BBYCT 137 key facts: June 2026
- Course code: BBYCT-137
- Subject: Plant Physiology and Metabolism
- Programme: Bachelor of Science (General) (BSCG); also listed in BSCM
- Blocks and units: 4 blocks, 16 units
- Maximum marks: 50
- Duration: 2 hours
- Questions in the June 2026 paper: 7 numbered questions, 12 answerable parts (Q1 compulsory, then any 4 of Q2 to Q7)
- Companion lab course: BBYCL-138 (4 demonstrations, 8 experiments)
- Solved on this page: 2 parts (Q4(b) and Q7(a)); all 12 in the paid file
BBYCT 137 Solved Question Paper June 2026 gives you complete, exam-length answers to the official IGNOU term-end paper of Plant Physiology and Metabolism, written for BSCG learners. Our botany team answered all 12 parts of the paper, from the Question 1 matching task to the Z-scheme, the Krebs cycle and the pentose phosphate pathway, with labelled diagrams wherever the paper asks for them.
1. What the June 2026 Solved Paper Covers
BBYCT 137 Plant Physiology and Metabolism is the IGNOU botany core course that explains how plants take in water and minerals, make and move food, respire and respond to hormones, light and stress.
The June 2026 paper tests that whole range in 50 marks. Question 1 alone draws on seven of the 16 units, from phloem structure and the Nernst equation to respiratory quotient and vernalisation. Questions 2 to 7 then ask for short notes, differences and long answers, with the Z-scheme set as a full 10-mark question.
Every part of the paper is answered in the full file, so you can check your own attempt line by line or revise the exact topics IGNOU chose this session. The answers follow the four official blocks, which you can read on the official BBYCT-137 course page on eGyanKosh.
2. Two Answers Solved in Full, Ten Held Back
This page solves 2 of the 12 parts in full, Question 4(b) on Münch's hypothesis and Question 7(a) on photoperiodism; the other 10 are listed below exactly as printed and answered only in the full file.
Münch's mass flow hypothesis for phloem transport
Question 4 (b): Discuss Münch's mass flow hypothesis for phloem transport. (5)
Münch's mass flow hypothesis, also called the pressure flow hypothesis, was proposed by the German botanist Ernst Münch in 1930. It explains phloem transport as a bulk flow of sugar solution through sieve tubes, driven by a gradient of turgor pressure between a source, where sugar is made, and a sink, where it is used or stored.
Physical model. Münch built the idea on a simple set-up. Two osmometers, A and B, are joined by a narrow tube and dipped in water. A holds a concentrated sugar solution and B a dilute one. Water enters A by osmosis, turgor pressure in A rises, and the solution is pushed through the tube into B. The flow continues until the two concentrations become equal.
Diagram to draw. Two bulbs joined at the top by a horizontal tube, both standing in a water bath. Label the left bulb A: source, high sugar, high turgor (the leaf) and the right bulb B: sink, low sugar, low turgor (the root or fruit). Mark the connecting tube as the sieve tube, with an arrow showing flow from A to B. Show water entering A from the bath by osmosis, water leaving B, and a dashed return arrow along the bath labelled xylem: water returns to the source. The full file carries this as a labelled figure.
How it works in the plant
- Loading at the source: in leaf mesophyll, sucrose is actively loaded into the sieve element and companion cell complex, which lowers the water potential inside the sieve tube.
- Water entry: water moves in by osmosis from the neighbouring xylem, so turgor pressure builds up at the source end.
- Bulk flow: the sap moves as a whole along the sieve tubes, from high pressure at the source to low pressure at the sink.
- Unloading at the sink: in roots, fruits and storage organs, sucrose is removed and used or stored, so water potential rises and water leaves the sieve tube.
- Water return: that water re-enters the xylem, so the circuit keeps running as long as loading and unloading continue.
Supporting evidence. Sap oozes out under pressure from cut phloem and from aphid stylets left in a sieve tube. Sucrose concentration falls steadily from source to sink. Girdling (removing a ring of bark) stops sugar movement below the ring, and sugar collects above it.
Limitations. The hypothesis gives the living sieve tube only a passive role, yet metabolic inhibitors slow translocation. It also struggles with reports of two-way movement within one sieve tube, and sieve plates add resistance to flow. Even so, a modified pressure flow model remains the most widely accepted explanation today.
Conclusion. Phloem sap moves by bulk flow from source to sink, pushed by a turgor gradient that loading and unloading of sucrose keep alive.
Photoperiodism and the role of the dark period
Question 7 (a): What is photoperiodism? Classify plants based on their response to day length and explain the role of the dark period in flowering. (5)
Photoperiodism is the response of a plant to the relative lengths of day and night, seen most clearly in the timing of flowering. W.W. Garner and H.A. Allard (1920) discovered it while studying Maryland Mammoth tobacco, which flowered only when days grew short. The day length that separates flowering from staying vegetative is called the critical day length.
| Class | Flowers when | Examples |
|---|---|---|
| Short-day plants (long-night plants) | Day is shorter than the critical day length, so the night is longer than a critical dark period | Xanthium, Chrysanthemum, Biloxi soybean, Maryland Mammoth tobacco |
| Long-day plants (short-night plants) | Day is longer than the critical day length | Hyoscyamus niger (henbane), spinach, radish, wheat |
| Day-neutral plants | Flowering does not depend on day length | Tomato, cucumber, cotton, sunflower |
| Dual day-length plants | Need one day length followed by the other | Long-short-day Bryophyllum; short-long-day Trifolium repens (white clover) |
Role of the dark period in flowering
- Night length is the real signal: Hamner and Bonner (1938) showed with Xanthium that flowering needs one unbroken dark period longer than about 8.5 hours. Breaking the light period with darkness had no effect.
- Night-break effect: a short flash of light in the middle of the long night stops flowering in short-day plants and can bring on flowering in long-day plants.
- Phytochrome: red light (about 660 nm) gives the strongest night break and far-red light (about 730 nm) cancels it. Phytochrome switches between the Pr and Pfr forms, and during a long night Pfr slowly falls.
- Leaves sense, the apex responds: the photoperiod is perceived in the leaves, and a flowering stimulus, named florigen by Chailakhyan, moves through the phloem to the shoot apex.
Conclusion. Plants read the length of the night, not the day, and phytochrome turns that signal into a decision to flower.
3. Questions Answered Only in the Full File
These 10 parts are printed exactly as they appear in the June 2026 paper, with IGNOU's own numbering and marks. Their answers, diagrams and tables are only in the paid file.
Question 1 (a): Match the items given in Column A with those in Column B. (4 × ½ = 2)
Question 1 (b): Fill in the blanks. (3 × 1 = 3)
(i) Cells undergo plasmolysis when kept in ............... solution.
(ii) At full turgor, the ψw of a cell will be ............... .
(iii) ............... is the plant hormone responsible for fruit ripening.Question 1 (c): Define the following terms. (5 × 1 = 5)
(i) Water potential (ii) Nernst equation (iii) Respiratory quotient (iv) Short-day plant (v) Vernalisation
| Column A | Column B |
|---|---|
| (i) Callose | (a) Xylem vessels |
| (ii) Water conduction | (b) Sieve plate pores |
| (iii) Prevents the flow of phloem sap from injured cells | (c) Wall invaginations |
| (iv) Transfer cells | (d) P-proteins |
Question 2: Write short notes on any two of the following. (2 × 5 = 10)
(i) Role of auxins and gibberellins in plant growth
(ii) Photorespiration and its significance
(iii) Enzyme inhibition (competitive and non-competitive)
(iv) Physiological functions of abscisic acid (ABA)Question 3: Differentiate between any four of the following. (4 × 2½ = 10)
(i) Diffusion and osmosis
(ii) Photosystem I and photosystem II
(iii) Abiotic stress and biotic stress
(iv) Paraheliotropic and diaheliotropic movement
(v) Anaerobic respiration and aerobic respiration
Question 4 (a): Explain the mechanism of stomatal opening and closing, including the role of guard cells. (5)
Question 5: Describe the Z-scheme of photosynthesis. Support your answer with a well labelled diagram. (10)
Question 6 (a): Describe the steps of the Krebs cycle with a labelled diagram. (5)
Question 6 (b): Describe the plant responses to salinity stress conditions. (5)
Question 7 (b): Explain the pentose phosphate pathway and its significance in plants. (5)
4. Block and Unit Syllabus
BBYCT-137 has 4 blocks and 16 units, and the June 2026 paper drew on 13 of those 16 units; only Units 3, 12 and 13 were left out. The last column shows which June 2026 parts come from each unit.
| Block | Unit | Core topics | June 2026 parts |
|---|---|---|---|
| Block 1: Water and Mineral Nutrition | Unit 1: Plant-Water Relations | Components of water potential; osmosis and plasmolysis; imbibition | Q1(b)(i), Q1(b)(ii), Q1(c)(i), Q3(i) |
| Block 1: Water and Mineral Nutrition | Unit 2: Water Transport | Transpiration and guard cell movement; cohesion-tension theory; root water pathways | Q1(a)(ii), Q4(a) |
| Block 1: Water and Mineral Nutrition | Unit 3: Mineral Nutrition | Criteria of essentiality; macronutrient and micronutrient deficiency; hydroponics | — |
| Block 1: Water and Mineral Nutrition | Unit 4: Nutrient Transport | Passive and active ion uptake; Nernst equation; carriers and pumps | Q1(c)(ii) |
| Block 2: Photosynthesis and Translocation of Photosynthates | Unit 5: Photosynthesis | Chlorophyll structure; absorption and action spectra; photosystems and light-harvesting complexes | Q3(ii) |
| Block 2: Photosynthesis and Translocation of Photosynthates | Unit 6: Photosynthesis Mechanism | Z-scheme; cyclic and non-cyclic photophosphorylation; Calvin-Benson cycle | Q5 |
| Block 2: Photosynthesis and Translocation of Photosynthates | Unit 7: C2, C4 and CAM Plants | Photorespiration across chloroplast, peroxisome and mitochondrion; Kranz anatomy; CAM | Q2(ii) |
| Block 2: Photosynthesis and Translocation of Photosynthates | Unit 8: Translocation in Phloem | Sieve tube structure; phloem loading and unloading; pressure flow | Q1(a)(i), Q1(a)(iii), Q1(a)(iv), Q4(b) (Sample 1) |
| Block 3: Enzymes and Respiration | Unit 9: Enzymes | Enzyme classification; Km and Vmax; types of inhibition | Q2(iii) |
| Block 3: Enzymes and Respiration | Unit 10: Respiration | Aerobic and anaerobic respiration; respiratory quotient; mitochondrial structure | Q1(c)(iii), Q3(v) |
| Block 3: Enzymes and Respiration | Unit 11: Respiration Mechanism | Glycolysis; Krebs cycle; pentose phosphate pathway | Q6(a), Q7(b) |
| Block 4: Nitrogen Metabolism and Plant Growth Regulators | Unit 12: Nitrogen Metabolism | Nitrate and nitrite reductase; ammonia assimilation; transamination | — |
| Block 4: Nitrogen Metabolism and Plant Growth Regulators | Unit 13: Biological Nitrogen Fixation | Symbiotic nitrogen fixers; nodule formation; nitrogenase and leghaemoglobin | — |
| Block 4: Nitrogen Metabolism and Plant Growth Regulators | Unit 14: Plant Growth Regulators | Auxins and gibberellins; cytokinins; abscisic acid and ethylene | Q1(b)(iii), Q2(i), Q2(iv) |
| Block 4: Nitrogen Metabolism and Plant Growth Regulators | Unit 15: Plant Response to Light and Temperature | Photoperiodism and phytochrome; vernalisation; light-driven leaf movements | Q1(c)(iv), Q1(c)(v), Q3(iv), Q7(a) (Sample 2) |
| Block 4: Nitrogen Metabolism and Plant Growth Regulators | Unit 16: Plant Stress | Abiotic and biotic stress; salinity tolerance; heat shock proteins | Q3(iii), Q6(b) |
Units 3, 12 and 13 still matter, because mineral deficiency, nitrate reduction and leghaemoglobin have all been asked in earlier June papers. If you need a slower walk through those units, our BBYCT 137 Study Material covers them in simple English.
5. Paper Pattern and Marks Split
The June 2026 paper carries 50 marks in 2 hours: Question 1 (10 marks) is compulsory, and you attempt any four of Questions 2 to 7 at 10 marks each.
| Question | What it asks | Marks | Choice | Units tested |
|---|---|---|---|---|
| Q1 | 4 matching pairs, 3 blanks and 5 definitions | 2 + 3 + 5 = 10 | Compulsory | 1, 2, 4, 8, 10, 14, 15 |
| Q2 | Short notes on hormones, photorespiration and enzyme inhibition | 2 × 5 = 10 | Any two of four | 7, 9, 14 |
| Q3 | Five pairs to differentiate, from diffusion to respiration types | 4 × 2½ = 10 | Any four of five | 1, 5, 10, 15, 16 |
| Q4 | Guard cell mechanism and phloem mass flow | 5 + 5 | Optional | 2, 8 |
| Q5 | Z-scheme with a labelled diagram | 10 | Optional | 6 |
| Q6 | Krebs cycle diagram and salinity responses | 5 + 5 | Optional | 11, 16 |
| Q7 | Photoperiodism and the pentose phosphate pathway | 5 + 5 | Optional | 11, 15 |
One change is worth noticing. The June 2022 and June 2024 papers let you choose four questions from Questions 2 to 8, a pool of seven. June 2026 cut the pool to six, so skipping a whole block has become riskier than before.
Seeing how the format moved across sessions is easier with the papers side by side; our IGNOU Previous Year Question Paper section groups past papers by course code so you can do exactly that.
6. Topics That Keep Returning in BBYCT 137
In the three official papers we checked (June 2022, June 2024 and June 2026), eight topic groups appeared every time, led by enzymes, photoperiodism, vernalisation and plant stress. Question 1 items are counted along with long questions.
| Topic group | Jun 2022 | Jun 2024 | Jun 2026 | Papers (of 3) |
|---|---|---|---|---|
| Enzyme activity, inhibition and allosteric enzymes | Q8(c) | Q7(a), Q7(b) | Q2(iii) | 3 |
| Photoperiodism and phytochrome | Q1(b)(ii), Q6(a) | Q6(b) | Q1(c)(iv), Q7(a) (Sample 2) | 3 |
| Vernalisation | Q6(b) | Q1(c)(iv) | Q1(c)(v) | 3 |
| Plant stress: pollutants, heat shock proteins, salinity | Q7(b) | Q8(ii) | Q3(iii), Q6(b) | 3 |
| Water relations: osmosis, imbibition, plasmolysis | Q1(c)(i) | Q1(c)(i) | Q1(b)(i), Q3(i) | 3 |
| Phloem transport and phloem sap | Q1(a)(iii) | Q3(a), Q3(b) | Q1(a), Q4(b) (Sample 1) | 3 |
| Auxins and gibberellins | Q4 | Q1(a)(iii) | Q2(i) | 3 |
| Abscisic acid and ethylene | Q8(a) | Q6(a) | Q1(b)(iii), Q2(iv) | 3 |
| Stomatal opening and closing | Q1(b)(i), Q7(a) | — | Q4(a) | 2 |
| Photorespiration | — | Q2(b) | Q2(ii) | 2 |
| Light reaction, photosystems and ATP synthesis | — | Q2(a), Q8(iv) | Q3(ii), Q5 | 2 |
| Krebs (TCA) cycle | Q5 | — | Q6(a) | 2 |
| Respiratory quotient and respiration types | — | Q1(c)(v) | Q1(c)(iii), Q3(v) | 2 |
| Ion uptake: active transport and Nernst equation | — | Q8(i) | Q1(c)(ii) | 2 |
| Macronutrients and deficiency symptoms | Q3(a), Q3(b) | Q4 | — | 2 |
| Glycolysis | Q1(a)(iv) | Q5 | — | 2 |
The count uses only papers we could open on IGNOU's own servers, so it covers three June sessions and no December papers yet. A topic seen twice here is still a strong candidate, and glycolysis and macronutrients, both skipped in June 2026, deserve a full revision before the next exam.
For predicted questions across more IGNOU courses, our IGNOU Solved Guess Paper page lists BBYCT-137 alongside the other BSCG botany codes.
7. How Our Answers Are Written and Checked
Each answer is written by our botany subject team from the official BBYCT-137 blocks, checked against earlier IGNOU papers and reviewed before release.
We start from the exact wording of the June 2026 paper. A 5-mark part gets about 250 to 350 words with one labelled diagram or table, while the 10-mark Z-scheme gets about 500 to 600 words and a full diagram. Names and years, such as Münch (1930) or Garner and Allard (1920), are checked against the blocks.
The file also shows where an old question returns in new words. The Krebs cycle came back in June 2026 after June 2022, and photorespiration repeated from June 2024, so those answers point out what changed in the wording.
8. Practical File Index Using the BBYCL-138 Lab
BBYCT-137 is a theory course; its practical work sits in the companion lab course BBYCL-138, and each exercise in that record file supports at least one part of the June 2026 paper.
| No. | Lab exercise | June 2026 part it supports |
|---|---|---|
| Demonstration 1 | Bolting | Q2(i), gibberellins in stem growth |
| Demonstration 2 | Effect of auxins on rooting of stem cuttings | Q2(i), auxins in root initiation |
| Demonstration 3 | Root respiration | Q3(v), aerobic and anaerobic respiration |
| Demonstration 4 | Suction due to transpiration | Q1(a)(ii), water conduction |
| Experiment 1 | Osmotic potential of cell sap by the plasmolytic method | Q1(b)(i) and Q3(i), plasmolysis and osmosis |
| Experiment 2 | Effect of light and wind on transpiration by an excised twig | Q4(a), guard cell response |
| Experiment 3 | Stomatal index and stomatal frequency in a mesophyte and a xerophyte | Q4(a), stomatal mechanism |
| Experiment 4 | Hill reaction | Q5, photolysis at PS II |
| Experiment 5 | Catalase activity and the effect of pH and enzyme concentration | Q2(iii), enzyme behaviour |
| Experiment 6 | Effect of light intensity and bicarbonate on oxygen evolution | Q5, light reaction output |
The six experiments above are the ones we have matched to this paper; check your BBYCL-138 manual for the remaining two. Doing the Hill reaction and the plasmolytic method in the lab makes Questions 5 and 3 far easier to write, because you have seen the result yourself. We also prepare the complete BBYCL-138 record file with aim, materials, procedure, observations and result; ask for it on the same WhatsApp number.
9. Solved File Index
The full file answers all 12 parts of the June 2026 paper: 2 are on this page and 10 are in the paid file only.
| Part | Topic | Marks | Unit | Where the answer is |
|---|---|---|---|---|
| Q1(a) | Matching: phloem and xylem structures | 4 × ½ = 2 | Units 2, 8 | Full file |
| Q1(b) | Three fill-in-the-blanks | 3 × 1 = 3 | Units 1, 14 | Full file |
| Q1(c) | Five one-mark definitions | 5 × 1 = 5 | Units 1, 4, 10, 15 | Full file |
| Q2 | Short notes, any two of four | 2 × 5 = 10 | Units 7, 9, 14 | Full file |
| Q3 | Differences, any four of five | 4 × 2½ = 10 | Units 1, 5, 10, 15, 16 | Full file |
| Q4(a) | Stomatal opening and closing | 5 | Unit 2 | Full file |
| Q4(b) | Münch mass flow hypothesis | 5 | Unit 8 | Sample 1 above |
| Q5 | Z-scheme with labelled diagram | 10 | Unit 6 | Full file |
| Q6(a) | Krebs cycle with diagram | 5 | Unit 11 | Full file |
| Q6(b) | Plant responses to salinity | 5 | Unit 16 | Full file |
| Q7(a) | Photoperiodism and dark period | 5 | Unit 15 | Sample 2 above |
| Q7(b) | Pentose phosphate pathway | 5 | Unit 11 | Full file |
Writing other BSCG papers this term? Our BSCG Question Paper collection covers the other botany, chemistry and zoology codes session by session, so you can plan every paper together.
10. Programmes That Include BBYCT 137
BBYCT 137 Plant Physiology and Metabolism is studied in the IGNOU BSCG under the botany discipline and is also listed in the newer BSCM, with the same code and the same term-end paper.
In the Bachelor of Science (General), BBYCT-137 is one of the botany core courses, alongside papers such as BBYCT-131 Biodiversity (Microbes, Algae, Fungi and Archegoniates) and BBYCT-135 Plant Anatomy and Embryology. Anatomy of xylem, phloem and stomata from BBYCT-135 feeds straight into Questions 1(a) and 4 here.
The Bachelor of Science (Multidisciplinary), BSCM, runs under IGNOU's four-year undergraduate structure and carries BBYCT-137 with the BBYCL-138 lab. Learners in both programmes sit the same June and December papers, so one solved file works for either; check your programme guide to confirm your semester.
11. How to Get the Full Solved Question Paper
Send "BBYCT-137 June 2026" on WhatsApp to 9899436384, and the full file with all 12 answered parts is shared on the same chat after payment.
- Message 9899436384 with the course code and your programme, BSCG or BSCM.
- Our IGNOU desk replies with the price and payment options.
- Receive the PDF with all 12 parts, including the 10 not shown here.
- Message the same number with any doubt while you revise.
12. BBYCT 137 Plant Physiology and Metabolism FAQs
How many answers does the full file contain, and how do I get it?
The full file answers all 12 parts of the June 2026 paper, from the Question 1 matching task, blanks and definitions to every long question from 2 to 7. This page shows 2 of those parts in full, so 10 are only in the file. Send BBYCT-137 June 2026 on WhatsApp to 9899436384, and our IGNOU desk replies with the price and shares the PDF on the same chat.
Which answers are shown on this page?
Two long answers are shown in full: Question 4(b) on Münch's mass flow hypothesis for phloem transport, and Question 7(a) on photoperiodism, the classes of plants by day length and the role of the dark period. Both are 5-mark parts. They show how we handle a labelled model diagram and a classification answer, the two answer styles this paper leans on most.
What is the exam pattern of the June 2026 paper?
The June 2026 BBYCT-137 paper carries 50 marks for 2 hours. Question 1 is compulsory and worth 10 marks, split into a 2-mark matching task, 3 blanks and 5 one-mark definitions. You then answer any four of Questions 2 to 7, each worth 10 marks. The June 2022 and June 2024 papers allowed a choice from Questions 2 to 8 instead.
Which BBYCT 137 topics repeat most in IGNOU term-end papers?
In the three official papers we checked, June 2022, June 2024 and June 2026, eight topic groups appeared every time: enzymes, photoperiodism, vernalisation, plant stress, water relations, phloem transport, auxins with gibberellins, and ABA with ethylene. Stomatal movement, photorespiration and the Krebs cycle appeared twice. Treat these as revision priorities rather than a promise of what IGNOU will set next.
Does BBYCT 137 have a practical exam?
Not within BBYCT-137 itself, which is a theory course with a 2-hour written paper. The practical work sits in the companion lab course BBYCL-138, with 4 demonstrations and 8 experiments such as the plasmolytic method, stomatal index and the Hill reaction. We also prepare the BBYCL-138 record file, and you can ask for it on the same WhatsApp number.
Which programmes include BBYCT 137?
BBYCT-137 is a botany core course of the IGNOU School of Sciences. It is studied in the Bachelor of Science (General), known as BSCG, and it also appears in the newer Bachelor of Science (Multidisciplinary) under the four-year structure, known as BSCM. Learners in both programmes write the same term-end paper, so one solved file serves either programme.
Are these official IGNOU answers?
No. IGNOU publishes question papers, not model answers. Our botany subject team wrote every answer after studying the official BBYCT-137 blocks and earlier term-end papers, and Academic Head Sheetal Kirola reviewed them. Unnati Educations is an independent study-support platform and is not affiliated with IGNOU, so use the file as a revision guide alongside your course blocks.
How long should a BBYCT 137 answer be for 5 and 10 marks?
The paper sets no word limit, but time does. With 50 marks in 120 minutes, a 5-mark part deserves about 10 to 12 minutes, which is roughly 250 to 350 words plus one labelled diagram or table. A 10-mark question such as the Z-scheme needs about 500 to 600 words and a full diagram. The two samples on this page follow the 5-mark length.
13. Who Wrote and Checked the BBYCT 137 Answers
The BBYCT 137 answers were written by the Unnati Educations botany team and reviewed by Sheetal Kirola.
Prateek Talwar, a Company Secretary who founded Unnati Educations to support IGNOU and NIOS learners, publishes the IGNOU solved-paper series. Sheetal Kirola, Academic Head (M.Ed.), reviews every IGNOU file we release and checks step counts, labels and scientist names against the BBYCT-137 blocks.