Biology ATAR Unit 2 Text: Chapter 9 Pages

Explain/describe/understand light dependent and light independent reactions in terms of: 1. The sites at which they occur 2. Requirements 3. Products 4. Factors affecting the rate of photosynthesis 5. The importance of ATP and ADP cycles for cell functioning

 Chloroplasts  Stroma  Grana  Thylakoids  Chlorophyll  Calvin cycle  C 3 photosynthesis Limiting factors  CO 2  Light intensity  Temperature  O 2  Nutrients

6CO 2 + 6H 2 O + light energy C 6 H 12 O 6 + 6O 2

Wavelength (nm) 10 –5 nm Increasing energy Visible light 650 nm 10 –3 nm 1 nm10 3 nm10 6 nm 1 m 10 3 m Radio waves Micro- waves Infrared X-rays UV Gamma rays

Chlorophyll light absorption

 Photosynthesis occurs in chloroplasts  In most plants, photosynthesis occurs primarily in the leaves where the chloroplasts are found A chloroplast contains:  Membrane – a double membrane  Stroma – a fluid  Chlorophyll – the green pigment that captures light for photosynthesis  Thylakoids – contain chlorophyll  Grana – stacks of thylakoids

A mechanical analogy of the light reactions NADPH Photosystem II e–e– Mill makes ATP Photon Photosystem I ATP e–e– e–e– e–e– e–e– e–e– e–e– Photon

H2OH2O ADP P LIGHT REACTIONS (in thylakoids) Light Chloroplast NADPH ATP O2O2 CALVIN CYCLE (in stroma) Sugar CO 2  NADP +

Animations  Calvin cycle  /student_view0/chapter39/calvi n_cycle.html /student_view0/chapter39/calvi n_cycle.html

Factors Affecting Photosynthesis CO 2 concentration  There are local variations to CO 2 levels in the air that occur in different habitats and at different times of the day. An increase in CO 2 will increase the rate of photosynthesis, until another factor limits it. Light intensity  The rate of photosynthesis increases as light intensity increases until another factor limits it. Only about 1% of the light that hits the plant is captured and converted to chemical energy.

Factors Affecting Photosynthesis Temperature  Photosynthesis relies on enzymes, and enzymes are temperature sensitive. The rate of photosynthesis increases with temperature, the optimum being between 20-40C, depending on the plant species High concentration of O 2  O 2 inhibits photosynthesis by competing with CO 2 for the active site of enzymes. Photosynthesis increases if the amount of O 2 is decreased. Nutrients  Chlorophyll contains nitrogen and magnesium. If the soil is deficient in these nutrients, the plant cannot make enough chlorophyll and the leaves appear yellow.

Photosynthesis: a review  The sugar produced by plants during photosynthesis provides the starting materials to make structural components such as cellulose  50% of this sugar goes toward cellular respiration (plants respire!)

Photosynthesis: a review  Most plants make considerably more food each day than they need  They stockpile this sugar as starch, storing it in roots and tubers. Energy is stored in fruit as fructose.  Plants not only produce fuel for themselves, but ultimately provide food for virtually all other organisms (heterotrophs)