- 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.
Robert Hooke first observed and named cells in cork. Robert Brown discovered the nucleus. The remaining statements are correct.
(a) Robert Brown discovered the cell.
- a. bacterial fermentation
- b. regeneration of old cells
- c. pre-existing cells
- d. abiotic materials
Virchow stated 'Omnis cellula-e cellula', meaning every cell arises from a pre-existing cell.
(c) pre-existing cells.
Cristae are infoldings of the inner mitochondrial membrane. Golgi cisternae are flattened disc-shaped sacs. Thylakoids are flat membranous sacs present in chloroplast stroma.
(a)-(ii), (b)-(iii), (c)-(i).
- a. Cells of all living organisms have a nucleus.
- b. Both animal and plant cells have a well defined cell wall.
- c. In prokaryotes, there are no membrane bound organelles.
- d. Cells are formed de novo from abiotic materials.
Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles. Animal cells do not have cell walls, and cells arise from pre-existing cells.
(c) In prokaryotes, there are no membrane bound organelles.
Mesosomes occur as vesicles, tubules and lamellae. They help in cell wall formation, DNA replication and distribution to daughter cells, respiration, secretion, increasing plasma membrane surface area and increasing enzymatic content.
A mesosome is an infolding of the plasma membrane in a prokaryotic cell.
Neutral solutes move passively across the membrane from higher to lower concentration. Polar molecules cannot pass freely through the hydrophobic lipid bilayer. They move through facilitated diffusion using carrier/channel proteins or by active transport using energy when movement is against the concentration gradient.
Neutral solutes move by simple diffusion; polar molecules need carrier proteins or active transport.
They occur in bacteria, cyanobacteria, mycoplasma and PPLO. Genetic material is naked and not enclosed by nuclear membrane. They usually have a cell envelope, cytoplasm, 70S ribosomes and often plasmids. Membrane-bound organelles are absent, but mesosomes and inclusion bodies may occur. Bacteria may show shapes such as bacillus, coccus, vibrio and spirillum.
Prokaryotic cells are small cells lacking a membrane-bound nucleus and membrane-bound organelles.
No single cell performs all body functions. Similar cells form tissues, tissues form organs, and organs form organ systems. This specialisation allows efficient performance of functions such as digestion, transport, respiration, excretion, coordination and reproduction.
In multicellular organisms, different cells, tissues and organs perform specialised functions.
All organisms are made of cells and products of cells. A unicellular organism performs all life activities within one cell, while multicellular organisms carry out functions through specialised cells and tissues. Anything less than a complete cell cannot live independently. Therefore, the cell is the smallest unit capable of independent life processes.
The cell is the basic structural and functional unit of all living organisms.
They act as passages for regulated movement of RNA and protein molecules between the nucleus and cytoplasm.
Nuclear pores are openings in the nuclear envelope formed where the two nuclear membranes fuse.
Lysosomes are Golgi-derived vesicles rich in hydrolytic enzymes active at acidic pH. Vacuoles are membrane-bound spaces containing water, sap, excretory products and other materials; plant vacuoles maintain turgor and ion concentration, while contractile vacuoles in Amoeba help osmoregulation.
Lysosomes mainly digest macromolecules, while vacuoles mainly store materials, maintain cell sap and help osmoregulation/excretion.