Inorganic Molecules and Their Roles in Living Systems

Classification of Compounds in Living Organisms

Compounds in living organisms are fundamentally divided into two categories: inorganic molecules and organic molecules. Inorganic molecules are characterized by several distinct properties. They are not produced by living organisms themselves but are instead obtained from the environment. Because they are small in size, they can pass through the cell membrane without the need for digestion. Generally, they do not provide energy; an exception is found in chemosynthetic organisms, which satisfy their energy requirements by oxidizing inorganic substances. These molecules serve as structural components, repair materials, and are typically regulatory. However, it is important to note that certain minerals like lead and mercury are toxic and do not serve a regulatory function.

The Vital Importance and Distribution of Water

Water is the most abundant substance in nature and within the structure of organisms. Its presence is of vital importance. In terms of molecular structure, a water molecule consists of two positively charged hydrogen atoms and one negatively charged oxygen atom ($H_2O$). The distribution of water within the human body varies significantly based on age, gender, and the specific organ or tissue.

At the systemic level, the water ratios in humans are as follows:

• Babies: $75\text{-}78\, \%$
• Adult Men: $60\, \%$
• Adult Women: $50\text{-}55\, \%$
• Elderly: $45\text{-}50\, \%$
• Adult Average: $70\text{-}75\, \%$

At the tissue and organ level, the water content is categorized as follows:

• Brain: $75\text{-}78\, \%$
• Muscles: $70\text{-}75\, \%$
• Blood: $90\, \%$
• Bones: $30\text{-}31\, \%$

Functional Properties of Water: Adhesion, Cohesion, and Solubility

Water exhibits several unique physical and chemical properties that facilitate life. Adhesion is the force of attraction between water molecules and a different surface or molecules. An example of this is water sticking to a glass surface. In plants, both adhesion and cohesion are crucial for transporting water from the roots to the leaves.

Cohesion is the attraction between water molecules themselves. This cohesive force creates surface tension, allowing very light insects to move across the surface of the water without sinking. Additionally, water is an excellent solvent. This property allows plants to absorb minerals and necessary nutrients from the soil. In animals, solubility ensures that metabolic activities occur efficiently and that substances are transported effectively throughout the body.

Thermal Regulation and Physical States of Water

Water has a very high heat capacity, meaning it absorbs and stores heat and does not release it quickly. This is essential for temperature balance on Earth. For instance, the sun heats the world throughout the summer, and while oceans absorb this massive energy, their temperatures only fluctuate by approximately $1\text{-}2$ degrees. Without this high heat capacity, Earth would reach temperatures too high for life in the summer and would quickly freeze in the winter. At a local level, coastal cities like Antalya or İzmir experience very minimal temperature differences between day and night. In contrast, inland steppe regions like Ankara or Konya experience freezing nights following very hot days because they lack the stabilizing effect of large water bodies.

Water also serves a critical role in metabolic waste removal and temperature regulation through processes like sweating. Furthermore, enzymes—the elements that speed up biochemical reactions—require a minimum environment of $15\, \%$ water to function. In environments with less than $15\, \%$ water, enzymes cannot operate, and metabolic activities may cease.

Unlike most substances, water expands when it freezes. Its volume increases while its mass remains constant, making ice less dense than liquid water. Consequently, in lake environments, ice floats to the top. This upper layer of ice acts as a thermal insulator, preventing the extreme cold of the atmosphere from reaching the water below. This ensures that the water beneath the ice remains at a temperature conducive to the survival of aquatic life.

Characteristics and Roles of Minerals

Minerals are inorganic molecules that organisms require but cannot produce themselves. Plants obtain them from the soil, while animals acquire them through food and water. They do not provide energy, but their absence leads to various deficiency diseases. They are found naturally in soil, water, and rocks in different forms and primarily act as regulators within biological systems.

Detailed breakdown of Specific Minerals and Their Functions

The following is an exhaustive list of minerals, their physiological roles, deficiency symptoms, and dietary sources:

• Iron ($Fe$): It is a component of hemoglobin, the substance that gives blood its red color. Deficiency leads to anemia (kansızlık). It is found in spinach and red meat.
• Phosphorus ($P$): It is involved in the structure of bones, teeth, DNA, and ATP. Deficiency causes bone weakness and developmental delay. It is found in meat, milk, and legumes.
• Iodine ($I$): It is part of the structure of the thyroxine hormone produced by the thyroid gland. Deficiency leads to goiter and mental retardation. It is found in seafood.
• Potassium ($K$): It regulates heart rhythm and nerve conduction. Deficiency leads to heart rhythm disorders. It is found in bananas, potatoes, and apricots.
• Sodium ($Na$): It regulates body fluid-electrolyte balance and nerve conduction. Deficiency causes loss of appetite and cramps. It is found in table salt and mineral water.
• Calcium ($Ca$): It contributes to bone and tooth structure and is effective in blood clotting. Deficiency leads to osteoporosis (bone loss). It is found in milk, cheese, and yogurt.
• Magnesium ($Mg$): It regulates enzyme activity, as well as the muscular and nervous systems. Deficiency causes nervous disorders and muscle cramps. It is found in nuts (hazelnuts, almonds) and leafy greens.
• Sulfur ($S$): It is part of the structure of some amino acids. Deficiency causes paleness in the skin and hair. It is found in meat, onion, and garlic.
• Zinc ($Zn$): It is effective on the immune system. Deficiency leads to immune weakness. It is found in seafood and hazelnuts.
• Fluorine ($F$): It protects dental and bone health. Deficiency leads to tooth decay. It is found in seafood.
• Chlorine ($Cl$): It contributes to the formation of stomach acid. Deficiency leads to digestive problems. It is found in table salt.

Summary Checklist for Inorganic Molecules

To distinguish between Water and Minerals based on their properties:

• Digestible: Neither water nor minerals are digested; both are small enough to pass the cell membrane.
• Energy Source: Neither water nor minerals are used as energy sources (excluding chemosynthesis).
• Produced by Living Organisms: Neither are produced by living organisms; they must be taken from the environment.
• Passing Cell Membrane: Both water and minerals pass through the cell membrane directly.
• Structural Component: Both serve as structural components in organisms.
• Regulatory Function: Both play roles in regulating vital activities.

Control Point: Review of Inorganic Knowledge

Based on biochemical definitions and the study guide:

• Cohesion is the attractive force between molecules of the same type.
• Sulfur is the mineral whose deficiency causes wilting in the young leaves of plants.
• Goiter is the disease that appears due to iodine deficiency.
• Adhesion is the attractive force between molecules of different types.
• Magnesium is a mineral found abundantly in green leafy plants and nuts.
• Zinc deficiency leads to a weakened immune system.
• Sodium is the mineral responsible for fluid-electrolyte balance in the body.
• Iron is the mineral responsible for oxygen transport in the blood.
• Calcium is a vital mineral for bone and dental health.
• Potassium deficiency causes irregularity in heartbeats.