Photosynthesis and Cellular Respiration

1
Photosynthesis and Cellular Respiration
2
Outline

• I. Photosynthesis
• A. Introduction
• B. Reactions
• II. Cellular Respiration
• A. Introduction
• B. Reactions

3
Photosynthesis

• Method of converting sun energy into chemical
  energy usable by cells
• Autotrophs self feeders, organisms capable of
  making their own food
• Photoautotrophs use sun energy e.g. plants
  photosynthesis-makes organic compounds (glucose)
  from light
• Chemoautotrophs use chemical energy e.g.
  bacteria that use sulfide or methane
  chemosynthesis-makes organic compounds from
  chemical energy contained in sulfide or methane

4
Photosynthesis

• Photosynthesis takes place in specialized
  structures inside plant cells called chloroplasts
• Light absorbing pigment molecules e.g. chlorophyll

5
Overall Reaction

• 6CO2 12 H2O light
• energy ? C6H12O6
  6O2 6H2O
• Carbohydrate made is glucose
• Water appears on both sides because 12 H2O
  molecules are required and 6 new H2O molecules
  are made
• Water is split as a source of electrons from
  hydrogen atoms releasing O2 as a byproduct
• Electrons increase potential energy when moved
  from water to sugar therefore energy is required

6
Light-dependent Reactions

• Overview light energy is absorbed by
  chlorophyll molecules-this light energy excites
  electrons and boosts them to higher energy
  levels. They are trapped by electron acceptor
  molecules that are poised at the start of a
  neighboring transport system. The electrons
  fall to a lower energy state, releasing energy
  that is harnessed to make ATP

7
Energy Shuttling

• Recall ATP cellular energy-nucleotide based
  molecule with 3 phosphate groups bonded to it,
  when removing the third phosphate group, lots of
  energy liberated superb molecule for shuttling
  energy around within cells.
• Other energy shuttles-coenzymes (nucleotide based
  molecules) move electrons and protons around
  within the cell
• NADP, NADPH NAD, NADP FAD, FADH2

8
Light-dependent Reactions

• Photosystem light capturing unit, contains
  chlorophyll, the light capturing pigment
• Electron transport system sequence of electron
  carrier molecules that shuttle electrons, energy
  released to make ATP
• Electrons in chlorophyll must be replaced so that
  cycle may continue-these electrons come from
  water molecules, Oxygen is liberated from the
  light reactions
• Light reactions yield ATP and NADPH used to fuel
  the reactions of the Calvin cycle (light
  independent or dark reactions)

9
(No Transcript)
10
(No Transcript)
11
Calvin Cycle (light independent or dark
reactions)

• ATP and NADPH generated in light reactions used
  to fuel the reactions which take CO2 and break it
  apart, then reassemble the carbons into glucose.
• Called carbon fixation taking carbon from an
  inorganic molecule (atmospheric CO2) and making
  an organic molecule out of it (glucose)
• Simplified version of how carbon and energy enter
  the food chain

12
(No Transcript)
13
Harvesting Chemical Energy

• So we see how energy enters food chains (via
  autotrophs) we can look at how organisms use that
  energy to fuel their bodies.
• Plants and animals both use products of
  photosynthesis (glucose) for metabolic fuel
• Heterotrophs must take in energy from outside
  sources, cannot make their own e.g. animals
• When we take in glucose (or other carbs),
  proteins, and fats-these foods dont come to us
  the way our cells can use them

14
Cellular Respiration Overview

• Transformation of chemical energy in food into
  chemical energy cells can use ATP
• These reactions proceed the same way in plants
  and animals. Process is called cellular
  respiration
• Overall Reaction
• C6H12O6 6O2 ? 6CO2 6H2O

15
Cellular Respiration Overview

• Breakdown of glucose begins in the cytoplasm
  the liquid matrix inside the cell
• At this point life diverges into two forms and
  two pathways
• Anaerobic cellular respiration (aka fermentation)
• Aerobic cellular respiration

16
C.R. Reactions

• Glycolysis
• Series of reactions which break the 6-carbon
  glucose molecule down into two 3-carbon molecules
  called pyruvate
• Process is an ancient one-all organisms from
  simple bacteria to humans perform it the same way
• Yields 2 ATP molecules for every one glucose
  molecule broken down
• Yields 2 NADH per glucose molecule

17
(No Transcript)
18
Anaerobic Cellular Respiration

• Some organisms thrive in environments with little
  or no oxygen
• Marshes, bogs, gut of animals, sewage treatment
  ponds
• No oxygen used anaerobic
• Results in no more ATP, final steps in these
  pathways serve ONLY to regenerate NAD so it can
  return to pick up more electrons and hydrogens in
  glycolysis.
• End products such as ethanol and CO2 (single cell
  fungi (yeast) in beer/bread) or lactic acid
  (muscle cells)

19
(No Transcript)
20
Aerobic Cellular Respiration

• Oxygen requiredaerobic
• 2 more sets of reactions which occur in a
  specialized structure within the cell called the
  mitochondria
• 1. Krebs Cycle
• 2. Electron Transport Chain

21
Krebs Cycle

• Completes the breakdown of glucose
• Takes the pyruvate (3-carbons) and breaks it
  down, the carbon and oxygen atoms end up in CO2
  and H2O
• Hydrogens and electrons are stripped and loaded
  onto NAD and FAD to produce NADH and FADH2
• Production of only 2 more ATP but loads up the
  coenzymes with H and electrons which move to the
  3rd stage

22
(No Transcript)
23
Electron Transport Chain

• Electron carriers loaded with electrons and
  protons from the Krebs cycle move to this
  chain-like a series of steps (staircase).
• As electrons drop down stairs, energy released to
  form a total of 32 ATP
• Oxygen waits at bottom of staircase, picks up
  electrons and protons and in doing so becomes
  water

24
(No Transcript)
25
Energy Tally

• 36 ATP for aerobic vs. 2 ATP for anaerobic
• Glycolysis 2 ATP
• Krebs 2 ATP
• Electron Transport 32 ATP
• 36 ATP
• Anaerobic organisms cant be too energetic but
  are important for global recycling of carbon

26
(No Transcript)
27
(No Transcript)
28
(No Transcript)