Photosynthesis and Respiration

• Two processes that are necessary for all life to exist on this planet

• Ultimately all energy comes from the sun and in must be converted into a usable form for living organisms

Photosynthesis and Respiration

• Plants depend on photosynthesis to derive their energy sources.

• Through evolution, plant cells have acquired chlorophylls to help carry out the photosynthetic reaction.

• Photosynthesis is carried out in two steps the photo stage (light dependant reaction) and the synthesis stage (light independent stage)

Photosynthesis

• Occurs in specialized organelles called chloroplasts

• These contain pigments which are specialized molecules that absorb specific colors of light.

• Main pigments are chlorophyll (green), xanthophylls (red) and carotene (yellow/orange)

Chloroplasts

• It is within the chloroplast that photosynthesis occurs

• The pigments absorb the light energy but it requires many enzymes to carry out the process of photosynthesis

Photo Stage

• The main purpose of this stage is to convert the sun’s energy into a form that can be used in the synthesis stage of photosynthesis

• Chlorophyll molecules arranged within the thylakoid membranes in clusters called photosystems

• Each photosystem is composed of a few hundred pigment molecules that act together

• Their combined function is to concentrate the sun’s energy so it can be converted to a form that the plant can use

(cont’d)

• When the energy reaches the reaction centre it us used to break water into 2 hydrogen and an oxygen molecule

• Enzymes in the thylakoid break the hydrogen atoms into protons and electrons

• This released energy is used to covert ADP and P into ATP

• ATP is required for the next stage of photosynthesis

Synthesis stage

• The main purpose of this stage is to make simple sugars by using energy from the photo stage and carbon dioxide

• The synthesis stage of photosynthesis takes place in the stroma (the fluid portion of the chloroplast)

• Energy from the photo stage is necessary to drive the synthesis of simple sugars

(cont’d)

• There are many separate reactions that make up the synthesis stage of photosynthesis and they are collectively called the Calvin cycle

Photosynthesis

• Through this process, the plant is able to convert sunlight, water, and CO2 into glucose and ATP.

• As a byproduct of this process, O2 is released. • The plant's ability to convert water and CO2 into

glucose and O2 also provides great benefit for animal species that depend on glucose for energy.

• The photosynthetic reaction can be summarized as follows: 6CO2 + 12H2O + sunlight -> C6H12O6 + 6H2O + 6O2

Respiration

• Cells, like all things, need energy to operate.

• MP3 players use batteries for energy, cells use adenosine triphosphate (ATP) for energy.

• Unlike MP3 players, cells can produce their own energy.

• People don't eat ATP, though. Their food consists mostly of proteins, lipids, and polysaccharides (sugars) which need to be broken down into ATP. 

Respiration

• Respiration can be either aerobic (in the presence of oxygen) or anaerobic (in the absence of oxygen). Anaerobic respiration may also be called fermentation. 

• In both cases the process begins with the initial breakdown of glucose through the process of glycolysis.

Cellular Respiration

• The four basic phases of respiration are :– Glycolysis– Transition Reaction– Krebs Cycle– Electron Transport chain

• Each phase is a series of complex reactions that results in the production of ATP (chemical energy for the cell)

Aerobic Respiration

The end products of glycolysis undergoes further breakdown through a process called aerobic respiration in most organisms.

• This process requires oxygen and yields much more energy than glycolysis.

Aerobic Respiration

• The end result of ATP would be the production of 36 ATP

• The energy conversion is as follows:

• C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)

Anaerobic Respiration

• Occurs in aerobic organisms when there is a lack of oxygen

• This type of respiration is very inefficient – only 2 ATP are produced

• The product of this type of respiration is lactic acid and 2 ATP

• When we exercise strenuously our muscles perform this type of respiration

• It is the lactic acid that build up in the muscle that causes pain after this type of exercise

Global Importance

• Read pages 86 – 91

• Answer questions 2,3,4,5