Who knows Essay

Submitted By christinalove4444
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Pages: 5

Tissues

Plant Life Duration

Duration: The life span of an individual plant

1) Herbaceous Plants

Annual
Plants live for a single growing season
Germinate, grow vegetatively, form flowers, and produce fruits and seeds

Biennial
Live for two years
Vegetative in the first year and produce flowers/fruits/seeds in the second year

Perennial
Live for three or more years
Flower and fruit every year once the plant has reached maturity

2) Woody Plants: always perennial

Shrubs
Have multiple woody stems

Trees
Have mainly one single woody stem
Trunk

Lianas
Are woody but can not sustain themselves
Need a physical support usually from other plants, rocks, buildings, etc
A vine is not a liana, vines are herbaceous where as lianas are woody

Extremes and Special Cases

Ephemeral
Only live for a couple of weeks
They do everything in this time such as germination, flower, reproduce, etc.
Annual plants

Extremely Longevive
These plants live for thousands of years
Monocarpy
Monocarpic plants are perennial
Produce flowers and fruits only one time and then they die
Agave spp.

Tissues: Classification

1) Meristems

Responsible for plant growth and development which come from mitotic cell division
Meristematic cells are the least differential cells
Small and tightly packed, no intracellular space
Thin cell wall
Dense protoplasm
Small vacuoles
Lack differential plastids (chloroplasts and chromoplasts)
Acorn to a massive tree

Meristem Classification

Based on their origin

Based on their position in plant
Lateral Meristems

Secondary Meristems
Growth in thickness
Vascular and Cork cambium form from the differentiation of primary cell tissue

Vascular cambium  secondary xylem inwards, secondary phloem outwards
Cork cambium  periderm (bark)

Why don’t plants develop cancer?
Plant tumors are very rare and are not as lethal as in animals because in plants it much more difficult for cells to escape tissue/organism controls
Plants are masters of mitosis!

Each cell has the potential to reproduce the entire plant organism

2) Parenchyma

Regular Storage Chlorenchyma Aerenchyma
Most common and abundant tissue
Primary or secondary origin
Consists of living cells
Various roles: storage of food, air, water, photosynthesis, etc. depending on the position of the plant or the ecology of that particular plant

3) Collenchyma

Supporting function
Living tissue that originates from parenchyma cells
Often found in the ribs of stems
Provides elasticity (herbaceous stems or leaves do not break when the wind blows)

4) Sclerenchyma

Mechanical function
Dead tissue
More specialized and diverse than collenchyma
Primary walls become very think with lignin, cells are dead of maturity
Primary or secondary origin
Sclereids: length and width are more or less equal
Fibers: Length much much longer than width, can be present in the roots, stems, and leaves

5) Xylem

Conducts raw sap – water and minerals – from the roots to the leaves
Treachery elements: dead, elongated cells with cell wall thickened with lignin
Still capable to fulfill their role of conducting water and minerals absorbed by the roots
Tracheids are primitive; thinner and longer
Vessel members are more evolved; shorter and wider

6) Phloem

Can have a primary or secondary origin
Transport sugars and other organic materials that resulted from photosynthesis, from the leaves to the rest of the plant
Sieve tubes are living, but nucleus disintegrates, so they require companion cells to function
Sieve tubes are long and connected by sieve plates

Most often Xylem and Phloem and associated in bundles

7) Epidermis

Always a primary tissue
Produced by primary meristem
Exterior of all organs
Normally one thick layer with the…