Question Video: Describing the Structure of the Phloem | Nagwa Question Video: Describing the Structure of the Phloem | Nagwa

Question Video: Describing the Structure of the Phloem Biology • Second Year of Secondary School

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Which of the following best describes the structure of the phloem? [A] The phloem is comprised of living sieve cells that form a long, continuous tube. [B] The phloem is comprised of many dead sieve cells that have pores in their cell walls to allow movement of substances through the plant. [C] The phloem is comprised of dead sieve cells that form a long, continuous tube. [D] The phloem is comprised of many living sieve cells that have pores in their cell walls to allow movement of substances through the plant.

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Video Transcript

Which of the following best describes the structure of the phloem? (A) The phloem is comprised of living sieve cells that form a long, continuous tube. (B) The phloem is comprised of many dead sieve cells that have pores in their cell walls to allow movement of substances through the plant. (C) The phloem is comprised of dead sieve cells that form a long, continuous tube. Or (D) the phloem is comprised of many living sieve cells that have pores in their cell walls to allow movement of substances through the plant.

Let’s remove the multiple-choice options for now and remind ourselves about the structure of the phloem. You may recall that translocation is the process whereby substances such as sucrose are transported around a plant in the phloem. The structure of the phloem can be represented by this simple diagram. The main transport vessel of the phloem is called the sieve tube. The sieve tube is made of living sieve cells, which are also known as sieve tube elements. These are stacked end on end to form one continuous tube.

The end walls of the sieve tube elements are called sieve plates. These contain pores which allow substances to move from one sieve tube element to the next. Sieve tube elements also contain plasmodesmata. Plasmodesmata are narrow pores located between each sieve tube element and its associated companion cell. And they allow substances to more easily diffuse into the sieve tube for transport in the phloem.

We now have enough information to answer the question. The statement which best describes the structure of the phloem is (D). The phloem is comprised of many living sieve cells that have pores in their cell walls to allow movement of substances through the plant.

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