Chapter 9 Transport In Plants 2.0 Flashcards
Describe and explain why multicellular plants require transport systems
-Multicellular plants have higher metabolic demands
-Larger sized plants need effective transport systems to move substances between the roots and leaves
-Small surface area to volume ratio meaning diffusion alone would be too slow to supply cells with everything they need.
What is the vascular system of a plant?
Series of transport vessels composed of the xylem and phloem which travel through the stems, roots and leaves.
The vessels are arranged in vascular bundles.
Describe the function of the xylem vessel
Transports water and mineral ions from the roots to the leaves
Explain the structure of the xylem vessel
The Xylem are hollow structures made by several columns of dead cells joined end to end.
The walls are thickened with lignin which helps to strengthen the structure and provides support preventing the vessel from collapsing.
Where lignification is incomplete there are gaps, bordered pits, which allow water to move between adjacent vessels.
The xylem has no ends walls so the vessel is uninterrupted allowing a continuous column of water to flow through
The xylem is also narrow so water is pulled by capillary action.
Describe the function of the phloem vessel
Transports sugars and assimilates in a solution up and down the plant following a biodirectional pathway.
Explain the structure of the phloem vessel
The phloem is composed of sieve tube elements and companion cells.
The sieve tube elements are living cells that join end to end to form the sieve tubes to allow the transportation of solutes.
Between cells the walls become perforated to form sieve plates that allow the phloem contents to flow through.
The cells have no nucleus, few organelles and a thin layer of cytoplasm which is connected to adjacent cell through holes in the sieve plates.
Companion cells
Linked to sieve tube elements through plasmodesmata
Contains a nucleus and an abundance of mitochondria to carry out the living functions of themselves and the sieve cells.
How is the phloem and xylem situated in a root cross section?
The xylem is at the centre surrounded by the phloem
The xylem is a cross shape
Why are the vascular bundles situated at the centre of the root cross section?
Help to withstand the tugging strains that result as the stems and leaves are blown in the wind.
Provides support for the root as it pushes through the soil.
How is the phloem and xylem situated in a stem cross section?
The xylem and phloem are around the outside of the stem
The phloem faces the outside of the oval and the xylem faces the inside of the oval.
Why are the vascular bundles situated around the outside of the stem?
Provides structural support and strength to reduce bending
How are the xylem and phloem situated in a leaf cross section?
Veins spread through the leaf with the primary Midrib vein travelling down the centre of the leaf.
Phloem is at the bottom of the vein
Xylem at the top of the vein
Why are the vascular bundles situated in the veins of leaves?
Builds a network that supports the structure of thin leaves
