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photosynthesis
Photosynthesis
2-D says, “We Monarchs really depend on photosynthesis! All that sunshine energy the plants absorb and store up by making sugar gets transferred into our bodies when we eat the plants’ nectar, and then we can use that energy for our body processes.”
Leaf Structure
Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. This process occurs in plants and some algae (Kingdom Protista). Plants need only light energy, CO2, and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.
Leaf Cross-Section
Photosynthesis takes place primarily in plant leaves, and little to none
occurs in stems, etc. The parts of a typical leaf include the upper and
lower
epidermis,
the
mesophyll,
the vascular bundle(s) (veins), and the
stomates.
The upper and lower epidermal cells do not have chloroplasts, thus
photosynthesis does not occur there. They serve primarily as protection for
the rest of the leaf. The stomates are holes which occur primarily in the
lower epidermis and are for air exchange: they let CO2 in and
O2 out. The vascular bundles or veins in a leaf are part of the
plant’s transportation system, moving water and nutrients around the plant
as needed. The mesophyll cells have chloroplasts and this is where
photosynthesis occurs.
Chlorplast
As you hopefully recall, the parts of a chloroplast include the outer and
inner membranes, intermembrane space,
stroma,
and
thylakoids
stacked in
grana.
The chlorophyll is built into the membranes of the thylakoids.
Chlorophyll looks green because it absorbs red and blue light, making these colors unavailable to be seen by our eyes. It is the green light which is NOT absorbed that finally reaches our eyes, making chlorophyll appear green. However, it is the energy from the absorbed red and blue light that is, thereby, able to be used to do photosynthesis. The green light we can see is not/cannot be absorbed by the plant, and thus cannot be used to do photosynthesis.
Overall Chemical Reaction
The overall chemical reaction involved in photosynthesis is:
6CO2 + 6H2O (+ light energy) ? C6H12O6 + 6O2.
This is the source of the O2 we breathe, and thus, a significant
factor in the concerns about deforestation.
There are two parts to photosynthesis. They are called the light
reaction and the dark reaction
Light Reaction
Central Structure of Chlorophyll The light reaction happens in the thylakoid membrane and converts light energy to chemical energy. This chemical reaction must, therefore, take place in the light. Chlorophyll and several other pigments such as beta-carotene are organized in clusters in the thylakoid membrane and are involved in the light reaction. Each of these differently-colored pigments can absorb a slightly different color of light and pass its energy to the central chlorphyll molecule to do photosynthesis. The central part of the chemical structure of a chlorophyll molecule is a porphyrin ring, which consists of several fused rings of carbon and nitrogen with a magnesium ion in the center.
Dark Reaction
Structure of ATP
The energy harvested via the light reaction is stored by forming a chemical
called
ATP (adenosine triphosphate),
a compound used by cells for energy storage. This chemical is made of the
nucleotide adenine bonded to a ribose sugar, and that is bonded to three
phosphate groups. This molecule is very similar to the building blocks for
our DNA.
The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to sugar. This reaction doesn’t directly need light in order to occur, but it does need the products of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar. Actually, notice that the first product of photosynthesis is a three-carbon compound called glyceraldehyde 3-phosphate. Almost immediately, two of these join to form a glucose molecule.
Most plants put CO2 directly into the Calvin cycle. Thus the first stable organic compound formed is the glyceraldehyde 3-phosphate. Since that molecule contains three carbon atoms, these plants are called C3 plants. For all plants, hot summer weather increases the amount of water that evaporates from the plant. Plants lessen the amount of water that evaporates by keeping their stomates closed during hot, dry weather. Unfortunately, this means that once the CO2 in their leaves reaches a low level, they must stop doing photosynthesis. Even if there is a tiny bit of CO2 left, the enzymes used to grab it and put it into the Calvin cycle just don’t have enough CO2 to use. Typically the grass in our yards just turns brown and goes dormant. Some plants like crabgrass, corn, and sugar cane have a special modification to conserve water. These plants capture CO2 in a different way: they do an extra step first, before doing the Calvin cycle. These plants have a special enzyme that can work better, even at very low CO2 levels, to grab CO2 and turn it first into oxaloacetate, which contains four carbons. Thus, these plants are called C4 plants. The CO2 is then released from the oxaloacetate and put into the Calvin cycle. This is why crabgrass can stay green and keep growing when all the rest of your grass is dried up and brown.
Note: lawn grass is supposed to go dormant in dry summer weather, and watering it a) wastes a lot of water, b) makes a lot of extra work for the homeowner, and c) wastes energy and causes a lot of pollution due to running the lawnmower all those extra, unnecessary times. Skip the unnecessary water, and you’ll both have a lot more time to enjoy doing other things and create less pollution.
There is yet another strategy to cope with very hot, dry, desert weather and conserve water. Some plants (for example, cacti and pineapple) that live in extremely hot, dry areas like deserts, can only safely open their stomates at night when the weather is cool. Thus, there is no chance for them to get the CO2 needed for the dark reaction during the daytime. At night when they can open their stomates and take in CO2, these plants incorporate the CO2 into various organic compounds to store it. In the daytime, when the light reaction is occurring and ATP is available (but the stomates must remain closed), they take the CO2 from these organic compounds and put it into the Calvin cycle. These plants are called CAM plants, which stands for crassulacean acid metabolism after the plant family, Crassulaceae (which includes the garden plant Sedum) where this process was first discovered.
THE MOST HAPPEST DAY IN MY LIFE
RAINY SEASON
nehru
Jawaharlal Nehru (Hindustani: [?d???a???r?la?l ?ne??ru] (
); 14 November 1889 – 27 May 1964) was the first Prime Minister of India and a central figure in Indian politics for much of the 20th century. He emerged as the paramount leader of the Indian independence movement under the tutelage of Mohandas Karamchand Gandhi
and ruled India from its establishment as an independent nation in 1947
until his death in office in 1964. Nehru is considered to be the
architect of the modern Indian nation-state: a sovereign, socialist,
secular, and democratic republic.
The son of Motilal Nehru, a prominent lawyer and nationalist statesman, Nehru was a graduate of Trinity College, Cambridge and the Inner Temple, where he trained to be a barrister. Upon his return to India, he enrolled at the Allahabad High Court, and took an interest in national politics, which eventually replaced his legal practice. A committed nationalist since his teenage years, Nehru became a rising figure in Indian politics during the upheavals of the 1910s. He became the prominent leader of the left-wing factions of the Indian National Congress during the 1920s, and eventually of the entire Congress, with the tacit approval of his mentor, Gandhi. As Congress President in 1929, Nehru called for complete independence from the British Raj and instigated the Congress's decisive shift towards the left.
Nehru and the Congress dominated Indian politics during the 1930s as the country moved towards independence. His idea of a secular nation-state was seemingly validated when the Congress, under his leadership, swept the 1937 provincial elections and formed the government in several provinces; on the other hand, the separatist Muslim League fared much poorer. But these achievements were seriously compromised in the aftermath of the Quit India Movement in 1942, which saw the British effectively crush the Congress as a political organisation. Nehru, who had reluctantly heeded Gandhi's call for immediate independence, for he had desired to support the Allied war effort during the Second World War, came out of a lengthy prison term to a much altered political landscape. The Muslim League under his old Congress colleague and now bête noire, Muhammad Ali Jinnah, had come to dominate Muslim politics in India. Negotiations between Nehru and Jinnah for power sharing failed and gave way to the independence and bloody partition of India in 1947.
Nehru was elected by the Congress to assume office as independent India's first Prime Minister, although the question of leadership had been settled as far back in 1941, when Gandhi acknowledged Nehru as his political heir and successor. As Prime Minister, Nehru set out to realise his vision of India. The Constitution of India was enacted in 1950, after which he embarked on an ambitious program of economic, social and political reforms. Chiefly, he oversaw India's transition from a monarchy to a republic, while nurturing a plural, multi-party democracy. In foreign policy, Nehru took a leading role in Non-Alignment while projecting India as a regional hegemon in South Asia.
Under Nehru's leadership, the Congress emerged as a catch-all party,
dominating national and state-level politics and winning consecutive
elections in 1951, 1957, and 1962.
He remained popular with the people of India in spite of political
troubles in his final years and failure of leadership during 1962 Sino-Indian War. In India, his birthday is celebrated as Children's Day.