Pairing of homologous chromosomes during zygotene stage of prophase I of meiosis I is called synapsis. Synapsis of three types:
1. Procentric synapsis: Pairing starts from middle of the chromosome.
2. Proterminal synapsis: Pairing starts from the telomeres.
3. Random synapsis: Pairing may start from anywhere.

S. No.	Habitat	Niche
1	A specific physical space occupied by an organism (species).	A functional space occupied by an organism in the same eco-system.
2	Same habitat may be shared by many organisms (species).	A single niche is occupied by a single species.
3	Habitat specificity is exhibited by organism.	Organisms may change their niche with time and season

(a) Anabaena azolla (blue green alga)
(b) Rhizobium
(c) Angiosperm roots

Biosphere Reserve (BR) is an international designation by UNESCO for representative parts of natural and cultural landscapes extending over large area of terrestrial or coastal! marine ecosystems or a combination thereof.

Most abundant gas - CO₂
Effect of CO₂ on the growth of plants
(i) Change in flowering seasons and pollinators
(ii) Change in Species distributional ranges
(iii) Species extinction
(iv) Low agricultural productivity in tropics
(v) Frequent heat waves (Weeds, pests, fungi need warmer temperature)
(vi) Increase of vectors and epidemics
(vii) Strong storms and intense flood damage
(viii) Water crisis and decreased irrigation

(i) Ecological density: It is the size of a population in relation to the numbers per unit of habitat space. (Available area or volume that can be colonized by a population). Eg. 1000 fish in the volume of water in the pond.
(ii) Crude density: It is the size of a population in relation to the numbers per unit of total space. Eg. 1000 fish in a pond.
(iii) Population density: It is usually expressed as the number of individuals per unit area or volume. Eg. 100 trees per acre.

(i) Bacillus thuringiensis is a soil dwelling bacterium which is commonly used as a biopesticide and contains a toxin called cry toxin. Scientists have introduced this toxin producing genes into plants and have raised genetically engineered insect resistant plants. Eg. Bt-cotton.
(ii) 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.

1. Polyspermy: An egg that has been fertilized by more than one sperm
2. When a sperm comes in contact with the zona pellucida layer of the ovum, it induces changes in the membrane of the ovum to block the entry of additional sperms.
3. The prevention of polyspermy ensures that only one sperm can fertilize a single ovum.

The primary endosperm nucleus divides immediately after fertilization. It develops into an endosperm which is a nutritive tissue and a regulatory structure. The zygote divides only after that to form an embryo so that it can get nourishment from the endosperm that has formed earlier.

The German Botanist Carl Correns's (1905) Experiment - In 4 0' clock plant, Mirabilis jalapa when the pure breeding homozygous red (R¹ R¹) parent is crossed with homozygous white (R ²R²), the phenotype of the F₁ hybrid is heterozygous pink (R¹R²). The F₁ heterozygous phenotype differs from both the parental homozygous phenotype. This cross did not exhibit the character of the dominant parent but an intermediate colour pink. When one allele is not completely dominant to another allele it shows incomplete dominance. Such allelic interaction is known as incomplete dominance. F₁ generation produces intermediate phenotype pink coloured flower.
When pink coloured plants of F ₁ generation were interbred in F₂ both phenotypic and genotypic ratios were found to be identical as 1 : 2 : 1(1 red: 2 pink: 1 white). Genotypic ratio is 1 R¹R¹ : 2 R¹R² : 1 R²R². From this we conclude that the alleles themselves remain discrete and unaltered proving the Mendel's Law of Segregation. The phenotypic and genotypic ratios are the same. There is no blending of genes. In the F₂ generation R¹ and R² genes segregate and recombine to produce red, pink and white in the ratio of 1 : 2 : 1. R ¹ allele codes for an enzyme responsible for the formation of red pigment. R² allele codes for defective enzyme. R¹ and R² genotypes produce only enough red pigments to make the flower pink. Two R¹R¹ are needed for producing red flowers. Two R²R² genes are needed for white flowers. If blending had taken place, the original pure traits would not have appeared and all F₂ plants would have pink flowers. It is very clear that Mendel's particulate inheritance takes place in this cross which is confirmed by the reappearance of original phenotype in F₂.

Morphological adaptations:
Root system is extensively developed. These roots may be of two types. They are Clinging roots and Aerial roots.
Clinging roots fix the epiphytes firmly on the surface of the supporting objects.
Aerial roots are green coloured roots which may hang downwardly and absorb moisture from the atmosphere with the help of a spongy tissue called velamen.
1. Stem of some epiphytes are succulent and develop pseudo bulb or tuber.
2. Generally the leaves are lesser in number and may be fleshy and leathery.
3. Myrmecophily is a common occurrence in the epiphytic vegetation to prevent the predators
4. The fruits and seeds are very small and usually dispersed by wind, insects and birds.

Botanical pest repellent and insecticide made with the dried leaves of Azadirachta indica Preparation of Bio-pest repellent
(i) Pluck leaves from the neem tree and chop the leaves finely.
(ii) The chopped up leaves were put in a 50-liter container and fill to half with water; put the lid on and leave it for 3 days to brew.
(iii) Using another container, strain the mixture which has brewed for 3 days to remove the leaves, through fine mesh sieve. The filtrate can be sprayed on the plants to repel pests.
(iv) To make sure that the pest repellent sticks to the plants, add 100 ml of cooking oil and the same amount of soap water. (The role of the soap water is to break down the oil, and the role of the oil is to make it stick to the leaves).
(v) The stewed leaves from the mixture can be used in the compost heap or around the base of the plants.

Afforestation is planting of trees where there was no previous tree coverage and the conversion of non-forested lands into forests by planting suitable trees to retrieve the vegetation. Example: Slopes of dams afforested to reduce water run-off, erosion and siltation. It can also provide a range of environmental services including carbon sequestration, water retention.
The Man who Single handedly Created a Dense Forest
(i) Jadav "Molai" Payeng (born 1963) is an environmental activist has single-handedly planted a forest in the middle of a barren wasteland.
(ii) This Forest Man of India has transformed the world's largest river island, Majuli, located on one of India's major rivers, the Brahmaputra, into a dense forest, home to rhinos, deers, elephants, tigers, and birds.
(iii) And today his forest is larger than CentraI Park.

Type of succession
Hydrosere
(i) The succession in a freshwater ecosystem is also referred to as hydrosere
(ii) Succession in a pond, begins with colonization of the pioneer's like phytoplankton and finally ends with the formation of climax community like forest stage. It includes the following stages
(a) Phytoplankton stage
It is the first stage of succession consisting of the pioneer Community like blue green algae, green algae, diatoms, bacteria, etc.,
The colonization of these organisms enrich the amount of organic matter and nutrients of pond due to their life activities and death.
This favors the development of the next several stages
(b) Submerged plant stage
As the result of death and decomposition of planktons, silt brought from land by rain water, lead to a loose mud formation at the bottom of the pond. Hence, the rooted submerged hydrophytes begin to appear on the new substratum.
Example: Chara, Utricularia, Vallisneria and Hydrilla etc.
The death and decay of these plants will build up the substratum of pond to become shallow. Therefore, this habitat now replaces another group of plants which are of floating type.
(c) Submerged free floating stage
During this stage, the depth of the pond will become almost 2-5 feet
Hence, the rooted hydrophytic plants and with floating large leaves start colonising the pond.
Example: Rooted floating plants like Nelumbo, Nymphaea and Trapa. Some free floating species like Azolla, Lemna, Wolffia and Pistia are also present in this stage.
By death and decomposition of these plants, further the pond becomes more shallow.
Due to this reason, floating plant species is gradually replaced by another species which makes new several stage.
(d) Reed-swamp stage
It is also called an amphibious stage.
During this stage, rooted floating plants are replaced by plants which can live successfully in aquatic as well as aerial environment.
Example: Typha, Phragmites, Sagittaria and Scirpus etc. At the end of this stage, water level is very much reduced, making it unsuitable for the continuous growth of amphibious Plants.
(e) Marsh meadow stage
When the pond becomes swallowed due to decreasing water level
Species of Cyperaceae and Poaceae such as Carex, Iuncus, Cyperus and Eleocharis colonise the area
They form a mat-like vegetation with the help of their much branched root system.
This leads to an absorption and loss of large quantity of water
At the end of this stage, the soil becomes dry and the marshy vegetation disappears gradually and leads to shurb stage
(d) Shrub stage
As the disappearance of marshy vegetation continues, soil becomes dry.
Hence, these areas are now invaded by terrestrial plants like shrubs (Salix and Cornus) and trees (Populus and Alnus).
These plants absorb large quantity of water and make the habitat dry.
Further, the accumulation of humus with a rich flora of microorganisms produce minerals in the soil, ultimately favouring the arrival of new tree species in the area
(e) Forest stage
It is the climax community of hydrosere.
A variety of trees invade the area and develop any one of the diverse type of vegetation.
Example: Temperate mixed forest (Ulmus, Acer and Quercus), Tropical rain forest (Artocarpus and Cinnamomum) and Tropical deciduous forest (Bamboo and Tectona).
In the 7 stages of hydrosere succession, stage 1 is occupied by pioneer community, while the stage 7 is occupied by the climax community. The stages 2 to 6 are occupied by several communities,

Artificial Seed
1. Artificial seeds or synthetic seeds (synseeds) are produced by using embryoids (somatic embryos) obtained through in vitro culture.
2. They may even be derived from single cells from any part of the plant that later divide to form cell mass containing dense cyptoplasm, large nucleus, starch grains, proteins, and oils etc.
3. To prepare the artificial seeds different inert materials are used for coating the somatic embryoids like agrose and sodium alginate.

1. Natural selection can be explained clearly through Industrial melanism.
2. Industrial melanism is classical case of natural selection exhibited by the peppered moth.
Biston Betularia
1. These were available in two colours, white and black. Before industrialization peppered moth both white and black coloured were common in England (Manchester).
2. Pre-industrialization witnessed white coloured background of the wall of buildings hence the white coloured moths escaped from their predators.
3. Post Industrialization the tree trunks become dark due to smoke and soot let out from the lndustries.
4. The black moths camouflaged on the dark bark of the trees and the white moths were easily identified by their predators (birds).
5. Hence the dark coloured moth population was selected and their number increased when compared to the white moths nature offered positive selection pressure to the black coloured moths.
6. The above proof shows that in a population organisms that can adapt will service and produce more progenies resulting in increase in population through natural selection.

(a) The figure 'F' represent ovulation.
Stage of oogenesis - Ovulatory or luteal stage of oogenesis
(b) (i) The ovarian hormone is progesterone which is released during ovulation.
(ii) The pituitary hormones are the follicle-stimulating hormone (FSH) and Luteinizing hormone (LSH) which are released during and ovulation from anterior pituitary gland.
(c) The endometrium of the uterus gets thickened and blood supply to the endometrium increase.
(d) Figure 'C' represents the secondary follicle and figure h represents the degenerating corpus luteum.

Secondary follicle	Corpus luteurn
lt is surrounded by layers of granulosa cells	Absence of granulosa cells
Theca layer is present	Theca layer is absent.

(i) Flower size Generally large
(ii) It small - aggregated to dense in florescence (eg) Asteraceae flower
(iii) Flower colour - brightly coloured
(iv) The adjacent parts of flower may also be brightly coloured (eg) Coloured bracts of Poinsettia, Bougainvillea
(v) Secretions - Scent, nectar
(vi) Flowers - if no secretion of nectar
(vii) Pollen - Consumed as food or used up to build hives
(viii) Production of foul odour - attracts flies and Beetles
(ix) Presence of juicy cells - juice sucked by insects.
(x) The above characteristic features of entomophilous flowers bring about successful pollination by insects.

Methionine - Lysine - Aspartic acid - Glycine

1. methamphetamine
2. Lysergic acid diethylamide (LSD)

SRY - Sex Determining region Y
TDF - Testes Determining Factor

Processed wheat flour, that has little fibre, is called Maida which is used extensively in making parota, naan and bakery products.

When buds are formed on the outer surface of the parent body, it is known as exogenous budding. E.g. Hydra.

The type of barrier that involves macrophages are the
(i) Phagocytic barriers which is a type of innate immunity.
(ii) In this mechanism, specialised cells such as monocytes, Neutrophils and tissue macro phages pha cytose and digest whole microorganisms.

If all producers are removed from ecosystem We tend to face the following hurdles.
(i) The Ecosystem cannot be balanced
(ii) The interlocking pattern of food chain is broken
(iii) The movement of energy transfer among the food chain cannot be established
(iv) As the green plants occupying the first trophic level (T₁) are producers - it affects majority of the food chain

1. It deals with the study of environment in relation to organisms.
2. It can be studied by considering individual organisms, population, community, biome or biosphere and their environment.

1. Avoid sex with unknown partner/multiple partner
2. Use condoms.
3. In case of doubt, consult a doctor for diagnosis and get complete treatment.