Energy

Energy - the ability to do work

Where does energy come from? Solar or chemical

Chemical Energy - An important compound that cells use to store and release energy is adenosine triphosphate (ATP).

ADP is also an energy-storing/transferring compound with only 2 phosphate groups. This is formed when we release energy from ATP. Energy is stored in the bond.

Solar Energy - plants gather the sun’s energy with light-absorbing molecules called pigments. The plant’s principal pigment is chlorophyll (Green light is not absorbed, it is reflected back).

Photosynthesis

The process by which autotrophs use solar energy to produce chemical energy (sugars and starches) is known as photosynthesis.

Formula

Factors

• Temperature (best between 0-35 degrees Celsius)

• Amount of water available

• Light (more intensity = more photosynthesis until it maxes out)

• Carbon dioxide level

Where does photosynthesis occur in the cell?

Chloroplast

Parts of a chloroplast

• Thylakoids - sac-like membranes; arranged in stacks called grana which contain chlorophyll; light dependent reactions take place here.

• Stroma - the fluid portion outside of the thylakoids; light independent reactions take place here.

Light-dependent reaction - takes place in the thylakoid membranes, requires light to occur

Light-independent reaction - takes place in the stroma. Does not require light, can happen anytime

Light-dependent reactions take in water and light creating ATP and NADPH and giving off oxygen as a byproduct.

Light-independent reactions use the energy from the NADPH and ATP to power the creation of the sugars (chemical energy). Carbon dioxide is absorbed for this purpose. This is also called the Calvin Cycle.

Cellular Respiration

the process that releases energy from food in the presence of oxygen; the “opposite” process of photosynthesis

Organisms get the energy they need from food

• energy stored in the food is expressed as calories

• food molecules being broken down release energy that is used to make ATP

• glucose is a carbohydrate that is broken down during cellular respiration to release the needed energy

The reaction takes place within the mitochondria:

3 steps to respiration

1. Glycolysis - takes place in the cell’s cytoplasm

2. Krebs Cycle - takes place in the matrix of the mitochondria

3. Electron Transport Chain - takes place along the cristae of the mitochondria

Glycolysis - gives 4 ATP molecules and 2 pyruvic acid for every glucose molecule; anaerobic process (no oxygen needed)

1 glucose + 2 ATP → 4 ATP and 2 pyruvic acids

Takes 2 ATP to get started so the net result is 2 ATP. Since it doesn’t use oxygen, it is a quick energy source when oxygen isn’t available.

Krebs Cycle (aka citric acid cycle) - releases more energy from the pyruvic acids made during glycolysis; uses several '“helper molecules”

2 pyruvic acids → 2 ATP, NADH, FADH2, and CO2

Electron Transport Chain - produces the most energy by using oxygen; aerobic process (uses high energy electrons from glycolysis and Krebs cycle to change ADP into ATP)

One glucose molecule yields 36 ATP.

Fermentation

if oxygen is not available (anaerobic conditions), the processes of the Kreb’s cycle and the electron transport chain won’t take place, so fermentation will take place in the cytoplasm of cells.

Products made by fermentation:

• Lactase

• alcohol + CO2

2 Types of Fermentation

1. Alcoholic fermentation (yeast and plants do this) - glycolysis takes place in the cytoplasm and then pyruvic avid is broken down and produces alcohol and carbon dioxide - 2 ATP made

2. Lactic Acid fermentation (animals do this) - glycolysis takes place and pyruvic acids are converted to lactic acids - 2 ATP made (lactic acid buildup leads to muscle soreness and cramping)

Energy and Exercise

Lactic acid fermentation can supply small amount of energy for about 90 seconds of activity; leaves a “burn” in the muscle (Quick Energy)

Cellular respiration releases energy more slowly; it is the only way to supply a continuous and more long term supply of ATP. (Long Term Energy) (stored energy (glycogen) in the human body lasts about 15-20 minutes, then the body will begin to break down fats)