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Introduction to photosynthesis

Sunlight plays a much larger role in our sustenance than we may expect: all the food we eat and all the fossil fuel we use is a product of photosynthesis, which is the process that converts energy in sunlight to chemical forms of energy that can be used by biological systems. Photosynthesis is carried out by many different organisms, ranging from plants to bacteria . The best known form of photosynthesis is the one carried out by higher plants and algae, as well as by cyanobacteria and their relatives, which are responsible for a major part of photosynthesis in oceans. All these organisms convert CO2 (carbon dioxide) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions. Electrons for this reduction reaction ultimately come from water, which is then converted to oxygen and protons. Energy for this process is provided by light, which is absorbed by pigments (primarily chlorophylls and carotenoids). Chlorophylls absorb blue and red light and carotenoids absorb blue-green light, but green and yellow light are not effectively absorbed by photosynthetic pigments in plants; therefore, light of these colors is either reflected by leaves or passes through the leaves. This is why plants are green.

What is photosynthesis?

Photosynthesis is a chemical process through which plants, some bacteria and algae, produce glucose and oxygen from carbon dioxide and water, using only light as a source of energy.

This process is extremely important for life on earth as it provides the oxygen that all other life depend on.

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What does the plant need glucose (food) for?

Just like humans and other living things, plants also need this food for many things. Le's see a few:

Glucose resulting from photosynthesis is used during respiration to release energy that the plant needs for other life processes.

The plant cells also convert some of the glucose into starch for storage. This can then be used when the plant needs them. This is why dead plants are a used as biomass, because they have stored chemical energy in them)

Glucose is also needed to make other chemicals such as proteins, fats and plant sugars that are all need for the plant to carry out essential growth and other life processes.

Water for Photosynthesis

Plants get the water they need for photosynthesis through their roots. The roots have a type of cell called a root hair cell - these project out from the root into the soil. Roots have a big surface area and thin walls, which allow water to pass into them easily.
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Root cells do not contain chloroplasts, as they are normally in the dark and cannot photosynthesis.

Plants need water for other important things such as:
provide dissolved minerals that keep the plants healthy
provide a medium for transporting minerals
keep the plant firm and upright
keep the plant cool and hydrated
allow other chemical reactions to occur in plant

Where does photosynthesis take place?

Photosynthesis takes place inside plant cells in small things called chloroplasts. Chloroplasts (mostly found in the mesophyll layer) contain a green substance called chlorophyll. Below are the other parts of the cell that work with the chloroplast to make photosynthesis happen.
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What role do these parts play?
Cell walls: provide structural and mechanical support, protect cells against pathogens, maintain and determine cell shape, control the rate and direction of growth and generally provide form to the plant.

Cytoplasm: provides the platform for most chemical processes, controlled by enzymes.

Cell membrane: acts as a barrier, controlling the movement of substances into and out of the cell.

Chloroplasts: As described above, simply contain chlorophyll, a green substance which absorbs light energy for photosynthesis.

Vacuole: the container that hold moisture, and keeps the plant turgid.

Nucleus: this contains genetic make (the DNA), which controls the activities of the cell.

Chlorophyll absorbs the light energy needed to make photosynthesis happen. It is important to note that not all the colour wavelengths of light are absorbed. Plants mostly absorb red and blue wavelengths — they do not absorb light from the green range.