Water: Definition, Structure, Chemical Formula, Water Cycle, Molecule, & Facts

Water: Definition, Structure, Chemical Formula, Water Cycle

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:56 PM IST

Water is a prerequisite for biology. It is a colourless, without flavour, and unscented natural fluid that forms a portion of every organism. Water is a topic of the chapter Biomolecules in Biology.

What is Water?- H₂O

The physical characteristics of water include high heat capacity, solvent properties, and cohesion are used in biological functions. In ecosystems, it plays such roles as nutrient cycling and providing habitats.

Therefore, it is vital for living organisms as essential for the functions of cells, regulation of temperature, and as a facilitator of metabolic reactions. The chemical formula for water is H₂O it is a molecular compound compounded by one oxygen and two hydrogen atoms covalently bonded and asymmetrically oriented so that the water molecule has a population of two hydrogen atoms and one oxygen atom; the polarity and the bent shape of the water molecule is conceptually significant.

This Story also Contains

What is Water?- H2O
Water Resources
Uses of Water
Chemical and Physical Properties of Water
Biological Significance of Water
Importance of Water:
Water Quality and Human Health
Environmental and Conservation Issues

Water: Definition, Structure, Chemical Formula, Water Cycle

Water Resources

Water can be derived from water resources like surface water like rivers, lakes, and seas; groundwater like aquifers; and atmospheric water like raindrops, sleet, snow, and mist. Another is through desalinated seawater and reclaimed wastewater especially in the arid zones as this is the fastest growing source of water supply.

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Uses of Water

Water is used in industries, automobiles and textile production.
Water is used in agriculture, irrigation and gardening.
Water is used to generate hydroelectricity, a renewable type of energy.

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Chemical and Physical Properties of Water

The chemical and physical properties of water are discussed below:

Chemical Properties of water

Water is a chemical composed of two atoms of hydrogen covalently bonded to an atom of oxygen.

The oxygen atom carries a partial negative while the two hydrogen atoms bear a partial positive charge making it a polar molecule.

Physical Properties of water - H₂O

Water exists in three states: the solid state as in ice, the liquid state as water and the gaseous state as steam or vapour.

Water can hold a lot of heat before it can force its temperature to rise considerably.

Steam is obtained from water which is a liquid hence it will cost a lot of energy to convert water into steam.

Water molecules also have cohesive properties meaning they stick together and have adhesive properties which means they stick to other substances.

It is therefore for the coherent forces at the surface of water to have a strong surface layer.

Solvent Properties

Water also displays polarity which, in addition to dissolving a lot of materials, is a great solvent.

Water is capable of ‘mixing’ or ‘dispersing’ with what is referred to as hydrophilic substances that are water-borne but unable to ‘mix’ or ‘disperse’ with hydrophobic or water-repellent substances.

It is also noteworthy that water most importantly is a solvent of nutrients and their transport and other processes within the cell.

Biological Significance of Water

The biological significance of water is discussed below:

Water in Cells

The cytoplasm mainly consists of water and it holds the salts, proteins, and other molecules that are involved in the different processes of a cell.

Water is one of the reagents in such biochemical transformations as hydrophysis and dehydration synthesis, which are vital for the human body.

It maintains the volume of cells and the transport of the substances by osmosis and diffusion through the cell membranes.

Water Cycle

Water cycle:

It includes a change of states such as evaporation in which water transforms into vapour, condensation in which vapour forms clouds, and precipitation in which water in any of its forms falls back on the surface of the earth.

Freshwater and marine ecosystems:

It also preserves the intensity and frequency of water bodies like rivers and lakes and marine ecosystems by managing salinity and water levels.

Role in plant life

Of course, water plays a very crucial role in plants, enabling them to synthesize nutrients, grow, and even produce oxygen.

Importance of Water:

Water helps with digestion, circulation and regulation of body temperature.
Water plays a vital role in the formation and regulation of weather and climate.
Water is also utilised in transportation of goods across rivers, canals, etc.

Water Quality and Human Health

Read about water quality and human health:

Common Diseases:

These diseases are cholera, typhoid, and dysentery which are diseases which are caused by waterborne pathogens and affect the human body through water.

Prevention And Treatment:

Measures aimed at controlling waterborne diseases include water and sanitation and promotion of correct hygienic practices while treatment includes administration of fluids and antibiotics.

Environmental and Conservation Issues

The environmental issues related to water are listed below

Water Scarcity

Causes:

The common reasons for water shortage include shortages of rainfall, extraction of water from wells, increased population, and water pollution.

Impact on agriculture, industry, and daily life:

This is because scarcity impacts crop production and many industrial processes. The non-availability of clean water for human needs causes economic and social problems.

Water Pollution

Sources:

Water pollution comes from industrial effluents, agricultural drainage, and sewage disposal classified as waterborne pollution sources.

Effects on Ecosystems and Human Health

Contaminated water damages the flow of living organisms in water sources. These pose serious health effects on human beings including waterborne ailments, contact sicknesses, and diseases.

Conservation Strategies

Sustainable usage practices:

Proper and suitable water usage should therefore be initiated, so that these water sources can be made more readily available in the long run.

Water conservation techniques:

Thus methods like harvesting rainwater and usage of drip irrigation aid in preserving water and can bring in more effectiveness in farming.

International efforts and policies:

As a result, global attempts and measures focus on fighting and regulating water scarcity and pollution through cooperation.

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Frequently Asked Questions (FAQs)

1. What are the unique properties of water that make it vital for life?

High specific heat: It refers to the properties of water that make it retain heat within it, this makes water control temperatures inside organisms and the physical vicinity.

Cohesion and adhesion: The water molecules have a tendency to coagulate or ‘stick together’ (cohesion) and with other materials/adhering to them (adhesion) which assists in the transport of nutrients and wastes in the organisms.

Solvent abilities: Water is a good solvent, it dissolves and carries off various substances that are vital to organelle functions.

Existence in different states: Water is in three states; solid, liquid, and gaseous, or ice, liquid water, and water vapor which has an extremely significant function in the promotion of heat balance and sustenance of life of structures in various forms.

2. How does water facilitate biological processes in cells?

Medium for biochemical reactions: It is used in the form of water which forms the solvent in which metabolism can occur within the cells.

Nutrient transport: The research concerning the delivery of dissolved nutrients and molecules is transported through Water.

Maintains cell structure: Water is also involved in making turgor and rigidity for bodily movements and cell construction and basic shape of cells as well

Osmosis: Drinking water is connected to osmosis which can be defined as the uptake of solutes and water in and nearby cells.

3. What are the common waterborne diseases and how can they be prevented?

Diseases: Some of these are cholera, typhoid, dysentery, and giardiasis the manifestations of which include vomiting and diarrhea.

Prevention: Sanitation since sewage impacts water sources and famous usage of clean water and bathing coupled with washing of hands.

4. How does water pollution affect ecosystems and human health?

Ecosystems: Contamination impacts and changes the water bodies and the HAB, eliminates the species’ habitats, and impacts the formation of HAB.

Human health: Consumption of water that has been contaminated leads to waterborne diseases like gastrointestinal diseases and also subjects the body to toxic elements like heavy metals and ailments that are longterm and caused by pollutants.

5. What are the effective methods for conserving water?

Water-saving fixtures flow faucets shower heads and toilets shall be installed to minimize water usage.

Rainwater harvesting: Conduct rainwater harvesting and storing for other water uses in the household such as watering the garden.

Efficient irrigation: Water should be watered through dripping systems, through irrigation systems in rather a smaller proportion.

Awareness and education: Inform local communities and other users of water about the necessity to save water and encourage them to modify their behaviors to decrease water consumption in households, industries, and agriculture.

6. What is the significance of water's cohesive and adhesive properties in plants?

Water's cohesive properties (attraction between water molecules) and adhesive properties (attraction to other substances) are crucial for plants. These properties enable the transport of water and nutrients from roots to leaves through capillary action in the xylem, a process known as transpiration pull.

7. How does water's polarity affect the formation of biological membranes?

Water's polarity influences the arrangement of phospholipids in biological membranes. The hydrophilic (water-loving) heads of phospholipids face the aqueous environments on both sides of the membrane, while the hydrophobic (water-fearing) tails face inward. This arrangement creates a stable bilayer structure that forms the basis of cell membranes.

8. How does water's high specific heat capacity affect living organisms?

Water's high specific heat capacity means it can absorb or release large amounts of heat with relatively small changes in temperature. This property helps organisms maintain stable body temperatures and protects aquatic ecosystems from rapid temperature fluctuations, which is crucial for the survival of many species.

9. What role does water play in maintaining cell structure and function?

Water is vital for maintaining cell structure and function. It provides the medium for cellular reactions, helps maintain cell shape through turgor pressure, and participates in the formation of biological membranes. Water also aids in the transport of nutrients and waste products within and between cells.

10. What is osmosis, and why is it important in living organisms?

Osmosis is the movement of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration. This process is crucial for maintaining water balance in cells, regulating cell volume, and facilitating the absorption of water in plant roots and animal intestines.

11. How does the structure of water contribute to its unique properties?

Water's structure, with its bent shape and uneven distribution of electrons, creates polar molecules. This polarity allows water to form hydrogen bonds between molecules, leading to properties like high surface tension, cohesion, adhesion, and its ability to dissolve many substances. These properties are crucial for biological processes.

12. Why is water called the "universal solvent"?

Water is called the "universal solvent" because it can dissolve more substances than any other liquid. This is due to its polar nature, which allows it to interact with and dissolve both polar and ionic compounds. This property is vital for transporting nutrients and waste in living organisms.

13. How does water's ability to form hydrogen bonds affect its boiling and freezing points?

Hydrogen bonds between water molecules require extra energy to break, resulting in higher boiling and freezing points compared to similar-sized molecules. This property ensures that water remains liquid at temperatures suitable for life processes on Earth, making it essential for the existence and functioning of living organisms.

14. How does water's surface tension affect small organisms?

Water's high surface tension creates a "skin-like" layer on its surface, allowing small organisms like water striders to walk on water. It also helps some plants and animals to float or move through water more easily. This property is crucial for many aquatic and semi-aquatic organisms' survival and locomotion.

15. What is the role of water in protein folding and stability?

Water plays a crucial role in protein folding and stability. It interacts with the hydrophilic regions of proteins, helping to stabilize their three-dimensional structure. The hydrophobic effect, driven by water, causes non-polar amino acids to cluster in the protein's interior, further contributing to the protein's final shape and function.

16. How does water contribute to the weathering of rocks and soil formation?

Water plays a significant role in the weathering of rocks and soil formation through physical and chemical processes. Physical weathering occurs when water freezes and expands in rock cracks, breaking them apart. Chemical weathering happens when water dissolves minerals or reacts with them, altering their composition. These processes are fundamental to the rock cycle and the creation of habitable environments for life.

17. How does the pH of water affect aquatic ecosystems?

The pH of water significantly impacts aquatic ecosystems. Most aquatic organisms have adapted to live within a specific pH range. Changes in water pH can affect the solubility of nutrients and toxic compounds, alter the availability of carbon dioxide for photosynthesis, and directly impact the physiology of aquatic organisms. Maintaining a stable pH is crucial for the health and biodiversity of aquatic environments.

18. What is the role of water in maintaining the Earth's climate?

Water plays a crucial role in Earth's climate system. It absorbs and distributes heat around the planet through ocean currents and atmospheric circulation. Water vapor in the atmosphere acts as a greenhouse gas, trapping heat and contributing to the Earth's overall temperature. The water cycle also influences weather patterns, precipitation, and the distribution of heat and moisture across the globe.

19. How does water's lower density as a solid (ice) impact aquatic ecosystems?

When water freezes, it expands and becomes less dense than liquid water. This causes ice to float, forming an insulating layer on the surface of bodies of water. This phenomenon protects aquatic life below the ice, allowing organisms to survive in cold climates and maintaining ecosystem balance.

20. What is the water cycle, and why is it important for life on Earth?

The water cycle, also known as the hydrologic cycle, is the continuous movement of water within the Earth and atmosphere. It includes processes like evaporation, condensation, precipitation, and runoff. This cycle is crucial for distributing water across the planet, maintaining climate patterns, and supporting life in various ecosystems.

21. What is water and why is it essential for life?

Water is a simple molecule composed of two hydrogen atoms and one oxygen atom (H2O). It is essential for life because it serves as a universal solvent, facilitates chemical reactions, regulates temperature, and is a key component of cellular processes. Without water, life as we know it would not exist.

22. What is the importance of water in digestion and nutrient absorption?

Water is essential for digestion and nutrient absorption. It helps break down food, dissolves nutrients for absorption, and forms the basis of digestive fluids. Water also facilitates the movement of food through the digestive tract and aids in the excretion of waste products.

23. How does water contribute to the process of photosynthesis?

In photosynthesis, water plays a crucial role as a reactant. It is split into hydrogen and oxygen during the light-dependent reactions, providing electrons for the electron transport chain and releasing oxygen as a byproduct. The hydrogen ions produced are used to synthesize ATP and NADPH, which are then used in the Calvin cycle to produce glucose.

24. How does water contribute to thermoregulation in living organisms?

Water helps regulate body temperature through its high specific heat capacity and high heat of vaporization. It can absorb or release large amounts of heat with minimal temperature change, and when it evaporates (as sweat in mammals), it removes significant amounts of heat from the body, helping to cool it down.

25. What is the significance of water's role as a reactant in cellular respiration?

In cellular respiration, water acts as a reactant in the electron transport chain. It serves as the final electron acceptor, combining with oxygen to form water molecules. This process is crucial for the generation of ATP, the energy currency of cells, making water an essential component of energy production in organisms.

26. How does water contribute to the process of seed germination?

Water is essential for seed germination. It triggers the activation of enzymes within the seed, initiating metabolic processes. Water absorption causes the seed to swell and break open the seed coat. It also serves as a medium for the transport of stored nutrients to the growing embryo and helps soften the seed coat to allow the emergence of the radicle (embryonic root) and plumule (embryonic shoot).

27. How does water contribute to the process of wound healing?

Water plays several important roles in wound healing. It provides the moist environment necessary for cell migration and proliferation. Water is also essential for the transport of nutrients and immune cells to the wound site. Additionally, proper hydration helps maintain skin elasticity and promotes the formation of new tissue. Dehydration can significantly impair the wound healing process.

28. How does water contribute to the process of meiosis and sexual reproduction?

Water plays several crucial roles in meiosis and sexual reproduction. It provides the aqueous environment necessary for chromosome movement and cell division. In many organisms, water is also essential for gamete transport and fertilization. In plants, water is vital for pollen tube growth and the movement of sperm cells to the egg.

29. What is the significance of water's role in enzyme function?

Water is crucial for enzyme function in several ways. It provides the medium in which enzymes operate, facilitates the movement of substrates to active sites, and participates directly in many enzymatic reactions. Water also helps maintain the three-dimensional structure of enzymes through hydrogen bonding and hydrophobic interactions, which is essential for their catalytic activity.

30. How does water contribute to the process of plant transpiration?

Water is central to plant transpiration. As water evaporates from leaf surfaces, it creates a negative pressure that pulls water up from the roots through the xylem, a process known as transpiration pull. This mechanism is crucial for the transport of water and dissolved minerals throughout the plant. Transpiration also helps regulate plant temperature and influences gas exchange through stomata.

31. What is the importance of water in maintaining blood pressure and circulation?

Water is a major component of blood and helps maintain blood volume and pressure. Proper hydration ensures efficient circulation, allowing for the transport of nutrients, oxygen, and waste products throughout the body. Water also helps regulate blood viscosity, which is crucial for normal cardiovascular function.

32. What is the importance of water in cellular waste removal?

Water is crucial for cellular waste removal. It serves as the primary component of urine, which carries waste products from cellular metabolism out of the body. In cells, water helps dissolve and transport waste molecules to organelles like lysosomes for breakdown or to the cell membrane for excretion. This process is essential for maintaining cellular health and overall organism function.

33. What is the importance of water in maintaining the pH balance in living organisms?

Water is essential for maintaining pH balance in organisms through its role in buffer systems. It acts as both a proton donor and acceptor, helping to neutralize small changes in pH. Water is also the medium in which buffer systems operate, allowing for the distribution and action of hydrogen ions and buffer molecules throughout the body.

34. What is the role of water in hormone signaling within organisms?

Water serves as the medium for hormone transport within organisms. Hormones, which are often water-soluble, travel through the bloodstream (which is mostly water) to reach their target cells. Additionally, water participates in many hormone-receptor interactions and subsequent cellular responses, making it integral to endocrine system function.

35. What is the significance of water's role in muscle contraction?

Water is essential for muscle contraction. It provides the aqueous environment necessary for the sliding filament mechanism of muscle fibers. Water also participates in the hydrolysis of ATP, which provides the energy for muscle contraction. Additionally, proper hydration is crucial for maintaining muscle elasticity and preventing cramping.

36. How does water's ability to expand when frozen affect soil formation and plant growth?

When water freezes in soil, it expands, creating cracks and spaces. This process, known as frost heaving, helps break down rocks and minerals, contributing to soil formation. While this can be beneficial for soil development, it can also damage plant roots if severe. However, the spaces created can improve soil aeration and water retention, potentially benefiting plant growth when managed properly.

37. How does water contribute to the process of DNA replication?

Water plays several important roles in DNA replication. It provides the medium in which the replication process occurs and participates in the hydrolysis reactions that break the hydrogen bonds between DNA base pairs, allowing the strands to separate. Water also interacts with DNA polymerase and other enzymes involved in replication, helping to maintain their structure and function.

38. How does water contribute to the process of evolution?

Water has played a significant role in evolution. As the medium in which life is thought to have originated, it provided the environment for the first chemical reactions leading to life. Water's properties have shaped the adaptations of organisms, influencing everything from body plans to physiological processes. The presence or absence of water in different environments has been a major selective pressure, driving the evolution of diverse life forms.

39. What is the role of water in maintaining the structure of nucleic acids?

Water is crucial for maintaining the structure of nucleic acids like DNA and RNA. It forms hydrogen bonds with the sugar-phosphate backbone, stabilizing the overall structure. Water molecules also interact with the nitrogenous bases, influencing base pairing and the helical structure of DNA. These interactions are essential for the proper function and stability of genetic material.

40. How does water contribute to the process of cellular differentiation?

Water plays a vital role in cellular differentiation by facilitating the movement and interaction of signaling molecules, transcription factors, and other regulatory proteins. It provides the medium for gene expression and protein synthesis, which are crucial for cell specialization. Water also influences cell shape and volume, which can affect cell fate and function during development.

41. How does water contribute to the process of neural signaling?

Water is crucial for neural signaling in several ways. It forms the bulk of the extracellular and intracellular fluids, providing the medium for ion movement during action potentials. Water is also involved in the formation and maintenance of the myelin sheath, which is essential for rapid signal transmission. Additionally, proper hydration is necessary for optimal neurotransmitter function and synaptic transmission.

42. What is the role of water in the immune system?

Water plays multiple roles in the immune system. It is the primary component of lymph, which transports immune cells throughout the body. Water also facilitates the movement of white blood cells and antibodies to sites of infection. Proper hydration is essential for the production of lymphocytes and other immune cells, as well as for the efficient functioning of mucous membranes, which act as a first line of defense against pathogens.

43. What is the significance of water's role in maintaining blood pH?

Water is crucial in maintaining blood pH through its involvement in buffer systems, particularly the bicarbonate buffer system. It provides the medium for the dissociation of carbonic acid into bicarbonate ions and hydrogen ions. This system helps neutralize small changes in blood pH, which is vital for proper enzyme function, oxygen transport, and overall physiological processes.

44. What is the role of water in maintaining the structure and function of cell organelles?

Water is crucial for maintaining the structure and function of cell organelles. It provides the aqueous environment necessary for biochemical reactions within organelles. Water also helps maintain the shape and integrity of organelles through osmotic pressure. In some organelles, like mitochondria and chloroplasts, water participates directly in energy-producing reactions.

45. How does water contribute to the process of thermoregulation in plants?

Water plays a key role in plant thermoregulation, primarily through transpiration. As water evaporates from leaf surfaces, it absorbs heat, cooling the plant. This process helps plants maintain optimal temperatures for photosynthesis and other metabolic processes. Water's high specific heat capacity also helps buffer plants against rapid temperature changes in their environment.

46. What is the importance of water in the formation and function of biofilms?

Water is essential for biofilm formation and function. It provides the hydrated matrix in which microorganisms embed themselves. This aqueous environment facilitates the movement of nutrients and signaling molecules within the biofilm community. Water also contributes to the structural integrity of the biofilm and helps protect the microorganisms from environmental stresses and antimicrobial agents.

47. How does water contribute to the process of protein synthesis?

Water is crucial for protein synthesis in several ways. It provides the medium for the movement of mRNA, tRNA, and ribosomes. Water molecules participate in the hydrolysis of GTP during translation, providing energy for the process. Additionally, water is involved in the formation of peptide bonds between amino acids and helps in the folding of the newly synthesized protein into its functional three-dimensional structure.

48. What is the role of water in maintaining the flexibility of connective tissues?

Water is essential for maintaining the flexibility and function of connective tissues like cartilage and tendons. It hydrates these tissues, allowing them to maintain their shape and elasticity. In cartilage, water interacts with proteoglycans to create a gel-like substance that provides cushioning and shock absorption. Proper hydration of connective tissues is crucial for joint health and overall mobility.

49. How does water contribute to the process of bacterial conjugation?

Water plays a crucial role in bacterial conjugation, the transfer of genetic material between bacteria. It provides the aqueous medium necessary for bacteria to come into close contact and form the conjugation bridge. Water also facilitates the movement of the plasmid DNA through this bridge from the donor to the recipient cell. The hydration of the cell membranes is essential for the formation and function of the conjugation apparatus.

50. What is the significance of water's role in maintaining the structure of the cell membrane?

Water is crucial for maintaining the structure and function of cell membranes. It interacts with the hydrophilic heads of phospholipids, helping to stabilize the bilayer structure. Water