Question

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

Short answer

c. stomata open

Step-by-step solution

Understanding Guard Cells

Guard cells are specialized plant cells located on the leaf surface and are responsible for controlling the opening and closing of stomata, which are tiny pores that facilitate gas exchange.

The Role of Swelling in Guard Cells

When guard cells swell due to the absorption of water, they change shape, causing the stomata to open. This occurs because the turgor pressure inside the guard cells increases, leading to the separation of the cell walls and opening of the pore.

Determine the Correct Outcome Based on Swelling

Given the options and the knowledge that swelling of guard cells results in stomatal opening, the correct answer to the question is that stomata open when guard cells swell.

Key concepts

Stomata

Stomata are small openings found on the surfaces of leaves and stems. They play a crucial role in gas exchange, allowing plants to take in carbon dioxide for photosynthesis and release oxygen as a byproduct. Each stoma (singular of stomata) is flanked by two guard cells that regulate its opening and closing.
Guard cells are essential for maintaining plant homeostasis. They prevent excessive water loss while ensuring enough carbon dioxide enters the plant for photosynthesis. This dual function helps the plant thrive even under varying environmental conditions.
When the stomata are open, water vapor can escape from the plant. This process is known as transpiration. Certain conditions, like high light intensity or low humidity, can prompt guard cells to swell, causing the stomata to open and enhance gas exchange.

Turgor Pressure

Turgor pressure is the pressure exerted by the fluid inside a plant cell against its cell wall. In guard cells, it plays a crucial role in the opening and closing of stomata. When guard cells become filled with water, they swell, and this causes the stomata to open. This is because the increased pressure within the cells pushes against the cell walls, leading to a change in shape.
If the turgor pressure decreases, which happens when water leaves the guard cells, the cells become flaccid. Consequently, the stomata close. This mechanism is a vital adaptation for conserving water under dry conditions.
Understanding turgor pressure can help you appreciate how plants manage water and nutrient movement, impacting their growth and survival directly.

Transpiration

Transpiration is the process of water movement through a plant and its evaporation from aerial parts like leaves, stems, and flowers. Around 90% of the water absorbed by a plant is lost through transpiration.
This process is essential for several reasons:

• Cooling: Like sweating in humans, transpiration helps cool the plant.
• Nutrient distribution: It aids in the transport of minerals from the soil to different parts of the plant.
• Water uptake: It creates a negative pressure in the roots, facilitating the uptake of water.

Even though transpiration involves water loss, it is crucial for nutrient uptake and maintaining plant health. The opening and closing of stomata are central to managing this water loss while maximizing carbon dioxide intake for photosynthesis.