Bio Topic 3 Flashcards
1a. [3 marks]
Sketch the complementary strand to complete the section of a DNA diagram.
k
1b. [1 mark]
Define mutation.
A change in the nucleotide sequence of a section of DNA coding for a specific trait.
1c. [4 marks]
Explain how evolution by natural selection depends on mutations.
Heritable characteristics are encoded for by genes and may be transferred between generations as alleles;
Evolution is a change in the allele frequency of a population’s gene pool over successive generations;
Species with more adaptive gene mutations to the environment, tend to survive more.
Species with more adaptive gene mutations to the environment, reproduce more and pass on their characteristics.
- [4 marks]
Outline how two parents could have a child with any of the four ABO blood groups.
k
3a. [2 marks]
Label the parts of the DNA diagram indicated by I, II, III and IV.
- Cytosine
- Phosphodiester bond
- Phosphate
- Deoxyribose
3b. [2 marks]
Explain how model making helped Watson and Crick to establish the structure of DNA.
a. decided to combine what was known about chemical content of DNA with information from X-ray diffraction studies OWTTE.
b. built scale models of components of DNA
c. then attempted to fit them together in a way that agreed with the data «from separate sources»
3c. [1 mark]
Distinguish between the chromosomes of eukaryotic cells and prokaryotic cells.
a. is linear in eukaryotes but circular in prokaryotes
3d. [1 mark]
Outline the role of the enzyme helicase in replication.
Unwinds/separates strands/double helix (by breaking hydrogen bonds)
3e. [2 marks]
Outline the role of the enzyme DNA polymerase in replication.
a. links nucleotides together to form a new strand of DNA
b. uses pre-existing strand of DNA as template
4a. [3 marks]
Outline how translation depends on complementary base pairing.
a. translation converts a sequence of mRNA nucleotides/codons to a sequence of amino acids/polypeptide/protein
b. «triplets of» nucleotides on «activated» tRNAs pair with complementary «triplets of» nucleotides on mRNA / vice versa
c. base pairing occurs when adenine pairs with uracil and guanine pairs with cytosine
4b. [4 marks]
Describe the polymerase chain reaction (PCR), including the role of Taq DNA polymerase.
a. PCR is process by which a small sample of DNA can be amplified/copied many times
b. PCR involves repeated cycling through high and lower temperatures «to promote melting and annealing of DNA strands»
c. «mixture» is heated to high temperatures to break «hydrogen» bonds between strands of DNA/to separate the double-stranded DNA
d. Taq DNA polymerase can withstand high temperatures without denaturing
4c. [8 marks]
Explain benefits and risks of using genetically modified crops for the environment and also for human health.
Environment benefits:
a. pest-resistant crops can be made
b. so less spraying of insecticides/pesticides
c. less fuel burned in management of crops
d. longer shelf-life for fruits and vegetables so less
spoilage
Environment risks:
g. non-target organisms can be affected
h. genes transferred to crop plants to make them
herbicide resistant could spread to wild plants making super-weeds
Health benefits:
k. nutritional value of food improved by increasing nutrient
content
l. crops could be produced that lack toxins or allergens
5a. [1 mark]
State the haploid number for horses.
32
5b. [2 marks]
Explain reasons that mules cannot reproduce.
a. because the chromosome number is not an even number/63
b. (so) cannot divide by two during meiosis/cannot perform meiosis/chromosomes cannot pair up during meiosis
5c. [2 marks]
Discuss whether or not horses and donkeys should be placed in the same species.
a. To be in same species two organisms must have the same genes arranged on the same chromosomes
b. members of same species produce fertile offspring and a mule is not fertile
