HL Biology Paper 2: Mistake's I've Made

Nitrogen is part of many important substances in living organisms.

Draw labelled diagrams to show a condensation reaction between two amino acids.

a. at least one of the amino acid structures completely correct

b. peptide bond shown with N–C and C=O and N–H correct

c. release of water clearly shown

TOP TIPS for a distinguish question, e.g “Distinguish between transcription and translation.”

1. really highlight the differences

2. what does one thing have that the other doesn’t

Explain what the R_f values represent in chromatography.

1. see image

2. each pigment has/is represented by a specific R_f «value»

3. used to identify different pigments

4. R_f «value» depends on solubility of the pigment in the solvent

DNA codes for the amino acid sequence of polypeptides. List two other functions of DNA.

1. Telomeres (form caps at the end of chromosomes) 

2. Coding for tRNAs/rRNAs 

3. Allows genes/traits/heritable characteristics to be passed to offspring

Hydrogen bonds can exist both within and between molecules in living organisms and have an impact on their structure and function. Explain the importance of hydrogen bonding for living organisms. (7)

1. Cohesion in wate stick together (due to hydrogen bonds) 

2. Adhesion between water and cell walls 

3. Solvent properties (due to hydrogen bonds) with polar/hydrophilic molecules 

4. High (specific) heat capacity so water temperature changes less 

5. Base pairing between bases in DNA by hydrogen bonding 

6. Base pairing between bases in RNA and DNA for transcription between codon and anticodon for translation 

7. Proteins have hydrogen bonding in secondary structure/α helix/β pleated sheet 

8. Proteins have hydrogen bonding between R groups in tertiary structure to maintain conformation 

Explain how enzymes catalyse chemical reactions. (3)

1. enzymes work by forming enzyme–substrate complexes 

2. binding of substrate to active site of enzyme 

3. enzyme changes shape slightly

4. decreases activation energy → increases rate of reaction 

explain the secondary structure of this protein molecule (3)

1. the secondary structure includes alpha helices/beta pleated sheets

2. spiral coils of this protein consist mainly of alpha helices

3. between oxygen and hydrogen atoms of amino acids on backbone

explain how enzymes catalyse chemical reactions

1. binding of substrate to the active site of the enzyme, forming enzyme-substrate complexes

2. enzymes bind to specific substrates

3. AE decreases and ROR increases

describe what happens to the membranes of an animal cell, during and immediatley after mitosis

1. nuclear membrane breaks down in prophase

2. nuclear membrane reforms around two new nuclei

3. plasma membrane pulled inwards at equator / cleavage furrow formed

4. membrane pinches apart to form two cells

explain transcription

1. RNA polymerase binds to the promoter

2. RNA nucleotides linked together to form a strand

3. RNA strand assembled on DNA template

4. RNA polymerase carries out transcription

5. uncoiling of DNA strands

6. 5’ end of nucleotides linked to 3’ end of growing RNA strand

7. complementary bas pairing

8. uracil instead of thymine in RNA

9. regulated by transcription factors