3. PLANT KINGDOM
Systems of Biological classification
1. Artificial classification systems
-
Earliest systems of classification.
- They were based on vegetative characters or superficial morphological characters such as habit, colour, number and shape of leaves, etc.
-
Linnaeus’s
artificial system of classification was based on the
androecium structure.
Drawbacks:
-
They separated the closely related species
since they were based on a few characteristics.
-
Equal weightage to vegetative and sexual
characteristics. This is not acceptable since the vegetative characters are
more easily affected by environment.
2. Natural classification systems
-
These are based on natural affinities
among organisms.
-
It considers external features and
internal features (ultrastructure, anatomy, embryology & phytochemistry).
-
E.g. Classification for flowering plants
given by George Bentham & Joseph Dalton Hooker.
3.
Phylogenetic classification systems
-
It is based on evolutionary
relationships among organisms.
-
This assumes that organisms in the same
taxa have a common ancestor.
Other sources to
resolve the problems in classification:
o
Numerical Taxonomy: It
is based on all observable characteristics. It is easily carried out using
computers. Number & codes are assigned to all the characters and the data
are processed. Thus, hundreds of characters can be equally considered.
o
Cytotaxonomy: It
is based on cytological information like chromosome number, structure,
behaviour etc.
o
Chemotaxonomy: It
uses chemical constituents of plants.
ALGAE
-
Algae are simple, thalloid, autotrophic, chlorophyll-bearing
and aquatic (fresh water & marine) organisms.
-
They also occur in moist stones, soils and
wood.
-
Some occur in association with fungi
(lichen) and animals (e.g., on sloth bear).
-
The form and size of algae is highly
variable.
o
Microscopic unicellular forms: E.g. Chlamydomonas.
o
Colonial forms: E.g. Volvox.
o
Filamentous forms: E.g. Ulothrix and
Spirogyra.
Reproduction:
-
Vegetative reproduction: By
fragmentation. Each fragment develops into a thallus.
-
Asexual reproduction: By
the production of spores. E.g. zoospores (most common). They are
flagellated (motile) and on germination gives rise to new plants.
-
Sexual reproduction: Through
fusion of two gametes. It is many types:
o
Isogamous: Fusion
of gametes similar in size. They may be flagellated (e.g. Ulothrix) or
non-flagellated (non-motile, e.g. Spirogyra).
o
Anisogamous: Fusion
of two gametes dissimilar in size. E.g. Some species of Eudorina.
o
Oogamous: Fusion
between one large, non-motile (static) female gamete and a smaller, motile male
gamete. E.g. Volvox, Fucus.
Benefits of algae:
☺
Through photosynthesis, they fix half of
the total CO2 on earth and increase the level of dissolved oxygen.
☺
They are primary producers and the basis
of the food cycles of all aquatic animals.
☺
Many marine algae (70 species) are used as
food. E.g. Porphyra, Laminaria and Sargassum.
☺
Agar
(from Gelidium & Gracilaria) is used to grow microbes
and in ice-creams and jellies.
☺
Some marine brown & red algae produce hydrocolloids
(water holding substances). E.g. algin (brown algae) and carrageen (red
algae). These are used commercially.
☺
Protein-rich unicellular algae like
Chlorella & Spirullina are used as food supplements by space
travellers.
Algae include 3
classes: Chlorophyceae,
Phaeophyceae and Rhodophyceae.
1. Chlorophyceae (green algae)
-
Unicellular, colonial or filamentous.
-
They are usually grass green due to the
pigments chlorophyll a and b in chloroplasts.
-
The chloroplasts may be discoid,
plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in different
species.
-
Most of them have one or more pyrenoids
(storage bodies) located in the chloroplasts. Pyrenoids contain protein besides
starch.
-
Some algae store food as oil droplets.
- They
have a rigid cell wall made of an inner layer of cellulose and an outer layer
of pectose.
- E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra &
Chara.
Reproduction:
o Vegetative
reproduction: By fragmentation or by formation of
different types of spores.
o Asexual
reproduction: By flagellated zoospores produced in
zoosporangia.
o Sexual
reproduction: Isogamous, anisogamous or oogamous.
2. Phaeophyceae (brown algae)
-
They are mostly marine forms.
-
They show great variation in size &
form. They range from simple branched, filamentous forms (E.g. Ectocarpus)
to profusely branched forms (e.g. kelps- 100 m in height).
-
They have chlorophyll a, c,
carotenoids & xanthophylls.
-
They vary in colour from olive green to
brown depending upon the amount of a xanthophyll pigment, fucoxanthin.
-
Food is stored as complex carbohydrates (laminarin
or mannitol).
-
The vegetative cells have a cellulosic
wall covered by a gelatinous coating of algin.
-
Protoplast contains plastids, central
vacuole and nucleus.
-
Plant body is
attached to substratum by a holdfast, and has
a stalk (stipe) and leaf like photosynthetic organ (frond).
- E.g. Ectocarpus, Dictyota, Laminaria, Sargassum &
Fucus.
Reproduction:
o
Vegetative reproduction: By
fragmentation.
o
Asexual reproduction: By
pear-shaped biflagellate zoospores (have 2 unequal laterally attached
flagella).
o Sexual
reproduction: Isogamous, anisogamous or oogamous. Union
of gametes occurs in water or within the oogonium (oogamous species). Gametes
are pear-shaped (pyriform) bearing 2 laterally attached flagella.
3. Rhodophyceae (red algae)
-
They have a red pigment, r-phycoerythrin.
-
Majority are marine especially in the
warmer areas.
-
They occur in both well-lighted regions
close to the surface of water and 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.
- E.g.
Polysiphonia, Porphyra, Gracilaria and Gelidium.
Reproduction:
o Vegetative
reproduction: By fragmentation.
o Asexual
reproduction: By non-motile spores.
o Sexual reproduction: Oogamous. By non-motile gametes. It has complex post fertilisation developments.
|
Classes |
Chlorophyceae
(Green algae) |
Phaeophyceae
(brown algae) |
Rhodophyceae
(Red algae) |
|
Major pigments |
Chlorophyll a, b |
Chlorophyll a, c, Fucoxanthin |
Chlorophyll a, d, Phycoerythrin |
|
Stored
food |
Starch |
Mannitol,
laminarin |
Floridean Starch
|
|
Cell wall |
Cellulose |
Cellulose and
algin |
Cellulose |
|
Flagellar number
& position of insertion |
2-8, equal,
apical |
2, unequal,
lateral |
Absent |
|
Habitat |
Fresh water,
salt water & brackish water |
Fresh water
(rare), salt water & brackish water |
Fresh
water (some), salt water (most) & brackish water |
It is so easy language and all information is covered in little words
ReplyDeleteThank you so much
ReplyDeleteThese are the best biology notes one can find on internet every point is covered in a simple and understandable language