Photosynthesis Flashcards
Define Photosynthesis
processes of Converting light Energy into Chemical Energy to produce organic compounds (cells make organic compounds (e.g. glucose) from inorganic molecules (CO2 and H2O) in the presence of sunlight)
Explain the light-dependent reaction
CO2 diffuses into the leaf through small pores and then enters the plant cells. Inside the plant cells, C02 diffuses into the chloroplast where photosynthesis takes place. Chloroplast use energy from light to transform CO2 and water into sugar (glucose) and oxygen. Note also that Water is also a product of photosynthesis. Thiswater is produced from the oxygen atoms in the carbon dioxide molecules. Inside the chloroplast are the thylakoids, the inner membrane that folds into grana where photosynthesis is carried out. During the light-dependent reactions, photosystems in the thylakoid are activated by a photon of light. For example, light energy strikes chlorophyll molecules in photosystem 2, energizing and exciting electrons out of the photosystem and into the electron transport chain. These electrons are replaced with electrons stripped from water through the process of photolysis which splits water as hydrogen molecules strip off from H20, producing oxygen as a by-product as a result of the absorption of light energy. Hydrogen, thus, loses its electrons to replace those excited out. The energized electron excited outflow through the electron transport chain, releasing energy that is used to pump hydrogen ions into the thylakoid, creating a concentration gradient that will power ATP synthase. These low-energy electrons are shuttled to photosystem 1. In photosystem 1, light energy absorbed energizes and excites the electrons out of the photosystem. These electrons then pass through an electron transport chain where they are used to reduce the electron carrier NADP+ into NADPH. The high concentration of hydrogen ions inside the thylakoid powers ATP synthase, producing ATP. The molecules of NADPH and ATP produced will be used to power the Calvin cycle (the light-independent reaction)
What portion of the electron magnetic spectrum do photosynthetic organisms (autotrophs)
photosynthetic organisms contain light-absorbing molecules called pigments that absorb only specific wavelengths of visible light while reflecting others. The visible light region in the electromagnetic spectrum is from wavelengths of white light and ranges from red (~700 nm) to violet (~400 nm) including the colors Red, Orange, Yellow, Green, Blue, and violent
State the wavelengths of light reflected and the wavelengths of light absorbed
1) yellow and green wavelengths of light are reflected (causes plants to appear with a green or yellow color)
2) Blue and Red wavelengths of light are absorbed (provide the energy used for photosythesis)
Why isnt a plant pigment based on the wavelengths of light absorbed
Electrons excited out of photosystems don’t go through the process of returning to their original energy level because proceed into the electron transport chain. Thus, ras a result, we don’t see red and blue light (wavelengths of light absorbed)
Describe the light-independent reaction (Calvin Cycle)
Calvin cycle takes place in the stroma, the cytoplasm of the chloroplast. The process begins with carbon fixation where CO2 molecules combine with Ribulose 1,5-bisphosphate (RUBP’s) creating a six-carbon molecule that splits into two three-carbon molecules called 3-Phosphoglycerate (PGA). The second stage is called reduction where molecules of ATP and NADP from the light-dependent reactions reduce CO2 (creating immediate molecules such as 1,3bisphosphoglycerate) until glyceraldehyde-3-phosphate (G3P’s) is produced. In the final step, RUBP is regenerated. For every three turns of the cycle, five molecules of glyceraldehyde-3-phosphate (G3P’s) are used to three molecules of RUBP. The remaining glyceraldehyde-3-phosphate (G3P’s) is then used to make glucose, fatty acids, or glycerol. It takes two molecules of glyceraldehyde-3-phosphate (G3P’s) to make one molecule of glucose phosphate. Thus, the Calvin cycle has to run six times to produce one molecule of glucose.
Distinguish between light-dependent reactions and the light-independent reactions
1) The light-dependent reactions convert light energy from the Sun into chemical energy (ATP)
2) The light-independent reactions use the chemical energy to synthesize organic compounds (e.g. carbohydrates)
State a waste product of the light-dependent reaction
1) Oxygen – oxygen is released from stomata as a waste product
Describe the relationship between photosynthesis and cell respiration
Photosynthesis (anabolic synthesis of organic compounds) is essentially the reverse of cell respiration (catabolic breakdown)
Distinguish between the Absorption spectrum and action spectrum and describe the correlation (Keynote: Im expected to know to draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis)
1) The absorption spectrum indicates the wavelengths of light absorbed by each pigment (e.g. chlorophyll)
2) The action spectrum indicates the overall rate of photosynthesis at each wavelength of light (shows the (wavelength of light involved in photosynthesis)
Correlation
There is a strong correlation between the cumulative absorption spectra of all pigments and the action spectrum
1) Both display two main peaks – a larger peak at the blue region (~450 nm) and a smaller peak at the red region (~670 nm)
2) Both display a trough in the green / yellow portion of the visible spectra (~550 nm)
Photosynthetic organisms do not rely on a single pigment to absorb light but instead benefit from the combined action of many. List 6 pigments
Carotene: an orange pigment. Xanthophyll: a yellow pigment. Phaeophytin a: a gray-brown pigment. Phaeophytin b: a yellow-brown pigment. Chlorophyll a: a blue-green pigment. Chlorophyll b: a yellow-green pigment.
Order the wavelengths of light in the visible light region from 10^-5nm to 10^3nm (400nm to 700nm)
nm = nanometers
Acronym (VBGYOR) – ROYGBV backwards
1) Violent light (400 - 450nm)
2) Blue light (450 - 500nm)
3) Green light (500 - 550nm)
4) Yellow light (550 - 600nm)
7) Orange light (600 - 650nm)
8) Red light (650 - 700nm)
Describe Angleman’s experiment
Angelman was a german scientist in the 19th century. He is credited to be the one who discovered the action spectrum of photosynthesis (wavelength of light involved in photosynthesis). He place a strand of spirogyra algae on a slide and add water onto it and added bacteria that need oxygen on the slide also. He then took a prism and held it over the slide. Place the prism over the slide in direct proximity to light, this broke the light that struck the slide into a spectrum and caused the bacteria on the slide that need oxygen to swim to the area of violet, blue and red light. This was significant because it led him to deduce that photosynthesis takes place through the use of violet, blue and red light because in that region was where oxygen the bacterium needed was produced.
Distinguish between the colors used by chlorophyll A and B
chlorophyll A:
1) Violet
2) Red
chlorophyll B:
1) Blue
2) Red
Which evolved first, chlorophyll A or B?D
chlorophyll A because blue-green algae (cyano) were the first bacteria to evolve which explains why chlorophyll A comes first. chlorophyll B came later.
