cell membrane-sc.912.l.14.2: relate structure to function for the components of plant and animal cells. explain the role of cell membranes as a highly selective barrier (passive and active transport).
1. what are the functions of the cell membrane?

2. the cell membrane is said to be \selectively permeable.\ what does this mean?

3. scientists today use the \fluid mosaic model\ to describe the structure of the cell membrane. define \fluid mosaic model.\

4. draw a simple sketch of the cell membrane. show the arrangement of each of the following: phospholipids, integral proteins, peripheral proteins, channel proteins, and carbohydrates. be sure to label each part of your drawing.

Question

cell membrane-sc.912.l.14.2: relate structure to function for the components of plant and animal cells. explain the role of cell membranes as a highly selective barrier (passive and active transport).
1. what are the functions of the cell membrane?

2. the cell membrane is said to be \selectively permeable.\ what does this mean?

3. scientists today use the \fluid mosaic model\ to describe the structure of the cell membrane. define \fluid mosaic model.\

4. draw a simple sketch of the cell membrane. show the arrangement of each of the following: phospholipids, integral proteins, peripheral proteins, channel proteins, and carbohydrates. be sure to label each part of your drawing.

Accepted Answer

### 1. What are the functions of the cell membrane?
# Brief Explanations:
The cell membrane has several key functions. It acts as a **selective barrier** to regulate the entry and exit of substances (like nutrients, waste, ions) between the cell and its environment. It provides **structural support** and helps maintain cell shape. It facilitates **cell - cell communication** (e.g., through receptor proteins for signaling molecules) and **cell recognition** (via carbohydrate - protein complexes on the surface, important for immune responses and tissue organization). It also participates in **attachment** (to other cells or the extracellular matrix in multicellular organisms) and helps in maintaining the **homeostasis** of the cell's internal environment by controlling the concentration of substances inside the cell.
# Answer:
- Acts as a selective barrier to regulate the passage of substances (nutrients, waste, ions, etc.) between the cell and its environment.
- Provides structural support and helps maintain cell shape.
- Facilitates cell - cell communication (through receptor proteins for signaling molecules).
- Enables cell recognition (via carbohydrate - protein complexes on the surface, important for immune responses and tissue organization).
- Participates in cell attachment (to other cells or the extracellular matrix in multicellular organisms).
- Helps maintain the cell's internal homeostasis by controlling the concentration of substances inside the cell.

### 2. The cell membrane is said to be “selectively permeable.” What does this mean?
# Brief Explanations:
"Selectively permeable" means that the cell membrane allows some substances to pass through it freely, some substances to pass through with the help of transport proteins or under certain conditions, and prevents other substances from passing through at all. Small, non - polar molecules (like oxygen, carbon dioxide) can usually diffuse across easily. Polar molecules (like water, through aquaporins) and ions (like sodium, potassium) have more restricted passage and often require specific transport mechanisms (passive or active). Large, charged, or hydrophilic molecules (like glucose in some cases) may not be able to cross without the aid of specific proteins. This selectivity is crucial for the cell to maintain its internal environment (homeostasis) by controlling what enters and exits.
# Answer:
A selectively permeable cell membrane means it allows some substances to pass through (e.g., small non - polar molecules like $O_2$, $CO_2$; water through aquaporins) freely or with the help of transport proteins, while preventing other substances (e.g., large, charged, or hydrophilic molecules without specific transporters) from passing through. It regulates the entry and exit of substances to maintain the cell's internal homeostasis.

### 3. Scientists today use the “fluid mosaic model” to describe the structure of the cell membrane. Define “fluid mosaic model.”
# Brief Explanations:
The fluid mosaic model describes the structure of the cell membrane as a **mosaic** of different components (phospholipids, proteins, carbohydrates) and **fluid** in nature. The phospholipid bilayer forms the basic structural framework. The phospholipids are in a fluid state, meaning they can move laterally (side - to - side) within their own layer. The "mosaic" part comes from the fact that proteins (integral, peripheral, channel, etc.) are embedded or associated with the phospholipid bilayer in a non - uniform, mosaic - like pattern. Some proteins span the entire membrane (integral proteins), while others are attached to the surface (peripheral proteins). Carbohydrates are often attached to proteins (glycoproteins) or lipids (glycolipids) on the outer surface, also contributing to the mosaic appearance. The fluidity of the membrane is due to the nature of the phospholipid tails (unsaturated tails increase fluidity as they have kinks that prevent tight packing) and the ability of proteins to move within the membrane plane (to some extent).
# Answer:
The fluid mosaic model is a model that describes the cell membrane structure. The cell membrane is a **fluid** phospholipid bilayer (phospholipids can move laterally) with a **mosaic** of proteins (integral, peripheral, channel, etc.) embedded in or associated with it. Carbohydrates (attached to proteins as glycoproteins or to lipids as glycolipids) are also part of this mosaic. Integral proteins may span the membrane, peripheral proteins attach to the surface, and the fluidity comes from the nature of phospholipid tails (unsaturated tails increase fluidity) and the ability of components to move within the membrane plane.

### 4. Draw a simple sketch of the cell membrane. Show the arrangement of each of the following: phospholipids, integral proteins, peripheral proteins, channel proteins, and carbohydrates. Be sure to label each part of your drawing.
# Brief Explanations:
1. **Phospholipids**: Draw a double layer (bilayer). Each phospholipid has a hydrophilic (polar) head (containing a phosphate group) and two hydrophobic (non - polar) tails (fatty acid chains). The heads face outward (toward the aqueous environment inside and outside the cell), and the tails face inward (forming the hydrophobic core of the membrane).
2. **Integral proteins**: These are proteins that span the entire phospholipid bilayer. Draw them as long, irregular - shaped structures that go from the outer surface to the inner surface of the bilayer. Some integral proteins are channel proteins (a type of integral protein), so you can show a channel protein as a protein with a pore (channel) running through it, allowing substances to pass from one side of the membrane to the other.
3. **Peripheral proteins**: These are attached to the surface of the phospholipid bilayer (either the inner or outer surface). Draw them as small, irregular - shaped structures sitting on the outside or inside of the bilayer, not spanning the entire membrane.
4. **Carbohydrates**: These are attached to proteins (glycoproteins) or lipids (glycolipids) on the **outer** surface of the membrane. Draw small branched or chain - like structures attached to the outer - facing parts of integral proteins (glycoproteins) or to the outer - facing phospholipid heads (glycolipids).

### Labeling:
- Label the "Phospholipid Bilayer" (showing the hydrophilic heads and hydrophobic tails).
- Label "Integral Protein" (the one spanning the membrane) and "Channel Protein" (a type of integral protein with a pore).
- Label "Peripheral Protein" (on the inner or outer surface).
- Label "Carbohydrate" (attached to glycoproteins or glycolipids on the outer surface).

(Note: Since this is a text - based description of a drawing, you can represent the phospholipid bilayer as two parallel lines of circles (heads) with lines (tails) between them. Integral proteins can be rectangles or irregular shapes crossing the two lines of heads. Peripheral proteins are small shapes on the outside of the head lines. Carbohydrates are small branches on the outer - side heads or integral proteins.)

# Answer:
- **Phospholipid Bilayer**: Draw two parallel rows of circles (representing hydrophilic heads) with lines (representing hydrophobic tails) connecting the circles between the two rows. The top row of heads faces the "outside cell" environment, and the bottom row faces the "inside cell" environment.
- **Integral Protein**: Draw a long, irregular - shaped figure (e.g., a rectangle with a wavy edge) that extends from the top row of phospholipid heads (outside) through the tails to the bottom row of heads (inside).
- **Channel Protein**: Draw an integral protein with a pore (a small opening) running through its center, from the outside to the inside of the membrane.
- **Peripheral Protein**: Draw a small, irregular - shaped figure (e.g., a small oval) attached to the top (outside) or bottom (inside) row of phospholipid heads, not crossing the tails.
- **Carbohydrates**: Draw small branched or chain - like structures attached to the top - facing (outside) phospholipid heads or to the part of the integral protein that is on the outside of the membrane.

### Labels:
- Label the two - row structure as "Phospholipid Bilayer (Heads - Hydrophilic; Tails - Hydrophobic)".
- Label the long protein crossing the bilayer as "Integral Protein".
- Label the integral protein with a pore as "Channel Protein (Allows substance passage)".
- Label the small protein on the surface as "Peripheral Protein".
- Label the branched/chain - like structures on the outside as "Carbohydrates (Attached to glycoproteins/glycolipids)".

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QUESTION IMAGE

Question

Explanation:

1. What are the functions of the cell membrane?

Answer:

2. The cell membrane is said to be “selectively permeable.” What does this mean?