6 &7 Photosynthesis and Cellular Respiration

• Epidermis: transparent covering over the top of the leaf that controls water loss
• Palisade layer: thick section of chloroplasts
• Spongy layer; storage of food and exchange of gases
• Stomata: pores in the leaf for gas exchange, found mainly in the lower leaf
• Vascular bundle: xylem: water and minerals, phloem: nutrients
• Photosynthesis is the process that converts energy from the sun into chemical energy that is used by living cells
• Solar energy is the ultimate source of energy for most living things
• 5% of the light energy is converted into carbohydrate molecules such as glucose (chemical energy)
• Light is a type of electromagnetic (EM) radiation familiar forms include: I-rays, microwaves and radio waves
• The short wavelengths have high energy and the long wavelengths have low energy
• Light is a mixture of photons
• Chloroplasts are membrane bound organelles in plant and algal cells that carry out photosynthesis.
• Chloroplasts have two limiting membranes, an outer and inner, these membranes enclose a interior space filled with a protein rich semiliquid called the stroma.
• Within the stroma is a system of membrane bound sacs called thylakoids which stack on top of one another for form columns called grana,
• Adjacent grana are connected to one another by unstacked thylakoids called lamellae.
• Photosynthesis takes place within the stroma and partly within the thylakoid membrane.
• Chlorophyll contains pigments such as chlorophyll A (blue-green) and B (yellow-green), and the carotenoids carotene (orange), xanthophylls (yellow).
• Chlorophyll A and B are the primary pigments involved in photosynthesis.
• Chlorophyll A is the only pigment that can transfer the energy of light to the carbon fixation reactions of photosynthesis.
• Each pigment absorbs different wavelengths of light.
• Chlorophyll a and b absorb pigments with energies in the blue-violet and red regions of the spectrum and reflect those with wavelengths between 500 nm and 600 nm (green) that is why our eyes see as green light.
• Carotenoids, which are hydrocarbons built into the thylakoid membrane, absorb blue wavelengths but reflect orange and yellow.
• With the onset of cooler autumn temperatures, plants stop producing chlorophyll molecules and disassemble those already in the leaves, causing the yellow, red and brown colors of leaves to become visible.
• The reactions of photosynthesis, also known as the Calvin cycle, are made up of two systems: light dependent reactions and dark reaction (carbon fixation).
• In light dependent reactions, ATP is created, NADPH is required, and must have chlorophyll.
• Dark reaction (carbon fixation), also known as the Calvin cycle, incorporates CO2 into carbohydrate (glucose).
• Light reactions occur in the stroma and thylakoid membrane of the chloroplast and are made up of two systems: Photosystem I and II.
• Solar Energy is captured when an electron in chlorophyll absorbs a photon.
• Electrons are high-energy particles present in all atoms.
• Before a proton of light strikes the electron has a relatively low amount of energy.
• After the photon is absorbed, the electron has a relatively high amount of energy and is said to be excited.
• Electrons are passed “downhill” through a series of electron acceptors within an electron transport chain; during this time energy is released and is used to set up the proton (H+) gradient.
• The proton gradient allows ADP to be phosphorylated to make ATP.
• 4 H+ + 4e- + 02
• 4 H+ go to the proton gradient
• 02 goes to the atmosphere
• Electrons are transferred “downhill” through a series of electron acceptors until they are picked up by the final acceptor NADP+ which is reduced (gains 2e- and 1 H+) and becomes NADPH.
• Oxidation occurs when elements/compounds lose electrons (or hydrogen) LEO – (lose of electrons)
• Reduction occurs when elements/compounds gain electrons (or hydrogen) GER – (gain of electrons)
• FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS

  1. wavelength of light: blue and red = increased rate

          green = decreased rate

  b. Intensity of light: dim light = decreased rate

  bright light = increased rate to a point

  c. Temperature: increased temperature = increased rate

  lowered rate = decreased rate to a point

  d. Concentration: increased carbon dioxide or water concentration = increased rate, usually it is the water 

                              concentration that limits the rate