Bio 004, College of the Desert

• Photosynthesis: conversion of light energy from the sun into chemical energy of sugar and other organic molecules.
• Examples: generally green plants, algae, and photosynthetic bacteria.

Chloroplasts: organelles that carry out photo-synthesis

Chlorophyll: green pigment found in chloroplasts.

Stomata (sing. stoma): pores in the epidermis of leaves where gas exchange occurs.

Guard Cells: specialized cells in plants that regulate the opening/closing of stomata. {Allow for gas exchange with the air surrounding the leaves and the chloroplasts inside}

Stroma: thick fluid found inside chloroplasts.

Thylakoids: elaborate system of interconnected membranous sacs (site of chlorophyll).

Grana: stacks of thylakoids (increases surface area for photosynthesis).

• Photosynthesis: Sunlight + 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• 1.CO₂ enters through stomata.
• 2.H₂O enters through roots.
• 3.O₂ and H₂O vapor exit through stomata.

• Photosynthesis Road Map:
• 1.NADP: electron carrier unique to plants.

• A Photosynthesis Road Map –2 Steps
• 1.Light Reaction: – converts solar energy to chemical energy Light drives the synthesis of ATP and NADPH.
• 2. Calvin Cycle: produces sugar from carbon dioxide ATP generated by the light reaction provides the energy for sugar synthesis.

• The Nature of Light:
• When sunlight shines on pigmented materials, the pigmented color (green) is reflected while the other colors (red & blue) are absorbed.

Chlorophyll a: absorbs blue-violet & red light: Direct participant in the light reactions

Chlorophyll b: absorbs blue & orange light: Indirect participant in the light reactions

• Carotenoids: absorbs mainly blue-green light.
• Absorb and dissipate excessive light energy-Pass energy on to chlorophyll a -Decrease of chlorophyll in the fall, allows persist carotenoids to show through.

• How Light Reactions Generate ATP/NADP :
• 1.When a pigment molecule absorbs a photon, one of the pigment’s electrons gains energy.
• 2.When electrons get “excited”, they become unstable and immediately release energy.
• 3.Most energy is released as heat – some energy is released as light.

Chemical Inputs: CO₂ from the air; ATP, NADPH from the Light Reaction.

Chemical Outputs: Energy-rich sugar molecule (glyceraldehyde-3-phosphate) used to produce glucose.

• The Calvin Cycle:
• 1.Chemical Inputs
• 2.Chemical Outputs

• C3 Plants: plants in which the Calvin cycle uses CO₂ directly from the air.
• First compound is a 3C molecule; Plants are common and widely distributed; Dry weather can reduce the rate of photo-synthesis.

• C4 Plants: plants in which the Calvin cycle uses CO₂ derived from a 4C compound.
• First compound is a 4C molecule: Evolved in hot regions of the tropics: Dry weather doesn’t affect them due to their independence from atmospheric CO₂

• CAM Plants: plants in which the Calvin cycle uses CO₂ that enters the stomata at night, becomes incorporated into a 4C compound.
• First compound is a 4C molecule: Evolved in arid regions: Stomata open at night while remaining closed during the day

• Water-Saving Adaptations:
• 1. C3 Plants
• 2. C4 Plants
• 3. CAM Plants

• Global Warming: slow, but steady rise in Earth’s surface temperatures.
• Resulting in melting polar ice, rising sea levels, extreme weather patterns, droughts, and the spread of tropical diseases: Aggravated by deforestation.

• Greenhouse Effect:warming of the atmosphere caused by CO₂, CH₄, and other gases that absorb infrared radiation, slowing its escape from earth: Makes the earth hospitable and habitable.
• CO₂ is one of the most important greenhouse gases.
• Removed from the atmosphere by photosynthesis
• Returned to the atmosphere by respiration, fires, and decomposers
• Substantial amount locked in forests, organisms, and fossil fuels