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Chemical Reactions in Photosynthesis

Grade 7
Jun 6, 2023


Step 1. Take a plant with green leaves and another with leaves of a different colour.

It is well known that photosynthesizing plants have carbohydrates stored within them.

Step 2. Now, conducting an iodine test will demonstrate that leaves with colours other than green also have stored carbohydrates, which will demonstrate that leaves with colours other than green also engage in photosynthesis since iodine changes to a blue-black colour when starch is present.

However, if the leaf does not become blue or black when iodine is added, that indicates that the plant from which it came does not engage in photosynthesis.

In addition to chlorophyll, such plants with non-green leaves that still exhibit photosynthesis contain non-green pigments called anthocyanins and carotenoids. These pigments are present in such high concentrations that they completely cover the chlorophyll’s green colour but still covered chlorophyll continues to carry out the photosynthesis process.

Experiment On Leave
Experiment On Leave

Can Green Patches in the Water of a Pond Produce Their Own Food?

We frequently notice some slimy, green patches in ponds or other bodies of still water. These green areas are caused by the presence of organisms known as algae, which contain chlorophyll, which gives the colour green.

Algae can produce their own food through the process of photosynthesis, just like autotrophic plants can. The occurrence of chlorophyll makes this possible.


Photosynthesis Concept

Phototrophs transform light energy into chemical energy through a process called photosynthesis, which is then used to energize cellular processes. Sugars, which are made from water and carbon dioxide, are used to store chemical energy.

Photosynthesis is a process used by all green plants and a few other autotrophic organisms to create food from carbon dioxide, water, and sunlight. The process of photosynthesis results in the production of oxygen.

In addition to green plants, other organisms can also participate in photosynthesis. Several prokaryotes are among them, including cyanobacteria, purple bacteria, and green Sulfur bacteria. Similar to green plants, these species also engage in photosynthesis. The numerous biological processes are then powered by the glucose created during photosynthesis.

Photosynthesis concept
Photosynthesis concept

Photosynthetic Pigments

In plants and blue-green algae, photosynthesis occurs in chloroplasts. Chloroplasts, or plastids with green color, are found in all the green portions of a plant, such as the green stems, leaves, and sepals. Only plant cells contain these cell organelles, which are found in the mesophyll cells of leaves.

Chlorophyll is a green pigment that can be found in the mesosomes of cyanobacteria and the chloroplasts of plant cells. By enabling plants to absorb energy from sunlight, this green pigment plays a crucial part in the process of photosynthesis. Chlorophyll is made up of a combination of chlorophylls a and b. Other than green plants, photosynthesis-capable species also include different types of chlorophyll, including chlorophyll-c1, chlorophyll-c2, chlorophyll-d, and chlorophyll-f.

Photosynthetic pigments
Photosynthetic pigments

Steps Involved in Photosynthesis

As stated earlier, photosynthesis takes place in leaves, and the specialized cell organelle responsible for this activity is known as the chloroplast. Structurally, a leaf consists of a petiole, an epidermis, and a lamina. In photosynthesis, carbon dioxide and sunlight are absorbed by the lamina.

  • During the process of photosynthesis, water is absorbed from the soil by the root hairs and transported to the leaves through the xylem vessels.
  • Carbon dioxide enters the plant through the stomata. In order to divide water molecules into hydrogen and oxygen, chlorophyll absorbs solar light energy.
  • In order to make glucose, carbon dioxide from the air and hydrogen from water molecules are combined. Additionally, as a waste product, oxygen is released into the atmosphere through the leaves.
  • While the remainder is stored in the roots, leaves, and fruits for later use, glucose is a source of nourishment for plants that provides energy for growth and development.

Equation of Photosynthesis

Certain bacteria that engage in photosynthesis, unlike plants, do not release oxygen as a byproduct of the process. Such bacteria are called anoxygenic photosynthetic bacteria. Oxygenic photosynthetic bacteria are those that do create oxygen as a byproduct of photosynthesis.

The two reactants in the photosynthesis reaction are carbon dioxide and water. These two reactants result in the production of two products: oxygen and glucose. As a result, the reaction of photosynthesis is regarded as an endothermic reaction because heat is utilized to carry out this function. The photosynthesis equation is as follows:

Equation of Photosynthesis
Equation of Photosynthesis

Factors Affecting Photosynthesis

The photosynthesis process needs a number of factorsincluding:

  • Light intensity: A higher rate of photosynthesis is produced by light. Low light levels, on the other hand, cause photosynthesis to occur at a slower rate.
  • The amount of CO2 present: A higher carbon dioxide concentration aids in speeding up photosynthesis. For photosynthesis, levels of carbon dioxide between 300 and 400 PPM are often sufficient.
  • Temperature: A temperature range of 25° to 35° C is necessary for the proper execution of photosynthesis.
  • Water: Since water is crucial to photosynthesis, a lack of it may cause issues with carbon dioxide uptake. The scarcity of water leads to the refusal of stomatal openings to retain the amount of water they have stored inside.
  • Pollution: Industrial pollution and other particles may condense on the surface of the leaf. This may prevent carbon dioxide from entering the system by blocking stomatal pores.

Stages of Photosynthesis

The two stages of photosynthesis are as follows:

Light reaction or light-dependent reaction

Dark reaction or light-independent reaction

Light reaction: The light reaction, which only takes place throughout the day when sunlight is present, is the first step of photosynthesis.

The light-dependent reaction happens in the chloroplasts’ thylakoid membranes in plants.

The photosystems are the Grana, membrane-bound sac-like structures found inside the thylakoid that function by collecting light.

Large complexes of protein and pigment molecules found inside the cells of plants function as these photosystems’ major components during the photosynthesis process.

Dark reaction: Carbon-fixing reaction is another name for the dark reaction.

Sugar molecules are created from water and carbon dioxide molecules in a process that is not dependent on light.

The chloroplast’s stroma is where the dark reaction takes place.

Chemical reactions in Photosynthesis


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