IB Biology/Molecular biology

Light and PhotosynthesisEdit

How does chlorophyll respond to the different wavelengths of light?

(Chlorophyll is found in the chloroplasts of plants. Plants are green because of the chlorophyll pigment. ) Chlorophyll absorbs certain wavelengths of light within the visible light spectrum. Green is obviously not absorbed, but reflected.

As shown in detail in the absorption spectra, chlorophyll absorbs light in the red (long wavelength) and the blue (short wavelength) regions of the visible light spectrum. Which Wavelengths have the most and least energy?

Looking at a visible light and electromagnetic radiation graphic, it can be noticed that the colour red has the least energy in visible light. This is because red has the longest wavelength of visible light and the longest frequency of any visible light colour. Red light has a wavelength of 610 - 740nm. Meaning that red has the least amount of energy level, whereas violet has the highest amount of visible light. Blue light has a wavelength that is shorter in the visible spectrum as compared to red light and has a higher energy. The visible light color with the moost energy is blue.

How Does Whitelight differ?

White light having a better balance of chlorophyll a, chlorophyll b, and the carotenoids and having all the photons of the visible light spectrum gave a better growth environment.

Outline the light-dependent reactions of photosynthesis.

  • (chlorophyll/antenna) in photosystem II absorbs light;
  • absorbing light/photoactivation produces an excited/high energy/free electron;
  • electron passed along a series of carriers;
  • reduction of NADP / generates NADPH H ;
  • absorption of light in photosystem II provides electron for photosystem I;
  • photolysis of water produces 2 H /O ;
  • called non-cyclic photophosphorylation;
  • in cyclic photophosphorylation electron returns to chlorophyll;
  • generates ATP by H pumped across thylakoid membrane / by chemiosmosis / through ATP synthetase/synthase;


Outline the light-independent reactions of photosynthesis.

  • reactions take place in the stroma
  • carbon dioxide reacts with RuBP
  • catalysed by RuBP carboxylase
  • GP formed
  • GP converted to triose phosphate
  • reduction reaction involving use of NADPH + H+
  • energy from ATP also needed from this conversion
  • triose phosphate converted to glucose(phosphate)/starch
  • RuBP regenerated from triose phosphate
  • Calvin cycle

Draw and label the structure of a chloroplast as seen in electron micrograph The structure consists of: double/inner and outer membrane/envelope – shown as two concentric continuous lines close together; granum/grana – shown as a stack of several disc-shaped subunits; (intergranal) lamella – shown continuous with thylakoid membrane; thylakoid – one of the flattened sacs; stroma; (70S) ribosomes/(circular) DNA / lipid globules / starch granules / thylakoid space

  1. REDIRECT [[1]]

Draw and label the absorption and action spectra

  1. REDIRECT [[2]]

Draw and label a simple representation of a photosystem, including chlorophyll molecules, the reaction center chlorophyll,and accessory pigments