Question

How plants make their own food by photosynthesis?

Answer 1

They make their own food thru the process of photosynthesis using light energy to make sugars from carbon dioxide (C02) and water (H20).

The three major functions that are basic to plant growth and development are:

• Photosynthesis – the process of capturing light energy and converting it to sugar energy, in the presence of chlorophyll using CO2 and H2O,

• Respiration – the process of metabolizing (burning) sugars to yield energy for growth, reproduction and other life processes, and

• Transpiration – the loss of water vapor through the stomata of leaves.

Photosynthesis

A primary difference between plants and animals is the plant’s ability to manufacture its own food. In photosynthesis carbon dioxide from the air and water from the soil react with the sun’s energy to form carbohydrates (sugars and starches). Photosynthesis literally means to put together with light.

The photosynthetic process occurs only in the chloroplasts, tiny subcellular structures contained in the cells of leaves and green stems. In photosynthesis, the sun’s energy combines hydrogen from water (H20) with carbon dioxide (CO2) turning them into carbohydrates. Oxygen (O2) is given off as a by-product of photosynthesis. The chemical equation for the process of photosynthesis is: 6CO2 + 6H20 + light C6H12O6 + 6O2

This process is directly dependent on the supply of water, light and carbon dioxide. Any one of the factors on the left side of the equation (carbon dioxide, water, or light) can limit photosynthesis regardless of the availability of the other factors. If any one of these factors is limiting, then the whole process slows down or stops. An implication of drought or severe restrictions on landscape irrigation is a reduction in photosynthesis and thus a decrease in plant vigor.

In a tightly closed greenhouse there can be very little fresh air infiltration and CO2 levels can become limiting. This in turn limits plant growth because the production of sugars needed to do the work involved with growing is limited. Many greenhouses provide supplemental CO2 to stimulate plant growth.

The rate of photosynthesis is somewhat temperature dependent. For example, with tomatoes, when temperatures rise above 96 degrees Fahrenheit the rate of food used by respiration rises above the rate that food is manufactured by photosynthesis. Plant growth comes to a stop and produce loses its sweetness.

Respiration

In respiration, plants (and animals) convert the sugars back into energy for growth and to energize life processes (metabolic processes). The chemical equation for respiration shows that the sugars from photosynthesis are combined with oxygen. Notice that the equation for respiration is the opposite of photosynthesis.

C6H12O6 + 6O2 6CO2 + 6H20 + energy

Chemically speaking, the process is similar to the oxidation that occurs as wood is burned, producing heat. When compounds combine with oxygen, the process is often referred to as burning. For example, athlete’s burn energy (sugars) as they exercise. The harder they exercise, the more sugars they burn so the more oxygen they need. That’s why at full speed, they are breathing very fast. Athletes take up oxygen through their lungs. Plants take up oxygen through the stomata in their leaves and through their roots.

Again, respiration is the burning of sugars for energy to grow and do the internal work of living. It is very important to understand that both plants and animals (including microorganisms) need oxygen for respiration. This is why overly wet or saturated soils are detrimental to both root growth and function, and the decomposition processes carried out by microorganisms in the soil.

The same principles regarding limiting factors are valid for both photosynthesis and respiration.