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
Phylum- Porifera Introduction:- About 5,000 species of sponges are known. Members of this phylum are commonly known as sponges. They are also known as ‘pore bearers’ as their body walls possess numerous tiny pores. Phylum- Porifera General Characteristic features:- (1) Habitat:- All sponges are aquatic. Most of them are marine but a few sponges live … Read more
kidneys In humans, the excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a uretha. Shape and Size of Kidneys:- Kidneys are reddish brown, bean-shaped structures situated between the levels of last thoracic and third lumber vertebra close to the dorsal inner wall of the abdominal cavity. Each … Read more
mitosis Mitosis was first observed by Strasburger in the plant cell and by Walter Flemming in animal cell Theterm mitosis was given by Walter Flemming in 1882. Definition:- Mitosis is a process in which a parent cell divides into two indentical daughter cells. These cells are indentical to each other as well as to the … Read more