MODULE 5: Ecosystem: Life Energy (Part 1)

• Self-feeders or Autotrophs - They produce their own food and sustain themselves without consuming other organism in order to survive. (Ex. plants, algae, certain protists, and some prokaryotes)
• Photosynthesis - the process by which plants use light energy from the sun and carbon dioxide to produce glucose, the sugar molecules and oxygen that they use for growth and nourishment.
• Chloroplast in mesophyll cell:

  A) lamella

  B) granum

  C) stroma (fluid matrix)

  D) thylakoid membrane

  E) outer membrane

  F) inner membrane

  G) thylakoid

  
• Epidermis - the outermost layer which secretes a waxy substance.
• Cuticle - A waxy substance that helps retain water inside the leaf cells.
• Stoma (stomata) - This is where carbon dioxide enters, and oxygen passes out.
• Guard cells - A pair of bean-shaped cells and an epidermal cell with chloroplast that regulates the opening and closing of the stomata.
• Mesophyll layer - Layers of cells between the upper and lower epidermis.
• spongy cells - loosely arranged cells.
• Stroma - a space between the inner and outer membrane which is the liquid part of the chloroplast.
• Granum - A complex network of stacked sacs.
• Thylakoids - Flattened sacs that contains green-colored pigments called chlorophylls that absorb light.
• Xylem and Phloem - Are responsible for the transport of water and food to the different parts of the plant.
• The Internal Structure of a Leaf:

  A) cuticle

  B) upper epidermis

  C) palisade mesophyll

  D) spongy mesophyll

  E) lower epidermis

  F) stoma

  G) guard cells

  H) vascular bundle

  I) xylem

  J) phloem

  
• The equation used to explain photosynthesis :

  A) 6CO2

  B) 6H2O

  C) C6H12O6

  D) 6O2

  
• Photosynthesis is divided into two stages:

  • The light-dependent reaction
  • Calvin cycle
• Light-dependent reaction Stage - occurs in the thylakoid membrane and requires a continuous supply of light.
• The chlorophyll is composed of two units of light-absorbing molecule, namely the Photosystem II (PSII) and Photosystem I (PSI)
• The light-dependent reaction begins when PSII receives light energy.
• A protein in the electron transport chain pumps hydrogen ions from the stroma into the thylakoid space.
• Photosystem I - absorb light and re-energize the electron.
• The chemical called NADP accepts the electron and hydrogen, and becomes NADPH - A high energy molecule.
• ATP synthase - allows the H+ ions to travel from the thylakoid to the stroma by diffusion and captures the energy of their movement by spinning and stores that energy in ATP.
• An enzyme found in the thylakoid membrane - uses energy of electrons from both PSII and PSI to create more ATP and to stop the production of NADPH.
• Calvin cycle - Occurs in the stroma of the chloroplast.
• Calvin Cycle can be divided into three phases:

  1. Carbon fixation
  2. Carbon dioxide (CO2) reduction
  3. Regeneration of RuBP
• Carbon Fixation - In this process, the carbon dioxide (C𝑂2) is captured in the atmosphere and diffuses into the stroma of a chloroplast, where they encounter molecules called the RuBP
• RuBP (Ribulosediphosphate) - a five-carbon sugar molecule.
• The enzymes used in this reaction (Carbon fixation) is called rubisco, and the results of the reaction is an unstable 6-carbon molecule that splits into two 3-carbon molecules called 3 phosphoglyceric acid (3PGA).
• Carbon dioxide reduction - In this process, we are adding electrons and energy to carbon dioxide molecule.
• When phosphoglycerate (3PGA) engages with ATP (from light dependent reaction) it becomes biphosphoglycerate (BPGA)
• BPGA combines with NADPH, which carries a high energy electron that got enhanced by light energy and is carrying a hydrogen proton.
• The NADPH is going to donate that high energy electron and hydrogen to BPGA and convert it into phosphoglyceraldehyde (PGAL)
• Regenaration of RuBP - In this phase, RuBP molecules is formed using ATP that combine with the 3GPA molecules. This cycle has to turn six times, each turn of cycle adds only one carbon atom for the incoming carbon dioxide.
• RuBP combine with additional carbon dioxide molecules to form the glucose molecule.
• The overall chemical equation of Calvin Cycle:

  3 CO2 + 6 NADPH + 5 H2O + 9 ATP → G3P + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi (Pi stands for inorganic phosphate)
• • NADP - Nicotinamide Adenine Dinucleotide Phosphate
  • NAD - Nicotinamide Adenine Dinucleotide
  • ATP - Adenosine Triphosphate
  • PGAL - Phosphoglyceraldehyde
  • FAD - Flavin Adenine Dinucleotide
  • ADP - Adenosine Diphosphate
• Chloroplast - Contains green pigments which trap energy from the sun. Organelles of Palisade and spongy cells.
• Palisade cells - are arranged like columns