Question

Arrange the following events in an order that explains the bulk flow of substances in the phloem from the source.

(A) Water diffuses into the sieve tube elements
(B) Leaf cells produce sugar by photosynthesis
(C) Solutes are actively transported into sieve elements
(D) Sugar is transported from cell to cell via the apoplast and/or symplast
Choose the correct answer from the options given below:

• A. (A), (B), (C), (D).
• B. (B), (D), (C), (A).
• C. (B), (A), (D), (C).
• D. (C), (B), (D), (A).

Hint:

Phloem transport: Sugars made in leaves move through symplast/apoplast → sieve tubes → water enters.

Answer 1

The Correct Option is B

Step 1: Understand the bulk flow process in phloem.
Phloem transport occurs via a process called bulk flow, where sugars are produced in the leaves and transported to other parts of the plant. Step 2: Sequence of events.
1. Leaf cells produce sugar by photosynthesis (B): Photosynthesis generates sugars in the leaves, which is the source of phloem transport.
2. Sugar is transported from cell to cell via the apoplast and/or symplast (D): The sugars move through the plant from cell to cell.
3. Solutes are actively transported into sieve elements (C): Sugars are actively loaded into the sieve tube elements from the surrounding cells.
4. Water diffuses into the sieve tube elements (A): Water enters the sieve tubes to balance the osmotic potential created by the sugar influx.
Step 3: Conclusion. Thus, the correct order is: \[ \text{B} \rightarrow \text{D} \rightarrow \text{C} \rightarrow \text{A} \]
Final Answer: \[ \boxed{\text{(B), (D), (C), (A)}} \]