importance of water a level biology essay

Importance of Water

Function of water.

Water is a major component of cells and makes up 60-70% of the human body. Life evolved in an environment where water was abundant. It has several properties that are important in biology.

Importance of water

• As a reactant in cells (e.g. photosynthesis, hydrolysis).
• Provides structural support in cells.
• Keeps organisms cool to maintain an optimum body temperature.

Properties of water

• Metabolic importance.
• High heat capacity.
• Heat of vaporization.
• Cohesive properties.
• Useful as a solvent.

1 Biological Molecules

1.1 Monomers & Polymers

1.1.1 Monomers & Polymers

1.1.2 Condensation & Hydrolysis Reactions

1.2 Carbohydrates

1.2.1 Structure of Carbohydrates

1.2.2 Types of Polysaccharides

1.2.3 End of Topic Test - Monomers, Polymers and Carbs

1.2.4 Exam-Style Question - Carbohydrates

1.2.5 A-A* (AO3/4) - Carbohydrates

1.3.1 Triglycerides & Phospholipids

1.3.2 Types of Fatty Acids

1.3.3 Testing for Lipids

1.3.4 Exam-Style Question - Fats

1.3.5 A-A* (AO3/4) - Lipids

1.4 Proteins

1.4.1 The Peptide Chain

1.4.2 Investigating Proteins

1.4.3 Primary & Secondary Protein Structure

1.4.4 Tertiary & Quaternary Protein Structure

1.4.5 Enzymes

1.4.6 Factors Affecting Enzyme Activity

1.4.7 Enzyme-Controlled Reactions

1.4.8 End of Topic Test - Lipids & Proteins

1.4.9 A-A* (AO3/4) - Enzymes

1.4.10 A-A* (AO3/4) - Proteins

1.5 Nucleic Acids

1.5.1 DNA & RNA

1.5.2 Nucleotides

1.5.3 Polynucleotides

1.5.4 DNA Replication

1.5.5 Exam-Style Question - Nucleic Acids

1.5.6 A-A* (AO3/4) - Nucleic Acids

1.6.1 Structure of ATP

1.6.2 Hydrolysis of ATP

1.6.3 Resynthesis of ATP

1.6.4 End of Topic Test - Nucleic Acids & ATP

1.7.1 Importance of Water

1.7.2 Structure of Water

1.7.3 Properties of Water

1.7.4 A-A* (AO3/4) - Water

1.8 Inorganic Ions

1.8.1 Inorganic Ions

1.8.2 End of Topic Test - Water & Inorganic Ions

2.1 Cell Structure

2.1.1 Introduction to Cells

2.1.2 Eukaryotic Cells & Organelles

2.1.3 Eukaryotic Cells & Organelles 2

2.1.4 Prokaryotes

2.1.5 A-A* (AO3/4) - Organelles

2.1.6 Methods of Studying Cells

2.1.7 Microscopes

2.1.8 End of Topic Test - Cell Structure

2.1.9 Exam-Style Question - Cells

2.1.10 A-A* (AO3/4) - Cells

2.2 Mitosis & Cancer

2.2.1 Mitosis

2.2.2 Stages of Mitosis

2.2.3 Investigating Mitosis

2.2.4 Cancer

2.2.5 A-A* (AO3/4) - The Cell Cycle

2.3 Transport Across Cell Membrane

2.3.1 Cell Membrane Structure

2.3.2 A-A* (AO3/4) - Membrane Structure

2.3.3 Diffusion

2.3.4 Osmosis

2.3.5 Active Transport

2.3.6 End of Topic Test - Mitosis, Cancer & Transport

2.3.7 Exam-Style Question - Membranes

2.3.8 A-A* (AO3/4) - Membranes & Transport

2.3.9 A-A*- Mitosis, Cancer & Transport

2.4 Cell Recognition & the Immune System

2.4.1 Immune System

2.4.2 Phagocytosis

2.4.3 T Lymphocytes

2.4.4 B Lymphocytes

2.4.5 Antibodies

2.4.6 Primary & Secondary Response

2.4.7 Vaccines

2.4.9 Ethical Issues

2.4.10 End of Topic Test - Immune System

2.4.11 Exam-Style Question - Immune System

2.4.12 A-A* (AO3/4) - Immune System

3 Substance Exchange

3.1 Surface Area to Volume Ratio

3.1.1 Size & Surface Area

3.1.2 A-A* (AO3/4) - Cell Size

3.2 Gas Exchange

3.2.1 Single-Celled Organisms

3.2.2 Multicellular Organisms

3.2.3 Control of Water Loss

3.2.4 Human Gas Exchange

3.2.5 Ventilation

3.2.6 Dissection

3.2.7 Measuring Gas Exchange

3.2.8 Lung Disease

3.2.9 Lung Disease Data

3.2.10 End of Topic Test - Gas Exchange

3.2.11 A-A* (AO3/4) - Gas Exchange

3.3 Digestion & Absorption

3.3.1 Overview of Digestion

3.3.2 Digestion in Mammals

3.3.3 Absorption

3.3.4 End of Topic Test - Substance Exchange & Digestion

3.3.5 A-A* (AO3/4) - Substance Ex & Digestion

3.4 Mass Transport

3.4.1 Haemoglobin

3.4.2 Oxygen Transport

3.4.3 The Circulatory System

3.4.4 The Heart

3.4.5 Blood Vessels

3.4.6 Cardiovascular Disease

3.4.7 Heart Dissection

3.4.8 Xylem

3.4.9 Phloem

3.4.10 Investigating Plant Transport

3.4.11 End of Topic Test - Mass Transport

3.4.12 A-A* (AO3/4) - Mass Transport

4 Genetic Information & Variation

4.1 DNA, Genes & Chromosomes

4.1.2 Genes

4.1.3 Non-Coding Genes

4.1.4 The Genetic Code

4.1.5 A-A* (AO3/4) - DNA

4.2 DNA & Protein Synthesis

4.2.1 Protein Synthesis

4.2.2 Transcription & Translation

4.2.3 End of Topic Test - DNA, Genes & Protein Synthesis

4.2.4 Exam-Style Question - Protein Synthesis

4.2.5 A-A* (AO3/4) - Coronavirus Translation

4.2.6 A-A* (AO3/4) - Transcription

4.2.7 A-A* (AO3/4) - Translation

4.3 Mutations & Meiosis

4.3.1 Mutations

4.3.2 Meiosis

4.3.3 A-A* (AO3/4) - Meiosis

4.3.4 Meiosis vs Mitosis

4.3.5 End of Topic Test - Mutations, Meiosis

4.3.6 A-A* (AO3/4) - DNA,Genes, CellDiv & ProtSynth

4.4 Genetic Diversity & Adaptation

4.4.1 Genetic Diversity

4.4.2 Natural Selection

4.4.3 A-A* (AO3/4) - Natural Selection

4.4.4 Adaptations

4.4.5 Investigating Natural Selection

4.4.6 End of Topic Test - Genetic Diversity & Adaptation

4.4.7 A-A* (AO3/4) - Genetic Diversity & Adaptation

4.5 Species & Taxonomy

4.5.1 Courtship Behaviour

4.5.2 Phylogeny

4.5.3 Classification

4.5.4 DNA Technology

4.5.5 A-A* (AO3/4) - Species & Taxonomy

4.6 Biodiversity Within a Community

4.6.1 Biodiversity

4.6.2 Index of diversity

4.6.3 Agriculture

4.6.4 End of Topic Test - Species,Taxonomy& Biodiversity

4.6.5 A-A* (AO3/4) - Species,Taxon&Biodiversity

4.7 Investigating Diversity

4.7.1 Genetic Diversity

4.7.2 Quantitative Investigation

5 Energy Transfers (A2 only)

5.1 Photosynthesis

5.1.1 Overview of Photosynthesis

5.1.2 Photoionisation of Chlorophyll

5.1.3 Production of ATP & Reduced NADP

5.1.4 Cyclic Photophosphorylation

5.1.5 Light-Independent Reaction

5.1.6 A-A* (AO3/4) - Photosynthesis Reactions

5.1.7 Limiting Factors

5.1.8 Photosynthesis Experiments

5.1.9 End of Topic Test - Photosynthesis

5.1.10 A-A* (AO3/4) - Photosynthesis

5.2 Respiration

5.2.1 Overview of Respiration

5.2.2 Anaerobic Respiration

5.2.3 A-A* (AO3/4) - Anaerobic Respiration

5.2.4 The Link Reaction

5.2.5 The Krebs Cycle

5.2.6 Oxidative Phosphorylation

5.2.7 Respiration Experiments

5.2.8 End of Topic Test - Respiration

5.2.9 A-A* (AO3/4) - Respiration

5.3 Energy & Ecosystems

5.3.1 Biomass

5.3.2 Production & Productivity

5.3.3 Agricultural Practices

5.4 Nutrient Cycles

5.4.1 Nitrogen Cycle

5.4.2 Phosphorous Cycle

5.4.3 Fertilisers & Eutrophication

5.4.4 End of Topic Test - Nutrient Cycles

5.4.5 A-A* (AO3/4) - Energy,Ecosystems&NutrientCycles

6 Responding to Change (A2 only)

6.1 Nervous Communication

6.1.1 Survival

6.1.2 Plant Responses

6.1.3 Animal Responses

6.1.4 Reflexes

6.1.5 End of Topic Test - Reflexes, Responses & Survival

6.1.6 Receptors

6.1.7 The Human Retina

6.1.8 Control of Heart Rate

6.1.9 End of Topic Test - Receptors, Retina & Heart Rate

6.2 Nervous Coordination

6.2.1 Neurones

6.2.2 Action Potentials

6.2.3 Speed of Transmission

6.2.4 End of Topic Test - Neurones & Action Potentials

6.2.5 Synapses

6.2.6 Types of Synapse

6.2.7 Medical Application

6.2.8 End of Topic Test - Synapses

6.2.9 A-A* (AO3/4) - Nervous Comm&Coord

6.3 Muscle Contraction

6.3.1 Skeletal Muscle

6.3.2 Sliding Filament Theory

6.3.3 Contraction

6.3.4 Slow & Fast Twitch Fibres

6.3.5 End of Topic Test - Muscles

6.3.6 A-A* (AO3/4) - Muscle Contraction

6.4 Homeostasis

6.4.1 Overview of Homeostasis

6.4.2 Blood Glucose Concentration

6.4.3 Controlling Blood Glucose Concentration

6.4.4 End of Topic Test - Blood Glucose

6.4.5 Primary & Secondary Messengers

6.4.6 Diabetes Mellitus

6.4.7 Measuring Glucose Concentration

6.4.8 Osmoregulation

6.4.9 Controlling Blood Water Potential

6.4.11 End of Topic Test - Diabetes & Osmoregulation

6.4.12 A-A* (AO3/4) - Homeostasis

7 Genetics & Ecosystems (A2 only)

7.1 Genetics

7.1.1 Key Terms in Genetics

7.1.2 Inheritance

7.1.3 Linkage

7.1.4 Multiple Alleles & Epistasis

7.1.5 Chi-Squared Test

7.1.6 End of Topic Test - Genetics

7.1.7 A-A* (AO3/4) - Genetics

7.2 Populations

7.2.1 Populations

7.2.2 Hardy-Weinberg Principle

7.3 Evolution

7.3.1 Variation

7.3.2 Natural Selection & Evolution

7.3.3 End of Topic Test - Populations & Evolution

7.3.4 Types of Selection

7.3.5 Types of Selection Summary

7.3.6 Overview of Speciation

7.3.7 Causes of Speciation

7.3.8 Diversity

7.3.9 End of Topic Test - Selection & Speciation

7.3.10 A-A* (AO3/4) - Populations & Evolution

7.4 Populations in Ecosystems

7.4.1 Overview of Ecosystems

7.4.2 Niche

7.4.3 Population Size

7.4.4 Investigating Population Size

7.4.5 End of Topic Test - Ecosystems & Population Size

7.4.6 Succession

7.4.7 Conservation

7.4.8 End of Topic Test - Succession & Conservation

7.4.9 A-A* (AO3/4) - Ecosystems

8 The Control of Gene Expression (A2 only)

8.1 Mutation

8.1.1 Mutations

8.1.2 Effects of Mutations

8.1.3 Causes of Mutations

8.2 Gene Expression

8.2.1 Stem Cells

8.2.2 Stem Cells in Disease

8.2.3 End of Topic Test - Mutation & Gene Epression

8.2.4 A-A* (AO3/4) - Mutation & Stem Cells

8.2.5 Regulating Transcription

8.2.6 Epigenetics

8.2.7 Epigenetics & Disease

8.2.8 Regulating Translation

8.2.9 Experimental Data

8.2.10 End of Topic Test - Transcription & Translation

8.2.11 Tumours

8.2.12 Correlations & Causes

8.2.13 Prevention & Treatment

8.2.14 End of Topic Test - Cancer

8.2.15 A-A* (AO3/4) - Gene Expression & Cancer

8.3 Genome Projects

8.3.1 Using Genome Projects

8.4 Gene Technology

8.4.1 Recombinant DNA

8.4.2 Producing Fragments

8.4.3 Amplification

8.4.4 End of Topic Test - Genome Project & Amplification

8.4.5 Using Recombinant DNA

8.4.6 Medical Diagnosis

8.4.7 Genetic Fingerprinting

8.4.8 End of Topic Test - Gene Technologies

8.4.9 A-A* (AO3/4) - Gene Technology

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End of Topic Test - Nucleic Acids & ATP

Structure of Water

The Importance of Water to Life

Properties and uses of water

Water is essential to living organisms. The list below shows some of its properties and uses.

Hydrogen bonds are formed between the oxygen of one water molecule and the hydrogen of another. As a result of this water molecules have an attraction for each other known as cohesion .

Cohesion is responsible for surface tension which enables aquatic insects like pond skaters to walk on a pond surface. It also aids capillarity, the way in which water moves through xylem in plants.

Water is a dipolar molecule, which means that the oxygen has a slight negative charge at one end of the molecule, and each hydrogen a slight positive charge at the other end. Try to learn all of the functions of water molecules given in the list. Water is used in so many ways that the chance of being questioned on the topic is high.

Other polar molecules dissolve in water. The different charges on these molecules enable them to fit into water’s hydrogen bond structure. Ions in solution can be transported or can take part in reactions. Polar substances which dissolve are hydrophilic and non-polar, which cannot dissolve in water, hydrophobic .

Water is used in photosynthesis , so it is responsible for the production of glucose. This in turn is used in the synthesis of many chemicals.

Water helps in the temperature regulation of many organisms. It enables the cooling down of some organisms. Owing to a high latent heat of vaporisation , large amounts of body heat are needed to evaporate a small quantity of water. Organisms like humans cool down effectively but lose only a small amount of water in doing so.

A relatively high level of heat is needed to raise the temperature of water by a small amount due to its high specific heat capacity. This enables organisms to control their body temperature more effectively.

Water is a solvent for ionic compounds. A number of the essential elements required by organisms are obtained in ionic form, e.g.: (a) plants absorb nitrate ions (NO 3 – ) and phosphate ions (PO 4 – ) in solution (b) animals intake sodium ions (Na + ) and chloride ions (Cl – ).

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Introduction

States of water, tasteless and odorless, color and appearance, charged substances in water, polar substances in water, non-polar compounds, amphipathic compounds, water as lubricant, water as a transport medium, water as reaction medium, what is the specific heat capacity of water, what is the importance of the high specific heat capacity of water, what is the importance of high heat of vaporization of water, what is the importance of water for living organisms.

Water is an inorganic compound essential for sustenance of all forms of life. It is the predominant compound present in all living systems. It is present in all living cells in different proportions ranging from 70% to 95%. The human body is made up of 70% water that is distributed differently among different types of cells. For example, our brain cells have 85% water while bone cells have only 20%. Water is not limited to living systems only, as it covers more than 71% of our earth.

The unique physical and chemical properties of water make it the most suitable molecule for all life forms. In this article, we will discuss some important properties of water and their role in supporting different forms of life.

All the physical and chemical properties of water depend on its chemical structure. Water is a molecule made up of one oxygen atom and two hydrogen atoms. The two hydrogen atoms are linked to the same oxygen atom via covalent bonds. The term water is used for the liquid state of H 2 O, the solid-state being called ice or snow and gaseous state vapors. 

The oxygen atom present in a water molecule has high electron affinity and electronegativity. It tends to pull the electrons of hydrogen towards itself. As a result, the water molecule becomes a dipole in which the negative charges are centered around oxygen making it a negative pole and the protons of hydrogen atoms make them positive poles. Oxygen in water molecules have a partial negative charge while hydrogen atoms carry partial positive charges.  

The angle between oxygen and hydrogen in water molecule is 104.5 o . The high electronegativity of oxygen and the presence of two lone pairs in water molecule makes it ideal for forming hydrogen bonds. Thus, all H 2 O molecules in water are bound together via hydrogen bonding. One molecule of water overall carries two lone pairs and two hydrogen atoms. Thus, four hydrogen bonds are formed per water molecule. 

General Physical Properties

Here are some of the important general physical properties of water.

As mentioned earlier, the term water is used for the liquid state of H 2 O. This liquid state of water exists at the range of temperature and pressure that is most suitable for the existence of life. At the normal atmospheric pressure at sea level, the liquid state of water exists between 0 to 100-degree Celsius temperature. 

At or below 0 o C, it changes into solid-state called ice as it is the freezing point of water. 

At or above 100 o C, it converts into its gaseous state, the water vapors. At normal atmospheric pressure, the boiling point of water is 100 o C.

The temperature range changes with the change in external atmospheric pressure. The boiling point decreases with a decrease in pressure and vice versa. This is the reason why water boils earlier on mountains where atmospheric pressure is very low.

Water is regarded as a tasteless and odorless compound in its purest form. The taste you feel while drinking water is not of pure water but is due to the substances that have been added to it during mineral processing. The taste one feels while drinking groundwater is also due to the minerals that get added to it from the surrounding environment. 

Although it is an odorless compound, humans and other organisms with a sense of smell can detect whether water is potable or from the smell coming out of it. water with a large amount of biological matter or salts gives a characteristic smell. A foul smell also starts coming from a long stand8ing water due to biological matter in it. 

Pure water appears blue when viewed in daylight against a pure white background due to the absorption of red light. However, natural water bodies may appear green due to the presence of algae or other suspended solid particles. 

Solvent Properties

Water is an ideal biologic solvent because of its unique chemical structure. It is an excellent solvent for a wide range of organic as well as inorganic substances. The great solvent properties of water are due to its ability to form dipoles and hydrogen bonds. 

When a charged substance is added to water it immediately breaks up into positive and negative ions. The water molecule tends to attract the individual ions towards their partial positive and partial negative poles. The forces of attraction among the ions in the substance are overcome by water-ion forces, the ions separate and get surrounded by water molecules. Water molecules form a hydration shell around each ion. In a hydration shell around a positive ion, a single ion is surrounded by various water molecules with oxygen atoms, carrying a partial negative charge, directed towards the ion while the hydrogen atoms directed outwards. The opposite is true for negative ions. In this way, ions are kept separate by hydration shells and they remain dissolved in water.

For example, if NaCl crystal is added to water, the ionic forces between Na + and Cl – are immediately overcome by the attraction of water molecules. As a result, Na + and Cl – separate, hydration shells are formed around individual ions and they are kept dissolved. 

Polar substances also carry partial positive and partial negative charges just like water molecules. When a polar substance is added to water, forces of attraction develop between its dipoles and dipoles of water. As a result, water molecules form hydration shells around individual molecules just like they form around the ionic species. The only difference is that ionic compounds are broken down into individual ions while in the case of non-ionic polar substances, hydration shells are formed around the entire molecule keeping its covalent bonds intact. 

Unfortunately, water proves to be a poor solvent for non-ionic, non-polar compounds due to its polarity. Such compounds do not dissolve in water. When non-polar substances are added to water, they clump together to form insoluble particles that keep floating in water. 

These are the compounds having both polar and non-polar parts, for example, phospholipids, cholesterol, etc. when such substances are added to water, the polar part of compound dissolves while the non-polar part remains undissolved. 

Hydrogen bonding also contributes to dissolving various substances in water. The compounds having functional groups with one or more hydrogen atoms bound to an electronegative atom are effectively dissolved in water due to polarity and the ability to form hydrogen bonds. Examples of such compounds include alcohols, carboxylic acids, amines, amino acids, etc. 

Because of these properties, all the chemical reactions in a cell take place in an aqueous environment. Enzymes that catalyze all the chemical reactions work only in the presence of water. The insolubility of fats, lipids and other non-polar substances in water maintains the membrane structures and is necessary for making compartments within a cell. 

Heat capacity

Heat capacity of a substance is its ability to absorb heat without much increase in its temperature. It is measured in terms of specific heat capacity defined as the amount of heat required in calories to raise the temperature of 1g of a substance by 1 o C. 

Recall that the temperature of a substance is a measure of the ability of its molecules to undergo random motion. As the temperature increases, the kinetic energy of the molecules increases, so does there random movements. Water has high heat capacity owning to the strong hydrogen bonds among its molecules. A tremendous amount of energy is required to break these bonds and render the water molecules free. Thus, water can absorb a large amount of heat with a minimum increase in its temperature. The specific heat capacity of water is 1 cal. or 4.18 joules. This is the maximum specific heat capacity of any liquid known to man. That is why water takes too long to heat.

It is evident from the above discussion that water can resist external temperature changes without any significant change in its own temperature. This property of water allows it to act as an efficient temperature stabilizer for living organisms as they are mainly made up of water (70 to 95%  body is made of water). It protects living organisms from drastic and rapid changes in the external environment. This is the reason why your body’s temperature does not rise while playing cricket in hot weather. 

The heat capacity of water is 5 times more than that of sand, making the aquatic environment a better habitat than land.

Heat of Vaporization

It is the amount of heat required to convert a liquid into its vapors. It is measured in terms of specific heat of vaporization defined as the amount of energy in calories required to convert one mole of a liquid into its gaseous state while the temperature remains constant. 

A liquid is converted into vapors when the kinetic energy of its molecule becomes greater than the attractive forces causing them to leave from the surface of liquid. Energy from external sources must be provided in the form of heat to serve this purpose. Water has a high heat of vaporization due to strong hydrogen bonds among its molecules. a large amount of energy is needed by water molecules to break the hydrogen bonds and leave from the surface of water. The specific heat of vaporization of water is around 586 calories/mole. 

This high heat of vaporization allows water to serve as a heat sink in living organisms. It provides a cooling effect when it is evaporated from living bodies in the form of perspiration in animals and transpiration. It is especially important for animals and plants living in hot habitats.

It is one of the primary functions of water in living bodies. It acts as an effective lubricant providing production against damage caused by friction. 

• It is a major component of synovial fluid, a lubricant in synovial membranes surrounding joints. 
• It is also present in meninges surrounding the brain, peritoneum surrounding the abdominal organs, pericardium around the heart, and pleural membranes guarding the lungs. In all these structures, water acts as a cushion protecting the vital organs from damage caused by trauma.  
• As a component of saliva and other secretions of the GIT, it acts as a lubricant that helps in forward propulsion of food. 
• Water in the form of tears forms a protective layer in the eyes protecting the cornea from friction caused by rubbing of eyelids.

Being an excellent solvent, water acts as an excellent transport medium for ionic and polar compounds. It is the major transport medium of blood for transporting glucose and other nutrients as well as gases. It is also used as a transport vehicle for both intracellular and extracellular transport of molecules. 

Recall that all the enzymes require an aqueous medium for proper functioning. All the metabolic reactions, therefore, require water as a reaction medium in which substances can dissolve and react in the presence of enzymes. 

Water is a molecule of life as it is essential for all the metabolic processes taking place in our body. 

A molecule of water is made up of one oxygen atom to which two hydrogen atoms are attached via covalent bonds making a bond angle of 104.5 o . 

All water molecules are held together via strong hydrogen bonds among them. One water molecule can make a total of 4 hydrogen bonds. 

In its pure form, water is tasteless and odorless liquid that appears blue against a white background. 

Due to its polarity and its ability to form hydrogen, it acts as an excellent solvent for polar as well as ionic substances. This property makes water a universal solvent although it cannot dissolve non-polar substances. 

Because of strong hydrogen bonding, water has two very important properties;

• High specific heat capacity
• High heat of vaporization

Because of high heat capacity, it acts as a temperature stabilizer in living bodies. 

The high heat of vaporization makes it a heat sink for living bodies providing cooling effect upon vaporization. 

Water also acts as an excellent lubricant providing a cushion effect to protect vital body organs. 

Water also acts as an ideal transport medium as well as reaction medium in living organisms. 

Frequently Asked Questions

The specific heat capacity of water is 4.18J or 1 cal. It is the highest specific heat capacity of any liquid present on the planet earth.

Because of the highest specific heat capacity, water can resist changes in external temperature. Thus, water act as a temperature stabilizer for living organisms, protecting them from the drastic effects of rapidly changing temperature in the external environment. 

Due to its high specific heat of vaporization, water provided a cooling effect to living organisms. This happens when water is evaporated in the form of perspiration or transpiration. 

About 70% of the total mass of living organisms is made up of water. It acts as a temperature stabilizer and lubricant. It is an excellent reaction medium within the living system. It also acts as a transport medium. 

• Harper’s Illustrated Biochemistry, 31 st Edition
• “Water, the Universal Solvent” .  USGS .  Archived  from the original on 9 July 2017. Retrieved 27 June 2017.
• Reece, Jane B. (31 October 2013). Campbell Biology (10 ed.).  Pearson . p. 48.  ISBN   9780321775658 .
• Ball, Philip (2008).  “Water: Water—an enduring mystery” . Nature.  452  (7185): 291–2.  Bibcode : 2008Natur.452..291B .  doi : 10.1038/452291a .  PMID   18354466
• Kotz, J.C., Treichel, P., & Weaver, G.C. (2005). Chemistry & Chemical Reactivity. Thomson Brooks/Cole.  ISBN   978-0-534-39597-1 .

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Essay 14: The biological importance of water

• Created by: bethanythomas101
• Created on: 10-04-18 15:21

The biological importance of water:

• Structure (Dipolar, Hydrogen bonds)
• Solvent (Hydrophobic/phillic interactions, proteins, nucleic acids, diffusion of molecules, dilution of toxic compunds- urea)
• Osmosis and turgidity (Effect on plants)
• Transport medium (Xylem, phloem, blood, lymph, secretion, excretion)
• High heat capacity (Temperature regulation)
• High heat of vapourisation (Cooling effect- sweating…
• Whole Syllabus

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The Biological Importance of Water

Water is by far one of the most important substances found on earth; it is vital for living organisms to survive and its structure plays a critical role in this.

The most important factor in the structure of a water molecule is its polarity. This occurs because the oxygen atom is larger and therefore of a higher electronegativity (3.44) than hydrogen atoms (2.2). The electronegativity or tendency to pull electrons closer towards itself, determines the polarity of an atom or molecule. For example, a water molecule consists of one oxygen atom and two hydrogen atoms. The high electronegativity of the oxygen atom gives it a slight negative charge (shown by δ-) while the relatively low electronegativity and the consequent drawing away of electrons gives the hydrogen atoms a slight positive charge (shown by δ+). This means that each individual water molecule is dipolar, it has two separate and opposite charges within the same molecule. This is important because it allows a weak ‘hydrogen bond’ to be formed between water molecules, making it a generally cohesive substance. We can observe these electrostatic attractions when rainwater is beaded up on a leaf. It has formed droplets of many water molecules ‘stuck’ to each other through hydrogen bonding. If water did not have a dipole, then it would spread out over the leaf in a thin layer making it much more difficult for water to get through the xylem in order to assist plant transpiration. The fact that the hydrogen bonds formed are relatively weak is significant as it allows for molecular mobility meaning processes like osmosis are a lot easier.

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The ability to form hydrogen bonds and its dipole nature makes water a very useful substance. For example, it is an excellent solvent meaning it can easily dissolve lots of other substances. In fact, water can dissolve more substances than any other liquid. This happens because when a molecule of a another substance mixes with water molecules (providing it is hydrophilic), the poles on either end of the molecule attract the oppositely charged ions of the molecule to be dissolved. As they are being pulled in opposite directions the molecules break apart into their ions which then form new hydrogen bonds with the water molecules. This is particularly useful in the blood where plasma is a solution carrying nutrients important for the body’s cells and also waste for removing from the body. However, even though it’s known as the ‘Universal solvent’ water is not able to dissolve hydrophobic substances. These are generally non-polar molecules and examples of hydrophobic liquids include oil and fat.

Another useful property of water is its high surface tension which acts like a thin ‘skin’ on the surface of the liquid. This is because of the cohesive forces acting between individual water molecules within the liquid. At the surface, the molecules only have this force in one direction, down towards the other water molecules. There is no such force between water and the molecules which make up the air as these are non-polar. Therefore, the surface molecules of water are drawn down towards other similar molecules creating a pressure or tension wherever water meets the air. This is why if you slightly overfill a glass or beaker with water, it will not run over but instead form a slight bubble (curved surface) to prevent from spilling. In the opposite fashion, when a narrow container such as a test tube is filled with water, a meniscus will be formed at the surface creating a curved edge of water. More useful examples of water’s surface tension include several species of insect and even reptile being able to effectively walk on water creating a whole new ecosystem on the surface of water masses such as ponds.

Similarly, the cohesion of water molecules pulling together creates ‘capillary action’. Capillary action or capillarity is when a small amount of water is pulled up through a narrow space, even though this sometimes means counteracting the force of gravity as in the example of a pipette or straw. This occurs because the adhesion forces between the water and glass molecules attract the first water molecules to the sides of the tube. The cohesive forces between the water molecules then attract more water upwards and this process continues until the gravitational force is too strong. Because of this property, water can travel along very narrow veins in roots and leaves much more easily than if it did not exist.

Also largely due to the hydrogen bonds in water, it has a relatively high boiling point and specific heat capacity. This is because, even though each individual hydrogen bond is quite weak, there are lots of them which means that it requires quite a lot of energy to break them all before the covalent bonds can even begin to be broken. A high heat capacity means that very large bodies of water such as oceans are able to ‘take in’ and hold lots of heat without actually warming up very much (the same is also true in reverse- it’s difficult to cool oceans down significantly) which acts as an excellent global temperature regulator.

As well as regulating global climates, water also plays a large part in homeostasis- the process of regulating internal body temperatures so that we don’t get sick from things like heat stroke and pneumonia. A common way our bodies can cool us down is by producing sweat on the surface of our skin. Because sweat is mainly water-based, when it evaporates in the heat, it is able to evaporate that heat energy with it leaving us feeling cooler.

A specific property that is unique to water as a naturally occurring substance and also makes life possible is the fact that water in its solid form is less dense than as a liquid meaning ice is able to float. This is because the individual water molecules expand and form an ordered pattern when frozen. They must join with the optimum number of other molecules in order to become a solid and, partly because of the angle at which the hydrogens are joined to the oxygen; this creates an expanded, hexagonal pattern. Ice being able to float means that large bodies of water freeze on the surface first allowing sea-life and marine ecosystems to be able to survive, even when the water is frozen over. The original layer of ice acts as insulation to the rest of the water and prevents it from freezing too far down. As it is widely believed that all life originated from simple undersea organisms, this suggests that no life would be possible if not for life being able to survive under water. In addition, if all the ice caps in the North Pole were to sink, the amount of water that would be displaced would entirely engulf all land.

Another important feature of the water molecule is that it’s an amphiprotic molecule meaning that it can both accept protons and be a proton donor. Therefore, in any amount of pure water or aqueous solution, water molecules can rearrange themselves by losing a hydrogen nucleus to form a hydroxide ion (OH-) and a free proton (H+), of which the proton will then react with another water molecule to form hydronium (H 3 O). In other words, the dynamic equilibrium equation for the autoionization of water is: 2H 2 O ←→  H 3 O +  + OH-. This characteristic makes water a good regulator of pH which is especially useful in cells alongside ongoing reactions.

Importantly, water is also transparent so living organisms are able to see through it. This is another factor making marine ecosystems possible and it also allows vision through the tears (saline solution) in our eyes.

Conclusively, the properties of water, due in large to its molecular structure, is what makes it possible for any form of life to survive. It sustains living organisms and balances systems both to create a suitable environment for life and with the organisms themselves, regulating specific variables like pH, temperature and, obviously, water content.

Teacher Reviews

Here's what a teacher thought of this essay.

Rebecca Lewis

**** The opening of this essay is exceptional, and there are some really good points throughout. The student provides a fantastic level of detail, and shows he has done some extra reading beyond the syllabus. Unfortunately later parts of the essay are a little less clear (the sections on specific heat capacity, and latent heat of vaporisation could be better written) and spends too long discussing the surface tension / cohesion properties conferred by hydrogen bonding. It would also be nice to have a little bit about water's role within metabolism (in hydrolysis) and its supporting roles (e.g. as hydroskeletons).

Document Details

• Author Type Student
• Word Count 1332
• Page Count 3
• Level AS and A Level
• Subject Science
• Type of work Homework assignment

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Structure of Water (A-level Biology)

Structure of water, the biological importance of water.

• Water makes up about 80% of a cell’s contents . Water has both intracellular (inside cells) and extracellular (outside cells) functions.
• Water has some key functions . Water has unique properties that make it essential for life. These will be explored in the next tutorial.
• The chemical formula for water is H2O . Water is made up of one atom of oxygen (O) and two atoms of hydrogen (H) and held together by covalent bonds .

• Water is a polar molecule . The electrons that are shared in the covalent bond between oxygen and hydrogen are unevenly distributed. Oxygen attracts the electrons more, giving oxygen a partial negative charge , which then gives the hydrogen atoms a partial positive charge .
• Hydrogen bonds form between water molecules . Because water is a polar molecule, hydrogen bonds form between water molecules. The partially positive hydrogens of one water molecule are electrically attracted to the partially negative oxygen atom of another water molecule. Many of the special properties of water are a consequence of its ability to form hydrogen bonds.

Table of Contents

The molecular structure of water is composed of two hydrogen atoms and one oxygen atom, represented as H2O.

The molecular structure of water contributes to its unique properties because the hydrogen bonds between the molecules give water its high surface tension, cohesiveness, and heat-absorbing abilities.

Water molecule polarisation occurs due to the uneven distribution of electrons within the molecule, with the oxygen atom having a slightly negative charge and the hydrogen atoms having a slightly positive charge. This creates a polar molecule, which allows water to dissolve ionic and polar substances.

The high heat capacity of water is significant because it allows water to absorb large amounts of heat without significantly increasing its temperature, helping to regulate the temperatures of living organisms and the environment.

Water and dissolved substances have a relationship where water acts as a solvent, allowing substances such as salts and sugars to dissolve and become evenly distributed in the water.

Water is important in biological processes because it is involved in numerous physiological and metabolic processes, including regulation of body temperature, transportation of nutrients, waste removal, and aiding in chemical reactions.

Water helps maintain homeostasis in living organisms by regulating their body temperature, assisting in the removal of waste, and supporting various chemical reactions necessary for survival.

Water’s polarity contributes to its ability to dissolve polar and ionic substances because the polar nature of water molecules allows them to attract ions and polar molecules, causing them to dissolve and become evenly dispersed in the water.

Water plays a vital role in chemical reactions in living organisms as it acts as a solvent, facilitating the reaction between different substances, and also participates in the reaction as a reactant or product.

Temperature changes can have an impact on the structure of water as heating can cause the water molecules to move faster and increase their kinetic energy, leading to changes in the hydrogen bonding between the molecules and the ability of water to dissolve substances.

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CIE 1 Cell structure

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