Energy and Environment Study Notes: Photosynthesis, Microbiology, and Immunity

UNIT 4: ENERGY, ENVIRONMENT, MICROBIOLOGY AND IMMUNITY

Topic 5: Energy Flow, Ecosystems and the environment

PHOTOSYNTHESIS

Photosynthesis is the process where most plants, algae, and some bacteria, such as cyanobacteria, convert light energy into chemical energy stored in chemical bonds of ATP and carbohydrates like glucose.

• Chemical Energy Storage:
    - In carbohydrates such as glucose, chemical energy is stored in covalent bonds between carbon, hydrogen, and oxygen atoms.
    - During respiration, glucose is broken down to form ATP.

• Role of ATP:
    - ATP (adenosine triphosphate) stores chemical energy in its phosphate bonds.
    - Upon hydrolysis of ATP, energy is released; some of it is usable energy while some is lost as heat. Usable energy is ultimately lost as heat after work is done.

• Photosynthesis Basics:
    - It utilizes inorganic molecules (water and carbon dioxide), chloroplast pigments, and light energy to synthesize organic molecules like glyceraldehyde phosphate (GALP), which is a 3-carbon sugar produced during photosynthesis.
    - Photosynthesis involves the reduction of CO2 to carbohydrates, requiring hydrogen from water. The elements of carbohydrates are Carbon, Hydrogen, and Oxygen, with sources being:
      - Carbon: carbon dioxide
      - Oxygen: carbon dioxide
      - Hydrogen: water

Overall Equation for Photosynthesis

• CO2 is reduced by hydrogen from photolysis of water, where water (H2O) is split by light into hydrogen ions, electrons, and oxygen molecules.
• Chloroplast pigments absorb light energy, leading to two key functions:
    1. Splitting water to generate hydrogen ions (H+), electrons (e-), and oxygen (O2).
    2. Exciting and emitting electrons.

Features of Chloroplast Structure

Chloroplast: A disc-shaped structure with a double membrane known as the chloroplast envelope.

• Key Structures and Their Functions:
    - Permeable Outer Membrane: Allows free movement of molecules like ions, water, and carbon dioxide.
    - Partially Permeable Inner Membrane: Regulates substance movement and contains transport proteins.
    - Stroma: The fluid-filled interior surrounding grana, containing enzymes for the Calvin cycle and products of the Light-dependent stage (LDS) such as ATP and NADPH.
    - Thylakoid: The site for light-dependent processes, consisting of membranes with photosystems, electron carriers, proton pumps, ATP synthase, and NADP+ reductase.
      - Thylakoids frequently stack to form grana, enhancing surface area for light-dependent reactions (LDS).
    - Granum: A stacked arrangement of thylakoids to maximize efficiency of LDS.
    - Chloroplast Pigments: Arranged in