Do you still remember about photosynthesis? Photosynthesis (carbon assimilation) is a process of converting phisical energy (light) into chemical energy (sugar). Basically, photosynthesis is a process of synthesizing compounds by using sunlight. However not all organism is capable of doing photosynthesisdirectly. Only plans and some bacteria are capable of caputuring the sunlight and using it for a process which is called photosynthesis. Through photosynthesis, plants are able to synthesize food in the form of sugar. Because of the ability to make its own food, plant is called autotroph organism or producer.
1. Experiment on photosynthesis
In 1779, Jan Ingenhousz, a physiologist from Dutch carried out an experiment by using aquatic plant (Hydrilla verticilata). There are three important things resulted from the experiment, which are: a. The gas released by plant is O2,
b. Sunlight is needed in the process, and
c. Only the green part releases O2.
Van Niel was the first person who stated tha O2 came from the break down of water. In 1941, Ruben and Kamen succeeded proving that O2 released during photosynthesis is from the breaking down of H2O, which is called photolysis. The equation of complete photosynthesis reaction is:
6CO2 + 6H2O + Sun Energy chlorophyll C6H12O6 + 6O2
(glucose)
According to the explanation above, we can make some conclusions as follows:
a. Photosynthesis uses sun’s energy to synthesize simple sugar,
b. Sugar is synthesized from raw material of H2O and CO2,
c. Photosynthesis waste material is O2.
d. Photosynthesis is conducted only by plant and a few bacteria.
Photosynthesis produces sugar from water and carbon dioxide (CO2), that iswhy it is also called carbon assimilation.
2. Site and Tool of Photosynthesis
Photosynthesis is analogous with a process occuring in “a factory”. Generally, “the factory” as the location of photosynthesis is leaf. Cell on leaves have complete equipments to capture the energy of sunlight. On particular plants which do not leaves, such as cactus, the photosynthesis equipments can be found on the upper layer cells of the stem.
In which part does photosynthesis occur? Photosynthesis occurs in palisade parenchyma and spongy parenchyma.
Palisade parenchyma are the middle part of the laef that are also known as mesoshyll. Theis cells countain many green concentric or oval organelles called chloroplasts. Chloroplasts can found in mesophyll, espescially in palisade layer. There is no chloroplast found in epidermis, except on guard cells of stomata.
On hydrilla sp. Leaves, its chloroplasts are concentric or oval, big and aesy to examine under the microscope.The organelle is easy to recognize because of its green colour that comes from the green pigment called chlorophyll. There are two types of chlorophylls on land plants, chlorophyll a and chlorophyll b.
3. Stages of Photosynthesis
Basically, photosynthesis occurs in two stages, as follows.
a. Light Reaction
Light reaction is a process of capturing energy of sunlight or a process that depends on the presence of light. It occurs in grana chloroplast. Some of the sunlight energy is coverted to chemical energy, that is high energy chemical compound. And then, the compound will be used in the process of making sugar. Some of the sun’s energy is also used in water photolysis (H2O) to produce hydrogen ion (H+) and O2. The hydrogen ion is combined with CO2 to form sugar (CH12O)n while O2 is released.
b. Dark Reaction
Dark reaction is a process that does not depend on the light. It occurs in stroma chloroplast. All equipments ti synthesize sugar are in this part. This reaction uses high energy compound produced in the light reaction. It does not depend on the presence of light directly, eventhough the process occurs at the same time with the light reaction. Therefore, this reaction is called dark reaction. Dark reaction occurs bacause of the presence of photosynthesis enzyme. The cycle in synthesizing sugar is named after its founder, Benson-Calvin.
The first result of photosynthesis is simple sugar called glucose (C6H12O6). Futhermore, some of them is converted to starch (amylum) and stored in leaves or other storage organs.
Based on the equation of photosynthesis reaction, we acan recognize photosynthesis through the release of O2, the presence of starch (amylum), and the absorption of CO2. In aquatic plants, such as Hydrilla sp., O2 is released in the form of gas bubble.
Sugar is a result of photosynthesis is used in many kinds of activities inside the plant’s body. Some of the sugar is broken down to produce energy which is necessary for doing many actovities. Some other is used to build or to form plant’s body. Plants need to grow, develop, reproduce, flower, form fuit, and form seed. Some other will become raw material synthesize another important substances required by palnts, for example protein, fat and vitamin. The other will be stored within the storage tissue, for examples yams, bulb, fruit, and seed.
4. Factors Influencing Photosynthesis
Photosynthesis is influenced by many factors, both internal and external factors. The internal factors are:
a. Leaf age,
b. Condition of stomata, and
c. Plant species.
The external factors are:
a. Concentration level of CO2 and O2,
b. Water availability,
c. Humidity and temperature, and
d. Light condition (intensity, duration, and colour of light)
Besides those four external factors, poisonous material, such as herbicide, oil spill, soap water, and heavy metal also give influence on photosynthesis.
Sunlight is the main source of photosynthesis. Albert Einstein stated that sunlight is photon (quantum). Light influence photosynthesis in three ways, which are intensity of light, duration of light, and colour of light. According to the colours, sunlight has sevev colours of light. The proof that sunlight is composed of several colours is the rainbrow.
Chlorophyll absorbs all light colours, except green. Light that is absorbed in large amount for photosynthesis are red light (±700 nm) and blue light (±450 nm). The energy of another light is also absorbed but in lower level. Green light is reflected by chlorophyll; that is why leaf looks green.
5. Transportation Mechanism on Plants
Generally, water and nutrients are absorbed by roots. Then, they will be carried to leaves. Leaf is a cetral activity to synthesize substances needed by plants. Some other subtances, such as O2 and CO2 are absorbed through leaves. Nutrients are also absorbed through leaves. The proof is that plants can be fertilized through leaves by using leaf fertilizer.In which part does the absorbtion of subtances by root occur? To answer the question, we need to understand to the anatomy of root and leaf cells as the means of absorbtion. Subtance absorbtion on plants is conducted through root hairs, stomata, or body surface that have not thickened yet.
On the top area of the root, there is a lot of root hair. Root hair is formed from epidermal cells on root which elongate outward. The elobgating cells will make area of absorption larger in order to absorb more subtances. On leaf, there are pores which function as doors for suntances to enter the cells. In addition, there are many intercellular spaces on leaf tissuethat can be passed through by subtances into the leaf cells.
How does the subtance absorption occur?
Absorbing a substance means removing the subtance from outside to the inside of the body. The energy of the movement is based on physical and chemical reactions that occur naturally, such as the differences of temperature, pressure, and concentration. For example, diffusion. Basically, diffusion is a spreading movement of subtance from higher concentration area to the lower one. In connection to the absorption, water diffuses into root hair cell after penetrating the cell membrane. The water movement is called osmosis.
The transportation of water from roots to the tip of the stems and leaves is conducted by xylem. Whereas the transportation of carbon assimilation (photosynthesis) product from leaves throughout the plant body is conducted by phloem.
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