1. Support a plant….be a stem!
Plant structure: Part II

2. Stem functions Support for leaves and flowers
Transport link to and from leaves, roots and reproductive parts using xylem and phloem
storing water and nutrients for future use (parenchyma)
can also help protect plan (eg. Can be spiny like in a cactus or raspberry plant)

3. Stem types Herbaceous plants – stems without wood
- Thin epidermis and photosynthetic
Woody plants – guess what? Stems with wood
thick, hard epidermis (bark) and usually no photosynthesis
All gymnosperms have woody
stems and are dicots

4. Anatomy of herbaceous stems
Vascular tissue consists of vascular bundles arranged in the ground tissue
Vascular bundles are long, continuous strands of xylem and phloem (xylem is always closer to the centre of the stem than the phloem)
Different arrangement for monocots (e.g corn) and dicots (e.g. dandelion)
Monocots – vascular bundles are throughout the ground tissue
Dicots – vascular bundles form a ring

6. Anatomy of woody stems Woody plants: Stems contain wood
More complex than herbaceous plant stems
Grow thicker due to vascular cambium, which is a layer of meristematic (undifferentiated) tissue in the vascular tissue that produces xylem and phloem cells
Xylem tissue is on the inside of the vascular cambium; phloem on the outside
‘Wood’ is actually many layers of xylem cells.

7. Layers of xylem cells: Sapwood – younger xylem which transport water and minerals to leaves Heartwood – older xylem full of resin, rigid to support tree

9. Other components of woody stems
Bark – all tissues outside of the vascular cambium including phloem, cork cambium and cork
Phloem – transports sugars throughout the plant
Cork cambium – meristematic tissue that produces cork – the outer layer of the tree; prevents water loss

10. Growth rings
Woody stems have obvious growth rings in temperate regions – growth only in spring and summer Spring – more xylem cells – thin wall – light coloured wood Summer – less xylem cells – thicker walls – darker ring Together – growth ring

13. Stem specializations
Not all stems give support to leaves and other parts; some are underground – stolons (spider plants)
Other stems have formed vines (e.g. Peas)
Tubers – e.g. Potatoes
Rhizomes – e.g. Iris

14. Getting to the root of it…
Plant Structure: Part III

15. Function of Roots Roots are responsible for:
Anchoring the plant to the ground
Extracting water and minerals from the soil
Storage of food (carbohydrates or sugar)

16. Typical root parts
1. Primary root – first root development from the seed
2. Secondary roots – smaller root branches growing sideways from the primary root
3. Root cap – a protective cap covering the growing region of the root tip. It is designed to drill the soil and it is able to guide the root growth by perceiving gravity.
4. Root hairs - are microscopic extension of the epidermal cells near the tip of a root. They absorb water and nutrients from the soil.

18. Types of Root Systems
1. Taproot system – large, thick, main root called a taproot; can have lateral roots; all covered with root hairs Gymnosperms and angiosperms dicots have taproot systems (dandelion) 2. Fibrous root system – many small roots with many lateral roots with root hairs; shallowers - In angiosperm monocots (grasses)

20. Structure of roots Root cap – protects
Epidermal cells – with fine root hairs – increase area of absorption
Vascular cylinder (stele) – centre of root and contains vascular tissues, xylem and phloem, some ground tissue
Endodermis – surrounds the vascular cylinder, innermost layer of cortex
Pericycle – between vascular cylinder and endodermis

22. Root adaptations Aerial roots – ivy and epiphyte orchids
Expanded roots – carrots
Toxin release – walnut tree roots release toxins into soil