Biological Classification 19
Life Cycles of Some Fungi
These can be described as follows
(i) Life Cycle of Rhizopus
The structural representation (sexual and asexual) of life cycle of
Rhizopus is as follows
Fragmentation
Vegetative
Reproduction
Sporangium
Chlamydospore
Oidia
Asexual
Reproduction
Rhizopus
mycelia
Sexual Progametangium(–)
Germ spores Reproduction
(+ or –) Progametangium
(+)
Gametangium (–)
Germ sporangium
Gametangium
Haplophase (n) (+)
Coenogamete (–)
Promycelium
Coenogamete
+
Azygospore
Meiosis Fertilisation
Diplophase (2n)
Zygospore
Life cycle of Rhizopus
20 Handbook of Biology
(ii) Life Cycle of Yeast
The diagrammatic representation of sexual cycle of Saccharomyces
cerevisiae is as follows
Dwarf strain
yeast cells B
Budding +
C +
A
Gametangia
–
Germinate
–
Plasmogamy
L Ascospore
D
Karyogamy
Ascospores
e
has
op
Mature
)
pl
e
(n
(2 has
ascus Zygote
Ha
p
lo
n)
E
p
Di
K Young
Germination
ascus
Large strain
yeast cell
Ascus mother F
J
cell
Meiosis Bud
G Budding
I
H
Life cycle of Saccharomyces cerevisiae
Heterothallism
The phenomenon of having two genetically different and compatible
sexual strains in two different thalli is called heterothallism. It was
discovered by Blakeslee in Mucor.
Biological Classification 21
Mushroom and Fairy Rings
Agaricus compestris is an edible mushroom. It is also called white
button mushroom. The fruiting body of Agaricus, arises in concentric
rings (called fairy rings or fungal flowers) from the mycelium present
in the soil.
Lichens
They have composite structure and consist of two dissimilar organisms
forming a symbiotic relationship between them.
Lichens are formed by
● Algal Part — Phycobiont — Provide food to fungi
● Fungal part — Mycobiont — Provide shelter to algae
Lichens are of three types on the basis of their structure
(i) Crustose lichens These are point-like, flat lichens, e.g., Caloplaca.
(ii) Foliose lichens These lichens have leafy structure,
e.g., Hypogymnia physodes.
(iii) Fruticose lichens These are branched lichen, form
filamentous branching, e.g., Cladonia evansii, Usnea australis,
etc.
Various forms of lichens are given below
Fungal fructification
Parmella
Graphis Cora
(foliose)
(crustose) (foliose)
Attaching disc
Pendent
branches
Podetia
Early
foliose
part Cladonia
Fungal (fruticose)
Usnea fructification
(fruticose)
Forms of lichens
Mycorrhiza
It is a symbiotic association between a fungus and a plant. Plants
prepare organic food and supply them to fungus and in return, fungus
supplies water and mineral nutrients to plants.
22 Handbook of Biology
D. Kingdom–Plantae (Eukaryotic, Chlorophyllous Organisms)
These are chlorophyllous and embryo forming organisms. Mostly
non-motile and function as the producers in ecosystem as they can fix
solar energy into chemical energy through the process of
photosynthesis. The cell wall in plants is cellulosic and stored food
material is in the form of starch.
A detailed account of plant kingdom is given in chapter 6.
E. Kingdom–Animalia (Multicellular, Eukaryotic Organisms)
The heterotrophic, eukaryotic organisms which are multicellular and
lack cell wall, present in this kingdom. Animals have advanced level of
tissue organisation, in which the division of labour is highly specific.
The two main groups among animals are Non-chordata and Chordata,
divided on the basis of the presence of notochord in them.
A detailed account of animal kingdom is given in chapter 7.
Viruses and Viroids
1. Viruses
The term ‘Virus’ means poisonous fluid. The word was coined by
Louis Pasteur. Viruses are very small (0.05-0.2 µm), infective,
nucleoprotein particles, which can be called as living because of the
presence of nucleic acid as genetic material and ability to produce their
own copy-viruses. They show only some properties of living beings,
otherwise they behave like non-livings. Hence, these are referred to as
the connecting link between living and non-living.
On the basis of nature of genetic material, the viruses are of two types
(i) Adenovirus DNA containing, e.g., HIV, etc.
(ii) Retrovirus RNA containing, e.g., Rous sarcoma virus, etc.
On the basis of their host, the viruses can be categorised as
(i) Animal virus (Zoophagineae), e.g., HIV, sarcoma, etc.
(ii) Plant virus (Phytophagineae), e.g., TMV, etc.
(iii) Bacterial viruses (Phagineae), e.g., T4 phage, etc.
Characteristics of Viruses
Characteristics of viruses are as follows
Living
●
They can replicate.
●
In host body, they can synthesise protein.
●
They cause diseases like other living organisms.
●
Similar gene mutation as living organism.
Biological Classification 23
Non-living
● Do not have protoplasm, and do not perform metabolism.
● These can be crystallised.
● They do not respire.
● In vitro culture is not possible.
Structure of Viruses
(i) Viruses are non-cellular and ultramicroscopic.
(ii) Virus has two components
(a) A core of nucleic acid called nucleoid.
(b) A protein coat called capsid.
Envelope, only in Capsomeres, together form
some larger viruses. capsid, a protein coat
usually highly symmetrical.
Genetic material, Core region
DNA or RNA inside capsid
Structure of a virus (generalised)
2. Viroids (RNA without a Capsid)
TO Diener (1917) introduced the term as ‘Subviral pathogens’. Viroids
are 100 times smaller than smallest virus. They are known to be
infectious for plants only (no animal), e.g., potato spindle tuber caused
by viroids.
Virion
An intact, inert, complete virus particle capable of infecting the host
lying outside the host cell in cell free environment is called virion.
Virusoids
These are like viroids, but located inside the protein coat of a true
virus. Virusoid RNA can be circular or linear. These are non-infectious
as they are replicated only in their host.
Prions/Slow Virus
The prions are smallest, proteinaceous infectious particles, i.e., disease
causing agents that can be transmitted from one animal to another.
3
Plant Kingdom
Plants : Producers of the Ecosystem
Plants are multicellular, photoautotrophic and embryo forming
(excluding algae) organisms placed in kingdom–Plantae. They have
cell wall, which is made up of cellulose and reserve food material in the
form of starch (sometimes fat as in seeds).
Plants are referred to as producers, because they have unique ability to
fix solar energy in the form of chemical energy, through the process of
photosynthesis. They supply the energy in ecosystem to other living
organisms, hence they are referred to as producers.
The plant kingdom is classified as
Plant Kingdom
Cryptogamae (non-flowering) Phanerogamae (flowering)
Thallophyta
(plant body is not divided Gymnosperms Angiosperms
into root, stem and leaves) (naked seeded plants) (covered seed)
Algae Bryophyta Pteridophyta
(non-embryophytes, (these are (these are embryo Monocotyledons Dicotyledons
lack seeds and embryophytes bearing plants which
vascular tissue.) without vascular form seed and contain
tissues.) vascular tissue as well.)
Ferns
Liverworts Hornworts Mosses
Algae (L. Alga–sea weeds)
These are eukaryotic, autotrophic (holophytic), chlorophyll containing,
non-vascular thallophytes. These are characterised by the absence of
embryonic stage and presence of non-jacketed gametangia. Mostly,
they are of aquatic habitat (both freshwater and marine).
The branch of Botany which deals with the study of algae is termed as
‘Algology or Phycology’. FE Fritsch is known as ‘Father of Algology’.
(Prof. MOP Iyengar is regarded as Father of Indian Algology).
Plant Kingdom 25
Classification of Algae (FE Fritsch; 1935)
Algal Class Colour Reserve Food Examples
Chlorophyceae Grass green Starch Chlamydomonas and
Spirogyra.
Xanthophyceae Yellow-green Fat Microspora and Botrydium.
Chrysophyceae Yellow-green and Carbohydrate and Amphipleura and
golden-brown leucosin Chrysosphaera.
Bacillariophyceae Brown and green Fat and volutin Pinnularia and Melosira.
Cryptophyceae Red and Carbohydrate and Cryptomonas.
green-blue starch
Dinophyceae Dark yellow, Starch and oil Peridinium and
brown-red Glenodinium.
Chloromonadineae Bright green Fatty compounds Vaucheria and Trentonia.
Euglenophyceae Grass green Paramylum Euglena and Phacus.
Phaeophyceae Brown coloured Laminarin and Laminaria and Fucus.
mannitol
Rhodophyceae Red coloured Floridean starch Polysiphonia and
Batrachospermum.
Myxophyceae Blue-green Protein granules Nostoc and Anabaena.
Characteristics of Algae
Important characteristics of algae are given below
Structure
Algae may be unicellular and multicellular.
1. Unicellular
It is of two types
(i) Motile, e.g., Chlamydomonas, etc.
(ii) Non-motile, e.g., Chlorella, etc.
2. Multicellular
It is of following types
(i) Colonial, e.g., Volvox, Hydrodictyon, etc.
(ii) Aggregation, e.g., Tetraspora, Prasinocladus, etc.
(iii) Filamentous, e.g., Ulothrix, Cladophora, etc.
(iv) Pseudoparenchymatous, e.g., Nemalion, etc.
(v) Siphonous, e.g., Vaucheria, etc.
(vi) Parenchymatous, e.g., Ulva, Fritschiella, etc.
(vii) Well-developed thallus, e.g., Chara, Sargassum, etc.
