○ All cells have primary cell wall, some cells have additional layers of cellulose
that increase the strength of the cell wall called secondary cell wall
○ Primary wall is located outside of secondary wall because additional cellulose
is produced at cell membrane
○ 3 plant tissues
■ Dermal
■ Ground
■ Vascular
● Dermal tissue
○ Function: protection
○ Epidermis is dermal tissue from the embryo apical meristem and is one cell
layer thick
■ Similar to skin of multicellular animal
■ Epidermis covered by cuticle which waterproof plants surface
■ Gas exchange occurs through stomata which are epidermal openings
that a pair of guard cells that regulate size of opening and controlling
water
loss and gas exchange
■ Trichomes: outgrowths of epidermal cells, hairlike
● Function: protect leaves from light intensity
■ Root hair which increase surface area for absorption of water and
minerals
● Ground Tissue
○ Carries out storage of carbohydrates and water, photosynthesis, and support
○ 3 types of cells of ground tissue
■ Parenchyma: most abundant cell in primary tissue (spongy and palidade
mesophyll)
● Primary cell walls, large vacuole, living at maturity
● Many chloroplast for photosynthesis
■ Collenchyma: living at maturity, irregular thickened primary walls
● Thickened cell walls provide flexible support for plant organs
■ Sclerenchyma: thick walls, secondary cells walls with ligden
● Ligden makes cell walls rigid
● Dead at maturity
● Strengthen tissue
● Give fruit a gritty texture
(Lec 1: Les 2)
3
● Example: fibers
● Vascular tissue (Xylem)
●
Vascular Tissue (Xylem)
○
Similar to an animal’s circulatory system except in plants, they have
separate transport systems for water and food molecules
○
Xylem is vascular tissue specialized for conducting water and minerals
○
In angiosperms, xylem is composed of conducting cells called vessels and
tracheids.
○
Both vessels and tracheids are dead at maturity
○
Cells are elongated in shape and form hollow tubes
○
Vessels are larger in diameter and stack end-to-end
○
Tracheids are smaller in diameter and have tapered ends that overlaps
○
Vessels conduct water more than efficiently than tracheids
○
Both tracheids and vessels have liquefied secondary cell walls and also
contribute to the support of the plant
○
In addition to these conducting cells, xylem often has
parenchyma cells for
lateral transport and storage, and fibers for additional strengthening
○
Secondary xylem produced by the vascular cambium forms wood
●
Vascular Tissue (Phloem)
○
