PLANT GROUPS - uobabylon.edu.iq

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PLANT GROUPS CHLOROPHYTA 1 PLANT GROUPS (3) General characteristic of the Chlorophyta 1 Habitat Aquatic (mainly fresh water), terrestrial in moist situations, a few Epiphytic 2 Pigments Chlorophyll a & b, β-carotene, α-carotene less prominent 3 Food Reserves Starch, rarely inulin, Oils & Fats 4 Cell Wall Component Cellulose, Crystalline glycoproteins 5 Reproduction Asexual & Sexual (Isogamy, An isogamy & Oogamy 6 Growth Forms Flagellate coccoid, Filamentous rarely Foliaceous or siphonaceous 7 Flagella Two or Four Occasionally numerous Flagella are present in all classes of algae except Cyanophyceae & Rhodophyceae. There number, nature and mode of Orientation are important. There are two types of flagella. 1) Acronematic or Whiplash types which are smooth & do not have hairs (Mastigonemes) on its surface. 2) Pantonematic or tinsel type which have hairs on its surface.

Transcript of PLANT GROUPS - uobabylon.edu.iq

PLANT GROUPS CHLOROPHYTA

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PLANT GROUPS

(3)

General characteristic of the Chlorophyta

1 Habitat Aquatic (mainly fresh water), terrestrial in

moist situations, a few Epiphytic

2 Pigments Chlorophyll a & b, β-carotene, α-carotene less

prominent

3 Food Reserves Starch, rarely inulin, Oils & Fats

4 Cell Wall Component Cellulose, Crystalline glycoproteins

5 Reproduction Asexual & Sexual (Isogamy, An isogamy &

Oogamy

6 Growth Forms Flagellate coccoid, Filamentous rarely

Foliaceous or siphonaceous

7 Flagella Two or Four Occasionally numerous

Flagella are present in all classes of algae except Cyanophyceae &

Rhodophyceae. There number, nature and mode of Orientation are important.

There are two types of flagella.

1) Acronematic or Whiplash types which are smooth & do not have hairs

(Mastigonemes) on its surface.

2) Pantonematic or tinsel type which have hairs on its surface.

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Flagella hairs are of two types

a) Fibrous solid hairs

b) Tubular hairs

Flagella in Algae & other plant except bacteria are composed of nine peripheral

doubled microtubules & two central single microtubules. This is commonly known

as (9 + 2 Pattern) of fibrils of flagellum these are produced in a matrix

surrounded by Flagellar membrane & Flagellar sheath.

Single central tubules

Peripheral doublet tubules

Radial spokes

Slide arm

Cross Section Showing (9 + 2) Pattern

ppppPPattern Pattern Pattern) Pattern

Membrane

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Cell Structure of Chlorophyta

Cellular organization in Chlorophyta as in all other Algae except Cyanophyta is

Eukaryotic the cells possess cell organelles

Cell Wall: The mature cell of green Algae possesses a definite cell wall.

Usually outer layer is pectic & inner cellulosic.

Chloroplast: Present in many type Reticulate, Peripheral, Stellate, Small

discoid & Spiral.

Pyrenoid: In most green Algae the plastids contain one or more specially

differentiated regions called Pyrenoids these are the major sites of starch

formantion in green Algae.

Eye Spot (Stigma): Most of the flagellated cells that show phototatic

movement have an Eye spot. In green Algae the Eye spot is always in the

Chloroplast near the flagellar bases in anterior portion.

Mitochondria, Golgi bodies, Endoplasmic reticulum, Ribosomes &

Contractile vacuole are present in the cell.

Reproduction

1) Vegetative Reproduction: Portion of the plant body get separated to form

new individuals without any obvious change in the protoplast, cell division

occur.

2) Asexual Reproduction

a) Zoospores are motile & naked spore produced within the

Zoosporangium. These frequently move with the help of flagella

which maybe two or more. In Chlamydomonas the Zoospore

Exactly similar to parent cell & are formed in variable numbers

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(4, 8, and 16). In Filamentous forms, in Ulothrix a cell produces up

to (8 or 16) biflagellate or quadri flagellate. In Oedogonium a single

multi flagellate Zoospore is formed from each cell.

b) Aplanospores are nonmotile & are produced in Aplanosporangia.

They are common occurrence in Chlorella.

c) Hypnospore these are thick walled non motile. Spores that undergo a

long resting period in Sphaerella.

d) Akinetes are the direct modification of vegetative cell which becomes

converted into a thick wall non motile resting spores is formed in

Chladophora.

e) Autospores they are non-motile spores resembling the parent cell in

shape & structure in Scendesmus.

f) Cysts these are resting cells enclosed in a thick envelope is known in

Vaucheria.

g) Palmella stage occasionally during unfavorable condition.

Sexual Reproduction

1) Isogamy

2) An isogamy

3) Oogamy

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Life Cycle

There are different types of life cycle in Chlorophyta classified into four categories

Haplontic life cycle: The main plant body is haploid & the Zygote

being the only diploid stage, in unicellular & filamentous forms.

Diplontic life cycle: The main plant body is diploid which forms

haploid gametes meiotically. Gametes fusion & form diploid Zygote which

directly germinates into a new plant in Cladophora.

Main Plant (1n)

Zygote (2n)

Fusion

Gamete (1n)

Gamete (1n)

Meiosis

Spore (1n)

Haplontic Life Cycle

e

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Isomorphic alternation of generation: Both haploid & diploid

phases are similar in external appearance, a haploid plant produces gametes & a

diploid plant produces Zoospores. The Zygote develops into a new diploid plant

without undergoing reduction division in Ulva.

Main Plant (2n)

Zygote (2n)

Gametangia

Meiosis

Gamete (+) Gamete (-)

Fusion

Diplontic Life Cycle

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Heteromorphic alternation of generation: The two phases of

life cycles are unequal in size different in external appearance; the Zygote does

not undergo a reduction division but develops into short diploid filament.

Plant (2n)

Plant (1n)

Meiosis

Spore (1n)

Gamete (1n)

Gamete (1n)

Fusion

Zygote

Isomorphic alternation of generation

Diplohaplontic Life Cycle

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Classification of Chlorophyta

Chlorophyta divided into (14) orders:

Order: Volvocales

Member of this order are Unicellular & Coenobial which are normally motile by

means of flagella.

1 Order Volvocales

2 Order Chlorosarcinales

3 Order Tetrasporales

4 Order Chlorococcales

5 Order Chlorellales

6 Order Zygnematales

7 Order Odeogoniales

8 Order Ulotricales

9 Order Chaetophorales

10 Order Chladophorales

11 Order Acrosiphoniales

12 Order Ulvales

13 Order Siphonales

14 Order Caulerpales

Coenobium a Colony of cells firmly allached to each other in which there is some

degree of co-ordination

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In life cycle of these members temporary resting stage, Palmella stage may occurs.

Member of this order represent most primitive, plant life which are widely

distributed in fresh water & soil. Some members are found in brackish & marine

waters. Volvox is known to cause water blooms.

Unicellular Volvocales

Family Chlamydomonadaceae

Genus Chlamydomonas

The Chlamydomonas cell represents most primitive member of living

green plants. It’s widely distributed in variety of habitats mainly in fresh water or

on moist water few species are found in brackish waters. Chlamydomonas

halophile & Chlamydomonas nivalis represent snow algae is found in the

Polar Regions imparting red colour. The red colour is due to red pigment

Haematochrome.

Solitary free swimming cell maybe ellipsoidal, sub cylindrical, spherical or

pyriform, two equal Acronematic flagella are located in the anterior region of the

cell which is responsible for motility. Cells have delicate to massive cup shaped

chloroplast. There is usually one Pyrenoid within a chloroplast. Usually there are

two contractile vacuoles near the base of flagella. A single nucleus lies in the

colourless cytoplasm.

The Stigma or red eye spot is embedded at one side of chloroplast & is

composed of carotenoid subunits about 75nm in diameter it maybe circular or oval.

Positive photo taxis.

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In asexual reproduction the cells of most species become non motile & their

nucleus undergo one or more Mitosis which are followed by Cytokinesis. In this

way (2, 4) or more young cells are formed within parental wall from which they

ultimately escape by rupture of the wall. Released young cells similar than the

parent which gradually enlarge to normal size & repeat the asexual cycle.

Chlamydomonas may also form Aplanospores, Hypnospores & Akinetes.

Sexual reproduction involves fusion of two haploid sexual units forming

diploid cell or Zygote. Some species are Homothallic (Self-compatible) & others

are Heterothallic (Self-incompatible) Gametic union maybe Isogamous, An

Isogamous or Oogamous.

Chlamydomonas

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Coenobial Volvocales

Family Volvocaceae

Genus Volvox

Is to be most evolved of Coenobial form the colony is spherical & appears as

small pin head on the surface of water. The colonies of most of the species are

visible to naked eyes.

The colonies are composed of many small vegetative or somatic cells, & a

few larger flagellate reproductive cells (Gonidia). Cells number of colonies in

different species ranges from (500-50000) cell per colony.

Life cycle of Chlamydomonas

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Colonies are spherical to ovoid & the biflagellate cells lie in single layer

within gelatinous colonial matrix. Each cell is surrounded by gelatinous sheath of

its own. In some species cells are joined to one another by conspicuous or delicate

cytoplasmic strands. The whole Coenobium moves & rotates by means of flagella

of individual cells. Most of the cells in a coenobium are vegetative & do not have

the capacity to form new individuals. Each vegetative cell is biflagellate with to

contractile vacuoles near the base of flagella. Other features of cells are cup shape

to laminate chloroplast, single Pyrenoid centrally located single nucleus &

anteriorly arranged eye spot.

For asexual reproduction few cells of Volvox coenobium differentiated as

asexual reproductive cells (Gonidia) by growing larger with disappearance of

flagella & gradually thickening, a number of daughter cell are produced by the

division & re division of gonidium which are held together as a new colony. Since

the number of Gonidia divide at the same time many new colonies are formed

simultaneously.

Sexual reproduction is strictly Oogamous. Depending on the species &

strains coenobia may contain ether eggs or sperms (Dioecious) or they may contain

both (Monoecious).

Both kinds of gametes are development from cells of the posterior half of the

coenobia. The egg cells are usually dense & darker in appearance than Gonidia

they enlarge without undergoing any division & loss their flagella during

development. Cells forming Antherozoids divide successively giving arise to

numerous spindle shaped biflagellate Antherozoids.

Non motile female gametes are much larger than the male gametes &

surrounded by a gelatinous sheath. The groups of sperms are liberated from their

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parent colonies & presumably by chemotactic stimulation swim to the surface of

female colonies, finally one sperm penetrate female colony & fertilize the egg. The

resulting zygote very soon develop thick wall & become red, zygote divides by

meiosis & a new coenobium is formed through the formation of single zoospore.

Coenobium of Volvox

Life Cycle of Volvox

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Order: Chlorococcales

This order contains non motile unicellular & colonial green Algae. Cell wall

is usually thin & there is no vegetative cell division. Cells lack flagella, contractile

vacuoles & eye spot. Asexual reproduction is achieved by Zoospores,

Aplanospores, Autospores & daughter coenobia. Sexual reproduction is by Iso or

anisogametes. These Algae are mainly present in fresh water reservoirs & in

terrestrial situations.

Division Chlorophyta

Class Chlorophyceae

Order Chlorococcales

Family Chlorellaceae

Genus Chlorella

This genus is found in various habitats. It is mainly present as plankton form

in fresh water, bodies & on terrestrial habitats rich in organic matter. Some species

are common on sub aerial habitats, Symbiotic association of Chlorella species

with Lichens & Animals (Hydra) are also found.

Cells are usually solitary or sometimes aggregated in groups being

enveloped by mucilage. The cells are small, spherical or ellipsoidal. Each cell

possesses a single parietal & usually Cup shaped chloroplast with one Pyrenoid.

Cells have thin cellulosic wall, centrally placed small nucleus & other Eukaryotic

organelles.

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Chlorella is an important tool for physiological experiments. It has widely

been used in the study of respiration & photosynthesis. It is also used for

purification of air in space capsules. An antibiotic Chlorellin is extracted from

this Alga. Chlorella is the first Alga to have been grown extensively in axenic

culture.

Cells have very high food value with about 50% proteins, 20% fats & 20%

carbohydrates & rich in amino acids & vitamins. Because of this, Scientists in

different countries are trying to cultivate it on mass scale. It may act as food of

future.

Reproduction is exclusively Asexual which is achieved by the production of

Autospores, 4, 8, 16 Autospores are produced by the division of mature cells &

are liberated by rupture of the parent cell wall. These non-motile spores develop

into new individuals.

Chlorella

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Colonial Chlorococcales

Division Chlorophyta

Class Chlorophyceae

Order Chlorococcales

Family Chlorellaceae

Genus Scenedesmus

Usually consists of a linear series of 4 or 8 cells (Sometimes 2-32)

coenobium. Cells joined together by the localised production of mucilage. This

genus is widely used in physiological studies outer cells of which frequently have

spines or projections.

Scenedesmus quadricauda

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Division Chlorophyta

Class Chlorophyceae

Order Chlorococcales

Family Chlorellaceae

Genus Pediastrum

Pediastrum is a common planktonic genus which consists of flat plate of

cells varying from 2-128 depending upon the species. The outer cells have

projections on the surface.

A number of biflagellate Zoospores are produced during asexual

reproduction. These are liberated in a vesicle within which they lose their flagella

& become arranged in the form characteristic of the present colony. The

biflagellate gametes are produced in the same way as Zoospores but are liberated

from the vesicle before fusing.

Pediastrum

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Different species of Scenedesmus

Different species of Pediastrum