Plasmolysis
Explanation: Imbibition is a special type of diffusion where water is absorbed by solids (like seeds or wood), causing an enormous increase in volume.
The opening and closing of stomata are primarily regulated by the cellular influx of:
- Potassium ions
- Sodium ions
- Chloride ions
- Calcium ions
Explanation: The active accumulation of potassium ions (K+) into guard cells lowers their water potential, causing water to enter, making them turgid and opening the stomata.
The symplastic movement of water occurs from cell to cell directly through cytoplasmic bridges called:
- Aquaporins
- Casparian strips
- Desmosomes
- Plasmodesmata
Explanation: The symplast pathway involves water traveling through the living cytoplasm, moving between adjacent cells via connecting plasmodesmata.
High tensile strength and capillarity allow water to ascend efficiently through narrow xylem tubes called:
- Sieve tubes
- Companion cells
- Lenticels
- Tracheary elements
Explanation: Tracheids and vessel elements (tracheary elements) are narrow, allowing water to rise via capillary action against gravity.
Fungi intimately associated with plant roots that heavily enhance water and phosphorus uptake form a:
- Mycorrhiza
- Root nodule
- Bacteroid
- Lichen
Explanation: A mycorrhiza is a mutualistic symbiotic relationship where fungal hyphae drastically increase the root's surface area for absorbing water and minerals like phosphorus.
Root pressure is primarily responsible for which observable phenomenon in plants?
- Guttation
- Photosynthesis
- Phloem loading
- Transpiration
Explanation: Positive root pressure forces water up the stem and out through leaf margins in liquid form, an observable phenomenon known as guttation.
Stomatal opening is primarily driven by the active cellular accumulation of:
- Sodium ions
- Potassium ions
- Calcium ions
- Chloride ions
Explanation: The active influx of potassium ions into guard cells lowers their water potential, drawing water in and causing the stomata to open.
C4 plants are considered more efficient than C3 plants because they uniquely lose:
- No water lost
- Double the water
- Half the water
- Equal water amount
Explanation: An evolutionary advantage of C4 plants is that they lose only half as much water as C3 plants for the same amount of CO2 fixed.
The chemical form in which carbohydrates are primarily transported through the phloem is:
- Glycogen
- Glucose
- Sucrose
- Starch
Explanation: While glucose is synthesized in leaves, it is converted into the non-reducing disaccharide sucrose for efficient and stable transport through the phloem.
Water exudation in the form of liquid droplets from leaf margins is famously known as:
- Guttation
- Bleeding
- Evaporation
- Transpiration
Explanation: Guttation is the loss of water in its liquid phase, typically observed early in the morning when root pressure is high.
If a plant cell's overall volume remains unchanged in a solution, the external solution is:
- Saturated
- Isotonic
- Hypotonic
- Hypertonic
Explanation: In an isotonic solution, the osmotic pressure perfectly matches the cytoplasm, resulting in zero net movement of water and no volume change.
The attraction of water molecules to polar surfaces like tracheary elements is called:
- Cohesion
- Imbibition
- Transpiration
- Adhesion
Explanation: Adhesion refers to the attraction of water molecules to solid polar surfaces, such as the walls of xylem vessels and tracheids.
When a plasmolysed cell is placed in pure water, the shrinking process is reversed, termed:
- Guttation
- Imbibition
- Deplasmolysis
- Exosmosis
Explanation: Placing a plasmolysed cell in a hypotonic solution causes endosmosis; the protoplast swells back against the cell wall in a process called deplasmolysis.
Which essential element is structurally immobile and typically not relocated from senescing leaves?
- Phosphorus
- Potassium
- Calcium
- Nitrogen
Explanation: Calcium is an integral component of the middle lamella (cell wall) and is structurally immobile, remaining in older leaves when they fall.
Water loss in its liquid phase from the margins of herbaceous leaves is termed:
- Evaporation
- Exudation
- Transpiration
- Guttation
Explanation: Unlike transpiration which is water loss as vapor, guttation is the loss of water in its liquid phase.
The strong cohesive force between water molecules is essential for maintaining the continuous water column during:
- Active absorption
- Root pressure generation
- Phloem loading
- Transpiration pull
Explanation: Cohesion (water-water attraction) ensures that the massive transpirational pull does not break the continuous water column in the xylem.
The structural adaptation that completely blocks the apoplastic flow of water in the root is the:
- Pericycle
- Epidermis
- Vascular cambium
- Casparian strip
Explanation: The Casparian strip in the endodermis is impregnated with water-impermeable suberin, forcing water to enter the symplast pathway.
The addition of solutes to pure water causes its overall water potential to become:
- Remains zero
- More positive
- More negative
- Highly unpredictable
Explanation: All solutions have a lower water potential than pure water due to the presence of dissolved solutes, making their water potential negative.
Movement of substances across a membrane from higher to lower concentration using specific protein channels without ATP is called:
- Active transport
- Simple diffusion
- Osmosis
- Facilitated diffusion
Explanation: Facilitated diffusion involves specialized membrane proteins that allow specific molecules to pass down their concentration gradient without the expenditure of ATP.
In tall canopy trees, the primary driving force pulling massive amounts of water upwards is:
- Capillarity
- Imbibition
- Transpiration pull
- Root pressure
Explanation: According to the cohesion-tension theory, the evaporative loss of water from leaves creates a strong negative pressure (transpiration pull).
The primary sinks actively demanding mineral elements in a plant are the apical and lateral:
- Bark tissues
- Meristems
- Mature leaves
- Xylem vessels
Explanation: Actively dividing tissues, such as the apical and lateral meristems, young leaves, and developing fruits, act as the primary sinks for translocated minerals.
Which classic experiment conclusively proved that phloem is responsible for food transport?
- Girdling experiment
- Bell jar experiment
- Potometer experiment
- Chromatography experiment
Explanation: The girdling (or ringing) experiment involves removing a ring of bark (containing phloem) from a trunk, causing swelling above the ring, proving phloem transports food downwards.
Porins are massive protein channels primarily found forming large pores in the outer membranes of:
- Plastids and mitochondria
- Lysosomes and peroxisomes
- Nuclei and vacuoles
- Golgi and ER
Explanation: Porins form huge pores in the outer membranes of plastids, mitochondria, and some bacteria, allowing molecules up to the size of small proteins to pass.
The continuous network of cell walls and intercellular spaces in plants constitutes the:
- Apoplast pathway
- Symplast pathway
- Transmembrane pathway
- Tonoplast pathway
Explanation: The apoplast is the system of adjacent cell walls that is continuous throughout the plant, except at the Casparian strips of the endodermis.
The mutual physical attraction between water molecules is biologically defined as:
- Cohesion
- Adhesion
- Capillarity
- Surface tension
Explanation: Cohesion is the strong intermolecular attraction between water molecules, giving the water column high tensile strength in the xylem.
Which property of water gives it high tensile strength in the xylem column?
- High freezing point
- Cohesion and adhesion
- Low heat capacity
- High specific heat
Explanation: The physical properties of cohesion (water-water attraction) and adhesion (water-vessel attraction) give the water column high tensile strength to resist pulling forces.
If the external surrounding solution is more dilute than the cell cytoplasm, it is termed:
- Isotonic
- Hypotonic
- Concentrated
- Hypertonic
Explanation: A hypotonic solution has a higher water potential (lower solute concentration) than the cytoplasm, causing water to diffuse into the cell.
The primary driving force for the upward movement of water in tall trees is:
- Capillary action
- Root pressure
- Transpiration pull
- Imbibition force
Explanation: The Cohesion-Tension theory states that the massive upward movement of water in tall trees is primarily driven by the transpirational pull from the leaves.
In xylem tissue, the transport of water and essential minerals is strictly:
- Unidirectional
- Bidirectional
- Circular
- Multidirectional
Explanation: Transport in the xylem is always unidirectional, moving strictly upwards from the roots to the stems and leaves.
Guttation is fundamentally driven by the physiological phenomenon of:
- Positive root pressure
- Transpiration pull
- Capillary action
- Imbibition force
Explanation: Positive root pressure, generated by active mineral absorption in the roots, pushes water up herbaceous stems, causing guttation.
In plant physiology, water potential is conventionally denoted by the Greek symbol:
Explanation: Water potential is represented by the Greek letter Psi and is expressed in pressure units such as Pascals (Pa).
Water moves into the hypertonic phloem sieve tubes at the source primarily by:
- Capillary action
- Active transport
- Osmosis
- Facilitated diffusion
Explanation: The high sucrose concentration (hypertonic state) in the phloem draws water from the xylem by osmosis, generating a high hydrostatic pressure.
Unlike xylem, the transport of organic food within the phloem is normally:
- Strictly upward
- Non directional
- Bidirectional
- Unidirectional
Explanation: Since the source-sink relationship is variable depending on the season or plant's needs, phloem transport is bidirectional.
The widely accepted mechanism explaining the massive translocation of sugars is the:
- Active transport theory
- Cohesion tension theory
- Root pressure theory
- Pressure flow hypothesis
Explanation: The pressure flow (or mass flow) hypothesis explains that sugars are translocated from source to sink driven by an osmotic pressure gradient.
If a plant cell is placed in a hypertonic solution, the cell will undergo:
- Active transport
- Deplasmolysis
- Plasmolysis
- Imbibition
Explanation: In a hypertonic solution, water moves out of the cell due to exosmosis, causing the protoplast to shrink away from the cell wall, a process called plasmolysis.
The active loading of sucrose into the phloem creates a local condition that is highly:
- Neutral
- Isotonic
- Hypotonic
- Hypertonic
Explanation: Loading sucrose into sieve tubes requires ATP and creates a hypertonic condition, which draws water into the phloem from the adjacent xylem.
The apoplast pathway of water movement is completely blocked in the endodermis by the:
- Tonoplast
- Epidermis
- Casparian strip
- Plasmodesmata
Explanation: The endodermis contains a band of water-impermeable waxy matrix called the Casparian strip, which forces water to enter the symplast pathway.
The inner wall of a guard cell facing the stomatal pore is uniquely:
- Thin and elastic
- Thin and rigid
- Thick and rigid
- Thick and elastic
Explanation: As stated in NCERT, the inner wall facing the pore is thick and elastic, allowing it to curve outward when turgid and regain its original shape when turgor is lost.
In a fully turgid plant cell, the exact value of the water potential is:
- Equal to zero
- Highly negative
- Highly positive
- Always variable
Explanation: In a fully turgid cell, the positive pressure potential exactly balances the negative solute potential, bringing the total water potential to zero.
To effectively open the stomatal pore, guard cells must absorb water and become:
- Desiccated
- Highly plasmolysed
- Fully flaccid
- Fully turgid
Explanation: When water enters the guard cells, they become fully turgid; their thin outer walls bulge outward, pulling the thick inner walls apart.
The initial loading of sucrose into sieve tube elements at the source requires:
- ATP energy
- Passive diffusion
- Osmosis
- Capillary action
Explanation: Phloem loading is an active transport process. Sucrose is moved into the companion cells and then into the sieve tube elements against a concentration gradient using ATP.