Energy cycles

Chapter 17: Energy for biological processes

17.1 Energy cycles

The need for energy

Why do organisms need energy?

The need for energy

• Active transport

• Anabolic reactions

• Movement of cilia, flagella and contractile filaments (muscles)

The need for energy

Where does this energy originate from?

The need for energy

The SUN is the ultimate source of energy for nearly all living organisms (the exceptions being a few deep sea chemosynthetic bacteria).

The need for energy

Where does this energy originate from?

Producers, autotrophs and photoautotrophs?

Producers (autotrophs)

An autotroph is an organism that can produce complex organic molecules from inorganic molecules (water, carbon dioxide, or other chemicals).

Autotrophs produce their own food, so are also called producers.

Photoautotrophs

Photoautotrophs use light energy to make complex organic molecules.

Light is trapped by chlorophyll molecules and this energy is used to drive the synthesis of glucose from CO₂ and water.

Respiration

Respiration is the process that breaks down these complex molecules to provide ATP.

Photosynthesis and Respiration

TASK: Write down the equations for photosynthesis and respiration (word and symbol).

Making and breaking bonds

Making and breaking bonds; which needs energy and which releases energy?

Making and breaking bonds

Making and breaking bonds; which needs energy and which releases energy?

Making bonds = releases energy

Breaking bonds = needs energy

Endothermic or exothermic

Whether a reaction is exothermic or endothermic depends on the total number and strength of bonds that are broken or formed during the reaction.

The atoms in small inorganic molecules like water and carbon dioxide are joined by strong bonds. Organic molecules such as glucose and amino acids contain more but weaker bonds.

Respiration and photosynthesis

In respiration, the total energy needed to break all the bonds in a complex organic molecule is less than the total energy released in the formation of all the bonds in the smaller inorganic molecules.

The excess energy is used to make ATP.

The reverse happens in photosynthesis when organic molecules are made from small inorganic molecules. The energy required is provided by the Sun.

Photosynthesis

TASK:

1. Draw out the molecules that are involved in photosynthesis:

2. Calculate how much energy is needed to break and make the bonds during photosynthesis (I've got a table on the next slide to help).

3. Calculate the total energy that is required to make one molecule of glucose from 6 molecules of water and carbon dioxide.

4. The breakdown of one glucose molecule results in the production of 38 ATP molecules. The formation of ATP requires 30.6kJ/mol. What percentage of the energy released from respiration goes into forming ATP?

Photosynthesis

Energy Transfer - Photosynthesis

​Bond	​Number of bonds involved in reaction	​Bond energy (kJ/mol)	Total (kJ/mol)​
​C=O	​	803​	​
​O-H	​	464​	​
C-C​	​	347​	​
C-H​	​	414​	​
C-O​	​	358​	​
O-H​	​	464	​
O=O	​	495	​

​ ​Bond	​Number of bonds involved in reaction	​Bond energy (kJ/mol)	Total (kJ/mol)​
​C=O	​12	803​	​9636
​O-H	​12	464​	​5568
C-C​	​5	347​	​1735
C-H​	​7	414​	​2898
C-O​	​7	358​	​2506
O-H	​5	464​	​2320
O=O	6	495	2970

Photosynthesis

TASK:

1. Draw out the molecules that are involved in photosynthesis:

2. Calculate how much energy is needed to break and make the bonds during photosynthesis (I've got a table on the next slide to help).

3. Calculate the total energy that is required to make one molecule of glucose from 6 molecules of water and carbon dioxide.

4. The breakdown of one glucose molecule results in the production of 38 ATP molecules. The formation of ATP requires 30.6kJ/mol. What percentage of the energy released from respiration goes into forming ATP?

​Bond	​Number of bonds involved in reaction	​Bond energy (kJ/mol)	Total (kJ/mol)​
​C=O	​12	803​	​9636
​O-H	​12	464​	​5568
C-C​	​5	347​	​1735
C-H​	​7	414​	​2898
C-O​	​7	358​	​2506
O-H	​5	464​	​2320
O=O	6	495	2970

​Energy required to make one molecule of glucose = 15,204 - 12,429 = -2775kJ/mol

Photosynthesis

TASK:

1. Draw out the molecules that are involved in photosynthesis:

2. Calculate how much energy is needed to break and make the bonds during photosynthesis (I've got a table on the next slide to help).

3. Calculate the total energy that is required to make one molecule of glucose from 6 molecules of water and carbon dioxide.

4. The breakdown of one glucose molecule results in the production of 38 ATP molecules. The formation of ATP requires 30.6kJ/mol. What percentage of the energy released from respiration goes into forming ATP?

​Energy required to make one molecule of glucose = 15,204 - 12,429 = -2775kJ/mol.

The energy needed to break bonds is the same as the energy that is released when those same bonds are formed.

Energy released from one molecule of glucose = 12,429 - 15,204 = +2775kJ/mol.

​Energy required to make one molecule of glucose = 15,204 - 12,429 = -2775kJ/mol.

The energy needed to break bonds is the same as the energy that is released when those same bonds are formed.

Energy released from one molecule of glucose = 12,429 - 15,204 = +2775kJ/mol.

38 molecules of ATP = 30.6kJ/mol x 38 = 1162.8

1163/2775 x 100 = 41.9% = 42%