Question

principles of life - chapter 4
use this worksheet as a study guide for chapter 4 - membranes. the lecture has been broken in subsections. you have a pdf version of the complete lecture slides available on blackboard.
i suggest you watch one video lecture, then complete the corresponding exercises in this worksheet. this will help you retain important information and let you know which points need to be reviewed.
if you have questions, write them down and bring them the lab meeting on wednesday.
cell structures and membranes - part 1

1. what are the three tenets of cell theory? what is their implication for the evolution of life on earth?
2. draw a phospholipid, indicating which part is hydrophobic and which part is hydrophilic. how are phospholipids arranged when placed in water?
3. why is it important for the cell to be able to regulate membrane fluidity?
4. list four factors that affect the fluidity of the cell membrane

Explanation:

1. Cell Theory Tenets and Evolution Implication: The three tenets of cell theory are that all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells come from pre - existing cells. This implies that all life on Earth has a common cellular origin, and evolution occurs at the cellular level through processes like genetic variation and natural selection in cells.
2. Phospholipid Structure and Arrangement: A phospholipid has a hydrophilic (water - loving) head group containing a phosphate and a glycerol, and two hydrophobic (water - fearing) fatty acid tails. When placed in water, phospholipids arrange themselves into a bilayer with the hydrophilic heads facing the water and the hydrophobic tails facing inward away from the water.
3. Importance of Membrane Fluidity Regulation: Membrane fluidity is important for cell function as it allows for the movement of membrane proteins, which are involved in processes like transport, cell - cell recognition, and signal transduction. It also enables the cell to change shape during processes like endocytosis and exocytosis.
4. Factors Affecting Membrane Fluidity: Temperature (higher temperatures increase fluidity), fatty acid chain length (shorter chains increase fluidity), degree of unsaturation of fatty acids (more double bonds increase fluidity), and cholesterol (acts as a buffer, increasing fluidity at low temperatures and decreasing it at high temperatures).

Answer:

1. The three tenets of cell theory are: all living organisms are made of one or more cells; the cell is the basic unit of life; all cells come from pre - existing cells. Implication for evolution: common cellular origin for life on Earth, evolution occurs at cellular level.
2. A phospholipid has a hydrophilic head (phosphate - glycerol) and hydrophobic tails (fatty acids). In water, they form a bilayer with heads facing water and tails inward.
3. Allows movement of membrane proteins for transport, recognition, and signal transduction; enables cell shape changes during endocytosis and exocytosis.
4. Temperature, fatty acid chain length, degree of unsaturation of fatty acids, cholesterol.