MODEL PAPER 2 — BIOLOGY STD 11 Science — Question

The basic structural organisation of a typical cell is as follows:
i. Nucleus, the central part, and brain of the cell, which is spherical in shape. Its number can be one or more per cell. It is denser than the surrounding cytoplasm. The nucleus is composed of chromosomes (contains the genetic material, i.e., DNA), nuclear membrane and centrioles (non-membrane bound organelle present in only animal cells, which helps in cell division).
ii. Cytoplasm, a semi-fluid matrix that occupies the volume of the cell. It is mainly composed of water with free-floating molecules. Inside the cytoplasm, all cellular activities like a gaseous exchange, elimination of wastes, hereditary mechanisms, etc., occur.
Eukaryotic cells also contain another cell membrane-bound distinct structures called cell organelles, like mitochondria, vacuoles, Endoplasmic Reticulum (ER), Golgi complex, etc.
The prokaryotic cells lack all these membrane-bound organelles. It is to be noted that as ribosomes are not bounded by a membrane and are found in all cells. Ribosomes are also found in chloroplasts (in plants) and mitochondria and on rough ER other than the cytoplasm. Animal cells contain another non-membrane bound organelle called centriole, which helps in cell division.
iii. Outer membrane, the boundary of the cell, which provides protection to the cell and controls the exchange of ions, molecules and other components in and out of the cell. The outer membrane of a cell contains cell wall (only in plant cells) and plasma membrane.