Energy Transformations VCE Biology Unit 3
Contents Energy Cellular Respiration Photosynthesis Storing Energy
Energy Energy exists in many forms: light, heat, sound, mechanical, electrical, chemical and kinetic. The law of conservation of energy (first law of thermodynamics) states that energy cannot be created or destroyed simply transferred or transformed. Green plants transform light energy into stored chemical energy (potential energy) in the chloroplasts. Plants and animals take that stored chemical energy and transform it to heat, sound and kinetic energy in many forms.
Energy The second law of thermodynamics states that entropy (randomness or chaos) of the universe is increasing. Therefore all energy tends to turn to heat energy as witnessed in the random movement of molecules. Biological systems are inherently inefficient. If we consider all the energy that arrived on the planet from the Sun as 100% only about 1% is trapped in photosynthesis, with 99% being reflected back into space. Of the 10% trapped in photosynthesis about 40% is released in cellular respiration that is 0.004% of the original light energy.
Energy Energy cannot be created of destroyed. Free energy is energy available to do work. When energy is transformed, some energy is lost usually as heat. Exergonic reactions result in a net release of energy. Endergonic reactions require an input of energy to occur. All energy transformations obey the laws of thermodynamics: The total energy in the universe is constant and has been since the Big Bang In the universe as a whole, the amount of free energy is declining and has been since the Big Bang
Cellular Respiration All organisms use the chemical energy carried in the phosphate bonds of adenosine triphosphate (ATP). It is the major source of energy for almost all cellular functions.
Cellular Respiration Cellular respiration commences in the cytosol surrounding the mitochondrion and is completed within the membranes of the mitochondrion. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy as 36 38 ATP It occurs in three stages: Glycolysis, Krebs Cycle and Electron Transport
Cellular Respiration Glycolysis This literally means splitting the glucose molecule. One glucose molecule becomes 2 pyruvate molecules, 2 NADH hydrogen acceptors and 2 molecules of ATP If adequate oxygen (aerobic) is present then the process continues in the mitochondria. In the absence of adequate oxygen (anaerobic) then fermentation follows. No more energy is released, however, toxins are produced: lactic acid in animals and alcohol and carbon dioxide in plants.
Cellular Respiration Krebs Cycle The pyruvate and NADH transfer to the membrane (cristae) of the mitochondria at a cost of 2 molecules of ATP. The pyruvate and NADH are transformed into 2 acetyl coenzyme A molecules, 4 electron carriers become charged, 2 CO 2 are produced and 2 more units of ATP are released.
Cellular Respiration Electron Transport On the cristae of the mitochondria the charged electron carriers react with a series of cytochromes causing ADP to form between 32 and 34 molecules of ATP and 6 molecules of H 2 O
Photosynthesis Photosynthesis occurs in the chloroplasts of plants light 6CO 2 + 12H 2 O C 6 H 12 0 6 + 6H 2 0 + 60 2 Chlorophyll There are some organisms that are chemosynthetic and make simple sugars from chemicals and there are also a number of other pigments capable of catalyzing photosynthesis.
Photosynthesis Light Dependent Stage The chlorophyll traps light energy and uses it to produce ATP and to split water in hydrogen ions and oxygen gas. This occurs on the grana of the chloroplast
Photosynthesis Light Independent Stage The ATP made in the first stage is used to combine carbon with hydrogen ions to form glucose and water as a waste. This occurs in the fluid matrix or stroma of the chloroplast.
Photosynthesis The rate of photosynthesis is affected by: Carbon dioxide the level of available CO 2 is critical to the speed of phs Light intensity light intensity is also a critical factor in the speed of phs Temperature phs occurs most quickly at 20 40 0 C Oxygen high oxygen concentrations have been found to inhibit phs Water a lack of water will cause the stoma to close, gas exchange to cease and phs to slow and finally cease. Chlorophyll the amount of the catalyst will affect the speed of reaction
Storing Energy Plants Plants create glucose in photosynthesis. The excess glucose is stored as starch for future use. Starch is a complex carbohydrate made of many glucose sub units. It is more efficient for the plant to store starch than to store glucose. Individual cells contain starch granules. The plant will store starch in fruits, tubers, bulbs and corms below the ground, fleshy stems and seeds.
Storing Energy Animals Animals store excess glucose as glycogen another complex carbohydrate made of many glucose molecules. Glycogen is stored in individual cells and in tissues associated with the major muscles and organs which demand large amounts of energy. About half a day s energy is stored as glycogen approx. 300g Excess glycogen is stored in adipose tissue as fat. Fat allows the animal to store energy more efficiently as it takes up less space and provides more energy than the same amount of carbohydrate. An animal will store about a months supply of energy as fat unless they hibernate.