Biology Today — December 2017

Economic

Importance

Carrageenan

Obtained from red algae

Chondrus crispus and issued

as pharmaceutical emulsifier,

cleaning agent and in textile,

leather and brewing industries.

Medicines

Red algae

Corallina is capable of

curing worm infections. Brown

algae Laminaria and Aseophyllum

have antibiotic properties while

Durvillea has vermifuge properties.

Antibiotics are also extracted

from green algae Chlorella and

Caulerpa.

Sewage

disposal

Green algae like

Chlamydomonas, Chlorella,

Scenedesmus are components

of sewage oxidation tanks which

provide aerobic conditions

for disposal of sewage by

decomposers.

Agar-agar

A phycocolloid

extracted from species of

red algae such as Gelidium and

Gracilaria is used as a solidifying

agent in culture medium.

Food

Certain algae are used as

food e.g., Porphyra, Laminaria,

Sargassum, etc., Chlorella is rich

source of proteins, hence used as

food supplement.

Photosynthesis

Nearly 50% of total

photosynthesis on earth is carried

out by algae. They are essential

for respiration of aquatic life.

Alginic acid

A phycocolloid obtained from

Phaeophyceae such as Laminaria,

Macrocystis, Fucus, etc., is used in

stabilising emulsions, flameproof

plastics and security

glass.

BRYOPHYTES

• Bryophytes are non-vascular terrestrial plants of moist habitats

Fig.: Some common bryophytes

Sporophyte

Coma

Stem

Leaf

Riccia Porella Sphagnum

in which a multicellular diploid sporophyte lives as a parasite on
an independent multicellular haploid gametophyte. It includes
over 25,000 species. This group requires water for fertilisation,
therefore called as “amphibians of plant kingdom”.

General Characteristics

• Bryophytes live in damp and shady habitats, often found in
  rainy season forming green carpets or mats on damp soil,
  rocks, walls, tree trunks, etc.


• The dominant phase of the plant is a free living gametophyte.


• Rhizoids (instead of roots) are present. They may be unicellular or multicellular.


• Vegetative reproduction is quite common. It may take place by fragmentation, tubers, gemmae buds, adventitious branches, etc.


• Accessory spores are not formed.


• Sexual reproduction is oogamous i.e., fusion of a non-motile passive egg cell and biflagellated active male gamete.


• Sex organs are multicellular and jacketed and are of two types : antheridium (male) and archegonium (female).


• Antheridium produces a number of flagellated male gametes called sperms or antherozoids.


• Archegonium is flask shaped with tubular single layered neck (having 5-
  rows of cells) and a swollen venter (1-2 layered wall) enclosing a sterile venter
  canal cell and a fertile egg.


• The sterile neck canal cells and venter canal cells of archegonium degenerate,
  gelatinise, absorb water and swell up into mucilage. It opens the lid of neck
  and leads a passage upto oosphere.


• An external layer of water is essential for the swimming of male gametes to
  archegonia.


• Fertilisation leads to formation of embryo inside archegonium. The embryo
  grows into a sporophyte, which is parasitic on gametophyte. Since it is dependent on gametophyte, it is called sporogonium.

Lid

Neck

Neck canal cells

Venter canal cells

Venter

Oosphere (Egg)

Archegonium

Antheridium Stalk

Stalk

Sperm

mother

cell

Jacket

Fig.: Antheridium and archegonium