Gymnosperm:- Gymnosperm means naked seed. The word 'gymnosperm' is derived from Greek words- 'gymnos', means naked and 'sperma' means seed. Gymnosperm are those seed plants in which the ovules are not enclosed in ovary and the pollen typically germinate on the surface of the surface of the ovule. The term 'gymnosperm' was introduced by Theophrastus in 300 B.C. General character s of gymnosperms :- All gymnosperm are perennial, none of them are herbs or annual. Double fertilization is absent. Pollination is of anemophilous type. Leaves are provided with thick cuticularised epidermis with waxy coating and sunken stomata. Vessel, xylem fibres and companion cells are absent in vascular tissue. Occurrence of transfusion tissue in the leaves. Ovules are not enclosed in an ovary. The reproductive organs are arranged in form of compact structures known as cones. The cones are Unisexual. Male cones are usually small an...
What is DNA? These instructions are found inside every cell and are passed down from parents to their children. It is a nucleic acid and is one of the four major types of macromolecules that are known to be essential for all forms of life. DNA is found in the nucleus, with a small amount of DNA also present in mitochondria in the eukaryotes. Structure of DNA The genetic material in most organisms is DNA or Deoxyribonucleic acid; whereas in some viruses, it is RNA or Ribonucleic acid. A DNA molecule consists of two polynucleotide chains i.e. chains with multiple nucleotides. Let’s understand the structure of this chain in detail. DNA and Its occurence:- The DNA molecule is composed of units called nucleotides, and each nucleotide is composed of three different components, such as sugar, phosphate groups, and nitrogen bases. Structure Of Polynucleotide Chain A nucleotide is made of the following components: Pentose sugar – A pentose sugar is a 5-carbon sugar. In c...