BIOLOGY 3 Marks Question

Artificial pacemaker: It is an artificial electronic device. It constantly sends a small amount of electrical charge to maintain rhythmicity of the heart. It is implanted in the upper thoracic region subcutaneously having a connection with the heart. It contains a pulse generator having a cell to produce electrical impulse. The lead in the form of a wire transmits the impulse. An electrode is connected to the portion of the heart where the impulse is transmitted.

The process in which the cells or tissues become structurally and functionally different is called differentiation.
In the plant body, all the cells are derived from the single-cell zygote. After division, the zygote undergoes some structural and functional changes, which are collectively called 'differentiation'. Example: In xylem elements, the changes in thickening occurs and perform the function of conduction of water, storage of food, etc.

There are 26 (twenty-six) vertebrae in total in our body. On the basis of location, they are the following:
i. Cervical vertebrae: Found in neck region; 7 in number.
ii. Thoracic vertebrae: Found in thoracic region; 12 in number.
iii. Lumbar vertebrae: Present in abdominal region; 5 in number.
iv. Sacrum: In the lowermost region of the vertebral column; 2 fused bones.
v. Coccyx: Lies Oat end of the vertebral column; vestigial tail bone.

For nucleic acids, the building block is a nucleotide. A nucleotide has three chemically distinct components. One is a heterocyclic compound, the second is a monosaccharide and the third is phosphoric acid or phosphate.
The heterocyclic compounds in nucleic acids are the nitrogenous bases named adenine, guanine, uracil, cytosine, and thymine. Adenine and guanine are substituted purines while the rest are substituted pyrimidines.
The skeletal heterocyclic ring is called as purine and pyrimidine, respectively. The sugar found in polynucleotides is either ribose (a monosaccharide pentose) or 2' deoxyribose. A nucleic acid containing deoxyribose is called deoxyribonucleic acid (DNA), while that which contains ribose is called ribonucleic acid (RNA).

Cycas is called living fossil since it has many characters of extinct pteridophytes and cycads. Cycads have fern-like foliage, leaf bases persistent; secondary growth occurs; dioecious plants have micro and megasporophylls on separate plants; sporophylls aggregated to form cones (strobila) (the exception is megasporophyll of Cycas), sperms are motile, plants are xerophytic found in warm weather. Cycads are grown for ornamental appeal.