Introduction to Photosynthesis AUTOTROPHS make their own food

Introduction to Photosynthesis

› AUTOTROPHS �make their own food. �Ex: Phototrophs…. Use light energy �Ex: Chemotrophs…Use inorganic compounds › HETEROTROPHS �Must eat org. mol. for energy (carbon source).

FM

Light �Form of energy › Other forms of energy are: �heat, electrical, kinetic, sound, chemical �Travels in waves (different wavelengths)

Wavelength (λ)

Photosynthesis (Psyn): � Process: Light chemical energy ( sugars) � Pigments used to capture light energy

� Light and Pigments �How do plants capture the energy of sunlight? In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll. Copyright Pearson Prentice Hall

�Plants gather the sun's energy with light-absorbing molecules called pigments. �The main pigment in plants is chlorophyll. �There are two main types of chlorophyll: �chlorophyll a �chlorophyll b Copyright Pearson Prentice Hall

�Chlorophyll absorbs light well in the blue-violet and regions of the visible spectrum. Estimated Absorption (%) 100 80 60 Chlorophyll b Chlorophyll a 40 20 0 (nm) 400 450 Wavelength 500 550 600 650 700 750 Wavelength (nm) Copyright Pearson Prentice Hall

�Chlorophyll does not absorb light well in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green. Estimated Absorption (%) 100 80 60 Chlorophyll b Chlorophyll a 40 20 0 400 450 500 550 600 650 700 750 Wavelength (nm) Copyright Pearson Prentice Hall

�Light is a form of energy, so any compound that absorbs light also absorbs energy from that light. �When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. �These high-energy electrons are what make photosynthesis work. Copyright Pearson Prentice Hall

Pigments

Chlorophyll a �Chlorophyll a › C 55 H 72 O 5 N 4 Mg › Molecular wt. 893. 5 › Blue-Green (Not on test)

Chlorophyll b �Chlorophyll b › C 55 H 70 O 6 N 4 Mg › Molecular wt. 907. 5 › Yellow-Green (Not on test)

Anthocyanin �C 15 H 11 + O �Blue, red, pp � fruit, flowers (Not on test)

ß Carotene �C 40 H 56 �Mol. wt. 536. 9 �Orange, Orange Red (Not on test)

Xanthophyll �C 40 H 56 O 2 �Mol. Wt. 568 �Yellow (Not on test)

Chromatography � Splitting apart pigments

� Evergreen plants › psyn. year round. � Deciduous plants › affected by temp. and light changes; leaves change color - drop. � Factors affecting the rate of psyn. › Temperature › Water availability › Intensity of light › CO 2 availability

KEY CONCEPT The overall process of photosynthesis produces sugars that store chemical energy.

Photosynthetic organisms are producers. Producers make their own source of chemical energy. � Plants use photosynthesis and are producers. � Photosynthesis captures energy from sunlight to make sugars. �

� Chlorophyll is a molecule that absorbs light energy. chloroplast • In plants, chlorophyll is found in organelles called chloroplasts. leaf cell leaf

Photosynthesis in plants occurs in chloroplasts. � Photosynthesis takes place in two parts of chloroplasts. › grana (thylakoids) › stroma grana (thylakoids) chloroplast stroma

� The light-dependent reactions capture energy from sunlight. – – take place in thylakoids water and sunlight are needed chlorophyll absorbs energy is transferred along thylakoid membrane then to light-independent reactions – oxygen is released

� The light-independent reactions make sugars. – take place in stroma – needs carbon dioxide from atmosphere – use energy to build a sugar in a cycle of chemical reactions

� The equation for the overall process is: 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 granum (stack of thylakoids) 1 s chloroplast un lig ht 6 H 2 O thylakoid 6 CO 2 3 6 O 2 2 energy stroma (fluid outside thylakoids) 1 six-carbon sugar 4 C 6 H 12 O 6