Adaptations to the Physical Environment II. Light A. Properties and Adaptations 1. Pigment Absorbances

Adaptations to the Physical Environment II. Light A. Properties and Adaptations 1. Pigment Absorbances

Adaptations to the Physical Environment II. Light A. Properties and Adaptations 2. C3 Photosynthesis

PS I e- acceptor PS II Water is split to harvest electrons; oxygen gas is released as a waste product. e- ADP+P ATP NADPNADPH 2H 2 O4e + 4H+ + 2O (O 2 ) Adaptations to the Physical Environment II. Light A. Properties and Adaptations 2. C3 Photosynthesis THE LIGHT REACTION

The Light Dependent Reaction e- 6 CO 2 C 6 (glucose) ATP ADP+ P Light Independent Reaction Light Dependent Reaction

The Light Dependent Reaction The Light Independent Reaction e- 6 CO 2 C 6 (glucose) ATP ADP+ P Light Independent Reaction Light Dependent Reaction

The Light Independent Reaction C5C5 RuBP CO 2 C6C6 A molecule of CO 2 binds to Ribulose biphosphate, making a 6-carbon molecule. This molecule is unstable, and splits into 2 3-carbon molecules of phosphoglycerate (PGA) 2 C 3 (PGA)

III. The Light Independent Reaction 6C56C5 RuBP 6CO 2 6C66C6 Now, it is easier to understand these reactions if we watch the simultaneous reactions involving 6 CO2 molecules 12 C 3 (PGA)

6C56C5 RuBP 6CO 2 6C66C6 12 C 3 2 C 3 C 6 (Glucose) 10 C 3 ATP ADP+P NADPH NADP 2 of the 12 PGA are used to make glucose, using energy from ATP and the reduction potential of NADPH… essentially, the H is transferred to the PGA, making carbohydrate from carbon dioxide. Adaptations to the Physical Environment II. Light A. Properties and Adaptations 2. C3 Photosynthesis THE LIGHT INDEPENDENT REACTION

The Light Independent Reaction 6C56C5 RuBP 6CO 2 6C66C6 12 C 3 2 C 3 C 6 (Glucose) 10 C 3 ATP ADP+P NADPH NADP More energy is used to rearrange the 10 C 3 molecules (30 carbons) into 6 C 5 molecules (30 carbons); regenerating the 6 RuBP. ATP ADP+P

Review: Need water (from the xylem) And CO 2 (through the stoma). Water vapor and waste O 2 Are released (through stoma) Sugars are shunted into the phloem, Next to the xylem in vascular bundles, and distributed to the rest of the plant.

Problem: If the rate of water loss through the stoma (determined by relative humidity and temperature of air, relative to leaf) IS GREATER THAN The rate of water absorption (dependent on amount of water and soil characteristics determining water availability) THE LEAF DRIES AND STOMATES CLOSE

Problem: If the rate of water loss through the stoma (determined by relative humidity and temperature of air, relative to leaf) IS GREATER THAN The rate of water absorption (dependent on amount of water and soil characteristics determining water availability) THE LEAF DRIES AND STOMATES CLOSE Water vapor is retained, but: - as photosynthesis continues, [CO 2 ] declines and [O 2 ] increases inside the closed leaf. - When [CO 2 ] is low, RuBP won’t bind it anymore and photosynthesis stops. Indeed, RuBP is broken down (photorespiration). - In hot, dry habitats, stomates close early in the day and C3 plants can’t make enough glucose to survive.

Adaptations to the Physical Environment II. Light A. Properties and Adaptations 2. C3 Photosynthesis 3. C4 Photosynthesis Many plants that live in dry habitats have a modified carbon fixation pathway Grasses, including important crops like cane and maize

Adaptations to the Physical Environment II. Light A. Properties and Adaptations 2. C3 Photosynthesis 3. C4 Photosynthesis Leaf Anatomy of a C4 Plant Note that the Bundle Sheath cells ARE surrounded by another layer of tissue – photosynthetic mesophyll

C4 - Spatial Separation Carbon fixation, by PEP occurs in the mesophyll. PEP can bind CO2 even at low CO2 concentrations.

C4 - Spatial Separation Carbon fixation, by PEP occurs in the mesophyll. PEP can bind CO2 even at low CO2 concentrations. The product, a C4 malate, is transferred to the bundle sheath and dissociates, recycling the PEP and releasing the CO2

C4 - Spatial Separation Carbon fixation, by PEP occurs in the mesophyll. PEP can bind CO2 even at low CO2 concentrations. The product, a C4 malate, is transferred to the bundle sheath and dissociates, recycling the PEP and releasing the CO2 So, CO2 is pumped into the BSC, keeping concentrations high enough for RUBP to bind CO2 in the Calvin Cycle and produce glucose, even when CO2 concentrations are low in the leaf because the stomates are closed.

Whereas C3 plants shut down at high light intensity and temp, C4 continue to photosynthesize

Adaptations to the Physical Environment II. Light A. Properties and Adaptations 2. C3 Photosynthesis 3. C4 Photosynthesis 4. CAM Photosynthesis Temporal Separation of Carbon Fixation and Calvin Cycle

Adaptations to the Physical Environment II. Light III. Heat Exchange A. Pathways of Exchange Radiation – E emitted from a surface Conduction – kinetic E trans. By contact Convection – moving air/liquid (boundary) Evaporation – exchange of latent E

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms 1. Heat Budget

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms 1. Heat Budget 2. Body Size and SA/V ratio

Bears White-tailed Deer Bergman’s Rule

humans

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms 1. Heat Budget 2. Body Size and SA/V Ratio 3. Effects of Temperature Increase metabolism, increase production of metabolic waste Increase evaporation Increase water demand

Cushion plants Cacti Concept of flux: The rate of exchange of energy or matter (water) is a function of: - SA/V - energy/matter concentration gradient - characteristics of the surface (covered by oils or hairs?) Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural Allen’s Rule Reduce limb length as latitude increases

increase edge/SA ratios, and increase SA/V ratios - maximize the loss of absorbed heat energy sun leaf - deeply cut; narrow shade leaf - broad

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural Hairs, spines, feathers… create boundary layer.

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological 3. Behavioral

Adaptations to the Physical Environment II. Light III. Heat Exchange A.Pathways of Exchange B.Effects on Organisms C.Adaptations 1. Structural 2. Physiological 3. Behavioral