Water

A1.1

Linking Questions:

How do the various intermolecular forces of attraction affect biological systems?

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What biological processes only happen at or near surfaces?

Guiding Questions:

What physical and chemical properties of water make it essential for life?

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What are the challenges and opportunities of water as a habitat?

https://unsplash.com/photos/NY7Fop0mkSg

SL & HL Content - A1.1 Water

A1.1.1: Water as the medium for life

A1.1.2: Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

A1.1.3: Cohesion of water molecules due to hydrogen bonding and consequences for organisms

A1.1.4: Adhesion of water to materials that are polar or charged and impacts for organisms

SL and HL Content

From the IB

SL & HL Content - A1.1 Water

A1.1.5: Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

A1.1.6: Physical properties of water and the consequences for animals in aquatic habitats

SL and HL Content

From the IB

SL & HL Key Terms

Hydrogen bonds

Polar covalent bonds

Cohesion

Adhesion

Solvent

Metabolism

Xylem

Surface tension

Capillary action

Hydrophobic

Hydrophilic

Buoyancy

Viscosity

Thermal conductivity

Specific heat capacity

Apoplast pathway

SL and HL Content

A1.1.1 Water as the medium for life

During the formation of the first cells, a small volume of water became enclosed in a membrane.

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Chemical reactions occurred between the solutes in a cell.

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After billions of years, most molecules of life are still dissolved in water.

A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

A1.1.2 Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

A1.1.3 Cohesion of water molecules due to hydrogen bonding and consequences for organism

Cohesion = Water molecules bind with other water molecules

A1.1.4 Adhesion of water to materials that are polar or charged and impacts for organisms

Adhesion = Water molecules bind with other surfaces

It takes a lot of energy for water to change state.

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There is a lot of hydrogen bonding between water molecules – the H-bonds need to be broken before a change in state can occur and this requires the absorption of energy (heat)

So, water is an excellent medium for living organisms as it is relatively slow to change temperature and thus supports the maintenance of constant conditions (internal and external)

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A1.1.5 Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Water is commonly referred to as the universal solvent due to its capacity to dissolve a large number of substances

Water can dissolve any substance that contains charged particles (ions) or electronegative atoms (polarity)

This occurs because the polar attraction of large quantities of water molecules can sufficiently weaken intramolecular forces (such as ionic bonds) and result in the dissociation of the atoms

The slightly charged regions of the water molecule surround atoms of opposing charge, forming dispersive hydration shells

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• All substances that dissolve in water are hydrophilic, including polar molecules such as glucose, and particles with positive or negative charges such as sodium and chloride ions.

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• Substances that water adheres to, cellulose for example, are also hydrophilic.

http://www.middleschoolchemistry.com/img/content/multimedia/chapter_5/lesson_7/glucose.jpg

hydrophilic

( water loving )

This term is used to describe substances that are chemically attracted to water.

A space filling molecular diagram of glucose showing the positive and negative charges

• Molecules are hydrophobic if they do not have negative or positive charges and are nonpolar
• All lipids are hydrophobic, including fats and oils
• Hydrophobic molecules dissolve in other solvents such as propanone (acetone)

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http://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Water_and_oil.jpg/450px-Water_and_oil.jpg

hydrophobic

( water fearing )

This term is used to describe substances that are insoluble in water

Blood plasma consists of mainly of water (95%) plus dissolved substances which it transports.

http://4.bp.blogspot.com/-71TuXJIWv8o/UChT59p73fI/AAAAAAAAAFY/B1zkMgT-dlA/s1600/Glucose.png

Glucose

• polar molecule hence freely soluble
• carried by the blood plasma

A1.1.5 Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Amino acids

• Positive and negative charges (due to the amine and acid groups) therefore soluble in water
• R group varies, can be polar, non-polar or charged
• R group determines the degree of solubility
• carried by the blood plasma

A1.1.5 Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Oxygen

• Non-polar molecule
• Due to the small size of an oxygen molecule it is soluble in water, but only just
• water becomes saturated with oxygen at relatively low concentrations
• As temperature increases the solubility of oxygen decreases
• At body temperature (37 °C) very little oxygen can be carried by the plasma, too little to support aerobic respiration
• hemoglobin in red blood cells carry the majority of oxygen
• Hemoglobin has (4) binding sites for oxygen

O = O

https://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/1GZX_Haemoglobin.png/480px-1GZX_Haemoglobin.png

A1.1.5 Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Fats

• Large, non-polar molecules
• insoluble in water
• They are carried in blood inside lipoprotein complexes (in the plasma)

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Cholesterol

• molecules are hydrophobic, apart
• from a small hydrophilic region at one end
• This is not enough to make cholesterol dissolve in water
• They are carried in blood in lipoprotein complexes (in the plasma)

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Lipoprotein complex

• Outer layer consists of single layer of phospholipid molecules
• hydrophilic phosphate heads of the phospholipids face outwards and are in contact with water
• The hydrophobic hydrocarbon tails face inwards and are in contact with the fats
• cholesterol molecules are positioned in the phospholipid monolayer - hydrophilic region facing outwards
• Proteins are also embedded in the phospholipid layer (hence the name)

A1.1.5 Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

Sodium Chloride

• ionic compound
• freely soluble in water
• dissolving to form sodium ions (Na+) and chloride ions (Cl-)
• carried in the blood plasma

http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.swf

A1.1.5 Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

A1.1.6 Physical properties of water and the consequences for animals in aquatic habitats

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A1.1.6 Physical properties of water and the consequences for animals in aquatic habitats

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Coolant

Buoyancy

Viscosity

Thermal conductivity

Specific heat capacity

A1.1.7 Extraplanetary origin of water on Earth and reasons for its retention

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HL

Competing theories as to where water on earth came from.

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Most widely supported: Asteroid colliding with earth delivered water.

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Once about every 20 million years, a large asteroid hits earth.

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How water was retained on earth after delivery by an asteroid

• Distance of earth from sun ensures that sunlight never raises temperatures high enough for water to boil.
• Due to its size, earth has strong gravity, holding the oceans tightly to its surface.

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A1.1.8 Relationship between the search for extraterrestrial life and the presence of water

Our distance from the sun is ‘just right’ - like the Goldilocks story. Hence we are in the “Goldilocks zone”

It is estimated that there are about 40 billion planets within a “Goldilocks zone”

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