Select the correct answer:
1. Chlorosis does not occur due to the deficiency of:
A) sulphur
B) magnesium
C) phosphorus
D) calcium
Answer: D) calcium
Explanation: Chlorosis (yellowing of leaves) is typically caused by deficiencies in magnesium, nitrogen, iron, or sulphur, which are needed for chlorophyll synthesis. Calcium deficiency usually causes other symptoms like stunted growth and necrosis of young leaves.
2. Most of the uptake of water and minerals from soil takes place through:
A) epidermal cells
B) root cap
C) root
D) root hair
Answer: D) root hair
Explanation: Root hairs are extensions of epidermal cells that greatly increase the surface area for absorption of water and minerals.
3. The sugar moves through phloem is mostly in the form of:
A) glucose
B) sucrose
C) maltose
D) lactose
Answer: B) sucrose
Explanation: Sucrose is the main transport sugar in plants because it is non-reducing and chemically stable, allowing it to be transported in high concentrations without being metabolized.
4. Which category of plants stores a small amount of water and has a thin cuticle?
A) Hydrophytes
B) Xerophytes
C) Mesophytes
D) Succulents
Answer: C) Mesophytes
Explanation: Mesophytes live in moderate environments with adequate water. They do not need to store large amounts of water or have thick cuticles like xerophytes, nor do they have reduced cuticles like hydrophytes.
5. What is a key role of leaves in managing waste in plants?
A) Storing waste materials
B) Producing chlorophyll
C) Absorbing water from the soil
D) Converting waste into energy
Answer: A) Storing waste materials
Explanation: Leaves can store waste materials (e.g., calcium oxalate crystals, resins, gums). When leaves senesce (age) and fall off, these wastes are removed from the plant.
6. When the rate of photosynthesis become equal to that rate of respiration in the plant body, which of the following pattern of
gaseous exchange occurs between plant and its environment:
A) Carbon dioxide is absorbed, and oxygen is released
B) Oxygen is absorbed, and carbon dioxide is released
C) Both carbon dioxide and oxygen are absorbed
D) Neither carbon dioxide nor oxygen are absorbed
Answer: D) Neither carbon dioxide nor oxygen are absorbed
Explanation: When photosynthesis and respiration rates are equal (compensation point), the amount of CO₂ released by respiration equals the amount used by photosynthesis, and the amount of O₂ released by photosynthesis equals the amount used by respiration. There is no net gas exchange.
7. What is the role of companion cells in the translocation process?
A) They store excess solutes in the phloem
B) They help regulate water potential in the xylem
C) They actively transport sugars into the phloem's sieve tube elements
D) They assist in the absorption of water by roots
Answer: C) They actively transport sugars into the phloem's sieve tube elements
Explanation: Companion cells are metabolically active and provide ATP for the active loading of sucrose into the sieve tube elements.
8. What drives the translocation of organic solutes in plants?
A) Differences in sugar concentration
B) Differences in leaf size
C) Differences in root structure
D) Differences in stem length
Answer: A) Differences in sugar concentration
Explanation: Translocation is driven by a pressure gradient created by differences in sugar concentration between the source (where sugar is produced) and the sink (where sugar is used or stored).
9. According to the TACT theory, what are the four factors that work together to move water and minerals up a plant?
A) Temperature, humidity, sunlight, and soil type
B) Transpiration pull, Adhesion, Cohesion, and Tension
C) Stomata, xylem, phloem, and roots
D) Leaves, stems, roots, and flowers
Answer: B) Transpiration pull, Adhesion, Cohesion, and Tension
10. What drives the bulk flow of water to the top of the plant according to the TACT theory?
A) Root pressure
B) Soil moisture
C) Solar energy from photosynthesis
D) Transpiration from the leaves
Answer: D) Transpiration from the leaves
Explanation: Transpiration creates a negative pressure (tension) that pulls water up the xylem.
1. Why gardeners like to use autumn leaves in their soil?
Answer: Gardeners like to use autumn leaves in their soil because they are a valuable source of organic matter. When leaves decompose, they release nutrients like nitrogen, phosphorus, and potassium back into the soil. They also improve soil structure, aeration, and water retention. Leaf mold (decomposed leaves) is an excellent soil conditioner. Additionally, using autumn leaves is a sustainable way to recycle garden waste and reduce landfill.
2. What is the effect of temperature on the rate of transportation?
Answer: Temperature significantly affects the rate of transpiration. As temperature increases, the kinetic energy of water molecules increases, causing them to evaporate more rapidly from the leaf surface. This increases the rate of transpiration. Higher temperatures also decrease relative humidity, which increases the water potential gradient, further increasing transpiration. However, extremely high temperatures can cause stomatal closure to conserve water, reducing transpiration.
3. Write any three osmotic adjustments in hydrophytes.
Answer: Hydrophytes (aquatic plants) show several osmotic adjustments:
1. Reduced Cuticle: They have a thin or absent cuticle, allowing water to enter directly.
2. High Solute Concentration: They maintain high internal solute concentrations to lower water potential and absorb water efficiently.
3. Aerenchyma: They have air-filled tissues (aerenchyma) for buoyancy and gas exchange.
4. Weak Root System: Roots are often reduced or absent as water is absorbed over the entire surface.
4. What is the pattern of gas exchange between plant and environment at the time of dawn and dusk?
Answer: At dawn and dusk, the rate of photosynthesis is low because light intensity is low. Respiration continues at a constant rate. Therefore, the net gas exchange is dominated by respiration: the plant absorbs oxygen (O₂) and releases carbon dioxide (CO₂). At
dawn, as light increases, photosynthesis gradually increases. At dusk, as light decreases, photosynthesis decreases. At the compensation point (when photosynthesis equals respiration), there is no net gas exchange.
5. Write any three osmotic adjustments in hydrophytes. (Repeat of Question 3)
6. What is the pattern of gas exchange between plant and environment at the time of dawn and dusk? (Repeat of Question 4)
7. White plants absorb carbon dioxide and release oxygen during daytime. (This statement is incorrect. White plants lack chlorophyll and cannot photosynthesize. They would only respire, absorbing O₂ and releasing CO₂. Green plants absorb CO₂ and release O₂ during daytime.)
8. Define following terms:
i. Osmotic adjustment:
Answer: Osmotic adjustment is the process by which cells accumulate solutes (e.g., ions, sugars, amino acids) to lower their internal water potential, allowing them to absorb water from the environment or maintain turgor pressure under stress conditions.
ii. Transpiration:
Answer: Transpiration is the loss of water vapor from the aerial parts of a plant, primarily through stomata in the leaves.
iii. Translocation:
Answer: Translocation is the transport of organic solutes (mainly sucrose) through the phloem from a source (where sugar is produced) to a sink (where sugar is used or stored).
iv. Micronutrients:
Answer: Micronutrients are essential elements required by plants in very small amounts (e.g., iron, manganese, zinc, copper, boron, molybdenum, chlorine).
v. Excretophores:
Answer: Excretophores are specialized structures or organs in plants where waste products are stored or excreted (e.g., leaves, bark, roots).
vi. Vascular bundle:
Answer: A vascular bundle is a strand of conducting tissue in plants, containing both xylem and phloem.
vii. Xylem:
Answer: Xylem is the vascular tissue that transports water and minerals from roots to the rest of the plant and provides structural support.
viii. Adhesion:
Answer: Adhesion is the attraction between water molecules and other substances (e.g., the walls of xylem vessels).
ix. Cohesion:
Answer: Cohesion is the attraction between water molecules due to hydrogen bonding, which helps maintain a continuous water column in the xylem.
9. Write the difference between:
Answer: Macronutrients are required in large amounts (e.g., N, P, K, Ca, Mg, S). Micronutrients are required in trace amounts (e.g., Fe, Mn, Zn, Cu, B, Mo, Cl).
Answer: Hydrophytes are adapted to aquatic environments (thin cuticle, aerenchyma). Xerophytes are adapted to dry environments (thick cuticle, sunken stomata, succulent tissues).
Answer: Monocot roots have a fibrous root system, many xylem bundles (polyarch), and a large pith. Dicot roots have a taproot system, fewer xylem bundles (2-6), and a small pith.
Answer: Transpiration is the loss of water vapor from leaves. Translocation is the transport of sugars through the phloem. (e) Translocation and ascent of sap
Answer: Translocation is the movement of sugars in the phloem. Ascent of sap is the movement of water and minerals in the xylem. (f) Xylem and phloem
Answer: Xylem transports water and minerals (unidirectional, mostly dead tissue). Phloem transports sugars (bidirectional, living tissue). (g) Pattern of gas exchange in leaves and roots
Answer: Leaves exchange gases through stomata (CO₂ in, O₂ out during photosynthesis). Roots exchange gases through root hairs and lenticels (O₂ in, CO₂ out during respiration).
1. State that nitrogen is important in protein synthesis and magnesium for chlorophyll formation.
Answer: Nitrogen and magnesium are essential macronutrients for plants, playing critical roles in protein synthesis and chlorophyll formation, respectively.
Nitrogen in Protein Synthesis:
Nitrogen is a key component of amino acids, which are the building blocks of proteins. It is also part of the nitrogenous bases in DNA and RNA, and ATP. Nitrogen is essential for the synthesis of enzymes, which catalyze all metabolic reactions. Deficiency of nitrogen causes stunted growth, chlorosis (yellowing of older leaves), and reduced protein content. Nitrogen is absorbed from the soil as nitrate (NO₃⁻) or ammonium (NH₄⁺) ions.
Magnesium in Chlorophyll Formation:
Magnesium is the central atom in the chlorophyll molecule.
Without magnesium, chlorophyll cannot be synthesized, leading to chlorosis (yellowing of leaves). Magnesium is also a cofactor for many enzymes, including those involved in photosynthesis and respiration. It is involved in the activation of enzymes and the stabilization of ribosomes. Deficiency of magnesium causes interveinal chlorosis (yellowing between veins) on older leaves.
In summary, nitrogen is crucial for protein synthesis, and magnesium is essential for chlorophyll formation. Both are vital for plant growth and development.
2. Explain the internal structure of root and root hair.
Answer: Internal Structure of Root: The root is composed of several distinct layers:
Epidermis (Rhizodermis): The outermost layer. It absorbs water and minerals. Root hairs are extensions of epidermal cells. Cortex: A wide zone of parenchyma cells between the epidermis and the endodermis. It stores food and conducts water towards the xylem. Endodermis: The innermost layer of the cortex. It has a Casparian strip (a waxy band) that forces water and minerals to pass through the cytoplasm of endodermal cells (symplast pathway) before entering the xylem. Pericycle: A layer of cells just inside the endodermis. It gives rise to lateral roots. Vascular Tissue: Located in the center. It contains xylem (for water transport) and phloem (for food transport). In dicots, xylem is star-shaped with 2-6 arms; in monocots, it is polyarch. Pith: The central region, made of parenchyma cells.
Root Hair:
Root hairs are thin, tubular extensions of epidermal cells.
They greatly increase the surface area for absorption of water and minerals. They have a thin cell wall, a large vacuole, and are short-lived.
In summary, the internal structure of the root is adapted for absorption, transport, and storage.
3. Describe how roots take up water and mineral salts by active and passive absorption.
Answer: Roots take up water and mineral salts through both passive and active absorption.
Passive Absorption:
Occurs along a concentration gradient (from high to low water potential). Water: Enters by osmosis. Soil water has a higher water potential than root hair cell sap. Minerals: Enter by diffusion and facilitated diffusion. Pathways: Apoplast (through cell walls and intercellular spaces) and symplast (through cytoplasm via plasmodesmata). No energy (ATP) is required.
Active Absorption:
Occurs against a concentration gradient (from low to high concentration). Requires energy (ATP) from respiration. Minerals: Absorbed by active transport using carrier proteins. Water: Can be absorbed actively due to the accumulation of ions in the root, which lowers water potential and draws water in by osmosis. Pathways: Primarily symplast, as the Casparian strip blocks the apoplast pathway.
In summary, passive absorption relies on diffusion and osmosis, while active absorption requires energy to move minerals against their concentration gradient.
4. Describe transpiration and relate this process with the cell surface and stomatal opening and closing.
Answer: Transpiration: Transpiration is the loss of water vapor from the aerial parts of a plant, primarily through stomata. It creates a transpiration pull that draws water up the xylem.
Relationship with Cell Surface:
The leaf has a large surface area for transpiration. The mesophyll cells have a large surface area for evaporation. The waxy cuticle reduces transpiration, except where stomata are present.
Relationship with Stomatal Opening and Closing:
Stomata are pores surrounded by guard cells. Opening: Guard cells actively take up K⁺ ions, lowering water potential. Water enters by osmosis, making guard cells turgid. The uneven thickening of guard cell walls causes them to bow outward, opening the pore. Closing: K⁺ ions leave guard cells, increasing water potential. Water leaves by osmosis, making guard cells flaccid. The pore closes. Factors: Light, CO₂ concentration, water stress (via abscisic acid), and temperature affect stomatal opening and closing.
In summary, transpiration is regulated by stomatal opening and closing, which are controlled by guard cell turgor.
5. Describe temperature, wind and humidity as factors affecting the rate of transpiration.
Answer:
1. Temperature:
As temperature increases, the kinetic energy of water molecules increases, causing faster evaporation from the leaf surface. Higher temperatures also increase the water-holding capacity of the air, decreasing relative humidity. Both factors increase the rate of transpiration.
2. Wind:
Wind removes the water vapor layer around the leaf, maintaining a steep water potential gradient. This increases the rate of diffusion of water vapor out of the leaf. Strong winds increase transpiration, but very strong winds can cause stomatal closure to conserve water.
3. Humidity:
High humidity decreases the water potential gradient between the leaf interior and the external environment. This reduces the rate of diffusion of water vapor out of the leaf. Low humidity increases the gradient and the rate of transpiration.
In summary, high temperature, wind, and low humidity increase transpiration, while low temperature, still air, and high humidity decrease it.
6. Explain the mechanism of food translocation by the theory of pressure flow mechanism.
Answer: The pressure flow mechanism (also called the pressure flow hypothesis) explains how sugars are transported in the phloem.
Steps:
1. Source (e.g., mature leaf): Sucrose is actively loaded into the sieve tube elements. This lowers the water potential in the phloem.
2. Water Uptake: Water enters the phloem from the xylem by osmosis, increasing the hydrostatic pressure.
3. Translocation: The high pressure at the source drives the flow of phloem sap through the sieve tubes to the sink.
4. Sink (e.g., root, fruit): Sucrose is actively unloaded from the phloem. Water leaves the phloem, decreasing the hydrostatic pressure.
5. Pressure Gradient: The difference in pressure between the source and sink drives the bulk flow of sap.
In summary, translocation is driven by a pressure gradient created by active loading at the source and active unloading at the sink.
7. Describe the process of gaseous exchange in plants.
Answer: Gaseous exchange in plants occurs through stomata, lenticels, and the general body surface.
1. Stomata:
Found mainly on leaves and young stems. Regulate the exchange of O₂ and CO₂. Opening and closing of stomata is controlled by guard cells.
2. Lenticels:
Found on woody stems and roots. Allow gas exchange between the atmosphere and internal tissues.
3. General Body Surface:
In aquatic plants, gases diffuse directly through the body surface.
Pattern of Exchange:
Daytime: Photosynthesis occurs, absorbing CO₂ and releasing O₂. Respiration occurs simultaneously, absorbing O₂ and releasing CO₂. Net effect: CO₂ absorbed, O₂ released. Night: Only respiration occurs. O₂ absorbed, CO₂ released.
In summary, gaseous exchange in plants occurs through stomata, lenticels, and the body surface, with the pattern depending on the balance between photosynthesis and respiration.
8. Describe the mechanism of adaptations of plants for the excretion.
Answer: Plants do not have a specialized excretory system like animals. They use various adaptations to manage and remove waste products.
1. Storage in Leaves:
Waste products like calcium oxalate crystals, resins, and gums are stored in leaves. When leaves senesce and fall, wastes are removed.
2. Storage in Bark:
Waste materials can be stored in the bark, which is shed periodically.
3. Storage in Roots:
Some wastes are stored in roots or root hairs, which are shed.
4. Excretion into the Soil:
Some waste products are excreted into the soil through roots.
5. Gaseous Exchange:
Gaseous wastes (CO₂, O₂) are removed through stomata and lenticels.
6. Transpiration:
Excess water is removed by transpiration.
In summary, plants manage waste through storage in leaves, bark, and roots, excretion into the soil, and gaseous exchange.
9. Explain osmotic adjustment in plants.
Answer: Osmotic adjustment is the process by which plants accumulate solutes to lower their internal water potential, allowing them to absorb water and maintain turgor under stress conditions (e.g., drought, salinity).
Mechanism:
Solute Accumulation: Plants synthesize and accumulate compatible solutes (e.g., proline, glycine betaine, sugars, polyols) and inorganic ions (K⁺, Cl⁻). Compartmentalization: Toxic ions (Na⁺, Cl⁻) are sequestered in vacuoles, while organic solutes are accumulated in the cytoplasm to balance osmotic pressure. Water Uptake: The lowered water potential allows water to enter the cell by osmosis, maintaining turgor pressure. Turgor Maintenance: Turgor pressure is essential for cell expansion, stomatal opening, and plant growth.
Significance:
Drought Tolerance: Helps plants survive water stress. Salt Tolerance: Helps plants survive in saline soils.
In summary, osmotic adjustment allows plants to maintain water balance and turgor under adverse conditions by accumulating solutes.
