Notes XI

1 LIVING WORLD

CLASS XI BIOLOGY NOTES

CHAPTER – 1: LIVING WORLD

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

amazingdiversity of living organisms. In order to facilitate the study of kinds and diversity of

organisms, biologists have evolved certain rules and principles for identification, nomenclature and

classification of organisms. The branchof biology dealing with these aspects is referred to as

Taxonomy.

Life is a characteristic that distinguishesobjectsthat havesignaling and self-sustaining

processesfromthose that do not, either because such functions have ceased (death), or else because

they lack such functions and are classified asinanimate. Biologyis the science concerned with the

study of life.

Characteristics features of Living things / Differences between living and non-living things:

a) Growth- Living organisms grow in mass and number.Living organisms show internal growth

due to addition of materials and formation of cells inside the body. Non living organism like

mountains, boulders, crystals also grow but due to addition of similar materials to their outer

surface.Growth, therefore, cannot be taken as a defining property of living organisms.

b) Reproduction – Many organisms like mules, sterile worker bees, infertile human couples do

not reproduce. Therefore, reproduction is not an all-inclusive characteristic of living

organism. However, no nonliving object has the power to reproduce or replicate.

c) Metabolism- The sum total of all types of chemical reactions occurring in an individual due to

specific interactions amongst different types of molecules in the interior of cells is called

metabolism. All activities of an organism including growth, movements, development,

reproduction etc. are due to metabolism.There are two types ofmetabolism- Catabolism and

Anabolism. Anabolism includes all the building up reactions to increase the mass of the

organism like photosynthesis. In catabolism breakdown reactions are involved, such as

respiration, digestion etc. no nonliving object show metabolism.An isolated metabolic

reaction(s) outside the body of an organism, performed in a test tube is neither living nor

non-living. Hence, while metabolism is a defining feature of all living organisms without

exception, isolated metabolic reactions in vitro are not living things but surely living

reactions. Hence, cellular organisation of the body is the defining feature of life forms.

d) Response to stimuli- It is the awareness of the surroundings and responding to external

stimuli. External stimuli may be physical, chemical or biological. Plants also responds to

stimuli like light, water, gravitation, pollution etc. All living organisms prokaryotic to

eukaryotic responds to different kinds of stimuli. Human being is only organism who is aware

of himself. Consciousness therefore, becomes the defining property of living organisms.

Biodiversity: is the variability among living organisms from all sources, including terrestrial, marine,

and other aquatic ecosystems and the ecological complexes of which they are part; this includes

diversity within species, between species, and of ecosystems.

Rangeof organisms present on earth (1.7 – 1.8 million)

Identification: Comparing similarities and differences with already known ones.

Nomenclature: Naming of organisms. The names are unique and universal.

Rules for nomenclature are provided by;

a) ICBN – International Code for Botanical Nomenclature
b) ICZN – International Code for Zoological Nomenclature

Binomial Nomenclature:

Carolous Linnaeus – Father of Taxonomy

Name with two parts: – Generic name (Genus) & Specific epithet (Species)

Guidelines and Principles for Nomenclature:

a) It should be in Latin / derived from Latin.
b) If it is written in Italics when types and underlined when handwritten.
c) It contains two parts, first word is Genus ; second word is Species.
d) Genus name starts with Capital while species name starts with small letters.
e) Name should be short, precise & easy to pronounce.
f) Name of the author is written is an abbreviated form after the species name. Ex.

MangiferaindicaLinn.

Example:

Mangiferaindica( Mango)

Homo sapiens ( Human)

Pantherapardus (Leopard)

Felisdomestica(Cat)

Classification – It is the process by which anything is grouped into convenient categories based on

some easily observable characteristics. Classification makes the study of organisms convenient..

(Category –taxa ).

Taxonomy – The process of classification on the basis of external and internal structure along with

internal structure of cell, development process and ecological information is known as taxonomy.

Systematics–

Different kinds of organisms and their relationships Linnaeus SystemaNaturae(evaolutionaryrelationships among organisms).

Taxonomical Hierarchy– Similarities decreases/ Differencesincreases.

Species -Species are the natural population of individuals or a group of population which

resemble one another in all essential morphological and reproductive characters so that they

are able to interbreed freely and produce fertile offspring.

Ex. – Pantheraleo, Pantherapardus, Pantheratigris.

1. Genus-it is a group of related species which resemble one another in certain correlatedcharacters. All species of genus presumed to have evolved from a common ancestor. Lion,Tiger, Leopard are closely related species and placed in same genusEx. – Panther.Panthera (Lion,Leopad,Tiger )
  1. Family- is a taxonomic category which contains one or more related genera. All genera of a
  family have some common features or correlated characters. Family Solanacaeae contains a
  
  number of genera like Solanum, Withania, Daturaetc
  
  Ex.-Panthera and Felis together into Felidae
  1. Order – This category includes one or more related families. Families felidae and canidae are
  included in same order carnivore ,Felidae (cat family) , Canidae(dog family) – Carnivora
  1. Class – A class is made of one or more related orders. Carnivora(tiger, cat, dog), Primates
  (monkeys )- Mammalian
  1. Phylum/Division – The term phylum is used for animals while division is used for plants
  Pisces, Amphibian, Reptilian, Aves& Mammals
  1. Kingdom – It is the highest taxonomic category. All plants are included in the kingdom
  Plantae while all animals belong to kingdom AnimaliaPlantae, Animalia.