Problem 12 - Biology Today and Tomorrow with Physiology

Question

When guard cells swell, _____. a. transpiration ceases b. sugars enter phloem c. stomata open d. root cells die

Step-by-Step Solution

Answer

When guard cells swell, c. stomata open.

Step 1: Understanding Guard Cells

Guard cells are specialized plant cells located on leaf surfaces. Their main function is to control the opening and closing of stomata, which are small pores that play a key role in gas exchange and water regulation in plants.

Step 2: Effects of Swelling on Guard Cells

When guard cells swell, it is because they have taken in water. This causes the cells to become turgid (firm and swollen) which leads to the opening of the stomata located between them.

Step 3: Identifying the Correct Answer

Given that swollen guard cells result in the opening of the stomata, the correct option is the one that mentions this effect.

Key Concepts

Guard Cells

Guard cells are remarkable components of a plant's anatomy. These cells are primarily found on the leaf surface. Their job is crucial; they control the opening and closing of tiny pores called stomata. This role is essential for plant survival as it directly influences gas exchange and water regulation. Each pair of guard cells surrounds a stoma, forming a gap that opens or closes depending on the guard cell’s state. When guard cells absorb water and swell, they become turgid. This turgidity is like puffing up a balloon, causing the stoma to open. Participating in such fluctuating water intake and release makes guard cells extremely dynamic. This also endows the plant with the ability to adjust to different environmental conditions. What's fascinating about guard cells is their capacity to "communicate" with the plant. They respond to the internal water status and even external environmental cues like light and humidity. Effortlessly managing these responses ensures that the plant maintains optimal internal conditions.

Gas Exchange in Plants

Gas exchange in plants is a critical process for maintaining healthy plant function and growth. This exchange primarily occurs through stomata, the tiny openings on leaves controlled by guard cells. Gas exchange involves the movement of oxygen, carbon dioxide, and water vapor between the plant and its environment. Here's how it typically works:

• Photosynthesis: During daylight, plants take in carbon dioxide through open stomata. They use this CO2 in combination with sunlight for photosynthesis to produce glucose and oxygen.
• Respiration: Oxygen, a by-product of photosynthesis, is released through these same stomata so it can be used by other organisms for respiration.
• Transpiration: Water vapor also leaves the plant through stomata, which is a part of the process known as transpiration. This helps in pulling water from the roots to the leaves.

The process of opening and closing stomata to regulate gas exchange is highly influenced by light. For instance, stomata tend to open in the morning as light initiates photosynthesis, thus promoting gas exchange. However, in conditions where water conservation is paramount, such as in drought, they may remain closed even in light to prevent water loss.

Water Regulation in Plants

Water regulation is vital for a plant's survival. Plants acquire water through their roots from the soil, but managing this water intake and preventing excessive water loss is key to their health. Guard cells play a pivotal role in this regulation by controlling the stomata opening. When water is plentiful, guard cells swell and open the stomata. This allows the plant to "breathe" and perform photosynthesis efficiently. Conversely, during periods of water scarcity, guard cells will release water, causing the stomata to close. This action helps to reduce water loss and maintain internal water balance. Other factors impacting water regulation include:

• Humidity: High humidity levels slow down transpiration rates, thus limiting water loss.
• Temperature: Increased temperatures can cause increased transpiration rates, leading to more water loss.
• Wind: Windier conditions may accelerate water loss as they remove the thin layer of moisture on leaf surfaces.

By regulating water through these mechanisms, plants ensure they stay hydrated and are able to sustain themselves, even in challenging environmental conditions.