describe membrane phospholipids. do they remain in the same place, or can they move within the membrane?
what biomolecule is the main working molecule in the plasma membrane? what functions can this molecule accomplish?
remembering that energy must be conserved, what do you think becomes of the energy extracted from food during cellular respiration?
in what two ways is the plasma membrane similar across all organisms?
what is passive transport? what are two examples of materials that move through passive transport?
two solutions have different concentrations of a dissolved substance, predict how water would move if the solutions are placed on opposite sides of a semipermeable membrane.
in lab applications diffusion bags can be used to show how water can pass through them but sucrose cannot. if we fill a bag with 15% sucrose and 85% water and place it in a beaker with 20% sucrose and 80% water. what will happen?

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Accepted Answer

### 1. Describe membrane phospholipids...
# Brief Explanations:
Membrane phospholipids have a hydrophilic head (phosphate - glycerol) and hydrophobic tails (fatty acids). They form a bilayer in the membrane. The hydrophobic tails face inward, and hydrophilic heads face outward (toward aqueous environments). They can move within the bilayer (lateral diffusion) but don't flip - flop easily between layers.
# Answer:
Membrane phospholipids have a hydrophilic head (with phosphate - glycerol) and hydrophobic fatty - acid tails. They form a bilayer (hydrophobic tails inward, hydrophilic heads outward, facing aqueous regions). They can move laterally within the bilayer but rarely flip between layers.

### 2. What biomolecule...
# Brief Explanations:
The main working molecule in the plasma membrane (for functions like transport, signaling) is the protein. Membrane proteins can be integral (spanning the membrane) or peripheral (attached to the surface). Functions include transport (e.g., channel proteins for passive transport, carrier proteins for active/passive), receptor (for signal transduction), and enzymatic activity.
# Answer:
The main working molecule in the plasma membrane is protein. Membrane proteins (integral/peripheral) function in transport (e.g., channels/carriers), signal reception (receptor proteins), and enzymatic activity.

### 3. Remembering that energy...
# Brief Explanations:
During cellular respiration, energy from food (like glucose) is conserved in ATP (adenosine triphosphate) and in the proton gradient (in oxidative phosphorylation). The energy from food is extracted by breaking down organic molecules (like glucose in glycolysis, Krebs cycle) and the energy is used to make ATP (via substrate - level phosphorylation and oxidative phosphorylation) and to create a proton gradient (used for ATP synthesis in chemiosmosis).
# Answer:
During cellular respiration, energy from food is conserved in ATP (adenosine triphosphate) and the proton gradient (in the mitochondria's inner membrane). The energy from food (e.g., glucose) is extracted by catabolic pathways (glycolysis, Krebs cycle) and used to generate ATP (via substrate - level and oxidative phosphorylation) and the proton gradient (for chemiosmotic ATP synthesis).

### 4. In what two ways...
# Brief Explanations:
The plasma membrane across all organisms is similar in having a phospholipid bilayer structure and containing membrane proteins (for transport, signaling, etc.). All cells have a phospholipid bilayer as the basic membrane structure (hydrophobic core, hydrophilic surfaces) and use membrane proteins for essential functions like transporting molecules in and out of the cell.
# Answer:
The plasma membrane across all organisms is similar in having a phospholipid bilayer (hydrophobic core, hydrophilic surfaces) and containing membrane proteins (for transport, signaling, enzymatic activity, etc.).

### 5. What is passive transport...
# Brief Explanations:
Passive transport is the movement of molecules across a membrane without the input of cellular energy (ATP). Two examples: 1. Simple diffusion: movement of small, non - polar molecules (e.g., $O_2$, $CO_2$) down their concentration gradient, directly through the phospholipid bilayer. 2. Facilitated diffusion: movement of polar/charged molecules (e.g., glucose, ions) down their concentration gradient, with the help of membrane proteins (channel or carrier proteins).
# Answer:
Passive transport is the movement of molecules across a membrane without using cellular energy (ATP), driven by concentration gradients. Examples: 1. Simple diffusion (e.g., $O_2$, $CO_2$ moving through the phospholipid bilayer down their concentration gradients). 2. Facilitated diffusion (e.g., glucose moving via carrier proteins, ions via channel proteins down their concentration gradients).

### 6. Two solutions...
# Brief Explanations:
Water moves by osmosis, which is the passive transport of water across a semipermeable membrane, down its water potential gradient (or from an area of lower solute concentration to higher solute concentration). If two solutions have different solute concentrations, water will move from the solution with lower solute concentration (higher water potential) to the solution with higher solute concentration (lower water potential) across the semipermeable membrane.
# Answer:
Water moves by osmosis (passive transport) across the semipermeable membrane. It moves from the solution with lower solute concentration (higher water potential) to the solution with higher solute concentration (lower water potential).

### 7. In lab applications...
# Brief Explanations:
The bag is semipermeable (allows water but not sucrose through). The bag has 15% sucrose (85% water) and the beaker has 20% sucrose (80% water). The beaker has a higher sucrose concentration (lower water potential) than the bag. So, water will move out of the bag (from higher water potential in the bag to lower water potential in the beaker) by osmosis. The bag will lose water, so its mass will decrease, and it may shrink.
# Answer:
The bag is semipermeable (water can pass, sucrose cannot). The beaker has a higher sucrose concentration (20% vs. 15% in the bag) and thus lower water potential. Water will move out of the bag (osmosis, from higher water potential in the bag to lower in the beaker). The bag will lose water, shrink, and its mass will decrease.

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Explanation:

1. Describe membrane phospholipids...

Answer:

2. What biomolecule...