BBYCT 135 Solved Guess Paper 2026 for Plant Anatomy and Embryology (IGNOU BSCG)

Sample 1 of 5  |  Block 2, Secondary Growth  |  5 + 5 = 10 marks  |  Last appeared: June 2025, December 2025, December 2024

Question. (a) Describe secondary growth in a typical dicotyledonous stem using a properly labelled diagram. (5) (b) Explain briefly the main features of unusual secondary growth (cambial variants) in stems and roots. (5)

Answer (a) Secondary growth in a typical dicotyledonous stem. Secondary growth is the growth in thickness produced by lateral meristems, which lay down secondary vascular tissues in the stem.

    
1. Cambium ring forms. Cells lying between the primary xylem and primary phloem become meristematic. This is the intrafascicular (fascicular) cambium.
    
2. Interfascicular cambium joins in. Cells between the bundles also become meristematic. Both types join to make one complete ring of vascular cambium.
    
3. Xylem inside, phloem outside. The ring divides. Cells cut off on the inner side become secondary xylem (wood). Cells cut off outside become secondary phloem.
    
4. Old phloem is crushed. As more wood is added the stem widens. The first-formed secondary phloem gets stretched, destroyed and replaced by new phloem.
    
5. Phellogen makes cork. Another lateral meristem, the phellogen (cork cambium), forms outside. It cuts off cells that become suberised and die, giving a protective cork layer.
    
6. Outer tissues are lost. Cortex and epidermis get compressed and destroyed. The epidermis is replaced by this new protective secondary tissue.
  

Answer (b) Cambial variants. In stems, four patterns occur. In Bignonia the cambium is normal in position but makes unequal amounts of xylem and phloem, giving a ridged and furrowed xylem cylinder with four phloem wedges. In Aristolochia, Vitis, Clematis and Tinospora the interfascicular cambium makes only ray-like parenchyma, so broad medullary rays and a fluted cylinder form. In Serjania the bundle groups are cut off and act as separate cylinders, each with its own cambium and periderm. In Chenopodium, Amaranthaceae, Tecoma, Salvadora, Avicennia and Bougainvillea, accessory cambia arise one after another and bury patches of phloem inside the xylem, which is interxylary or included phloem.

In roots the variants appear mainly in storage roots. In beet root (Beta vulgaris) the first cambium soon stops and several concentric cambia form from pericycle and phloem, producing storage parenchyma seen as alternate dark and light rings. In sweet potato (Ipomoea batatas) secondary cambia arise in the parenchyma around single vessels or vessel groups, cutting tracheary elements towards the vessel and sieve tubes away from it.

Diagram required. The PDF carries a two-part figure showing the complete cambium ring and the stem after two years of growth.

Sample 2 of 5  |  Blocks 1 and 2, Leaf and Protective Features  |  10 marks  |  Last appeared: December 2025, June 2024

Question. Define the term guard cells. How do guard cells control stomatal pore opening and closing? Discuss with the help of an appropriate diagram. Also mention the types of stomata based on morphology.

Answer. Stomata include a pore called stoma surrounded by specialised cells called guard cells. An aperture (pore) along with two guard cells surrounded by subsidiary cells constitutes a stoma.

    
1. Turgor pressure is the switch. The guard cells open or close the stomatal pore by changing turgor pressure. This controls the rate of transpiration and gas exchange.
    
2. Water enters and the pore opens. When internal pressure rises, the pectin-rich guard cells expand along their long axis, the two cells bend apart and the pore opens.
    
3. Uneven wall thickening. The wall next to the pore is thicker than the opposite wall, so the cell must curve when it swells.
    
4. Potassium moves in and out. Movement of water between guard cells and neighbouring cells is controlled by changes in water potential as potassium ions are transported between the two cells.
    
5. Water leaves and the pore closes. When guard cells lose water they become flaccid, the two cells come together and the pore is closed.
    
6. In grasses (dumb-bell type). The ends are thin-walled and the middle is thick. On absorbing water the ends swell and push the narrow middle regions apart, opening the pore.
    
7. Role of subsidiary cells. The pore, guard cells and subsidiary cells together form the stomatal complex. Subsidiary cells store large amounts of water and ions.
  

Types of stomata based on morphology. Graminaceous, with dumb-bell shaped guard cells as in grasses. Anomocytic, with no subsidiary cells, as in Ranunculus and Boerhaavia. Anisocytic, with three subsidiary cells of unequal size, as in Brassicaceae, Bryophyllum and Kalanchoe. Paracytic, with two subsidiary cells parallel to the long axis of the pore, as in Rubiaceae and Phaseolus. Diacytic, with two subsidiary cells at right angles to the pore, as in Caryophyllaceae. Tetracytic, with four subsidiary cells, two polar and two lateral, as in Rhoeo and Tradescantia. Actinocytic, with a circle of radially elongated subsidiary cells, as in Vitis.

Diagram required. Surface view of kidney-shaped and dumb-bell shaped guard cells in the open and closed condition.

Sample 3 of 5  |  Block 3, Structural Organisation of Flower  |  10 marks  |  Last appeared: December 2023 (recent-paper gap)

Question. List the various types of ovules and describe the structure of an ovule with the help of a labelled diagram.

Answer. Ovule (megasporangium) is the structure which develops into seeds. It consists of a central mound of tissue known as nucellus which is enclosed by one or two coverings called integuments.

    
1. Integuments. They cover the ovule and mature into the seed coat. An ovule may be unitegmic or bitegmic. The bitegmic condition is common in Polypetalae and monocots, unitegmic in Sympetalae.
    
2. Micropyle. The small opening left by the integuments at the apical end, and the main passage for entry of the pollen tube.
    
3. Micropylar and chalazal poles. The end with the micropyle is the micropylar pole. The opposite end, where the funiculus is attached, is the chalazal pole.
    
4. Funiculus. The stalk-like structure through which the ovule is attached to the placenta.
    
5. Nucellus. A homogeneous mass of tissue inside the integuments that differentiates to form the female gametophyte. When it persists in the mature seed it is called perisperm, as in black pepper.
    
6. Tenuinucellate and crassinucellate. If the megaspore mother cell stays hypodermal with a single nucellar layer above it, the ovule is tenuinucellate. If nucellar divisions bury the sporogenous cell in a mass of tissue, it is crassinucellate.
    
7. Hypostase and endothelium. Hypostase cells at the base of the embryo sac aid nutrient transport and water balance. In unitegmic ovules the innermost integument layer becomes the endothelium or integumentary tapetum.
    
8. Obturator. An outgrowth of the placenta, funiculus, integument or style projecting towards the micropyle, giving mechanical and chemical guidance to the pollen tube.
  

Six types of ovules. Anatropous, the commonest type, where the micropylar end lies parallel and close to the funiculus. Orthotropous, where the micropyle faces upward in line with the funiculus. Campylotropous, curved but less than anatropous. Hemianatropous, where the micropyle lies at right angles to the funiculus. Amphitropous, where nucellus and embryo sac curve like a horse-shoe. Circinotropous, which first becomes anatropous and then curves further until the micropyle faces upward.

Diagram required. One longitudinal section of an anatropous ovule plus a strip showing all six ovule types side by side.

Sample 4 of 5  |  Block 4, Endosperm  |  10 marks  |  Last appeared: June 2025, December 2025, June 2023

Question. Write a note on the nature of endosperm. Describe the different types of endosperm with suitable diagrams.

Answer. The most agreeable view regarding the morphological nature of the endosperm in angiosperms is that it is undifferentiated tissue that shows different degrees of polyploidy and its function is to provide nutrition for growth of the embryo.

    
1. In gymnosperms it is haploid. The endosperm is gametophytic tissue formed by continued free nuclear divisions of the functional megaspore.
    
2. In angiosperms it is triploid. It develops from the primary endosperm nucleus formed by fusion of the polar nuclei with a male nucleus.
    
3. An old debate. Strasburger (1900) termed the fusion of the second male gamete vegetative fertilisation, and many embryologists treated the endosperm as a second or distorted embryo.
    
4. The evolutionary advantage. In angiosperms endosperm develops only if an embryo has also developed, whereas in gymnosperms it develops even without an embryo, which causes wastage.
  

Three types of endosperm. In the nuclear type the primary endosperm nucleus undergoes free nuclear divisions without wall formation, the free nuclei are pushed to the periphery by the expanding central vacuole, and wall formation is centripetal. It is common in cereals, and in young coconut the liquid syncytium is exactly this stage. In the cellular type every division is immediately followed by wall formation, so no free nuclear stage occurs, as in Balsam, Petunia, barley, grasses and Utricularia. In the helobial type the nucleus moves to the chalazal end, a transverse wall divides the embryo sac into a large micropylar chamber and a small chalazal chamber, free nuclear divisions occur in the micropylar chamber, and the chalazal chamber is eventually crushed. It is intermediate between the other two and is found mainly in monocots.

Diagram required. A three-panel figure showing nuclear, cellular and helobial endosperm.

Sample 5 of 5  |  Blocks 1 to 4 mixed  |  5 × 2 = 10 marks  |  Appeared in all six analysed sessions

Question. Differentiate between any two of the following: (i) Simple and Complex tissues (ii) Meristematic and Permanent tissues (iii) Heartwood and Sapwood (iv) Tenuinucellate and Crassinucellate ovules (v) Syngamy and Triple fusion (vi) Nuclear and Cytoplasmic male sterility.

Answer, showing one pair from the set. A differentiate question appears in every session and scores best when written as a table with four or five points of difference.

The complete file works out all six pairs in this format, so whichever two the examiner offers, a ready table is available.