1. CHAPTER 5 The Working Cell
Modules 5.10 – 5.21

2. 5.10 Membranes organize the chemical activities of cells
MEMBRANE STRUCTURE AND FUNCTION
5.10 Membranes organize the chemical activities of cells
Membranes organize the chemical reactions making up metabolism  
Cytoplasm
Figure 5.10

3. Membranes are selectively permeable
They control the flow of substances into and out of a cell
Membranes can hold teams of enzymes that function in metabolism

4. 5.11 Membrane phospholipids form a bilayer
Phospholipids are the main structural components of membranes
They each have a hydrophilic head and two hydrophobic tails
Head
Symbol
Tails
Figure 5.11A

5. In water, phospholipids form a stable bilayer
The heads face outward and the tails face inward
Water
Hydrophilic heads
Hydrophobic tails
Water
Figure 5.11B

6. 5.12 The membrane is a fluid mosaic of phospholipids and proteins
Phospholipid molecules form a flexible bilayer
Cholesterol and protein molecules are embedded in it
Carbohydrates act as cell identification tags

7. The plasma membrane of an animal cell
Glycoprotein
Carbohydrate (of glycoprotein)
Fibers of the extracellular matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments of the cytoskeleton
Proteins
CYTOPLASM
Figure 5.12

8. 5.13 Proteins make the membrane a mosaic of function
Some membrane proteins form cell junctions
Others transport substances across the membrane
Figure 5.13
Transport

9. Many membrane proteins are enzymes
Some proteins function as receptors for chemical messages from other cells
The binding of a messenger to a receptor may trigger signal transduction
Messenger molecule
Receptor
Activated molecule
Figure 5.13
Enzyme activity
Signal transduction

10. 5.14 Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
They spread from areas of high concentration to areas of lower concentration
Molecule of dye
Membrane
EQUILIBRIUM
EQUILIBRIUM
Figure 5.14A & B

11. 5.15 Osmosis is the passive transport of water
Hypotonic solution
Hypertonic solution
In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration
Selectively permeable membrane
Solute molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water molecule
Selectively permeable membrane
Solute molecule with cluster of water molecules
NET FLOW OF WATER
Figure 5.15

12. 5.16 Water balance between cells and their surroundings is crucial to organisms
Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution
The control of water balance (osmoregulation) is essential for organisms
ISOTONIC SOLUTION
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
ANIMAL CELL
(1) Normal
(2) Lysing
(3) Shriveled
Plasma membrane
PLANT CELL
Figure 5.16
(4) Flaccid
(5) Turgid
(6) Shriveled

13. 5.17 Transport proteins facilitate diffusion across membranes
Small nonpolar molecules diffuse freely through the phospholipid bilayer
Many other kinds of molecules pass through selective protein pores by facilitated diffusion
Solute molecule
Transport protein
Figure 5.17

14. 5.18 Cells expend energy for active transport
Transport proteins can move solutes across a membrane against a concentration gradient
This is called active transport
Active transport requires ATP

15. Active transport in two solutes across a membrane
FLUID OUTSIDE CELL
Phosphorylated transport protein
Active transport in two solutes across a membrane
Transport protein
First solute 1
First solute, inside cell, binds to protein 2
ATP transfers phosphate to protein 3
Protein releases solute outside cell
Second solute 4
Second solute binds to protein 5
Phosphate detaches from protein 6
Protein releases second solute into cell
Figure 5.18

16. 5.19 Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane
a vesicle may fuse with the membrane and expel its contents (exocytosis)
FLUID OUTSIDE CELL
CYTOPLASM
Figure 5.19A

17. or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B

18. Material bound to receptor proteins
Three kinds of endocytosis
Pseudopod of amoeba
Food being ingested
Plasma membrane
Material bound to receptor proteins
PIT
Cytoplasm
Figure 5.19C

19. 5.20 Connection: Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Phospholipid outer layer
LDL PARTICLE
Receptor protein
Protein
Cholesterol
Plasma membrane
Vesicle
CYTOPLASM
Figure 5.20

20. 5.21 Chloroplasts and mitochondria make energy available for cellular work
Enzymes and membranes are central to the processes that make energy available to the cell
Chloroplasts carry out photosynthesis, using solar energy to produce glucose and oxygen from carbon dioxide and water
Mitochondria consume oxygen in cellular respiration, using the energy stored in glucose to make ATP

21. Chemicals recycle among living organisms and their environment
Sunlight energy
Nearly all the chemical energy that organisms use comes ultimately from sunlight
Chloroplasts, site of photosynthesis
CO2 + H2O
Glucose + O2
Mitochondria sites of cellular respiration
Chemicals recycle among living organisms and their environment
(for cellular work)
Heat energy
Figure 5.21