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Class xi biology notes
UNIT I DIVERSITY IN THE LIVING WORLD
Chapter 2 : Biological Classification
UNIT II STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS
Chapter 5 : Morphology of Flowering Plants
Chapter 6 : Anatomy of Flowering Plants
Chapter 7 : Structural Organisation in Animals
UNIT III CELL : STRUCTURE AND FUNCTIONS
Chapter 8 : Cell : The Unit of Life
Chapter 10 : Cell Cycle and Cell Division
UNIT IV PLANT PHYSIOLOGY
Chapter 11 : Photosynthesis in Higher Plants
Chapter 12 : Respiration in Plants
Chapter 13 : Plant Growth and Development
UNIT V HUMAN PHYSIOLOGY
Chapter 14 : Breathing and Exchange of Gases
Chapter 15 : Body Fluids and Circulation
Chapter 16 : Excretory Products and their Elimination
Chapter 17 : Locomotion and Movement
Characteristics of Living World
Growth
Growth is an essential characteristic of all living things. Some non-living things, such as clouds, exhibit growth. As a result, growth is not a defining characteristic of Life. Non-living things, on the other hand, grow as a result of the accumulation of matter from outside. A living being's growth, on the other hand, is caused by internal processes such as cell division. The majority of plants grow indeterminately, whereas animal growth is definite
Reproduction
Through the process of reproduction, all living beings produce offspring. Reproduction is critical for maintaining a species' lineage. Sexual and asexual reproduction are the two main types of reproduction. Honey bee drones and sterile organisms do not reproduce. As a result, growth is not a distinguishing feature of living organisms.
Metabolism
A living organism's chemicals are constantly changing. This is known as metabolism. Metabolism is divided into two processes: anabolism and catabolism.
Anabolism
The process of synthesis of any substance is called anabolism, e.g. photosynthesis.
Catabolism
The process of breaking up of a substance is called catabolism, e.g. respiration. It is defining property of life.
Response to External Stimuli
External stimuli elicit responses in all living organisms. External stimuli include light, heat, chemicals, other organisms, and so on. The ability to respond to external stimuli is critical for an organism's survival. It is a defining characteristic of life.
Diversity of Living World
The number and types of organisms present on earth refer to biodiversity. Number of species described is 1.7-1.8 million.
Taxonomy(Systematics)
It is the study of organism identification, classification, nomenclature, and documentation. Systematics (Latin for "systema") refers to the systematic arrangement of organisms. Linnaeus wrote the book Systema Naturae.
Processes of Taxonomy
Characterization is the understanding of an organism's characteristics such as external and internal structure, cell structure, development process, ecological information, and so on.
Identification: Nomenclature is only possible if the organism is correctly described and we know what organism the name refers to. This is called identification.
Classification is the division of organisms into useful categories (taxa) based on similarities and differences in their characteristics.
Nomenclature (naming) is the process of assigning standardised names to organisms so that they are known by the same name all over the world.
Carolus Linnaeus proposed the two-component naming system (Binomial nomenclature). Botanical names are determined by the rules outlined in the International Code of Botanical Nomenclature (ICBN). Zoological names are derived from
Universal Rules of Binomial Nomenclature
Scientific names are usually written in Latin and italicised. The first word is the genus name (also known as the generic name), and the second word is the species name (specific epithet). The names are underlined when written by hand. The names appear in italics. The first name (Genus) begins with a capital letter, while the second name (Species) begins with a small letter. For example, Homo sapiens—Homo is the genus name, and sapiens is the species name.
The author's name appears after the specific epithet, that is, at the end of the biological name, and is written in abbreviated form, for example, Mangifera indica Linn. It indicates that Linnaeus was the first to describe this species.
Nomenclature and Identification:
Different languages have different names for the same organism. It is impossible for anyone to remember the names of organisms in all languages. As a result, a standardised system of organism nomenclature is required. A consistent system of nomenclature and identification aids scientists in their systematic study of living things. The International Code for Botanical Nomenclature (ICBN) applies to plants, while the International Code for Zoological Nomenclature (ICZN) applies to animals.
Most biological names are written in Latin. Italics are used to emphasise them.
A biological name typically consists of two terms. The first term refers to the genus, while the second refers to the species.
When handwritten, the biological name is underlined.
The biological name's first term begins with
Taxonomic Categories
Various steps of the classification hierarchy are called taxonomic categories. Each The category represents a rank and is commonly referred to as the taxon.
Species: A species is a group of individuals with the ability to interbreed among themselves. Members of a species share many characteristics. For example, all tigers are referred to as Panthera tigris. Because they can all interbreed, they are all classified as one species.
Genus: A genus is a group of closely related species. Panthera is the genus name for the lion (Panthera leo), leopard (Panthera pardus), and tiger (Panthera tigris). Solanum also includes potatoes, tomatoes, and brinjal.
A family is a collection of closely related genera. Potato and chilli, for example, are members of the Solanaceae family. Similarly, the genera Panthera and Felis are members of the same family.
Similarly, the genera Panthera and Felis are members of the Felidae family.
Order refers to a group of closely related families. Convolvulaceae and Solanaceae, for example, are plant families in the order Polymoniales. Felidae and Concidae are also members of the order Carnivora.
Class: A class is a group of orders that are closely related. For example, the orders Primata and Carnivora are classified as Mammalia.
Phylum: A phylum is a group of closely related classes. The term phylum has been replaced with division in the Plant Kingdom. Pisces, Amphibia, Reptilia, Aves, and Mammalia are all members of the Phylum Chordata.
The Kingdom refers to the collection of all related phyla. For example, the Plant Kingdom includes all autotrophic eukaryotic organisms with chloroplasts. Similarly, all heterotrophic organisms that are eukaryotic and do not have a cell wall are classified as Animal Kingdom.
MUSEUM
A museum is a collection of preserved plants and animals for research and education. A museum houses Preserved specimens in containers or jars in preservative solutions. Plant and animal specimens that have been preserved as dry specimens.
After collecting, killing, and pinning, insects are preserved in insect boxes. Larger animals, such as birds and mammals, are stuffed. Animal skeleton collections.
ZOOLOGICAL PARKS (ZOOS)
These are facilities where live wild animals are kept in safe environments under human supervision. It allows you to learn about their eating habits and behaviour.
KEY
It is a device that is used to identify each species within a group of organisms based on similarities and differences.
The keys are based on the contrasting characters in a pair known as a couplet. It represents the decision between two opposing options. Each statement in the key is referred to as a lead.
Flora, Manuals, Monographs & Catalogues
These are some other methods for documenting descriptions. They also aid in proper identification.
Flora is a detailed account of the habitat and distribution of plant species in a given area.
Manuals help in providing information for identification of names of species found in an area.
Monographs contain information about a single taxon.
NCERT Solutions
This chapter expands on fundamental concepts such as What is Living?, Diversity in the Living World, Taxonomic Categories, Taxonomical Aids, and others. The living world is diverse. Millions of plant and animal species have been identified and described to date, but many more are yet to be discovered. Taxonomic studies of various plant and animal species are useful in agriculture, forestry, and industries in general for understanding our resources and their diversity. Taxonomists have created a number of taxonomic aids to aid in the identification, naming, and classification of organisms.
1. Why are living organisms classified?
Solution:
There are millions of species that are known by their local or vernacular names. These local names would vary from place to place, even within a country. This would lead to confusion in identifying and studying specific species. Hence to standardize the naming and studying of living organisms it should be called by a common name throughout the world. To achieve this, the organisms are named and classified according to their characters. Classification is based on similarities and differences in their characters
2. Why are the classification systems changing every now and then?
Solution:
Continuous discovery of organisms, and new species and organisms are added often. An early system of classification takes note of only habit and habitats of organisms. Gradually external morphology became toll for classification. After this, morphology and embryology are taken to consideration followed by phylogenetic relation, cytology of an organism. Modern-day uses biochemical techniques to classify the organisms based on their nucleic acid components and they are grouped based on their phylogeny
3. What different criteria would you choose to classify people that you meet often?
Solution:
We classify the people that we often meet on the following attributes
• Gender
• Age
• Skin colour
• Religion
• Language
• Education
• Profession
• Hobbies
• Nature
4. What do we learn from identification of individuals and populations?
Solution:
By identifying individuals and populations, we learn following things
• Sex
• Skin colour
• Native place
• Mother tongue
• Food habit
• Religion
• Caste
5. Given below is the scientific name of Mango. Identify the correctly written name.
Mangifera Indica
Solution:
The answer is Mangifera indica. Here Mangifera is its genus name first letter of which is always written capital and indica is its species name which is always written in lowercase.
6. Define a taxon. Give some examples of taxa at different hierarchical levels.
Solution:
A taxon is the name of a level of hierarchy in the system of classifying organisms.
Following are the hierarchical levels.
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species
Ex. Phylum is category and Porifera is taxon of sponges
7. Can you identify the correct sequence of taxonomical categories?
(a) Species Order Phylum Kingdom
(b) Genus Species Order Kingdom
(c) Species Genus Order Phylum
Solution:
Option a) and c) are the correct sequence of taxonomical categories both in ascending orders in these cases
8. Try to collect all the currently accepted meanings for the word ‘species’. Discuss with your teacher the meaning of species in case of higher plants and animals on one hand, and bacteria on the other hand.
Solution:
A group of individual organisms with fundamental similarities are called species. It is the basic unit of classification. Species are also defined as the individuals that share the same gene pool.
Higher plants and animals: Criteria of reproductive isolation can be used to classify the species.
Bacteria: interbreeding and reproductive isolation cannot be used in case of bacteria here gene pool can be used to classify species.
9. Define and understand the following terms:
(i) Phylum (ii) Class (iii) Family (iv) Order (v) Genus
Solution:
i) Phylum is a taxonomical hierarchy below Kingdom and above Class. It is a taxon with one or more classes organisms with similar characters.
ii) Class is a taxonomical hierarchy higher than Order and lower than Phylum. Class includes related to orders of the organisms. Example: Presence of notochord in mammals.
iii) Family has a group of related genera with still less number of similarities as compared to genus and species. Example: Fox and dog belongs to the same family. It is a group of entities below Order and above Genus.
iv) Order is a taxon below higher than Family and lower than class. Order being a higher category is the assemblage of families which exhibit a few similar characters.
v) Genus comprises a group of related species which has more characters in common in comparison to species of other genera. Ex:Lion, tiger and leopard are classified under genus Panthera. It is above species and below Family.
10. How is a key helpful in the identification and classification of an organism?
Solution:
Key is a taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities. It represents the choice between two opposite characters. It is helpful in identifying contrasting characters. They are a pair of two contrasting characters where selection of one character leads to the rejection of another character when species, family or genera is identified.
If an entitiy is not recorded already, attempst are made to firstc check and recheck its discovery before naming it. Hence, eveny entitiy can be classified whether it is unknown or known.
11. Illustrate the taxonomical hierarchy with suitable examples of a plant and an animal.
Solution:
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