Chloroplasts migrate in response to different light intensities. Under weak light, chloroplasts gather at an illuminated area to maximize light absorption and photosynthesis rates (the accumulation response). In contrast, chloroplasts escape from strong light to avoid photodamage (the avoidance response).

Chloroplasts work to convert light energy of the Sun into sugars that can be used by cells. It is like a solar panel that changes sunlight energy into electric energy. The entire process is called photosynthesis and it all depends on the little green chlorophyll molecules in each chloroplast.

Chloroplasts do move in a cell. They jostle and slide and scoot around the cell, often sticking near the edges of the cell but sometimes seeming to fill the cell entirely with constant motion. The motion is common to the interior of cells and is called cyclonic or cytoplasmic streaming.

sunlight

What happens when light is absorbed by a molecule such as chlorophyll? The energy from the light excites an electron from its ground energy level to an excited energy level (Figure 19.7).

Chloroplasts Capture Sunlight When light strikes chlorophyll (or an accessory pigment) within the chloroplast, it energizes electrons within that molecule. The excited electrons leave chlorophyll to participate in further reactions, leaving the chlorophyll “at a loss”; eventually they must be replaced.

Once the electron reaches PSI, it joins its chlorophyll a special pair and re-excited by the absorption of light. NADP +start superscript, plus, end superscript reductase transfers electrons to the electron carrier NADP +start superscript, plus, end superscript to make NADPH.

A photon of light energy travels until it reaches a molecule of chlorophyll. The photon causes an electron in the chlorophyll to become “excited.” The energy given to the electron allows it to break free from an atom of the chlorophyll molecule. Chlorophyll is therefore said to “donate” an electron (Figure 5.12).

In photosynthesis, chlorophyll absorbs energy to transform carbon dioxide and water into carbohydrates and oxygen. This is the process that converts solar energy to a form that can be utilized by plants, and by the animals that eat them, to form the foundation of the food chain.

Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light.

blue

Wavelengths absorbed by chlorophyll and other photosynthetic pigments generate electrons to power photosynthesis. Chlorophyll a reflects green and yellow-green wavelengths. Accessory photosynthetic pigments, including chlorophyll b and beta-carotene, absorb energy that chlorophyll a does not absorb.

Structure of leaves

Blue light produces more lush greenery. Blue light is necessary for plants to regulate plant growth, as it helps to create strong stems and also helps create the chlorophyll necessary for plant processes. Red light is needed by plants to flower, but if a plant receives too much red light it will become brittle and die.

Green light

White light is the most effective light for photosynthesis because it provides a wide range of colored lights for various pigments to use. Red has a long wavelength, allowing it to radiate more energy and allow for an increased rate of photosynthesis in plants.

White light having a better balance of chlorophyll a, chlorophyll b, and the carotenoids and having all the photons of the visible light spectrum gave a better growth environment.

Red and yellow light is longer wavelength, lower energy light, while the blue light is higher energy. It seems strange that plants would harvest the lower energy red light instead of the higher energy green light, unless you consider that, like all life, plants first evolved in the ocean.

Red & blue light are most effective for plant growth, while yellow & green have minimal effect. UV light can damage plants, causing leaves to burn. Growers often use supplemental light to optimize plant growth.