1. Stems
Section 12.3

2. Stems Learning Goal: To explore the structure and anatomy of a stem.
Success Criteria:
I know I am succeeding when I can…
describe the main structures and functions of plant stems
distinguish between herbaceous and woody plant stems
describe the types of cells found in stem tissues
identify examples of specialized plant stems
identify examples of ways that humans use plant stems

3. Stems
transports water and dissolved substances throughout the plant body
supports the branches, leaves, and flowers
store water and carbohydrates
may have protection features(ex. thorns)

4. Structure of Stems herbaceous plants
have stems that do not contain wood
stems are pliable, carry out photosynthesis, and have a thin epidermis

5. Structure of Stems Cont’d…
woody plants
have stems that contain wood
stems are hard, have bark, and do not usually carry out photosynthesis
all gymnosperms have woody stems
most woody angiosperms are eudicots
Monocots do not produce wood, but some have tissues that have a similar function, such as the stems of some palms and bamboos

6. Anatomy of a Herbaceous Stem
a vascular bundle is a long, continuous strand of vascular tissue that consists of xylem and phloem
the xylem is always closer to the centre of the stem, and the phloem is always closer to the outside of the stem
run continuously from the root to the leaves

7. Anatomy of a Herbaceous Stem Cont’d…
in monocots, the vascular bundles are found throughout the ground tissue of the stem
Vascular bundles are arranged differently in monocot and eudicot stems.

8. Anatomy of a Herbaceous Stem Cont’d…
in eudicots, the vascular bundles form a ring

9. Anatomy of a Woody Stem woody stems grow thicker over time
each year the vascular cambium (a layer of meristematic cells) divide to form new xylem and phloem cells
the xylem tissue is on the inside of the vascular cambium and the phloem tissue is on the outside
What we call “wood” is actually many layers of xylem tissue cells.
Sapwood is the younger xylem through which water and minerals are transported to the leaves.
Eventually, the cells in older xylem layers fill up with resins and oils and they no longer conduct water.
These older xylem layers form the heartwood. Heartwood is very rigid and helps support the tree.
Bark consists of all the tissues found outside the vascular cambium. It includes phloem, cork cambium, and cork.
The phloem transports sugars made in the leaves throughout the plant.
The cork cambium is a layer of meristematic tissue that produces cork, the tough, outer layer of the tree that prevents water loss from the stem. As the stem increases in size, the cork often cracks and may flake off the tree. Bark protects plants from some herbivores and, in the case of certain tree species, including Ontario’s red and white pine, can even offer protection from low-temperature fi res

10. Anatomy of a Woody Stem Cont’d…
produces “annual rings” that allow us to determine the age of trees
In temperate regions , growth occurs in the spring and summer
in the spring the xylem cells produced are larger and lighter in spring then in the summer
results in each ring having light wood on one side and dark wood on the other

11. Stems Learning Goal: To explore the structure and anatomy of a stem.
Success Criteria:
I know I am succeeding when I can…
describe the main structures and functions of plant stems
distinguish between herbaceous and woody plant stems
describe the types of cells found in stem tissues
identify examples of specialized plant stems
identify examples of ways that humans use plant stems

12. Homework
Answer 12.3 questions #5 on page 557