Suggest the advantages of using mitochondrial DNA. (To construct a phylogenetic tree)

There is no recombination in mitochondrial DNA from parent to offspring, hence changes in DNA sequence is solely due to the accumulation of mutations over time, so it can reliably be linked to the molecular clock.

Mitochondrial DNA has a faster mutation rate compared to nuclear DNA, hence it is useful for comparing individuals within a species/closely related species, as it requires discernible differences between DNA of organisms being compared.

Images: synapses/synaptic cleft

The pre-synaptic cell is the one with all the secretory vesicles.

Describe the role of mitosis in maintaining genetic stability.

1. Produces two nuclei/cells with same number of chromosomes as parent cell
2. thus daughter cells are genetically identical to parents
3. DNA replicated via semi-conservative replication during interphase to give exact copies
4. Each strand of parental DNA acts as template for the exact replication to form the new daughter strand
5. through complementary base pairing
6. In prophase, chromatin condenses to form chromosome which exists as 2 identical chromatids joined by single centromere
7. During metaphase, sister chromatids are attached to microtubulues from either pole
8. During anaphase, centromere divides and microtubules shorten
9. which ensures sister chromatids are separated to opposite pole during anaphase
10. ensuring equal distribution of chromosomes to daughter nuclei
11. In asexual reproduction, mitosis produces genetically identical daughter cells
12. which are clones

During anaphase, centromere divides, it doesn't split
DNA is replicated, not duplicated

Images: nucleus

It's important to get used to how organelles look in micrographs.

Nucleus (which is euchromatin and which is heterochromatin?)

Role of NAD in oxidative phosphorylation

1. Organic molecules are oxidised during glycolysis, link reaction and Krebs cycle, producing high energy electrons and protons. 
2. NAD serves as a mobile proton and electron carrier, carrying these electrons and protons to the electron transport chain on cristae of mitochondria.  
3. High energy electrons in NADH reduce electron acceptors of ETC; NAD is re-oxidised. 
4. Electrons passing down the ETC is coupled to production of ATP. Protons liberated in the oxidation of NADH establish the proton motive force. Reoxidation of NADH allows regeneration of coenzyme NAD⁺ so they can pick up more electrons and protons from Krebs cycle etc. so that these reactions can continue.
5. 1 reduced NAD to 3 ATP through oxidative phosphorylation.

Describe the structure of a beta-pleated sheet of a spider silk protein.

Hydrogen bonds form between the C=O group of a peptide in one strand and the N-H group of another peptide in the adjacent strand. R-groups project above and below the beta-pleated sheet.

Outline the procedure of a titration experiment to determine the concentration of ammonia in the organic layer.

NB: Given 0.010 mol dm^-3 hydrochloric acid, methyl orange indicator and lab apparatus commonly used for titration.

1. Fill up a burette with 50.00cm³ of 0.010mol/dm³ HCl
2. Using a dry pipette, transfer 10.0 cm³ of the organic layer into a 250cm³ conical flask.
3. Using a measuring cylinder, add 20 cm³ of deionised water into the conical flask, then add 2-3 drops of methyl orange. 
4. Titrate the resulting mixture against 0.010mol/dm³ HCl until the colour of methyl orange changes from yellow to orange.
5. Repeat the titration until 2 consistent readings are obtained.