Chapter 7 - Photosynthesis Flashcards
Autotroph
An organism that makes its own food, sustaining itself without eating other organisms or its own molecules.
Includes plants, algae, and numerous bacteria.
Photoautotroph
An organism that obtains energy from sunlight, and carbon from CO2 by photosynthesis.
Ex. Plants, algae
Heterotroph
An organism that cannot make its own organic food molecules, and must obtain them from consuming other organisms or their organic products
Ex. Humans
Chloroplasts
Function to convert light energy into chemical energy via photosynthesis.
The inner membrane has thick fluid called stroma which holds DNA, ribosomes, and enzymes.
In the stroma is thylakoids which contains pigment called chlorophyll.
(Note: a stack of thylakoids = granum
Photosynthesis
The process used by plants in which sunlight is used to make chemical energy that can be metabolized to fuel the plants activities.
2 stages:
1. light dependent reactions
2. The Calvin Cycle
NADP+
(Nicotinamide adenine dinecluotide phosphate)
Accepts H ions and elections, which reduces it to NADPH then it stores the potential energy in the ions and electrons until they are ready to be used by the Calvin cycle
Photon
A fixed quantity of light energy
The shorter the wavelength the greater the energy.
The longer the wavelength the lower its energy.
Colour is based on the different wavelength (red = long wavelength, blue = short wavelength)
Absorbtion spectrum
A graph of wavelengths showing which pigments absorb certain colours.
Chlorophyll a
The main pigment of plants used for photosynthesis. Does not absorb green which is why plants appear as green.
Excited electrons
Electrons excite when the molecule they are held in absorbs a photon.
The electron goes into a high energy state and transfers the electron into an e- shell that is further away which gives it more energy, but it’s less stable so it springs back down to where it was. As it goes back it releases heat and light (at a lower wavelength).
Photosystems
Protein complexes embedded in the membrane (two of them PSII and PSI)
Takes light and puts it into pigment molecules which transfer their energy down a chain until it goes into a pair of chlorophyll a molecules. Then the energy gets passed on as an excited electron to an electron acceptor.
Photosystem II
A photosystem which takes the excited electrons (from the splitting of water) energy and uses it to pump H
H ions/protons against their concentration gradient. The H’s go ATP synthase to generate ADP into ATP. The electron is passed to photosystem I
Photosystem I
Another photosystem where even more light comes in to further excited the electrons and those electrons made from both photosystems get carried by NADP which reduces it to NADPH. Those electrons get carried to the Calvin cycle along with the ATP in other to make G3P -> glucose
Accessory pigments
Secondary light absorbing pigments in the thylakoid membrane, and they increase the range of light that can be utilized by the plant for photosynthesis.
Ez. Carotenoids
Light dependant reactions
Occurs in the thylakoid membrane.
- light comes into photosystem II and light energy travels down pigment molecules into chlorophyll a
- water splits which excites an electron which will get propelled into the primary electron acceptor and then carried down into photosystem I.
- Photosystem I does the same process but the electron at the end will attach to and reduce NADP to NADPH which goes to the Calvin cycle.
- H protons from the splitting of water have been floating around in the thylakoid space, they go to ATP synthase and turn ADP to ATP which goes to the Calvin cycle
The Calvin Cycle
Occurs in the stroma.
Step 1 - start with (3)CO2 RUBISCO enzyme will carbon fixate it meaning it will add (3) ribulose bisphosphate molecules to it and rearrange them to (6) 3-PGA molecules.
Step 2 - ATP and NADPH will reduce the (6) 3-PGA and generate (6) G3P.
Step 3 - 1 of the (6) G3P will leave the cycle, the other 5 will use ATP to regenerate into our starting molecule 5C molecule: ribulose bisphosphate.
Carbon fixation
Taking CO2 out of the air and attaching it to a molecule of G3P
Carried out by enzyme RUBISCO
What 2 physical factors affect the rate of photosynthesis?
Temperature - the lower the temp, the slower the rate
Light availability - decrease in light, decrease is rate
What happens when an object absorbs a certain wavelength?
The wavelength can no longer bounce back into you eye, so you can’t see it.
(i.e. if it absorbs red you may see greens)
If the entire spectrum of visible light is absorbed, we see black.
Conversely, if an object doesn’t absorb any light at all, we see white
Which molecule is both a reactant and a product in photosynthesis?
H2O
