Interphase involves a series of changes that prepare a cell for division. It is the period during which the cell experiences growth and DNA replication in an orderly manner. Interphase is divided into three phases.
(i) G1 phase
(ii) S phase
(iii) G2 phase
G1 phase – It is the stage during which the cell grows and prepares its DNA for replication. In this phase, the cell is metabolically active.
S phase – It is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per cell) doubles, but the chromosome number remains the same.
G2 phase – In this phase, the cell continues to grow and prepares itself for division. The proteins and RNA required for mitosis are synthesised during this stage.
Which of the following is not correct?
(a) Robert Brown discovered the cell.
(b) Schleiden and Schwann formulated the cell theory.
(c) Virchow explained that cells are formed from pre-existing cells.
(d) A unicellular organism carries out its life activities within a single cell.
Mention the ploidy of the following:
protonemal cell of a moss;
primary endosperm nucleus in dicot,
leaf cell of a moss;
prothallus cell of a fern;
gemma cell in Marchantia;
meristem cell of monocot,
ovum of a liverwort, and
zygote of a fern.
What is the site of gaseous exchange in an insect?
Briefly describe the structure of the following:
(a) Brain
(b) Eye
(c) Ear