Biology - Chapter 8

Question 1

What is the cell membrane composed of?

Answer 1

Cell membranes are made up of a bi-layer of phospholipids.

• The “head” is Hydrophilic ( = water loving)
• The “tail” is Hydrophobic ( = water fearing)

Question 2

What is the role of proteins?

Answer 2

Proteins may be attached or suspended between these phospholipids.

They are important for:

• Transport of substances across the membrane
• Cell to cell communication

Question 3

What is the other name for the cell membrane model?

Answer 3

The fluid mosaic model.

• Molecules making up the membrane are in constant motion giving membranes flexibility to change shape.

Question 4

How does the cell membrane know what to let in?

Answer 4

There are two determining factors:

• Particle size: small molecules like H2O can get in where others like glucose cannot.
• Membrane proteins: Proteins that stick out of the membrane bind to certain molecules and transport them inside the cell in many ways.

Question 5

What is a concentration gradient?

Answer 5

Describes the amount of solute in a solution. It is the difference in concentration between two areas or two solutions.

• Particles always tend to move down the concentration gradient. This means that they will move from the solution with the higher concentration to the solution with the lower concentration.

Question 6

What is passive transport, and what are the three types?

Answer 6

Passive transport is when materials move across the membrane without using any energy.

The three types are:

1. Diffusion
2. Osomis
3. Facilitated diffusion

Question 7

What is diffusion?

Answer 7

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

Question 8

What is osmosis?

Answer 8

Osmosis is the diffusion of water molecules across a membrane. Water moves from where there are more water molecules (but fewer solute particles) to where there are fewer water molecules (but more solute particles).

Question 9

What is facilitated diffusion?

Answer 9

When particles are helped across a membrane by transport proteins. This process always occurs down a concentration gradient, therefore, no energy is needed.

There are two types of transport proteins:

1. Carrier proteins
2. Channel proteins

Question 10

What is active transport?

Answer 10

Occurs when particles must move against a concentration gradient from an area of low concentration to an area of high concentration.

Question 11

What are the three types of endocytosis?

Answer 11

1. Phagocytosis: endocytosis of large particles “food” (we say the cell is eating)
2. Pinocytosis: endocytosis of fluid particles (we say the cell is drinking)
3. Receptors: proteins protruding from the membrane surface, they detect specific compounds that need to be transported in.

Question 12

What is exocytosis?

Answer 12

Exocytosis is the reverse of endocytosis.

• The membrane of the vesicle or vacuole fuses with the cell membrane releasing the contents to the outside of the cell.