Systems of Biological classification - It considers external features and internal features
1. Artificial classification systems (ultrastructure, anatomy, embryology & phytochemistry).
- E.g. Classification for flowering plants given by George
- Earliest systems of classification.
Bentham & Joseph Dalton Hooker.
- They were based on vegetative characters or superficial
3. Phylogenetic classification systems
morphological characters such as habit, colour, number
and shape of leaves, etc. - It is based on evolutionary relationships among organisms.
- Linnaeus’s artificial system of classification was based - This assumes that organisms in the same taxa have a
on the androecium structure. common ancestor.
Drawbacks: Other sources to resolve the problems in classification:
o Numerical Taxonomy: It is based on all observable
- They separated the closely related species since they were
characteristics. It is easily carried out using computers.
based on a few characteristics.
Number & codes are assigned to all the characters and the
- Equal weightage to vegetative and sexual characteristics.
data are processed. Thus, hundreds of characters can be
This is not acceptable since the vegetative characters are
equally considered.
more easily affected by environment.
o Cytotaxonomy: It is based on cytological information like
2. Natural classification systems chromosome number, structure, behaviour etc.
- These are based on natural affinities among organisms. o Chemotaxonomy: It uses chemical constituents of plants.
ALGAE
- Algae are simple, thalloid, autotrophic, chlorophyll- ☺ Some marine brown & red algae produce hydrocolloids
bearing and aquatic (fresh water & marine) organisms. (water holding substances). E.g. algin (brown algae) and
- They also occur in moist stones, soils and wood. carrageen (red algae). These are used commercially.
- Some occur in association with fungi (lichen) and animals ☺ Protein-rich unicellular algae like Chlorella & Spirullina
(e.g., on sloth bear). are used as food supplements by space travellers.
- The form and size of algae is highly variable. Algae include 3 classes: Chlorophyceae, Phaeophyceae
o Microscopic unicellular forms: E.g. Chlamydomonas. and Rhodophyceae.
o Colonial forms: E.g. Volvox.
o Filamentous forms: E.g. Ulothrix and Spirogyra.
1. Chlorophyceae (green algae)
Reproduction: - Unicellular, colonial or filamentous.
- Vegetative reproduction: By fragmentation. Each - They are usually grass green due to the pigments
fragment develops into a thallus. chlorophyll a and b in chloroplasts.
- Asexual reproduction: By the production of spores. E.g. - The chloroplasts may be discoid, plate-like, reticulate, cup-
zoospores (most common). They are flagellated (motile) shaped, spiral or ribbon-shaped in different species.
and on germination gives rise to new plants. - Most of them have one or more pyrenoids (storage bodies)
- Sexual reproduction: Through fusion of two gametes. It located in the chloroplasts. Pyrenoids contain protein
is many types: besides starch.
o Isogamous: Fusion of gametes similar in size. They - Some algae store food as oil droplets.
may be flagellated (e.g. Ulothrix) or non-flagellated - They have a rigid cell wall made of an inner layer of
(non-motile, e.g. Spirogyra). cellulose and an outer layer of pectose.
o Anisogamous: Fusion of two gametes dissimilar in size. - E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara.
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 Reproduction:
cycles of all aquatic animals. o Vegetative reproduction: By fragmentation or by
☺ Many marine algae (70 species) are used as food. E.g. formation of different types of spores.
Porphyra, Laminaria and Sargassum. o Asexual reproduction: By flagellated zoospores
☺ Agar (from Gelidium & Gracilaria) is used to grow produced in zoosporangia.
microbes and in ice-creams and jellies. o Sexual reproduction: Isogamous, anisogamous or
oogamous.
1
, 2. Phaeophyceae (brown algae) o Sexual reproduction: Isogamous, anisogamous or
- They are mostly marine forms. oogamous. Union of gametes occurs in water or within the
oogonium (oogamous species). Gametes are pear-shaped
- They show great variation in size & form. They range from
(pyriform) bearing 2 laterally attached flagella.
simple branched, filamentous forms (E.g. Ectocarpus) to
profusely branched forms (e.g. kelps- 100 m in height). 3. Rhodophyceae (red algae)
- They have chlorophyll a, c, carotenoids & xanthophylls. - They have a red pigment, r-phycoerythrin.
- They vary in colour from olive green to brown depending - Majority are marine especially in the warmer areas.
upon the amount of a xanthophyll pigment, fucoxanthin. - They occur in both well-lighted regions close to the surface
- Food is stored as complex carbohydrates (laminarin or of water and at great depths in oceans where relatively little
mannitol). light penetrates.
- The vegetative cells have a cellulosic wall covered by a - The red thalli of most of the red algae are multicellular.
gelatinous coating of algin. - Some of them have complex body organisation.
- Protoplast contains plastids, central vacuole and nucleus. - The food is stored as floridean starch which is very
- Plant body is attached to substratum by a holdfast, and has similar to amylopectin and glycogen in structure.
a stalk (stipe) and leaf like photosynthetic organ (frond). - E.g. Polysiphonia, Porphyra, Gracilaria and Gelidium.
- E.g. Ectocarpus, Dictyota, Laminaria, Sargassum & Fucus.
Reproduction:
Reproduction: o Vegetative reproduction: By fragmentation.
o Vegetative reproduction: By fragmentation. o Asexual reproduction: By non-motile spores.
o Asexual reproduction: By pear-shaped biflagellate o Sexual reproduction: Oogamous. By non-motile
zoospores (have 2 unequal laterally attached flagella). 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 &
2-8, equal, apical 2, unequal, lateral Absent
position of insertion
Fresh water, salt water & Fresh water (rare), salt water & Fresh water (some), salt water
Habitat
brackish water brackish water (most) & brackish water
BRYOPHYTES
- They are called amphibians of the plant kingdom because - Zygotes do not undergo meiosis immediately. They
they can live in soil but need water for sexual reproduction. produce a multicellular body called a sporophyte.
- They occur in damp, humid and shaded localities. - Sporophyte is not free-living but attached to the
- Their body is more differentiated than that of algae. It is photosynthetic gametophyte and derives nourishment from
thallus-like and prostrate or erect, and attached to the it. Some cells of the sporophyte undergo meiosis to form
substratum by unicellular or multicellular rhizoids. haploid spores. They germinate to form gametophyte.
- They lack true roots, stem or leaves. They may possess Importance of Bryophytes:
root-like, leaf-like or stem-like structures.
☺ Some mosses provide food for herbaceous mammals,
- The main plant body is haploid. It produces gametes, hence
birds and other animals.
is called a gametophyte.
☺ Species of Sphagnum (a moss) provide peat. It is used as
- The sex organs in bryophytes are multicellular.
fuel. It has water holding capacity so that used as packing
- The male sex organ (antheridium) produces biflagellate
material for trans-shipment of living material.
antherozoids. The female sex organ (archegonium) is
☺ They are ecologically important because of their role in
flask-shaped and produces a single egg.
plant succession on bare rocks/soil. Mosses along with
- Antherozoids are released to water and meet archegonium.
lichens decompose rocks making the substrate suitable for
An antherozoid fuses with the egg to form zygote.
the growth of higher plants.
2
, ☺ Since mosses form dense mats on the soil, they can Mosses
prevent soil erosion. - The predominant stage of the life cycle of a moss is the
The bryophytes are divided into liverworts and mosses. gametophyte. It consists of two stages.
Liverworts o Protonema stage: The first stage which develops
directly from a spore. It is a creeping, green, branched
- They grow usually in moist, shady habitats such as banks
and frequently filamentous stage.
of streams, marshy ground, damp soil, bark of trees and
o Leafy stage: The second stage which develops from the
deep in the woods.
secondary protonema as a lateral bud. They consist of
- Their plant body is thalloid. E.g. Marchantia. Thallus is
upright, slender axes bearing spirally arranged leaves.
dorsi-ventral and closely appressed to the substrate. The
They are attached to soil through multicellular and
leafy members have tiny leaf-like appendages in two rows
branched rhizoids. This stage bears the sex organs.
on the stem-like structures.
- Vegetative reproduction: By fragmentation and
- Asexual reproduction: By fragmentation of thalli, or by
budding in the secondary protonema.
the formation of gemmae (sing. gemma). Gemmae are
- Sexual reproduction: The antheridia & archegonia are
green, multicellular, asexual buds that develop in small
produced at the apex of leafy shoots. After fertilisation,
receptacles (gemma cups) on the thalli. Gemmae are
zygote develops into a sporophyte, consisting of a foot,
detached from the parent body and germinate to form new
seta and capsule. The sporophyte in mosses is more
individuals.
elaborate than that in liverworts. The capsule contains
- Sexual reproduction: Male and female sex organs are
spores. Spores are formed after meiosis. Mosses have an
produced on the same or different thalli. Sporophyte is
elaborate mechanism of spore dispersal.
differentiated into a foot, seta and capsule. After meiosis,
- E.g. Funaria, Polytrichum and Sphagnum.
spores are produced within the capsule. These spores
germinate to form free-living gametophytes.
PTERIDOPHYTES
- They include horsetails and ferns. - The spores germinate to give inconspicuous, small,
- They are found in cool, damp, shady places. Some flourish multicellular, free-living, mostly photosynthetic thalloid
well in sandy-soil conditions. gametophytes called prothallus.
- Evolutionarily, they are the first terrestrial plants to possess - Prothallus requires cool, damp, shady places to grow. Also,
vascular tissues (xylem & phloem). it needs water for fertilization. So, the spread of pteridophytes
- In bryophytes, the dominant phase in the life cycle is the is limited and restricted to narrow geographical regions.
gametophyte. In pteridophytes, the dominant phase (main - The gametophytes (prothallus) bear male and female sex
plant body) is a sporophyte. It is differentiated to true organs called antheridia and archegonia, respectively.
root, stem & leaves. These organs have well-differentiated - Water is needed for transfer of antherozoids (male
vascular tissues. gametes from antheridia) to the mouth of archegonium.
- The leaves in pteridophyta are small (microphylls) as in - Antherozoid fuses with the egg in the archegonium to form
Selaginella or large (macrophylls) as in ferns. zygote. Zygote develops to a multicellular well-
- Economic importance: They are used for medicinal differentiated sporophyte.
purposes and as soil-binders and ornamentals. - Most of the pteridophytes produce similar kinds of spores
REPRODUCTION: (homosporous plants). Others produce two kinds of
- The sporophytes bear sporangia that are subtended by spores, macro (mega) & micro spores. They are
heterosporous. E.g. Selaginella & Salvinia.
leaf-like appendages called sporophylls. In some cases,
sporophylls may form distinct compact structures called - The megaspores & microspores germinate and give rise
to female and male gametophytes, respectively. The
strobili or cones (E.g. Selaginella, Equisetum).
- Sporangia produce spores by meiosis in spore mother cells.
3
1. Artificial classification systems (ultrastructure, anatomy, embryology & phytochemistry).
- E.g. Classification for flowering plants given by George
- Earliest systems of classification.
Bentham & Joseph Dalton Hooker.
- They were based on vegetative characters or superficial
3. Phylogenetic classification systems
morphological characters such as habit, colour, number
and shape of leaves, etc. - It is based on evolutionary relationships among organisms.
- Linnaeus’s artificial system of classification was based - This assumes that organisms in the same taxa have a
on the androecium structure. common ancestor.
Drawbacks: Other sources to resolve the problems in classification:
o Numerical Taxonomy: It is based on all observable
- They separated the closely related species since they were
characteristics. It is easily carried out using computers.
based on a few characteristics.
Number & codes are assigned to all the characters and the
- Equal weightage to vegetative and sexual characteristics.
data are processed. Thus, hundreds of characters can be
This is not acceptable since the vegetative characters are
equally considered.
more easily affected by environment.
o Cytotaxonomy: It is based on cytological information like
2. Natural classification systems chromosome number, structure, behaviour etc.
- These are based on natural affinities among organisms. o Chemotaxonomy: It uses chemical constituents of plants.
ALGAE
- Algae are simple, thalloid, autotrophic, chlorophyll- ☺ Some marine brown & red algae produce hydrocolloids
bearing and aquatic (fresh water & marine) organisms. (water holding substances). E.g. algin (brown algae) and
- They also occur in moist stones, soils and wood. carrageen (red algae). These are used commercially.
- Some occur in association with fungi (lichen) and animals ☺ Protein-rich unicellular algae like Chlorella & Spirullina
(e.g., on sloth bear). are used as food supplements by space travellers.
- The form and size of algae is highly variable. Algae include 3 classes: Chlorophyceae, Phaeophyceae
o Microscopic unicellular forms: E.g. Chlamydomonas. and Rhodophyceae.
o Colonial forms: E.g. Volvox.
o Filamentous forms: E.g. Ulothrix and Spirogyra.
1. Chlorophyceae (green algae)
Reproduction: - Unicellular, colonial or filamentous.
- Vegetative reproduction: By fragmentation. Each - They are usually grass green due to the pigments
fragment develops into a thallus. chlorophyll a and b in chloroplasts.
- Asexual reproduction: By the production of spores. E.g. - The chloroplasts may be discoid, plate-like, reticulate, cup-
zoospores (most common). They are flagellated (motile) shaped, spiral or ribbon-shaped in different species.
and on germination gives rise to new plants. - Most of them have one or more pyrenoids (storage bodies)
- Sexual reproduction: Through fusion of two gametes. It located in the chloroplasts. Pyrenoids contain protein
is many types: besides starch.
o Isogamous: Fusion of gametes similar in size. They - Some algae store food as oil droplets.
may be flagellated (e.g. Ulothrix) or non-flagellated - They have a rigid cell wall made of an inner layer of
(non-motile, e.g. Spirogyra). cellulose and an outer layer of pectose.
o Anisogamous: Fusion of two gametes dissimilar in size. - E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara.
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 Reproduction:
cycles of all aquatic animals. o Vegetative reproduction: By fragmentation or by
☺ Many marine algae (70 species) are used as food. E.g. formation of different types of spores.
Porphyra, Laminaria and Sargassum. o Asexual reproduction: By flagellated zoospores
☺ Agar (from Gelidium & Gracilaria) is used to grow produced in zoosporangia.
microbes and in ice-creams and jellies. o Sexual reproduction: Isogamous, anisogamous or
oogamous.
1
, 2. Phaeophyceae (brown algae) o Sexual reproduction: Isogamous, anisogamous or
- They are mostly marine forms. oogamous. Union of gametes occurs in water or within the
oogonium (oogamous species). Gametes are pear-shaped
- They show great variation in size & form. They range from
(pyriform) bearing 2 laterally attached flagella.
simple branched, filamentous forms (E.g. Ectocarpus) to
profusely branched forms (e.g. kelps- 100 m in height). 3. Rhodophyceae (red algae)
- They have chlorophyll a, c, carotenoids & xanthophylls. - They have a red pigment, r-phycoerythrin.
- They vary in colour from olive green to brown depending - Majority are marine especially in the warmer areas.
upon the amount of a xanthophyll pigment, fucoxanthin. - They occur in both well-lighted regions close to the surface
- Food is stored as complex carbohydrates (laminarin or of water and at great depths in oceans where relatively little
mannitol). light penetrates.
- The vegetative cells have a cellulosic wall covered by a - The red thalli of most of the red algae are multicellular.
gelatinous coating of algin. - Some of them have complex body organisation.
- Protoplast contains plastids, central vacuole and nucleus. - The food is stored as floridean starch which is very
- Plant body is attached to substratum by a holdfast, and has similar to amylopectin and glycogen in structure.
a stalk (stipe) and leaf like photosynthetic organ (frond). - E.g. Polysiphonia, Porphyra, Gracilaria and Gelidium.
- E.g. Ectocarpus, Dictyota, Laminaria, Sargassum & Fucus.
Reproduction:
Reproduction: o Vegetative reproduction: By fragmentation.
o Vegetative reproduction: By fragmentation. o Asexual reproduction: By non-motile spores.
o Asexual reproduction: By pear-shaped biflagellate o Sexual reproduction: Oogamous. By non-motile
zoospores (have 2 unequal laterally attached flagella). 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 &
2-8, equal, apical 2, unequal, lateral Absent
position of insertion
Fresh water, salt water & Fresh water (rare), salt water & Fresh water (some), salt water
Habitat
brackish water brackish water (most) & brackish water
BRYOPHYTES
- They are called amphibians of the plant kingdom because - Zygotes do not undergo meiosis immediately. They
they can live in soil but need water for sexual reproduction. produce a multicellular body called a sporophyte.
- They occur in damp, humid and shaded localities. - Sporophyte is not free-living but attached to the
- Their body is more differentiated than that of algae. It is photosynthetic gametophyte and derives nourishment from
thallus-like and prostrate or erect, and attached to the it. Some cells of the sporophyte undergo meiosis to form
substratum by unicellular or multicellular rhizoids. haploid spores. They germinate to form gametophyte.
- They lack true roots, stem or leaves. They may possess Importance of Bryophytes:
root-like, leaf-like or stem-like structures.
☺ Some mosses provide food for herbaceous mammals,
- The main plant body is haploid. It produces gametes, hence
birds and other animals.
is called a gametophyte.
☺ Species of Sphagnum (a moss) provide peat. It is used as
- The sex organs in bryophytes are multicellular.
fuel. It has water holding capacity so that used as packing
- The male sex organ (antheridium) produces biflagellate
material for trans-shipment of living material.
antherozoids. The female sex organ (archegonium) is
☺ They are ecologically important because of their role in
flask-shaped and produces a single egg.
plant succession on bare rocks/soil. Mosses along with
- Antherozoids are released to water and meet archegonium.
lichens decompose rocks making the substrate suitable for
An antherozoid fuses with the egg to form zygote.
the growth of higher plants.
2
, ☺ Since mosses form dense mats on the soil, they can Mosses
prevent soil erosion. - The predominant stage of the life cycle of a moss is the
The bryophytes are divided into liverworts and mosses. gametophyte. It consists of two stages.
Liverworts o Protonema stage: The first stage which develops
directly from a spore. It is a creeping, green, branched
- They grow usually in moist, shady habitats such as banks
and frequently filamentous stage.
of streams, marshy ground, damp soil, bark of trees and
o Leafy stage: The second stage which develops from the
deep in the woods.
secondary protonema as a lateral bud. They consist of
- Their plant body is thalloid. E.g. Marchantia. Thallus is
upright, slender axes bearing spirally arranged leaves.
dorsi-ventral and closely appressed to the substrate. The
They are attached to soil through multicellular and
leafy members have tiny leaf-like appendages in two rows
branched rhizoids. This stage bears the sex organs.
on the stem-like structures.
- Vegetative reproduction: By fragmentation and
- Asexual reproduction: By fragmentation of thalli, or by
budding in the secondary protonema.
the formation of gemmae (sing. gemma). Gemmae are
- Sexual reproduction: The antheridia & archegonia are
green, multicellular, asexual buds that develop in small
produced at the apex of leafy shoots. After fertilisation,
receptacles (gemma cups) on the thalli. Gemmae are
zygote develops into a sporophyte, consisting of a foot,
detached from the parent body and germinate to form new
seta and capsule. The sporophyte in mosses is more
individuals.
elaborate than that in liverworts. The capsule contains
- Sexual reproduction: Male and female sex organs are
spores. Spores are formed after meiosis. Mosses have an
produced on the same or different thalli. Sporophyte is
elaborate mechanism of spore dispersal.
differentiated into a foot, seta and capsule. After meiosis,
- E.g. Funaria, Polytrichum and Sphagnum.
spores are produced within the capsule. These spores
germinate to form free-living gametophytes.
PTERIDOPHYTES
- They include horsetails and ferns. - The spores germinate to give inconspicuous, small,
- They are found in cool, damp, shady places. Some flourish multicellular, free-living, mostly photosynthetic thalloid
well in sandy-soil conditions. gametophytes called prothallus.
- Evolutionarily, they are the first terrestrial plants to possess - Prothallus requires cool, damp, shady places to grow. Also,
vascular tissues (xylem & phloem). it needs water for fertilization. So, the spread of pteridophytes
- In bryophytes, the dominant phase in the life cycle is the is limited and restricted to narrow geographical regions.
gametophyte. In pteridophytes, the dominant phase (main - The gametophytes (prothallus) bear male and female sex
plant body) is a sporophyte. It is differentiated to true organs called antheridia and archegonia, respectively.
root, stem & leaves. These organs have well-differentiated - Water is needed for transfer of antherozoids (male
vascular tissues. gametes from antheridia) to the mouth of archegonium.
- The leaves in pteridophyta are small (microphylls) as in - Antherozoid fuses with the egg in the archegonium to form
Selaginella or large (macrophylls) as in ferns. zygote. Zygote develops to a multicellular well-
- Economic importance: They are used for medicinal differentiated sporophyte.
purposes and as soil-binders and ornamentals. - Most of the pteridophytes produce similar kinds of spores
REPRODUCTION: (homosporous plants). Others produce two kinds of
- The sporophytes bear sporangia that are subtended by spores, macro (mega) & micro spores. They are
heterosporous. E.g. Selaginella & Salvinia.
leaf-like appendages called sporophylls. In some cases,
sporophylls may form distinct compact structures called - The megaspores & microspores germinate and give rise
to female and male gametophytes, respectively. The
strobili or cones (E.g. Selaginella, Equisetum).
- Sporangia produce spores by meiosis in spore mother cells.
3
