Cell Biology and Structure

Peroxisomes are membrane-bound organelles that contain enzymes for oxidation reactions, particularly breaking down fatty acids and detoxifying harmful substances. Unlike mitochondria and chloroplasts, peroxisomes do not contain DNA or ribosomes. They are believed to have evolved from the endoplasmic reticulum and cannot replicate independently - they must be synthesized by the cell. Mitochondria, chloroplasts, and nuclei all contain their own DNA.

In Spirogyra, the nucleus is suspended by cytoplasmic strands that radiate from the central axis to the cell periphery. These delicate strands of cytoplasm provide structural support, holding the nucleus in place within the large vacuolated cell. The chloroplasts are arranged in helical spirals, while the vacuole occupies most of the cell's interior volume.

SO2 primarily affects the entire cell membrane system by dissolving in cellular fluids to form sulfurous acid. This acidic disturbance damages plasma membranes and internal organelle membranes, disrupting membrane integrity, transport processes, and cellular homeostasis. The nucleus, cell wall, and plasmodesmata are not the primary targets.

Interferons (IFNs) are a group of signaling proteins. 

Potassium is required for the activity of enzymes involved in protein synthesis. Thus, protein synthesis in bacteria would suffer due to the deficiency of potassium.

Samples are passed through propylene oxide in the process of embedding. After treating with propylene oxide, samples are infiltrated with an epoxy resin and then embedded directly in water-miscible acrylic resin.

The spindle pole body (SPB) is the microtubule organising centre in yeast cells, functionally equivalent to the centrosome. Unlike the centrosome the SPB does not contain centrioles. The SPB organises the microtubule cytoskeleton, which plays many roles in the cell. It is important for organising the spindle and thus in cell division.

Metachromasis is the phenomenon of certain tissues and cell components showing colour other than their fundamental one, e.g. basic aniline stain.

 Protein synthesis in an animal cell occurs in ribosomes present in cytoplasm as well as in mitochondria.

 The main organelle involved in modification and routing of newly synthesized proteins to their destinations is endoplasmic reticulum.The endoplasmic reticulum serves many general functions, including the folding of protein molecules in sacs called cisternae and the transport of synthesized proteins in vesicles to the Golgi apparatus.

The pyrenoid structures of Spirogyra stores starch.

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.

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.

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.