Chloroplasts Chloroplasts are the sites of photosynthesis. All green parts of a plant, including green stems and unripened fruit, have chloroplast, but leaves are the major site of photosynthesis in most plants. 500,000 chloroplasts per square millimeter of leaf surface. Plants are the primary producers of food for all land animals.
Chloroplasts It is the light energy absorbed by chlorophyll that drives the synthesis of food molecules in the chloroplast. Chloroplasts are found mainly in the cells of mesophyll, the tissue in the interior of the leaf. Carbon dioxide enters the leaf, and oxygen exits, by way of microscopic pores called stomata.
In the Presence of Light In the presence of light, the green parts of plants produce carbohydrates (glucose) and oxygen from carbon dioxide and water.
Light Reactions We can simplify the equation by indication only the net consumption of water: 6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2
Light Reactions cont. The two stages of photosynthesis are known as the LIGHT REACTIONS (the photo part of photosynthesis) and the CALVIN CYCLE (the synthesis part) Light reaction: Take-up water and produces oxygen Dark reaction (Calvin cycle): Takes-up carbon dioxide and makes glucose
Calvin Cycle (dark reactions) IIt is in the dark reactions that plants make glucose. TThe glucose made will be used to power the metabolism of the plant, growth, etc. SSome glucose will be used to make cellulose, another carbohydrate that is used for structural support. WWhat glucose is not used, will be stored as amylose / amylopectin (plant starch) IInteresting to note that humans have evolved the capacity to produce and enzyme in saliva called amylase. RRemember that in animals, glucose consumed but not metabolism will be stored as lipids (FAT) for later energy needs.
Edible starches are found in a very diverse array of plants, primarily in storage organs such as tubers and seeds. Starch is synthesized in specialized plastids known as amyloplasts and also in chloroplasts. Starch is a major component of the "average" dietary intake of man and animals. Calculated in calories, about four-fifths of the worlds food is provided by three grain crops (maize, wheat and rice) and three tuber crops (potato, yam and cassava). On a dry-weight basis starch is by far the major component of the edible portions of these crops, providing between 60% to 90% of the dry weight. As well as its uses in nutrition, starch is also an important component in manufacturing a wide range of industrial products such as paper, textiles and building materials. Furthermore, chemically modified starch and starch derivatives are used widely throughout industry. World-wide, maize represents the major commercial source of starch, whereas wheat starch is of only minor significance in the starch industry.maize