3.2 - Water

Water makes a very efficient transport medium within plants. Explain why.

-Cohesion between water molecules means that when water is transported through the body, molecules will stick together. -Adhesion occurs between water molecules and other polar molecules and surfaces -The effects of adhesion and cohesion result in water exhibiting capillary action. This is the process by which water can rise through a narrow tube against the force of gravity.

What is cohesion and adhesion? And what is surface tension?

-Cohesion= it moves as one mass because the molecules are attracted to each other -Adhesion= the water molecules are attracted to other materials -Water molecules are more strongly cohesive to each other than they are to air, this results in water having a 'skin' of surface tension

State 3 properties of water

-It is less dense in it's solid state (ice) -It has cohesive and adhesive properties -It has an unusually high boiling point

What makes water useful as a solvent?

-Many of the solutes in an organism can be dissolved. -Cytosol is mainly water. -Water acts as a medium for chemical reactions -Water helps to transport dissolved compounds into and out of cells

Water is a polar molecule and acts as a solvent. Explain why this is essential for life.

-The cystosol of prokaryotes and eukaryotes is mainly water -Many solutes are also polar, such as proteins, amino acids and nucleic acids -Water acts as a medium for chemical reactions -It also helps transport dissolved compounds into and out of cells

Why is water polar?

Because the oxygen atom attracts shared bonding electrons away from the hydrogen atoms

What does dipole mean?

Having 2 charges

Water must absorb a large amount of energy before it becomes a gas. Explain why this property is biologically significant/ significant for life.

Heat is easily lost by evaporation of water. And sweating in animals, and transpiration in plants cause rapid cooling.

Ice is less dense than water. Explain why this property is biologically significant/ significant for life.

Ice floats and therefore insulates the underlying water. Aquatic organisms can survive under the ice. Other organisms can live on the ice surface.

Water provides a constant environment. Explain why?

Ice floats, and so forms on the surface of ponds and lakes. This forms an insulating layer. Aquatic organisms (e.g. fish) would not be able to survive freezing temperatures if their habitat froze solid.

Water has a high specific heat capacity. What does this mean?

It can absorb a lot of energy for only a small rise in temperature

Water is stable. What does this mean?

It does not change temperature or become a gas easily, therefore providing a constant environment

Suggest, with reasons, which properties make it such an important component of blood

It is a transport medium (can transport oxygen, CO2, and other substances) It is a polar solvent (proteins, amino acids, enzymes, glucose and many other biological molecules are polar) Ions in the blood are charged (for example, salt, NaCl is broken down into Na+ and Cl-) Water is a coolant, so relatively resistant to temperature change

Water is colourless, and has a high transmission of visible light. Explain why this property is biologically significant/ significant for life.

Light penetrates tissue and aquatic environments

Water is also a reactant in some chemical processes. Give 2 examples of these processes.

Photosynthesis and hydrolysis (e.g. the hydrolysis of maltose)

Name 2 reactions that water is involved in.

Photosynthesis and the hydrolysis of maltose

Water has a high latent heat of fusion. What does this mean?

Significant amounts of energy are required before water will change state

What is responsible for the unique properties of water?

The hydrogen bonding

Explain why water is a polar molecule

The oxygen atom is more electronegative than the 2 hydrogen atoms, so attracts the shared electrons, giving the oxygen a slight negative charge and the hydrogens each a slight positive charge

Are hydrogen bonds between water molecules constantly there?

They break and reform between the constantly moving water molecules

Why is cohesion between water molecules important in plants?

This means that the water molecules 'stick' together, allowing water to be pulled up the xylem in a continuous column

True or false? A key feature of water is their dipole nature

True

True or false? Dipole means having 2 charges.

True

True or false? In ice the hydrogen bonds hold the water molecules in a rigid lattice form

True

True or false? In liquid water the molecules are continually moving and the hydrogen bonds continually break and reform.

True

True or false? In water, there is a small negative charge on the oxygen

True

True or false? In water, there is a small positive charge on each of the 2 hydrogens

True

True or false? Ionic compounds are polar.

True

Water has a low viscosity. Explain why this property is biologically significant/ significant for life.

Water flows easily through very small spaces (e.g. through capillaries, xylem vessels, spaces within plant cell walls)

Water has a high surface tension. Explain why this property is biologically significant/ significant for life.

Water forms droplets on surfaces and runs off. Small organisms can "walk" on water surfaces (e.g. pond skaters)

Water remains a liquid over a wide temperature range. Explain why this property is biologically significant/ significant for life.

Water is a liquid medium for aquatic life (lakes, rivers, the sea) Water is also a medium inside cells

Water is adhesive. What does this mean?

Water is attracted to other materials

Why does water have a high surface tension?

Water molecules are more cohesive to each other than they are adhesive to air, giving water a 'skin' of surface tension

Water is cohesive. What does this mean?

Water moves as one mass because the molecules are attracted to each other

Water has a high latent heat of vaporisation. What does this mean?

Water must absorb a large amount of energy to evaporate

Explain why water has a high specific heat capacity.

Water's high heat capacity is a property caused by hydrogen bonding among water molecules. When heat is absorbed, hydrogen bonds are broken and water molecules can move freely. When the temperature of water decreases, the hydrogen bonds are formed and release a considerable amount of energy.

Water is cohesive. Explain why this property is biologically significant/ significant for life.

-This makes water an excellent transport medium. For example in the transport of blood. -Hydrogen bonding "sticks" water molecules together. For example in plants continuous columns of water can be pulled up the xylem without breaking. -Water is not easily compressed so provides good support. For example, amniotic fluid.

Explain how water affects the temperature within cells

-Water acts as a coolant, helping to buffer temperature changes during chemical reactions in cells, because of the large amounts of energy needed to break the hydrogen bonds -Maintaining constant temperatures in cellular environments is important, as enzymes are often only active in a narrow temperature range

Describe and explain the boiling point of water.

-Water has an unusually high boiling point (It is a small molecule, much lighter than carbon dioxide and oxygen, yet it unlike them, it is a liquid at room temperature) -This is because of the intermolecular forces between the water molecules (hydrogen bonds) -It takes a lot of energy to break these bonds, and allow the water molecules to escape and become a gas

Water forms the basis of the stroma in chloroplasts and the matrix in mitochondria. Describe which properties of water make it such an important component of these particular organelles.

-Water is a transport medium, so allows the movement of substrates and enzymes -Water is necessary for metabolic reactions to occur -Water is a polar solvent, so polar biological molecules can dissolve in it -Water is a substrate for some reactions -Water does not change state easily, so the chloroplasts and mitochondria are relatively resistant to temperature change

Most substances are denser in their solid state than in their liquid state, but this is not the case for water/ice. Explain why.

-When water turns into ice it becomes less dense -As water freezes the hydrogen bonds fix the positions of the polar molecules slightly further apart than the average distance in the liquid state -This produces a giant, rigid but open structure, with every oxygen at the centre of a tetrahedral arrangement of hydrogen atoms -For this reason ice floats

What is a polar molecule?

A molecule that is covalently bonded, but the electrons are not shared equally. The molecule therefore has regions of positivity and regions of negativity.

What is a metabolite?

A substance formed in or necessary for metabolism

Water is a good solvent for other polar species (charged molecules and ions). Explain why this property is biologically significant/ significant for life.

All metabolic reactions occur in water. Water is the main transport medium in organisms.

Water can absorb a lot of energy for only a small rise in temperature. Explain why this property is biologically significant/ significant for life.

Aquatic environments are stable. Organisms can maintain stable internal temperatures despite fluctuations in external temperature.

Water requires significant amounts of energy before it will become a solid. Explain why this property is biologically significant/ significant for life.

Cell contents are unlikely to freeze

True or false? In ice the molecules are continually moving and the hydrogen bonds continually break and reform.

False

True or false? In water, there is a small negative charge on each of the 2 hydrogens

False

True or false? In water, there is a small positive charge on the oxygen

False

What is a hydrogen bond?

When a molecule contains a hydrogen atom bonded to another atom, that is considerably more electronegative, then the other atom will gain a slight negative charge, and the hydrogen a slight positive charge. The intermolecular bond between the slightly positive hydrogen of one molecule, and the slightly negative atom of another molecule, is called a hydrogen bond.