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Photosynthesis is needed for all life on earth. Both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space and convert it into chemical compounds that every living thing uses to power its metabolism. The energy of sunlight is captured and used to energize electrons. These are then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis almost 200 million years ago. Source: p1

Plants, algae, and a group of bacteria called cyanobacteria are the only living things able to do photosynthesis. Because they use light to make their own food, they are called photoautotrophs. Other living things, such as animals, fungi, and most other bacteria, are termed heterotrophs. This is because they must rely on the sugars produced by photosynthetic living things for their energy needs. A third very interesting group of bacteria make sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds. Hence, they are referred to as chemoautotrophs. Source: p2

Photosynthesis is a multi-step process that needs sunlight, carbon dioxide, and water as substrates. After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate, simple carbohydrate molecules that can later be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive. Source: p4

In plants, photosynthesis usually takes place in leaves. These are made of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll. The gas exchange of carbon dioxide and oxygen occurs through small, controlled openings called stomata. These also play roles in the regulation of gas exchange and water balance. The stomata are usually located on the underside of the leaf. This helps to reduce water loss. Each stoma is flanked by guard cells that control the opening and closing of the stomata by swelling or shrinking in response to osmotic changes. Source: p7

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. For plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double membrane envelope. Within the chloroplast are stacked, disc-shaped structures called thylakoids. Inside the thylakoid membrane is chlorophyll, a pigment responsible for the initial interaction between light and plant material, and many proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen. A stack of thylakoids is called a granum, and the liquid-filled space surrounding the granum is called stroma. Source: p8

Only certain living things, called photoautotrophs, can perform photosynthesis. They need the presence of chlorophyll, a specialized pigment that absorbs certain portions of the visible spectrum and can capture energy from sunlight. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules and release oxygen as a waste product into the atmosphere. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place, and starch accumulates. In prokaryotes, such as cyanobacteria, the process is less localized and occurs within folded membranes, extensions of the plasma membrane, and in the cytoplasm. Source: p14