Earth Science: Biology – Evolution – Cells
“Every cell comes from another cell,” physician Rudolf Virchow observed as early as 1855. Biologists refer to cells as the “building blocks of life,” since all living things, including animals, plants, and fungi, are made up of cells.
A single cell can even form a complete unicellular organism.
Earth Science: Biology – Evolution – Cell Organelles
Within eukaryotic cells, special structures called organelles provide an effective labor division. Suspended within a thick fluid called the cytosol, they form the cytoplasm, which surrounds the cell’s nucleus.
The cell’s complex construction becomes visible under a high-powered microscope. Every cell is protected by a plasma membrane. It consists of a double layer of lipid molecules, in which proteins are embedded. Some of these proteins help transport substances in and out of the cell. Receptors on the outside of the membrane recognize transport or signal substances approaching the cell. Within the cell’s cytoplasm, biological membranes create separate compartments for various metabolic reactions.
The cell’s large nucleus serves as its command center. It contains the chromosomes, whose DNA (deoxyribonucleic acid) carries the necessary genetic information for the cell’s maintenance and reproduction. The exchange of substances between the nucleus and cytoplasm occurs through pores in the nuclear membrane. The capsule-shaped ribosomes translate instructions provided by the DNA for the construction of proteins.
Various membrane systems, such as the rough and smooth endoplasmic reticulum, produce fats or process membrane proteins. The Golgi apparatus, in contrast, marks and activates proteins. Furthermore, it organizes membrane components such as lipids and transports these to the cell membrane. Lysosomes that contain digestive enzymes, are also created by the Golgi apparatus.
Buildup and breakdown
Animal cells derive their energy from the breakdown of food. This takes place in the mitochondria. Cells with very high levels of metabolic activity, have a correspondingly larger number of mitochondria. Plant cells can use sunlight to produce nutrients with the aid of chloroplasts.
Within the cell, mitochondria and plastids, such as chloroplasts, have their own genetic material and reproduce through cell division. The cellular metabolism accumulates waste products, which can become toxic. Saclike peroxisomes and lysosomes absorb these substances, thus purifying the cytoplasm.
PROKARYOTES AND EUKARYOTES
The presence of specialized compartments within cells is a characteristic of eukaryotes. Prokaryotes. on the other hand, are microorganisms with a less differentiated cell structure.
Their genetic material is not contained in a true nucleus surrounded by a nuclear membrane; instead it floats freely within the cytoplasm, usually as ring-shaped strands of DNA. Prokaryotes lack other typical organelles such as plastids. mitochondria, and Golgi bodies. However, an outer cell membrane is common to both cell types.