Plant Physiology & Botany — Part 2: 23 MCQs with Explanations

Transpiration creates transpiration pull that facilitates ascent of sap from roots to leaves through xylem vessels.

Guttation occurs when root pressure forces xylem sap out through hydathodes, typically at night when transpiration is low.

Xylem consists of tracheids and vessel elements that form continuous tubes for upward transport of water and dissolved minerals.

Roots exhibit positive geotropism (grow downward with gravity); stems show negative geotropism (grow upward against gravity).

Cohesion-tension theory: transpiration pull creates negative pressure; cohesive forces between water molecules and adhesive forces to xylem walls enable continuous water column ascent.

Mutualism: bacteria receive carbohydrates from plant; plant receives fixed nitrogen (ammonia) usable for amino acid synthesis.

Roots lack chlorophyll and are non-photosynthetic; photosynthesis occurs in green aerial parts (stems, leaves) containing chloroplasts.

Assimilation: plant roots absorb NO₃⁻ or NH₄⁺ and convert them to amino acids via enzymatic reactions (e.g., glutamine synthetase pathway).

Calvin cycle uses ATP and NADPH to fix CO₂ into organic molecules: RuBisCO catalyzes CO₂ + RuBP → unstable 6C intermediate → 2 molecules of 3-phosphoglycerate.

Transpiration pull (cohesion-tension theory) is primary mechanism; root pressure and capillarity contribute minimally, especially in short plants.

Thigmotropism: coiling of tendrils around support structures (e.g., in pea plants) due to differential growth stimulated by touch.

Photosynthesis fixes inorganic carbon into glucose and other organic molecules using light energy.

Guttation occurs when root pressure forces xylem sap out through hydathodes at leaf margins, typically at night when transpiration is minimal.

Assimilation incorporates inorganic nitrogen into organic molecules; plants absorb NO₃⁻ or NH₄⁺ and convert them to amino acids via enzymatic pathways.

Stigma is the receptive surface of pistil where pollen grains land and germinate during pollination.

Hydrotropism: roots grow toward regions of higher moisture; important for water acquisition especially when gravity cues are absent.

Photolysis: 2H₂O → 4H⁺ + 4e⁻ + O₂ occurs in photosystem II during light-dependent reactions; electrons replace those lost by chlorophyll.

Pistil (carpel) consists of stigma, style, and ovary containing ovules that develop into seeds after fertilization.

Negative geotropism (negative gravitropism): shoots grow upward against gravity; roots show positive geotropism growing downward with gravity.

Cuticular transpiration accounts for 5-10% of total water loss; stomatal transpiration accounts for 90-95%.

Roots provide anchorage; stems support aerial parts, transport substances via vascular tissue, and may photosynthesize if green.

Most plants absorb nitrogen as nitrate ions (NO₃⁻) or ammonium ions (NH₄⁺) through root hairs; only legumes with Rhizobium can use atmospheric N₂.

Leaves have broad lamina with mesophyll containing chloroplasts, stomata for gas exchange, and vascular bundles for transport—optimized for photosynthesis.

Chlorophyll is insoluble in Water .

Red is the correct answer to “Of the following, which one causes higher production of food in green plants”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

It is hydrophobic is the correct answer to “Which of the following statement about the head of a chlorophyll molecule is incorrect”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Photosynthesis carried out by terrestrial plants is 10% of total photosynthesis.

Net yield of H2O in Photosynthesis is 0 molecule .

PS I has chlorophyll a molecule which absorbs maximum light of 700 nm.

Visible light used in photosynthesis ranges from: 380 750 nm in wavelength .

The percentage of light absorbed by the leaf is 1% .

Green is the correct answer to “Which of the following light is least absorbed by the plants”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

About 10% % of photosynthesis is carried by terrestrial plants, while rest occurs in ocean, lakes, and ponds.

Gibberellins may be substituted for Red light, therefore promote flowering in long day plants.

Abscisic acid promotes flowering in short day plants and inhibits in long day plants, which of the following is antagonistic to abscisic acid in terms of flowering Gibberellins .

Microspore of a seed plant that contain male gametophyte including the gamete is called Pollen grain .

Which of the following plant group first formed true leaves Lycopsida .

Of the following which one is not the characteristic of the plants included in psilopsida Rhizoids bear Rhizome .

They Are heterotrophes is the correct answer to “Which of the following statement about plants is incorrect”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Venus flower basket is also known as Euplectella .

Most of the photosynthesis on earth is carried by Algae .

Mycorrhizae are found in about 95% vascular plants.

Root like structure in saprotrophic fungi are called Rhizodis .

Strong chlorosis is due to the deficiency of Nitrogen in plants.

Stunted growth of roots is due to the deficiency of Phosphorus in plants.

Nodules on roots of leguminous plants have Nitrogen fixing bacteria.

All of the insectivorous plants are true Autotrophes .

The leaf is bilobed with midrib between them. The plant is Dionaea .

1% is the correct answer to “What percentage of light reaching the earth is used in photosynthesis”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Exposure to low temperature stimulates plants to flower. This is called Vernalisation .

The trioses which are intermediate in respiration and photosynthesis are Both of these .

C55H70O6N4Mg is the correct answer to “Which of the following is the empirical formula of chlorophyll b”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

The mechanism of stomatal movement is related to the branch of Biology called Physiology .

Chlorophyll is a/an Organic molecule.

Thylakoids is the correct answer to “On which of the following component of chloroplast chlorophyll is arranged”. Items of this type are drawn from the Plant Physiology & Botany — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Chlorophyll molecule contrains Mg2+ as central metal ion.

Cuticular transpiration is 5-7% of total transpiration.

Out of total organisms on earth, 17.60% are vascular plants.

Animals that eat plants are called Herbivores .

Chloroplasts contains the green chemical called chlorophyll.

All of the following are elements that plants need in very small amounts except Hydrogen .

Smallest disease causing agents in plants are viroids.

Fungi resemble plants because they lack Centriole .