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Course: AP®︎/College Biology > Unit 3
Lesson 4: PhotosynthesisPhotosynthesis review
Key Terms
| Term | Meaning |
|---|---|
| Photosynthesis | The process by which plants, algae, and some bacteria convert light energy to chemical energy in the form of sugars |
| Photoautotroph | An organism that produces its own food using light energy (like plants) |
| ATP | Adenosine triphosphate, the primary energy carrier in living things |
| Chloroplast | The plant cell structure where photosynthesis occurs |
| Thylakoids | Disc-like structures within a chloroplast that help absorb light |
| Grana | Stacks of thylakoids in a chloroplast |
| Chlorophyll | A pigment found in the thylakoid that absorbs light energy and uses it to produce carbohydrates |
| Stroma | Fluid-filled space surrounding the grana |
Photosynthesis reaction
During photosynthesis, photoautotrophs use energy from the sun, along with carbon dioxide and water, to form glucose and oxygen.
The overall equation for photosynthesis is:
The stages of photosynthesis
There are two main stages of photosynthesis: the light-dependent reactions and the Calvin cycle.
| Stage | Location | Events | Requires sunlight? |
|---|---|---|---|
| Light-dependent reactions | Thylakoid membrane | Light energy is captured by chloroplasts and stored as ATP | Yes |
| Calvin cycle | Stroma | ATP is used to create sugars that the plant will use to grow and live | No |
Common mistakes and misconceptions
- Photosynthesis and cellular respiration are almost opposite processes. Looking at their equations, they differ only in the form of energy that is being absorbed or released. However, they are not simply the reversal of each other, as each one takes place in its own particular series of steps.
- Plants are green because chlorophyll reflects green light. Many people think that chlorophyll is green because it wants to absorb and use green light. However, this is not true. The color we see is actually the color of light that is being reflected. Therefore, chlorophyll reflects green light, while absorbing red and blue light.
Want to join the conversation?
If you heavily breath on a plant, will it help growth considering it needs CO2, water, sunlight?(45 votes)
In an open environment, probably not by any noticeable amount. However, if you put the plant in a sealed container such as a greenhouse and sit in the greenhouse for a while then the CO2 concentration will rise. So in a sealed container the answer is yes but just a plant sitting in your house or outside breathing on it won't make a huge difference.(46 votes)
the electron carrier for photosynthesis. NADH(without the P for photosynthesis :) ) is used in cellular respiration. They carry electrons to and fro and are subsequently oxidized or reduced. They need to carry the electrons because electrons are high charge substances(18 votes)
- Isn't a stack of thylakoids actually called a granum?(14 votes)
how does the plant reléase the oxgen(7 votes)
through stomata on the back of it's leaves(14 votes)
How do trees survive when they lose their leaves in the winter? How can photosynthesis still occur without the chloroplasts in the leaves? Do they keep energy in storage to use during the season?(5 votes)
Deciduous trees store energy and resources within their bark, which can be used during the winter months when they have no leaves. Additionally, their physiological process change and slow down, as to not consume as much energy compared to the warmer months. It's a bit like hibernation for trees, where they stock up on resources and decrease energy consumption to make it through the winter.
Evergreen trees (like the firs you see during Christmas time) have special adaptations to the cold that negate the need for this period of dormancy.
Does this help?(10 votes)
Calvin Cycle: ATP is used to create sugars that the plant will use to grow and live.
My question is where does the ATP come from? Light-dependent reactions make ATP with the light energy, but the Calvin cycle seems to already have it so that it can convert into sugars... Does the Calvin cycle happen after the light-dependent reactions occurs or is the Calvin cycle independent? An example of my question:
Does photosynthesis happen like this?
LDR: Light energy + H2O = ATP + NADPH + O2
And then after that:
Calvin Cycle: ATP + NADAPH + CO2 = sugar
?
Sorry if I got some things wrong @~@(8 votes)
The Calvin cycle is dependent on the Light-dependent reactions, and almost in the same way Light-dependent reactions are dependent on "The Calvin Cycle". The "light-dependent reactions" receive light, and provide energy for the Calvin cycle. After used by the Calvin cycle, the molecules go back to the thylakoids to be reenergized in a way. So it is almost like a constant cycle between the two areas. For clarity refer to the diagram given above.(4 votes)
- "Light energy is captured by chloroplasts and stored as ATP"
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?(5 votes)
ATP is not sugar, it is a nucleotide. The carbon atoms needed to build sugar molecules are taken from the CO2 that the plant absorbs. CO2 is converted into glucose during the Calvin cycle, which is an anabolic pathway and therefore needs ATP to actually build up the molecules.(7 votes)
- during what stage of photosynthesis are ATP and NADPH converted to ADP + Pi and NADP+(6 votes)
During the Calvin Cycle, the ATP and NADPH are broken down into ADP, Pi, and NADP+ to provide energy for the cycle. Then, after passing through, the used-up molecules react to bind together into ATP and NADPH again.(4 votes)
How often do they(plants) produce the Oxygen?? Is it a continuing process, I mean.. Don't they stop or pause producing it??(4 votes)- Every time that the process of photosynthesis happens, it produces 1 molecule of oxygen along with the ATP and NADPH. However, only one molecule of oxygen is hardly anything compared to actual air space; much, much more must be produced to actually make a difference. It will therefore continue producing a larger quantity.
Also, photosynthesis is light-dependent;(the first cycle is directly dependent on light energy, and the Calvin cycle is dependent on the first cycle. In fact, they both rely on each other to complete each individual cycle!) Think of a time when there is no light. Night! During that time, no oxygen, ATP, or NADPH is being made because a source of light energy is not available. However, a plant still has enough energy to survive because of cellular respiration, so it is not a problem.
In short, a plant does take a break from producing oxygen when the process of photosynthesis is not occurring.(7 votes)
"Light energy is captured by chloroplasts and stored as ATP"
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?(3 votes)- ATP itself is not composed of sugar.
When light energy is captured by the chloroplast, it, along with carbon dioxide and water, gets converted to ATP, NADPH, and oxygen (light-dependent reactions). The ATP and NADPH then enter the Calvin cycle and fuel the synthesis of molecules that eventually become sugar molecules.
These sugar molecules can then be sent to the plant cell's mitochondrion to undergo cell respiration, which produces even more ATP that can be used to fuel the plant cell's many complex processes.(13 votes)
