7.7 - Xylem and Phloem

Question 1

Adaptations of companion cells

Answer 1

They are connected to sieve tube elements through pores (plasmodesmata).
The cytoplasm contains a large nucleus, many mitochondria to release energy for the active transport of substances through the sieve tube elements, and many ribosomes for protein synthesis.

Question 2

Adaptations of sieve tube elements

Answer 2

They are connected end-to-end to form sieve tubes.
They have sieve plates with pores at their ends to allow flow of sugars and amino acids.
They lack nuclei and most organelles.
They have only a thin layer of cytoplasm

Question 3

What does phloem transport and made up of?

Answer 3

Phloem tissue transports sugars and amino acids (assimilates) around plants. It is mostly made up of sieve tube elements and companion cells.

Question 4

Adaptations of xylem vessels

Answer 4

• They are elongated, hollow tubes without end walls.
• They lack organelles.
• Their walls are thickened with lignin for support.
• They have non-lignified pits that allow movement of water and ions into and out of vessels.

Question 5

What do xylem transport and provide to a plant?

Answer 5

Xylem tissue transports water and mineral ions around plants. It also provides structural support.

Question 6

Why do plants need transport systems?

Answer 6

• They are multicellular with a low surface area to volume ratio.
• Diffusion is too slow to meet their metabolic needs.
• Substances must be moved over long distances.