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BBYCT-135: Plant Anatomy and Embryology

BBYCT-135: Plant Anatomy and Embryology

IGNOU Solved Assignment Solution for 2021-22

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Assignment Code: BBYCT-135/TMA/2021-2022

Course Code: BBYCT-135

Assignment Name: Plant Anatomy and Embryology

Year: 2021-2022 (1st July 2021 to 30th June 2022)

Verification Status: Verified by Professor


Note: Attempt all questions. The marks for each question are indicated against it.


Q1. a) Define the following terms: (1×5=5)


i) Adventitious roots

Ans) Roots which develop or arise from the other parts of the plant but not from the radical are called adventitious roots.


ii) Cuticle

Ans) A cuticle or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homologous, differing in their origin, structure, function, and chemical composition.


iii) Heterophylly

Ans) Marked changes in leaf morphology induced by environmental conditions; the ability to display such changes. Having more than one type of leaf on the same plant.


iv) Tapetum

Ans) The tapetum is a specialised layer of nutritive cells found within the anther, of flowering plants, where it is located between the sporangenous tissue and the anther wall. Tapetum is important for the nutrition and development of pollen grains, as well as a source of precursors for the pollen coat.  The cells are usually bigger and normally have more than one nucleus per cell.


v) Pollinia

Ans) A pollinium (plural pollinia) is a coherent mass of pollen grains in a plant that are the product of only one anther, but are transferred, during pollination, as a single unit. This is regularly seen in plants such as orchids and many species of milkweeds (Asclepiadoideae). Usage of the term differs: in some orchids two masses of pollen are well attached to one another, but in other orchids there are two halves (with two separate viscidia) each of which is sometimes referred to as a pollinium.


Q1. b) State whether these statements are ‘True’ or ‘False’: (1×5=5)


i) Funiculus is the stalk by which seeds are attached to a fruit wall.

Ans) True

ii) Collenchyma is composed of living cells with lignified cell wall.

Ans) True


iii) Outer and inner tangential walls of the endothecial cells help in dehiscence of anther.

Ans) True


iv) In dichogamy, the androecium and gynoecium mature at the same time.

Ans) False.


v) In most of the angiosperms the division of the zygote is transverse resulting in formation of a small apical cell and a large basal cell.

Ans) True


Q2. a) Explain different types of meristems found in plants with the help of a well labelled diagram. (5)

Ans) The meristems have been classified into different types on the basis of origin, development, position, plane of division and function in the plant body.


Based on their position in the plant body, meristems have been classified into three types:

  1. Apical meristem - These are in the growing points such as apices of primary stem and root.

  2. Lateral meristem - These are located and arranged parallel to the sides of the organs. They divide periclinally or radially. They help in increasing the diameter of stem or root. Example- vascular cambium, cork cambium.

  3. Intercalary meristem - the meristem lies between the regions of permanent tissues. It is considered as part of the primary meristem. It is present at the base of the leaves in monocotyledons and internodal region of grasses.


a) Structure of meristematic cells; b) location of various meristems.

Q2. b) Enumerate the major features of Tunica Corpus Theory of shoot apical organization.(5)

Ans) Schmidt first suggested the theory in 1924. According to the idea, there are two different zones in the shoot apex of angiosperms. The peripheral layer is made up of one or more layers of unevenly organised cells called tunica that shed along the cell division plane. The cells in the Tunica region divide in anticlinal directions, while the cells in the Corpus area divide in multiple planes. This idea does not establish a link between tissue layers and formation. Tunica and the corpus layer have different initials. The greater size and vacuolated contents of these cells distinguish them. Species to species, the number of initials in two zones varies.


The number of tunica layers found in different species or even individuals of the same species at various phases of shoot apex development could be due to plastochron periodicity. In Daphne pseudo-mezerum, Hare observed three to seven layers in the tunica area. Seasonal growth fluctuations could be to blame for these layers. The exterior layers of the corpus of some dicotyledonous families, like as Malvaceae and Lauraceae, are uniform and resemble tunica. The corpus has been hypothesised to have stratified cells that occasionally show periclinal divisions. As the two zones that are viewed as morphological entities are prone to fluctuations, the idea becomes more flexible.


Q3.a) Enlist the major characteristic features of halophytes. (5)

Ans) These are a special type of plants, which grow in saline soil with a high concentration of sodium chloride, magnesium sulphate and magnesium chloride and/or other salts. Halophytes are found near saline lakes (Sambhar lake) and on the coasts of oceans.


Characteristics of Halophytes:

  1. Halophytes of subtropical places are herbs, and those found in tropical zone are shrubs and trees.

  2. The roots are present closer to the surface.

  3. Adventitious roots that develop from the main stem of halophytic plants support these plants, after entering into the soil.

  4. A special type of roots is developed in halophytes, which are called pneumatophores. These roots arise vertically from the ground  and contain numerous pores called Lenticels  for the exchange of O2 and CO2.

  5. Stems are fleshy and covered with hairs.

  6. The leaves of halophytes are less developed and fleshy.

  7. Most of the halophytes show vivipary. The seeds germinate inside the fruit, which is still attached to the parent tree. The germinated seeds fall on the soil and begin their development.


Q3. b) List various types of simple and complex tissues. Describe complex tissues with suitable diagrams. (5)


Simple Tissues

There are five types of simple tissue: epidermis, parenchyma, collenchyma, sclerenchyma, and cork Epidermis covers the outer surfaces of leaves, young roots, and stems. As plants (especially woody plants) age, the epidermis (a primary tissue) on stems and roots is replaced by bark (a secondary tissue). Stomates are found with epidermal cells on leaves and stems but not on roots. Epidermal cells are living. They are almost entirely covered on the outer surface by a waxy cuticle, which retards water passage.


Complex Tissues

There are two kinds of complex tissues: xylem and phloem. Both are conducting tissues; xylem being involved in the movement of water from the roots to the upper parts of the plant and phloem being involved in transporting the products of photosynthesis. These tissues are somewhat different in angiosperms than in gymnosperms.

Xylem and Phloem in Angiosperms. Several tissues are derived from the apical meristem; one of these is procambium, which gives rise to the cambium. In a woody plant, the cambium is a cylinder of meristematic cells one cell in thickness and lying just below the bark. Its divisions produce xylem toward the center and phloem toward the outside. The xylem has two kinds of conducting cells, tracheids and vessels, and two kinds of nonconducting cells, fibres and parenchyma.


Structure of a) tracheids, Vessels and fibers; b) secondary wall thickenings in tracheary  elements.

a) Longitudinal view; and b) Transverse view of the phloem structure


Q4. Describe the secondary growth in dicot stem with the help of a well labelled diagram. (10)

Ans) Both interstellar (within the stele) and extrastellar (outside the stele) sections of the stem experience secondary growth in thickness and width. The cells that make up secondary tissues are produced by lateral meristems. The vascular cambium, a circular ring that lays down cells that make secondary vascular tissues, is formed when the lateral meristems extend and merge together. The cells in the vascular bundles between the primary xylem and primary phloem become meristematic and join the stem's vascular cambium. More cells become meristmatic between the vascular bundles. As a result, in a cross section of the stem, the vascular cambium appears as a continuous ring of tissue, with xylem and pith on the inside and phloem, cortex, and epidermis on the outside of the interfascicular cambium/cambium ring.


Diagrammatic representation of secondary growth in a dicot stem upto two year (stages (1-4) in T.S.).


Q5. a) List various types of ovules and describe them with outline diagrams. (5)

Ans) Throughout development, different plant species have varying degrees of curvature in their ovules. The micropyle's position in relation to the funiculus shifts. This divides the ovules into several groups.


Ovules can be classified into six types:

1. Anatropous - This is the most common type of ovule found in angiosperms. In this type, the micropylar end comes and lies parallel and close to the funiculus.


2. Orthotropous - In this type, the micropyle faces upward away from the chalaza and lies straight in the same line with respect to funiculus.

3. Camplyotropous - In this type, the ovule is curved but the curvature is much less than that in anatropous condition.


4. Hemianatropous - In this type, the micropyle comes and lies at right angles to the funiculus.


5. Amphitropous - In this type, the nucellus and the embryo sac become curved like a horseshoe.


6. Circinotropous - In this type, the ovule first becomes anatropous then the curvature continues till the micropyle faces upward.


Types of Ovules. a) Orthotropous; b) Circinotropous; c) Anatropous; d) Hemianatropous; e) Amphitropous; f) Campilotropous.


Q5. b) Define apomixis and list its types. Discuss various causes of apomixis and its importance. (5)

Ans) Apomixis can be defined as a means of asexual reproduction were fertilisation. The term was first coined by botanist Hans Winkler. The seed of a plant is developed without fertilisation.


Types of Apomixis:

1. Recurrent Apomixis

When meiosis in the megaspore mother cell is disrupted, an embryo sac emerges from that cell or from a neighbouring cell. As a result, the egg cell is diploic. Without fertilisation, the embryo develops directly from the diploid egg-cell. Crepis, Taraxacum, Poa (blue grass), and Allium (onion) are examples of plants that do not require pollination. Pollination appears to be required in Malus (apple) and Rudbeckia, either to drive embryo development or to create viable endosperm.

2. Non -recurrent Apomixis

Without fertilisation, an embryo develops directly from a normal egg cell (n). Because an egg cell is haploid, the resultant embryo is haploid as well.

3. Adventive Embryony

In oranges and roses, for example, embryos develop from a single cell or a group of cells in the nucellus or in the integuments. It is not classified as recurrent apomixis since it occurs outside the embryo sac, yet it is regenerated with the same accuracy. As in Citrus, Opuntia, many embryos may grow simultaneously within the embryo sac, resulting in poly-embryony.

4. Vegetative apomixis

In Poabulbosa, Allium, Agave, and grass species, the inflorescence produces vegetative buds or bulbils rather than flowers. They're not difficult to duplicate.



The development of apomicts occurs because of various reasons such as:

  1. bypassing of meiosis during embryo sac formation (apomeiosis),

  2. development of an embryo from egg independent of fertilization (process known as parthenogenesis), and

  3. formation of viable endosperm by fertilization-independent process or

  4. after fertilization with a sperm cell.


The significance of Apomixis

Apomixis is the process of producing seeds without involving meiosis or syngamy. It is crucial in the generation of hybrid seeds. Apomixis prevents the loss of certain traits in the hybrid, allowing it to be propagated from seeds without the need for repeated hybridization.


Apomixis is significant for crop improvement because it results in the creation of large genetically homogenous populations with improved hybrid vigour. Rapid creation and multiplication of superior forms through seed germplasm are among the agronomic benefits of apomixis. Because of their genetic consistency and disease tolerance, adventive embryos are important in agriculture and horticulture.


Q6. Describe syngamy and triple fusion in angiosperms with the help of a well labelled diagram. Enlist the major functions of endosperm in plants. (10)

Ans) a) Syngamy- Fusion of the male gamete with the nucleus of the egg cell is called syngamy, this results in the formation of the diploid zygote.

Triple fusion- Fusion of a male gamete with two polar nuclei, to produce triploid primary endosperm nucleus IS called triple fusion.


The process of double Fertilization or Triple fertilization.

The fusion process occurs in the embryo sac of the angiosperms. In the event of fertilization, when the stigma meets the pollen grains, it germinates, giving rise to the pollen tube which enters the ovule through the style.

  1. This pollen tube then penetrates one of the synergids, post which two male gametes are released.

  2. One of the two male gametes fuses with the nucleus of the egg cell to produce the zygote, this process is called syngamy.

  3. A primary endosperm nucleus, triploid in nature is formed when the other male gamete combines with the two polar nuclei that are found in the central cell.

  4. Since the process involves the combining or fusing of three haploid nuclei, it is known as triple fusion.

  5. The result, consequence of the process of triple fusion is the formation of the endosperm.


Major functions of endosperm in plants

  1. Endosperm stores the food reserve and is important for the growth of an embryo.

  2. They provide protection to the developing embryo and supply nutrients.

  3. They have capability to regulate gene expression and seed germination.

  4. Endosperm induces signals according to environmental conditions and regulates embryonic growth.

  5. The endosperm contains cytokinin, which regulates cellular differentiation.

  6. It may induce abortion of seeds from the genetically mismatched cross.


Endosperm has a very important role in the development of embryo in most of inter-varietal and interspecific crosses embryos fail to form because failure of endosperm formation.


Q7. a) Describe the structure of a mature embryo sac with the help of a well labelled diagram. (5)



Seed coat development in cotton a) L.S. of ovule showing mature embryo sac; b) A portion of integuments from ovule after 2-3 days of pollination.


Q7. b) Trichomes play important role in plants, Justify the statement. (5)

Ans) Trichomes defend the leaf from microbiological organisms, aphids, and insects, and maintain a layer of still air on the leaf surface, preventing excessive water loss through transpiration.


Trichomes defend plants from predators and adverse weather. The trichomes on the leaf surface protect the plant from biological pests and animals. Sharp and stiff hairs (certain cucurbits), a dense hair coating (Gnaphalium), sting hairs (as in nettles). Some plants, including Tragia cannabina, grow stinging hairs to deter herbivores. When an animal contacts hair, the hairs break off and irritate the animal.


Some animals refuse to eat cannabis due to the bitter chemical secreted by the glandular trichomes. Trichomes are resin glands that create oils that protect and discourage pests. These compounds also protect the plant from harsh weather and fungi.


Non-glandular trichomes produce a dense surface coating surrounding leaves, protecting them from infections and harsh weather conditions. These trichomes also exude mucilage that attracts insects to the plant leaves.


Non-glandular trichomes in the plant's roots help it absorb water and minerals. Trichomes are tubular structures that extend outward to absorb soil water and nutrients.


Trichomes also help eliminate excess harmful chemicals and salts (as reported in plants as Atriplex), Wax protects plants from excessive heat and sunlight, while essential oils from plants like Cymbopogon act as insect repellents. Cannabis (marijuana) trichomes recently found to contain a mind-altering chemical. These compounds have been shown to help patients. Trichomes begin to develop on the plant at the onset of growth and finish with flowering.


Q8. Differentiate between Intraspecific and Incompatibility Interspecific incompatibility. List the methods to overcome incompatibility and discuss the significance of incompatibility. (3+4+3)

Ans) Incompatibility is of two types:


1. Intraspecific incompatibility

Intraspecific incompatibility, also known as self-incompatibility, is when two organisms of the same species are incompatible. Pollen grains and stigmas from the same species might sometimes be incompatible. As a result, germination is slowed down. A mixture of chemically or irradiatedly treated compatible pollen and live incompatible pollen is utilised to pollinate the plant in the mixed pollination technique. Through proteins released by modified compatible pollen, the stigma is protected from recognising incompatible pollen.


2. Interspecific Incompatibity

In this review, interspecific incompatibility is defined as any of the post-pollination processes that impede the generation of hybrid zygotes combining the genomes of two separate fertile species or viable eco types by preventing pollen germination or abnormal pollen tube behaviour. In contrast to the self-incompatibility mechanism that limits inbreeding, this phenomenon hinders gene flow across species and creates upper limits to outbreeding and panmixis. As a result, interspecific incompatibility contributes to population isolation, favouring speciation and the progressive growth of variation within the genus and family. It primarily serves as a breeding barrier between sympatric species, but it also aids in the rejection of foreign germplasm travelling in allopatric pollen grains, as well as the isolation of invaders introduced as seed. It refers to the incompatibility between different species, which prohibits fertilisation between different species' gametes.


Methods to overcome incompatibility

Method # 1. Mixed Pollination

The stigma is pollinated with incompatible and chemically treated compatible pollen in this method. Chemicals are utilised that do not disrupt the wall-held proteins. The proteins leached from compatible pollen hide the inhibitory reaction generated by incompatible pollen at the stigma's surface in this approach.


Method # 2. Bud Pollination

Self-incompatibility could be overcome in a significant number of plant species, such as Petunia and Brasicca, by self-pollination a few days before anthesis. The stigma does not produce exudate in the bud stage, and the incompatibility reaction emerges right before anthesis.


Method # 3. Styler Pollination

The stigma surface is the site of incompatibility in several Nicotiana species. When the stigma lobes are removed and the style's cut surface is dusted with self-pollen, the pollen tubes grow unhindered through the style. Agar sucrose is sometimes spread on the wounded surface to create a fake stigma.


Method # 4. Intraovarian Pollination

In this technique a known amount of pollen and basal medium are injected in the ovary with the help of a hypodermic syringe. Seeds are successfully obtained following proper fertilization.


Method # 5. Test tube Pollination

In this method the pollen grains and ovules are cultured side by side in the nutrient medium and the technique is excellent for employing placental pollinations e.g., in Petunia.


Method # 6. Treatment of Style with Heat

In Liliuml self-incompatibility is suppressed when the styles are subjected to a temperature of 50-C for five minutes.


Method # 7. Irradiation

In some instances, incompatibility genes have been mutated using irradiation. For instance, Lycopersicon peruvianum self-incompatible clones were given gamma radiations treatments and the seed set was obtained.


Method # 8. Treatment with Chemicals

Several chemicals like 2-4, D, kinetin, chlorophenoxyacetic acid, etc. have been used to overcome incompatibility.


Method # 9. Use of CO2

Following self-pollination, when the carpels were enclosed with high concentrations of CO2 (3-5 percent), there was a good percentage of seed set in Brassica sp. such as B. campestris and B. oleracea. CO2 was fixed non-photosynthetically to generate malate, according to Malik, Dhaliwal, and Singh's model. It also increases the activity of the pentose phosphate shunt, which was formerly a source of lowering power (NADPH). As an osmoregulatory solute, malate was used.


Method # 10. Parasexual Hybridization

In this approach the protoplasts from desirous genotypes were isolated enzymatically and fused under controlled conditions. The culturing of these protoplasts were affected and the whole plants could be raised in some plant species.


Significance of Incompatibity

Incompatibility determines the degree of inbreeding and outbreeding of plants. Self- incompatibility is a natural way to circumvent extensive selfing that promotes homozygous individuals and eventually causes inbreeding depression (accumulation of lethal recessive genes). The prevention of inbreeding results in high genetic diversity. Genetic diversity is important for maintaining the health and survival of species. The process also leads to the production of hybrids.


9. Differentiate between: (2×5=10)


Q9. a) storied and non-storied cambium

Ans) The initials of the axial system are elongated and pointed. They are usually called fusiform (spindle-shaped) initials. They are relatively short in Robinia. In tangential sections the fusiform cambial cells occur in horizontal tiers. Cambium thus organized is referred to as storied or stratified. The contrasting type would be non-storied or non-stratified cambium. In the non-storied cambium the fusiform initials overlap one another and do not appear in horizontal tiers in tangential views.


In this type of cambium the ends of cambial fusiform cells typically overlap much more extensively and in a seemingly random manner. In non-storied cambia there is no lateral alignment. In vessel less dicotyledons the fusiform initials may reach a maximum length of 6200 μm. Thus, non-storied initials are longer. They are also of more common occurrence


Q9. b) amoeboid and glandular tapetum

Ans) There are two forms of tapetum: glandular and amoeboid. The cells in glandular or secretory tapetum retain their identity and location but break up later in the microspore formation process. The cells of the amoeboid tapetum alter shape and position during ontogeny to generate a periplasmodium.


Q9. c) self and cross pollination

Ans) Depending on the source of the pollen, pollination is of two types:

1. Self-pollination - Pollen is transferred from the anther to the stigma of the same bloom or a different blossom on the same plant. This can happen in either unisexual or bisexual flowers that grow on the same plant.


2. Cross-pollination - Pollen is transferred from one bloom to the stigma of another flower of the same kind of plant. It can be found in monoecious and dioecious plants alike.


Q9. d) psychophily and hymenophily

Ans) The pollination carried out with the help of butterflies is referred as

Psychophily. Butterflies help in the pollination of flowers that produce colourful, showy fragrant flowers. The flowers have long nectar filled tubes. This type of pollination is called as Psychrophile.


Bees pollinate showy, colourful, and fragrant flowers. The nectar guides function to attract and guide bees. Bee pollination is also referred as Hymenopterophily or Melittophily.


Q9. e) open and closed style

Ans) Open style - The number of canals in the hollow style corresponds to the number of carpels. These are stylar canals. The stylar canal is surrounded by canal cells, a type of glandular cell. These canals have a thick tangential wall coated with glandular epidermis. The canal's wall is smooth but twisted (Aegle, Fritillaria). In some plants, like citrus, the inner tangential wall of canal cells is thick and fibrillar. Large multinucleated canal cells Mitochondria, dictyosomes, free ribosomes, and smooth and rough ER populate the cytoplasm. The secretory product is mostly delivered to the canal cells by plasmodesmata.


Closed Style

The solid style has a central stand of elongated cell transmitting tissue. Transmitting tissue extends from the stigmatic secretory tissue along the style. The transmitting tissue contains plasmodesmata-bearing cells. Transmitting tissue cells have tiny transverse but substantial lateral walls. The concentric layers are also visible. The innermost wall layer is formed of pectic compounds and hemicelluloses, while the outermost wall layer is composed of pectic substances. Layer 3 is loosely grained, high in pectin, and low in cellulose. Middle lamella area is rich in pectin. The transmitting tissue cells have mitochondria and dictyosomes. The plastids are big with many of amyloplasts, polysomes, and ER (spherical or ellipsoidal). The transmission tissue cells do not divide but elongate.


Q10. Write short notes on: (2×5=10)


Q10. a) advantages of cross pollination

Ans) Cross-pollination is the transfer of pollen from anthers of flowers of one plant to the stigma of a flower of another plant of the same species.


The advantages of cross-pollination are as follows:

  1. Offspring produced are healthier

  2. New varieties can be produced through cross-pollination of two varieties of the same species or two species

  3. Seeds that are produced are abundant and viable

  4. Results in new varieties because cross-pollination can be carried out between two different varieties of the same species or even two species.


Q10. b) parthenocarpy

Ans) Fruit formation without fertilisation is called parthenocarpy. The fruit is seedless and looks like a normal fruit. Naturally occurring parthenocarpy can be found in pineapple, banana, cucumber, grape, orange, grapefruit, persimmon, and breadfruit varieties. A sort of artificial pollination with dead or changed pollen or pollen from a different type of plant can be used to induce seedless parthenocarpic fruit in non-parthenocarpic varieties and in naturally parthenocarpic varieties out of season. Parthenocarpic development can also be induced using synthetic growth agents in the form of paste, injection, or spray.


Q10. c) pneumatophores

Ans) Pneumatophores are specialized root structures that grow out from the water surface and facilitate the aeration necessary for root respiration in hydrophytic trees such as many mangrove species (e.g., Avicennia germinans and Laguncularia raecemosa), bald cypresses, and cotton (tupelo) gum (Nyssa aquatica).


Q10. d) commercial cork

Ans) The periderm layers of Quercus suber are used to make commercial cork (cork oat tree). Cork is economically essential due to its low heat conductivity, excellent compressibility, durability, moisture resistance, and vibration absorption.


The cork layers are formed by additional stelar secondary growth. Cork is cut to various sizes and thicknesses. Most of the cork's qualities come from the air in its cells. This versatile material is used to make bobbins, rollers, soundproofing materials, refrigeration chambers and caps.


Q10. e) insectivorous plants

Ans) A plant which fulfills its nitrogenous need by eating insects is called an insectivorous plant. A plant that captures and digests insects either passively (as the common pitcher plant or the sundew) or by the movement of certain organs (as the Venus's-flytrap)


Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods. However, carnivorous plants generate energy from photosynthesis.

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