Question

Assertion: Water is often the limiting factor for plant growth and productivity. Reason: Large amount of water is required by plants.

Short answer

The assertion and reason are correct as water is crucial for various growth processes in plants. When unavailable in significant amounts, it limits their growth and productivity.

Step-by-step solution

Understanding the Assertion

The assertion states that water is often the limiting factor for plant growth and productivity. This means that without enough water, plants cannot grow and produce at their full potential.

Understanding Why Water is Essential for Plants

Plants require water for numerous critical processes such as photosynthesis, transpiration, transportation of nutrients, cell structure, and more. Without a sufficient amount of water, these processes cannot occur properly, which would limit the growth and productivity of the plant.

Understanding the Reason

The reason states that a large amount of water is required by plants. Given the different processes that require water, as mentioned in the step above, it is clear why plants would need a large quantity of water to properly function and grow.

Linking the Assertion and Reason

Now, linking the assertion and the reason, if plants do not get a sufficient amount of water to sustain these critical processes, their growth and productivity will be limited. Thus, the reason given correctly explains the assertion.

Key concepts

Photosynthesis

Photosynthesis is a fundamental process that underpins life on Earth, and it's crucial for plant growth. What is photosynthesis? Simply put, it's a chemical process by which plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy in the form of glucose. During this process, plants take in carbon dioxide (CO2) from the air and water (H2O) from the soil, utilizing the light energy to produce glucose and releasing oxygen (O2) as a byproduct.

The equation for photosynthesis can be represented as:

• 6CO2 + 6H2O + light energy → C6H12O6 + 6O2.

Water's role in photosynthesis is vital. It's the source of the hydrogen atoms that are incorporated into glucose, which is later used for energy and growth. When there is not enough water available, the rate of photosynthesis decreases, directly impacting plant productivity. Thus, water availability can be directly linked to a plant's ability to produce its own food and sustain its growth.

Transpiration

Transpiration is like the plant version of sweating and plays a critical role in plant water relations and climate control. What is transpiration? It's the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released into the atmosphere. Essentially, it's how plants lose water. It might sound counterproductive, but transpiration is essential for pulling water through the plant. This movement of water allows for the transport of important nutrients from the soil to the growth sites within the plant and also helps to maintain the plant's temperature.

Factors such as temperature, humidity, wind, and soil water supply can affect the rate of transpiration. If plants don't have enough water, they cannot maintain a high rate of transpiration which can result in reduced nutrient uptake and overheating. Understanding transpiration is important for managing plant hydration and ensuring that they have the required water supply to stay healthy and productive.

Plant Productivity

Plant productivity is essentially a measure of how well a plant converts light, water, and carbon dioxide into biomass and yield. Productivity is a function of the plant's physiological processes, including both photosynthesis and transpiration.

Plant productivity can be influenced by a variety of factors such as water availability, light intensity, nutrient availability, and the efficiency with which a plant carries out photosynthesis and transpiration. A decrease in water supply can have a ripple effect on plant health since it compromises the plant's ability to photosynthesize, transpire, and transport nutrients, ultimately leading to stunted growth and reduced yield.

In agriculture and horticulture, understanding the factors affecting plant productivity is crucial for improving crop yields and sustainability. Adequate water supply is paramount as it affects almost every aspect of plant health and development. Thus, practices such as irrigation management are critical to ensure that plants have the required amount of water to optimize their growth and productivity.