Tag: unit of living - cell

• The endoplasmic reticulum is a membrane-bound organelle within the cytoplasm of a cell which is responsible for modifying and packaging of proteins (rough) and also involved in lipid and steroid synthesis (smooth).
• The eukaryotic cell with few endoplasmic reticula is considered to be embryonic cells in the early stages of development, egg cells or resting cells where the above function is not actively performed as in a well-developed cell.
• So, the correct answer is 'All the above'.

• The nucleus is a double membrane-enclosed organelle which contains the genetic information and is known as the controlling centre of the cell.
• The mitochondria is a double-membraned cell organelle, known as the powerhouse of the cell which is present in all eukaryotic cells.
• Plastids are a pigment containing double membrane-bound organelle which is the site of manufacture and storage of chemical compounds.
• So, the correct answer is 'All of the above'.

Euglenoids are unicellular flagellate protists. They are without the cell wall. The body is covered by thin and flexible pellicle which is a protein-rich layer. The pellicle has oblique but parallel stripes called myonemes. The pellicle is composed of fibrous elastic protein, the small amount of lipid and carbohydrates and maintains a definite shape. It is flexible enough to permit temporary changes in the body shape.

Paramecium is a tiny unicellular protozoan which shows the holozoic mode of nutrition. It shows the presence of a large number of cilia on whole body surface. It engulfs food using cilia. During unfavourable condition, it forms cysts. Under the favourable condition, the cyst releases many organisms. It contains contractile vacuole for osmoregulation. Excess water is thrown out through contractile vacuole outside. It uses trichocysts for capturing prey.

The defining characteristic of a eukaryotic cell compared to a prokaryotic cell is the presence of a true, membrane-bound nucleus.

Vacuoles are non-cytoplasmic areas present inside the cytoplasm which are separated from the latter by specific membranes. Vacuoles are believed to be formed by expansion and pinching off from ER. Tonoplast is the covering of the vacuole. It is a selectively permeable membrane. It separates the vacuoles from the cytoplasm.

Eukaryotes are the organisms which have membrane bound cell organelles as well as membrane bound nucleus. All the kingdoms except kingdom monera are eukaryotes. Monera is a kingdom of prokaryotes. It includes the most primitive forms of life which developed from an early stock called progenote. Being the earliest forms of life, monerans are adapted to all types of habitats. Population wise they are the most numerous of all organisms. They are found everywhere, wherever organic matter can be present or can be supported. They have very little morphological differentiation. Archaebacteria and eubacteria are the two major groups of monera.

A eukaryote is the organism with complex features, i.e, it is apart from the prokaryotic cell it has membrane-bound organelles, especially the nucleus, which contains the genetic material enclosed by the nuclear membrane. A eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes (including the endoplasmic reticulum, Golgi apparatus, chloroplasts, and mitochondria).