Photosynthesis: An Introduction - (GCSE Biology)
Photosynthesis: An Introduction
Photosynthesis
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- Photosynthesis makes glucose using light energy. Light energy is used by cells in plants in order to convert carbon dioxide and water into glucose and oxygen.
- Photosynthesis occurs in 2 main stages:
1. Water is split into oxygen gas and hydrogen ions with the help of the energy transferred by light.
2. The hydrogen ions combine with carbon dioxide to form glucose.
Chemical Equation
Energy Transfer in Photosynthesis
- Photosynthesis takes place in chloroplasts. Chloroplasts are small organelles in plant cells. Chloroplasts have pigments that can be used to trap light. The most common pigment is the green-coloured chlorophyll. Chlorophyll transfers light energy into chemical energy in molecules to make carbohydrates including glucose.
- Photosynthesis is an endothermic reaction. Energy is taken in by living cells as heat energy in photosynthesis. A reaction that takes in heat energy is an endothermic reaction.
- Photosynthetic organisms are the main producers of food on earth. They use light energy to build carbohydrates that can be passed down to other organisms down the food chain. Thus, photosynthetic organisms contribute the most to biomass on earth.
Respiration and Photosynthesis
You might have noticed that the reactants and products of aerobic respiration and photosynthesis are the opposite – the reactants of respiration are the products of photosynthesis and the reactants of photosynthesis are the products of respiration. So the net exchange of carbon dioxide and oxygen in plants depends on the intensity of light:
- Plants respire all the time during the day and the night. They respire constantly so that they can continuously get the energy they need for internal processes and survive.
- Photosynthesis only occurs during the day. Photosynthesis is driven by light energy so can only occur during the day when light intensity is high.
- Plants produce more oxygen and glucose during the day due to photosynthesis than they use in respiration. So in the day, they use more carbon dioxide than they produce.
- During the night, no photosynthesis takes place. This is because there is no sunlight. Only respiration occurs so at night, they take up oxygen and release carbon dioxide.
Investigating Net Exchange in Plants
You can investigate the changes in carbon dioxide by using hydrogencarbonate which is initially orange. When carbon dioxide concentration increases, it turns yellow. When carbon dioxide concentration decreases, it turns purple.
- Set up 4 tubes with hydrogen-carbonate.
- Place similar sized leaves in 3 tubes, trapping them with a bung.
Leave the 4th tube empty – this will be your control. - Wrap one of the tubes with a leaf in foil, another in gauze and leave the third unwrapped.
- Leave the tubes for an hour or two and observe the colour changes:
- Control tube – no colour change
- Tube with leaf and with foil – changes to yellow as only respiration takes place and no photosynthesis, so carbon dioxide concentration increases
- Tube with leaf and gauze – no colour change as respiration is taking place but also little photosynthesis so any carbon dioxide produced will be taken up
- Uncovered tube with leaf – changes to purple as both respiration and photosynthesis are taking place but due to the high light intensity, more carbon dioxide is taken up in photosynthesis so the concentration of carbon dioxide decreases.
Photosynthesis in GCSE Biology is the process by which plants and some other organisms convert light energy into chemical energy in the form of glucose. This chemical energy is then used as a source of fuel for the organism’s metabolic processes.
Photosynthesis is important in GCSE Biology because it is the primary process by which plants produce the food and oxygen that sustain life on Earth. Photosynthesis also plays a crucial role in regulating the levels of carbon dioxide in the atmosphere, and it is responsible for the production of the vast majority of the world’s oxygen supply.
The two stages of photosynthesis in GCSE Biology are the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle).
During the light-dependent reactions in GCSE Biology, light energy is absorbed by chlorophyll and other pigments in the chloroplasts, and it is used to power the production of ATP and NADPH. These energy-rich compounds will then be used to power the light-independent reactions.
During the light-independent reactions in GCSE Biology, the energy stored in ATP and NADPH is used to drive the production of glucose from carbon dioxide and water. This process is known as the Calvin cycle and it is where the majority of the glucose produced by photosynthesis is synthesized.
Chlorophyll is the pigment in plants that absorbs light energy and drives the light-dependent reactions of photosynthesis in GCSE Biology. Chlorophyll gives plants their green color and it is essential for the process of photosynthesis.
The real-world applications of photosynthesis in GCSE Biology include:
Agriculture: Photosynthesis is the basis for food production and it is essential for the growth of crops and other plants used for food and fuel.
Renewable energy: Photosynthesis is a source of renewable energy and it is being explored as a potential source of biofuel.
Environmental regulation: Photosynthesis helps regulate the levels of carbon dioxide in the atmosphere, and it is an important component of the global carbon cycle.
Medical and pharmaceutical applications: Photosynthesis is being studied for its potential to produce valuable compounds, such as antibiotics and anticancer drugs, and for its role in the development of new medical technologies, such as artificial photosynthetic systems.
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