Paper 1

Question 1

What are the components of a DNA nucleotide

Answer 1

Nitrogenous base, deoxyribose sugar, phosphate group

Question 2

Describe semi conservative replication

Answer 2

• Enzyme DNA helicase breaks the hydrogen bonds between base pairs and separates part of the two polynucleotide strands
  
  • Individual DNA nucleotides in the nucleus attach (hydrogen bonding) to the exposed bases of each template strand due to specific complementary base pairing
  • Forming two new complementary strands.
  • DNA polymerase joins the DNA nucleotides in each new strand together by phosphodiester bonds in condensation reactions
    The two DNA molecules are identical to each other and to the original DNA.’

Question 3

Describe crossing over

Answer 3

Crossing over + genetic recombination
- In meiosis during prophase of the first division (meiosis I) homologues pairs lie side by side to form a bivalent
- The chromatids intertwine, break and equivalent portions of chromatids are exchanged
○ New combination of alleles (recombinants) - genetic recombination
The number formed is relatively low because crossing over is rare

Question 4

Describe chromosome muttations

Answer 4

• Mutation in number of chromosomes can arise spontaneously due to chromosome nom-disjunction during meiosis
  
  • Homologues pairs of chromosomes are not separated during meiosis 1 so both members of the homologues pair move to one pole
    This results in one gamete with an extra chromosome and a gamete with one less chromosome

Question 5

Clasification rrancks

Answer 5

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

Question 6

Types of adaptions

Answer 6

Behavioural - way an organism acts (fish swim in groups)
Physiological - processes which occur within the body (sloths have a low metabolism which means they can survive on food which contains a low number of calories)
Anatomical - structural features of an organism (polar bears are camouflaged against the snow )