• Photosynthesis
• Other Influences of Light
• The Eye
• Bioluminescence

Photosynthesis

Photosynthesis is the process of creating organic matter from water combined with CO2. It greatly depends on light. This is the most important biological and chemical process, because life on Earth depends on this transformation of solar energy into chemical energy. The process occurs in the green parts of a plant which contains chloroplasts. One cell of a plant contains 40-50 chloroplasts. Chloroplasts are tiny bodies which contain a granular substance called tylakoid. Tylakoids contain chlorophyll. Tylakoids are in a fluid called stroma. The chlorophyll is the pigment for transformation of sun energy into chemical energy. There are a few types of chlorophyll. They are known as chlorophyll A, B, C and D, but for the photosynthesis the most important chlorophylls are chlorophyll A and B.

Besides the chlorophyll, inside the tylakoids are other types of pigment. They are known as Carotin and Xsantofil

The Carotin receives light energy and transmits it to the electrons of the chlorophyll, which transforms the light energy into chemical. A certain amount of this energy becomes attached to ATP (adenosine triphosphat), and the rest of it remains free in the tylakoid. The energy which remains free in the tylakoid, affects the water molecules, which desintegrate into Oxygen and Hydrogen. Oxygen leaves out of a plant. This part of the photosynthesis is called the light phase, because it happens under the direct influence of sunlight.

The next phase of the photosynthesis is known as a dark phase, because a plant doesn’t need the sunlight. All products from the light phase from the tylakoid passes into the stroma. In the series of the complex steps from Hydrogen and CO2, glucose is formed. Then, from glucose combined with Nytrogen, Sulphur and Phosphorus from the soil, a plant produces starch, fat, albumen, vitamins and other complex substances neccessary for a life. These substances, which are of great importance for nutrition are then distributed through the whole plant, by diffusion and osmosis.

The importance of photosynthesis is that Oxygen is produced, which can be used by living things for breathing. There are two points in a 24-hour period when the photosynthesis and the inner breathing of a plant are in equilibrium. These points are called the compensation points and they occur at dawn and the dusk. At that time the photosynthesis produces exact quantities of Carbon hydrates and Oxygen needed for the inner breathing. The inner breathing produces exact quantity of CO2 and water for the process of photosynthesis.

Other Influences of Light

The plants don’t have a nervous system, but they react on certain stimulations. Particular parts of some plants bend toward the source of light, or away from it. The light effects the germination and efflorescence.

When the body is exposed to sunlight, Vitamin D forms in the skin. Vitamin D has an important role in accumulation of calcium in bones and regulating the ratio of calcium and phosphorus in blood, and metabolism of mineral salts.

Some insects orientate themselves by using the effect of polarization. They can do this because of the special structure of their eyes.

The Eye

The eye is the organ of sight that sends impulses to the brain when it is stimulated by the rays of light reflected from an object. The brain interprets these impulses and forms a picture. An eye consists of a hollow, spherical shell – the eyeball, which is made of several layers and structures. The eye is located in the skull’s hollows and it is protected by eyelids and eyelashes.

The parts of the eye are:

1.Retina, the tissue layer on the back side of the eyeball, composed of the pigment’s layer and the nerve’s layer

2. Suspensory ligament

3. Cornea, the transparent continuation of the sclera which refracts the rays of light on the lens.

4. Pupil

5. Lens, the transparent body which focuses the light rays

6. Anterior chamber, the space between the cornea and the iris, filled with the fluid consisting glucose, salts and proteins

7. Iris, nontransparent disc of the tissue with the blood vessels and the central opening (the pupil)

8. Ciliary body

9. Muscle

10. Posterior chamber, the space behind the lens filled with the dense fluid, which keeps the form of the eyeball, protects retina and helps in refraction of the light

11. Blind spot

12. Blood vessels

13. Optic nerve

14. Fovea centralis, the part with the yellowish tissue at the centre of the retina, cones and this is the field of the sharpest sight.

15. Sclera, the white eye’s covering

The light reflected from an object we watch falls on the cornea, passes through the anterior chamber of the eye and falls on the lens. The lens refracts the rays of the light and guides it toward the retina. The light passes through the posterior chamber and falls on the fovea centralis. The converse picture is formed here. The light, on the retina, causes disintegration of the albumen Rodopsin. The product of the disintegration of the Rodopsin stimulates the rods and the cones. They transfer this stimulation to the neurones, from where the stimulation passes to the brain by optic nerves. A correct picture is formed at the brain.

Refraction of the eye is the way in which the rays of light are refracted in the eye. Various defects of eye refracion:

Short-sightedness This is an inborn defect. Short- sighted people have streched eyeballs, that causes the picture of the objects to fall in front of the retina. The defect can be declined by wearing appropriate glasses with the concave lenses.
Long-sightedness This is an inborn defect, too. The eyeball is short and therefore the picture doesn’t fall on the retina, but rather behind it. We can decline the effect by wearing glasses with convex lenses.
Astigmatism This is defect in bending the light rays in the system of he eyelens. The rays passing through the astigmatic lens don’t fall at the common focus. People with this defect feel tired and experience blurred sight. The sight can be corrected by wearing correcting glasses with special lenses.

Bioluminiscence

Bioluminiscence is the lighting of living beings. Some one-cell organisms give off light as a whole, while in insects and fishes special glands secrete luminescent substances. Bioluminescence is most commonly found in sea animals. Most sea animals in deep waters have organs which radiate light colored in variuous colors. Some of these animals can eject protective clouds of colored liquid.

The flickering of small animals on the ocean surface, especially in the summer, can be a beautiful sight.

An equally beautiful scene, but this time on the land, is made by swarms of fireflies in summer evenings.

Bioluminescence can also be caused by some bacteria, on dead fish or rotten wood.

Even a potato cut in half can radiate light.