Heating a substance makes the molecules move faster. Cooling a substance makes the molecules move slower.

Temperature

The energy of motion is called kinetic energy. The kinetic energy of particles of matter determines the state of matter. Particles of solids have the least kinetic energy and particles of gases have the most.

These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions.

The process is called photosynthesis. When chlorophyll breaks down, yellow pigments in leaves become visible. As days get shorter and colder in the autumn, chlorophyll molecules break down. Leaves quickly lose their green color.

Poor drainage or improper watering Water issues — either too much or too little — are the leading reason behind yellow leaves. In overly wet soil, roots can’t breathe. They suffocate, shut down and stop delivering the water and nutrients plants need. Underwatering, or drought, has a similar effect.

Leaves are green because of a pigment known as chlorophyll. The chlorophyll masks the colors of any other pigments in the leaf cells. In the autumn, chlorophyll breaks down revealing other colors present in the leaf. You just studied 15 terms!

So, plants and their leaves look green because the “special pair” of chlorophyll molecules uses the red end of the visible light spectrum to power reactions inside each cell. The unused green light is reflected from the leaf and we see that light.

Plants are green because their cells contain chloroplasts which have the pigment chlorophyll which absorbs deep-blue and red light, so that the rest of the sunlight spectrum is being reflected causing the plant to look green.

In the summer, leaves appear green due to an abundance of chlorophyll, a green colored substance in plant cells that uses sunlight to produce food for the tree. Leaves finally fall when cells break down and harden at the point of attachment to the tree.