Diversity in the Living World 🌿 Official Notes By AI BIOLOGY CLASS 11 Chapter1 NEET

 

Diversity in the Living World 🌿

Definition of Biology

Biology is the science of life forms and living processes. The living world comprises an amazing diversity of living organisms.

Early Perception of Living Organisms

Early man could easily perceive the difference between inanimate matter and living organisms. Early man deified some of the inanimate matter (wind, sea, fire, etc.) and some among the animals and plants. A common feature of all such forms of inanimate and animate objects was the sense of awe or fear that they evoked.

Importance of Systematic Description

Societies which indulged in anthropocentric view of biology could register limited progress in biological knowledge. Systematic and monumental description of life forms brought in, out of necessity, detailed systems of identification, nomenclature, and classification.

Ernst Mayr (1904-2004)

Ernst Mayr, the Harvard University evolutionary biologist, was one of the 100 greatest scientists of all time. He pioneered the currently accepted definition of a biological species and made significant contributions to ornithology, taxonomy, zoogeography, evolution, systematics, and the history and philosophy of biology.

1.1 Diversity in the Living World

The living world is home to a wide range of living types, from cold mountains to hot springs, and from deciduous forests to oceans and deserts. The beauty of a galloping horse, migrating birds, or a valley of flowers evokes awe and wonder.

What is Life?

The question "what is life?" has two implicit questions within it. The first is a technical one and seeks an answer to what living is as opposed to non-living, and the second is a philosophical one, and seeks an answer to what the purpose of life is.

Biodiversity

Biodiversity refers to the number and types of organisms present on earth. There are approximately 1.7-1.8 million known species, and new organisms are continuously being identified.

Need for Standardized Naming

Local names for organisms vary from place to place, even within a country. To facilitate communication and study, scientists have established procedures to assign a scientific name to each known organism.

Binomial Nomenclature

Binomial nomenclature is a system of providing a name with two components: the generic name and the specific epithet. This system was given by Carolus Linnaeus and is practiced by biologists worldwide.

Example: Mango (Mangifera indica)

Component	Description
Mangifera	Genus
indica	Specific epithet

Universal Rules of Nomenclature

• Biological names are generally in Latin and written in italics.
• The first word in a biological name represents the genus, while the second component denotes the specific epithet.
• Both words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.
• The first word denoting the genus starts with a capital letter, while the specific epithet starts with a small letter.

Example: Mangifera indica Linn.

• Mangifera (genus)
• indica (specific epithet)
• Linn. (author's abbreviation)## Systematics and Taxonomic Categories 🌿

Systematics is the branch of study that focuses on knowing more about different kinds of organisms and their diversities, as well as the relationships among them. The word systematics is derived from the Latin word systema, which means systematic arrangement of organisms.

Taxonomic Categories

Classification is not a single step process but involves a hierarchy of steps, in which each step represents a rank or category. Since the category is a part of overall taxonomic arrangement, it is called the taxonomic category, and all categories together constitute the taxonomic hierarchy.

Taxonomic Hierarchy

Category	Description
Species	A group of individual organisms with fundamental similarities
Genus	A group of related species which has more characters in common
Family	A group of related genera with still less number of similarities
Order	An assemblage of families which exhibit a few similar characters
Class	A category that includes related orders
Phylum/Division	A category that includes classes with a few similar characters
Kingdom	The highest category that includes all animals or plants from various phyla or divisions

Species

"A group of individual organisms with fundamental similarities"

• Mangifera indica, Solanum tuberosum (potato), and Panthera leo (lion) are examples of species

Genus

"A group of related species which has more characters in common"

• Panthera is a genus that includes species like Panthera leo (lion), Panthera tigris (tiger), and Panthera pardus (leopard)
• Solanum is a genus that includes species like Solanum tuberosum (potato) and Solanum melongena (brinjal)

Family

"A group of related genera with still less number of similarities"

• Solanaceae is a family that includes genera like Solanum, Petunia, and Datura
• Felidae is a family that includes genera like Panthera (lion, tiger, leopard) and Felis (cats)

Order

"An assemblage of families which exhibit a few similar characters"

• Polymoniales is an order that includes families like Convolvulaceae and Solanaceae (plant families)
• Carnivora is an order that includes families like Felidae (lions, tigers, leopards) and Canidae (dogs)

Class

"A category that includes related orders"

• Mammalia is a class that includes orders like Primata (monkeys, gorillas, gibbons) and Carnivora (lions, tigers, leopards)

Phylum/Division

"A category that includes classes with a few similar characters"

• Chordata is a phylum that includes classes like Mammalia, Aves (birds), and Reptilia (reptiles)
• Plantae is a kingdom that includes divisions like Angiospermae (flowering plants) and Gymnospermae (conifers)

Kingdom

"The highest category that includes all animals or plants from various phyla or divisions"

• Animalia is a kingdom that includes all animals from various phyla like Chordata, Arthropoda, and Mollusca
• Plantae is a kingdom that includes all plants from various divisions like Angiospermae and Gymnospermae

Plant Kingdom 🌱 Chapter 3 biology OFFICIAL NOTES

 

3.1 Algae 🔵

Algae are chlorophyll-bearing, simple, thalloid, autotrophic, and largely aquatic organisms. They occur in a variety of habitats, including:

• Moist stones
• Soils
• Wood
• Fungi (lichen)
• Animals (e.g., on sloth bear)

Algae have a highly variable form and size, ranging from:

• Colonial forms like Volvox
• Filamentous forms like Ulothrix and Spirogyra (Figure 3.1)

Some marine forms, like kelps, form massive plant bodies.

Reproduction

Algae reproduce by:

• Vegetative reproduction: by fragmentation. Each fragment develops into a thallus.
• Asexual reproduction: by production of different types of spores, the most common being zoospores. They are flagellated (motile) and on germination give 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)
  • Non-flagellated (non-motile) but similar in size (as in Spirogyra)
  • Fusion of two gametes dissimilar in size (as in species of Eudorina)
  • Fusion between one large, non-motile (static) female gamete and a smaller, motile male gamete (as in Volvox, Fucus)

Importance

Algae are useful to man in a variety of ways:

• At least half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis.
• 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 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, is 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 travelers.

Classification

Algae are divided into three main classes:

3.1.1 Chlorophyceae 💚

• 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 localized in definite chloroplasts.

Characteristic	Description
Cell wall	Inner layer of cellulose and outer layer of pectose
Vegetative reproduction	By fragmentation or by formation of different types of spores
Asexual reproduction	By flagellated zoospores produced in zoosporangia
Sexual reproduction	Shows considerable variation in the type and formation of sex cells, and may be isogamous, anisogamous, or oogamous

3.1.2 Phaeophyceae 🟡

• 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 meters.
• They possess chlorophyll a, c, carotenoids, and xanthophylls.

Characteristic	Description
Cell wall	Cellulosic wall usually covered on the outside by a gelatinous coating of algin
Food storage	As complex carbohydrates, which may be in the form of laminarin or mannitol
Vegetative cells	Have a centrally located vacuole and nucleus
Plant body	Attached to the substratum by a holdfast, and has a stalk (the stipe), and a leaf-like photosynthetic organ (the frond)

3.1.3 Rhodophyceae 🔴

• 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 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.

Characteristic	Description
Food storage	As floridean starch, which is very similar to amylopectin and glycogen in structure
Vegetative cells	Have a centrally located vacuole and nucleus
Plant body	Attached to the substratum by a holdfast, and has a stalk (the stipe), and a leaf-like photosynthetic organ (the frond)

Table 3.1 Divisions of Algae and their Main Characteristics

Class	Common Name	Pigments	Food	Cell Wall	Flagellar Number and Position	Habitat
Chlorophyceae	Green algae	Chlorophyll a, b	Starch	Cellulose	2-8, equal, apical	Fresh water, brackish water, salt water
Phaeophyceae	Brown algae	Chlorophyll a, c, fucoxanthin	Mannitol, laminarin	Cellulose, algin	2, unequal, lateral (rare)	Fresh water, brackish water, salt water
Rhodophyceae	Red algae	Chlorophyll a, d, phycoerythrin	Floridean starch	Cellulose, pectin, poly sulphate esters	Absent (some), poly	Fresh water, brackish water, salt water (most)

3.2 Bryophytes 🌿

Bryophytes include the various mosses and liverworts that are found commonly growing in moist shaded areas in the hills (Figure 3.2).

Characteristics

Bryophytes are also called amphibians of the plant kingdom because these plants can live in## Bryophytes 🌿

Characteristics:

• Non-vascular plants that do not have true roots, stems, or leaves
• Plant body is thallus-like and prostrate or erect
• Attached to substratum by unicellular or multicellular rhizoids
• Lack true roots, stems, or leaves
• May possess root-like, leaf-like, or stem-like structures

Life Cycle:

• Main plant body is haploid and produces gametes (gametophyte)
• Sex organs are multicellular
• Male sex organ is called antheridium and produces biflagellate antherozoids
• Female sex organ is called archegonium and produces a single egg
• Antherozoids are released into water and come into contact with archegonium
• An antherozoid fuses with the egg to produce a zygote
• Zygote develops into a multicellular body called a sporophyte
• Sporophyte is not free-living and is attached to the photosynthetic gametophyte
• Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores
• Spores germinate to produce gametophyte

Economic Importance:

• Some mosses provide food for herbaceous mammals, birds, and other animals
• Species of Sphagnum provide peat that has been used as fuel and as packing material for trans-shipment of living material

Ecological Importance:

• First organisms to colonize rocks
• Decompose rocks, making the substrate suitable for the growth of higher plants
• Form dense mats on soil, reducing the impact of falling rain and preventing soil erosion

Liverworts 🌿

Characteristics:

• Thalloid plant body
• Dorsiventral and closely appressed to the substrate
• Leafy members have tiny leaf-like appendages in two rows on stem-like structures

Asexual Reproduction:

• Fragmentation of thalli
• Formation of specialized structures called gemmae (sing. gemma)
• Gemmae are green, multicellular, asexual buds that develop in small receptacles called gemma cups
• Gemmae become detached from the parent body and germinate to form new individuals

Sexual Reproduction:

• Male and female sex organs are produced either on the same or on different thalli
• Sporophyte is differentiated into a foot, seta, and capsule
• After meiosis, spores are produced within the capsule
• Spores germinate to form free-living gametophytes

Mosses 🌿

Characteristics:

• Predominant stage of the life cycle is the gametophyte
• Gametophyte consists of two stages: protonema stage and leafy stage
• Protonema stage develops directly from a spore and is a creeping, green, branched, and frequently filamentous stage
• Leafy stage develops from the secondary protonema as a lateral bud and consists of upright, slender axes bearing spirally arranged leaves
• Attached to the soil through multicellular and branched rhizoids

Vegetative Reproduction:

• Fragmentation
• Budding in the secondary protonema

Sexual Reproduction:

• Sex organs are produced at the apex of the leafy shoots
• After fertilization, the zygote develops into a sporophyte, consisting of a foot, seta, and capsule
• Sporophyte is more elaborate than that in liverworts
• Capsule contains spores
• Spores are formed after meiosis
• Elaborate mechanism of spore dispersal

Examples of Mosses:

• Funaria
• Polytrichum
• Sphagnum## Angiosperms 🌼

Angiosperms, also known as flowering plants, are a group of plants that have evolved to produce flowers, fruits, and seeds. In contrast to gymnosperms, angiosperms have ovules and pollen grains that are developed in specialized structures called flowers.

Characteristics of Angiosperms

• Seeds are enclosed in fruits: Angiosperms produce seeds that are protected by a fruit or a covering. • Wide range of habitats: Angiosperms can be found in diverse environments, from the smallest Wolffia to tall trees of Eucalyptus (over 100 meters). • Provide various products: Angiosperms are a source of food, fodder, fuel, medicines, and other commercially important products.

Classification of Angiosperms

Angiosperms are divided into two classes:

Class	Description
Dicotyledons
Monocotyledons

Importance of Angiosperms

Angiosperms play a vital role in our ecosystem and provide numerous benefits to humans and the environment.

"Angiosperms are an exceptionally large group of plants occurring in wide range of habitats."