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Photosynthesis

Artificial leaf Artificial leaf to mimic photosynthesis for energy Plants convert sunlight into energy through photosynthesis. Can we do the same? An artificial photosynthesis system or a photoelectrochemical cell that mimics what happens in plants could potentially create an endless, relatively inexpensive supply of all the clean "gas" and electricity we need to power our lives – and in a storable form, too. Artificial photosynthesis has particularly strong prospects in the realm of hydrogen fuel, as this process can effectively be used to efficiently produce hydrogen gas in high quantities. Let's learn more about photosynthesis and understand the principles and pathways behind it.

Learning Objectives

After completing the topic, the student will be able to:

  • Predict what happens if plants does not perform photosynthesis.
  • Define and distinguish autotrophs and heterotrophs.
  • Evaluate how autotrophs are able to produce their own food.
  • Analyze how chloroplasts acts as the sites of photosynthesis in plants.
  • Summarize the overall process of photosynthesis.
  • Define photophosphorylation and appreciate its significance.
  • Evaluate how the light reactions convert solar energy to the chemical energy of ATP and NADPH.
  • Understand how the Calvin cycle uses ATP and NADPH to convert CO2 to sugar.
  • Evaluate how different photosynthetic modes allow plants to adapt to particular environments.
Green Plants Green Plants– Source of Photosynthesis Photosynthesis is a process used by plants, primarily takes place in plant leaves, and often occurs in stems, etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundles, and the stomata. Since upper and lower epidermal cells do not have chloroplasts, photosynthesis does not occur there. Chloroplasts are abundant in mesophyll cells of leaf and is the site for photosynthesis. The stomata are holes, which occur primarily in the lower epidermis and are for exchange for gases: they let CO2 in and O2 out, a process called transpiration. It is a typical process used by plants and other organisms to absorb the sun's energy for splitting water's hydrogen from oxygen. Hydrogen combines with carbon dioxide to form glucose and release oxygen.
Photosynthesis

Green plants are extremely significant because they are the only organisms with the biochemical ability to "make" chemically complex organic food for themselves, starting with simple inorganic substances.

The green plants, also called the producers, trap the solar energy and convert it into chemical energy of the food. Food is required to provide energy. The compound that can be easily broken down in order to yield energy is glucose.

Thus, the plants synthesize glucose, which is stored in the form of starch by a process called photosynthesis. 'Photo' means 'light' and 'synthesis' means 'to build', thus 'photosynthesis' means 'building up by light'.

The plants use the energy in sunlight to prepare food from carbon dioxide and water in the presence of chlorophyll. Chlorophyll is present in the green colored bodies called 'chloroplasts' inside the plant cells. In fact, the leaves of a plant are green because they contain tiny green colored bodies called chloroplasts (which contain chlorophyll).

The process by which living plant cells, containing chlorophyll, produce food substances (glucose and starch), from carbon dioxide and water, by using light energy is called photosynthesis. They release oxygen as a waste product in this process. Photosynthesis is the only biological process, which releases oxygen into the atmosphere. The oxygen supports all life on earth.

Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems, etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundle(s) (veins), and the stomata. The upper and lower epidermal cells do not have chloroplasts, thus photosynthesis does not occur there.

The stomata are holes, which occur primarily in the lower epidermis and are for air exchange: they let CO2 in and O2 out. The vascular bundles or veins in a leaf are part of the plant’s transportation system, moving water and nutrients around the plant as needed. The mesophyll cells have chloroplasts and this is where photosynthesis occurs.

Priestleys experiment Priestley's experiment Joseph Priestley discovered oxygen and that plants release it
The discovery of Photosynthesis

Joseph Priestley experiment: Ever had a sip of soda and wondered at the fact how a little fizz makes it different from other fruit juices? Joseph Priestley added fizz in our life with the discovery of soda water and oxygen. Today everyone knows oxygen is extremely important for us to breathe. Humans, animals and plants all need this gas to live. Joseph Priestley was the first person to discover oxygen.  He also invented soda water, the substance that makes soft drinks so fizzy. Priestley's studies and experiments in air also lead to the first discovery of photosynthesis. He showed how a burning candle in an inverted jar used up air and how keeping a plant in that jar could then produces oxygen by photosynthesis.

It is interesting to learn about those simple couple of experiments that led to a gradual development in our understanding of photosynthesis. Joseph Priestley in 1770 performed a series of experiments that revealed the essential role of air in the growth of green plants.

Priestley observed that a candle burning in a closed space – a bell jar, soon gets blow out. Similarly, a mouse would soon suffocate in a closed space. From this results, he concluded that a burning candle or an animal that breathe the air, both somehow, damage the air. But when he placed a mint plant in the same bell jar, he found that the mouse stayed alive and the candle even continued to burn. However, Priestley discovered that if a plant is placed in atmosphere lacking oxygen, it soon replenishes the oxygen, and a mouse can survive in the resulting mixture. Priestley thought that it was simply the growth of the plant that accounted for this.

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