Inside the chloroplast

Three of the four factors arrive from outside. The fourth is built into the cell, and it is the one that makes the other three add up to anything.

Figure to be added

Figure 2.3 — a chloroplast as it appears under an electron microscope: a lens-shaped body with a double membrane round the outside and a dense stack of internal layers filling it, photographed in green.

The chloroplast

A double-membraned organelle contained only in plant cells. Within it is a green pigment, chlorophyll, and by means of that pigment solar energy is absorbed.

Pigment and organelle are not the same word

The chloroplast is the structure; the chlorophyll is the green substance inside it. It is the chlorophyll that absorbs the light, and the chloroplast that holds it in place and houses the machinery that uses what it captures. Confusing the two is easy, and the two words look alike on purpose.

Activity 2.1

You need a leaf of hydrilla or Vallisneria, a glass slide and a microscope.

Place a piece of a hydrilla or Vallisneria leaf on a glass slide with a drop of water and observe it under a microscope.
Observe how the chloroplasts containing chlorophyll move towards the direction from which sunlight is being received.

The chloroplasts move, and that is the point

An organelle that shifts position inside a living cell to face the light is not a passive container. The plant is aiming its chloroplasts, which is only worth doing if what they absorb matters. It is also the clearest evidence you can see with a school microscope that light and chlorophyll belong together.

Chlorophyll is in the chloroplast

The chloroplast is a double-membraned organelle found only in plant cells. The chlorophyll inside it is the green pigment that absorbs solar energy.