Xylem & Phloem

Question 1

Why do plants need a transport system

Answer 1

• 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

Question 2

Xylem

Answer 2

Transports water and mineral ions as well as providing structural support

Question 3

Adaptations

Answer 3

• 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 4

Phloem

Answer 4

Transport sugars and assimulates

Question 5

Adaptations of sieve tube elements

Answer 5

• 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 6

Adaptations of companion cells

Answer 6

• 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