Messenger substances, also known as signaling molecules, work by binding to specific receptors on target cells. This binding triggers a series of biochemical reactions within the cell, leading to a specific response. This response can include changes in gene expression, alterations in cell metabolism, or activation of signaling pathways. Ultimately, messenger substances play a crucial role in coordinating communication between different cells and tissues in the body, allowing for proper physiological functions and responses to various stimuli. **

Ion substances are compounds made up of positively and negatively charged ions, such as sodium chloride (NaCl) or calcium carbonate (CaCO3). These substances are held together by electrostatic forces between the ions. Molecule substances, on the other hand, are made up of covalently bonded atoms, such as water (H2O) or carbon dioxide (CO2). These substances are held together by sharing electrons between the atoms. In summary, ion substances are composed of charged ions held together by electrostatic forces, while molecule substances are composed of covalently bonded atoms held together by shared electrons. **

Substances that can be identified under black light include certain bodily fluids like urine, semen, and saliva due to their fluorescent properties. Additionally, certain minerals such as calcite, fluorite, and certain types of paint or dyes can also be detected under black light. Some insects and marine animals also have fluorescent properties that can be seen under black light. **

Substances that can be identified under ultraviolet light include minerals, certain chemicals, bodily fluids (such as blood or urine), and some organic compounds. This is because these substances either naturally fluoresce or have been treated with fluorescent dyes that react to ultraviolet light. By exposing these substances to ultraviolet light, they emit visible light of different colors, allowing for their identification and analysis. **

Elemental substances belong to the group of pure substances, which are made up of only one type of atom. These elemental substances are the building blocks of all matter and cannot be broken down into simpler substances by chemical means. Examples of elemental substances include hydrogen, oxygen, carbon, and gold. **

Elementary substances belong to the category of pure chemical elements. These are the basic building blocks of matter and cannot be broken down into simpler substances by ordinary chemical reactions. Examples of elementary substances include hydrogen, oxygen, carbon, and iron. Each element is defined by its unique atomic structure and properties. **

Polar substances dissolve in polar substances because they have similar intermolecular forces. Polar substances, such as water, have a partial positive and partial negative charge, which allows them to form hydrogen bonds with other polar molecules. When a polar substance is added to a polar solvent, the partial charges on the solvent molecules attract and surround the solute molecules, causing them to separate and disperse evenly throughout the solvent. This allows the polar solute to dissolve in the polar solvent, forming a homogeneous mixture. **

Yes, organic substances can split and combine with other substances through chemical reactions. For example, organic compounds can undergo processes such as hydrolysis, where they split into smaller molecules by reacting with water. Additionally, organic substances can also combine with other substances through synthesis reactions, where new organic compounds are formed by combining smaller molecules. These chemical reactions are fundamental to the behavior and properties of organic substances in living organisms and in the environment. **