2.1.2 Biological molecules

Question 2

What are polar molecules

Answer 2

Molecules that have regions of negativity and regions of positivity

Question 3

Why is water a polar molecule

Answer 3

Oxygen exerts a greater attraction over shared electrons so oxygen becomes delta negative whilst hydrogen becomes delta positive

Question 4

Hydrogen bonds

Answer 4

As oxygen is delta negative and hydrogen is delta positive, oxygen and hydrogen of different water molecules will be attracted to each other therefore a hydrogen bond will form between them

Question 5

Because water is a liquid at room temperature, it can:

Answer 5

Provide habitat for living things in rivers, lakes and seas
Form a major component of the tissues in living organisms
Provide a reaction medium for chemical reactions

Question 6

Density of water

Answer 6

Water initially becomes more dense as it gets colder until about 4 degrees Celsius. As it goes from 4 degrees Celsius to freezing point, because of its polar nature, the water molecules align themselves in a structure that is less dense than liquid water ( called an open lattice structure)
Because ice is less dense that water:
Aquatic animals have a stable environment in which to live throughout the winter
Ponds and other bodies of water are insulated against the extreme cold. The layer of ice reduces the rate of heat loss from the rest of the pond.
Ice is less dense than water so floats, protecting the rest of the body of water from the cold so it doesn’t freeze

Question 7

Water as a solvent

Answer 7

Water is a good solvent for many substances found in living things. This includes ionic solutes such as sodium chloride and glucose. Because what is polar, the positive and negative parts of the water molecules are attracted to the positive and negative parts of the solute. The water molecules cluster around these charged parts if the solute molecules or ions and will help to separate them and keep them apart.
Because what is a good solvent:
Molecules and ions can move around and react together in water, many reactions happen in the cytoplasm of cells with is over 70% water i.e water is a good reaction medium
Molecules and ions can be transported around living things whilst dissolved in water

Question 8

Waters cohesion and surface tension

Answer 8

Hydrogen binding between molecules pulls them together, they demonstrate cohesion. The water molecules at the surface of water are all hydrogen bonded to the molecules beneath then, hence are more attracted to the water beneath them than the air above. This means the surface of the water contracts ( as the molecules are being pulled inwards) and it gives the surface of the water an ability to resist force applied to it. This is known as surface tension
Because of cohesion and surface tension:
Columns of water in plant vascular tissue are pulled up the xylem tissue together from the roots
Insects like pond skaters can walk in water

Question 9

Waters high specific heat capacity

Answer 9

Water molecules are held together quite tightly by hydrogen bonds. Therefore, you have to put in a lot of energy to raise the temperature. This means water does not heat up or cool down easily.
Living things need a stable environment for enzyme controlled reactions to happen properly
Aquatic organisms need a stable environment in which to live
Water tends to be a liquid over a wide range of temperatures making it an important component of living organisms and habitat for aquatic organisms

Question 10

Waters high latent heat of vaporisation

Answer 10

Because the molecules are held together by hydrogen bonds, a relatively large amount of energy is needed for water molecules to evaporate. Therefore, water can help to cool living things and keep their temperature stable. For example, mammals are cooled when sweat evaporates and plants are cooled when water evaporates from mesophyll cells

Question 11

Water as a reactant

Answer 11

Water is also a reactant in reactions such as photosynthesis and in hydrolysis reactions such as digestion of starch, proteins and lipids.

Question 12

What elements do carbohydrates contain

Answer 12

Carbon, hydrogen and oxygen

Question 13

Monosaccharides

Answer 13

A single sugar unit- glucose, fructose and ribose

Question 14

Disaccharide

Answer 14

Two monosaccharides linked together- lactose, sucrose

Question 15

Polysaccharide

Answer 15

Glycogen, cellulose, starch
Two or more monosaccharides

Question 16

What is the chemical formula of glucose

Answer 16

C6H12O6

Question 17

What type of monosaccharide is glucose

Answer 17

A hexose monosaccharide

Question 18

Are glucose molecules polar and soluble in water

Answer 18

Glucose molecules are polar and soluble in water. This is due to the hydrogen bonds that form between the hydroxyl groups and water molecules. This solubility means water is dissolved in the cytosol of the cell

Question 19

Alpha glucose

Answer 19

Draw it

Question 20

Beta glucose

Answer 20

Draw it

Question 21

Glycosidic bond

Answer 21

Formed between two glucose molecules

Question 22

Pentose monosaccharides

Answer 22

Sugars that’s contain 5 carbon atoms. Ribose is the sugar present in RNA nucleotides and deoxyribose is the sugar present in DNA nucleotides

Question 23

Starch

Answer 23

Many alpha glucose molecules can be joined by glycosidic bonds to form starch.

Question 24

Amylose

Answer 24

One of the polysaccharides in starch is called amylose. It is formed by alpha glucose founded together by only 1-4 glycosidic bonds. The angle of the bind means that this long chain of glucose twists to form a helix which is further stabilised by hydrogen binding within the molecule. This makes the polysaccharide much more compact, and much less soluble than the glucose molecules used to make it

Question 25

Amylopectin

Answer 25

Another starch molecule. Made my 1-4 glycosidic bonds between alpha molecules but there are also some glycosidic bonds formed by condensation reactions between carbon 1 and 6 in two glucose molecules, this means amylopectin had a branched structure, with the 1-6 branching points occurring approximately once in every 25 glucose subunits

Question 26

Glycogen

Answer 26

Forms more branches than amylopectin, which means it is more compact and less space is needed for it to be stored. This is important as animals are mobile, unlike plants.

Question 27

Amylopectin and glycogen

Answer 27

Coiling or branching of these polysaccharides them very compact, which is ideal for storage. The branching also means there are many free ends where glucose can be added or removed. This speeds up the processes of storing or releasing glucose molecules required by the cell. Insoluble, branched and compact

Question 28

How is glucose released for respiration form starch or glycogen

Answer 28

They undergo hydrolysis reactions, requiring the addition of water molecules. These reactions are catalysed by enzymes

Question 29

Cellulose

Answer 29

Beta glucose molecules can join together and form a polymer if alternate beta molecules are turned upside down. Cellulose is therefore unable to coil or form branches, it forms a straight chain molecule. Cellulose has a high tensile strength. Cellulose molecules make hydrogen bonds with each other forming microfibrils. Those microfibrils join together forming macrofibrils which combine together to produce fibres. These fibres are wrong and insoluble and used to make cell walls.