The cone in the retina of eye is an example of

1. Analyze the question The question asks about the level of biological organization of a cone in the retina. The levels run from cell → tissue → organ → organ system → organism.

2. Explain the concept

• Cell: the basic structural and functional unit of life.
• Tissue: a group of similar cells doing the same job.
• Organ: different tissues working together for a specific function.
• System: a group of organs working together.

3. Solution The retina is the light-sensitive layer at the back of the eye. It contains two types of photoreceptor cells:

• Rods, which work in dim light and detect black and white.
• Cones, which work in bright light and detect colour.

A single cone is one specialized cell. It has an outer segment containing light-sensitive pigment, an inner segment with mitochondria, a nucleus, and a synaptic terminal. It is not a group of cells, so it is not a tissue. Many rods and cones together, along with other neurons, make up the retina (nervous tissue), and the retina is part of the eye (an organ).

4. Answer The cone is a specialized cell, so the answer is A.

5. Exam tip Ask yourself: "Is it one unit or many?" Rods, cones, red blood cells, neurons and sperm cells are all single specialized cells. Remember the order C-T-O-S-O: Cell, Tissue, Organ, System, Organism.