photosynthesis

• ATP is the molecule that traps and transfers energy for cell reactions
• Metabolic reactions in cells take place in many small steps that require small amounts of energy
• Large numbers of ATP molecules are continuously required in a cell
• ATP is composed of:

  • A base (adenine)
  • A sugar (ribose)
  • Three phosphate groups, hence the name adenosine triphosphate
• When energy is needed in a cell, ATP is broken down into ADP (adenosine diphosphate) and phosphate, releasing energy
• ADP and the phosphate group can be re-formed back to ATP by the addition of energy
• ATP is produced during respiration in cells and also during photosynthesis
• NADPH is used in anabolic (synthetic) reactions to add hydrogen to the substrate
• In photosynthesis, a molecule called NADP+ is present in the chloroplast
• Light energy is used to make NADPH in photosynthesis
• NADPH can be used to manufacture sugar by reducing carbon dioxide
• NADP stands for photosynthesis
• Photosynthesis is the process in which plants make food (carbohydrates) and oxygen using energy from the sun, water from the soil, and carbon dioxide from the atmosphere
• Photosynthesis converts light energy into chemical energy
• Plants use photosynthesis to make food
• Animals get their food from plants
• Photosynthesis produces oxygen needed in respiration to release energy
• Photosynthesis removes carbon dioxide from the air
• The leaf is the primary site of photosynthesis
• Chloroplasts contain chlorophyll, the pigment needed for photosynthesis
• Most chloroplasts are found along the edges of the palisade (top) layer of the leaf to absorb sunlight
• Leaf adaptations include:

  • Stomata for gaseous exchange, mostly on the lower epidermis, open during the day for carbon dioxide intake and closed at night to reduce transpiration
  • Air spaces between spongy mesophyll cells allow for diffusion of CO2 and H2O within the leaf
  • Thin leaves for rapid diffusion of CO2 in and oxygen out, and to allow all cells to capture light
  • Cuticle prevents excessive water loss and is transparent to allow light for photosynthesis
  • Leaves are flattened to give a large surface area for maximum absorption of light and CO2
• • Xylem vessels bring water for photosynthesis and phloem sieve tubes translocate food like sucrose
• Internal structure of a chloroplast includes thylakoids, stacked together forming a Granum (grana) in the light stage, and the stroma (liquid part of chloroplast) in the dark stage
• Requirements for photosynthesis include light, water, carbon dioxide, and chlorophyll
• Products of photosynthesis include glucose, oxygen, and chemical energy
• Photophosphorylation is the process of adding a phosphate group to ADP to form ATP using light energy
• Light Stage of photosynthesis:

  • Light is absorbed by chlorophyll in the grana of the chloroplast
  • Water is split using light energy to produce oxygen, protons, and electrons
  • Electrons are energized by light and passed to chlorophyll
  • Glucose is formed by combining high-energy electrons and protons from the proton pool with carbon dioxide
• Sources of light for plants include sunlight and artificial light, with sunlight being the natural source and artificial light used in greenhouses to stimulate growth
• Plants get carbon dioxide externally from the atmosphere and internally from their own cellular respiration, sometimes using artificial sources like burning gas in a greenhouse to stimulate growth
• Water for plants is absorbed from the soil by the roots and used for photosynthesis
• Limiting factors of photosynthesis include light, CO2, or water shortages that slow down the process, with light increasing the rate until a saturation point is reached
• NADP (Nicotinamide Adenine Dinucleotide Phosphate) acts as an electron acceptor during the Light Stage of photosynthesis
• Higher Level photosynthesis includes two stages:

  • Light Stage (Light dependent stage) with Cyclic and Non-Cyclic Photophosphorylation
  • Dark Stage (Calvin cycle, Light independent stage)
• Dark Stage (Calvin Cycle):

  • Takes place in the stroma of the chloroplast
  • Controlled by enzymes and affected by temperature
  • Carbon dioxide combines with protons and electrons to form glucose, using energy from breaking down ATP and NADPH
  • Reduction occurs when electrons are added to anything
  • Carbon Dioxide is reduced to glucose
• Main events in photosynthesis include light energy absorption, water splitting, electron and proton movement, oxygen release, energy transfer to electrons, and glucose formation
• Differences between light and dark stages of photosynthesis