Unit 4: Energy, Environment, Microbiology and Immunity
Unit 4 — Complete A Level and AS source — IAL Edexcel Modular Revision Notes & Topical Questions
5 min read 9 parts Lesson 2 of 8 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
Unit 4 — Complete A Level and AS source notes — IAL EDEXCEL MODULAR notes: Summarise photosynthesis, ecosystems, climate change, microbiology, immunity and forensics.Overall equation — 6CO2 + 6H2O → C6H12O6 + 6O2 in light with chlorophyll.Light-dependent reactions — in the thylak…
- Light-independent reactions (Calvin cycle)
- Trophic level
- Energy transfer
- Succession
- Population estimates
- Abiotic measurements
Part 1 of 7Photosynthesis
1
Overall equation
- 6CO2 + 6H2O → C6H12O6 + 6O2 in light with chlorophyll.
2
Light-dependent reactions
- Light-dependent reactions in the thylakoid membranes light energy splits water (photolysis),
- and the released electrons pass along an electron transport chain.
- Protons are pumped to make ATP by chemiosmosis, and NADP is reduced.
3
Light-independent reactions (Calvin cycle)
- Light-independent reactions (Calvin cycle) in the stroma, CO2 is fixed onto RuBP by rubisco to form glycerate 3-phosphate (GP).
- GP is reduced to glyceraldehyde 3-phosphate (GALP) using ATP and reduced NADP.
- Five out of every six GALP molecules regenerate RuBP, and the rest make glucose, sucrose, starch, cellulose, amino acids and lipids.
Part 2 of 7Ecosystems and the environment
Trophic level
- Trophic level the feeding level of an organism in a food chain.
Energy transfer
- Energy transfer it is inefficient because energy is lost in respiration, in waste and in uneaten parts.
Succession
- Succession the predictable change in a community from pioneer species to a climax community, which has greater biodiversity than early stages.
Population estimates
- Population estimates population = mean per quadrat × , and percentage cover = squares containing the species ÷ total squares × 100.
- (total area ÷ quadrat area)
Abiotic measurements
- Abiotic measurements light in lux, temperature in °C and soil pH with a probe.
Part 3 of 7Climate change
1Enhanced greenhouse effect
Enhanced greenhouse effect increase in the greenhouse effect caused by human activity raising the concentration of greenhouse gases (CO2, CH4),
- so more infrared radiation is trapped.
- Atmospheric CO2 rose from about 280 ppm pre-industrial to over 420 ppm.
2Calculations
- Calculations percentage change = (new − original) ÷ original × 100, and Q10 = rate at (T + 10) °C ÷ rate at T °C, usually 2–3 for enzyme reactions.
| Evidence | Measures | Limitation |
|---|---|---|
| Temperature records | Direct readings since about 1850 | Short span and fewer early records |
| Tree rings | Ring width reflects growing conditions | Other factors, such as nutrients, affect width |
| Pollen in peat | Past plant species | Pollen can be blown in |
| Ice cores | CO2 in bubbles, temperature from isotopes | Only polar locations |
1
Carbon cycle
- Carbon cycle combustion of fossil fuels releases carbon stored for millions of years: CH4 + 2O2 → CO2 + 2H2O.
- Mature forests are close to carbon neutral, whereas growing forests are net sinks.
- Models that extrapolate data predict future temperatures but have uncertainty.
- Rate of change from a graph change in y ÷ change in x, for example ppm per year.
2
Temperature and development practicals
- Temperature and development practicals other variables are kept constant and extremes of temperature avoided.
Part 4 of 7Microbiology and immunity
Bacterial growth
- Bacterial growth bacteria divide by binary fission,
- so with a generation time of 20 minutes, 50 cells after 3 hours (9 generations) become 50 × 29 = 25 600 cells.
Aseptic technique
- Aseptic technique flame loops and bottle necks, work near a Bunsen flame, tape (not seal) plates and incubate at 25 °C, not 37 °C, to avoid growing human pathogens.
Tuberculosis
- Tuberculosis caused by Mycobacterium tuberculosis, spread by droplets, with bacteria surviving inside macrophages and forming tubercles.
T killer cells
- T killer cells they bind complementary antigen on infected body cells and destroy them, for example with perforin that makes pores in the membrane.
B cells
- B cells they form plasma cells that secrete antibodies, and memory cells.
Part 5 of 7Forensics
Forensics
Succession on a corpse
- Succession on a corpse blowflies arrive first, then flesh flies, then beetles feeding on drier tissue, then mites and soil organisms.
- The community present indicates the stage reached and so the time since death.
DNA profiling
- DNA profiling it relies on PCR amplification and gel electrophoresis.
Evolutionary relationships
- Evolutionary relationships they are inferred from DNA and protein sequence similarity using bioinformatics.
- Bioinformatics is the use of computer software and databases to store and analyse biological data.
Part 6 of 7More from the specification
More from the specification
Photosynthetic Pigments and Chromatography
- Leaf pigments are separated by chromatography using an organic solvent inside a chromatography chamber.
- (chlorophyll a, chlorophyll b, carotene, xanthophyll)
Light-Dependent Reactions and Photosystems
- In the thylakoid membranes of the chloroplast, light energy is absorbed by accessory pigments in photosystem II and I to excite electrons.
Photolysis of Water
- Light-driven splitting of water in photosystem II generates hydrogen ions (protons), electrons,
- and waste oxygen gas.
- (2H₂O → 4H⁺ + 4e⁻ + O₂)
Carbon Dioxide Fixation and Light Intensity
- Carbon dioxide is fixed into carbohydrates in the Calvin cycle;
- increasing light intensity increases the rate of glucose produced until another factor becomes limiting.
Photosynthetic Pigments and Chromatography
- Leaf pigments are separated by chromatography using an organic solvent inside a chromatography chamber.
- (chlorophyll a, chlorophyll b, carotene, xanthophyll)
Light-Dependent Reactions and Photosystems
- In the thylakoid membranes of the chloroplast, light energy is absorbed by accessory pigments in photosystem II and I to excite electrons.
Photolysis of Water
- Light-driven splitting of water in photosystem II generates hydrogen ions (protons), electrons,
- and waste oxygen gas.
- (2H₂O → 4H⁺ + 4e⁻ + O₂)
Carbon Dioxide Fixation and Light Intensity
- Carbon dioxide is fixed into carbohydrates in the Calvin cycle;
- increasing light intensity increases the rate of glucose produced until another factor becomes limiting.
Light intensity
- The amount of light reaching a plant.
Hydrogen
- A flammable gas that burns with a squeaky pop.
Solvent
- The liquid that a solute dissolves in.
Chloroplast
- Organelle where photosynthesis takes place.
Chromatography
- A technique to separate substances in a mixture.
Absorption
- Movement of digested molecules into the blood or lymph.
Photophosphorylation
- Production of ATP using light energy.
Part 7 of 7More on this topic
- Specific immunity
- B lymphocytes produce antibodies that bind a matching antigen, and T lymphocytes coordinate responses or destroy infected cells.
Key terms
| Term | Meaning |
|---|---|
| GALP | Glyceraldehyde 3-phosphate, a 3-carbon sugar phosphate made in the Calvin cycle. |
| Trophic level | Feeding level of an organism in a food chain. |
| Enhanced greenhouse effect | Increase in the greenhouse effect due to human activities raising greenhouse gas concentrations. |
| T killer cell | Lymphocyte that destroys infected body cells displaying a specific antigen. |
| Bioinformatics | Use of computers and databases to store and analyse biological data. |
Avoid these mistakes
1
Saying the Calvin cycle needs no ATP — it uses ATP and reduced NADP.
2
Confusing GP and GALP — GP is formed first and is reduced to GALP.
3
Describing the greenhouse effect as the ozone hole — it is trapping of infrared radiation by greenhouse gases.
4
Forgetting to subtract the original value in a percentage change calculation.
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