Aiou 6451 solved Assignment 1& 2 semester spring 2023 free download pdf
Course: Biology-I (6451) Semester: Spring, 2023
Level: B.Ed. (2.5/4-Year) Credit Hours: 03
Assignment2
Q.1 How Reproduction of Lichens Differs Based on Their Types
Lichens, the incredible symbiotic organisms formed by the mutualistic relationship between fungi and algae or cyanobacteria, showcase diverse reproductive strategies based on their types. Let’s delve into the intriguing world of lichen reproduction and understand the variations in their reproductive mechanisms.
Types of Reproduction in Lichens
- Fragmentation: This mode of reproduction is common in crustose lichens. It involves the breaking off of fragments from the thallus. Each fragment can grow into a new lichen when favorable conditions are met.
- Soredia Formation: Foliose and fruticose lichens often reproduce through soredia formation. Soredia are powdery structures containing both fungal hyphae and algal cells. When dispersed, soredia can establish new lichen colonies.
- Ascospores: Asexual reproduction in lichens involves the production of ascospores, which are spores contained within specialized structures called asci. These spores are released into the environment and can give rise to new lichen thalli when they encounter compatible photobionts.
Understanding the different modes of lichen reproduction provides valuable insights into their resilience and ability to colonize diverse habitats.
Q.2 Internal and External Morphology of Funaria
Funaria, commonly known as “cord moss” or “spore moss,” is a fascinating genus of bryophytes. To appreciate its beauty and ecological significance, let’s explore both its internal and external morphology.
Internal Morphology of Funaria
The internal structure of Funaria comprises distinct features that contribute to its growth and reproductive processes. Key internal structures include:
- Seta: The central axis of Funaria, also known as the seta, supports the sporangium at its tip. The seta plays a crucial role in elevating the sporangium for efficient spore dispersal.
- Sporangium: Located at the tip of the seta, the sporangium is a specialized structure responsible for the production and release of haploid spores through meiosis. These spores disperse, leading to the development of the haploid gametophyte generation.
External Morphology of Funaria
The external morphology of Funaria exhibits unique characteristics that distinguish it from other bryophytes. Key external features include:
- Gametophyte Body: Funaria’s gametophyte body appears as a dense clump of tiny leaves. These leaves form a rosette pattern at the apex of the seta, contributing to the plant’s aesthetically pleasing appearance.
- Seta Structure: The seta of Funaria is elongated and raises the sporangium above the gametophyte body. This elevation facilitates the effective release of spores into the environment.
Understanding Funaria’s internal and external morphology is essential for appreciating the ecological roles and adaptations of this remarkable bryophyte.
Q.3 Evaluating Sporophyte According to the Modification Theory
The Modification Theory, proposed by botanist Karl Goebel, provides valuable insights into the evolution of the sporophyte generation in bryophytes. Let’s discuss how this theory helps in evaluating the sporophyte.
The Sporophyte Generation in Bryophytes
The sporophyte generation in bryophytes is a vital phase in their life cycle. It is responsible for producing spores that give rise to the gametophyte generation. The sporophyte is a multicellular structure that depends on the gametophyte for nutrition and protection.
Understanding the Modification Theory
Karl Goebel’s Modification Theory proposes that the sporophyte generation in bryophytes has evolved from the gametophyte generation through modifications over time. This evolutionary transition has led to the dependence of the sporophyte on the gametophyte.
According to the theory, the sporophyte is essentially an advanced modification of a gametophyte structure. It retains certain features of the gametophyte while developing new characteristics that enhance its role in reproduction.
Evaluating Sporophyte Evolution
By examining the sporophyte in various bryophyte species, researchers can observe the gradual modifications that have occurred during the course of evolution. The dependence of the sporophyte on the gametophyte provides evidence of its evolutionary origin from the gametophyte generation.
The Modification Theory sheds light on the complexities of plant evolution and highlights the intimate relationship between the gametophyte and sporophyte generations in bryophytes.
Q.4 Short Answers
i. Composition of Drop/Excaudate
Drop or excaudate is a fluid produced by the elaters in the capsule of mosses. This fluid aids in the dispersal of spores through hygroscopic movements, promoting the distribution of spores to new locations.
ii. “Foam Stage” of Archegonial Development
The “foam stage” refers to a phase in archegonial development where mucilage is secreted, resulting in the formation of a foam-like structure. This structure protects the developing archegonium and facilitates the release of spores.
iii. Definitions of Terms
- Mycobiont: The fungal partner in a lichen symbiosis.
- Photobiont: The algal or cyanobacterial partner in a lichen symbiosis.
iv. Two Types of Cytoplasm in the Egg of Pinus
The two types of cytoplasm found in the egg of Pinus are:
- Animal Cytoplasm: Surrounding the centrally located vacuole.
- Vegetal Cytoplasm: Surrounding the animal cytoplasm and occupying most of the egg’s volume.
Q.5 Short Answers
i. Mode of Action of Pollination in Angiosperms
The mode of action of pollination in angiosperms varies based on the method of pollen transfer. Two primary modes are:
- Insect Pollination: Many angiosperms rely on insects as pollinators. Insects are attracted to flowers by bright colors, enticing scents, and nectar rewards. As they visit flowers, they inadvertently pick up and transfer pollen grains between flowers.
- Wind Pollination: Some angiosperms, especially trees like oaks and pines, adopt wind pollination. These plants produce lightweight and abundant pollen grains that are easily carried by the wind to reach neighboring flowers.
ii. Deposition of Pollen Grains on the Stigma of the Carpel
When pollen grains reach the stigma of the carpel, they may hydrate and germinate. A pollen tube grows from the hydrated pollen grain, penetrating the stigma and style, ultimately reaching the ovary where fertilization takes place.
iii. Embryo-Sac and Cell Arrangement
Embryo-sac, also known as the female gametophyte, is a crucial structure in the reproduction of angiosperms. It typically consists of eight nuclei and seven cells, including three antipodal cells, two synergid cells, the egg cell, and two polar nuclei. These cells play essential roles in the fertilization process.
iv. The Novel Phenomenon of Double Fertilization in Angiosperms
Double fertilization is a unique and pivotal process in the life cycle of angiosperms. Unlike other plants, angiosperms produce two fertilization events:
- One sperm cell fuses with the egg cell to form the zygote, which develops into the embryo.
- Another sperm cell fuses with two polar nuclei to form a triploid cell, which develops into the endosperm, providing nourishment to the developing embryo.
Double fertilization ensures the efficient utilization of resources and contributes to the success of angiosperms in diverse ecosystems.
In conclusion, lichens’ diverse reproductive strategies, Funaria’s intriguing morphology, and the evolutionary insights provided by the Modification Theory in bryophytes showcase the wonders of the botanical world. Additionally, understanding the pollination and fertilization processes in angiosperms sheds light on the intricate mechanisms that underpin plant reproduction. Nature’s mysteries continue to captivate and inspire researchers and enthusiasts alike.