Photosynthesis

Plants are great food providers. Why do you think they are called great food providers? As you go through the activities in this module, you will understand how plants provide food and help to make the flow of energy in the ecosystem possible.

You will understand how each plant structure helps in the process of food making, as well as the factors that may affect the rate of food production done by plants.

Photosynthesis is a process of food making done by plants and other autotrophic organisms. The presence of chlorophyll enables these organisms to make their own food. Autotrophic organisms require light energy, carbon dioxide (CO2), and water (H2O) to make food (sugar).

In plants, photosynthesis primarily takes place in the leaves and little or none in stems depending on the presence of chlorophyll. The typical parts of the leaves include the upper and lower epidermis, mesophyll spongy layer, vascular bundles, and stomata. The upper and lower epidermis protects the leaves and has nothing to do with photosynthetic processes. Mesophyll has the most number of chloroplasts that contain chlorophyll. They are important in trapping light energy from the sun. Vascular bundles - phloem and xylem serve as transporting vessels of manufactured food and water. Carbon dioxide and oxygen were collected in the spongy layer and enters and exits the leaf through the stomata.

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 absorbs white light but it look green because white light consists of three primary colors: red, blue, and green. Only red and blue light are absorbed thus making these colors unavailable to be seen by our eyes while the green light is reflected which makes the chlorophyll looks green. However, it is the energy from red light and blue light that are absorbed and will be used in photosynthesis. The green light that we can see is not absorbed by the plant and thus, cannot be used in photosynthesis.

There are two stages of photosynthesis: (a) Light-dependent Reaction and (b) Calvin Cycle (dark reaction). Light-dependent reaction happens in the presence of light. It occurs in the thylakoid membrane and converts light energy to chemical energy. Water one of the raw materials of photosynthesis is utilized during this stage and facilitates the formation of free electrons and oxygen. The energy harvested during this stage is stored in the form of ATP (Adenosine Triphosphate) and NADPH (Nicotinamide Adenine Dinucleotide Phosphate Hydrogen). These products will be needed in the next stage to complete photosynthetic process.

Calvin Cycle (dark reaction) is a light-independent phase that takes place in the stroma and converts carbon dioxide (CO2) into sugar. This stage does not directly need light but needs the products of light.

Key Concepts:

Plants have green pigments called chlorophyll stored in the chloroplast. This pigment aids in capturing light energy from the sun that enables plants to change it into chemical energy stored in the food. This process is called photosynthesis.

Key Concepts:

Stomata are found on the lower surface of the leaf that allows the entrance of carbon dioxide needed for photosynthesis. They also serve as exit point for the oxygen produced during photosynthesis.

Carbon dioxide is one of the important materials to enable plants to produce food.

Key Concepts:

The factors that affect the rate of photosynthesis are temperature, carbon dioxide, water, and light. Providing the plant with the right amount of these materials will ensure good quality and quantity of the harvest.

Cellular Respiration

All heterotrophic organisms including man, depend directly or indirectly on plants and other photosynthetic organisms for food. Why do we need food? Organisms need food as the main source of energy. All organisms need energy to perform essential life processes.

The food must be digested to simple forms such as glucose, amino acids, and triglycerides. These are then transported to the cells. The immediate energy source of the cells is glucose. Glucose inside the cell is broken down to release the stored energy. This stored energy is harvested in the form of adenosine triphosphate (ATP), ATP is a high-energy molecule needed by working cells.

Glycolysis

In glycolysis, the 6-carbon sugar, glucose, is broken down into two molecules of a 3-carbon molecule called pyruvate. This change is accompanied by a net gain of 2 ATP molecules and 2 NADH molecules.

Krebs Cycle

The Krebs Cycle occurs in the mitochondrial matrix and generates a pool of chemical energy (ATP, NADH, and FADH2) from the oxidation of pyruvate, the end product of glycolysis.

Pyruvate is transported into the mitochondria and loses carbon dioxide to form acetyl-CoA, a 2-carbon molecule. When acetyl-CoA is oxidized to carbon dioxide in the Krebs Cycle, chemical energy is released and captured in the form of NADH, FADH2, and ATP.

The electron transport chain allows the release of the large amount of chemical energy stored in reduced NAD (NADH) and reduced FAD (FADH2). The energy released is captured in the form of ATP (3 ATP per NADH and 2 ATP per FADH2).

The electron transport chain (ETC) consists of a series of molecules, mostly proteins, embedded in the inner mitochondrial membrane. This phase of cellular respiration produces the greatest number of chemical energy in the form of ATP.

In the following activities, you will learn how the chemical energy of "food" molecules is released and partially captured in the form of ATP (Adenosine Triphosphate). You should first learn about the part of the cell where ATP is produced.

Key Concepts:

Materials are recycled through the processes of photosynthesis in the chloroplast and respiration in the mitochondrion. However, the flow of energy is one-way.

Through the process of photosynthesis, plants and other chlorophyll-bearing organisms produce food for themselves. In photosynthesis, plants capture light energy and convert it into chemical The summary equation for photosynthesis is as follows:

energy stored in food.

Carbon dioxide + water

sunlight

chlorophyll

glucose + oxygen

Photosynthesis occurs in the chloroplast found in the leaves of plants. Essentially, the two major stages in photosynthesis are:

Light reaction phase Calvin Cycle

Improved farming practices enhance photosynthesis that result in good harvest.

Cellular respiration occurs in the mitochondria of the cells.

Organisms release stored energy in food through the process of respiration.

Respiration breaks down glucose into carbon dioxide, water and energy (ATP) in the presence of oxygen.

The summary equation of respiration is as follows:

Glucose oxygen + carbon dioxide + water + ATP The breakdown of glucose involves three major steps: glycolysis, Krebs cycle; electron transport chain