Photosynthesis IN Higher Plants flash cards

1. 1.Define photosynthesis.

   The physico-chemical process by which green plants use light energy to synthesise organic compounds (carbohydrates) from CO2 and water, releasing O2.

   Hint: Light-driven food making

2. 2.Write the overall balanced equation of photosynthesis.

   $6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O$ (in presence of light and chlorophyll).

   Hint: 12 water molecules used

3. 3.Why is water written on both sides in the modern photosynthesis equation?

   Because 12 H2O are used and 6 H2O are newly formed; this shows that the O2 released comes from water, not CO2.

   Hint: O2 source proof

4. 4.Who showed that O2 released in photosynthesis comes from water?

   Ruben and Kamen, using radioactive isotope $O^{18}$ (heavy oxygen) in water.

   Hint: O-18 tracer

5. 5.Which experiment showed that only the green parts of a leaf produce starch?

   The variegated leaf / half-covered leaf starch test (with iodine) — only chlorophyll-containing, illuminated parts turn blue-black.

   Hint: Iodine on variegated leaf

6. 6.Priestley's bell jar experiment demonstrated what?

   That plants restore to air whatever burning candles or breathing animals remove — i.e. plants release O2 (release of a substance that supports combustion).

   Hint: Candle, mouse, mint plant

7. 7.What did Jan Ingenhousz add to Priestley's conclusion?

   That sunlight is essential and only the green parts of plants release O2 (bubbles from green parts in light).

   Hint: Light needed; green parts

8. 8.Julius von Sachs demonstrated what about photosynthesis product?

   That glucose (stored as starch) is produced in green parts (chloroplasts) of plants.

   Hint: Starch = product

9. 9.What did T.W. Engelmann discover using Cladophora and a prism?

   The action spectrum of photosynthesis — aerobic bacteria accumulated in blue and red light regions, showing these are most effective.

   Hint: Prism + bacteria + alga

10. 10.What is an action spectrum?

    A graph of the rate (effectiveness) of photosynthesis versus wavelength of light.

    Hint: Rate vs wavelength

11. 11.What is an absorption spectrum?

    A graph showing the amount of light absorbed by a pigment at different wavelengths.

    Hint: Absorption vs wavelength

12. 12.In which two regions of the spectrum is photosynthesis maximum?

    Blue ($\approx$450 nm) and red ($\approx$660-700 nm) regions.

    Hint: Blue and red

13. 13.Cornelius van Niel's contribution to understanding photosynthesis?

    Using purple/green sulphur bacteria, he showed photosynthesis is essentially a light-driven reaction where H2 from a hydrogen donor reduces CO2; O2 comes from water.

    Hint: H2S bacteria, general equation

14. 14.Write van Niel's general equation of photosynthesis.

    $2H_2A + CO_2 \rightarrow 2A + CH_2O + H_2O$ (in bacteria H2A = H2S, so sulphur is released instead of O2).

    Hint: H2A as hydrogen donor

15. 15.Where does photosynthesis occur in the plant cell?

    In the chloroplast.

    Hint: Green plastid

16. 16.Name the two main functional parts of a chloroplast.

    The membranous grana (thylakoids — for light reaction) and the fluid stroma (for dark/biosynthetic reactions).

    Hint: Grana + stroma

17. 17.What are thylakoids and grana?

    Thylakoids are flattened membranous sacs; a stack of thylakoids is called a granum (plural grana).

    Hint: Stacked coins

18. 18.Which reactions occur in the thylakoid membranes?

    The light reactions (photochemical phase) — trapping light, water splitting, formation of ATP and NADPH.

    Hint: Grana = light phase

19. 19.Which reactions occur in the stroma?

    The dark reactions (biosynthetic phase / Calvin cycle) — fixation of CO2 into sugars.

    Hint: Stroma = carbon fixation

20. 20.Why are the light and dark reactions so named?

    Light reaction depends directly on light; dark reaction does not directly require light (though it uses ATP/NADPH from light reaction).

    Hint: Direct light dependence

21. 21.Is the term 'dark reaction' fully accurate?

    No — the biosynthetic phase does not need darkness; it just does not use light directly. It depends on products (ATP, NADPH) of the light reaction.

    Hint: Not carried out in dark

22. 22.Name the four classes of photosynthetic pigments in higher plants.

    Chlorophyll a, chlorophyll b, xanthophylls, and carotenoids (carotenes).

    Hint: a, b, xantho, caroten

23. 23.Which is the chief / most abundant photosynthetic pigment?

    Chlorophyll a — the main pigment involved in trapping light and the reaction centre.

    Hint: Bright/blue-green, primary

24. 24.What colour is chlorophyll a versus chlorophyll b?

    Chlorophyll a is bright or blue-green; chlorophyll b is yellow-green.

    Hint: a = blue-green

25. 25.What are accessory pigments and give examples.

    Pigments (chl b, xanthophylls, carotenoids) that absorb light and transfer energy to chl a; they also protect chl a from photo-oxidation.

    Hint: Widen absorption + protect

26. 26.Which pigment is the primary pigment and which act as accessory pigments?

    Chlorophyll a is the primary/reaction-centre pigment; chl b, carotenoids and xanthophylls are accessory pigments.

    Hint: chl a = reaction centre

27. 27.Why do leaves appear green?

    Because chlorophyll absorbs blue and red light strongly but reflects/transmits green light.

    Hint: Green is reflected

28. 28.What is the role of carotenoids besides light absorption?

    They protect chlorophyll from photo-oxidation (act as protective agents against excess light).

    Hint: Prevent photo-oxidation

29. 29.What is a photosystem (light harvesting complex, LHC)?

    An organised array of hundreds of pigment molecules (antenna) bound to proteins, with a single reaction-centre chlorophyll a.

    Hint: Antenna + reaction centre

30. 30.What is the function of antenna pigments in a photosystem?

    They absorb light of different wavelengths and funnel the energy to the reaction-centre chlorophyll a.

    Hint: Harvest and transfer energy

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