Photosynthesis Takes place only in autotrophs (make their own food) (e.g. plants, Archaea, also some Protists and Bacteria) Basically, light energy is used to make CO 2 and H 2 O into sugars (chemical energy). O 2 and H 2 O are waste products. Happens in the chloroplast of the plant cell

Others… Chemosynthesis …getting energy from chemicals Bacteria by hydrothermal vents at bottom of ocean take chemicals out of water, break them down and get energy from them. Some called heterotrophs have to eat other things for food. (e.g. animals, fungi, also some Protists and Bacteria)

Chemosynthesis

2 steps Light Dependent Reactions –Also just called Light Reactions –Must have light to take place Light Independent Reactions –Also called Dark Reactions or Calvin Cycle –Can happen in light or dark

Light Dependent Reactions Happens in the thylakoid (inside membranes) of the chloroplast Chlorophyll (green chemical) traps sunlight Energy is used to split water into O 2 (waste product) and H 2 Energy from H 2 is stored as ATP and NADPH

ATP & NADPH ATP is the molecule all cells use as energy It has an amino acid (adenine) a sugar (ribose) and 3 phosphates. Energy stored in the phosphates’ bonds Break bond…use energy…become ADP + P ADP + P + energy = ATP NADP+ carries 2 electrons and a hydrogen atom

ATP and NADPH The energy from light is passed from protein to protein in the thylakoid membrane as part of an electron transport chain. As H+ ions and electrons are moved into/out of the thylakoid membrane, energy is stored in ATP and NADPH used in the light independent reactions.

Electron Transport Chain

Summary of Photosynthesis

Light Independent Reactions CO 2 is made into 3-carbon sugars in a process called carbon fixation Uses the ATP and NADPH from the light reactions Water is a waste product, but is reused by the cell and not given off These sugars are the end product of photosynthesis. They are used by the plant as energy and stored for later use. Happens in the stroma (open areas) of the chloroplast

Summary of Photosynthesis

Summary of Photosynthesis In the chloroplast… 6 CO H 2 O and light energy makes sugars (CH 2 O) + O 2 (waste) (Actually it takes 12 H 2 O, but there’re 6 H 2 O left over, so they cancel out) CH 2 O is a generic formula for a carbohydrate (sugars). You could also write C 6 H 12 O 6 ATP and NADPH are energy carriers from light dependent reactions to light independent reactions

Technically… Photosynthesis does not make glucose (C 6 H 12 O 6 ) It makes a 3-carbon sugar called G3P which is used to make other organic compounds, like cellulose (many sugars linked together) used in the cell wall. The sugars can be used for energy by the plant (in the mitochondria) or to build structures

So why… Have you been taught that the end product is glucose? Scientists (and teachers) often say that it makes glucose, because it is one of the things photosynthesis can make, and it helps show the relationship between photosynthesis and cell respiration (next unit).

Factors Affecting Photosynthesis Temperature: –between 0 o C and 35 o C is best. Light: –“perfect” amount –More is good, up to a certain point Water –“perfect amount” –More is good up to a certain point