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BIOLOGY PAPER 4 PROCESSES
TOPIC 5:
5A: Light Dependent Reactions in the Thylakoids:
1
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Electrons leave chlorophyll & pass to electron carriers and start going down
electron transport chain through redox reactions
- Energy released from here generates ATP from ADP + Pi
(Photophosphorylation in PSI)
3
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NADPH is generated from NADP+, H+ & 2e5
...

2
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4
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5/6 of GALP regenerates RuBP with help of 1 x ATP

5A: Cyclic Photophosphorylation:
1
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Travels down electron transport chain using electron carriers through redox
reactions
3
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Electron is recycled back to PSI & process repeats

5A: Non-Cyclic Photophosphorylation:
1
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Electrons travel down electron transport chain through carriers to PSI & lose
energy through redox reactions
3
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PHOTOLYSIS OF WATER occurs & used to replace 2e- lost in PSII
5
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ATP + NADPH is used in Light Independent Reactions

5C: Geological Isolation → Speciation:
1
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AKA
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Isolated populations accumulate different chance mutations
3
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By natural selection, organisms with beneficial alleles survive for longer,
reproduce more & pass down these alleles
5
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2
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4
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Pre-existing mutation in population
Environment changes so new selection pressures are added
Organisms with useful allele for new environment, survive & reproduce
Alleles are passed on to their offspring
Beneficial alleles increase in frequency throughout the population
- Allows for higher chance in survival

5C: Decomposition Cycle:
1
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Inorganic ions assimilated by plants
3
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5
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7
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2
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4
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New viral particles are assembled & leave host cell by exocytosis
- Viral DNA remains in the nucleus & the process repeats again

6A: Binary Fission:
1
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Enzymes break circular pieces of DNA
- Allows DNA strands to unwind & be replicated
3
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New cell membrane & cell wall material extends inwards
- Forms a septum; divides into 2 daughter cells; each contains circular
chromosome attached to cell membrane
- Plasmids often divide at the same time; daughter cells usually contain a
copy of original genome & any plasmids present in parent cell

6A: 4 Stages of the Growth Curve:
1
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LOG/EXPONENTIAL PHASE:
- Rate of bacteria reproduction is close to/at theoretical maximum
3
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DEATH/DECLINE PHASE:
- Reproduction nearly ceases & death rate increases
- Population falls

6A: Counting Cells Using a Haemocytometer:
Haemocytometer: thick microscope slide with rectangular indentation & engraved grid
lines used to count cells divided into 4 corner squares with 16 smaller grids within it
- Holds 0
...
Dilute sample of nutrient broth by HALF with equal parts TRYPAN BLUE
- Trypan blue dyes dead cells BLUE; allows the identification of living cells
so you can count them
2
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Take a sample of the solution

2
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1 dilution)

3
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01 dilution)
4
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6A: How Tuberculosis Infects the Body:
1
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ACTIVE STAGE:
- When the immune system is weakened, the bacteria activates & slowly
destroys the lung tissue which leads to:
- Breathing problems; coughing; weight loss; fever etc
...

2
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4
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weight loss; dementia; cancer; serious infections
-

Final stage is ALWAYS DEATH

6B: Non-Specific Response: Inflammation:
1
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MAST CELLS RELEASE HISTAMINES:
- Mast cells found in CONNECTIVE TISSUE BELOW SKIN & AROUND BLOOD
VESSELS
- When tissue is damaged, mast cells & basophils release HISTAMINES
(chemical released by tissue due to allergic reactions)
3
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INCREASED BLOOD FLOW:
- Plasma, leucocytes & antibodies are forced out capillaries
- Causes SWELLING &, often, PAIN
5
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2
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4
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Macrophage engulfs bacteria
2
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Macrophage APC binds to T-helper cell
4
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Bacterium antigen binds to B cell with complimentary receptor
2
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B cell becomes an Antigen Presenting Cell (APC)
4
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B cell divides into B-MEMORY CELLS & B-EFFECTOR CELLS
6
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Plasma cells secrete ANTIBODIES

6B: Cell Mediated Response: T Cell Response:
Mainly for VIRAL INFECTIONS or when HUMORAL RESPONSE FAILS
1
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Host cell presents antigens on MHC’s; becomes an Antigen Presenting Cell
(APC)
3
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Cytokines from activated T helper cell causes T killer cell to divide and
differentiate to ACTIVE KILLER CELLS & T KILLER MEMORY CELLS
5
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T killer cells release chemicals
- Causes LYSIS in APC as pores form in the membrane --> APC dies

6B: MRSA:
-

Resistant to commonly used antibiotics
To reduce/slow the evolution of SUPERBUGS in the evolutionary race, we need to
reduce the selection pressures that may be causing their evolution

6B: Clostridium Difficile:
-

More common in areas where antibiotic use has been high
Linked to Hospital Acquired Infections
Exists naturally in the gut but kept under control by the NATURAL GUT FLORA
Use of antibiotics disturbs the natural balance and allows C
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Heart stops pumping blood
2
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Muscle cells use all ATP in muscles; muscle fibres = PERMANENTLY
CONTRACTED
4
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ANAEROBIC BACTERIA (EARLY COLONISERS):
- DOES NOT require oxygen to thrive in lactic acid conditions
- After death, the anaerobic bacteria takes control of the body and
reproduces freely
- Enzymes start to break down cells

2
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BLOWFLIES:
- Sensitive to smell of dead organisms so they ARRIVE QUICKLY
- Attracted to moisture & smells of natural openings in the body (eg
...
)
- Lays eggs in body; eggs hatch & start feeding on tissue & breaking it down
- PUPATE; turn into FLIES; MATE; & cycle starts again

3
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PARASITE WASPS:
- Lays eggs in FLY & BEETLE LARVAE
5
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CARCASS, HAM & HIDE BEETLES:
- Body is TOO DRY for maggots
- They're strong at chewing
- Feeds on remains of MUSCLES & CONNECTIVE TISSUES
7
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SEPARATION:
- Mixture is placed in PCR machine & heated to 90-95C for 30 secs
- DNA strands SEPARATE
2
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ELONGATION:
- Mixture is heated to 75C for at least 60 secs
- 75C = optimum temperature for TAQ POLYMERASE to build
COMPLEMENTARY DNA STRANDS

4
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DNA sample is cut into fragments using RESTRICTION ENDONUCLEASES
- Leaving sticky ends of varying lengths
2
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Add DNA samples to individual wells & add “MARKER” samples to one well
containing fragments of known sizes for comparison
4
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Smaller fragments move FASTER towards POSITIVE ANODE than LARGER ones
(so it moves FURTHER)
- Due to NEGATIVE CHARGE on phosphate group
6
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Compare SIZE, WIDTH, & POSITION of bands with REFERENCE SAMPLE



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