Cells and control study guide

Stem cells are undifferentiated cells that have the capacity to develop into many different cell types. Their unique ability to self-renew and differentiate into specialized cells makes them a promising tool in regenerative medicine and disease treatment. For instance, they can be used to grow new tissues and organs, replace damaged cells, or deliver targeted therapies. However, their use is also associated with a range of ethical concerns, potential medical risks, and practical challenges. Ethical considerations often revolve around the source of stem cells, particularly embryonic stem cells, while medical risks include the potential for tumour formation, immune rejection, and transmission of diseases. Research continues to explore ways to maximise the benefits and minimise the risks of stem cell therapies.

The human eye functions as a sensory receptor, converting light stimuli into nerve impulses that the brain interprets as vision. Its structure is highly specialised for this role. Light first enters the eye through the cornea, a transparent, curved outer layer that performs most of the initial focusing. The iris, a coloured muscular diaphragm, controls the size of the pupil, regulating the amount of light entering the eye. Behind the pupil, the lens, a flexible, biconvex structure, fine-tunes the focusing of light onto the retina. The retina, lining the back of the eye, contains millions of specialised light-sensitive cells called photoreceptors. These are divided into two main types: rod cells and cone cells. Rod cells are highly sensitive to dim light and are responsible for black-and-white vision and vision in low light conditions. Cone cells require brighter light and are responsible for colour vision and high visual acuity. When light strikes these photoreceptors, they generate electrical signals, which are then transmitted to the brain via the optic nerve for processing.