Mass transport in Plants: Plant Structure

Why do plants need mass transport systems?

Plants need transport systems because:

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

To achieve transport in plants what two main transport tissues are utilised?

Xylem tissue = enables water as well as dissolved minerals to travel up the plant in the passive process of transpiration

Phloem tissue = enables sugars to reach all parts of the plant in the active process of translocation

Draw a labelled diagram of a plant leaf

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Describe the vascular bundle in the roots

Xylem and phloem are components of the vascular bundle, which enable the transport of substances as well as provide structural support

The xylem vessels are arranged in an X shape in the centre of the vascular bundle. This enables the plant to withstand various mechanical forces such as pulling

The X shape arrangement of xylem vessels is surrounded by endodermis, which is an outer layer of cells which supply xylem vessels with water

Has an inner layer of meristem cells known as the pericycle

Describe the vascular bundle in the stem

The xylem is located on the inside in non-wooded plants to provide support and flexibility to the stem

Phloem is found on the outside of the vascular bundle

There is a layer of cambium in between the xylem and phloem, which are meristem cells involved in the production of new xylem and phloem tissue

Describe the vascular bundle in the leaf

The vascular bundles forms the midrib and veins of a leaf

Dicotyledonous leaves have a network of veins, starting at the midrib and spreading

What are do xylem tissue transport and how are they adapted for this xylem tissue

Transports water and mineral ions around plants. Also provides structural support. Mostly made up of xylem vessels

They are elongated, hollow tubes without end walls, therefore they can form a continuous column

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

They are thickened with a tough substance called lignin, which is deposited in spiral patterns to enable the plant to remain flexible

What do phloem tissues transport and how are they adapted for this?

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

Adaptations of sieve tube elements

Connected end-to-end to form sieve tubes

Have sieve plates with pores at their ends to allow flow of sugars and amino acids

Lack nuclei and most organelles

Have only a thin layer of cytoplasm

Adaptations of companion cells:

Connected to sieve tube elements through pores (plasmodesmata)

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