Life Sciences

This paper answers the question of how cells can achieve differentiation, pointing out that cell differentiation is the result of differential expression of genes (also known as sequential expression), that is, different cells or cells of the same species in the same organism only express part of the gene at different time periods, and takes different development stages of the human body as examples for explanation.

This article focuses on the question of "why do somatic cells of the same organism have the same genome?", explaining that all somatic cells of the same organism are produced by the same fertilized egg through mitosis. During mitosis, the chromosomes are copied once and the cells divide once. Therefore, the genomes of daughter cells and parent cells are the same. It also explains that the differences in shape, function, and physiological characteristics of cells with the same genomes are the result of cell differentiation.

This article describes the formation process of sperm and egg. After male puberty, the testicular spermatogonia undergoes 6 mitosis and 1 meiosis to produce sperm cells, and the sperm cells develop into sperm; the oogonia in female embryo becomes primary oocytes, and meiosis after puberty forms secondary oocytes. After fertilization, the number and development of female primary oocytes are also mentioned.

This article explains the reason why sperm and eggs only contain one genome: human somatic cells have two genomes, female cells contain 46 23 pairs of homologous chromosomes, and male cells contain 46 22 pairs of homologous XY; the single genome of germ cells originates from meiosis, which halves the genome, including steps such as chromosome duplication and synapsis.

This article focuses on "Why is the nucleus the 'headquarters' for manipulating cell activities" and points out that the orderly activity of organelles in living cells depends on the nucleus as the core. Enucleated eggs cannot develop, and single cells cannot survive. Most eukaryotic cells contain nuclei, and the life activities of multicellular differentiated cells are all under the unified command of the nucleus.

This article focuses on "a cell is an independent kingdom" and introduces that a cell is composed of a cell membrane, cytoplasm, organelles and nucleus. The cell membrane is similar to a border line to regulate the entry and exit of substances. The mitochondria convert chemical energy into biological energy. The lysosomes clear waste and poisons. The ribosomes synthesize proteins, and each structure and function are clear, confirming that the cell is an independent kingdom with complete functions.

This article focuses on "Are all cells invisible to the human eye?" and points out that Hooke first discovered cells through a microscope. Most of the cells were 10-100 microns in diameter and were invisible to the naked eye; although nerve cells were 1 meter long, they were extremely thin and colorless. It also showed that chicken egg cells, etc. are also difficult to be seen by the naked eye, and egg shells and protein are not components of egg cells.

Discovery and cognitive process of cells

This article focuses on "Who first proposed that cells are the basic unit of organisms?" and introduces the exchange of research on animal and plant cells between German botanist Schleidan and zoologist Schwang in 1838, establishing that cells are biological structures, functions, and reproductive units, forming the cell theory. This theory was listed by Engels as one of the three major discoveries in natural science in the 19th century.

This article introduces the process of continuous adjustment of the biological classification system with the development of cognition: from Linnai's two-boundary classification, to Haeckel's proposal that the protozoa realm should form three realms after the invention of the microscope, to Whitaker's five-boundary theory and Riedel's four-boundary adjustment, there is still controversy in the academic community in the 21st century about whether viruses are independently bounded, reflecting that the classification system is based on scientific understanding of biological evolution.

In the 18th century, Lin Nai and other scholars established a classification ladder centered on realm, phylum, class, order, family, genus, and species, making it clear that species are the basic unit.

This article focuses on the issue of whether mankind will die out, and mentions two serious biological extinction events in history: a large-scale lava explosion in Siberia 250 million years ago caused 95% biological destruction, and a near-Earth asteroid hit the earth 65 million years ago caused the extinction of dinosaurs; It also quoted Princeton University's Gott's calculation based on the Copernican principle, pointing out that there is a 95% probability that humans will become extinct between about 641025 and 97.5 million years ago, and believes that humans can survive for a long time.