Problem 1 - Campbell Biology

Question

Which of the following is an adaptation that enhances the uptake of water and minerals by roots? \begin{equation}\begin{array}{l}{\text { (A) mycorrhizae }} \\ {\text { (B) pumping through plasmodesmata }} \\ {\text { (C) active uptake by vessel elements }} \\ {\text { (D) rhythmic contractions by cells in the root cortex }}\end{array}\end{equation}

Step-by-Step Solution

Answer

Option A (mycorrhizae)

Step 1: Understand the Question

Determine what the question is asking: identify an adaptation that enhances the uptake of water and minerals by roots.

Step 2: Evaluate Each Option

Examine each given option to see if it matches the described adaptation.

Step 3: Analysis of Option A (mycorrhizae)

Mycorrhizae are symbiotic associations between fungi and plant roots, known to increase the surface area for water and mineral absorption. This is a known adaptation.

Step 4: Analysis of Option B (pumping through plasmodesmata)

Plasmodesmata are channels between plant cells that allow transport and communication. They do not pump water and minerals, but rather facilitate movement through diffusion.

Step 5: Analysis of Option C (active uptake by vessel elements)

Vessel elements are part of the xylem and transport water. They do not play a significant role in active uptake.

Step 6: Analysis of Option D (rhythmic contractions by cells in the root cortex)

There is no known biological mechanism in roots involving rhythmic contractions for the uptake of water and minerals.

Step 7: Determine the Best Answer

Review the evaluations of each option. Option A (mycorrhizae) is the adaptation that enhances water and mineral uptake by roots.

Key Concepts

Water Uptake

Plants rely on specific adaptations in roots to effectively absorb water from the soil. The primary method of water uptake is through osmosis, where water moves from areas of high water potential (soil) to low water potential (root cells). Roots have root hairs that increase the surface area, allowing more water to be absorbed.
In addition to root hairs, the **root cortex** helps transport water inward towards the xylem, which then distributes the water throughout the plant. The endodermis, a layer of cells surrounding the xylem, acts as a selective barrier, ensuring only necessary water and minerals pass through.
**Main points about water uptake:**

• Root hairs increase surface area for absorption
• Water moves via osmosis from soil to root cells
• The root cortex and endodermis facilitate inward transport

Mineral Absorption

Mineral absorption in plants is crucial for their growth and development. Minerals dissolved in soil water are taken up by root hairs and transported through the root cortex into the xylem. Unlike water, minerals often require active transport due to their low concentration in the soil.
Active transport involves root cells using energy (ATP) to move minerals against their concentration gradient. Ion-specific transporters in the root cell membranes ensure that essential nutrients like nitrogen, potassium, and phosphorus are efficiently absorbed.
**Key aspects of mineral absorption:**

• Minerals are absorbed along with water
• Active transport is needed for low-concentration minerals
• Ion-specific transporters help in absorption

Mycorrhizae

Mycorrhizae are symbiotic associations between fungi and plant roots that greatly enhance the plant's ability to absorb water and minerals. The fungal hyphae extend far into the soil, exceeding the reach of root hairs, thus increasing the effective surface area for absorption.
This relationship is mutually beneficial: the plant provides the fungi with carbohydrates derived from photosynthesis, while the fungi supply the plant with essential nutrients like phosphorus and nitrogen. There are two main types of mycorrhizae:

• **Ectomycorrhizae:** The fungal hyphae form a dense network around the root, penetrating the root but not the individual cells.
• **Endomycorrhizae (or arbuscular mycorrhizae):** The fungal hyphae penetrate root cells, forming arbuscules that facilitate nutrient exchange.

The presence of mycorrhizae increases the plant's tolerance to various stresses, including drought and poor soil conditions, significantly contributing to plant health and ecosystem dynamics.