Lesson 3: Stems & Roots

Unit 5 Plants

Functions of Stems

Economic value: wood products/lumber

Connect the vascular tissue in the leaves to the vascular tissue in the roots, allowing water and dissolved substances to be transported throughout the body

Function of Stems

Raise and support the leaves (maximizing photosynthesis) and reproductive organs (maximizing the likelihood of being pollinated and producing fruits and seeds)

Stem Structures – Herbaceous Plants

Herbaceous Plants: plants that have stems that do not

contain wood Relatively pliable stems Stems carry out photosynthesis Thin epidermis

Anatomy of Herbaceous Stems Vascular tissue in herbaceous plant stems are

arranged in vascular bundles Vascular bundles contain xylem and phloem

Xylem is always closer to the centre of the stem Phloem is always closer to the outside of the stem In monocots:▪ Vascular bundles found through out the ground tissue

In dicots:▪ Vascular bundles form a ring

Monocot Herbaceous Stem (ex: corn)

Eudicot Herbaceous Stem (ex: alfalfa)

Stem Structures – Woody Plants

Woody plants: Stems that contain wood Woody stems are relatively hard Have bark Usually do not carry out photosynthesis

Anatomy of Woody Stems

Wood stems grow thicker every year due to the presence of the vascular cambium

Vascular Cambium: the meristematic cell layer in the vascular tissue that divides to form new xylem and phloem tissue

Xylem is on the inside of the vascular cambium

Phloem is on the outside

Wood – Sapwood and Heartwood

Wood is many layers of xylem tissue cells

Sapwood is the younger xylem through which water and minerals are transported to the leaves

Eventually, the older xylem fills up with resin and oils and they no longer conduct water forming the heartwood which is very rigid and helps support the tree

https://www.youtube.com/watch?v=jrXSHLyAQeQ

Bark consists of all tissues found outside the vascular cambium Phloem▪ transports sugars made in the leaves

throughout the plant. Cork cambium▪ meristematic tissue that produces cork

Cork▪ the tough, outer layer of the tree that

prevents water loss from the stem

Growth Rings

Growth only happens in the spring and summer

In spring, vascular cambium grows rapidly, producing large xylem cells that have relatively thin walls that form a layer of lighter-coloured wood

In summer, fewer xylem cells are produced and they have thicker cells walls that form a layer of darker-coloured wood

The spring and summer wood together forms one growth ring

Roots

Function of Roots: Anchors the plant Keeps it upright Absorbs waters and nutrients (0ther

than carbohydrates) Store water and carbohydrates

Root Systems

Taproot: a root system composed of a large, thick root; can have smaller lateral roots

Fibrous: a root system made up of many small, branching roots

General Structure of Roots

Tip of root contains the root cap and a meristem

Root Cap: mass of cells that form a protective covering for the meristem at the root tip; allows the root to penetrate the soil with minimal damage

Roots

Root hairs project out of the epidermis and increase the surface area allowing for greater water and nutrient absorption

Root cortex is a region of parenchyma cells beneath the epidermis where carbohydrates can be stored and water can be transported fro the epidermis to the xylem

Endodermis: is the innermost layer of cells in the root cortex

Endodermis

The endodermis cell walls are wrapped with a wax-like substance forming a continuous barrier called the Casparian strip. The Casparian strip prevents substances from passing through the spaces between the endodermal cells

Monocot and Eudicot Roots

Vascular tissue is arranged differently in monocot roots and eudicot roots

Homework Questions