bioneethub.in Establishment of sex through differential development in an early stage of life is called sex determination. Sex of human beings and insects like grasshopper, firefly, Drosophila etc. is determined genetically. Chromosomal basis of sex determination:- The foundation of this type was laid down by Henking (18999). He traced a specific nuclear structure all through spermatogenesis … Read more
The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events from one menstruation till next is called the menstrual … Read more
In flowering plants, male and female gametes are non-motile, therefore, they have to be brought together for fertilization. The transfer of pollen grains to stigma is called pollination. Pollination types:- Depending on the source of pollen, pollination is of three types:- Autogamy:- The transfer of pollen grain from the anther to the stigma of the … Read more
gametogenesis In testis, the immature male germ cells, spermatogonia produce sperms by a process called spermatogenesis that begins at puberty. Spermatogenesis occurs in four stages:- (i) Spermatocytogenesis:- In spermatocytogenesis, the spermatogonia present on the inside wall of the seminiferous tubules multiply by mitotic division and increase in numbers. Each spermatogonia is diploid containing 46 chromosomes. … Read more
These are the group pigments molecules which take part in the conversion of light energy into the chemical energy. The photosynthetic units are called Photosystem I (PS-I) and Photosystem II (PS-II). Each unit has a reaction centre of a specific chlorophyll a molecule which absorbs light energy of long wavelength. These centre can release electron … Read more
Echinodermata literally means ‘spiny or prickly skinned’ (greek, echinos –spiny, derma-skin). They possess an endoskeleton (internal skeleton) of calcareous ossicles (small bones), embedded in skin. Similarities with chordates:- (i) They have tube within tube type of body plan which has envolved along deuterostomic evolutionary line. (ii) They possess a true coelom called enterocoelom. (iii) They … Read more
Root are cylindrical, underground and non-green part develop from radical. They lack nodes, leaves, buds but give rise to endogenous lateral branches. Exceptions- Root of sweet potato and Dalbergia bear buds. Root move in the direction of gravity ( positive geotropism) and against the direction of light (negative photosyntropism). The main root and its lateral … Read more
human beings, the digestive system consists of alimentary canal and the associated glands (these glands help in digestion of food). Alimentary canal:– It start with mouth and opens outside through the anus. The mouth leads to the buccal cavity or oral cavity. The oral cavity has a number of teeth and muscular tongue. Teeth:- Majority … Read more
The animals of this phylum have a dorso-ventrally flatted body. Their upper (dorsal) and lower (ventral) body surfaces are flat and that’s why they are commonly called flatworm. General characteristic Features of platyhelminthes:- (1) Habit and habitat:- These are mostly endoparasites as they live inside the body of other animals (called hosts); some flatworms are … Read more
A leaf is a lateral, generally flattened structure borne on stem. It developed at the node and bears a bud in axil. It originates from the shoot apical meristem and arranged in an acropetal order of the stem. Leaves are the most important vegetative organ for photosynthesis and transpiration. Parts of a Leaf A typical … Read more