1. Chapter 23: Plant Tissues & Systems
Section 1

2. Specialized Plant Cells
Remember plant cells have unique structures
Cell wall
Central vacuole
3 types of specialized plant cells
Parenchyma
Collenchyma
Sclerenchyma

3. Paranchyma “puh-REN-kuh-muh”
Usually loosely packed cube- shaped or elongated cells
Contain large central vacuole
Have thin, flexible cell walls
Involved in many metabolic functions: photosynthesis, storage of water and nutrients, healing
Usually form main part of nonwoody plants
Ex. Fleshy part of apple

4. Collenchyma “koh-LEN-kuh-muh”
Cells walls thicker than parenchyma
Cell walls irregular in shape
Thicker walls provide more support for plant
Usually grouped in strands
Specialized for supporting areas of plant that are still lengthening
Ex. Celery stalks – lots of collenchyma

5. Sclerenchyma “skluh-REN-kuh-muh”
Thick, even, stiff cell walls
Support and strengthen plant in areas where growth is finished
Usually dies at maturity
Rough texture of pear is from presence of sclerenchyma cells

7. Tissue Systems
Cells that work together to perform specific function make tissue
In plants, arranged into systems
Dermal system
Ground system
Vascular system
Systems further organized into 3 major plant organs – roots, stems, leaves

8. Dermal Tissue System Forms outside covering of plants
In young plants, made of epidermis “ep-uh- DURH-muhs” – the outer layer made of parenchyma cells
In some species, epidermis more than 1 cell thick
Outer epidermal wall often covered by waxy layer called the cuticle  prevents water loss

9. Some epidermal cells of roots develop hairlike extensions that increase water absorption
Openings in leaf and stem epidermis are stomata  help regulate the passage of gases and moisture in and out of plant
In woody stems and roots, epidermis replaced by dead cork cells

11. Ground Tissue System Dermal tissue surrounds the ground tissue system
Has all 3 types of cells
Functions in storage, metabolism, support
Paranchyma most common cell
Nonwoody roots, stems, leaves made mostly of ground tissue

12. Cactus stems have large amounts of parenchyma cells for storing water
Plants growing in very wet soil have parenchyma with large air spaces to allow air to reach roots
Nonwoody plants that need to be flexible to withstand wind have large amount of collenchyma cells
Sclerenchyma found where hardness is advantage, i.e. seed coats, cacti spines

13. Vascular Tissue
Vascular tissue supports the plant body and transports water and nutrients throughout the plant.
The two kinds of vascular tissue are xylem, a water-conducting tissue, and phloem, a tissue that carries dissolved food.
Both xylem and phloem consist of long, slender cells that connect almost like sections of pipe, as shown in the figure.

14. All seed plants have xylem cells called tracheids.
Xylem: Tracheids
All seed plants have xylem cells called tracheids.
As they mature, tracheids die, leaving only their cell walls. These cell walls contain lignin, a complex molecule that gives wood much of its strength.

15. Xylem: Tracheids
Openings in the walls connect neighboring cells and allow water to flow from cell to cell.
Thinner regions of the wall, known as pits, allow water to diffuse from tracheids into surrounding ground tissue.

16. Xylem: Vessel Elements
Angiosperms have a second form of xylem tissue known as vessel elements, which are wider than tracheids and are arranged end to end on top of one another like a stack of tin cans.
After they mature and die, cell walls at both ends are left with slit-like openings through which water can move freely.

17. Xylem: Sieve Tube
Elements
Unlike xylem cells, phloem cells are alive at maturity. The main phloem cells are sieve tube elements, which are arranged end to end, forming sieve tubes. The end walls have many small holes through which nutrients move from cell to cell.

18. Xylem: Sieve Tube
Elements
As sieve tube elements mature, they lose their nuclei and most other organelles. The remaining organelles hug the inside of the cell wall and are kept alive by companion cells.

19. Phloem: Companion Cells
The cells that surround sieve tube elements are called companion cells.
Companion cells keep their nuclei and other organelles through their lifetime.

20. Growth in Meristems
Plant growth starts in meristems “MER-i-stemz”  regions where cells continuously divide
Apical “AP-i-kuhl” meristems  plant grows in length
Located at tips of stems and roots

21. Some monocots have intercalary “in-TUHR-kah-ler- ee” meristems located above bases of leaves and stems
Allow grass leaves to quickly regrow after being cut

22. Gymnosperms and most dicots also have lateral meristems  allow stems and roots to increase in diameter
Located near outside of stems and roots
2 types
Vascular cambium
Cork cambium

23. Vascular cambium  produces additional vascular tissues
Located between xylem and phloem

25. Cork cambium  produces cork
Located outside phloem
Cork cells replace epidermis in woody stems and roots
Protects plant
Cork  dead cells that provide protection and prevent water loss

27. Primary growth  increase in length
Made by apical and intercalary meristems
Secondary growth  increase in diameter
Made by lateral meristems
By vascular cambium and cork cambium