Photosynthesis Chapter 8

Energy in Living Systems…. Energy is the ability to do work. Autotrophs – Living things that can use energy from the sun or chemicals to make their own food. Green plants and some bacteria and algae. Heterotrophs – living things that must eat other living things for energy.

Energy in Cells… ATP, or adenosine triphosphate is the form of energy cells make to do everyday functions. ADP, or adenosine diphosphate is ATP without the final phosphate group. Therefore it has less energy than ATP. ADP is used over and over again to be turned into ATP.

What does ATP look like? *Only a small amount of ATP is on hand at a time, It is just regenerated over and over again!

How do plants make ATP and other molecules for long term energy? Photosynthesis – Plants use the energy in sunlight to turn water and carbon dioxide into carbohydrates and oxygen. 6H 2 O + 6CO > C 6 H 12 O 6 + 6O 2

Scientists who contributed to our knowledge of photosynthesis: Jan van Helmont – concluded most of the mass of a tree comes from water (*partially true) Joseph Priestley – used a bell jar, candle, and mint plant to conclude plants release oxygen Jan Ingenhousz – concluded aquatic plants only produce oxygen bubbles in the presence of sunlight

Jan van Helmont’s experiment Jan Ingenhousz’s experiment

Pigments of Photosynthesis… Chlorophyll – green pigment in plants that absorbs blue-violet and red, and reflects green. Chlorophyll is present in the chloroplasts of a plant cell.

Structure of a Chloroplast…

Structure of a chloroplast… The light-dependent reactions take place on the thylakoid membrane. Thylakoids are the “pancake” structures. Stacks are called grana. The Calvin cycle takes place in the stroma (the fluid the thylakoids float in).

Making ATP using light energy.. The energy from the sun is absorbed by the chlorophyll in the thylakoid membrane. NADP+ is an electron carrier that carries high energy electrons and two hydrogen ions. Turns into NADPH. The H+ ions are created when sunlight hits the thylakoid and water is split, creating free oxygen, a waste product.

Light reactions, continued… The NADPH carries the electrons and the H+ ions to the membrane where the H+ ions are pumped into the inside of the thylakoid. The pressure of the H+ ions builds up, and the H+ ions are forced back out of the membrane through a structure called ATP synthetase.

Making ATP… As the H+ ions and their energy move through the ATP synthetase, the protein rotates and creates 3 ATPs for every turn.

1948 – Melvin Calvin traces the path of carbon: the Calvin Cycle… The ATP and the NADPH created in the light-independent reactions combined with carbon dioxide to assemble carbohydrates in the Calvin Cycle. The Calvin cycle can also produce other sugars, amino acids, and lipids.

The Calvin cycle…

Factors affecting photosynthesis: Water – a shortage of water will slow or stop photosynthesis. Temperature – Plant enzymes function in specific temperature ranges. Light intensity – The brighter the light is, the more photosynthesis can occur. But only to a certain extent.