1. Unit 4 – Animal Systems This unit will focus on human systems
In unicellular (single-celled) organisms, the single cell performs all life functions - it functions independently.
However, multicellular (many celled) organisms have various levels of organization within them. Individual cells may perform specific functions and also work together for the good of the entire organism. The cells become dependent on one another.
Multicellular organisms have the following 5 levels of organization ranging from simplest to most complex:
levels of organization:
cells → tissues → organs → organ systems → organism

2. Level 1 - Cells
Are the basic unit of structure and function in living things.
May serve a specific function within the organism
Examples- blood cells, nerve cells, bone cells, etc.

3. Level 2 - Tissues
Made up of cells that are similar in structure and function and which work together to perform a specific activity
Examples - blood, nervous, bone, etc.
Humans have 4 basic tissues: connective, epithelial, muscle, and nerve.

4. Level 3 - Organs
Made up of tissues that work together to perform a specific activity
Examples - heart, brain, skin, etc.

5. Level 4 – Organ Systems
Groups of two or more tissues that work together to perform a specific function for the organism.
Examples - circulatory system, nervous system, skeletal system, etc.
The Human body has 11 organ systems - circulatory, digestive, endocrine, excretory (urinary), immune (lymphatic), integumentary, muscular, nervous, reproductive, respiratory, and skeletal.

6. Level 5 - Organism
Entire living things that can carry out all basic life processes. Meaning they can take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce.
Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protist.
Examples - bacteria, amoeba, mushroom, sunflower, human

7. Chapter 28, questions 1-2, p856
How does the process of cell determination differ from the process of cell differentiation?
In cell determination, stem cells commit to becoming a certain type of cell, such as a muscle cell. In cell differentiation, cells develop the actual structures and functions that make them specialized cells.
Briefly define and give an example of each of the five levels of organization in multicellular organisms.
- A cell is the smallest unit of life (example: neuron). A tissue is a group of similar cells that work together to perform a specialized function (example: nerve tissue). Organs consist of two or more types of tissues that function together (example: brain). Organ systems consist of two or more organs working together (example: nervous system).

8. What organ systems must work together to bring oxygen to the body’s cells?
- The respiratory system brings oxygen into the body. Part of the muscular system coordinates the movement of the lungs. The circulatory system picks up oxygen from the lungs and delivers it to body cells.
A cell has undergone determination to become an endocrine gland cell. If it is transplanted to a leg muscle, what do you think would happen to this cell?
Because determination is usually not reversible, the cell and its daughter cells will continue to develop as endocrine cells.

9. Question 5, p856
In the spring, tadpoles lose their tails as part of their life cycle. At a certain stage in development, the human fetus acquires individual fingers and toes. What occurs in some cells of both species to explain these changes?
Both are examples of programmed cell death, or apoptosis

10. Questions 1-2, p861
A system to maintain homeostasis must have at least four parts that function together. Name these parts and briefly explain what each one does.
Sensors gather information. A control center analyzes and compares the information to the desired value. Communication systems send messages from the control center to regulate the change. Targets receive and respond to the message.
What is the main difference between the way negative feedback and positive feedback mechanisms regulate change in the body.
- Negative feedback loops counteract change to return to a set point, while positive feedback loops accelerate change away from a set point.

11. When a newborn baby nurses, the mother’s body is stimulated to produce milk. What would happen to the milk supply if the mother chose to bottle feed rather than breast feed?
- A baby nursing creates a positive feedback loop that causes the mother’s body to lactate. Bottle feeding eliminates the stimulus.
Suppose you go on a long hike in hot weather. Describe a possible negative feedback loop that would keep your body from overheating.
- Sensors would detect a rise in body temperature, increasing blood flow to the skin, activating sweat glands, and increasing heart and breathing rates.

12. Reptiles regulate their body temperature by changing their environment
Reptiles regulate their body temperature by changing their environment. A snake, for instance, must lie in the sunlight to warm its body. Mammals, on the other hand, can regulate their internal environment to gain or lose heat. How might this ability give mammals an advantage over reptiles?
- Mammals can live in a wider range of habitats and tolerate rapid changes in external conditions.

13. Questions 1-2, p865
Why do organ systems in the body need to work so closely together?
- All body systems contribute to maintenance of homeostasis. What happens in one system may require response from another.
Explain why a long-term disruption of homeostasis can often be more damaging to the body than a short term disruption is.
Long-term disruption can produce a type of chain reaction in which more and more organ systems are affected over time. The result can be permanent damage to organs and possibly death.

14. Why would giving synthetic insulin to people with Type 1 diabetes restore their glucose homeostasis?
- In Type 1 diabetes, no insulin is made. When synthetic insulin is given to people with Type 1 diabetes, glucose can enter cells, so blood sugar levels return to normal.
If you lived in Alaska for the whole year, what changes might occur in your calcium and phosphorus levels during the winter versus the summer?
During the winter months, because there is little sunlight, and your skin is fully covered with clothing, you would be exposed to very little UV light. As a result, you would produce less vitamin D, and calcium and phosphorus levels in your body would decrease. In summer, your skin would be exposed to sunlight far more often. The increase in vitamin D production would result in an increase in calcium and phosphorus levels.

15. Question 5, p865
Some animals can store more glucose – in the form of glycogen – in their bodies than can other animals. What might be the evolutionary advantage of having these extra energy stores?
- Answer may include the development of more efficient cellular metabolism, the ability to survive on a irregular food supply, or the ability to mobilize extra glucose rapidly to provide energy in fight-or-flight situations.