Plant Physiology

31. Which one of the following statements is/are correct for a vascular bu

Which one of the following statements is/are correct for a vascular bundle in which xylem and phloem are jointly situated along the same radius ?

  • These are called conjoint vascular bundles.
  • Cambium may be present in such vascular bundles.
  • Conjoint vascular bundles are always of closed type.

Select the answer using the code given below :

[amp_mcq option1=”1 only” option2=”1 and 2 only” option3=”2 and 3 only” option4=”1, 2 and 3″ correct=”option2″]

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Statement 1 is correct: Vascular bundles in which xylem and phloem are jointly situated along the same radius are called conjoint vascular bundles. Statement 2 is correct: Cambium may or may not be present between xylem and phloem in conjoint bundles. If present, they are called open conjoint bundles, characteristic of dicot stems. Statement 3 is incorrect: Conjoint vascular bundles can be open (with cambium) or closed (without cambium, characteristic of monocot stems).
Conjoint vascular bundles have xylem and phloem on the same radius and can be open (with cambium) or closed (without cambium).
Radial vascular bundles have xylem and phloem arranged on different radii, alternating with each other (typical of roots). Conjoint bundles are characteristic of stems and leaves. Collateral conjoint bundles have xylem towards the center and phloem towards the periphery. Bicollateral conjoint bundles have phloem on both sides of the xylem.

32. After few days of sowing of maize seeds in the soil, irrespective of t

After few days of sowing of maize seeds in the soil, irrespective of their position, the radicle always grows downwards, whereas the coleoptile always grows upwards. This phenomenon is known as :

[amp_mcq option1=”Phototropism” option2=”Hydrotropism” option3=”Chemotropism” option4=”Geotropism” correct=”option4″]

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The phenomenon described is the directed growth of plant parts in response to gravity. The radicle (root) grows downwards towards gravity (positive geotropism), while the coleoptile (shoot) grows upwards away from gravity (negative geotropism). This response to gravity is known as geotropism, or more modernly, gravitropism.
Geotropism is the directional growth of plant parts in response to gravity.
Phototropism is the growth response to light (shoots are typically positive phototropic, roots negative). Hydrotropism is the growth response to water (roots are typically positive hydrotropic). Chemotropism is the growth response to chemicals.

33. Which among the following correctly shows the pathway of water movemen

Which among the following correctly shows the pathway of water movement in a root ?

[amp_mcq option1=”Pericycle → Endodermis → Cortex → Epidermis” option2=”Epidermis → Pericycle → Endodermis → Cortex” option3=”Epidermis → Endodermis → Cortex → Pericycle” option4=”Epidermis → Cortex → Endodermis → Pericycle” correct=”option4″]

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Water is absorbed by root hairs, which are extensions of epidermal cells. From the epidermis, water moves inward through the cortex. It then crosses the endodermis (where the Casparian strip regulates passage), enters the pericycle, and finally moves into the xylem for upward transport. The correct pathway is Epidermis → Cortex → Endodermis → Pericycle.
Water enters the root through the epidermis, moves through the cortex, endodermis, pericycle, and finally into the xylem.
Water can move through the cortex via two main pathways: the apoplast pathway (through cell walls and intercellular spaces) and the symplast pathway (through the cytoplasm connected by plasmodesmata). The Casparian strip in the endodermis forces water to enter the symplast, providing a selective barrier.

34. Which one of the following is a secondary metabolite produced by some

Which one of the following is a secondary metabolite produced by some plants?

[amp_mcq option1=”Starch” option2=”Terpenoids” option3=”Malate” option4=”Sugar” correct=”option2″]

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The correct answer is Terpenoids.
Primary metabolites are directly involved in the normal growth, development, and reproduction of an organism. Examples include carbohydrates (like starch, sugar), lipids, proteins, nucleic acids, and simple organic acids (like malate). Secondary metabolites are not directly involved in these essential processes but often have ecological functions, such as defense against herbivores or pathogens, or attracting pollinators.
Terpenoids are a large class of organic compounds derived from five-carbon isoprene units. They are classic examples of secondary metabolites found in plants, known for diverse functions including fragrances, flavors, pigments, and defense compounds. Starch, malate, and sugar are primary metabolites essential for energy storage, metabolism, and transport in plants.

35. Eagle fern, horsetail, chrysanthemum grow well in

Eagle fern, horsetail, chrysanthemum grow well in

[amp_mcq option1=”acidic soil” option2=”extremely alkaline soil” option3=”neutral soil” option4=”highly alkaline soil” correct=”option1″]

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Eagle fern (Pteridium aquilinum) is widely recognized as an indicator plant for acidic soils. It thrives in low-pH conditions where many other plants struggle. Horsetail (Equisetum species) can tolerate various soil conditions but is often found in damp, acidic, or nutrient-poor soils. While Chrysanthemums prefer slightly acidic to neutral soil, Eagle fern is a particularly strong indicator of acidity among the listed plants. Therefore, acidic soil is the most likely common condition where these plants grow well.
– Soil pH is a crucial factor affecting plant growth and distribution.
– Some plants are indicators of specific soil pH ranges.
– Eagle fern is strongly associated with acidic soils.
– Horsetail and Chrysanthemum also have preferences or tolerances that can include acidic conditions.
Soil acidity (low pH) can affect nutrient availability and the presence of toxic substances (like aluminum). Plants adapted to acidic soils have mechanisms to cope with these conditions. Extremely alkaline soils (high pH) present different challenges, such as nutrient deficiencies (e.g., iron, zinc) and are favoured by different plant species (calcicoles).

36. Plants, which survive by withdrawing water from their cells to prevent

Plants, which survive by withdrawing water from their cells to prevent ice formation during extreme cold up to -40 ° C, are known as:

[amp_mcq option1=”Frost sensitive” option2=”Frost tolerant” option3=”Frost resistant” option4=”Chilling resistant” correct=”option2″]

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Plants that survive extreme cold by withdrawing water from their cells to prevent intracellular ice formation are known as frost resistant or freeze tolerant.
Frost resistance or freeze tolerance involves various physiological adaptations that allow plants to survive temperatures below freezing. Mechanisms include supercooling (preventing ice formation even below the freezing point) or dehydrating cells to allow ice to form only in extracellular spaces, preventing lethal damage from intracellular ice crystals.
Frost sensitive plants are damaged or killed by freezing temperatures. Chilling resistant plants can tolerate low temperatures above freezing (typically 0-15 °C). The description in the question specifically points to mechanisms that prevent freezing damage at sub-zero temperatures.

37. Which one of the following provides buoyancy to aquatic plants to help

Which one of the following provides buoyancy to aquatic plants to help them float?

[amp_mcq option1=”Aerenchyma” option2=”Tracheid” option3=”Guard cell” option4=”Sclerenchyma” correct=”option1″]

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Aerenchyma provides buoyancy to aquatic plants.
Aerenchyma is a modified parenchyma tissue found in many aquatic and wetland plants. It contains large air spaces (lacunae) that provide buoyancy, allowing the plant to float on the water surface. These air spaces also facilitate gas exchange (oxygen and carbon dioxide) to submerged tissues.
Tracheids are components of xylem involved in water transport and support. Guard cells surround stomata and regulate gas exchange but are not involved in buoyancy. Sclerenchyma provides mechanical support and strength due to its thick, lignified cell walls. Only aerenchyma is specifically adapted for providing buoyancy through its air-filled cavities.

38. Pneumatophores are specialized structures for:

Pneumatophores are specialized structures for:

[amp_mcq option1=”maintaining turgor pressure in cells.” option2=”providing physical support to plants in marshy lands.” option3=”oxygen inhalation by plants.” option4=”carbon dioxide release during photosynthesis.” correct=”option3″]

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Pneumatophores are specialized root structures that grow upwards from the soil in plants found in waterlogged or anaerobic conditions, such as mangrove swamps. Their primary function is to facilitate the diffusion of oxygen into the root system, essentially acting for oxygen inhalation by the plant roots in oxygen-poor soil.
– Pneumatophores are negative geotropic roots, growing vertically upwards out of the mud or water.
– They possess pores (lenticels) on their surface that allow for gas exchange.
– They contain spongy tissue (aerenchyma) that stores and transports air to the submerged roots.
– Examples of plants with pneumatophores include various mangrove species (like *Avicennia* and *Sonneratia*) and some other wetland plants.
– They are an adaptation to anaerobic conditions where oxygen is scarce in the soil due to waterlogging.
– Other specialized root structures in mangroves include prop roots and buttress roots, which provide physical support, but pneumatophores are specifically for gas exchange.

39. Heliophile plants require mean maximum illumination of:

Heliophile plants require mean maximum illumination of:

[amp_mcq option1=”30,000 lux.” option2=”20,000 lux.” option3=”10,000 lux.” option4=”40,000 lux.” correct=”option1″]

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Heliophile plants, also known as sun-loving plants, require high light intensity for optimal growth. While the exact threshold varies depending on the source and context, values around 30,000 lux or higher are typically associated with conditions suitable for heliophytes.
Heliophile plants are adapted to thrive in direct sunlight and require high illumination levels for maximum photosynthetic activity.
In contrast, sciophyte plants (shade-tolerant plants) require much lower light intensities, often below 5,000 lux. The mean maximum illumination experienced by plants varies significantly depending on latitude, time of day, season, and environmental factors like cloud cover and canopy shading. Full sunlight can exceed 100,000 lux.

40. Which one among the following is not a part of vascular bundle in pl

Which one among the following is not a part of vascular bundle in plants ?

[amp_mcq option1=”Phloem” option2=”Xylem” option3=”Cambium” option4=”Endodermis” correct=”option4″]

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A vascular bundle in plants is the primary conducting strand, composed mainly of xylem and phloem, which transport water, minerals, and sugars. In dicotyledonous plants and gymnosperms, cambium is also present between xylem and phloem, facilitating secondary growth. The endodermis, however, is a layer of ground tissue that surrounds the vascular cylinder (stele), particularly prominent in roots and some stems, and is not considered part of the vascular bundle itself.
– Vascular bundles contain xylem (water transport) and phloem (sugar transport).
– Cambium is involved in secondary growth and is part of the vascular bundle structure in plants with secondary growth.
– The endodermis functions as a selective barrier controlling the movement of substances into the vascular cylinder via the Casparian strip.
Vascular bundles can be arranged differently in different plant organs and species (e.g., scattered in monocot stems, in a ring in dicot stems, forming a central cylinder in roots). The endodermis plays a crucial role in filtering substances absorbed by the root before they enter the xylem.
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