Cell - Structure and Functions - III

The plasma membrane (cell membrane) has a fluid mosaic structure composed of phospholipids (lipids), embedded proteins, and carbohydrates attached to proteins (glycoproteins) and lipids (glycolipids). These carbohydrates form the glycocalyx on the cell surface and are important for cell recognition.

Mitochondria are organelles that generate most of the cell's ATP supply through cellular respiration (Krebs cycle and electron transport chain). This energy production role has earned them the nickname 'powerhouse of the cell'. They have their own DNA and are thought to have originated from ancient bacteria.

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. Oxygen and carbon dioxide move across the plasma membrane by diffusion - O₂ enters the cell (high outside, low inside) and CO₂ leaves the cell (high inside, low outside). This is the primary mechanism for gaseous exchange.

Amoeba engulfs food through endocytosis, specifically phagocytosis, where the cell membrane extends around the food particle and envelops it. Diffusion and osmosis involve passive movement of molecules, while plasmolysis is water loss from plant cells.

Ribosomes are cellular structures where proteins are synthesized, translating mRNA into amino acid chains. While the nucleus contains DNA and the endoplasmic reticulum has ribosomes attached to it, only ribosomes themselves perform the actual protein synthesis.

 The answer is Cellulose.

Cell theory states that all organisms are composed of cells, the cell is the basic unit of life, and cells arise from pre-existing cells. Option C incorrectly states cells have 'organs' when they have 'organelles' - organs are tissue-level structures in multicellular organisms.

The Golgi apparatus consists of stacked, flattened membrane-bound sacs called cisternae (cisterns). Grana are stacks of thylakoids in chloroplasts, stroma is the fluid in chloroplasts, and vacuoles are storage organelles.

Osmosis is the passive movement of water molecules across a semi-permeable membrane from a region of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration). Diffusion is general molecular movement, endocytosis involves engulfing material, and plasmolysis is plant cell shrinkage due to water loss.

Genes are specific, functional segments of DNA that code for particular proteins or traits. Chromosomes are structures containing DNA and proteins, chromatin is the complex of DNA and proteins, and chromatids are duplicated chromosome copies. Only genes represent functional DNA segments.

The key difference is that RER (Rough Endoplasmic Reticulum) has ribosomes attached to its surface, which is why it appears rough under a microscope. SER (Smooth Endoplasmic Reticulum) lacks ribosomes and has different functions like lipid synthesis. Neither contains DNA.

Amino acids and sugar

The Golgi apparatus functions as the cell's packaging and distribution center - it stores, modifies, packages, and transports proteins and lipids received from the endoplasmic reticulum to their destinations. Protein synthesis occurs at ribosomes, not the Golgi.

RNA, specifically messenger RNA (mRNA), carries genetic information from DNA in the nucleus to ribosomes in the cytoplasm where protein synthesis occurs. DNA remains in the nucleus, the nucleus is the organelle containing DNA, and the nucleolus produces ribosomal RNA.

Muscle cells require tremendous energy (ATP) for contraction, so they contain the highest number of mitochondria among the options. Hair and skin cells have lower energy demands. Mature red blood cells lack mitochondria entirely.

Both bacilli (bacteria) and honey bees (eukaryotes) possess ribosomes for protein synthesis and use DNA as their genetic material that is inherited. While bacteria lack membrane-bound organelles like lysosomes and a defined nuclear membrane, they share ribosomes and DNA-based genetics with all living organisms.

A hen's egg is a single cell that is clearly visible to the naked eye, measuring several centimeters. While some neurons can be very long (giant squid axons can be meters long), they're microscopic in diameter. Option D is false because large eggs like those of birds are definitely visible.

Mycoplasma, bacteria, and cyanobacteria are all prokaryotic organisms - they lack a true nucleus and membrane-bound organelles. Algae and fungi are eukaryotic. Viruses are not considered living organisms and are neither prokaryotic nor eukaryotic. Note: 'cynobacteria' should be spelled 'cyanobacteria'.

Nerve cells (neurons) are post-mitotic, meaning they exit the cell cycle permanently and do not divide after reaching maturity. This is unlike blood cells, muscle cells, and bone cells which can undergo division or regeneration. Neurons remain in G0 phase throughout life.

Cell theory states that all living organisms are composed of cells, and the cell is the basic structural and functional unit of life. This is a fundamental principle - cells arise only from pre-existing cells (not spontaneously), organelles cannot survive independently, and not all cells have cell walls (animal cells lack them).