The substances containing iron and responsible for oxygen transport are:

Hemoglobin and Hemerythrin.

Explanation:

Oxygen transport is a vital process in living organisms, and it requires specialized molecules that can bind and carry oxygen efficiently. Two important substances that contain iron and are responsible for oxygen transport are hemoglobin and hemerythrin.

Hemoglobin:

Hemoglobin is a protein found in red blood cells and is responsible for carrying oxygen from the lungs to the body's tissues. It consists of four subunits, each containing a heme group. The heme group contains an iron atom that can bind to oxygen molecules. When oxygen binds to the iron in hemoglobin, it forms a reversible complex called oxyhemoglobin. This complex is stable in the presence of oxygen but releases oxygen when exposed to tissues with lower oxygen concentrations.

Hemerythrin:

Hemerythrin is another iron-containing protein that plays a role in oxygen transport. It is found in certain marine invertebrates, such as marine worms and brachiopods. Hemerythrin also contains iron atoms that bind to oxygen, but unlike hemoglobin, it does not require heme groups. Instead, it uses iron atoms coordinated with histidine residues to bind oxygen. Hemerythrin has a distinct pink color when oxygenated, which gives it its name.

Comparison between Hemoglobin and Hemerythrin:

- Hemoglobin is mainly found in vertebrates, while hemerythrin is found in certain marine invertebrates.
- Hemoglobin consists of four subunits, while hemerythrin can have varying numbers of subunits.
- Hemoglobin uses heme groups to bind oxygen, while hemerythrin uses iron atoms coordinated with histidine residues.
- Hemoglobin transports oxygen in red blood cells, while hemerythrin transports oxygen in the circulatory system of marine invertebrates.

In conclusion, while hemoglobin is the most well-known iron-containing protein responsible for oxygen transport in vertebrates, hemerythrin is another important protein found in certain marine invertebrates. Both proteins have iron atoms that bind to oxygen, allowing for efficient oxygen transport in different organisms.