light reactions of photosynthesis

the calvin cycle

The second stage of photosynthesis is the production of glucose from carbon dioxide. This process occurs in a continuous cycle, named after its discover, Melvin Calvin. The Calvin cycle uses CO2 and the energy temporarily stored in ATP and NADPH to make the sugar glucose.


the light reactions

Photosynthesis begins with the light reactions. It is during these reactions that the energy from sunlight is absorbed by the pigment chlorophyll in the thylakoid membranes of the chloroplast. The energy is then temporarily transferred to two molecules, ATP and NADPH, which are used in the second stage of photosynthesis. ATP and NADPH are generated by two electron transport chains. During the light reactions, water is used and oxygen is produced. These reactions can only occur during daylight as the process needs sunlight to begin.

the products

What is produced by the plant cell during photosynthesis? The products of photosynthesis are glucose and oxygen. This means they are produced at the end of photosynthesis. Glucose, the food of plants, can be used to store energy in the form of large carbohydrate molecules. Glucose is a simple sugar molecule which can be combined with other glucose molecules to form large carbohydrates, such as starch. Oxygen is a waste product of photosynthesis. It is released into the atmosphere through the stomata. As you know, animals need oxygen to live. Without photosynthetic organisms like plants, there would not be enough oxygen in the atmosphere for animals to survive.

the chemical reaction

The overall chemical reaction for photosynthesis is 6 molecules of carbon dioxide (CO2 ) and 6 molecules of water (H2 O), with the addition of solar energy. This produces 1 molecule of glucose (C6 H12 O6 ) and 6 molecules of oxygen Stomata are special pores that allow gasses to enter and exit the leaf. (O2 ). Using chemical symbols, the equation is represented as follows: 6CO2 + 6H2 O C6 H12 O6 + 6O2 . Though this equation may not seem that complicated, photosynthesis is a series of chemical reactions divided into two stages, the light reactions and the Calvin cycle ( Figure 1.3).


the process of photosynthesis

in the presence of sunlight carbon dioxide

Photosynthesis takes place in the organelle of the plant cell known as the chloroplasts. Chloroplasts are one of the main differences between plant and animal cells. Animal cells do not have chloroplasts, so they cannot photosynthesize. Photosynthesis occurs in two stages. During the first stage, the energy from sunlight is absorbed by the chloroplast. Water is used, and oxygen is produced during this part of the process. During the second stage, carbon dioxide is used, and glucose is produced. Chloroplasts contain stacks of thylakoids, which are flattened sacs of membrane. Energy from sunlight is absorbed by the pigment chlorophyll in the thylakoid membrane. There are two separate parts of a chloroplast: the space inside the chloroplast itself, and the space inside the thylakoids ( Figure 1.1). The inner compartments inside the thylakoids are called the thylakoid space (or lumen). This is the site of the first part of photosynthesis. The interior space that surrounds the thylakoids is filled with a fluid called stroma. This is where carbon dioxide is used to produce glucose, the second part of photosynthesis. The chloroplast is the photosynthesis fac- tory of the plant.


the reactants

What goes into the plant cell to start photosynthesis? The reactants of photosynthesis are carbon dioxide and water. These are the molecules necessary to begin the process. But one more item is necessary, and that is sunlight. All three components, carbon dioxide, water, and the suns energy are necessary for photosynthesis to occur. These three components must meet in the chloroplast of the leaf cell for photosynthesis to occur. How do these three components get to the cells in the leaf? Chlorophyll is the green pigment in leaves that captures energy from the sun. Chlorophyll molecules are located in the thylakoid membranes inside chloroplasts. The veins in a plant carry water from the roots to the leaves. Carbon dioxide enters the leaf from the air through special openings called stomata ( Figure 1.2).

instructional diagrams

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chloroplasts are one of the main differences between plant and animal cells.

-->  a. true

b. false

photosynthesis can only occur during daylight hours.

-->  a. true

b. false

what molecules are necessary to begin photosynthesis?

a) carbon dioxide and oxygen

-->  b) carbon dioxide and water

c) glucose and oxygen

d) glucose and water

which best describes chlorophyll?

a) chlorophyll carries water from the roots to the leaves.

b) carbon dioxide enters the leaf through chlorophyll.

-->  c) chlorophyll is the green pigment in leaves that captures energy from the sun.

d) chlorophyll is the site of photosynthesis in the leaf cell.

which of the following does not occur during the light reactions?

a) energy is transferred to atp and nadph.

b) energy from sunlight is absorbed.

-->  c) glucose is produced from carbon dioxide.

d) water is used and oxygen is produced.

what is the waste product of the photosynthesis process?

a) glucose

b) carbon dioxide

c) water

-->  d) oxygen

which of the following is true concerning glucose?

a) glucose can be considered the food of plants.

b) glucose is a simple sugar molecule.

c) glucose can be used to store energy in large molecules, such as starch.

-->  d) all of the above are true concerning glucose.

diagram questions

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