Cells & Living Things

Question 1

Describe the main points of cell theory.

Answer 1

• Cells are the structural unit of all living things
• Cells are the functional unit of life; carrying out all living processes
• Every cell arises from a pre-existing cell
• Cells contain hereditary material

Question 2

What are the seven essential components that define life (MRS GREN)?

Answer 2

Movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

Question 3

All living things (6);

Answer 3

• are complex and have an organised structure
• take in energy from their surroundings and use it
• maintain a composition that is chemically different from their external environment
• respond to stimulus
• are able to reproduce
• grow and develop

Question 4

What is the cytoplasm?

Answer 4

Consisting of mainly water (cytosol) and organelles, it holds the components of a cell in place.

Question 5

What are the main functions of the cell membrane?

Answer 5

It separates the contents of the cell from the extracellular environment, regulates the passage of substances intercellularly, enables cells to recognise one another and other substances such as hormones, and enables attachment of the cytoskeleton.

Question 6

What is the phospholipid bilayer comprised of?

Answer 6

A phospholipid bilayer consisting of hydrophilic heads (polar phosphate group) and hydrophobic tails (non-polar lipids)

Question 7

Describe the basic definition of the cell membrane.

Answer 7

The cell membrane is responsible for controlling what enters and exits the cell.

Question 8

What is the fluid mosaic model?

Answer 8

• The word ‘fluid’ in the name of the model refers to the ability of both lipids and proteins to continuously move in the membrane. This characteristics is critical for membrane structures in areas such as permeability, or ease of movement of molecules across the membrane.
• The term ‘mosaic’ refers to the pattern formed by the variety of integral and peripheral proteins associated with the phospholipid bilayer

Question 9

What components does the cell membrane consist of?

Answer 9

• Two layers of phospholipid molecules
• Integral proteins (permanently in the bilayer)
• Peripheral proteins (which tend to move temporarily and are not a permanent part of the membrane)
• Cholesterol (positioned between the phospholipids in animal cells only)
• Glycoproteins (membrane proteins with carbohydrate chains attached)
• Glycolipids (phospholipids with carbohydrate chains attached)

Question 10

Why are phosphate heads, as part of the phospholipid bilayer, labelled as polar?

Answer 10

It has a charge associated with it and therefore can interact with water molecules. Thus, the cell membrane is impermeable to water soluble or polar molecules.

Question 11

How do hormones bind with the cell membrane?

Answer 11

Hormones bind to the complementary protein receptors on the outside of cell membranes.

Question 12

Describe cell adhesion.

Answer 12

Integral proteins can stick out and bind to specific protein molecules on adjacent cells or attach to the cytoskeleton.

Question 13

What is the role of cholesterol in the cell membrane?

Answer 13

It contributes to regulating the fluid nature of phospholipids.

Question 14

What are the characteristics of prokaryotes? (8)

Answer 14

• Small (1-10 um diameter)
• Little internal organisation
• Circular DNA
• No nucleus
• No membrane-bound organelles
• Single chromosome
• Most have a cell wall
• Unicellular organisms

Question 15

What are the characteristics of eukaryotes?

Answer 15

• Larger (10-100 um diameter)
• Complex internal organisation
• DNA linear with histones present
• Has nucleus
• Contains membrane-bound organelles
• Two or more chromosomes
• Cell wall in some cells
• Unicellular or multicellular