1 - Water and Carbohydrates

Question 1

What is a monomer?

Answer 1

Smaller units from which larger molecules are made

Question 2

Structure of water?

Answer 2

Covalent bonds between oxygen and hydrogen and a difference in electronegativity - polar molecule with partial positive and partial negative charge This means there is hydrogen bonding between the molecules.

Question 3

How is water good at keeping a constant body temperature?

Answer 3

High specific heat capacity

Question 4

How does water cool an organism?

Answer 4

Has a high latent heat of vaporisation, meaning when we sweat and the water evaporates off our skin, there is a cooling effect as the average kinetic energy of the water molecules is lowered.

Question 5

What is a solvent?

Answer 5

A liquid in which other substances can dissolve

Question 6

What is a solute?

Answer 6

A molecule that can dissolve in a liquid

Question 7

Water as a solvent?

Answer 7

The charged regions of water separate molecules and allow them to move freely. Means water is good for metabolic reactions and for transporting substances (such as in the blood)

Question 8

What is surface tension and cohesion?

Answer 8

• Hydrogen bonding between molecules means that water sticks together in a column
• When there is no water molecule above another, the uneven distribution of attraction forms a thin ‘skin’ layer called surface tension - Can support insects and small aquatic creatures

Question 9

What do carbohydrates contain?

Answer 9

Carbon, hydrogen and oxygen Cx(H2O)y

Question 10

What are the monosaccharides?

Answer 10

Simple sugars

• glucose
• fructose
• galactose

Question 11

What are the disaccharides?

Answer 11

Double sugars

• glucose + glucose –> maltose
• glucose + fructose –> sucrose
• glucose + galactose –> lactose

Question 12

What are the polysacchardies?

Answer 12

Large molecules form many monosaccarhides

• Starch
• Glycogen
• Cellulose

Question 13

Glucose

Answer 13

C6H12O6 (Hexose sugar)
Energy source
Alpha glucose –> OH below carbon
Beta glucose –> OH above carbon

Question 14

Ribose and deoxyribose

Answer 14

Deoxyribose has no OH on its second carbon

Question 15

How are disaccharides formed?

Answer 15

Condensation reaction between two monosaccharides

• Forms disaccharide and H20
• OH and HO are broken to form bond with oxygen remaining
• 1,4 glycosidic bond

Question 16

Structure of starch

Answer 16

Polysaccharide
Made from only Alpha glucose
Contains amylose (unbranched) - good because compact - and amylopectin (branched) - glycosidic bonds broken down easily - glucose released quickly
Both alpha 1,4 and alpha 1,6 glycosidic bonds
Used for Energy store in plants
Insoluble in water - good for storage as it does not alter osmosis

Question 17

Cellulose

Answer 17

Polysaccharide
Found in plant cell walls
Long chains of Beta glucose molecules
Beta glucose 1,4 glycosidic bonds
Chains for microfibrils in a layered network
Joins in condensation reaction where every other Beta glucose is rotated 180 degrees
Forms glycosidic bond at oxygen on top
Extra strength because of hydrogen bonds

Question 18

Glycogen

Answer 18

Polysaccharide
Animal energy store
Alpha 1,6 and 1,4 glycosidic bonds
Branched structure - Good for storage
Less dense and more soluble than starch and broken down more rapidly - higher metabolic rate in animals

Question 19

Test for reducing sugars

Answer 19

Add Benedict's reagent (solution) (Blue)
Heat sample - bring to boil (Water bath)
Observe for colour change/ coloured precipitate
Qualitative test
Blue - none
Green/ yellow - low conc
Orange - med conc
Red - high conc
More accurate way is to filter and weigh
Always use an excess to make sure all the sugar reacts

Question 20

Test for non reducing sugars

Answer 20

Add HCl
Boil for 5 mins
Add NaHCO3
Add Benedict's Reagent (solution)
Heat
Observe for colour change
Qualitative test
Blue - none
Green/ yellow - low conc
Orange - med conc
Red - high conc

Question 21

What are Polymers?

Answer 21

Large, complex molecules composed of long chains of monomers

Question 22

Test for starch

Answer 22

Add iodine dissolved in potassium iodide solution - if starch present then changes from browny-orange to a dark, blue-black colour

Question 23

Importance of water?

Answer 23

Metabolite
Solvent
Temperature control
Very cohesive - water transport in plants

Question 24

How to produce a calibration curve and find the concentration of (reducing sugars)?

Answer 24

Produce benedicts test for known concentrations of sugars
Use calorimeter to find colour intensity and plot on a calibration curve
Find the concentration of sample from calibration curve