Photosynthesis (11)

Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen from carbon dioxide and water.

Plant Cells have Green Chloroplasts. The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments e.g. CHLOROPHYLL

Held in position => exposed to light Transparent cuticle and epidermis => allows light to pass through Flat => large surface area Thin => sun to penetrate lowest tissues easily.

6CO2 + 6H2O =Light energy= C6H12O6 + 6O2

Sac-like photosynthetic membranes inside chloroplast.

Stack of thylakoids.

Gel-filled space inside chloroplast outside the thylakoid.

Gel-filled space OUTSIDE chloroplast but inside the cell membrane.

Light dependent phase (Light phase) and Light independent phase (dark phase)

Takes place in the GRANA of the chloroplast. Requires LIGHT. CHLOROPHYLL molecules trap light energy, which activates chlorophyll . Electrons become energised Kinetic Light energy is converted Potential chemical energy. Energised electrons used to: • Split WATER molecules (PHOTOLYSIS). OXYGEN leaves chloroplast. Energy rich HYDROGEN moves to light independent phase carried by NADP • Form high energy ATP (PHOSPHORYLATION). (ADP + P => ATP) Energy rich HYDROGEN and ATP are used in next phase

Takes place in the STROMA of the chloroplast Also called the CALVIN CYCLE Does NOT require light Uses energized H2 and ATP from light phase, as well as CO2 Energised H atoms to bond with CO2 to make GLUCOSE This reaction requires energy => use ATP Glucose can now be used to make other organic compounds eg. Starch Glucose can be used during respiration

Sun’s energy stored as chemical energy in glucose Releases OXYGEN as a waste product => used in respiration (to release E for living organisms) Keeps the CARBON DIOXIDE concentration fairly constant Fossils fuels store products of photosynthesis

Light intensity, Carbon Dioxide and Temperature

As light intensity increases, rate of photosynthesis increases But it levels off as it reaches maximum rate Any further increase in light intensity will not result in an increase in photosynthesis Why? Dark phase reactions happening as fast as it can, can’t go any faster

As carbon dioxide concentration increases, rate of photosynthesis increases But it levels off at a point Biochemical reactions can’t go any faster Any further increase in carbon dioxide will not result in an increase in photosynthesis

Temperature low = rate of photosynthesis low Temperature increases = rate of photosynthesis increases Until the Optimum temperature is reached ENZYMES If temperature too hot, rate drops because enzymes DENATURE