Unit 1 Levels of Organization
PART 3: CELLULAR LEVEL OF ORGANIZATION
LEARNING OBJECTIVES
PARTS OF A CELL
1. Briefly explain the functions of the three main cell parts.
THE PLASMA MEMBRANE
2. Describe the plasma membrane’s structure.
3. Classify membrane proteins on the basis of function.
4. Explain the importance of membrane fluidity to plasma membrane function.
5. Explain how the plasma membrane’s structure makes it semipermeable.
6. Discuss the factors that contribute to an electrochemical gradient.
TRANSPORT ACROSS THE PLASMA MEMBRANE
7. Differentiate between passive and active membrane transport.
8. Define diffusion and describe several factors that affect it.
9. Compare simple diffusion with facilitated diffusion.
10. Explain the principle of osmosis.
11. Describe what happens to a cell placed in an isotonic, hypotonic, or hypertonic solution.
12. Compare primary active transport with secondary active transport.
13. Compare endocytosis with exocytosis.
CYTOPLASM
14. Describe cytosol’s chemical composition and function.
15. Construct a chart that describes cytoplasmic organelles’ structure and function.
NUCLEUS
16. Describe the structure and function of the nucleus.
17. Explain how genes are organized in non-dividing and dividing cells.
PROTEIN SYNTHESIS
18. Discuss how DNA and RNA store genetic information.
19. Define gene expression.
20. Describe the sequence of events in gene transcription.
21. Describe the sequence of events in mRNA translation.
CELL DIVISION
22. Define cell division. State the two types of cell division and the purpose of each type.
23. Define somatic cell cycle. List the events that occur during the cycle’s interphase.
24. Describe the stages and events of mitosis.
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Red River College
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Unit 1 Levels of Organization
METABOLIC REACTIONS
25. Define metabolism.
26. Explain the role of ATP in anabolism and catabolism.
METABOLIC REACTIONS
27. Describe oxidation-reduction reactions.
28. Describe three mechanisms of ATP generation.
CARBOHYDRATE METABOLISM
29. Describe the mechanism of glucose movement into body cells.
30. Describe glucose catabolism.
31. Describe glucose anabolism.
LIPID AND PROTEIN METABOLISM
32. Describe the transport of lipids by lipoproteins.
33. Briefly describe lipid catabolism and metabolism.
34. Briefly describe protein catabolism and anabolism.
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Red River College
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Unit 1 Levels of Organization
PART 3: CELLULAR LEVEL OF ORGANIZATION
LEARNING ACTIVITIES
PARTS OF A CELL
The cell is divided into 3 main parts: plasma membrane, cytoplasm, and nucleus (Figure 3.1).
Use Table 3.2 to complete the following chart:
Cell Part
Plasma
Membrane
General Function
-
Cytoplasm
Nucleus
-
Cytosol;
-
Organelles,
Draw a generalized cell
PLASMA MEMBRANE
Structure of the Plasma Membrane
The plasma membrane is composed of:
1. A lipid bilayer
2. Membrane proteins
See Figure 3.2 for an illustration of plasma membrane structure.
Fluid mosaic model - ____________________________________________________________
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Red River College
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Unit 1 Levels of Organization
The Lipid Bilayer
The lipid bilayer is composed of two back-to-back layers made up of 3 types of lipid.
1. Phospholipids
2. Cholesterol
3. Glycolipids
Draw the Lipid Bilayer
Phospholipids – make the plasma membrane a bilayer because they are amphipathic.
o Phosphate heads are hydro__________.
o Fatty acid tails are hydro__________.
Phospholipids make the plasma membrane fluid.
o They are not chemically bonded to each other – they can move about laterally.
Phospholipids prevent large polar molecules from crossing the plasma membrane.
o Water-soluble molecules __________ cross the plasma membrane.
o Lipid-soluble molecules __________ cross the plasma membrane.
Cholesterol is interspersed among the other lipids in both layers of the membrane.
Cholesterol molecules maintain the plasma membrane’s fluidity.
o They prevent hydrophobic interactions between phospholipid tails, which could cause
crystallization of the bilayer and decrease membrane fluidity
Glycolipids make the lipid bilayer asymmetric.
o They are only found on the extracellular side of the bilayer.
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Unit 1 Levels of Organization
Arrangement of Membrane Proteins
Membrane proteins are classified based on their location in the plasma membrane:
1. Integral proteins –
a. Transmembrane proteins 2. Peripheral proteins –
Functions of Membrane Proteins
Proteins comprise a small portion of the plasma membrane, but give it most of its functions.
Functions of membrane proteins
Ion channel
Carrier
Receptor
Enzyme
Linker
Cell identity marker
See Figure 3.3 for an illustration of membrane protein function.
Membrane Fluidity
Membranes are fluid structure.
o Phospholipids and many membrane proteins easily rotate and move sideways in their
own half of the bilayer.
Fluidity allows the plasma membrane to:
1. Interact with its other components (e.g. assembly of membrane proteins).
2. Move (e.g. phagocytosis).
3. Seal when torn or punctured.
Explain the importance of membrane fluidity to plasma membrane function.
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Unit 1 Levels of Organization
Membrane Permeability
The plasma membrane’s structure makes it semipermeable.
o The lipid bilayer allows passage of _________________ substances but not _________
substances.
o Ion channels and carriers allow passage of ________ substances but not _____________
substances.
Gradients Across the Plasma Membrane
Concentration gradient –
o Due to the plasma membrane’s selective permeability.
o Examples:

Na+

K+
Electrical gradient –
o Typically, the plasma membrane’s inner surface is more __________ charged and the
outer surface is more __________ charged.
o This charge difference is termed the membrane potential.
Electrochemical gradient – the combined influence of the concentration and electrical
gradients on ion movement.
o Example: Na+ movement through a membrane channel
TRANSPORT ACROSS THE PLASMA MEMBRANE
Substances move across the plasma membrane via passive or active membrane transport
processes:
Passive Processes
Active Processes
Direction substance moves
Energy requirements
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Unit 1 Levels of Organization
For definitions of membrane transport processes, see Table 3.1 Transport of Materials Into and
Out of Cells.
Passive Transport Processes - Diffusion
Diffusion –
Several factors affect diffusion rate:
1. Steepness of the concentration gradient
2. Temperature
3. Mass of the diffusing substance
4. Surface area
5. Diffusion distance
3 types of diffusion across the plasma membrane:
Definition
Substances Transported
Simple diffusion
Facilitated diffusion
Osmosis
Water movement (osmosis) can also be expressed with reference to the solute:
o Water moves from areas of __________ solute concentration to areas of __________
solute concentration.
For each of the diagrams, draw an arrow to indicate net water movement (if applicable):
0.5% Solute Solution
0.9% Solute Solution
1.5% Solute Solution
0.9% Solute
Solution
0.9% Solute
Solution
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Solution
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Unit 1 Levels of Organization
Osmotic Equilibrium –
o Equilibrium is reached when water’s hydrostatic pressure on the receiving side of the
membrane is high enough to counteract osmosis.
Osmotic Pressure –
o Osmotic pressure is directly related to solute concentration:

Higher solute concentration = __________ osmotic pressure.

Lower solute concentration = __________ osmotic pressure.
o Osmotic pressure describes a solution’s tendency to draw water into it:

Higher osmotic pressure = __________ tendency to draw water in.

Lower osmotic pressure = __________ tendency to draw water in.
Tonicity –
o Three types of solutions:
1. Isotonic
2. Hypertonic
3. Hypotonic
Hypertonic
Isotonic
Hypotonic
Solute concentration
Osmotic pressure
Net water
movement
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Red River College
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Unit 1 Levels of Organization
What happens to a red blood cell (0.9% solute) when it is suspended in an isotonic saline
solution? _______________.
What happens to a red blood cell (0.9% solute) when it is suspended in a hypertonic saline
solution? _____________________________________. This is called _____________________.
What happens to a red blood cell (0.9% solute) when it is suspended in a hypotonic saline
solution? _____________________________________. This is called _____________________.
See Figure 3.9 Tonicity and its effects on red blood cells.
Active Transport Processes
Active transport processes move substances across the plasma membrane against their
chemical or electrical gradients; ATP is always required.
Active membrane transport processes include:
1. Primary active transport
2. Secondary active transport
3. Endocytosis
4. Pinocytosis
Definition
Substances Transported
Primary active transport
Secondary active transport
Endocytosis
Pinocytosis
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Unit 1 Levels of Organization
CYTOPLASM
Cytoplasm is divided into 2 components:
o Cytosol
o Organelles
Types of Organelles (use Table 3.2 to complete the chart):
Part
Structure
Functions
Cytoskeleton
Centrosome
Cilia and
flagella
Ribosome
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Golgi complex
Lysosome
Peroxisome
Mitochondrion
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Unit 1 Levels of Organization
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