Tennessee Biology I EOC LS1 (The Human Body and Homeostasis): a complete overview of feedback, the levels of organization, transport and gas exchange, the nervous and endocrine systems, and immunity

What the body-systems part of LS1 demands

The From Molecules to Organisms (LS1) core idea extends from cells up to the whole organism and how it stays alive. This guide covers the body-systems part: how the body keeps its internal conditions stable (homeostasis), how it is organized, and how its major systems transport materials, control responses, and defend against disease. (The cell and biochemistry parts of LS1 are in the cells and transport guide and the biochemistry and energy guide.) The recurring crosscutting concepts are structure and function and stability and change (through feedback).

This guide ties together the matching topic pages, each with its own practice questions: homeostasis and feedback, levels of organization and body systems, transport and gas exchange in the body, the nervous and endocrine systems, and the immune system and disease.

Homeostasis and feedback

Homeostasis is the maintenance of a stable internal environment. It works through feedback loops (stimulus, receptor, control center, effector, response). Negative feedback, the main mechanism, opposes a change and returns a condition toward its set point: sweating when too hot, shivering when too cold, and insulin or glucagon adjusting blood glucose. Positive feedback (rarer) amplifies a change to complete a process, as in childbirth.

Levels of organization

From smallest to largest: cell, tissue, organ, organ system, organism. Similar cells form tissues, tissues form organs, organs form organ systems, and the systems form the organism. The major systems (circulatory, respiratory, digestive, nervous, endocrine, immune, muscular, skeletal, excretory) are interdependent and must work together, which is the basis of homeostasis.

Transport and gas exchange

The circulatory system transports oxygen, nutrients, and wastes in the blood, pumped by the heart. The respiratory system exchanges gases at the lungs: in the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out, by diffusion. The two systems work together: the respiratory system loads and unloads gases, and the circulatory system carries them to and from the cells for cellular respiration.

Control: nervous and endocrine systems

The nervous system uses fast electrical signals through neurons along a stimulus-response pathway (receptor, sensory neuron, central nervous system, motor neuron, effector). The endocrine system uses hormones carried in the blood for slower, longer-lasting control (growth, metabolism, blood glucose). Fast and brief (nervous) versus slow and sustained (endocrine); both maintain homeostasis.

The immune system

A pathogen causes disease. Non-specific defenses (skin, inflammation, engulfing white blood cells) act against all invaders; specific defenses use lymphocytes to make antibodies against a particular antigen. Memory cells remain after infection, giving a faster second response (immunity). A vaccine uses a harmless form or piece of a pathogen to produce antibodies and memory cells without the disease.

Check your knowledge

A mix of recall and reasoning questions covering the body-systems part of LS1. Attempt them under timed conditions, then check against the solutions.

1. Define homeostasis and give one example. (2 marks)
2. State the difference between negative and positive feedback. (2 marks)
3. List the levels of organization from smallest to largest. (2 marks)
4. Explain why organ systems must work together. (2 marks)
5. State how oxygen and carbon dioxide are exchanged in the lungs and by what process. (2 marks)
6. State two differences between the nervous and endocrine systems. (2 marks)
7. Describe the stimulus-response pathway. (3 marks)
8. State what an antibody does. (1 mark)
9. Explain how a vaccine gives immunity without causing disease. (2 marks)