Unit 1 (IB Questions)

The water molecule is

Slightly negative near the oxygen atom and slightly positive near the hydrogen atoms.

Between which atoms do hydrogen bonds form in water?

Oxygen and hydrogen atoms in different water molecules

Describe the cause of the attraction between molecules of water (4). 

Water is polar;

O atom more negative;

H atoms more positive;

This causes «strong» hydrogen bonds to form between the molecules (4)

Draw two water molecules with notation to indicate their polarity and their hydrogen bonds.

Distinguish between intramolecular and intermolecular forces in water molecules with examples (4).

intramolecular forces occur within molecules;

example intramolecular force: covalent bonds;

intermolecular forces occur between molecules;

example intermolecular force: hydrogen bonds (4)

Outline the origin of water of Earth.   (2)

evidence shows that water traveled to Earth on asteroids;

distance from the sun ensures that water doesn’t boil;

gravity due to Earth’s size holds oceans near its surface and water vapor within its atmosphere  (2)

What is the difference between cohesion and adhesion?

cohesion is an attraction between water molecules

Which statement about water is correct?

Water’s solvent properties allow living things to transport a variety of polar molecules

State the role of capillary action in plants. (1)

transports water upwards against gravity (1)

Describe the properties of water that make it a useful component of blood.  (4)

a. water is a polar molecule / hydrogen bonding;

b. (makes it) (versatile) solvent;

c. example of dissolved substance (eg salts/proteins or other example);

d. (water is) fluid/liquid at body temperature;

e. example of transported material (eg nutrients/metabolic wastes/gases/hormones/blood cells or other example);

f. high heat capacity/specific heat allows water to carry heat without warming up;

g. (allows) blood to move heat (for warming/cooling/homeostasis);   

Explain cohesion and adhesion and two ways they are useful for living things (3).

cohesion: ability water molecules to stick together

hydrogen bonds between water molecules make water cohesive;

cohesive properties help in transpiration pull/movement of water in plants;

high surface tension allows some animals to stride across its surface;

adhesion: attraction of water molecules to other polar substances

the polarity of water molecules allows them to be attracted to other polar substances

adhesion helps in transpiration pull/movement water in plants;

What is a consequence of the specific heat capacity for liquid water, ice and water vapor?

Less energy is needed to warm water vapor than liquid water.

What physical property of water allows organisms to use it as a habitat because they do not need as much energy to float at a particular depth?

Buoyancy

Explain why aquatic habitats are more thermally stable than air.  (4)

water has a higher specific heat capacity than air;

water must gain a large amount of heat energy to break hydrogen and raise its temperature;

equal amount of energy must be lost to lower the temperature of water;

temperature of water remains more stable than that of air   (4)

Explain why aquatic warm-blooded animals are at a higher risk the loss of body heat than land-based warm-blooded animals. (3)

rate at which heat moves through a body is thermal conductivity;

water has a higher thermal conductivity than air;

air is a thermal insulator;

more body heat can be transferred between blood and water per unit time  (3)

Describe how the energy requirements for movement in water and air habitats differ due to buoyancy and viscosity.    (4)

air is less dense than water and provides less buoyant force;

organisms must spend more energy to stay aloft in air than float in water;

water is more viscous than air;

organisms spend more energy to move through water than air (4)

What chemical reaction is taking place when two amino acids bond to become a dipeptide?

Condensation

How many water molecules are needed to hydrolyze a polysaccharide made up of 23 monosaccharides?

22

A. Which of the following terms correctly describe the molecule?

I. monosaccharide

II. ribose

III. carbohydrate

B. Which of the following correctly describes the molecule above?

I and III only/alpha-D-glucose

State two monosaccharides.  (2) 

monosaccharides

glucose/ribose/deoxyribose/fructose/other example  (2) 

Outline three properties and uses of glucose. (3)

yields energy when oxidized via respiration; 

soluble in water and easily transported;

stable & good for energy storage in small amounts;

does not increase water uptake by cell    

Outline condensation and hydrolysis reactions.  (4)

condensation reactions involve joining subunits/molecules/monomers;
with the release of water;
hydrolysis reactions involve splitting molecules into subunits/molecules/monomers; with the addition of water;

Which molecules are polysaccharides?

starch, glycogen, cellulose

What distinguishes cellulose from glycogen and starch?

Cellulose has a structural role and starch and glycogen function in energy storage.

A polymer of alpha-D-glucose in plants has 1,4 linkages and no 1,6 linkages. Which molecule is it?

Amylose

Which carbohydrates are used to provide energy storage in plants and animals?

C. plants: starch and animals: glycogen

Describe the structure and function of starch in plants. (3)

1. «starch» is a polysaccharide;

    b.composed of alpha-glucose molecules c. contains amylose which is a linear/helical molecule 

   d. amylose contains alpha-1,4 linkages

   e. contains amylopectin which is a branched molecule 

   f.  Amylopectin contains alpha-1,4 linkages and alpha-1,6 linkages

   Function:

   e. storage of glucose/energy in plants 

   f. storage form that does not draw water  

Describe the structure and function of glycogen. (5)

Polysaccharide;

composed of alpha-glucose monomers; contains alpha-1,4 linkages and alpha-1,6 linkages; a branched molecule; storage glucose/energy;  found in animals;

Describe the structure and function of cellulose.   (5) 

polysaccharide;

composed of beta-glucose monomers;

composed of straight chains;

strength and support of cell walls; found in plants

Which of the following describes the molecule below.

1. saturated

2. polyunsaturated

3. cis configuration

4. trans configuration

b. I and III only

A ________has two fatty acids and a polar phosphate group attached to a glycerol.

phospholipid

Outline the variation in structure of fatty acids.    (4)

fatty acids share a common structure but differ in total number of carbon atoms in the chain;

saturated fatty acids have no double bonds between carbon atoms;

unsaturated have double bond(s);

unsaturated can differ in location of double bonds;

monounsaturated have one double bond / polyunsaturated have more than one double bond;

cis fatty acids have hydrogen atoms on same side of double bond and trans have them on opposite side;

Outline the structure of phospholipids. (3)

two fatty acids bonded to one glycerol;

ester bonds link fatty acids and glycerol;

phosphate group attached to glycerol

Describe the organization of phospholipids into the lipid bilayer. (3)

phospholipids form bilayers in aqueous (water-based) solutions;

polar/hydrophilic phosphate heads face out/towards water

nonpolar/hydrophobic hydrocarbon tails face in/away from water

Which of the following is true regarding triglycerides containing cis-unsaturated fatty acids?

 They are classified as oils and reduce the risk of heart disease.

What type of molecule is shown in the diagram to the right?

A. starch C. phospholipid

B. triglyceride D. glycogen 

How many water molecules are produced in the formation of the molecule to the right?

B. Triglyceride/ 3 molecules

Outline the structure of a triglyceride.  (2)

three fatty acids bonded to one glycerol;

ester bonds link fatty acids and glycerol;

Outline the properties of triglycerides that make them suitable for long-term energy storage and thermal insulation. (4)

chemically stable/energy is not lost over time; fat droplets do not draw in water/affect cells; fat releases twice as much energy per gram than carbohydrates/energy stored with fat produces half the body mass; poor conductors of heat/used as insulators in body; liquid at body temperature so absorbs shock

What is the molecule to the right?            

A. Amino acid

B. Ribose

C. Deoxyribose

D. Lactose

A. Amino acid

Which of the following correctly shows a peptide bond between two amino acids?

C.

What contributes to the structure of a polypeptide?

Sequence of amino acids linked by peptide bonds

Draw and label the general structure of an amino acid.   (5)

C in middle 

b. COO– or COOH group at one side 

c. NH₂ or NH₃⁺ at other side

d. R group on top or bottom of central carbon

e. H at opposite side of R group

Explain the primary and secondary structures of proteins.   (6)

primary structure 

(number and) sequence of amino acids;
joined by peptide bonds

secondary structure 

repetitive folding pattern;

held by H-bonds;

between amino and carboxyl groups within backbone;

α-helix / β-sheet;     

Which best describes the tertiary structure of a protein?

The three dimensional structure formed from interactions between amino acid side groups

Which interactions can stabilize tertiary and quaternary protein structure?

I. hydrogen bonds

II. peptide bonds

III. hydrophobic interactions

C. I and III only

What is denaturation?

A structural change of a protein that results in the loss of its biological properties

Distinguish between the secondary structure and tertiary structure of proteins.    (3)

secondary structure	tertiary structure
refers to regular repeating regions within the overall protein structure	refers to the protein overall / 3-D;
secondary structure α helix/β sheets	while tertiary is globular/fibrous;
forces between amino and carboxyl groups/atoms within backbone in secondary structure	while intramolecular forces between R-groups for tertiary structure;
H-bonds	H-bonds /disulfide bonds / ionic bonds / hydrophobic interactions;

Define quaternary structure in proteins. (1)

the linking together of two or more polypeptides to form a protein

Amino acid polarity is an important factor in determining the functions of proteins. Explain the significance of polar and non-polar amino acids.  (4)

polar amino acids have hydrophilic R groups, non-polar have hydrophobic R groups;
non-polar amino acids in center of water-soluble proteins stabilize their structure;
polar amino acids on surface of proteins make them water-soluble;

non-polar amino acids cause proteins to remain embedded in membrane;
polar amino acids create hydrophilic channels/protein pores in membranes;
enzyme active site specificity depends on amino acids present/polar and
non-polar amino acids can play a role in substrate interactions at the active site;

Distinguish between fibrous and globular proteins with named examples (4).

Fibrous protein:

example: collagen / myosin / actin / other example;

not water soluble;

long/narrow shape/ no tertiary  structure;

structural/movement functions;

Globular protein:

example: insulin/ hemoglobin / other named example;

water soluble;

rounded shape/tertiary structure;

conformation/shape is necessary for function

examples of both fibrous and globular protein needed to gain the mark.