PLANT KINGDOM

ALGAE
Table of content :

■ Introduction
■ General characteristics. Of algae
■ Habitat
■ Morphology of algae
■ Reproduction
■ Classification of algae
■ Economic Importance of algae
Introduction :

■ According to the traditional system of

classification of plants by Eichler in 1883,
Kingdom Plantae was classified into two sub
kingdoms. They are Cryptogamae and
Phanerogamae. He classified plants like this
mainly on the basis of the reproductive structures
called flowers. Those plants with hidden flowers
and seeds are included under the subkingdom
Cryptogamae and those that bear flowers and
seeds were classified in the sub -kingdom
phanerogamae
General characteristics of algae :

■ They are the thallophytes which are composed of chlorophyll pigment and show
an autotrophic mode of nutrition. They are able to prepare their own food
■ The chlorophyll containing, photosynthetic, non-vascular, thalloid and aquatic
plants are called algae. Carolus Linnaeus termed the plants with such
characteristics as ‘algae’. Robert Whittaker placed them in Kingdom Plantae.
They have no true roots and true shoots with leaves. They lack flowers, fruits
and seeds. Even after that, they are included under the plant kingdom by Eichler.
Approximately 1 million species of algae were discovered! They are the first
plant group that emerged from the unicellular aquatic organisms like
cyanobacteria or blue-green algae. Let's see how algae evolved.
Habitat :

■ The mutualistic or symbiotic relationship between algae or cyanobacteria with

fungi forms another organism called lichen. Algae is living among filaments of
fungi species. The function of algae is to prepare food, in return fungi provide
protection to algae. The algal partner of the lichen is called phycobiont and the
fungal partner is called mycobiont
■ Algae are predominantly aquatic plants which can be found in both marine and
freshwater habitats. Some algae occurs in moist surfaces of stones, soil, wood
and even snow. The aquatic algae are called hydrophytes. Terrestrial algae are
called saprophytes. There are some algae that reside with fungi to form lichens
Morphology of Algae

■ The small and simple forms of algae can be free living. But the large forms of
algae have leaf-like blades called lamina with photosynthetic tissues. They also
have stem-like stalks called stipe and a hold fast for attaching to the
substratum.
■ The thallus of algae can range from microscopic, colonial, aggregates of cells,
fine filaments to flattened sheets of cells. The smallest algae is the unicellular
form called Chlamydomonas and the largest algae is Macrocystis or kelp, which
can grow up to 60 metres in length.
■ The size and the shape of the algal plant body is very diverse.
Reproduction :

■ Vegetative reproduction
■ Usually the vegetative reproduction occurs through the cell division and
fragmentation of the thallus. Cell division or binary fission
■ When the mother cell divides into two daughter cells, new plants are formed from
them. This can be exclusively seen in Chlamydomonas and Pleurococcus.
Fragmentation
■ The algal body breaks into several parts or fragments and each fragment will
develop into a new individual. This is called fragmentation and is usually seen in
filamentous forms of algae like Ulothrix, Spirogyra etc.
■ Asexual reproduction
■ Only one parent is involved in the asexual reproduction. The protoplast of an algal
cell divides into several protoplasts and then they will escape from the mother cell to
develop into new plants. These are called asexual spores.
■ Types of asexul spores
■ There are two types of asexual spores, mitospores and meiospores.
■ Mitospores
■ These spores are formed through mitosis. Mitospores have the same set of
chromosomes as that of parent cells
■ Meiospores
■ These are formed through meiosis. But meiospores will show genetic variations
which helps in the species adaptation.
■ Sexual reproduction
■ The sex organs or gametangia are not protected with the covering of sterile cells or
we can say they are non-jacketed. Sexual reproduction involves the fusion of
gametes.
■ Types of sexual reproduction
■ There are three major types of sexual reproduction. They are as follows:
■ Isogamy
■ Anisogamy
■ Oogamy
■ Isogamy
■ The fusion of morphologically and physiologically similar types of gametes is called
isogamy. The gametes can be motile or flagellated and non motile or non-flagellated,
but similar in size. Such gametes are called isogametes. Examples include
Spirogyra, Chlamydomonas.
■ Anisogamy
■ Fusion of two gametes that are dissimilar in size is called anisogamy. The gametes
can be motile or non motile here. This is also known as heterogamy. Examples
include Ectocarpus and Eudorina
■ Oogamy
■ Fusion of large, non-motile female gamete with small, motile male gamete is called
oogamy. Examples include Volvox and Fucus.
Classification of Algae :

■ The algae are classified into three major classes on the basis of pigmentation,
chemical nature of assimilatory products, type of flagellation etc. The classes of
algae are as follows:
■ Chlorophyceae
■ Phaeophyceae
■ Rhodophyceae
Chlorophyceae
Chlorophyceae are the most recent algae in evolutionary history and it is the ancestor of all
green plants. The members of Chlorophyceae are commonly called green algae and include
around 7000 living species.
Salient features of Chlorophyceae :
1. These are freshwater or marine algae with a unicellular or multicellular body.
2. Some green algae are terrestrial and they can grow anywhere.
3. Cells are eukaryotic and contain cellulosic cell walls inside and pectose in the outer
layer.
4. They occur in various shapes and sizes.
5. The chief pigments include chlorophyll a and b that are located in definite chloroplast. It
possess 𝛼, 𝛽 and 𝛾 carotenes too.
6. Thallus is usually green due the dominance of chlorophyll a and b.
7. Reserve food materials include starch and very rarely oils. Starch is stored in pyrenoids.
Phaeophyceae
It includes the brown algae which is different from other algae because of their
characteristic olive green, golden yellow or deep brown colour. There are about
2000 species of brown algae and are mostly marine. This colouration is mainly
due to the presence of the xanthophyll called fucoxanthin. They can be observed
in different sizes
Salient features of Phaeophyceae
1. These are marine algae with a unicellular or multicellular body.
2. They possess well organised and highly differentiated thallus.
3. Absence of unicellular, colonial and unbranched filamentous forms.
4. They are mostly branched, filamentous or flat ribbon shaped.
5. They possess eukaryotic cells.
6. They have a special type of excretory granule present in vesicles.
7. A cellulosic wall usually covers vegetative cells.
8. They also possess a gelatinous coating of algin outside the cell
Rhodophyceae
It includes the red algae which are characterised by the distinctive
red colouration. Red algae are the most beautifully colured
members of sea weeds. 5000 species of red algae have been
discovered. Out of these 50 species are freshwater forms and the
rest are marine.
Salient features of Rhodophyceae
1. The major constituents of the cell wall are cellulose, pectic
compounds and polysulphate esters.
2. Total absence of a flagellated and motile stage in the life cycle.
3. In most multicellular forms, vegetative cells are interconnected
by pit connections, often called plasmodesmata.
4. They usually reproduce through vegetative reproduction.
5. Asexual reproduction occurs through non-motile spores.
Types of algae
Economic Important of algae :

Algae have always been directly or indirectly linked with the life of mankind and some animals as
sources of food, fodder and manure. They are used in agriculture, horticulture, fisheries etc. At the
same time some algae may be harmful to man and animals.
Positive impact
■ Marine algae are commonly used as food, since they contain greater amounts of minerals and
vitamins.
■ The important algae consumed by human beings are as follows:
■ Chlorophyceae like Monostroma, Caulerpa and Ulva.
■ Phaeophyceae like Laminaria, Alaria and Ecklonia.
■ Rhodophyceae like Porphyra, Gracilaria, Gelidium and Eucheuma.
■ Seaweeds can be used to make vermifuge, anaesthetics and ointments due to their vitamin
and mineral contents.
Negative impact
■ Algal blooms will cause entire populations of aquatic forms to leave an area or
die.
■ Algal blooms can cause thick, green muck which will have bad impacts on clear
water, businesses, property values and recreation.
■ It may create toxins that are detrimental to fish and other animals.
■ Algal toxins consumed by shellfish and small fish may move up the food chain
and will have a bad impact on larger animals such as turtles, sea lions, birds
and dolphins.
■ Algal blooms will consume more oxygen and as they die and decompose more,
will result in hypoxia.