Question

Assertion: Transpiration occurs when stomata are open. Reason: Transpiration occurs only through stomata.

Short answer

The assertion is true, and the reason is false.

Step-by-step solution

Analyze the Assertion

First, one should understand what is being stated in the assertion: Transpiration occurs when stomata are open. This is true. Transpiration is the process by which water is lost in the form of water vapour from the aerial parts of the plant, and it primarily occurs through the stomata when they are open.

Analyze the Reason

Next, we look at the reason: Transpiration occurs only through stomata. Although stomata are the primary sites of transpiration, some transpiration does occur through the plant’s cuticle, so this statement is not entirely accurate. Hence, while most transpiration takes place through stomata, it doesn't occur only through stomata.

Evaluate Assertion and Reason Relationship

The next step is to evaluate if the reason is an explanation for the assertion. The reason suggests that the stomata being the sole site for transpiration is the cause for the occurrence of transpiration when the stomata are open. However, as explained in Step 2, transpiration occurs not only through stomata, making the reason incorrect as an explanation for the assertion. Therefore, the conclusion is that the assertion is true, and the reason is false.

Key concepts

Stomatal Transpiration

Transpiration is a vital process in plants, often compared to sweating in animals, where water vapor is lost through small openings called stomata. These pores, mostly found on the underside of leaves, facilitate gas exchange, allowing for the uptake of carbon dioxide for photosynthesis while simultaneously enabling the release of oxygen and water vapor.

During stomatal transpiration, guard cells surrounding each stoma actively regulate its opening and closing, balancing the plant's need for carbon dioxide with water conservation. When the guard cells swell with water, they curve apart, opening the stoma. Conversely, when they lose water, they become flaccid, and the stoma closes. This regulation is crucial not only for photosynthesis but also to prevent excessive water loss under dry or hot conditions.

Factors Affecting Stomatal Transpiration

Environmental factors significantly influence stomatal transpiration. Light, temperature, humidity, and wind speed can either increase or decrease the rate at which plants transpire. For instance, high light intensities result in the opening of stomata to capitalize on photosynthesis, leading to increased transpiration. In contrast, lower humidity or higher wind speed can elevate transpiration rates by moving the humid air away from the leaf surface, encouraging more water to vaporize.

Plant Water Loss

Water is indispensable for plants, but they also consistently lose it through a process called transpiration. Plant water loss primarily happens through stomatal transpiration, as previously discussed, but other pathways also contribute to this phenomenon. The cuticle, a waxy layer on the leaf surface, is not entirely impervious and can allow minimal water vapor to pass through, known as cuticular transpiration. Additionally, lenticels in the woody stems enable a small fraction of water loss.

Understanding the balance of water uptake and loss is paramount for plant survival. Roots absorb water from the soil, which travels through the plant's vascular system and eventually evaporates into the atmosphere. While transpiration helps in nutrient transport and temperature regulation, excessive water loss can lead to wilting and stress, affecting plant growth and development.

Adaptations to Minimize Water Loss

Plants have developed various adaptations to reduce water loss, particularly in arid environments. These include a thicker cuticle, reduced leaf area, sunken stomata, and the ability to close stomata during the hottest parts of the day. Additionally, some plants have evolved CAM (Crassulacean Acid Metabolism) photosynthesis, where stomata open at night to minimize water loss while still securing carbon dioxide for daytime photosynthesis.

Biology NEET Preparation

Aspiring medical students in India know that the National Eligibility cum Entrance Test (NEET) is a critical step on the path to a career in medicine. Biology is a major section of this exam, and thoroughly understanding concepts like transpiration is essential for success.

For effective NEET preparation, students should build a strong foundation in core biology concepts, diving deep into processes such as plant physiology, including transpiration and its significance. Because NEET questions can integrate concept application with critical thinking, it's crucial to not just memorize facts but to comprehend the fundamental principles that underlie biological processes.

Strategies for Mastering NEET Biology

Preparing for the biology segment of NEET demands dedication and strategic study. Focus on NCERT textbooks, as they are the primary reference for the exam. Embrace diverse learning tools such as diagrams, flowcharts, and tables to visualize complex cycles and processes. Regularly practice with mock tests and past years' question papers to build confidence and time management skills. Recognizing the interconnection between different topics, such as the link between photosynthesis and transpiration, can help in answering application-based questions more effectively. And finally, never underestimate the need to clarify every doubt, however small, to ensure a comprehensive understanding of each topic.