Cells as the basic units of

The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.

The nucleolus is a structure within the nucleus responsible for ribosome synthesis. It assembles ribosomal RNA (rRNA) and proteins to form ribosomal subunits.

Rough ER contains ribosomes and is involved in protein synthesis and modification. Smooth ER lacks ribosomes and is involved in lipid synthesis, carbohydrate metabolism, and detoxification.

The Golgi body is a stack of flattened membrane-bound sacs called cisternae. It modifies, sorts, and packages proteins and lipids synthesized in the ER for transport to other organelles or secretion.

Mitochondria have a double membrane; the inner membrane is folded into cristae. They contain their own circular DNA, encoding some mitochondrial proteins, which supports the endosymbiotic theory.

Ribosomes are responsible for protein synthesis (translation). 80S ribosomes are found in the cytoplasm of eukaryotic cells, while 70S ribosomes are found in prokaryotes, chloroplasts, and mitochondria.

Lysosomes contain hydrolytic enzymes. They break down cellular waste, debris, and foreign materials through phagocytosis and autophagy, playing a crucial role in intracellular digestion.

Centrioles organize microtubules, forming the spindle fibers during cell division. Microtubules provide structural support, facilitate intracellular transport, and form cilia and flagella.

Chloroplasts are organelles in plant cells responsible for photosynthesis, containing chlorophyll. Their circular DNA encodes some of the proteins needed for their function, also supporting the endosymbiotic theory.

Plasmodesmata are channels that cross plant cell walls, connecting the cytoplasm of adjacent cells. They allow for the transport of water, nutrients, and signaling molecules between cells.

ATP (adenosine triphosphate) provides energy for cellular processes. It releases energy through hydrolysis, driving energy-requiring reactions such as muscle contraction and active transport.

Viruses are non-cellular structures consisting of a nucleic acid core (DNA or RNA) surrounded by a capsid made of protein. Some viruses also have an outer envelope made of phospholipids.

Viruses contain either DNA or RNA as their genetic material. This nucleic acid is enclosed within a protein capsid.

Plant cells contain chloroplasts, a cell wall (composed of cellulose), and a large central vacuole, which are not found in animal cells.

Bacterial cell walls are primarily composed of peptidoglycan, a polymer consisting of sugars and amino acids. This provides structural support and protection for the cell.