Topic 1 : Lifestyle, Health and Risk

Explain the meaning of water being a ‘polar’ molecule

• water has a partially positive region shown by H+ and a partially negative region, shown by O-

State and explain some properties of water

• water is used as a solvent - due to being a polar molecule water molecules can form hydrogen bonds with other polar molecules or solute molecules

• water is a liquid - so has the ability to flow due to it’s polar nature and so it is cohesive

• water can be used as a transport medium - it is adhesive so can travel up the xylem by sticking to the xylem wall against the gravitational pull

What are carbohydrates?

• sources of and stores of energy

• organic substances containing carbon, hydrogen and oxygen in the ratio 1:2:1

Define what are monomers and polymers and give examples of each

monomer - smallest unit from which larger molecules are made from e.g monosaccharides

polymers - molecules made from a chain of monomers joined together e.g polysaccharides, polypeptides

What are monosaccharides and what is the general formula for them? examples?

• they are single and simple sugars

• C_nH_2nO_n

• e.g glucose, fructose and galactose

State properties of monosaccharides

• sweet- taste

• soluble in water (H2O)

State and draw the two different types of glucose

alpha glucose

beta glucose

State the roles for alpha and beta glucose

• alpha glucose - forms polysaccharide molecules e.g starch and glycogen / the main substrate for respiration / the form in which carbohydrate is transported in mammalian blood

• beta glucose - monomer unit for cellulose providing structural support and tensile strength in cell walls

State the roles for the monosaccharide fructose and galactose

• fructose - helps to attract animals for pollination / forms with glucose to form the disaccharide sucrose

• galactose - forms with glucose to form the disaccharide lactose (found in milk)

State the type of sugar for monosaccharides and their molecular formula

• triose - C₃H₆O₆ e.g glyceraldhyde

• tetrose - C₄H₈O₄ e.g therose

• pentose - C₅H₁₀O₅ e.g ribose

• hexose - C₆H₁₂O₆ e.g glucose

State and draw the two monosaccharides of pentose

• ribose - a component of RNA C₅H₁₀O₅

• deoxyribose - a component of DNA C₅H₁₀O₄

What are disaccharides and how are they formed? give examples

• formed when 2 monosaccharides join together by glycosidic bonds in a condensation reaction

• e.g - sucrose (sugar stored in sugar cane), maltose (sugar found in germinating seeds) and lactose (milk sugar)

Explain the meaning of the following terms:

• condensation

• hydrolysis

• catalysts

• condensation - the joining of two molecules which involves the removal of water (H₂O)

• hydrolysis - addition of water (H₂O) to break molecules e.g the gylcosidic bonds in a disaccharide

• catalyst - speeds up the rate of reaction without being used up by providing an alternative pathway with a lower activation energy

State how each of the following disaccharides are produced:

• maltose

• sucrose

• lactose

• maltose - when two alpha glucose join together to form maltose (malt sugar)

• sucrose - when a glucose molecule and a fructose molecule join together to form sucrose (table sugar)

• lactose - when a glucose molecule and a galactose molecule join together to form lactose (milk sugar)

only maltose and lactose are linked by 1-4 glycosidic bonds

Draw a diagram to show the formation of sucrose and label the glycosidic bonds

linked by a 1,2 glycosidic bond

Draw a diagram to show the formation of maltose and label the glycosidic bonds

formed by 1,4 glycosidic bonds

State and explain three functions of disaccharides

• provide the body with a quick-release source of energy - only made up of two sugar molecules so are easy to break down by the digestive system and absorbed into the bloodstream

• easily soluble in water - due to the presence of many hydroxyl groups so can form many hydrogen bonds when aqueous

• sweet in taste

Define the term polysaccharides and give examples

polysaccharides - repeated chains of many monosaccharides joined tother by glycosidic bonds in a condensation reaction

e.g starch, glycogen, amylose and amylopectin

How can the structure of polysaccharides differ? What does this suggest?

• can be branched or unbranched - being branched increases the rate at which a polysaccharide can be broken down

• straight or coiled - Being straight makes the molecules suitable for constructing cellular structures e.g. cellulose / Being coiled makes a molecule more compact and suitable for storage e.g. amylose in starch

Where and why are starch and glycogen useful as storage molecules?

starch - main storage polysaccharide in plants

glycogen - main storage polysaccharide in animals and fungi

• Compact; large quantities can be stored

• Insoluble; they will have no osmotic effect

State the properties of starch and what is it formed from

• insoluble

• compact

• highly branched

• made of 2 polysaccharides: Amylose + Amylopectin

State and explain the properties of amylose

• unbranched helix shape - The helix shape enables it to be more compact and thus more can be more easily stored

• held together by H-bonds within molecules

• has 1,4 - glycosidic bonds between alpha-glucose molecules

State and explain the properties of amylopectin

• branched molecule - branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage

• has 1,4-glycosidic and 1,6-glycosidic bonds at branch points

Describe the formation of glycogen

• formed through joining alpha-glucose molecules in a condensation reaction

• forming 1,4 and 1,6 glycosidic bonds

Explain how the structure of glycogen relates to its role as an energy storage

• it is highly branched so many terminal glucose molecules are broken down at the same time (hydrolysis)

• stored as granules in muscles/liver - enables a high celullar respiration rate

• It contains both 1,4 and 1,6 glycosidic bonds

• compact - lots can be stored in a small space

• large molecule therefore insoluble - has no osmotic effect and so will not diffuse out of the cell easily

Describe and explain the structure of cellulose

• a polysacchride made by joining together two or more beta-glucose molecules in a condensation reaction to form water

• beta-gluose molecules are held together by 1,4 glycosidic bonds —→ this is done due to the inversion of the B-glucose moolecules

• there are hydrogen bonds that hold the chain in place, giving cellulose its strength

Draw and label the different bonds in a cellulose structure

Describe and explain the function of cellulose

• high tensile strength - allows cellulose to be streched without breaking thus can withstand turgor pressure

• main structural component of cell walls due to the hydrogen bonds providing it’s strength