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: Understanding Phloem Bulk Flow.
Phloem transport relies on bulk flow, where sugars synthesized in leaves are moved to other plant regions.Step 2: Event Sequence.
1. Photosynthesis in leaf cells produces sugar (B): Sugars are created in leaves via photosynthesis, initiating phloem transport.
2. Sugar moves cell-to-cell via apoplast/symplast (D): Sugars are transported between cells.
3. Solutes actively enter sieve elements (C): Sugars are actively loaded into sieve tube elements.
4. Water enters sieve tube elements via diffusion (A): Water diffuses into sieve tubes, balancing osmotic pressure from sugar influx.
Step 3: Summary. The correct sequence is: \[\text{B} \rightarrow \text{D} \rightarrow \text{C} \rightarrow \text{A}\]
Final Answer: \[ \boxed{\text{(B), (D), (C), (A)}} \]