Which plant cells lack a nucleus?
A) sieve cells
B) xylem
C) companion cells
D) both companion and parenchyma cells
E) both xylem and sieve-tube cells
Why is the answer E?
nevermind I get it
The answer to this question is E) both xylem and sieve-tube cells. To understand why, let's break down the options and analyze each one:
A) Sieve cells: These are part of the phloem tissue in plants that are responsible for transporting sugars and other organic molecules. Sieve cells, however, do contain a nucleus. Therefore, option A is not the correct answer.
B) Xylem: Xylem is a specialized tissue in plants that transports water and minerals from the roots to the rest of the plant. Xylem cells, including tracheids and vessel members, do not have a nucleus at maturity. The presence of a nucleus would interfere with the efficient flow of water and minerals through their interconnected vessels. Therefore, option B is part of the correct answer.
C) Companion cells: Companion cells are specialized parenchyma cells that are closely associated with the sieve-tube elements in the phloem tissue. These cells are responsible for supporting the metabolic needs of the sieve-tube elements. Companion cells do have a nucleus for carrying out essential cellular functions. Therefore, option C is not the correct answer.
D) Both companion and parenchyma cells: Parenchyma cells are a type of simple plant cells that perform various functions, including storage, photosynthesis, and gas exchange. Parenchyma cells possess a nucleus as they are actively involved in metabolic processes. Therefore, option D is not the correct answer.
E) Both xylem and sieve-tube cells: As mentioned earlier, xylem cells (tracheids and vessel members) lack a nucleus at maturity. In addition, sieve-tube elements of the phloem, such as sieve cells or sieve tube members, also lack a nucleus. This absence of a nucleus allows for a more efficient flow of fluids through these cells. Therefore, option E is the correct answer.
In conclusion, the correct answer is E) both xylem and sieve-tube cells because both of these cell types lack a nucleus.