xylem and phloem Flashcards
why do plants need transport systems
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.
what does xylem tissue do?
transports water and mineral ions around plants. It also provides structural support. It is mostly made up of xylem vessels.
list the adaptions of the xylem?
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.
what does phloem tissue do?
Phloem tissue transports sugars and amino acids (assimilates) around plants.
what is phloem tissue mostly made up of?
sieve tube elements and companion cells.
what are the adaptions of the sieve tube elements?
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.
what are the adaptions of companion cells?
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.
