Chemical Elements And Biological Compounds

Question 1

Inorganic ions are also called what?

Answer 1

Electrolytes or minerals

Question 2

What cellular processes are inorganic ions important in?

Answer 2

Muscle contraction
Nervous coordination
Maintaining osmotic pressure in cells and blood

Question 3

4 examples of inorganic ions?

Answer 3

Magnesium
Iron
Phosphate ions
Calcium

Question 4

Explain water

Answer 4

Water is a medium for metabolic reactions and an important constituent of cells me being 65-95% of the mass of many plants and animals. About 70% of each individual human is water.

The water molecule is a dipole, meaning it has a positively charged end (hydrogen) and a negatively charged end (oxygen), but no overall charge.

A molecule with separated changed is called ‘polar’. The charges are very small and are written as d+ and d-, to distinguish them from full charges (- +).

Hydrogen bonds can form between the d+ on a hydrogen atom on one molecule and the d- on an oxygen atom of another, hydrogen bonds are weak, but collectively are very difficult to break which gives water a wide range of physical properties vital to life

Question 5

The properties of water?

Answer 5

It's a solvent
It is a metabolite
It has High specific heat capacity
It has High latent heat of vaporisation 
Cohesion
High surface tension 
High density
Transparent

Question 6

Explain the property of water (solvent)

Answer 6

Living organisms obtain their key elements from aqueous solution. Water is an excellent solvent. Because water molecules are dipoles, they attract charged particles, such as ions, and other polar molecules, such as glucose. These then dissolve in water, so chemical reactions take place in solution. Water acts a transport medium.

E.g. In animals, plasma transports dissolved substances and in plants, water transports minerals in the xylem, and sucrose and amino acids in the phloem. Non-polar molecules, such as lipids, do not dissolve in water

Question 7

Explain the property of water ( metabolite )

Answer 7

Water is a metabolite: water is used in many biochemical reactions as a reactant

E.g. With carbon dioxide to produce glucose in photosynthesis.

Many reactions in the body involve hydrolysis, where water splits into a molecule. E.g. Maltose + water —> glucose + glucose

In condensation reactions, water is a product. E.g. Glucose + fructose —-> sucrose + water

Question 8

Explain waters Hugh specific heat capacity

Answer 8

This means a large amount of heat is needed to raise its temperature. This is because the hydrogen bonds between water molecules restrict their movement, resisting an increase in kinetic energy and therefore, resisting an increase in temperature.

This prevents large fluctuations in water temperature, which is important in keeping aquatic habitats stable, so that organisms do not have to adapt to extremes of temperature. It allows enzymes within cells to work efficiently.

Question 9

Explain waters high latent heat of vaporisation

Answer 9

This means a lot of heat energy is needed to change it from a liquid to a vapour. This is important for example in temperature control, where heat is used to vaporise water from sweat on the skin or from a leafs surface. As the water evaporates, the body cools.

Question 10

Explain waters property, cohesion

Answer 10

Water molecules attract each other forming other hydrogen bonds. Individually these are weak but,because there are many of them, the molecules stick together in a lattice. This sticking together is called cohesion. It allows columns of water to be drawn up xylem vessels in plants

Question 11

Explain waters high surface tension

Answer 11

At ordinary temperatures water has the highest surface tension of any liquid except Mercury. In a pond, cohesion between water molecules at the surface produces surface tension so that the body of an insect, such as the pond skater, is supported.

Question 12

Explain waters high density

Answer 12

Water is denser than air and, as a habitat for aquatic organisms, provides support and buoyancy. Water has a maximum density at 4*C. Ice is less dense than liquid water, because the hydrogen bonds hold the molecules further apart than they are in liquid. So ice floats on water. It is a good insulator and prevents large bodies of water losing heat and freezing completely, so organisms beneath it survive

Question 13

Explain waters transparency

Answer 13

Water is transparent, allowing light to pass through. This lets aquatic plants photosynthesise effectively

Question 14

What are carbohydrates?

Answer 14

Organic compounds containing the elements carbon, hydrogen and oxygen

Question 15

What is the basic unit of a carbohydrate?

Answer 15

A monosaccharide

Question 16

What do two monosaccharides combine to form?

Answer 16

A disaccharide.

Many monosaccharide molecules combine to form a polysaccharide

Question 17

What is a monosaccharide?

• general formula
• names determined by?
• example

Answer 17

Small organic molecules and are the building blocks for the larger carbohydrates. Monosaccharides have the general formula (CH2O)n and their names are determined by the number of carbon atoms (n) in the molecule. A triode sugar has three carbon atoms; a pentose has five and a hexose has 6.

Glucose is a hexose sugar. The carbon atoms of a hexose are labelled 1-6

Question 18

What formula do all hexose sugars share?

Answer 18

C6H12O6, but they differ in their molecular structure .

Question 19

What happens to the carbon atoms of monosaccharides when the sugar is dissolved in water?

Answer 19

The carbon atoms make a ring and they can alter their binding to make straight chains,with the rings and chains in equilibrium

Question 20

How many isomers does glucose have?

Answer 20

2

Question 21

What are the isomers of glucose?

Answer 21

Alpha and beta , based on the positions of an OH and a H.

These different forms result in biological differences when they form polymers, such as starch and cellulose.

Question 22

Monosaccharides have many functions and can act as:

Answer 22

A source of energy in respiration. Carbon - hydrogen and carbon - carbon bonds are broken to release energy, which is transferred to make adenosine triphosphate (ATP)

Building blocks for larger molecules. Glucose, for example, is used to make the polysaccharides starch,glycogen and cellulose.

Intermediates in reactions, e.g. Trioses, are intermediates in the reactions of respiration and photosynthesis.

Constituents of nucleotides, e.g. Deoxyribose in DNA , ribose in RNA, ATP and ADP

Question 23

What are disaccharides?

Answer 23

Composed of two monosaccharide units bonded together with the formation of a glycosidic bond and the elimination of water. This is an example of a condensation reaction.

Question 24

How to test for presence of sugars?

Answer 24

Equal volumes of Benedicts reagent and the solution being tested are heated to at least 70*C. If a reducing sugar, such as glucose, is present, the solution will turn from blue through green, yellow and orange and finally brick-red precipitate forms.

These sugars donate an electron to reduce copper (II) ions in copper sulfate, to red copper (I) oxide.

Some disaccharides, such as sucrose, are non reducing sugars and give a negative result, I.e. The solution remains blue. Sucrose can only be detected if it is broken down to its constituent monosaccharides, for example by heating with hydrochloric acid. Benedicts reagent needs alkaline conditions to work, so alkali is added, Benedicts reagent is then added and heated as before, if the solution now turns red then a non reducing sugar was initially present

Question 25

What are polysaccharides?

Answer 25

Large,complex polymers. They are formed from very large numbers of monosaccharide units, which are their monomers, linked by glycosidic bonds

Question 26

What is the problem with glucose being the main source of energy in cells?

Answer 26

It must be stored in a certain way. It is soluble in water and so it would increase the concentration of the cell contents, and consequently draw water in by osmosis. This problem is avoided by converting the glucose into a storage product, a polysaccharide, starch which:

Is insoluble so it has no osmotic effect

Cannot diffuse out of a cell

Is a compact molecule and can be stored in a small space

Carries a lot of energy in its C-H and C-C bonds

Question 27

What is the main store of glucose for plants?

Answer 27

Starch. Starch grains are found in high concentrations in seeds and storage organs such as potato tubers

Question 28

What is starch made of?

Answer 28

Alpha glucose molecules bonded together in two different ways, forming the two polymers, amylose and amylopectin

Question 29

Structure of amylose?

Answer 29

A linear, u branched molecule with alpha 1,4 glycosidic bonds forming between the first carbon atom (C1) on one glucose monomer and the fourth carbon atom (C4) on the adjacent one. This is repeated, forming a chain, which coils into an alpha helix

Question 30

Structure of amylopectin?

Answer 30

Has chains of glucose monomers joined with alpha 1,4 glycosidic bonds. They are cross linked with alpha 1,6 glycosidic bonds and fit inside the amylose. When a glycosidic bond firms between the C1 atom on one glucose molecule and the C6 atom on another, a side branch is seen, alpha 1,4 glycosidic bonds continue on from the start of the branch.

Question 31

Explain glycogen

Answer 31

The main storage product in animals is glycogen. It used to be called animal starch because it is very similar to amylopectin. It also has alpha 1,4 and alpha 1,6 bonds. The difference is that glycogen molecules have shorter alpha 1,4- linked chains and so are more branched than amylopectin

Question 32

Explain cellulose

Answer 32

Cellulose is a structural polysaccharide and its presence in plant cell walls makes it the most abundant organic molecule on earth.

Cellulose consists of many long, parallel chains of beta glucose units. The glucose monomers are joined by beta 1,4 glycosidic bonds, and the beta link rotates adjacent glucose molecules by 180*. This allows hydrogen bonds to form between the OH groups of adjacent parallel chains and contributes to celluloses structural stability.

Between 60-70 cellulose molecules become tightly cross linked to for, bundles called microfibrils. The microfibrils are, in turn, held in bundles called fibres,. A cell wall has several layers of fibres, which run parallel within a layer but at an angle to the adjacent layers. This laminated structure also contributes to the strength of the cell wall.

Cellulose fibres are freely permeable, because there are free spaces between the fibres. Water and it’s so lutes can penetrate through these spaces in the cell wall, to the cell membrane

Question 33

Explain chitin

Answer 33

Chitin is a structural polysaccharide, found in exoskeleton of insects and in fungal cell walls. It resembles cellulose, with its long chains of beta 1,4 linked monomers, but has groups derived from amino acids added, to form heteropolysaccharide. It is strong, waterproof and lightweight. Like cellulose, the monomers are rotated through 180* in relation to their neighbours, and the long parallel chains are cross linked to ew hotbed by hydrogen bonds, forming microfibrils

Question 34

Explain lipids

Answer 34

Like carbohydrates, lipids contain carbon, hydrogen and oxygen but, in proportion to the carbon and hydrogen, they contain much less oxygen. They are non polar compounds and so are insoluble in water, but dissolve in organic solvents, such as propanone and alcohols

Question 35

Explain triglycerides

Answer 35

They are formed by the combination of one glycerol molecule and three molecules of fatty acids. The glycerol molecule in a lipid is always the same but the fatty acid component varies. The fatty acids join to glycerol by condensation reactions, whereby three molecules of water are removed and ester bonds are formed between the glycerol and fatty acids

Question 36

What is a phospholipid

Answer 36

A special type of lipid. Each molecule has the unusual property of having one end that is soluble in water.