EOC Review—Cell Energy

Photosynthesis! carbon dioxide + water + sunlight  glucose + oxygen (waste)

Photosynthesis—Chemical reaction that converts the sun’s energy into chemical energy stored in food Happens in the cells of autotrophs (such as plants) In the plant cell, the chloroplasts absorb the sun’s energy and store it in food molecules (food=glucose, carbohydrates, sugars, etc) Chemical Reaction: Carbon Dioxide + Water + Sunlight  Glucose + Oxygen Autotrophs are making food for themselves, but all organisms get food from photosynthesis (heterotrophs get it from eating plants or animals that ate plants) inputs=reactants outputs=products

Cellular Respiration! ATP Carbon dioxide (waste) Water (waste) glucose (food) + oxygen  carbon dioxide (waste) + water (waste) + ATP

Cellular Respiration—chemical reaction that converts the energy in food into energy cells can use (ATP) Cellular respiration happens in mitochondria of cells Food (glucose) and oxygen molecules are sent to the mitochondria where they are broken and the energy stored in the food molecule is transferred to ATP molecules Chemical Reaction: Glucose + Oxygen  Carbon Dioxide + Water + ATP Happens in ALL cells to transfer energy from food molecules to ATP molecules, which is the only energy that cells can actually use. inputs=reactants outputs=products (ATP)

What is this ATP molecule? It is stored energy that the cell can use when it needs ‘fuel’. To release the energy, a phosphate (P) is broken off. The left-over molecule (ADP) can be recycled back to ATP; cellular respiration uses the energy from food molecules to ‘push’ the third P back on to convert ADP back to ATP, ready for use by the cell for energy!

Heterotrophs don’t do photosynthesis, so where do they get the ‘ingredients’ for cellular respiration? From eating other organisms and from breathing!

What if there is not enough oxygen for cellular respiration? Fermentation happens! The first step of cellular respiration breaks the glucose into two pieces. This does not require oxygen and produces a little bit of ATP for the cell (not nearly as much as all of cellular respiration, but some is better than none!). If there is not enough oxygen available for cellular respiration, the cell just performs this first step to gain some ATP; this is called FERMENTATION. Waste products of fermentation include lactic acid or alcohol. Aerobic-chemical reaction requires oxygen (ex-cellular respiration) Anaerobic-chemical reaction does not require oxygen (ex-fermentation)

Photosynthesis and cellular respiration are cyclic in an ecosystem Photosynthesis and cellular respiration are cyclic in an ecosystem. The products of cellular respiration are used for photosynthesis and the products of photosynthesis are used for cellular respiration. Photosynthesis uses the sun’s energy to make food for the ecosystem and cellular respiration converts the energy in the food to ATP (energy cells can use).

These reactions contribute to the carbon cycle on Earth because photosynthesis uses carbon dioxide (CO2) from the atmosphere to make food/glucose (C6H12O6) for the biosphere and cellular respiration uses food/glucose (C6H12O6) from the biosphere to make carbon dioxide (CO2) waste, which goes into the atmosphere.