Structure of transport tissues

Leaf, root, stem, and vascular bundles

Why do plants need transport systems

• to move sucrose and oxygen to roots and shoots for respiration

• To move ions from roots to leaves

• Plants can be very large, multicellular

• Stems, trunks and roots have a small surface area to volume ratio so diffusion is too slow

Define dicotyledonous plant

A plant whose seeds contain two cotyledons, organs that store food for developing plants (have two shoots when growing)

Define vascular system

Transport vessels that run through roots, stems and leaves (eg xylem and phloem)

Identify and label the tissues in this organ

Identify and label the tissues in this organ

Identify and label the tissues in this organ

Describe the role of the parenchyma

Packing material in the root and stem

Describe the role of the epidermis

Prevents water loss

Define vascular bundle

Arrangement of xylem and phloem tissue

Describe the arrangement of the vascular bundle in the stem

• Around the edge of plant to give strength and support

• Phloem closest to the outside edge

Describe the arrangement of the vascular bundle in the root

• in the middle of the root

  • Protects bundle from tugging strains in the wind

• Xylem forms an X shape

Describe the arrangement of the vascular bundle in the leaf

• midrib is main vein carrying vascular tissue

  • Give support to structure of leaf

• Xylem closest to upper side of the leaf

• Smaller branching veins also carrying vascular bundles

Describe and explain the structure of leaves

• Waxy cuticle - prevents transpiration

• Upper epidermis - transparent to allow light to enter leaf

• Palisade mesophyll - contains lots of chloroplasts to absorb light

• Spongy mesophyll - air spaces allow gases to diffuse

• Guard cells - control opening and closing of stomata

• Stomata - allow gases exchange - carbon dioxide enters, oxygen (and water) leaves

Label the different tissues

Describe how plants carry out gas exchange in the leaves

• oxygen and carbon dioxide exit the leaf through the stomata by diffusion

• Photosynthesis maintains gas concentration gradients in the leaf

• Guard cells open the stomata during the day and close the stomata at night

• Oxygen and carbon dioxide move through air spaces in spongy mesophyll

• Carbon dioxide dissolves in moisture in mesophyll cell walls

Explain how water is absorbed by the roots

By root hair cells via osmosis

What is the role of the xylem

• transport of water and mineral ions

• From roots upwards

• Provides mechanical support

Describe the structure of the xylem

• continuous column

• Made from dead cells

• Lignin to strengthen - either spiral or annular (rings)

• Pores/pits in outer cellulose wall allows water to leave xylem into adjacent leaf cells or xylem vessels

Explain why lignin is essential in the wall of a xylem vessel

• Provides support to prevent collapse of the xylem

  • Necessary because transpiration produces tension

• Waterproofs cell

  • Cell dies and creates continuous hollow tube

• Narrow tube enables adhesion between water molecules and wall

What is the role of the phloem

• transport of sugars (eg sucrose)

• From source (eg leaves) to sink (storage tubers, growing shoots)

Describe the structure of the phloem

• Sieve tube elements

• Companion cells

• Plasmodesmata between sieve tube elements and companion cells

  • Connects cytoplasm of the cells

  • Allows diffusion of sucrose from one cell to an adjacent cell

Describe the structure of sieve tube elements

• long and narrow cells connected together to form the sieve tube

• Connected by porous sieve plates at end of sieve elements

• No nuclei or vacuole, reduced numbers of organneles

  • Allows maximum space for the translocation of materials

• Little cytoplasm

• Thick and rigid cell walls

Describe the structure of companion cells

• infolding plasma membrane - increases surface area to volume ration

  • Allows for more material exchange

• Many mitochondria - provides ATP for active transport of materials between phloem and source/sink

• Transport proteins within plasma membrane move materials into or out of the phloem

• Plasmodesmata between companion cells and sieve tube elements