Notes
Organization and homeostasis
Cells → tissues → organs → organ systems. Homeostasis keeps conditions stable, mostly through negative feedback (reverses a change). Positive feedback increases a change (childbirth).
Systems at a glance
| System | Main parts | Main job |
|---|---|---|
| Digestive | Mouth, stomach, small and large intestine, liver, pancreas | Break down and absorb food |
| Circulatory | Heart, arteries, veins, capillaries, blood | Transport materials |
| Respiratory | Trachea, bronchi, lungs, alveoli, diaphragm | Gas exchange |
| Nervous | Brain, spinal cord, nerves | Fast electrical signals |
| Endocrine | Pituitary, thyroid, adrenal glands, pancreas | Hormones for slower, lasting control |
| Immune | White blood cells, skin, lymph nodes | Defense against pathogens |
Key ideas
- Most nutrients are absorbed through villi in the small intestine; the large intestine absorbs water.
- Arteries carry blood away from the heart; veins return it. Gas exchange happens by diffusion in the alveoli.
- Neurons pass signals with neurotransmitters at synapses. Reflexes go through the spinal cord.
- Insulin lowers blood sugar; glucagon raises it.
- Immunity: barriers → nonspecific response → specific response with B cells (antibodies) and T cells. Memory cells make vaccines work.
Topics in this unit
Each topic has its own short notes and practice.
Practice
The response reverses the change, keeping blood sugar near its set point.
The lungs take in oxygen and the blood carries it to cells.
Damaged villi reduce the surface area for absorbing nutrients.
Hormones like adrenaline produce longer-lasting effects than a nerve signal.
Memory cells from the first infection give long-term immunity.
Nerves send fast electrical and chemical signals; hormones travel in the blood.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A student measures her pulse and breathing rate at rest, then after 5 minutes of jumping jacks. At rest: 70 beats per minute and 14 breaths per minute. After exercise: 130 beats per minute and 32 breaths per minute. After 10 minutes of rest, both return close to resting levels.
(a) Explain why heart rate and breathing rate increase during exercise.
Show the answer and scoring guide
Muscles do more cellular respiration to make ATP, so they need more oxygen and produce more carbon dioxide. Faster breathing brings in more oxygen and removes CO2, and a faster heart rate moves blood faster to deliver oxygen and carry away CO2.
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(b) Describe how oxygen gets from the air in the lungs into the blood.
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Air reaches the alveoli, tiny air sacs surrounded by capillaries. Oxygen diffuses from the high concentration in the alveoli across their thin walls into the lower concentration in the blood, where it binds to hemoglobin in red blood cells.
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(c) Explain how the return to resting rates is an example of homeostasis and identify the type of feedback.
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When exercise stops, the body's demand for oxygen falls and CO2 levels drop, so the body lowers heart and breathing rates back toward their set points. This keeps conditions stable, which is homeostasis. It is negative feedback because the response reverses the change.
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