Chapter 29, Problem 1TYU

Which structure or compartment is part of the symplast?

1. A.    the interior of a vessel element
2. B.     the interior of a sieve tube
3. C.     the cell wall of a mesophyll cell
4. D.    an extracellular air space

Summary Introduction

Introduction:

The symplast of a plant involve inner plasma membrane that facilitates diffusion of water and its solutes. The plasmodesmata forms the channel for the direct flow sugars, amino acids, and ions and other small molecules between cells. Transport of sugars is also occurs from mesophyll cells to sieve tubes through symplast.

The apoplastic pathway allows the molecules and water to move from epidermis to the cortex to reach endodermis. After reaching to endodermis, solutes are forced to choose symplastic pathway by the casparian strip. Solutes are filtered passively, and they reach to the pericycle and moved to the xylem for the transport to distant parts of the plant.

Answer to Problem 1TYU

Correct answer:

Sieve tube are the living that are tubular in shape and form a web by connecting the plant from end to end from the cortex of the root through the cytoplasm of the cells present in between the cells of root hair and the xylem and form the  symplastic pathway. Therefore option (B) is correct.

Explanation of Solution

Reason for correct statement:

Phloem sap moves through the sieve tubes from a sugar source to the sugar sink via symplastic path or apoplastic path (depend on the species).

Option (B) is given as “the interior of a sieve tube”.

“Interiors of a sieve tube helps in maintain the sucrose and organic molecule concentration by active transport using symplastic pathway”, it is the right answer.

Hence, option (B) is correct.

Reasons for incorrect statements:

Option (A) is given as “the interior of a vessel element”.

The apoplastic pathway involves everything external to the plasma membrane that is the cell wall, interior portion of vessel elements and extracellular spaces. So, it is a wrong answer.

Option (C) is given as “the cell wall of the mesophyll cell”.

The cell wall of the mesophyll cell is a part of the apoplastic pathway. So, it is a wrong answer

Option (D) is given as “an extra cellular air space”.

As, the apoplastic pathway involves the extracellular spaces and tracheids. So, it is a wrong answer

Hence, options (A), (C), and (D) are incorrect.

Conclusion

The interior of a sieve tube is a part of symplast and helps in transport of sucrose from sugar source to sugar sink.