Problem 153 - Objective Biology for NEET

Question

Which of the following are correct for gymnosperms? I. They are heterosporous. II. They are the first vascular plants. III. Posses fruits IV. Requires water for fertilization. (a) I (b) I and II (c) II and III (d) I, II, III and IV

Step-by-Step Solution

Answer

The correct answer is (a) I. Only the statement 'They are heterosporous' is true for gymnosperms.

Step 1: Understand the terms

In this step, understanding the terms is important. 'Heterosporous' means that a plant produces two different types of spores, male and female. Gymnosperms are indeed heterosporous as they generate megaspores (female) and microspores (male). 'Vascular plants' is a large group of plants that have specialized tissues for conducting water, minerals, and photosynthetic products. Gymnosperms are vascular plants, but they are not the first ones; the first vascular plants were Pteridophytes. 'Possess fruits': gymnosperms do not bear fruits, they have unclosed seeds. 'Requires water for fertilization': gymnosperms, unlike ferns and mosses, do not require water for fertilization. The pollen grains of gymnosperms are transferred by wind to the ovules, thus does not need water.

Step 2: Match the definitions with the statements

If we now look at the statements, it can be seen that: 'They are heterosporous': this is true for gymnosperms. 'They are the first vascular plants': this is not true; Pteridophytes were the first vascular plants. 'Possess fruits': this is not correct for gymnosperms, sperms. 'Requires water for fertilization': this is also not true for gymnosperms.

Step 3: Choose the correct letter based on the match

Now that it's clear which statements are true or false, it's possible to identify the correct letter. Statement I is true, but all the other statements are false. Therefore, the answer is (a) I

Key Concepts

Heterosporous Plants

Heterosporous plants are a pivotal concept in understanding the reproduction of certain plant species, including gymnosperms. These plants produce two distinct types of spores: megaspores and microspores. Megaspores develop into female gametophytes, while microspores become male gametophytes. This differentiation plays a crucial role in the life cycle of these plants, as it leads to the production of seeds without the need for water to facilitate the movement of sperm to egg, unlike their ancestors the Pteridophytes and other non-seed plants like mosses. Gymnosperms, such as pine trees, exemplify heterosporous plants and have adapted to a wide range of environments partly due to this reproductive strategy.

To help students better understand this, remember that 'mega' means large and in this context relates to the larger spores or female gametophytes, while 'micro' means small, corresponding to the smaller male gametophytes. Understanding this distinction is crucial for students preparing for exams such as the NEET Biology test.

Vascular Plants

Vascular plants are characterized by a specialized transportation system consisting of xylem and phloem tissues. This system allows for efficient transport of water, minerals, and nutrients throughout the plant. The presence of vascular tissues also enables these plants to achieve greater heights and structural support than non-vascular plants. Gymnosperms, an ancient group of vascular plants, including common conifers, are integral in studying plant evolution as they showcase key adaptations for life on land. While gymnosperms are among the first seed plants, they are not the first vascular plants, an honor that belongs to the earlier-evolved group, Pteridophytes.

For a clearer understanding, imagine vascular plants as cities with an extensive network of roads (vascular tissues) facilitating traffic flow (movement of water and nutrients), rather than a town with simple paths where resources must travel more slowly and less efficiently.

Plant Fertilization

Plant fertilization is the process by which a male gamete (sperm) fuses with a female gamete (egg) to form a zygote, eventually developing into a seed. In gymnosperms, fertilization is independent of water, which is a significant evolutionary leap from earlier plants. The male gametes are contained within pollen grains, which are carried by the wind to the female ovules. Once a pollen grain lands on a compatible ovule, it germinates, forming a pollen tube that allows the sperm to reach and fertilize the egg, leading to seed formation.

Students should note that this mechanism of wind pollination enables gymnosperms to reproduce in a variety of environments, even those where water is scarce, which has contributed to their success and spread across different habitats.

Gymnosperms Characteristics

Gymnosperms are a group of seed-producing plants that are notable for their 'naked seeds,' meaning their seeds are not enclosed within a fruit. One of their distinguishing characteristics is the absence of flowers; they instead have cones or strobili where reproduction takes place. Another characteristic is their vascular system comprised of tracheids, which helps them transport water and nutrients effectively. Gymnosperms are also perennial, typically with woody stems, and include various species such as pines, spruces, and cycads.

To assimilate this information, one might think of gymnosperms as the architects of a timeless design, foregoing the flashy allure of flowers for the sturdy practicality of cones and exposed seeds. Their simple yet effective reproduction system bypasses the need for a water medium, allowing them to dominate many terrestrial landscapes.