Plant Kingdom 1 Flashcards
explain artificial system of classification
gross superficial morphological
characters such as habit, colour, number and shape of leaves, etc. They
were based mainly on vegetative characters or on the androecium
structure (system given by Linnaeus). Such systems were artificial; they
separated the closely related species since they were based on a few
characteristics. Also, the artificial systems gave equal weightage to
vegetative and sexual characteristics; this is not acceptable since we know
that often the vegetative characters are more easily affected by
environment.
explain natural classification systems
natural classification systems developed,
which were based on natural affinities among the organisms and consider,not only the external features, but also internal features, like ultrastructure, anatomy, embryology and phytochemistry. Such a
classification for flowering plants was given by George Bentham and
Joseph Dalton Hooker.
which classification system are used in present times
At present phylogenetic classification systems based on
evolutionary relationships between the various organisms are acceptable.
This assumes that organisms belonging to the same taxa have a common
ancestor. We now use information from many other sources too to help
resolve difficulties in classification. These become more important when
there is no supporting fossil evidence.
what is numerical taxonomy
Numerical Taxonomy which is
now easily carried out using computers is based on all observable
characteristics. Number and codes are assigned to all the characters and
the data are then processed. In this way each character is given equal
importance and at the same time hundreds of characters can be
considered.
what are the two types of taxonomy
Cytotaxonomy that is based on cytological information like
chromosome number, structure, behaviour and chemotaxonomy that
uses the chemical constituents of the plant to resolve confusions, are also
used by taxonomists these days.
describe algae
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a variety
of other habitats: moist stones, soils and wood. Some of them also occur
in association with fungi (lichen) and animals (e.g., on sloth bear).
they possess chlorophyll a and beta-carotene. They are covered by a mucilaginous sheath which prevents the dessication.
what are different forms in whcih algae may occur
The form and size of algae is highly variable (Figure 3.1). The size
ranges from the microscopic unicellular forms like Chlamydomonas, to
colonial forms like Volvox and to the filamentous forms like Ulothrix and
Spirogyra. A few of the marine forms such as kelps, form massive plant
bodies.
explain vegetative reproduction and asexual reproduction in algae
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.
explain sexual reproduction in algae
Sexual reproduction
takes place through fusion of two gametes. These gametes can be
flagellated and similar in size (as in Chlamydomonas/Ulothirix) 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 some
species of Chlamydomonas is termed as anisogamous. Fusion between
one large, non-motile (static) female gamete and a smaller, motile male
gamete is termed oogamous, e.g., Volvox, Fucus.
explain the economic importance of algae
-At least a half of the total
carbon dioxide fixation on earth is carried out by algae through
photosynthesis. Being photosynthetic they increase the level of dissolved oxygen in their immediate environment. They are of paramount importance as primary producers of energy-rich compounds which form the basis of the food cycles of all aquatic animals.
-Many species of Porphyra, Laminaria and Sargassum are among the 70 species of marine algae
used as food.
-Certain marine brown and red algae produce large amounts
of hydrocolloids (water holding substances), e.g., algin (brown algae) and carrageen (red algae) which are used commercially. Agar, one of the commercial products obtained from Gelidium and Gracilaria are used to grow microbes and in preparations of ice-creams and jellies.
-Chlorella a unicellular alga, rich in proteins is used as food supplement even by
space travellers.
describe 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.Green algae usually have a rigid cell wall made of an inner layer of cellulose
and an outer layer of pectose.
On the basis of pigments (Chl ‘a’, Chl ‘b’, Carotenoids), stored food (starch) & cell
wall (made up of cellulose and pectose), green algae are considered similar to higher
plants.hey are the most advanced algae.
how is food stored in chlorophyceae
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.
Pyrenoids consist of protein centre surrounded by starch
explain reproduction in chlorophyceae
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
describe phaephyceae
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.
give the information in phaeophyceae:
(i) pigments
(ii)colour
(iii) stored food
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.
