Photosynthesis

• Energy and Life

  • living organisms need energy to survive
  • organisms get their energy from food
  • the energy in most foods comes from the sun through photosynthesis
• Obtaining food autotrophs and heterotrophs

  • autotrophs: organisms which make their own food: plants, algae & some bacteria
  • photoptrophs
  • use sunlight to make their own food (chemical energy - glucose)
  • ex. plants, algae, and some bacteria
  • chemoautrophs
  • use chemicals to make their own food (chemical energy)
  • ex. some bacteria that live in extreme environments - thermal vents in ocean
  • heterotrophs: organisms that must obtain energy from the food they eat or absorb - eat autotrophs or other heterotrophs, and some decompose like mushrooms
• Chemical energy and ATP

  • energy comes in many forms incluing light, heat electricity
  • energy can be stored in chemical compounds
  • energy in chemical compound is stored in the bonds that hold atoms together - electrons
  • when the bonds are broken, the energy (electrons) can be released and reused elsewhere
• Chemical energy and ATP

  • chemical reactions are constantly occurring in the cells of living organisms
  • energy is constantly being released as bonds are broken in chemical reactions
  • An important chemical compound that cells use to release and store energy is adenosine triphosphate (ATP)
  • The chemical energy used to make ATP comes from glucose in food
  • The chemical energy (electrons) that is stored & used in organisms is glucose and then ATP
• Chemical energy and ATP

  • ATP consisted of 3 molecular parts: adenine, ribose, 3 phosphate group - the three phosphate groups are the key to ATP's ability to store and release energy

  A) ribose

  B) 3-Phosphate group

  
• Chemical energy and ATP

  • Storing energy
  • ADP has two phosphate groups instead of three
  • A cell can store small amounts of energy by adding a phosphate group to ADP
  • Releasing energy
  • Energy from ATP is released by breaking bonds between phosphates - this releases electrons (energy)
• Chemical energy and ATP

  • Energy use
  • the energy from ATP is needed for many cellular activities, including:
  • active transport across cell membranes
  • protein synthesis
  • muscle contraction
  • most cells have only a small amount of ATP because it's not a good way to store large amounts of energy - it's like carrying around a million dollars in $1 bills rather than storing in bigger bills.
  • cells can regenerate ATP from ADP as needed by using the energy in foods like glucose
  • these characteristics of ATP make it exceptionally useful as the basic energy source of all cells
• Photosynthesis: an overview

  • Photosynthesis is the process in which green plants convert sunlight energy into chemical energy called glucose
  • Photosynthesis uses light energy to change carbon dioxide & water into glucose (chemical energy) and oxygen (waste)
  • Chemical equation: 6CO2 + 6H2O -> C6H12O6 + 6O2
• Light and Pigments & Compound Needed for Photosynthesis

  • Light
  • Light is made up of vibrating electric and magnetic fields which are like a wave
  • The wavelength determines the light's color and energy
  • shorter wavelengths -> higher energy
  • Visible light has many different wavelengths or colors: ROY, G, BIV
  • Red, orange, yellow, green, blue, indigo, violet
  • All these colors put together makes white light
• Light and Pigments & Compound Needed for Photosynthesis

  • Pigments
  • Plant cells have pigments
  • substances that adsorb visible light and help harness the energy of the light
  • The major pigment in plant cells is chlorophyll
  • Pigments are held in chloroplasts where photosynthesis occurs
  • There are two main types of chlorophyll: a & b
  • Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum
  • Chlorophyll doesn't absorb light well in the green region of the spectrum - green light is reflected by leaves, which is why plants look green
• Light and Pigments & Compound Needed for Photosynthesis

  • Pigments
  • Light is a form of energy, so any compound that absorbs light also absorbs energy from that light
  • When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels to these electrons
  • These electrons are what make photosynthesis work
  • Accessory Pigments - (orange & yellow) absorb additional wavelengths of light & become visible when the chlorophyll breaks down in the fall
• How do the compounds needed for photosynthesis get into the plant?

  • Carbon dioxide
  • There are slits that open to the environment called stoma. It's here that CO2 (required reactant) and O2 (product) exchange occur
  • Water
  • Water enters a plant through its roots. Vascular tissues called xylem, draws water up the stem into the leaves of plants where photosynthesis occurs.
• The Reactions of Photosynthesis

  • Inside a Chloroplast: two major regions of chloroplast
  • Thylakoids
  • Sac-like photosynthetic membranes
  • These membranes contain pigments which absorb light
  • Arranged in stacks known as grana
  • Stroma
  • Space around the stacks of thylakoids
  • Contains enzymes that catalyze the formation of glucose from carbon dioxide, water and light energy
• The Reactions of Photosynthesis

  • Light-Dependent Reactions: in thylakoid membranes
  • Pigments absorb light energy to break bonds in water
  • water becomes oxygen and H+
  • chlorophyll is "excited" by light energy and releases its electrons (e-)
  • energy carriers called ATP and NADPH are created to transport the release e- & H+ to the next reaction where they will be used to make glucose
  • Oxygen gas (from splitting water) is a waste product the cell doesn't need/use and is released through stomata
• The Reactions of Photosynthesis

  • Light-Independent Reaction (Calvin Cycle): in stomata
  • Doesn't need light
  • Uses the energy of ATP & NADPH to convert CO2 into glucose
• The Reactions of Photosynthesis

  • The two sets of photosynthetic reactions work together
  • The light-dependent reactions trap sunlight energy in chemical form (ATP & NADPH)
  • The light-Independent reactions use that chemical energy to produce stable, high energy sugars from carbon dioxide & water = glucose
• Factors Affecting Photosynthesis

  • Water
  • Water enters the cells and leaves of a plant through the roots. It's required for photosynthesis but also to maintain turgor in the vacuoles of plant cells
  • Temperature
  • As temperature increases, the rate of photosynthesis increases until 25 degrees (C) where the rate levels off as the temperature continues to rise.
  • As temperature decreases, enzymes needed to make chlorophyll slow down, so less chlorophyll is synthesized and photosynthesis slows down
• Factors Affecting Photosynthesis

  • Light Intensity
  • As light increases, photosynthesis increases until the light reaction is saturated with light
  • Photoinhibition - when photosynthesis slows because extra light energy ultimately makes substances that harm the plant