IB Biology Sub-topic C3.1 Notes

Biological systems

This topic primarily focuses on the integration of biological systems into the body to coordinate different actions. The hierarchy of organization to perform this is:

1. Atoms and molecules comprise the chemical level.
2. Organelles and structural components of cells comprise the organelle level.
3. Cells the basic subunits of living organism comprise the cellular level.
4. Groups of cells form tissues, comprising the tissue level.
5. Two or more tissue type come together to form organs, comprising the organ level.
6. Finally, the organism is composed of multiple cooperating organ systems that forms the organism.

Successful integration of these body systems leads to emergent properties that could otherwise not be exhibited at individual levels. However, for an organism to function well, it must coordinate multiple processes at multiple levels.

For example, the cardiovascular system is a body system that must integrate with all the other body’s systems to permit life processes to occur: 

1. Organs including the heart and the vasculature must integrate in function to permit efficient transport of substances around the body at the correct pressure. 
2. The tissue level must also integrate to permit the cardiac muscles to contract as needed.
3. At the cellular level adequate levels of glucose and oxygen must be provided to enable the mitochondria to generate the ATP needed by the muscle fibres.

However, the heart must be connected to other organs in order to respond appropriately to different events occurring around the body. Cue signalling.

Signalling

Effective communication between cells, tissues and organs and ensure effective integration of organs around the body. The two key signalling systems that undertake this are the endocrine system and the nervous system. They work together and independently to maintain homeostasis in the body in different ways, nature, and durations.

1. The nervous system communicates via electrical impulses that are rapid but also short lived. Nervous signalling is typically used when rapid responses are required, such as reflexes.
2. The endocrine system relies on the secretion of hormones into the blood to elicit a response at target tissues. This takes much longer and often has a prolonged response, although hormonal communication can still be fast such as when adrenaline secretion evokes the ‘fight or flight’ response.