TRANSPORT TRANSPORT IN PLANTSIN PLANTS

Lesson 1Learning Objectives1.Draw a labelled transverse section drawing of dicot roots, stems

and leaves to show positions of xylem and phloem tissue.2.State the functions of xylem and phloem and how they are

adapted for their functions.

Outline Vascular bundle Xylem Phloem

Transport system in plants

Xylem Phloem

Vascular Bundle

The vascular bundles extend continuously from root to the stem and leaves.

Vascular bundle in root

Cross section of a dicot root

phloemxylem

1 In a dicotyledonous root, the xylem and phloem are not bundled together. Instead, they alternate with each other.

1 xylem and phloem alternate with each other.

2 The cortex of the root is also a storage tissue. The innermost layer of root cortex is called the endodermis.

endodermis

1 xylem and phloem alternate with each other.

2 cortex

3 The epidermis of the root is the outermost layer of cells. It bears root hairs. It is also called the piliferous layer.

1 xylem and phloem alternate with each other.

2 cortex

3 piliferous layer

4 Each root hair is a tubular outgrowth of an epidermal cell. This outgrowth increases the surface area to volume ratio of the root hair cell. The absorption of water and mineral salts is increased through this adaptation.

Vascular bundle in root

1 xylem and phloem alternate with each other.

2 cortex

endodermis3 piliferous layer

4 root hair

Vascular bundle in stem

Cross section of a dicot stem

1 In a dicotyledonous stem, the xylem and phloem are grouped together to form vascular bundles.

2 The vascular bundles are arranged in a ring around a central region called the pith.

1 vascular bundles

2 pith

1 vascular bundles

3 The phloem lies outside the xylem with a tissue called the cambium between them. Cambium cells can divide and differentiate to form new xylem and phloem tissues, giving rise to a thickening of the stem.

xylemcambium

phloemvascular bundle

2 pith

1 vascular bundles

3 cambium

4 The region between the vascular bundles and the epidermis is the cortex. Both the cortex and the pith serve to store up food substances, such as starch.

2 pith

1 vascular bundles

3 cambium

4 cortex

5 The stem is covered by a layer of cells called the epidermis. The epidermal cells are protected by a waxy, waterproof cuticle that greatly reduces evaporation of water from the stem.

Vascular bundle in stem

2 pith

1 vascular bundles

3

4 cortex

5 epidermis

xylem

cambium

phloem

vascular bundle

Test yourself: Root? Stem? Leaf?

Vascular bundle

How to identify xylem vessels from phloem?

Xylem

Different pattern of lignification

annularspiral pitted

PhloemPhloem consists mainly of sieve tubes and companion cells.

Phloem – Sieve tubes

Phloem – Companion cell

Exercise

1.Draw and label a vascular bundle in root and stem. Show the positions of xylem and phloem clearly.

2.Draw a table of comparison between xylem and phloem.

Learning Objectives

1.Draw a labelled transverse section drawing of dicot roots, stems and leaves to show positions of xylem and phloem tissue.

2.State the functions of xylem and phloem and how they are adapted for their functions.