TN BOTANY 1st Midterm Exam Last - Tamil Nadu Board Botany

Reproduction and Genetics in Flowering Plants

Key Short Questions and Exam Patterns

Important questions for midterm exams are frequently drawn from the chapters on asexual and sexual reproduction in plants, and classical genetics. Focus is placed on concise answers, use of keywords, and inclusion of diagrams where required. Most questions are repeated across years, especially for 2-mark, 3-mark, and 5-mark formats.

• 2-mark questions: Write short, direct answers with key terms and diagrams if mentioned in the textbook.
• 3-mark and 5-mark questions: Structure answers with clear points, include diagrams, and label all parts as per textbook style.…

Reproduction and Genetics in Flowering Plants

Key Short Questions and Exam Patterns

Important questions for midterm exams are frequently drawn from the chapters on asexual and sexual reproduction in plants, and classical genetics. Focus is placed on concise answers, use of keywords, and inclusion of diagrams where required. Most questions are repeated across years, especially for 2-mark, 3-mark, and 5-mark formats.

• 2-mark questions: Write short, direct answers with key terms and diagrams if mentioned in the textbook.
• 3-mark and 5-mark questions: Structure answers with clear points, include diagrams, and label all parts as per textbook style.
• One-mark questions: Study all book-back questions thoroughly; sometimes questions are asked from inside the text as well.

Structure and Function of Pollen Kit

The pollen kit is a yellow to orange-colored, sticky covering found on the surface of pollen grains. It is mainly contributed by the tapetum layer of the anther and is rich in carotenoids and flavonoids. The sticky nature aids in the dispersal of pollen grains, especially in entomophilous (insect-pollinated) plants.

• Key features:
  • Contributed by the tapetum.
  • Contains carotenoids and flavonoids.
  • Sticky, yellow to orange in color.
  • Essential for pollen adhesion and transfer.
• Diagram: Draw the pollen grain with the pollen kit, label exine, intine, vegetative cell, and generative cell.

Definitions of Stomium, Melittophily, Myrmecophily

Several terms are repeatedly asked in exams:

• Stomium: The region in the anther where the cell wall is thin and does not thicken, allowing the anther to dehisce and release pollen grains. It is located at the junction between two sporangia.
• Melittophily: Pollination carried out by bees. Flowers pollinated by bees are often blue in color, reflecting ultraviolet light, and have nectar guides.
• Myrmecophily: Pollination carried out by ants. Example: Mango (Mangifera) and Acacia.

Drawing and Labelling the Male Gametophyte

The male gametophyte in flowering plants is represented by the pollen grain. It consists of a large vegetative cell and a smaller generative cell, with the generative cell having a spindle-shaped nucleus. The vegetative cell is larger and occupies most of the cytoplasm.

• Diagram instructions:
  • Draw an inverted Y-shaped pollen grain.
  • Label exine (outer, rough), intine (inner, smooth), vegetative cell, and generative cell.
  • Mark the spindle-shaped nucleus in the generative cell.

Classical Genetics: Back Cross, Test Cross, Rediscovery of Mendelism

Genetics questions focus on Mendelian crosses and the scientists who rediscovered Mendel’s work.

• Back Cross: Crossing an F1 hybrid with either of its parents (dominant or recessive). If crossed with the recessive parent, it is called a test cross.
• Test Cross: Crossing an F1 hybrid with the recessive parent to determine the genotype. A 1:1 ratio indicates heterozygosity; a 1:0 ratio indicates homozygosity.
• Scientists who rediscovered Mendelism: Hugo de Vries (Holland), Carl Correns (Germany), Erich von Tschermak (Austria).

Mendel’s Seven Contrasting Traits

Mendel studied seven pairs of contrasting traits in pea plants. These are frequently asked as a list or in tabular form.

• Plant height: Tall vs. Dwarf
• Seed color: Yellow vs. Green
• Seed shape: Round vs. Wrinkled
• Pod color: Green vs. Yellow
• Pod shape: Inflated vs. Constricted
• Flower color: Purple vs. White
• Flower position: Axillary vs. Terminal

Extra-Chromosomal Inheritance (Cytoplasmic Inheritance)

Inheritance of certain traits is controlled by genes present in the cytoplasm, such as chloroplast genes. In the case of leaf color in the 4 o’clock plant (Mirabilis jalapa), the progeny’s leaf color is determined by the cytoplasm of the female parent.

• Key points:
  • Leaf color is controlled by the chloroplast genome.
  • Inheritance is strictly maternal.
  • All progeny will have the leaf color of the female parent, regardless of the male parent’s genotype.

Endosperm: Definition and Types

Endosperm is formed from the primary endosperm nucleus immediately after fertilization and provides nutrition to the developing embryo. There are three types based on the mode of development:

• Nuclear Endosperm: Free nuclear divisions occur without immediate cell wall formation.
• Cellular Endosperm: Cell wall formation follows each nuclear division.
• Helobial Endosperm: Combination of nuclear and cellular types; free nuclear divisions at the micropylar end and cellular at the chalazal end.

Parthenocarpy: Definition, Types, and Significance

Parthenocarpy is the development of fruit without fertilization, resulting in seedless fruits. It is significant in horticulture and commercial fruit production.

• Types:
  • Genetic Parthenocarpy: Due to hybridization or mutation (e.g., citrus, cucumber).
  • Environmental Parthenocarpy: Induced by environmental factors like low temperature or frost (e.g., pear).
  • Chemically Induced Parthenocarpy: Induced by spraying hormones like auxins and gibberellins.
• Significance:
  • Production of seedless fruits.
  • Useful for making jams, jellies, sauces, and fruit drinks.
  • Higher proportion of edible part due to absence of seeds.

Microsporogenesis: Steps and Diagram

Microsporogenesis is the process by which microspores (pollen grains) are formed from microspore mother cells in the anther.

• Steps:
  • Sporogenous cells undergo mitosis to form sporogenous tissue.
  • Each cell of the sporogenous tissue becomes a microspore mother cell (diploid).
  • Microspore mother cells undergo meiosis to produce microspore tetrads (haploid).
  • Microspores separate and develop into pollen grains.
• Diagram: Draw the sequence from sporogenous tissue to microspore tetrad to mature pollen grain.

Grafting and Layering: Differentiation

Grafting and layering are two methods of artificial vegetative propagation.

• Grafting: Requires two plants—a stock (root system) and a scion (shoot system). The scion is attached to the stock, and they grow together as one plant.
• Layering: Involves only one plant. A branch is bent to the ground, covered with soil, and roots develop at the covered part. The new plant is then separated from the parent.

Pollination Mechanisms: Porogamy, Chalazogamy, Mesogamy

Pollination mechanisms are classified based on the route taken by the pollen tube to reach the embryo sac.

• Porogamy: Pollen tube enters through the micropyle.
• Chalazogamy: Pollen tube enters through the chalaza.
• Mesogamy: Pollen tube enters through the integuments.

Anemophilous Plant Characteristics

Anemophilous (wind-pollinated) plants have specific floral adaptations to facilitate pollination by wind.

• Key features:
  • Flowers are pendulous and arranged in spikes.
  • Inflorescence axis is elongated and projects beyond the leaves.
  • Perianth is absent or highly reduced.
  • Flowers are small, inconspicuous, and colorless.
  • No scent or nectar.
  • Stamens are numerous; ovules are few.
  • Pollen grains are light, minute, and produced in large numbers for long-distance dispersal.

Short Notes on Apomixis and Polyembryony

• Apomixis: Formation of seeds without fertilization. Diploid cells from the nucellus or integuments directly develop into embryos, bypassing the normal sexual process.
• Polyembryony: Occurrence of more than one embryo in a seed. Used for producing disease-free plants and maintaining hybrid vigor.

Exam Presentation Tips

• Always use textbook diagrams and label all parts clearly.
• Focus on writing key points and keywords as per the textbook.
• Avoid adding extra information not present in the textbook.
• For 3-mark and 5-mark questions, structure answers with bullet points and diagrams.
• For definitions and short notes, keep answers concise and to the point.