On the basis of origin, antigens are classified into exogenous antigens and endogenous antigens.
The antigens which enter the host from the outside in the form of microorganisms, pollens, drugs, or pollutants are called exogenous antigens. The antigens which are formed within the individual are endogenous antigens. The best examples are blood group antigens.

The organisms which possess the characters of two different groups (transitional stage) are called connecting links.
Eg: Peripatus (connecting link between Annelida and Arthropoda), Archeopteryx (connecting link between Reptiles and Aves).

GIFT - Gamete Intra-Fallopian Transfer
(i) Transfer of an ovum collected from a donor into the fallopian tube. In this the eggs are collected from the ovaries and placed with the sperms in one of the fallopian tubes.
(ii) The zygote travels toward the uterus and gets implanted in the inner lining of the uterus.

When the insects ingest the toxin crystals their alkaline digestive tract denatures the insoluble crystals making them soluble. The cry toxin then gets inserted into the gut cell membrane and paralyzes the digestive tract. The insect then stops eating and starves to death.

(i) Throughout pregnancy the uterus undergoes periodic episodes of weak and strong contractions.
(ii) These contractions called Braxter-Hick's contractions lead to false labour.

The 5' end of the mRNA of prokaryotes has a special sequence which precedes the initial AUG start codon of mRNA. This ribosome binding site is called the Shine - Dalgamo equence or S-D sequence.

Organisms have three phases in its life cycle.
(i) Juvenile phase/ vegetative phase is the period of growth between the birth of the individual upto reproductive maturity.
(ii) Reproductive phase/maturity phase the organisms reproduce and their offsprings reach maturity period.
(iii) Senescent phase begins at the end of reproductive phase when degeneration sets in the structure and functioning of the body.

Certain characters are controlled by non - nucleas genomes found in chloroplast, Mitochondria, infective agents and plasmids, and do not reveal Mendelian pattern of Inheritance. This is called as extra chromosomal inheritance. They exhibit maternal influence in their pattern of inheritance. Eg. Inheritance of the shell coiling pattern in fresh water snail Limnaea peregra.

S.No	Humoral Immunity	Cell mediated immunity
i.	When Pathogens are destroyed by the production of antibodies, it is known as antibody mediated or hurmoral immunity.	When Pathogens are destroyed by cells without producing antibodies it is known as cell mediated immunity.
ii.	This is brought about by B cells with the aid of antigen presenting cells and T helper cells.	This is brought about by T cells, macrophages and natural killer cells

Curcumin extracted from turmeric - yellow colour - good anti oxidant fight against cancer - anti inflammatory, anti diabetic, anti bacterial, antifungal and anti viral activities - stops platelets from clotting.

(i) They help for detailed floristic and faunistic studies
(ii) These groves provide a number of ecosystem services to the neighborhood like protecting watershed, fodder, medicinal plants and microclimate control

Co-evolution: The interaction between organisms, when continues for generations, involves reciprocal changes in genetic and morphological characters of both organisms. This type of evolution is called co-evolution. It is a kind of co-adaptation and mutual change among interactive species.

No.	Tundra Biome	Taiga Biomes
1.	This is almost treeless plain in the northern parts of Asia, Europe, and North America.	Taiga is a forest of coniferous trees such as spruce, fir and pine.
2.	Winters are long with little daylight, summers are short, with long daylight hours.	Summer temperature ranges from 10octo 21oPc.
3.	Because of the severe winters, many of the animals are migratory. For E g: the many shore birds and water fowl such as ducks and geese, nest in the Tundra during the summer and migrate south for the winter.	Important migratory herbivores include moose, elk, deer and reindeer. Moose and reindeer migrate to the Taiga for winter and to Tundra for summers.

(a) Eutrophication:
1. Eutrophication is defined as the process of nutrient enrichment of water and consequent loss of species diversity in water bodies.
2. Increased nutrient content of the water body causes algal bloom, excess growth of algae, especially planktonic algae.
3. It covers the water surface, secrete toxins and reduces the dissolved oxygen content of water.
4. These toxins inhibit the growth of other algae and plants and cause death of aquatic animals.
5. O₂ deficiency may be a cause for death of animals (BOD).
(b) Algal Bloom:
1. A rapid growth of microscopic algae (or) cyanobacteria in water, often resulting in a coloured scum on the surface.
2. Rapid increase of accumulation in the population of algae in fresh water (or) marine water and is recognized by the discoloration in the water from their pigments.

1. The foreign DNA that is introduced is called the transgene and the animals that are produced by DNA manipulations are called transgenic animals or the genetically engineered or genetically modified organisms.
2. Transgenic animals are also used for producing products useful for mankind. E.g: Transgenic cow (rosie), which produced human protein enriched milk (2.4 g/L).
3. The milk contained the human alpha lactalbumin and was nutritionally a more balanced product for human babies than natural cow's milk.

(i) Development of human society is inevitable. Natural habitats are destroyed for the purpose of settlement, agriculture, mining, Industries and construction of highways
(ii) As a result species are forced to adapt to the changes in the environment or move to other places. If not, they become victim to predation, starvation, disease and eventually die or results in human animal conflict.
(iii) Over population, urbanization, Industrialization and agricultural advancements require additional land, water and raw materials every year.
(iv) This is made possible only through fragmentation or destruction of natural habitats by filling wetlands, ploughing grasslands, cutting down trees, forest, desilting rivers, constructing transport ways, caving mountains, extracting, ores, changing the course of rivers and filling of seashore.

1. Milk is converted into curd with the help of bacteria like Lactobacillus acidophilus Lactobacillus lactis and Streptococcus lactis are commonly called Lactic Acid Bacteria (LAB).
2. The LAB bacteria grow in milk and convert it into curd, thereby digesting the milk protein casein.
3. A small amount of curd added to fresh milk as a starter or inoculum contains millions of Lactobacilli, which under suitable temperature \(\left(\leq 40^{\circ} \mathrm{C}\right)\) multiply and convert milk into curd by fermentation.
4. Curd is more nutritious than milk as it contains a number of organic acids and vitamins.

Cryopreservation (- 195.C)
1. Cryopreservation, also known as Cryo conservation.
2. A process by which protoplasts, cells, tissues, organelles, organs, extracellular matrix, enzymes or any other biological materials are subjected to preservation by cooling to very low temperature of -196^oC using liquid nitrogen.
3. At this extreme low temperature any enzymatic or chemical activity of the biological material will be totally stopped and this leads to preservation of material in dormant status.
4. Later these materials can be activated by bringing to room temperature slowly for any experimental work.
5. Protective agents like dimethyl sulphoxide, glycerol or sucrose are added before cryopreservation Process.
6. These protective agents are called cryoprotectants, since they protect the cells, or tissues from the stress of freezing temperature.

1. Fitness according to Darwin refers ultimately and only to reproductive fitness
2. Those individuals who are better fit in an environment leave more progeny than the others the populations come to posses more fit individuals as nature selects for fitness.
3. The so called fitness is based on characteristics which are inherited hence there must be. genetic basis for getting selected and to evolve.

A - Barrier methods
B - Lactational amenorrhoea
C - Tubectomz
D - CuT

Properties of Vectors:
1. Vectors are able to replicate autonomously to produce multiple copies of them along with their DNA insert in the host cell.
2. It should be small in size and of low molecular weight, less than 10 Kb (kilo base pair) in size so that entry/transfer into host cell is easy.
3. Vector must contain an origin of replication so that it can independently replicate within the host.
4. It should contain a suitable marker such as antibiotic resistance, to permit its detection in transformed host cell.
5. Vector should have unique target sites for integration with DNA insert and should have the ability to integrate with DNA insert it carries into the genome of the host cell. Most of the commonly used cloning vectors have more than one restriction site. These are Multiple Cloning Site (MCS) or polylinker. Presence of MCS facilitates the use of restriction enzyme of choice.

Structural gene	Regulatory gene	operator gene
They are concerned with the transcription of mRNA for the synthesis of particular polypeptide	It controls the functioning of operator gene	It determines the functioning of operator gene
They function only when RNA polymerases join	It produces a repressor or apo- repressor for blocking operator gene	It works only when it is not blocked by repressor
They function by forming mRNA for specific polypeptide	It functions through the formation of mRNA of repressor or apo-repressor	It functions through the presence (or) absence of repressor

Human Ovum
a - Vitelline membrane
b - Nucleus
c - Zona Pellucida
d - Corona radiata

Sex determination in honeybees
sex determination is as follows
1. Haploid sex determination is seen in honeybees, it is based on the number of sets of chromosome, an individual receives.

2. When the ovum is fertilized by a male gamete the zygote (2n = 32) develops into a female i.e., a queen or worker.
3. When the haploid ovum develops by parthenogenesis. i.e., without fertilization, a male individual, called drone is formed as adult male.
4. The male honeybees (drone) is haploid (with n = 16) and forms sperms by mitosis.

(i) "Wuchereria bancrofti".
(ii) Chronic inflammation of the lymph nodes. Obstruction of lymph in the vessels of the lower limb.
(iii) Transmitted through an agent/vector called Female Culex mosquito.

1. Sexual reproduction is considered to be a better mode of reproduction because it creates a hybrid that has more vigor than the parents.
2. It also creates the variation in off springs making its survival better.
3. The fact that most of the eukaryotes reproduce sexually in evidence of its evolutionary success.
4. In many animals, it is actually the only mode of reproduction.

Incomplete Dominance	Co-dominance
When one allele is not completely dominant to another allele.	lt occurs due to simultaneous expression of both alleles in the heterozygote.
E.g: Flowers colour of Mirabilis Jalapa	E.g:  ABO blood group system in human beings.

Endothecium is a single layer of radially elongated cells, The inner tangential wall of this cell develops bands of a cellulose, The cells are hygroscopic. The stomium of anther lobe lack these thickenings. Stomium along with the hygroscopic nature of endothecium helps in the dehiscence of anther

The widely accepted model of DNA recombination during crossing over is Holliday's hybrid DNA model.

Steps involved are:
1. Homologous DNA molecules are paired side by side with their duplicated copies of DNAs
2. One strand of both DNAs cut in one place by the enzyme endonuclease.
3. The cut strands cross and join the homologous strands forming the Holliday structure or Holliday junction.
4. The Holliday junction migrates away from the original site, a process called branch migration, as a result heteroduplex region is formed.
5. DNA strands may cut along through  the vertical (V) line or horizontal (H) line.
6. The vertical cut will result in heteroduplexes with recombinants.
7. The horizontal cut will result in heteroduplex with non recombinants.

Plants \(\rightarrow\) Grasshopper \(\rightarrow\) Frog \(\rightarrow\) Snake \(\rightarrow\) Hawk