Photosynthesis and Photosynthesis and Cellular RespirationCellular Respiration

How do cells obtain organic compounds for energy?

Heterotrophs: Cannot make their own food Autotrophs: Can make their own food

– Photoautotrophs: Use energy from the sun (photosynthesis) to produce organic compounds (glucose)

Plants, algae and some bacteria

– Chemoautotrophs: Use energy stored in inorganic compounds (chemosynthesis) to produce organic compounds

Some bacteria found at the hydrothermal vents of the seafloor

Photosynthesis

Method of converting light energy from the sun into chemical energy that cells can use – Divided into the light-dependent and light-independent

reactions

Photosynthesis takes place in chloroplasts– The parts of a chloroplast are as follows:

Thylakoids- disk-shaped structures that contain the pigment chlorophyll (absorbs the sunlight)

Grana- A stack of thylakoidsStroma- Liquid between grana

Draw a Chloroplast

Overall Photosynthesis Reaction

6CO2 + 6 H2O + light energy → C6H12O6 + 6O2

•On the left of the arrow are the reactants (the components that “react” together).•On the right of the arrow are the products. •Identify how a plant obtains the reactants.

Light-dependent Reactions

Chlorophyll (in thylakoids) absorbs the light energy– Plants have 2 types: Chlorophyll A and Chlorophyll

B Water molecules are split apart producing H and

O2

Electrons flow throughout the thylakoid membrane (electron transport chain)

Energy compounds ATP and NADPH are produced

Light-independent Reactions (Dark Reactions)

Occur in the stroma ATP and NADPH from the light reactions are

used to fuel the break down of CO2 and the reassembling of the atoms to produce glucose.

This reassembling is called “carbon fixation”. Carbon fixation occurs in a series of reactions

called the Calvin Cycle.

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 don’t come to us the way our cells can use them

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

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

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

Anaerobic Cellular Respiration

Some organisms thrive in environments with little or no oxygen

– Marshes, bogs, gut of animals, sewage treatment ponds

No oxygen used= ‘an’aerobic 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)

Aerobic Cellular Respiration

Oxygen required=aerobic 2 more sets of reactions which occur in a

specialized structure within the cell called the mitochondria– 1. Kreb’s Cycle– 2. Electron Transport Chain

Kreb’s 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

Electron Transport Chain

Electron carriers loaded with electrons and protons from the Kreb’s 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

Energy Tally

36 ATP for aerobic vs. 2 ATP for anaerobic

– Glycolysis 2 ATP

– Kreb’s 2 ATP

– Electron Transport 32 ATP 36 ATP

Anaerobic organisms can’t be too energetic but are important for global recycling of carbon