11.1 Life Science Systems and the Human Body
Key Takeaways
- GED Science life science questions often test how body systems work together, not isolated vocabulary alone.
- Cells, tissues, organs, and organ systems form a hierarchy that helps explain health, disease, exercise, nutrition, and injury scenarios.
- Homeostasis uses feedback responses, such as sweating or hormone release, to return body conditions toward a useful range.
- Tables and graphs about heart rate, breathing, temperature, or blood sugar usually ask for a trend, a comparison, or a supported conclusion.
- A strong health-science answer identifies the variable being changed, the body response being measured, and whether the data support the claim.
Body Systems as Evidence Systems
GED Science expects you to reason with life science in realistic contexts. A question may describe exercise, illness, nutrition, injury, or a simple experiment, then ask which conclusion follows from the data. You do not need medical training. You do need to connect a body response to the system doing the work.
Levels of Organization
Life science starts with structure. Small parts combine into larger working systems.
| Level | Example | GED Use |
|---|---|---|
| Cell | Muscle cell | Basic unit that performs a function |
| Tissue | Muscle tissue | Many similar cells working together |
| Organ | Heart | Structure with a specific job |
| Organ system | Circulatory system | Organs cooperating to perform a major function |
| Organism | Human body | All systems interacting |
A GED item may ask why damage to one organ affects another system. For example, lungs exchange oxygen and carbon dioxide, but the circulatory system must move those gases through the blood. If lung function drops, oxygen delivery to muscle cells can also drop because the systems are connected.
Major System Connections
The body is not a set of separate machines. The nervous system sends fast electrical signals. The endocrine system sends slower chemical signals called hormones. The digestive system breaks food into usable molecules. The respiratory system exchanges gases. The circulatory system transports oxygen, nutrients, hormones, and wastes. The excretory system helps remove wastes and regulate water and salts.
Many GED questions focus on homeostasis, which means keeping internal conditions within a useful range. Sweating cools the body. Shivering produces heat. Insulin helps lower high blood glucose after a meal. These are feedback responses: a change is detected, a response occurs, and the condition moves back toward the target range.
Reading Body-Response Data
A student records these values before and after moderate exercise.
| Time | Heart Rate (beats/min) | Breathing Rate (breaths/min) |
|---|---|---|
| Rest | 72 | 14 |
| 5 min exercise | 108 | 24 |
| 10 min exercise | 126 | 30 |
| 5 min recovery | 92 | 18 |
The trend is clear: both heart rate and breathing rate increase during exercise and decrease during recovery. A supported conclusion is that exercise raises the body's demand for oxygen and waste removal. An unsupported conclusion would be that the student has a heart disease. The table does not compare the student to a medical standard or show long-term symptoms.
When interpreting a graph or table, ask three questions:
- What was changed or compared?
- What was measured?
- Does the conclusion match the pattern without adding new facts?
Health Experiments on the GED
In a health experiment, the independent variable is the factor changed by the researcher, such as sleep time, exercise level, or food type. The dependent variable is the measured response, such as reaction time, pulse, or blood glucose. Controlled variables are kept the same so the test is fair.
If two groups take different vitamins but also eat different diets, the result is hard to interpret. Diet becomes a possible confounding factor. GED questions often reward the answer that improves the design: use a control group, keep conditions the same, increase sample size, or repeat the trial.
The safest GED habit is to explain body systems with evidence. Name the system, describe the function, and tie the data pattern to that function.
A table shows that a student's heart rate rises from 74 beats per minute at rest to 124 beats per minute during exercise, while breathing rate rises from 15 to 29 breaths per minute. Which conclusion is best supported?
After a meal, a person's blood glucose rises. The pancreas releases insulin, and blood glucose later moves back toward its usual range. What process does this describe?