Solved UD Worksheet - Long-distance transport in plants Fill ... - Free Printable

To solve the problem and complete the table comparing Phloem and Xylem, let's go through each row systematically. Here is the explanation and the completed table:

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Worksheet – Long-distance transport in plants

#### Table: Comparison of Phloem and Xylem

| Aspect | Phloem | Xylem |
|---------------------------------|-----------------------------------------------------------------------------|---------------------------------------------------------------------------|
| Direction of transport | Up or Down (depends on the concentration of solutes) | Up (from roots to leaves/shoots) |
| Force causing transport | Translocation | Transpiration pull |
| Source of this force | Active transport driven by ATP (energy from respiration) | Root pressure and cohesion-tension mechanism |
| Cells doing transport | Sieve tube elements (sieve tubes) | Tracheids and vessel elements (xylem vessels) |
| Other cells in tissue | Companion cells, phloem parenchyma, phloem fibers | Xylem parenchyma, xylem fibers |
| Transport cells lignified? | No | Yes (except for tracheids in some cases) |
| Transport cells w/ membrane?| Yes (sieve plates allow movement but are still membrane-bound) | No (dead cells with no membranes) |
| Materials transported - major| Organic substances (e.g., sugars, amino acids, hormones) | Water and dissolved minerals (ions) |
| Materials transported - minor| Nutrients and signaling molecules | Trace elements and some organic compounds |
| What happens if tissue is punctured or cut? | Sap oozes out slowly (due to low pressure) | Sap under tension may "shoot" out (due to high negative pressure) |
| Animal that feeds on this tissue | Aphids, scale insects, mealybugs (feed on phloem sap) | None directly; animals may damage xylem but do not feed on it |

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Explanation of Each Row

1. Direction of transport:
- Phloem: Transport occurs both upward and downward, depending on the concentration gradient of solutes. This is called source-to-sink transport.
- Xylem: Transport is primarily upward, from roots to leaves/shoots.

2. Force causing transport:
- Phloem: The force is translocation, which involves active transport and mass flow driven by osmotic gradients.
- Xylem: The force is transpiration pull, where water evaporates from leaves, creating a negative pressure that pulls water up from the roots.

3. Source of this force:
- Phloem: Energy from ATP (produced by cellular respiration) drives the active transport of solutes.
- Xylem: Root pressure (osmotic pressure in roots) and the cohesion-tension mechanism (water column tension due to transpiration) generate the force.

4. Cells doing transport:
- Phloem: Sieve tube elements form the conducting pathway. They are alive at maturity but lack nuclei and other organelles.
- Xylem: Tracheids and vessel elements are the conducting cells. They are dead at maturity and have thickened secondary walls.

5. Other cells in tissue:
- Phloem: Companion cells support sieve tube elements by providing energy and regulating transport. Phloem parenchyma and fibers are also present.
- Xylem: Xylem parenchyma cells store nutrients and provide structural support. Xylem fibers add strength.

6. Transport cells lignified?
- Phloem: Sieve tube elements are not lignified.
- Xylem: Vessel elements are heavily lignified, while tracheids may be less lignified in some cases.

7. Transport cells w/ membrane?
- Phloem: Sieve tube elements have sieve plates, which are perforated membranes allowing free movement of substances but are still membrane-bound.
- Xylem: Tracheids and vessel elements are dead cells with no functional membranes.

8. Materials transported - major:
- Phloem: Organic substances like sugars (e.g., sucrose), amino acids, hormones, and other nutrients.
- Xylem: Water and dissolved minerals (e.g., ions like calcium, potassium, etc.).

9. Materials transported - minor:
- Phloem: Some signaling molecules and trace nutrients.
- Xylem: Trace elements and some organic compounds (e.g., plant hormones).

10. What happens if tissue is punctured or cut?
- Phloem: Since phloem operates under low pressure, cutting it results in slow oozing of sap.
- Xylem: Xylem operates under high negative pressure (tension). Cutting it can cause sap to "shoot" out due to the sudden release of tension.

11. Animal that feeds on this tissue:
- Phloem: Many insects, such as aphids, scale insects, and mealybugs, feed on phloem sap.
- Xylem: Animals do not directly feed on xylem sap, though they may damage xylem during feeding or burrowing.

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Final Answer:

\boxed{
\begin{array}{|c|c|c|}
\hline
\textbf{Aspect} & \textbf{Phloem} & \textbf{Xylem} \\
\hline
\text{Direction of transport} & \text{Up or Down (depends on solute concentration)} & \text{Up (from roots to leaves/shoots)} \\
\hline
\text{Force causing transport} & \text{Translocation} & \text{Transpiration pull} \\
\hline
\text{Source of this force} & \text{ATP-driven active transport} & \text{Root pressure and cohesion-tension mechanism} \\
\hline
\text{Cells doing transport} & \text{Sieve tube elements} & \text{Tracheids and vessel elements} \\
\hline
\text{Other cells in tissue} & \text{Companion cells, phloem parenchyma, phloem fibers} & \text{Xylem parenchyma, xylem fibers} \\
\hline
\text{Transport cells lignified?} & \text{No} & \text{Yes (except tracheids in some cases)} \\
\hline
\text{Transport cells w/ membrane?} & \text{Yes (sieve plates)} & \text{No (dead cells)} \\
\hline
\text{Materials transported - major} & \text{Organic substances (sugars, amino acids, hormones)} & \text{Water and dissolved minerals} \\
\hline
\text{Materials transported - minor} & \text{Nutrients and signaling molecules} & \text{Trace elements and some organic compounds} \\
\hline
\text{What happens if tissue is punctured or cut?} & \text{Sap oozes out slowly} & \text{Sap may "shoot" out} \\
\hline
\text{Animal that feeds on this tissue} & \text{Aphids, scale insects, mealybugs} & \text{None directly} \\
\hline
\end{array}
}