Mark schemes to learn

Question 1

Describe how the primary structure of a protein results in a protein with a 3D structure

Answer 1

1. Primary structure=Sequence of amino acids
2. Amino acids have different R groups
3. Bonding occurs between R groups
4. Bonding determines the folding of a polypeptide

Question 2

Describe the cardiac cycle

Answer 2

Atrial systole:

1. Blood under low pressure flows into the atria and atria fills up
2. Atria contracts, increasing pressure
3. High BP blood is forced through atrioventricular valves into ventricles

Ventricular systole:

1. Ventricles contract from bottom upwards, increasing pressure and forcing AV valves shut
2. High BP blood forces through semilunar valves
3. Blood flows out the heart

Diastole:

1. Atria and ventricles relax and elastic recoil lowers pressure
2. High BP blood is drawn back to ventricles
3. Low pressure in atria draws blood into the heart from the veins

Question 3

Compare and contrast the structure of globular and fibrous proteins

Answer 3

• Globular proteins are spherical and fibrous proteins elongated strands
• Globular proteins are soluble and fibrous proteins are insoluble
• Globular proteins have no repeated sequence of amino acids but fibrous proteins do
• Both are polypeptides and have a quaternary structure

Question 4

Give the definition of a gene

Answer 4

a sequence of bases on a DNA molecule that codes for a

sequence of amino acids in a polypeptide chain.

Question 5

Explain how the structure of the lungs enables rapid gas exchange

Answer 5

• Many alveoli creates large surface area
• High concentration gradient is maintained by circulation
• Thin walls allowing a shorter diffusion distance
• Capillary network creating large surface area for gas exchange

Question 6

Why is water a good solvent

Answer 6

• Polar molecule
• Hydrogen bonds
• Charged= can be dissolved

Question 7

Describe how the structure of glycogen is related to its function as a storage molecule

Answer 7

• Compact so more can be stored

- Many terminal ends for rapid hydrolysis

Question 8

Give the definition for an allele

Answer 8

A different form of the same gene which determine a characteristic

Question 9

Compare and contrast the structure of cellulose and amylopectin

Answer 9

• Cellulose contains b-glucose and amylopectin contains a-glucose
• Cellulose contains 1-4 glycosidic bonds but amylopectin contains 1-4 and 1-6

Question 10

Explain why offspring may be genetically different

Answer 10

During meiosis, Independent assortment means that the homologous pairs line up randomly , causing variation. Crossing over means that the 4 chromatids over lap at the chiasma then break off, swapping parts of the DNA. furthermore, each zygote is formed from different gametes

Question 11

Describe translation

Answer 11

mRNA attached to the ribosome 
tRNA is attached to a (specific) amino acid 
tRNA anticodon binds to mRNA codon 
peptide bonds form between amino acids 
process involves {start / stop} codons