1. Topic 1.1 Review

2. Essential Idea: The evolution of multicellular organisms allowed cell specialization and cell replacement.

3. U1.1.1: According to the cell theory, living organisms are composed of cells.
The cell theory consists of three statements:
All organisms are made of cells.
Cells are the most basic unit of life.
All cells come from pre-existing cells.
Cell theory is the culmination of hundreds of years of research, which has been facilitated by advances in technology.
Light microscope – advantages? Disadvantages?
Electron light microscope – advantages? Disadvantages? Types?
Many scientists contributed to the cell theory.
Hooke
van Leeuwenhoek
Schleiden
Schwann
Pasteur

4. Pasteur’s experiment

5. U1.1.2: Organisms consisting of only one cell carry out all functions of life in that cell.
All cells must carry out the 7 functions of life in order to survive. They are:
Metabolism: all chemical processes in the cell
Growth: expansion in size
Reproduction: passing on of hereditary traits
Response: all organisms respond to stimuli
Homeostasis: the ability to maintain stable internal conditions
Nutrition: the need for organic material for energy/building materials
Excretion : elimination of wastes and toxins

6. U1.1.3: Surface area to volume ratio is important in the limitation of cell size.
Rather than have one large cell, large organisms will be divided into many small cells.
Cells are limited in their size because a certain surface area to volume ratio must be maintained to allow cells to exchange materials efficiently.
The surface area of the cell determines the amount of material that can be exchanged.
The volume of the cell determines the rate of heat and waste production and the rate of resource consumption.
The larger the cell, the lower the surface area: volume ratio. This is inefficient!
In order to increase surface area without greatly increasing volume, cells will increase in-folding or projections.
Remember, folds/wrinkles, projections = more surface area!

7. U1.1.4: Multicellular organisms have properties that emerge from the interaction of their cellular components.
For organisms that are multicellular, the ability of cells to differentiate means they can have emergent properties.
Emergent properties = the sum is more than the parts
Example: mitochondria produce ATP, ribosomes synthesize proteins, the Golgi apparatus sorts, modifies and ships proteins, etc., but all components of the cell work together to allow the cell to function.
At the organismal level, each differentiated cell (nervous, muscle, epithelial, etc.) work together to give the organism functions and abilities that are greater than each individual cell could provide.

8. U1.1.5: Specialized tissues can develop by cell differentiation in multicellular organisms.
Cells can differentiate into many different types of cells, each with different functions (muscle cells, nerve cells, hepatic cells, etc.).
When these cells work together, they form tissues, such as muscle tissue, liver tissue, skin, etc.
Each tissue has its own function, and working together, allow the organism to meet all of the functions of life.

9. U1.1.6: Differentiation involves the expression of some genes and not others in a cell’s genome.
Each cell in an organism has more or less identical DNA.
The totality of the organism’s genes is known as its genome.
What determines the type of cell is which genes of the DNA are expressed. This leads to differentiation.
Once a cell begins to express genes to differentiate into a particular type of cell, it will not change to a different pathway, and is committed.

10. U1.1.7: The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
Stem cells are undifferentiated cells that have the ability to divide into any type of cell.
Human embryos consist of stem cells, and they are essential to ensure that the organism develops the types of cells and tissues needed to survive.
Many types of tissues retain stem cells throughout life, and can differentiate for growth and repair.
Some tissues lack stem cells (nervous tissue, muscle tissue), but there is hope that the therapeutic use of embryonic stem cells can help repair damaged tissue.

11. Examples of therapeutic stem cell use

12. A1.1.1: Questioning the cell theory using atypical examples, including striated muscles, giant algae, and aseptate fungal hyphae.
Theories are always being evaluated and occasionally modified as new evidence is gained.
The cell theory holds true for most living things, but there are a couple of exceptions.
Skeletal muscle: made of muscle fibers, which are extremely long cells that contain many nuclei.
Giant algae: can grow relatively large (~10 cm) so should be made of many small cells, but only contain one nucleus so are considered just one large cell.
Aseptate fungi: much like muscle cells, these fungi contain thread-like hyphae, which are long and thin and contain many nuclei.

13. Exceptions to the cell theory
Giant algae
Aseptate fungal hyphae

14. A1.1.2: Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
All organisms carry out all of the functions of life to survive. Paramecia are heterotrophic single-celled protists found in pond water. There are also many types of autotrophic organisms, such as Chlorella or Chlamydomonas.
Examples of how these organisms carry out life functions:
Nutrition: P – consumes other organisms; C – makes organic material via photosynthesis.
Growth: P – increases in size and biomass by consumption of organic materials from food; C – increases in size and biomass through production of organic material.
Response: P – reacts to stimuli by swimming away from electric charge; C – responds to stimuli by swimming towards light source
Excretion: P – expels CO2 from respiration; C – expels oxygen from photosynthesis
Metabolism: both use enzymes for metabolic processes (building/breaking down)
Homeostasis: both maintain stable internal conditions (expel excess water from contractile vacuoles)
Reproduction: both reproduce either sexually or asexually

15. Paramecium and Chlamydomonas

16. A1.1.3: Use of stem cells to treat Stargardt’s disease and one other named condition.
Stargardt’s macular dystrophy is a disease that destroys photoreceptor cells in the eye, causing blindness. In 2010, a woman had retinal cells derived from embryonic stem cells implanted into her eyes and had improvement in vision.
Blood stem cells taken from human umbilical cords and placentas can be harvested, tissue typed, stored, to be used with a human match following bone marrow destruction by chemotherapy in the treatment of leukemia.

17. A1.1.4: Ethics of therapeutic stem cells from specially created embryos, from the umbilical cord blood of a newborn baby and an adult’s own tissues. (Expect the command terms Discuss or Evaluate).
For:
Suffering will be greatly reduced.
Early embryos are just balls of cells.
Early embryos lack a nervous system and can’t feel pain.
If the embryos are produced deliberately, then no individual would’ve been denied a chance at life.
Large numbers of embryos produced by IVF (in vitro fertilization) will never be implanted, so let’s use them for science instead.
Against:
An embryo is a human life, and harvesting the stem cells kills the embryo.

18. S1.1.1: Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells. Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs.
Remember to bring a ruler and a basic calculator for the exam!
Magnification = size of image (measured w/ ruler) ÷ actual size of object (use scale bar)
Actual size = Size of image (w/ruler) ÷ magnification
Remember to convert units; if given μm and mm, choose one! mm = 1,000 μm

19. Topic 1.4 Review

20. Essential idea: Membranes control the composition of cells by active and passive transport.

21. U1.4.1: Particles move across membranes by simple diffusion, facilitated diffusion, osmosis, and active transport.
There are two ways that movement across the membrane can be classified: passive or active.
For passive transport, there are three different types of movement:
Simple diffusion
Osmosis
Facilitated diffusion
No matter which type of passive transport is done, it will always satisfy two conditions:
No energy on the part of the cell is invested
Molecules will move down their concentration gradient (from high concentration to low concentration)

22. Types of passive transport
Simple diffusion
Solutes move through the membrane directly
Solute must meet one of three conditions
Small
Uncharged (no ions)
Nonpolar
Solutes will move down their gradients, regardless of the concentration of other solutes
Osmosis
The diffusion of water ONLY
Water will move down its gradient; the movement will be from high water to low water concentration, OR from low solute to high solute concentration

23. S1.4.1: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions.
Solutions can be classified in one of three ways, according to their solute concentrations:
Hypertonic – high solute concentration; salt water or sugar water
Hypotonic – low solute concentration; distilled water
Isotonic – same concentration of solutes inside and outside of the cell
Water will always move from a hypotonic solution to a hypertonic solution. In isotonic solutions, water reaches a dynamic equilibrium.
It is possible to estimate the osmolarity (total concentration of solutes) of a tissue by determining its mass before and after immersion in solutions of known osmolarities.

25. A1.4.2: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
Animal cells can be damaged by osmosis. It’s important to place tissues in isotonic solutions.

26. Facilitated diffusion
If a molecule is too large, polar, or charged, then facilitated diffusion will allow the passage of the molecule into/out of the cell.
Facilitated diffusion requires two things:
A transport protein
A concentration gradient
Transport proteins can come in two varieties:
Protein channels
Gated channels

27. Active transport
Active transport is the movement of molecules against their concentration gradient (from low conc. to high conc.).
Active transport has two requirements:
Energy investment in the form of ATP
A protein pump
A cell will do active transport to maintain homeostasis or concentration gradients.

28. A1.4.1: Structure and function of sodium-potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
Sodium-potassium pumps follow a cycle events that leads to repolarization of the membrane of neurons.
Three Na+ ions attach to the inside of the pump from the cytoplasm.
1 ATP molecule transfers a phosphate group to the pump, causing a conformation change.
The pump opens to the outside of the cell, releasing the Na+ ions. Two K+ ions will attach to the pump, which will reopen toward the inside of the neuron, sending the K+ ions toward the interior.
Potassium and sodium can also move passively through the membrane of neurons through ion-specific channels.

29. Na – K pump and potassium channels

30. U1.4.2: The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis.
There are two mechanisms in which cells will move substances into and out of the cell
Endocytosis – taking materials into the cell
Exocytosis – pushing materials out of the cell
Endocytosis allow the cell to bring in large materials, materials in bulk, as well as water.
Exocytosis will remove metabolic waste products.
Both endo- and exocytosis involve the use of vesicles, and require ATP.

31. U1.4.3: Vesicles move materials within cells.
Vesicles are small sac-like objects used to transport materials within the cell.
The steps of endocytosis:
Cell either reaches out or pinches inward at the membrane
This segment of the membrane pinches off and forms a vesicle
This vesicle can then move about the cell, or be broken down by lysosomes
Exocytosis is similar:
The vesicle moves toward the membrane
The vesicle will fuse with the membrane
The contents of the vesicle will be pushed out of the cell

32. Endocytosis and exocytosis

33. Topic 1.6 Review

34. Essential idea: Cell division is essential but must be controlled.

35. U1.6.1: Mitosis is the division of the nucleus into two genetically identical daughter nuclei.
Mitosis is the process by which the cell will divide the contents of its nucleus.
This process is followed by cytokinesis, which is the division of the cytoplasm and its contents.
The end result of mitosis is 2 genetically identical daughter cells.
Mitosis is used for a variety of functions, including growth, development, repair, and asexual reproduction.

36. Mitosis

37. U1.6.2: Chromosomes condense by supercoiling during mitosis.
In order to effectively move DNA around during mitosis, it is essential that it first be condensed into chromosomes.
This is accomplished by supercoiling.
The DNA will first wrap around histone proteins, which produces nucleosomes. These will then further condenses into solenoids
Solenoids will group together into looped domains and then coil further into chromosomes.

38. Supercoiling of DNA

39. U1.6.3: Cytokinesis occurs after mitosis and is different in plant and animal cells.
Cytokinesis is the division of the cytoplasm and its contents and begins during late telophase.
The process differs depending on whether the cell is from a plant or an animal.
For animals, a contractile ring of actin will form in between the two cells. The loop will gradually contract, forming a cleavage furrow on the surface of the cell. Eventually the loop will close far enough to split the cell into two separate cells.
For plant cells, a cell plate will form between the two cells. This forms as a result of vesicles carrying cellulose. These segments of cellulose will fuse, forming the cell plate, which will extend in both directions until it forms the fourth wall of the plant cells’ cell walls.

40. Cytokinesis in plant and animal cells

41. U1.6.4: Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.
The longest portion of the cell cycle is known as interphase. It consists of three smaller phases:
Gap 1 (G1)
Synthesis (S)
Gap 2 (G2)
During Gap 1, the cell is undergoing normal growth and function.
During Synthesis, the cell will replicate its DNA in preparation for nuclear division (mitosis).
During Gap 2, the cell will continue to grow and prepare for mitosis, including an increase in organelles and cytoplasm. Additionally, the DNA will begin to condense into chromosomes in preparation for mitosis.

42. The Cell Cycle

43. U1.6.5: Cyclins are involved in the control of the cell cycle.
In order to control the various aspects of the cell cycle, there are two main categories of proteins: cyclins and kinases.
Kinases are a form of enzyme that activate or inactivate other proteins required for passing through the various checkpoints of the cell cycle. They are inactive until they combine with the cyclins. Because of this, they are known as cyclin-dependent kinases (CDKs).
The kinases are present in a more or less constant concentration in the cell, while the cyclin concentration varies throughout the cycle.

44. The role of cyclins and kinases

45. U1.6.6: Mutagens, oncogenes, and metastasis are involved in the development of primary and secondary tumors.
Some genes may mutate, or have a spontaneous change of the DNA sequence.
The genes that lead to the development of tumors are called oncogenes. The mutations in these oncogenes leads to a loss of the regulatory mechanisms of the cell cycle, resulting in cancer.
There are two types of tumors:
Primary – also known as benign, these tumors form but remain localized at the site of formation
Secondary – also known as malignant, these tumors will break away, or metastasize, from the original site, and affect other regions of the body
Mutagens are any substance that leads to the development of a mutation. Examples include cigarette smoke, UV radiation, and x-rays.

46. A1.6.1: The correlation between smoking and incidence of cancers.
There is a strong positive correlation between smoking and the development of cancers, especially cancers of the lungs, trachea, and bronchi.

47. A1.6.2: Identification of phases of mitosis in cells viewed with a microscope or in a micrograph.

48. S1.6.1:Determination of a mitotic index from a micrograph.
The mitotic index is the ratio of cells in mitosis vs. those in interphase.
Mitotic index = # of cells in mitosis/total # cells
A tissue with cancer will have a higher mitotic index than normal tissue.
Aggressive cancers will have higher mitotic indices than less aggressive cancers.
A high mitotic index can lead to a less optimistic prognosis than a lower index.
Example: There are 1200 cells in a field of vision. Of these 1200, are in interphase. What is the mitotic index?