👉 In some organisms, if the body
breaks into distinct pieces (fragments) each fragment grows into an
adult capable of producing offspring (e.g., Hydra). This is also a mode
of asexual reproduction called fragmentation.
👉PROCESSES OF RECOMBINANT DNA TECHNOLOGY
Recombinant DNA technology involves several steps in specific sequence such as isolation of DNA, fragmentation of DNA by
restriction endonucleases, isolation of a desired DNA fragment,
ligation of the DNA fragment into a vector, transferring the
recombinant DNA into the host, culturing the host cells in a
medium at large scale and extraction of the desired product.
👉DECOMPOSITION
You may have heard of the earthworm being referred to as the farmer’s
‘friend’. This is so because they help in the breakdown of complex organic
matter as well as in loosening of the soil. Similarly, decomposers break
down complex organic matter into inorganic substances like carbon
dioxide, water and nutrients and the process is called decomposition.
Dead plant remains such as leaves, bark, flowers and dead remains of
animals, including fecal matter, constitute detritus, which is the raw
material for decomposition. The important steps in the process of
decomposition are fragmentation, leaching, catabolism, humification and
mineralisation.
👉Detritivores (e.g., earthworm) break down detritus into smaller particles.
This process is called fragmentation. By the process of leaching, water soluble
inorganic nutrients go down into the soil horizon and get precipitated
as unavailable salts. Bacterial and fungal enzymes degrade detritus into
simpler inorganic substances. This process is called as catabolism.
👉Decomposition involves three processes, namely fragmentation of
detritus, leaching and catabolism.
👉Causes of biodiversity losses: The accelerated rates of species
extinctions that the world is facing now are largely due to human
activities. There are four major causes (‘ The Evil Quartet ’ is the sobriquet
used to describe them).
(i) Habitat loss and fragmentation:
👉The causes of high
extinction rates at present include habitat (particularly forests) loss
and fragmentation, over -exploitation, biological invasions and
co-extinctions.
👉In lower organisms like
yeast and hydra, we observe budding. In Planaria (flat worms), we observe
true regeneration, i.e., a fragmented organism regenerates the lost part of
its body and becomes, a new organism.
👉The fungi, the filamentous algae,
the protonema of mosses, all easily multiply by fragmentation.
👉Reproduction in fungi can take place by vegetative means –
fragmentation, fission and budding. Asexual reproduction is by spores
called conidia or sporangiospores or zoospores, and sexual reproduction
is by oospores, ascospores and basidiospores.
👉Basidiomycetes
Commonly known forms of basidiomycetes are mushrooms, bracket fungi
or puffballs. They grow in soil, on logs and tree stumps and in living
plant bodies as parasites, e.g., rusts and smuts. The mycelium is branched
and septate. The asexual spores are generally not found, but vegetative
reproduction by fragmentation is common. The sex organs are absent,
but plasmogamy is brought about by fusion of two vegetative or somatic
cells of different strains or genotypes. The resultant structure is dikaryotic
which ultimately gives rise to basidium. Karyogamy and meiosis take
place in the basidium producing four basidiospores. The basidiospores
are exogenously produced on the basidium (pl.: basidia). The basidia are
arranged in fruiting bodies called basidiocarps. Some common members
are Agaricus (mushroom) , Ustilago (smut) and Puccinia (rust
fungus).
👉The algae reproduce by vegetative, asexual and sexual methods.
Vegetative reproduction is by fragmentation. Each fragment develops into
a thallus. Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated
(motile) and on germination gives rise to new plants. Sexual reproduction
takes place through fusion of two gametes. These gametes can be
flagellated and similar in size (as in Ulothrix) or non-flagellated (non-motile)
but similar in size (as in Spirogyra). Such reproduction is called
isogamous. Fusion of two gametes dissimilar in size, as in species of
Eudorina is termed as anisogamous. Fusion between one large, nonmotile
(static) female gamete and a smaller, motile male gamete is termed
oogamous, e.g., Volvox, Fucus.
👉Chlorophyceae
The members of chlorophyceae are commonly called green algae. The
plant body may be unicellular, colonial or filamentous. They are usually
grass green due to the dominance of pigments chlorophyll a and b. The
pigments are localised in definite chloroplasts. The chloroplasts may be
discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in
different species. Most of the members have one or more storage bodies
called pyrenoids located in the chloroplasts. Pyrenoids contain protein
besides starch. Some algae may store food in the form of oil droplets.
Green algae usually have a rigid cell wall made of an inner layer of cellulose
and an outer layer of pectose.
Vegetative reproduction usually takes place by fragmentation or by
formation of different types of spores. Asexual reproduction is by
flagellated zoospores produced in zoosporangia. The sexual reproduction
shows considerable variation in the type and formation of sex cells and it
may be isogamous, anisogamous or oogamous. Some commonly found
green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara
👉Phaeophyceae
The members of phaeophyceae or brown algae are found primarily in
marine habitats. They show great variation in size and form. They range
from simple branched, filamentous forms (Ectocarpus) to profusely
branched forms as represented by kelps, which may reach a height of
100 metres. They possess chlorophyll a, c, carotenoids and xanthophylls.
They vary in colour from olive green to various shades of brown depending
upon the amount of the xanthophyll pigment, fucoxanthin present in
them. Food is stored as complex carbohydrates, which may be in the
form of laminarin or mannitol. The vegetative cells have a cellulosic wall
usually covered on the outside by a gelatinous coating of algin. The
protoplast contains, in addition to plastids, a centrally located vacuole
and nucleus. The plant body is usually attached to the substratum by a
holdfast, and has a stalk, the stipe and leaf like photosynthetic organ –
the frond. Vegetative reproduction takes place by fragmentation. Asexual
reproduction in most brown algae is by biflagellate zoospores that are
pear-shaped and have two unequal laterally attached flagella.
Sexual reproduction may be isogamous, anisogamous or oogamous.
Union of gametes may take place in water or within the oogonium
(oogamous species). The gametes are pyriform (pear-shaped) and bear
two laterally attached flagella. The common forms are Ectocarpus, Dictyota,
Laminaria, Sargassum and Fucus
👉Rhodophyceae
The members of rhodophyceae are commonly called red algae because of
the predominance of the red pigment, r-phycoerythrin in their body. Majority
of the red algae are marine with greater concentrations found in the warmer
areas. They occur in both well-lighted regions close to the surface of water
and also at great depths in oceans where relatively little light penetrates.
The red thalli of most of the red algae are multicellular. Some of them
have complex body organisation. The food is stored as floridean starch
which is very similar to amylopectin and glycogen in structure.
The red algae usually reproduce vegetatively by fragmentation. They
reproduce asexually by non-motile spores and sexually by non-motile gametes. Sexual reproduction is oogamous and accompanied by complex
post fertilisation developments. The common members are: Polysiphonia,
Porphyra (Figure 3.1c), Gracilaria and Gelidium.
👉Liverworts
The liverworts grow usually in moist, shady habitats such as banks of
streams, marshy ground, damp soil, bark of trees and deep in the woods.
The plant body of a liverwort is thalloid, e.g., Marchantia. The thallus is
dorsiventral and closely appressed to the substrate. The leafy members
have tiny leaf-like appendages in two rows on the stem-like structures.
Asexual reproduction in liverworts takes place by fragmentation of
thalli, or by the formation of specialised structures called gemmae
(sing. gemma). Gemmae are green, multicellular, asexual buds, which
develop in small receptacles called gemma cups located on the thalli.
The gemmae become detached from the parent body and germinate to
form new individuals. During sexual reproduction, male and female sex
organs are produced either on the same or on different thalli. The
sporophyte is differentiated into a foot, seta and capsule. After meiosis,
spores are produced within the capsule. These spores germinate to form
free-living gametophytes.
👉Mosses
The predominant stage of the life cycle of a moss is the gametophyte which
consists of two stages. The first stage is the protonema stage, which
develops directly from a spore. It is a creeping, green, branched and
frequently filamentous stage. The second stage is the leafy stage, which
develops from the secondary protonema as a lateral bud. They consist of
upright, slender axes bearing spirally arranged leaves. They are attached
to the soil through multicellular and branched rhizoids. This stage bears
the sex organs.
Vegetative reproduction in mosses is by fragmentation and budding
in the secondary protonema. In sexual reproduction, the sex organs
antheridia and archegonia are produced at the apex of the leafy shoots.
After fertilisation, the zygote develops into a sporophyte, consisting of a
foot, seta and capsule. The sporophyte in mosses is more elaborate than
that in liverworts. The capsule contains spores. Spores are formed after
meiosis. The mosses have an elaborate mechanism of spore dispersal.
Common examples of mosses are Funaria, Polytrichum and Sphagnum
👉Algae usually reproduce vegetatively by
fragmentation, asexually by formation of different types of spores and sexually by
formation of gametes which may show isogamy, anisogamy or oogamy.
👉Phylum – Porifera
Members of this phylum are commonly known
as sponges. They are generally marine and mostly
asymmetrical animals (Figure 4.5). These are
primitive multicellular animals and have cellular
level of organisation. Sponges have a water
transport or canal system. Water enters through
minute pores (ostia) in the body wall into a central
cavity, spongocoel, from where it goes out
through the osculum. This pathway of water
transport is helpful in food gathering, respiratory
exchange and removal of waste. Choanocytes
or collar cells line the spongocoel and the canals.
Digestion is intracellular. The body is supported
by a skeleton made up of spicules or spongin
fibres. Sexes are not separate (hermaphrodite),
i.e., eggs and sperms are produced by the same
individual. Sponges reproduce asexually by
fragmentation and sexually by formation of
gametes. Fertilisation is internal and development
is indirect having a larval stage which is
morphologically distinct from the adult.
