Chapter 13 — Plant life processes
Plants exchange matter with their surroundings
A green plant does not obtain all its food by “eating soil.” Roots absorb water and mineral nutrients from the soil solution; leaves take in carbon dioxide from air; photosynthesis uses light energy to build energy-rich organic molecules. In a simplified balanced representation, 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, with light and chlorophyll-associated machinery involved. The equation is a net summary, not a statement that one direct step in a leaf converts six individual molecules into glucose. Oxygen released during photosynthesis comes from water in the deeper biochemical account. For police-level questions, focus first on inputs, outputs, light requirement and chloroplast function.
Photosynthesis and respiration occur in the same plant. Respiration releases usable energy from organic molecules for cellular work; it is not a process performed only by animals or only at night. In daylight, both photosynthesis and respiration occur in many green cells, while net gas exchange can depend on their relative rates. At night, photosynthesis dependent on light stops, but respiration continues. Thus “plants take in only CO₂ and never O₂” is false. A question about the net gas released from a green leaf in strong light is different from one about whether its mitochondria respire.
The process depends on several limiting factors. If light is scarce, adding more carbon dioxide may not immediately raise the rate in a simple experimental comparison. If carbon dioxide is scarce, more light alone may have little additional effect. Temperature also influences enzymes, so “warmer always increases photosynthesis” is too absolute. The limiting-factor idea asks which required input or condition is currently restricting the rate. In an MCQ graph, identify the variable on each axis and look for a plateau before choosing an explanation.
Water transport and transpiration
Root hairs provide a large surface for water and dissolved-mineral uptake. Water enters roots through physical and biological processes and moves through xylem toward stems and leaves. Transpiration is the loss of water vapour from aerial plant parts, much of it through stomata in the simplified leaf account. Evaporation from leaf surfaces and cohesion of water contribute to the transpiration-pull explanation of upward water movement. Root pressure can matter in some contexts, but it is not a universal sole cause of water rising in a tall tree.
Stomata are small pores in the leaf epidermis bounded by guard cells. They permit gas exchange and influence water loss. They do not “manufacture oxygen”: photosynthesis in chloroplast-containing cells produces oxygen, which can leave through stomata. Stomatal opening and closing respond to plant state and environmental conditions. A school question might ask why a plant wilts during severe water shortage; water loss and reduced cell turgor are central. Yet wilting alone does not prove that the root system was damaged; multiple causes can lead to the observation.
Water and dissolved minerals mainly move in xylem. Products of photosynthesis move through phloem from sources to sinks. A mature leaf can be a source of sugar, while a growing root or fruit can be a sink. Direction in phloem depends on where source and sink are, so “food always moves downward” is an unreliable shortcut. In a particular plant at a particular time, material can move upward to a growing shoot. A good exam response names the tissue and transported substance before discussing direction.
Mineral nutrients are essential for plant growth but should not be confused with calories of food. Nitrogen can be taken up in usable inorganic forms and built into proteins and nucleic acids. Nitrogen fixation converts atmospheric nitrogen into biologically useful forms through certain microorganisms or other processes. Most plants cannot directly use atmospheric N₂ gas merely because it surrounds a leaf. Legumes can have associations with nitrogen-fixing bacteria in root nodules, but not every root swelling is proof of nitrogen fixation. The named organism and relationship matter.
Reproduction in flowering plants
A flower can contain reproductive structures. The stamen includes an anther that produces pollen; the pistil or carpel includes stigma, style and ovary in the basic model. Ovules lie inside the ovary. Pollination transfers pollen from anther to stigma. Fertilisation is the fusion of male and female gametes after the pollen reaches the appropriate structures and the process proceeds. These are separate events. A flower can be pollinated without successful fertilisation; a question that equates pollen landing with gamete fusion has skipped stages.
After successful fertilisation in a typical flowering plant, an ovule develops into a seed and the ovary develops into a fruit. The seed contains an embryo and stored reserves or supporting tissues depending on species. A fruit is therefore a botanical structure derived from the flower, not simply “any sweet edible plant part.” Tomato is a fruit botanically, even when used as a vegetable in cooking. A potato tuber is a modified stem, not a seed; it can support vegetative propagation through buds. Culinary categories and botanical categories answer different questions.
Seeds disperse by wind, water, animals or mechanical processes depending on their structures and environment. A light winged seed may be carried by wind; a fleshy fruit may be eaten and its seeds transported by animals. Dispersal is not the same as germination. Germination begins the growth of a new plant under suitable conditions, generally requiring water, oxygen and an appropriate temperature for the seed. Light needs vary among species. The presence of a seed alone does not guarantee that it is viable or that conditions permit growth.
Vegetative propagation produces new plants from non-seed structures such as stems, roots or leaves in suitable species. It can preserve many features of a parent plant because it does not involve the same sexual recombination as seed formation. Yet “vegetative offspring are guaranteed genetically identical in every respect” overstates reality: mutation and other changes can occur. Common school examples include potato tubers with eyes and sugarcane stem cuttings. Do not call every underground plant part a root; some are modified stems.
Tropisms and plant responses
Plants respond to directional stimuli. Phototropism is directional growth in response to light; gravitropism concerns gravity. A young shoot often grows toward light, while a root usually grows downward in response to gravity in a simple seedling demonstration. These are growth responses, not animals' rapid locomotion. A plant hormone such as auxin participates in growth responses, but an MCQ that says auxin alone explains every visible plant movement is too broad. Some leaves fold rapidly due to changes in cell water pressure rather than slow directional growth.
Transpiration, photosynthesis and respiration can be connected in a causal diagram. Stomata allow carbon dioxide entry for photosynthesis and also provide a pathway for water vapour loss. Closing them may save water but can limit carbon dioxide uptake. The balance depends on conditions and plant adaptations. A desert plant may have structures and behaviours that reduce water loss, but no single adaptation belongs to all desert species. For an exam question, match the named structure to its likely function without claiming it makes the plant independent of water.
Worked process route
Suppose a diagram labels A as xylem and B as phloem. A question says material X is absorbed from the soil, while material Y is manufactured in mature leaves and sent to growing fruits. The expected matching is X through xylem and Y through phloem. The answer follows origin and destination, not a memorised “up/down” phrase. If the fruit is above the leaves, phloem transport of Y may be upward in that path, illustrating why direction alone is a weak identifier.
Another item describes pollen grains on a stigma and later a developing seed. Pollen arrival establishes pollination; development of a seed implies that the later reproductive sequence succeeded. The ovule, not the whole ovary, gives rise to the seed in the basic angiosperm account; the ovary gives rise to the fruit. In a four-option question, one distractor often reverses these two. Write “ovule→seed, ovary→fruit” beside the diagram before selecting.
Leaf structure links the processes together
A leaf is an organ containing several tissues. Its epidermis forms an outer covering, and a cuticle can reduce water loss. Mesophyll cells carry out much of the photosynthesis in a typical green leaf. Air spaces provide pathways for gases within the leaf. Veins contain xylem and phloem, connecting the leaf's production and exchange processes to the rest of the plant. These structures solve different problems: xylem supplies water, phloem transports sugars, stomata regulate exchange with air, and chloroplasts carry out photosynthetic reactions. A pore is a route for movement rather than the site of every reaction involving the moving gas.
Consider carbon dioxide travelling from the atmosphere into a photosynthesising leaf. It passes through an open stoma, diffuses through internal air spaces and reaches cells where it can be used in carbon fixation. Water has a different entry route, normally through roots and then xylem. The two materials eventually participate in photosynthesis but do not have to enter through the same structure. This is a useful way to reject a diagram that labels phloem as the normal entry route for atmospheric carbon dioxide or root hairs as the main site of light absorption.
Many school diagrams show stomata predominantly on the lower surface of a terrestrial broad leaf. Treat this as a common pattern rather than a rule for every leaf. Floating leaves can have stomata on the upper surface, while submerged leaves have different arrangements. Leaf orientation, habitat and species influence the distribution. Guard cells control the size of each stomatal opening through changes involving their water balance and internal chemistry. Opening a pore can improve carbon dioxide supply while increasing the opportunity for water loss, so its effect cannot be judged from one process alone.
Read photosynthesis measurements without confusing gross and net rates
Imagine an aquatic plant in a teaching experiment. At one light level its photosynthetic oxygen production is 12 arbitrary units per minute while oxygen use in respiration is 4 units per minute. Its net oxygen release is 12 − 4 = 8 units per minute. If an instrument reports only net release, the reading is not the gross photosynthetic production. At a lower light level, gross production might be 4 and respiratory use 4, giving zero net exchange. Photosynthesis and respiration can both be occurring even when their opposing effects balance.
This balance illustrates the light compensation point under the stated conditions. Below it, respiratory use can exceed photosynthetic production; above it, net release becomes positive. The calculation is a simplified interpretation of measured gas exchange, not a universal numerical value for all plants. Rate depends on species, temperature, carbon dioxide, leaf condition and measurement method. In a graph question, locate where the net exchange crosses zero and read the axis label. A plateau in a positive rate curve is different from a zero crossing: one concerns a limit on further increase, the other a balance between opposing processes.
Bubble counting in an aquatic-plant demonstration is only an approximate indicator of gas release. Ten large bubbles need not contain the same gas volume as ten small ones. Some oxygen dissolves in the water, and other conditions can affect the observation. Measuring gas volume over a fixed time is generally a stronger quantitative comparison when the collection method is suitable. In either case, control temperature, plant size or leaf area, and the time allowed for adjustment. If a lamp is moved closer, both light intensity and temperature may change; an experiment intended to test light must address this possible confounding factor.
Evidence from starch and controlled comparisons
A starch test provides indirect evidence about carbohydrate accumulation in a leaf. Iodine gives a blue-black colour when sufficient starch is present under the test conditions. It does not directly measure the instantaneous rate of photosynthesis or detect oxygen. A plant may be kept in darkness before an experiment to reduce previously stored leaf starch, making later comparisons easier to interpret. The purpose is to reduce an alternative explanation for a positive result: starch that was already present before the treatment.
Suppose two comparable regions of one suitable leaf receive different light exposure while other relevant conditions are similar. After preparation and testing, the illuminated region gives a stronger starch result than the covered region. This supports a role for light in starch accumulation under the experiment's conditions. It does not prove that the covered cells are dead or that all plant tissues must be green to survive. A separate comparison involving green and non-green regions of a variegated leaf examines another feature. Keep the tested variable distinct from the reagent used to observe the result.
The logic of a control can be tested without memorising a laboratory recipe. A treatment removes carbon dioxide around one leaf, while a comparable leaf has ordinary access to it. Light, water supply, duration and other relevant conditions should remain comparable. If several factors change together, the difference in starch results cannot be assigned confidently to carbon dioxide alone. Practical demonstrations involving heated alcohol or chemical absorbents belong in supervised laboratories; the exam task is to understand the variable, comparison and inference. Observation supports a stated conclusion within the limits of the design.
Transpiration data and the meaning of a proxy
A potometer estimates water uptake by a cut shoot under a particular setup. Water uptake is often used as a proxy for transpiration, but the two are not exactly identical because water can be retained, used in growth or participate in metabolism. Leaks or damage can also distort readings. If a stem asks what the instrument measures most directly, choose water uptake. If it asks what process the reading is commonly used to estimate, transpiration is the relevant process. This distinction between direct observation and inferred process appears across experimental science.
Suppose a device records 0.6 mL water uptake in 15 minutes. The average uptake rate is 0.6/15 = 0.04 mL per minute, or 2.4 mL per hour if that rate continues unchanged. A second shoot takes up 0.9 mL in 15 minutes, giving 0.06 mL per minute. Before attributing the difference to wind, compare leaf area and other conditions. A larger shoot can lose more water simply because it has more exposed leaf area. Expressing results per unit leaf area may help when the biological question requires that comparison.
Dry air commonly increases the water-vapour gradient from a leaf to its surroundings, while high humidity reduces it. Air movement can remove humid air close to the leaf. Higher temperature can increase evaporation, but plant responses such as stomatal closure can modify the result. Therefore, a school question about one factor usually assumes other factors are controlled and the stomata remain sufficiently open. Wilting reflects loss of turgor when water supply cannot meet the relevant losses; watering a plant and immediately seeing no recovery does not establish a single cause without further evidence.
Flower-to-seed route: more precise labels
The pollen grain is a structure involved in the male reproductive phase; it should not simply be equated with one free-swimming sperm cell. On a compatible stigma, pollen can germinate and produce a pollen tube. Male gametes are delivered towards the embryo sac in the ovule. In the typical angiosperm account, one male gamete fuses with the egg to form the zygote; another participates in formation of the primary endosperm nucleus. These two fusion events underlie the term double fertilisation. The embryo develops from the zygote, while endosperm commonly provides nutrition to the developing embryo.
For the common diploid-parent model, the egg and male gamete are haploid, so their fusion restores a diploid zygote. Fusion of the other male gamete with the two polar nuclei typically produces a triploid primary endosperm nucleus. This numerical account requires the stated conventional embryo-sac arrangement; it is not a substitute for recognising the structures. A stem asking what becomes the embryo points to the zygote. A stem asking which part develops into a seed points to the ovule. One names a cell and developmental product; the other names the larger structure surrounding that development.
Self-pollination and cross-pollination concern the origin and destination of pollen. Transfer within the same flower and transfer between flowers on the same plant both differ genetically from transfer between separate plants. At introductory level, the crucial distinction is that pollination is transfer, whereas fertilisation is fusion. Wind-pollinated flowers often have exposed reproductive structures and abundant light pollen; insect-pollinated flowers may have scent, nectar or conspicuous parts. These are patterns of adaptation, so identify the combination described rather than treating one colourful petal as proof of a particular pollinator.
Germination and vegetative propagation: use structure as evidence
A seed takes up water, resumes active metabolism and mobilises stored reserves as germination proceeds. The young plant can initially use stored food before its leaves supply enough photosynthetic production. This explains why “a seed needs sunlight to obtain energy for every initial germination step” is not a universal rule. Oxygen supports aerobic respiration in the usual teaching example, and a suitable temperature supports enzyme activity. Dormancy can prevent a viable seed from germinating immediately even when several external conditions appear favourable. A dead seed and a dormant viable seed are different explanations for failure to germinate.
A potato tuber has nodes with buds, commonly called eyes, supporting its identification as a modified stem. A sweet potato is a storage root. Ginger is a rhizome, another modified stem, and an onion bulb includes a short stem with fleshy storage leaves. These examples show why underground position or food storage alone cannot classify a plant part. Look for nodes, internodes, buds and structural relationships. Vegetative propagation from suitable parts can preserve a desirable combination of characteristics, but it can also carry pathogens with planting material; seed formation and vegetative propagation have different practical advantages.
Retrieval practice with reasons
Question 1: A leaf releases 9 units of oxygen per minute net and uses 3 units per minute in respiration. Under the simple model, gross photosynthetic production is 12 units per minute. Question 2: A shoot takes up 1.2 mL in 20 minutes. Its average uptake is 0.06 mL per minute. These answers require identifying whether the supplied figure is a difference or a directly measured total before selecting a formula.
Question 3: A seed-bearing structure develops from an ovary. It is a fruit in the botanical account, regardless of its sweetness. Question 4: A starch result is positive in an illuminated leaf region. This detects accumulated starch; it does not directly identify the number of oxygen molecules released. Question 5: A potato piece with a viable eye grows into a new plant. This demonstrates vegetative propagation from a modified stem, not fertilisation inside the tuber. For each case, state the observation first and the supported inference second.
Recall and review
Name the inputs and outputs in a simple net photosynthesis equation and explain why plants also respire. Trace water through root and xylem and sugars through phloem. Distinguish stomatal gas exchange from the chloroplast's photosynthesis. Put pollination, fertilisation, seed and fruit formation in causal order. Compare seed dispersal with germination and a potato tuber with a seed. Finally, identify a limiting factor from a graph that plateaus. Attempt the chapter practice set, then use the explanations to revisit any uncertain concepts.
Figure 13. Original chapter diagram.
Figure 13.1. A measured net rate is the difference between two processes
Practice 31 questions
Choose one answer for each item. The answer key and explanations follow this chapter set.
1. Pollination that is carried out by wind is known as:
A. Anemophily B. Entomophily C. Hydrophily D. Ornithophily
2. The growth of plant roots towards moist soil, in response to water, is called:
A. Phototropism B. Geotropism C. Hydrotropism D. Thigmotropism
3. The loss of water in the form of vapour from the aerial parts of a plant, mainly through stomata, is called:
A. Guttation B. Absorption C. Transpiration D. Translocation
4. Match List I (Plant) with List II (Main mode of seed/fruit dispersal):
List I: A. Coconut B. Xanthium C. Castor D. Drumstick
List II: 1. Water 2. Wind 3. Animals 4. Explosive (bursting) mechanism
A. A-3, B-1, C-4, D-2 B. A-1, B-4, C-3, D-2 C. A-1, B-3, C-4, D-2 D. A-2, B-3, C-4, D-1
5. Match List I (Type of pollination) with List II (Agent):
List I: A. Anemophily B. Hydrophily C. Entomophily D. Ornithophily
List II: 1. Birds 2. Wind 3. Insects 4. Water
A. A-2, B-4, C-3, D-1 B. A-3, B-4, C-2, D-1 C. A-4, B-2, C-3, D-1 D. A-2, B-4, C-1, D-3
6. Match List-I (Plant) with List-II (Vegetative part or method used for propagation):
List-I: (a) Potato (b) Ginger (c) Bryophyllum (d) Sugarcane
List-II: (i) Rhizome (ii) Notches along the leaf margin (iii) Eyes (buds) on the tuber (iv) Stem cuttings
A. a-iii, b-i, c-iv, d-ii B. a-i, b-iii, c-ii, d-iv C. a-ii, b-i, c-iii, d-iv D. a-iii, b-i, c-ii, d-iv
7. The stamen, the male reproductive part of a flower, consists of:
A. Stigma and style B. Ovary and ovule C. Sepal and petal D. Anther and filament
8. Which part of the pistil receives the pollen grains during pollination?
A. Ovary B. Style C. Anther D. Stigma
9. Spirogyra, the slimy green thread-like growth seen in ponds and commonly called 'pond silk', belongs to which group?
A. Bryophytes B. Algae C. Pteridophytes D. Fungi
10. Under Whittaker's Five Kingdom Classification, blue-green algae (cyanobacteria) are placed in which kingdom?
A. Monera B. Fungi C. Plantae D. Protista
11. Which of the following plants is a pteridophyte?
A. Cycas B. Funaria C. Selaginella D. Marchantia
12. Which of the following tree-like plants is a monocot?
A. Banyan B. Neem C. Mango D. Coconut
13. Which plant group is called the 'amphibians of the plant kingdom' because it needs water for fertilisation?
A. Gymnosperms B. Pteridophytes C. Algae D. Bryophytes
14. In the traditional school classification below, which seedless plant group has true vascular tissues and differentiated roots, stems and leaves?
A. Bryophytes B. Algae C. Pteridophytes D. Angiosperms
15. Transfer of pollen from the anther to the stigma of the same flower, or of another flower on the same plant, is called:
A. Fertilisation B. Self-pollination C. Vegetative propagation D. Cross-pollination
16. Consider the statements. I: Vegetative propagation normally produces offspring genetically very similar to the parent because it does not involve fusion of gametes. II: Gymnosperm seeds are enclosed within a fruit. Which statement(s) is/are correct?
A. Only I B. Only II C. Both I and II D. Neither I nor II
17. Consider the following statements:
Statement I: Pteridophytes reproduce by forming seeds.
Statement II: Bryophytes lack true vascular tissue.
Which of the above is/are correct?
A. Only I B. Only II C. Both I and II D. Neither I nor II
18. Which of the following is NOT a usual textbook trait of monocotyledonous plants?
A. Reticulate (net-like) leaf venation B. Fibrous root system C. Floral parts usually in multiples of three D. A single cotyledon in the seed
19. Which of the following is NOT a monocotyledonous plant?
A. Gram B. Rice C. Maize D. Banana
20. Which of the following is NOT one of the kingdoms in Whittaker's Five Kingdom Classification?
A. Fungi B. Archaea C. Protista D. Monera
21. In grafting a fruit plant, what is the scion?
A. The rooted lower plant that receives the graft B. The shoot piece selected for its desired above-ground traits C. A seed formed after cross-pollination D. The underground rhizome used for propagation
22. Which condition is NOT universally required for every viable seed to germinate?
A. Access to water B. Access to oxygen C. A temperature suitable for that species D. Direct sunlight
23. In which year did R.H. Whittaker propose the Five Kingdom Classification of living organisms?
A. 1959 B. 1975 C. 1966 D. 1969
24. Match List I (Plant hormone) with List II (Main function):
List I: A. Auxin B. Gibberellin C. Cytokinin D. Abscisic acid
List II: 1. Bolting (stem elongation) 2. Apical dominance 3. Stomatal closure under water stress 4. Delay of leaf senescence
A. A-1, B-2, C-4, D-3 B. A-4, B-1, C-2, D-3 C. A-2, B-1, C-3, D-4 D. A-2, B-1, C-4, D-3
25. According to the balanced equation of photosynthesis, how many molecules of oxygen are released for every one molecule of glucose formed?
A. 6 B. 3 C. 12 D. 1
26. In woody stems and bark, exchange of gases takes place through small pores called:
A. Stomata B. Nectaries C. Lenticels D. Hydathodes
27. The Calvin cycle, often called the light-independent stage of photosynthesis, occurs in which chloroplast compartment?
A. Outer membrane B. Thylakoid membrane C. Intermembrane space D. Stroma
28. The oxygen released during photosynthesis comes from the splitting of:
A. Chlorophyll B. Water C. Glucose D. Carbon dioxide
29. Which is a common school-level example of a cultivated day-neutral plant, whose flowering is not strongly triggered by a critical day length?
A. Chrysanthemum B. Tomato C. Spinach D. Wheat
30. Which is a standard short-day (long-night) plant example in photoperiodism?
A. Spinach B. Chrysanthemum C. Wheat D. Tomato
31. The naturally occurring form of the plant hormone auxin is:
A. Indole-3-acetic acid (IAA) B. Gibberellic acid (GA3) C. Abscisic acid (ABA) D. Zeatin
Answers and explanations
1. A. Anemophily is pollination by wind, as in maize and grasses. Entomophily is by insects, hydrophily by water (for example Vallisneria) and ornithophily by birds.
2. C. Hydrotropism is directional growth in response to water: roots grow towards moist soil. Phototropism is a response to light, geotropism to gravity and thigmotropism to touch, as when tendrils coil around a support.
3. C. Transpiration is the loss of water vapour from leaves and other aerial parts, mainly through stomata. It cools the plant and creates the pull that draws water and minerals up the xylem; translocation refers to the movement of food in phloem.
4. C. Coconut floats on water thanks to its fibrous husk (A-1); Xanthium's hooked fruits cling to animal fur (B-3); castor capsules burst open explosively (C-4); drumstick has winged seeds carried by wind (D-2).
5. A. Anemophily is wind pollination (maize, grasses), hydrophily is water pollination (Vallisneria), entomophily is by insects and ornithophily by birds. Hence A-2, B-4, C-3, D-1.
6. D. Potato grows from the eyes (buds) of the tuber (iii), ginger from rhizomes (i), Bryophyllum forms plantlets in the notches of its leaf margin (ii) and sugarcane is propagated from stem cuttings (iv): a-iii, b-i, c-ii, d-iv.
7. D. A stamen has an anther, which produces pollen grains, borne on a stalk called the filament. Stigma, style and ovary form the pistil (female part); sepals and petals are non-reproductive whorls.
8. D. The stigma is the sticky tip of the pistil that receives pollen. The style is the connecting tube through which the pollen tube grows, the ovary contains ovules, and the anther belongs to the stamen (male part).
9. B. Spirogyra is a filamentous green alga with spiral chloroplasts; its thallus body has no true root, stem or leaf. Fungi lack chlorophyll, and bryophytes and pteridophytes are land plants with more complex bodies.
10. A. Blue-green algae are prokaryotes with no true nucleus, so they belong to Monera along with bacteria, despite the word 'algae' in their name. Protista holds single-celled eukaryotes like Amoeba and Paramecium.
11. C. Selaginella (spike moss) is a pteridophyte that reproduces by spores and has vascular tissue. Funaria is a moss and Marchantia a liverwort (both bryophytes), while Cycas is a gymnosperm.
12. D. Coconut is a monocot despite growing as a tall tree; classification depends on cotyledon number, not height. Mango, neem and banyan are dicots with net-veined leaves and tap roots.
13. D. Bryophytes (mosses, liverworts) live on land but their male gametes must swim through a film of water to reach the egg, hence 'amphibians of the plant kingdom'. Algae are largely aquatic; gymnosperms do not need surface water for fertilisation.
14. C. Pteridophytes such as ferns have xylem and phloem and differentiated organs, while the listed algae and bryophytes lack true vascular tissue. Angiosperms also have vascular tissue but produce flowers and seeds. The question uses the traditional grouping rather than claiming a single living group literally was the first ancestor of all later plants.
15. B. Self-pollination keeps pollen within the same plant (pea and wheat are examples). Cross-pollination moves pollen between flowers of two different plants of the same species; fertilisation is the later fusion of male and female gametes.
16. A. Only I is correct. Ordinary vegetative propagation copies the parent genotype without sexual recombination, although somatic mutations can occur. Gymnosperms bear seeds that are not enclosed in a fruit; enclosed seeds characterise angiosperms.
17. B. Statement I is wrong: pteridophytes such as ferns are seedless and reproduce by spores, often seen as brown sori under the leaves. Statement II is correct: bryophytes have no xylem or phloem, which keeps them small and restricted to damp places.
18. A. Monocots commonly have one cotyledon, fibrous roots, floral parts in threes and parallel leaf venation. Net-like (reticulate) venation is more usual in dicots. These are diagnostic trends rather than exception-free rules across every species.
19. A. Gram is a dicot, with two cotyledons, net-veined leaves and a tap root. Rice, maize and banana are monocots, with one cotyledon, parallel venation and fibrous roots; banana is a monocot despite its tree-like height.
20. B. Whittaker's five kingdoms are Monera, Protista, Fungi, Plantae and Animalia. Archaea was recognised later as a separate domain in Carl Woese's three-domain system (1990), not as one of Whittaker's kingdoms.
21. B. The scion is the shoot or bud piece attached to a rooted stock (rootstock). The scion is chosen for desirable shoot and fruit traits; the stock contributes the root system and can affect vigour and tolerance. Grafting is a vegetative propagation method.
22. D. Viable seeds generally need water, oxygen and a suitable temperature. Direct sunlight is not universally required: many seeds germinate underground in darkness, while some species have specific light requirements. The question says “universally” to allow that species differ.
23. D. The American ecologist R.H. Whittaker proposed the five kingdoms — Monera, Protista, Fungi, Plantae and Animalia — in 1969, using cell structure, body organisation, mode of nutrition and phylogenetic relationships as criteria.
24. D. Auxin maintains apical dominance (A-2); gibberellin causes bolting/stem elongation (B-1); cytokinin promotes cell division and delays leaf senescence (C-4); abscisic acid closes stomata during drought (D-3).
25. A. 6CO2 + 6H2O + light → C6H12O6 + 6O2 (in presence of chlorophyll). So one glucose molecule is accompanied by the release of 6 O2 molecules; the same 6:1 ratio appears in reverse in aerobic respiration.
26. C. Lenticels are lens-shaped openings in the bark of woody stems that allow gas exchange for respiration. Stomata do this on leaves, hydathodes release liquid water (guttation) and nectaries secrete nectar.
27. D. The Calvin cycle runs in the stroma, the fluid region surrounding the thylakoids. It fixes CO₂ using ATP and NADPH supplied by light reactions on thylakoid membranes. “Light-independent” means the cycle has no direct photon-capture step; it does not mean a healthy photosynthesising leaf normally completes the cycle without products of light reactions.
28. B. In the light reaction, water molecules are split (photolysis) in the thylakoids, releasing oxygen. Carbon dioxide is fixed into sugar in the Calvin cycle and does not supply the released O2; glucose is the product, not the source.
29. B. Cultivated tomato is commonly described as day-neutral: it can flower across a range of day lengths. Chrysanthemum is a standard short-day example, while spinach and many wheat types respond to longer days. Photoperiod responses can differ across species and cultivars, so the answer is a general teaching example.
30. B. Chrysanthemum is a standard short-day example: flowering is favoured when uninterrupted night duration crosses a critical value. Spinach is a long-day example; cultivated tomato is a common day-neutral example. Particular cultivars and growing conditions can vary, so this is the textbook classification.
31. A. IAA is the principal natural auxin, made at the shoot tip and responsible for cell elongation, apical dominance and tropic bending. GA3 is a gibberellin, ABA is the stress hormone and zeatin is a natural cytokinin.