Water: Definition, Structure, Chemical Formula, Water Cycle
Water (H₂O) is the most vital biological molecule, making up over 70% of living cells. It has unique properties like high heat capacity, polarity, cohesion, and solvent ability, enabling crucial biological functions such as metabolism, temperature regulation, and nutrient transport.
This Story also Contains
- What is Water?
- Chemical and Physical Properties of Water
- Solvent Properties
- Biological Significance of Water
- Water Cycle and Ecosystem Role
- Importance of Water in Daily Life
- Water Quality and Human Health
- Environmental and Conservation Issues
- Water NEET MCQs (With Answers & Explanations)
What is Water?
Water is the most abundant substance in living systems, making up 70% or more of the weight of most organisms. It plays important roles in ecosystems such as nutrient cycling and providing habitats. Therefore, it is vital for the functioning of cells, regulation of temperature, and as a facilitator of metabolic reactions.
The chemical formula for water is H₂O, a molecular compound consisting of one oxygen and two hydrogen atoms covalently bonded and asymmetrically. The polarity and the bent shape of the water molecule is conceptually significant.
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.
Chemical and Physical Properties of Water
The chemical and physical properties of water are discussed below:
Chemical Properties
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.
pH: It is a measure of how acidic or basic the water is. The most frequently encountered range is 6.5-8.0. Changes in pH may alter the concentration of other substances in water to a more toxic form.
Salinity: It is a measure of the amount of salts in the water. Dissolved ions increase salinity and conductivity. Salt and other substances affect the quality of water.
Hardness: It is a natural characteristic of water which can enhance its consumer acceptability for drinking purposes. The hardness of water is due to calcium and magnesium minerals that are naturally present.
Physical Properties
The physical properties of water are related to the appearance of water. Water exists in three states: the solid state as in ice, the liquid state as water and the gaseous state as steam or vapour.
Temperature: It is a measure of the average energy of water molecules, measured in degree Celsius or degree Fahrenheit. It determines the amount of oxygen that can be dissolved in water, rate of photosynthesis by algae and other aquatic plants and timing of reproduction.
Color: Color of water is primarily a concern of water quality. Colored water gives the appearance of being unfit to drink. Color can be reduced or removed through the use of coagulation, settling and filtration techniques.
Turbidity: It is a measure of light transmitting properties of water and is composed of suspended and colloidal material.
Specific Heat: Water has high specific heat. It is the amount of energy required to change the temperature of a substance. Because it has high specific heat, it can absorb large amounts of heat energy before it begins to get hot.
Cohesion and Adhesion: 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 is known as a universal solvent because of its polarity many compounds can dissolve in water. 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. 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. It maintains the volume of cells and the transport of the substances by osmosis and diffusion through the cell membranes.
Role in Metabolic Reactions
Water acts as a universal solvent. It helps in the biochemical reactions by dissolving reactants and aiding in enzyme activity. It participates directly in many metabolic reactions and helps maintain the proper environment for cellular metabolism.
Osmoregulation and Transport
Water plays a crucial role in osmoregulation i.e. maintaining the balance of fluids and solutes within cells and tissues. It also serves as the main medium for transport of nutrients, gases, hormones, and waste materials in both plants and animals, ensuring smooth physiological functioning.
Role in Plants
Water plays a very crucial role in plants. It is essential for crop production, plant growth, germination of seeds and metabolism. In addition, water enables plants to synthesize nutrients, and even produce oxygen by the process of photosynthesis.
Water Cycle and Ecosystem Role
Water is essential to all organisms and its availability influences the rates of ecosystem processes, particularly primary production and decomposition in terrestrial ecosystems.
Water cycle:
The main processes driving the water cycle are evaporation of water by solar energy, condensation of water vapor into clouds, and precipitation. Transpiration by terrestrial plants also moves significant volumes of water into the atmosphere. Surface and groundwater flow can return water to the oceans, completing the water cycle.
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.
Importance of Water in Daily Life
Water has several important functions in daily life, such as:
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 is used in industries, automobiles and textile production.
Water has a major role in agriculture, irrigation and gardening.
Water is also used to generate hydroelectricity, a renewable type of energy.
Water Quality and Human Health
Water quality depends on the dissolved components in water. Any alteration in water can make it unfit for drinking and cause diseases in humans.
Waterborne Diseases
Waterborne diseases are caused by drinking contaminated water. These diseases are cholera, typhoid, and dysentery 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
The common reasons for water shortage include shortages of rainfall, extraction of water from wells, increased population, and water pollution. 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
Water pollution comes from industrial effluents, agricultural drainage, and sewage disposal classified as waterborne pollution sources.
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.
Water Conservation Strategies
Proper and suitable water usage should therefore be initiated, so that these water sources can be made more readily available in the long run. 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
Global attempts and measures focus on fighting and regulating water scarcity and pollution through cooperation.
Water NEET MCQs (With Answers & Explanations)
Important topics for NEET exam are:
Properties of Water (Chemical and Physical)
Biological Significance
Practice Questions for NEET
Q1. A water molecule can form a maximum of _____ hydrogen bonds
1
2
3
4
Correct answer: 4) 4
Explanation:
Each water molecule (H₂O) can form a maximum of four hydrogen bonds with neighboring water molecules due to its polar nature. The oxygen atom in water has two lone pairs of electrons, each capable of forming a hydrogen bond with a hydrogen atom from another water molecule. Additionally, the two hydrogen atoms in water can individually form hydrogen bonds with the oxygen atoms of adjacent water molecules. This results in a tetrahedral arrangement in ice, where each water molecule is hydrogen-bonded to four others. However, in the liquid state, the hydrogen bonding network is dynamic, with molecules constantly breaking and reforming bonds.
Hence, the correct answer is option 4) 4.
Q2. Water shows surface tension due to
Cohesion
Adhesion
Both
None
Correct answer: 1) Cohesion
Explanation:
Cohesion causes surface tension in water.
The force that attracts water molecules due to hydrogen bonds is called cohesion. A "tight" surface layer is produced at the surface by the higher pull that nearby molecules at the sides and below exert on the water molecules. Water can resist outside forces and form droplets because of this.
Hence, the correct answer is option 1) Cohesion.
Q3. Water molecules are bent-shaped due to
Pulling of electrons by electronegative hydrogen atom
Pulling of electrons by electronegative oxygen atom
Losing of electrons by electronegative oxygen atom
All of these
Correct answer: 2) Pulling of electrons by electronegative oxygen atom
Explanation:
The electronegative oxygen atom pulls electrons causing water molecules to be bent.
Because it is more electronegative than hydrogen oxygen has a stronger attraction for the shared electrons in the O-H bonds. This causes hydrogen to become partially positively charged and oxygen to become partially negatively charged. The water molecule also contains two lone pairs of electrons on its oxygen atom. With a bond angle of roughly 104.5°, the hydrogen atoms are forced closer together by these lone pairs creating a bent (V-shaped) structure.
Hence, the correct answer is option 2)Pulling electrons by electronegative oxygen atom.
Also Read:
Frequently Asked Questions (FAQs)
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.
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.
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.
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.
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.