Photosynthesis and Cellular Respiration

Energy Energy that living things gain from eating comes indirectly from the sun. Plants receive this energy directly, while we receive the energy indirectly. This energy makes organic compounds found in our food.

Flow of Energy

Autotrophs Organisms that use energy from sunlight to make organic compounds Most are photosynthetic Ex: Plants Some do not have access to sunlight, and use chemical energy instead Ex: bacteria in extreme environments

Photosynthesis The process by which light energy is converted to chemical energy

Heterotrophs Organisms that must get energy from food Humans and other animals Go through cellular respiration processes for energy

Cellular Respiration Releases energy from food to make ATP Energy released gradually through chemical reactions ATP is a result of these reactions ATP goes wherever it is needed in the cells

ATP ATP (Adenosine Triphosphate) goes to the areas that need energy in the cell A phosphate group breaks off to release the energy needed and forms ADP. ATP  ADP + P + Energy

Let’s Look at Photosynthesis and Cellular Respiration a little closer!

Photosynthesis All foods that we eat eventually lead back to plants. These plants go through photosynthesis to get their energy. Ex: Hamburger Beef comes from cow that ate grass.

Photosynthesis Photosynthesis occurs in chloroplasts of plant cells and cell membrane of bacteria. 3CO2 + 3H2O  C3H6O3 + 3O2

Three Stages of Photosynthesis 1.) Energy is captured from sunlight 2.) Light energy is converted to chemical energy (stored in ATP and NADPH) 3.) Chemical energy in ATP and NADPH power the formation of organic compounds Steps 1 & 2 are light-dependent NADPH is an energy carrier molecule

Stage 1: Energy is Captured From Sunlight When sun shines on us, there are several types of radiation hitting us at different wavelengths. We can only see visible light and sunlight contains all of the wavelengths of visible light.

Stage 1: Energy is Captured From Sunlight How do we see light?

Stage 1: Energy is Captured From Sunlight We see light through light-absorbing substances called pigments. These absorb and reflect certain wavelengths. These pigments are held in disk-shaped thylakoids in chloroplasts. These pigments are held in clusters.

Two Types of Pigments to Know Chlorophyll Reflects green and yellow light so we see leaves as green. Carotenoids Reflects yellow and red light so we see leaves as yellow and orange in fall.

Stage 1: Energy is Captured From Sunlight Light strikes thylakoid Energy transferred to electrons in pigments Electrons now “excited” and jump to higher energy level These electrons used to power Stage 2 Electrons used now replaced through water molecules This forms oxygen gas (O2)

Stage 2: Light Energy is Converted to Chemical Energy The excited electrons from Stage 1 jump through molecules along the thylakoid membrane. Like a basketball being passed down a line of people This is known as an electron transport chain One chain helps make ATP One chain helps make NADPH

Electron Transport Chain: ATP Excited electrons move through protein Electrons lose energy, energy used to pump in H+ ions Eventually these ions diffuse out of the thylakoid through a carrier protein This protein causes ADP to add a phosphate group and it becomes ATP

Electron Transport Chain: NADPH Excited electrons combine with hydrogen ions and NADP+ Forms NADPH

Stage 3: Energy Stored in Organic Compounds Carbon dioxide fixation: transfer of carbon dioxide to organic compounds “dark reaction” or light-independent Most common method of carbon dioxide fixation is the Calvin Cycle

Calvin Cycle 1.) Each carbon dioxide molecule is added to a five-carbon compound. 2.) Each of the three resulting six-carbon compounds is unstable and immediately splits, forming a total of six three- carbon compounds. 3.) One of the resulting three-carbon sugars is used to make organic compounds that the organism uses for energy. 4.) The five other three-carbon sugars are used to regenerate the five-carbon compound that began the cycle.

Factors that Affect Photosynthesis Light Rate of Photosynthesis increases as light intensity increases Carbon Dioxide Concentration Same as light Temperature Enzymes assist reactions and have to stay within certain temperature range