ScienceWhat is photosynthesis in biology | Types, Importance

What is photosynthesis in biology | Types, Importance

What is photosynthesis in biology

Plants and some other organisms like bacteria to grow need a mixture of carbon dioxide, water, and energy, the chemical process which use these resources to manufacture glucose is called photosynthesis in biology.


What is photosynthesis in biology
Where does the energy for photosynthesis come from?

This energy comes from sunlight which contains a wave and particle.

The particles or photons are the smallest units of light. The wave that has mentioned above is electromagnetic spectrum, this includes Radio Waves, Infrared, Visible Light, UV Light, X rays, and Gamma rays (All measured by wavelength). Photosynthesis organisms just use Visible Light.


Why does the plants looks green

There are pigments in photosynthesis organisms that cause the green color in plants. This color comes from the reflection of Visible Light. Plants appear green because they reflect the green and yellow wavelength of Visible Light and absorbs blue and red to use the energies of this two-wavelength for providing the energy of photosynthesis.

Why sky looks Blue

Photosynthesis organisms

Plant cells have some structures such as mitochondrion, ribosomes, nucleolus, vacuole, chloroplast, etc. A structure that specialized just for plant cells and the process of photosynthesis have done in it is the chloroplast. In the chloroplast, there are other structures called thylakoid which is surrounded by fluid tilled space, the stroma.


How does photosynthesis work step by step

Photosynthesis consists of two sets of reaction: light dependent reactions and Calvin cycle (Does not depend on light)
Light dependent reactions occur in the thylakoid and include 3 steps.

Light Absorbing: Thylakoid has a membrane and light-absorbing happens by some molecules that exist in the membrane of the thylakoid.

There are pairs of photosystems, photosystem l, and photosystem ll. These two works provide the energy for other reactions that will happen in the stroma. Photosystems have pigments, chlorophyll, and carotenoid. These pigments absorb the photons of light, light energy excites electrons to a higher state in pigments, these electrons transfers by other pigments that exist in the photosystems until they reach the reaction center. The reaction center contains chlorophyll molecules and will pass the electrons to a series of proteins located on the thylakoid’s membrane.

Electron Transport Chain: The energized electrons are passed from photosystem l to an electron transport chain. The electrons lost by photosystem l, are replaced by oxidation of water in thylakoid which producing oxygen gas, hydrogen ions, and free electrons. Throughout the electrons pass the electron transport chain, the energy of electrons use to pump hydrogen ions from the stroma to the thylakoid, this creates a concentration gradient that will use to generate ATP. Low energy electrons which came from photosystem l to photosystem ll, re-energized and past another electron transport chain which is located after photosystem ll. While electrons pass it, they are used to reduce the electron carrier NADP+ to NADPH.

Generation of ATP: We mentioned about concentration gradient of hydrogen ions above, so this is used to generate ATP by a protein molecule called ATP synthase. ATP synthase is separated from the electron transport chain and photosystems but it’s on the thylakoid’s membrane. This molecule phosphorylates ADP to ATP and transfers the hydrogen ions from inside of the thylakoid (Lumen) to the stroma. ATP synthase is the only way to transfer hydrogen ions and produce ATP in the chloroplast.

Calvin Cycle: This step doesn’t depend on light, but indirectly depends because the products that the Calvin cycle uses comes from light-dependent reactions. (ATP and NADPH). Calvin cycle is serious of reactions that reduce carbon dioxide to produce carbohydrates glyceraldehyde_3_phosphate. This cycle has three steps:

  • Carbon fixation: in this step carbon dioxide and Ribulose 1,5_bisphosphate( RuBP) are used to produce six-carbon molecules which rapidly disintegrates into three-carbon molecules. In this step one carbon dioxide molecule has added to RuBP by an enzyme called Ribulose_1,5_bisphophate carboxylase/oxygenase ( RuBisCO)
  •  Reducing: Here Calvin cycle uses ATP and NADPH that had produced in Light_dependent reactions. Electrons of ATP and NADPH reduce to have glyceraldehyde_3_phosphate( G3P)
  • Regenerating of RuBP: Some molecules of G3P are used to reform RuBP. Here Calvin cycle also uses some ATP’S electrons.
    Other G3Ps make glucose phosphate. The Calvin cycle has to happen six times to produce one molecule of glucose.


Is photosynthesis anabolic or catabolic

Anabolism and catabolism are both refer to metabolism reactions. Catabolism is to breaking down and oxidizing large molecules to provide the energy for anabolism. Anabolism is to consuming the energy that had generated in catabolism to synthesize large and complex molecules.

Photosynthesis is among anabolic reactions because this process uses energy in form of ATP and NADPH to produce complex molecules such as glucose and fructose.


Types of photosynthesis in plants

There are three types of photosynthesis in plants:

C3 carbon fixation: In C3 plants carbon fixation directly got happened after receiving carbon dioxide, ATP, and NADPH.

C4 carbon fixation: In C4 plants carbon fixation happens in two different cells, first one happens in mesophyll cells( carbon dioxide fixed with three carbon molecule to have four carbon molecule which going to provide carbon dioxide for Calvin cycle in another cell. An enzyme cause this fixation). The second one happens in bundle sheath cells (Calvin cycle as the last process of carbon fixation in C4 plants). High temperature, high light intensity, and lack of water cause this cell separation in carbon fixation of C4 plants.

CAM photosynthesis: In CAM plants carbon fixation happens at two different times, first at night and second at day. These plants are grown up in dry condition, high sunlight, and lack of water, they can’t even open stomas to absorb carbon dioxide, so the first step of carbon fixation (To fix carbon dioxide with three_carbon molecule to have four carbon molecule by an enzyme) happens in night and second and last step (Calvin cycle) happen in the day while stomas are closed. All process of carbon fixation in CAM plants is in bundle sheath cell. Stoma is a structure located on leave and some other parts of plants, they behave like a gate and can be open and close to absorbing carbon dioxide.


Why is photosynthesis important

Without photosynthesis life on the earth would be impossible because:

  • No photosynthesis means no plants, no foods to animals and humans.
  • No photosynthesis means no oxygen to breathe
  • No photosynthesis means no balance between carbon dioxide and oxygen of the atmosphere


Photosynthesis vs chemosynthesis

Oxygen gas is necessary for photosynthesis but what do some organisms do that life in places without oxygen like some bacteria?

The answer is in chemosynthesis. Some bacteria live in mines, deep oceans, or craters of underwater volcanoes, there’s no oxygen to photosynthesis so chemosynthesis happens. Due to scientist’s researches, chemosynthetic bacteria are the oldest organisms that had lived on earth. Chemosynthesis is an oxidative reaction, bacteria use this reaction to produce organic matter from minerals.

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