NOTES ON ALGAE KINGDOM

 

Plant Kingdom 

The plant kingdom is the study of various subgroups of plants each one having special features. Plant kingdom classification has changed over time. Earlier, Monera and Fungi were also a part of the plant classification but now they are not a part of the plant kingdom. Recently, the plant kingdom has been divided under Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.

1. Algae: Algae are aquatic organisms containing chlorophyll. These organisms are autotrophic in nature and sometimes occur in association with fungi and other animals such as lichen and sloth bear.

• Mostly, algae occur in moist stones, fresh water, stones and wood. Based on its size, algae can be Chlamydomonas (microscopic unicellular), Volvox (colonial forms), Ulothrix and Spirogyra (filamentous).
• These organisms are usually vegetative in nature and reproduce sexually as well as asexually. Algae reproduce asexually by forming different types of spores, commonly known as Zoospores.
• These spores become motile on germination and give rise to new plants. Algae reproduce through sexual means as well, which involves the fusion of gametes. Fusion of gametes can be of various types:

a. When gametes are flagellated and their sizes are similar. E.g. Chlamydomonas

b. When gametes are non-flagellated and their sizes are similar. E.g. Spirogyra and this type of reproduction are called Isogamous.

c. Fusion of gametes can be dissimilar in size as seen in some species of Chlamydomonas. This type of reproduction is known as Anisogamous. Another type of fusion is between a motile male gamete and one large non-motile female gamete. This type of reproduction is termed oogamous. This can be seen in species of Volvox and Fucus.

Algae is proven to be a useful organism to the environment in many ways:

• Algae help in carbon dioxide fixation through photosynthesis.
• It increases the level of dissolved oxygen in the environment.
• Algae are the primary producers of energy-rich compounds which are the basis of food cycles of the aquatic animals.
• Some types of brown and red algae produce hydrocolloids.
• Some species of algae such as Gelidium and Gracilaria produces agar.

Algae are divided majorly into three classes:

i. Chlorophyceae: These types of algae are usually seen in fresh or marine water and are commonly known as Green algae.

• They are multicellular in nature and their forms can vary from unicellular to parenchymatous. Their primary pigments include lycopene, lutein, violaxanthin, chlorophyll a, e and beta- carotene etc.
• They reproduce sexually (reproduction can be isogamous, oogamous, anisogamous), asexually (formation of zoospores) and vegetatively (fragmentation). Their cell wall is usually made up of cellulose.

ii. Phaeophyceae: These types of algae are found in marine water and are commonly known as Brown algae.

• They are multicellular in nature and their forms show great variation ranging from simple branched forms to profusely branched ones. Their primary pigments include fucoxanthin, lutein, violaxanthin, chlorophyll a, c and beta- carotene etc.
• They reproduce sexually (reproduction can be isogamous, oogamous, anisogamous), asexually (formation of zoospores) and vegetative (fragmentation).
• Their flagella are usually unequal.
• Their cell wall is cellulosic and is covered by a gelatinous coating of algin.

iii. Rhodophyceae: These are generally seen in marine water and are commonly known as Red algae because of the presence of a dominating red pigment.

• They are multicellular in nature having a complex body organization.
• Their primary pigments include fucoxanthin, myoxaxanthin, g-phycoerythrin, allophycocyanin and chlorophyll a, d and beta- carotene etc but chlorophyll c is absent.
• They reproduce sexually (reproduction can be oogamous) and asexually (fragmentation).
• There is no formation of zoospores occurs in this type of algae. Their life cycle is usually Haplobiontic and Diplobiontic.

Division Of Algae and their Main Characters

Classes	Common Name	Major Pigments	Stored Food	Cell wall	Flagellar number and  Position of Insertion	Habitat
Chlorophyceae	Green Algae	Chlorophyll a,b	Starch	Cellulose	2-8, equal, apical	Freshwater, Brackish water, salt water
Phaeophyceae	Brown Algae	Chlorophyll a, c, fucoxanthin	Mannitol, Laminarin	Cellulose and align	2, Unequal, lateral	Freshwater (rare), Brackish water, salt water
Rhodophyceae	Red Algae	Chlorophyll a,d, Phycoerythrin	Floridean Starch	Cellulose, Pectin and poly sulphate esters	Absent	Freshwater(some), Brackish water, salt water (most)

 

2. Bryophytes: These are terrestrial plants quite small in sizes like mosses and liverworts. These plants live in moist as well as sandy areas and are dependent on water for their reproduction. This is why these are called amphibians of the plant kingdom. Such plants lack true stems, leaves or stem. These plants reproduce sexually by producing gametes.

• The main part of the plant is haploid in nature and hence is called Gametophyte. Their male sex organ is antheridium and their biflagellate is called Antherozoids.
• Their female sex organ is flask-shaped and produces a single egg.
• Antherozoids are released in water where it fuses with egg and produces a zygote which further produces sporophyte which further takes nutrition from photosynthetic gametophyte and produces haploid spores.
• These plants do not have any specialized tissues for water transport.

Fig: Bryophytes (Liverwort)

3. Pteridophytes: These are the oldest vascular plants. They are used for medicinal purposes and soil binders. These plants are found in cool, damp and shady places.

• Their main plant body is a sporophyte which further develops into Sporophytes which bear sporangia which are extended leaf-like appendages called sporophylls that undergo meiotic division.
• The spores further germinate and give rise to inconspicuous, multicellular photosynthetic thalloid gametophytes which are known has prothallus. Pteridophytes are further divided into Psilopsida, Lycopsida, Sphenopsida and Pteropsida.

a) Psilopsida: These are the oldest vascular plants known which lack roots with plant body differentiated. Their aerial is naked and sporangia are cauline and their position of presence is either terminal or lateral. E.g. Psilotum, Tmesipteris.

b) Lycopsida: These are the plants with differentiated plant body and smaller leaves with the single unbranched vein. Their sporangia develop on the axil of sporophylls which later form compact strobila. E.g. Lycopodium, Selaginella.

c) Sphenopsida: These are the plants with differentiated stem (into nodes and internodes). Their leaves are usually microphyllus which are seen in whorls at each node. Additionally, their sporangia are born on sporangiophores which form compact cones of fertile branches. E.g. Equisetum.

Fig: Equisetum

d) Pteropsida: These are the plants with differentiated plant body and megaphyllous leaves. Their sporangia develop on the ventral surface of sporophylls. E.g Dryopteris, Pteridium, Polypodium.

4. Gymnosperms: These are the plants with exposed ovaries as their ovules are not enclosed by ovary wall before and after fertilization.

• These are the plants which include medium-sized trees or shrubs. Their roots are tap roots which are in fungal association in the form of mycorrhiza while in some other plants some specialized roots which are called coralloid roots which are associated with nitrogen-fixing cyanobacteria.
• Their leaves are well adapted to extreme temperature, needle-like leaves, humidity and wind. Water loss in such plants is done by their thick cuticle and sunken stomata.
• Gymnosperms are heterosporous in nature i.e. they produce haploid microspores and megaspores and their nucleus is well protected by ovule.

5. Angiosperms: These are the plants where ovules and pollen grains are developed in specialized structures called flowers. These are the group of plants which occur in a wide range of habitats.

• They are divided into two categories dicotyledons and monocotyledons
• Dicotyledons are the plants which two cotyledons in their seeds while monocotyledons have only one.
• The male sex organ in a flower is called stamen and the female sex organ is pistil.
• The pistil is enclosed inside ovary and ovary in enclosed into many ovules.
• Female gametophytes are enclosed in within ovules called Embryo sacs.
• Each embryo sac produces- two synergids, one egg cell, one antipodal and two polar nuclei. The polar nuclei produce a diploid secondary nucleus.
• The process of their fertilization called as double fertilisation which involves the fusion of an egg cell with a male gamete to form the zygote. This is known as Syngamy
• The other male gamete fuses with the diploid endosperm nucleus to form PEM (primary endosperm nucleus). Because of the involvement of two fusions, this process is termed as double fertilization. During these events, ovules develop into seeds and ovaries develop into fruits.

Fig: Life cycle of an angiosperm

All the best!
Team CDS JOURNEY