PBL 2: Meristems and Plant Tissues

Question 1

Plant tissue and types

Answer 1

Plant tissue: collection of similar cells conducting the same function

Types:
-Permanent tissues, which lost their ability of cell division
-Meristematic tissues, actively dividing cells.

Question 2

Simple permanent tissue

Answer 2

Only have primary walls, made of cellulose+hemicellulose

-Parenchyma: Most common, permeable,
weak
-Collenchyma: Unevenly thickened wall, plastic support, can be reshaped
-Sclerenchyma: Primary+ thick secondary wall, elastic support, maintains the leaf’s shape

Question 3

Complex permanent tissue

Answer 3

More than one type of cell, i.e:
-Epidermis: the outermost layer, consists of a single layer of parenchyma cells, covered by wax and cutin.

-Ground tissues/cortex: internal layer to the epidermis, parenchyma that later undergoes photosynthesis.

-Pith: Internal to the vascular tissue
-Vascular tissue: Xylem+Phloem

Question 4

Epidermis Function

Answer 4

-Transpiration, protection from bacteria, insects, fungi.
-Reflective to prevent overheating
-Gas exchange
-Can have trichomes: protection, prevents water loss, can contain chemicals

Question 5

Ground tissue Function

Answer 5

Food storage, transportation, secretion, photosynthesis
-Aerenchyma cells: allows for plant to flow on water by filling intercellular spaces with air.

Question 6

Xylem

Answer 6

Dead and hollow sclerenchyma cells, conduct water+minerals, made of tracheids and vessel elements.
-Only flows in one direction

Question 7

Tracheids

Answer 7

Transfer water via pit membranes (tracheids overlap), found in flowering plants and ferns.

Question 8

Vessel Elements

Answer 8

Provide movement of water with less friction due to perforations in primary walls.
-Perforations of adjacent cells align and form a vessel

Question 9

Phloem

Answer 9

Distributes sugars+minerals, no secondary walls, living cells.
-Flows in any direction
-Accompanied by companion cells with nucleus

Question 10

Sieve Elements

Answer 10

Made up of sieve tube elements and sieve cells.
-Parenchyma cells, living cells with cytoplasm, no nucleus, enlarged plasmodesmata called sieve pores.

Question 11

Sieve Cell

Answer 11

Elongated and spindle shaped cell with sieve areas.
-Associated with albuminous cells

Question 12

Sieve tubes

Answer 12

Stacked cells with aligned sieve areas (sieve plates) on bottom+upper end
-Have companion cells, which lead sugars in and out of cell

Question 13

Apical Meristem (Meristematic tissue)

Answer 13

Growth of the tips of the roots+shoots, produced primary meristems and then primary tissues.

Process of cell division: One cell remains meristem, the other one becomes the primary meristem, the latter of which can differentiate into:
1. Provascular tissue: xylem+phloem
2.Protoderm: epidermis
3.Ground tissue: pith+cortex

Question 14

Lateral Meristem (Meristematic tissue)

Answer 14

Responsible for secondary tissue growth in stem+roots,
-Increases stem & roots in diameter

Structure: In the vascular bundle,
1. the xylem is internal to the phloem
2. In between this is the vascular cambium
3. The fusion of cambium cells forms a ring.

Question 15

Vascular cambium (meristematic tissue)

Answer 15

Consists of two cell types:

1. Fusiform initials:
   -thin primary wall, longitudinal cell division, produces two cells: (one remains meristem, other develops into phloem/xylem depending on position)
2. Ray initials:
   -short+cubica, storage&transport function between xylem and phloem, and vice versa

Question 15

Cork cambium (meristematic tissue element)

Answer 15

Produced when cells die and parenchyma cells are reactivated in the external layers:
-serves as a protective layer, production of phloem cells.

Question 16

More info on the cork cambium

Answer 16

-Cell division: inner cell remains cork cambium, outer cambium becomes cork cell (periderm=cork cell layers)

-Mature cork cells produce suberin (waterproof)
-Regions (lenticels) allow for gas diffusion into intercellular spaces.

Question 17

Growth ring

Answer 17

Cambium cells that keep adding new layers of phloem+xylem