Unit 10 - Biological Molecules and Metabolic Pathways
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Pathways in Photosynthesis
Photosynthesis is the process where light energy from the sun is converted
into chemical energy which is used to make large organic molecules from
inorganic substances. Molecules that contain carbon are known as organic
molecules. Photosynthesis is a process vital for human survival as it releases
oxygen into the surroundings. It also makes the food we consume. The
equation for photosynthesis is the reverse of the equation for respiration. The
word equation for photosynthesis is Carbon dioxide + Water
→
Glucose + oxygen. The balanced equation is written as 6CO2 + 6H20 →
C6H12O6 + 6O2. 6 carbon dioxide molecules and 6 water molecules are
transformed into a sugar molecule (glucose) and 6 oxygen molecules by light
energy which is absorbed by chlorophyll. In the plant cell, water loses
electrons as it is oxidised, and carbon dioxide is reduced as it
gains electrons. Glucose is used by the plant as a food source.
Photosynthesis is important to an ecosystem as herbivores eat
plants which contain glucose and oxygen, and this provides
them with energy. Carnivores who eat herbivores will then also obtain energy as they have consumed
the herbivore that ate the plant with glucose and oxygen. Photosynthesis is also important because it
reduces levels of CO2 as it uses CO2 from the surroundings to produce oxygen.
Britannica, T. editors of Encyclopedia (26/10/2018) what is the basic formula for photosynthesis? Available at:
https://www.britannica.com/question/What-is-the-basic-formula-for-photosynthesis (Accessed date:21/12/2022)
National Geographic society (15/7/2022) photosynthesis. Available at:
https://education.nationalgeographic.org/resource/photosynthesis (Accessed date:21/12/2022)
Chloroplasts
Photosynthesis occurs in plant cells but also some bacteria cells. Plant cells
contain chloroplasts. Chloroplasts are where photosynthesis occurs. Chloroplasts
are between 2-10m long and are surrounded by a double membrane. The outer
membrane allows small ions to move through it (permeable) and the inner
membrane is less permeable as it contains transport proteins. These transport
proteins control what molecules enter and leave the cytoplasm and stroma inside
chloroplasts. The folds in the inner membrane are called lamellae which are
stacked up. The granum and stroma are 2 separate regions in chloroplasts. The
granum look like stacks of plates and each membrane bound sac is called a thylakoid. In thylakoids, ATP
is synthesized, and light is absorbed in light-dependent reactions. The enzymes required for the light-
independent stage are in the stroma which is a fluid-filled matrix. The stroma also contains ribosomes,
DNA, starch, and oil. Electron carriers, ATP synthase enzymes, and photosynthetic pigments are all
needed for light-dependent reactions. A large surface area is provided for the ATP synthase enzymes,
photosynthetic pigments, and electron carriers due to the thylakoid membranes inside the granum.
Photosystems allow maximum absorption of light energy as the photosynthetic pigments are specially
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