Structure of a phospholipid molecule in the cell membrane, highlighting the hydrophilic head and hydrophobic tails.

Let’s go through each question step by step to make sure we understand and answer correctly.

---

Section A: Introduction

A#1: Every cell is surrounded by a cell membrane/plasma membrane.
→ This is a fact you just need to remember. All cells have this outer layer.

A#2: What does the cell membrane do?
It has 3 main jobs:
- Protects the cell (like a skin or wall).
- Lets good stuff in (water, oxygen, food) and bad/waste stuff out (carbon dioxide, wastes).
- Allows messages (like signals from other cells) to enter and leave.

So the answer is:
*Protects the cell and allows substances such as water, oxygen, food, carbon dioxide & wastes into & out of the cell. Allow messages to enter & leave the cell.*

---

Section B: Homeostasis

B#1: Give 2 examples of how our bodies maintain homeostasis.
Homeostasis means keeping things stable inside your body even when outside changes.

Example 1: Your body stays at about 98.6°F — that’s normal temperature. If it gets too hot or cold, your body fixes it.

Example 2: When you’re hot, you sweat — sweat cools you down and removes extra heat.

So answers are:
a. constant body temperature of 98.6°F
b. we perspire/sweat to cool our body & keep from overheating; gets rid of the excess heat

B#2: Define homeostasis.
Simple definition: *Maintaining stable conditions inside the cell even though the environment changes.*

B#3: Identify the 2 organic molecules that form the cell membrane and all other membranes in the cell.
These are the building blocks of every membrane in your cells.

Answer:
a. phospholipids
b. proteins

(Phospholipids make the basic structure, proteins help with transport and signaling.)

B#4: What are some roles of the cell membrane?
This is the same as A#2 — so just refer back:
*See question A#2*

---

Section C: Lipid Bilayer

C#1: Identify the type of lipid that forms the cell membrane.
The special fat-like molecule that makes up the membrane is called phospholipids.

C#2: What is a phospholipid?
It’s an organic molecule that builds the cell membrane and all internal membranes (like around mitochondria, nucleus, etc.).

Answer: *A type of organic molecule that forms the cell membrane & all membranes inside the cell.*

C#3: Label the hydrophilic & hydrophobic parts of the phospholipid.

Look at the diagram:

- The round top part says “Polar head” → this loves water → hydrophilic head
- The two long tails say “Fatty acid tail (nonpolar)” → these hate water → hydrophobic tails

So label them:
→ Hydrophilic head (points to the polar head)
→ Hydrophobic tails (point to the fatty acid tails)

---

Now let’s double-check everything for accuracy:

✔ All definitions match standard biology terms.
✔ Examples of homeostasis are correct and common.
✔ Phospholipids and proteins are indeed the two key molecules in membranes.
✔ Diagram labeling matches scientific understanding: heads love water, tails avoid it.

Everything checks out!

---

Final Answer:

A. Introduction
1. cell membrane/plasma membrane
2. Protects the cell and allows substances such as water, oxygen, food, carbon dioxide & wastes into & out of the cell. Allow messages to enter & leave the cell.

B. Homeostasis
1. a. constant body temperature of 98.6°F
b. we perspire/sweat to cool our body & keep from overheating; gets rid of the excess heat
2. Maintaining stable conditions inside the cell even though the environment changes.
3. a. phospholipids
b. proteins
4. See question A#2

C. Lipid Bilayer
1. Phospholipids
2. A type of organic molecule that forms the cell membrane & all membranes inside the cell.
3. Hydrophilic head → points to “Polar head”
Hydrophobic tails → point to “Fatty acid tail (nonpolar tail)”