1.6 Cell division
∑ - Understandings:
∑ - Mitosis is division of the nucleus into two genetically identical daughter nuclei.
∑ - Chromosomes condense by supercoiling during mitosis.
∑ - Cytokinesis occurs after mitosis and is different in plant and animal cells.
∑ - Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm.
ß - Skill: Identification of phases of mitosis in cells viewed with a microscope or in a micrograph.
Mitosis Description
Diagrams
Prophase
Metaphase
Anaphase
Telophase
interphase prophase metaphase anaphase telophase
http://www.clt.astate.edu/mhuss/mitosis1.jpg
ß - Skill: Determination of a mitotic index from a micrograph.
The Mitotic index = number of cells containing visible chromosomes (in mitosis) divided by the total number of cells in field of view.
Complete Lab Practical 1 on “Stages of Mitosis in a Garlic Bulb Root Tip”
∑ - Cyclins are involved in the control of the cell cycle.
http://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Cyclin_Expression.svg/800px-Cyclin_Expression.svg.png
Cyclin D – causes G0 to move to G1 and G1 to move to S phase
Cyclin E – causes the cell to prepare for replication in S phase
Cyclin A – activates DNA replication in S phase
Cyclin B – causes the mitotic spindle to begin to form and other tasks needed in the preparation of mitosis
∑ - Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours.
Applications and skills:
Application: The correlation between smoking and incidence of cancers.
A correlation is a relationship between two variable factors
There is a strong positive correlation between smoking and cancer
Surveys have shown that the more cigarettes that one smokes per day, the higher the death rate due to cancer.
The main cancers involved are cancer of the mouth, pharynx, larynx, esophagus and lungs
http://islaslab.blogspot.ca/2014_04_01_archive.html More detailed tables in your text
1.1 Introduction to Cells
∑= IB Understandings
Cell Theory
The main part of cell theory consists of three main aspects:
1) Cells are the basic unit of structure in all living things (smallest unit of life)
2) All living organisms are composed of cells.
3) New cells are formed from pre-existing cells.
The two scientists given credit to the first two parts of cell theory are Theodor Schwann and Matthias Schlieden (1839).
Rudolf Virchow came up with the 3rd aspect that all cells come from pre-existing cells.
4) More recently, scientists have added another aspect of the cell theory that states “All cells contain hereditary information (DNA) which is passed on from cell to cell during cell division”
∑ According to the cell theory, living organisms are composed of cells.
Over the years many living organisms, both unicellular and multicellular, have been studied under microscopes and all have been found to be composed of cells.
Cells vary extensively in size and shape but contain certain commonalities such as a cell membrane, genetic material, chemical reactions catalysed by enzymes and the production of energy (ATP) through respiration.
Applications and skills: ß
ß Application: Questioning the cell theory using atypical examples, including striated muscle, giant algae, and aseptate fungal hyphae.
Exceptions to General Cell Structure
Fungal Cells can have multiple nuclei (multi-nucleated).
Fungi have cell walls made out of chitin surrounding threadlike structures called hyphae
Aseptate hyphae are one long continuous cell that is not separated by dividers called septa and therefore have many nuclei
Striated muscle cells are made up of contractile filaments that slide past each other. They have a single surrounding membrane but can contain possibly 100’s of nuclei.
Giant algae – Some uncommon algae exist that can actually grow up to approximately 1 cm. An example of this is Acetabularia, which is a genus of green algae. One would expect a cell of this size would consist of many cells, as it would have difficulty getting rid of metabolic waste.
Extra example
Red Blood Cells are biconcave disks that carry oxygen to different tissues.
RBC lack a cell nucleus, cellular organelles and cannot synthesize protein
http://arquivosilva.blogspot.ca/2012/08/acetabularia-desafia-genes.html
ß - Skill: 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. (Practical 1)
**This lab skill could be completed at the same time as the investigation of the paramecium and euglena.**
Using the formula
Magnification = size of the image/actual size of the specimen
Size of the image is how large a specimen appears in a photograph or a drawing.
The actual size of the specimen simply means how big the specimen actually is.
Calculate Magnification:
Scale bars are also used on many micrographs (photographs under a microscope), using a line to represent the actual scale or size of the image.
The scale shows that half of a red blood cell is about 3 µm
Actual image size is therefore based on the scale bar. You can then measure the size of the image with a ruler, convert the result into µm’s and calculate magnification.
Note: The size of objects in digital images of microscope fields could be analysed using graticule baselines and image-processing software.
***Complete introduction to microscope activity on the use of microscope, drawing cells and cell structure and calculating magnification***
Complete data based questions on page 6 and 7 of your textbook.
∑ Organisms consisting of only one cell carry out all functions of life in that cell.
a) Metabolism – the chemical reactions that occur in organisms in order for them to maintain life, such as the synthesis of ATP during cellular respiration.
b) Response – organisms respond to their environment.
c) Homeostasis – maintaining a stable internal environment within the cell.
d) Growth – increase in size (volume and surface area) until the cell is too large to function efficiently.
e) Reproduction – the majority of prokaryotes reproduce through binary fission while single cell eukaryotes reproduce generally asexually, however some can also reproduce sexually through meiosis and then mitosis.
f) Nutrition – creating or synthesizing their own organic molecules or consuming organic molecules.
∑ Surface area to volume ratio is important in the limitation of cell size.
Side Length | SA (cm²) | Volume (cm³) | SA/Volume Ratio |
---|---|---|---|
1 | 6 | 1 | 6:1 |
5 | 150 | 125 | 1:2:1 |
10 | 600 | 1000 | 3:5 |
100 | 60,000 | 1,000,000 | 3:50 |
1000 | 6,000,000 | 1,000,000,000 | 3:500 |
ß - Application: Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.
(Paramecium and Euglena can be observed with a light microscope)
Paramecium
Showing paramecium movement, feeding and other life processes
https://www.youtube.com/watch?v=WFpBRfLtbIo
Euglena
Showing flagellum movement of the Euglena
https://www.youtube.com/watch?v=jl0TzaWUQWk&feature=endscreen
∑ Multicellular organisms have properties that emerge from the interaction of their cellular components.
∑ Specialized tissues can develop by cell differentiation in multicellular organisms.
∑ Differentiation involves the expression of some genes and not others in a cell’s genome.
∑ 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.
Bone Marrow Transplants
Non-therapeutic uses include creating meat (muscle fibres) for human consumption that has been grown in a lab.
https://www.youtube.com/watch?v=2o0MCZwL_VE
https://www.youtube.com/watch?v=QO9SS1NS6MM
ß - Application: Use of stem cells to treat Stargardt’s disease and one other named condition.
http://www.bbc.co.uk/news/health-15025009
https://www.youtube.com/watch?v=zPvaVLNrvrc
ß - Application: Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby and from an adult’s own tissues.
The sources of stem cells are as follows:
Embryonic stem cells – fertilize the egg with sperm, fusion forms a zygote, the cell will now divide by mitosis till it is about 12-16 cells. These are all embryonic stem cells. They can differentiate into any cell type but have a higher risk of becoming tumour cells. There is also less chance that the cells have genetic damage as they are very new and don’t have time to accumulate mutations like adult stem cells.
Documentary on understanding embryonic stem cells
https://www.youtube.com/watch?v=nYNBNZJ8Xck
Umbilical Cord Stem Cells – stem cells obtained from the cord, can be frozen and used later on in life. These are easily obtained and stored after birth.
https://www.youtube.com/watch?v=C4rYL0frngM
(Good video on cord stem cells)
Adult Stem Cells – obtained from some adult tissue such as bone marrow. They are difficult to obtain and have less growth potential and limited capacity to differentiate when compared to embryonic stem cells; however, they are fully compatible with adult’s tissue (no rejection) and there is less chance for a malignant tumour to occur.
https://www.youtube.com/watch?v=w9wIxe4WGFg
(Adult Stem Cells cure blindness video)
Ethical Concerns
1.4 Membrane transport
∑ - Understandings:
∑ - Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
https://www.youtube.com/watch?v=Ptmlvtei8hw&t=11s
∑- The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
Endocytosis
Exocytosis
Video showing endocytosis and exocytosis
https://www.youtube.com/watch?v=K7yku3sa4Y8
Diagram of Endocytosis and Exocytosis (to the right)
Applications and skills:
ß - Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
http://bio1151.nicerweb.com/Locked/media/ch07/pump.html
http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
***Using your textbook and the online resource, create a diagram explaining the steps of active transport of sodium and potassium and the use of the facilitated diffusion of potassium ions in axons during nerve impulse transmission.***
ß - Application: 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.
Hypertonic solution – Is a solution with higher osmolarity (higher solute concentration) than the other solution. If cells are placed into a hypertonic solution, water will leave the cell causing the cytoplasm’s volume to shrink and thereby forming indentations in the cell membrane.
Hypotonic solution – Is a solution with lower osmolarity (lower solute concentration) than the other solution. If cells are placed in a hypotonic solution, the water will rush into the cell causing them to swell and possibly burst.
Both of the above solutions would damage cells, therefore isotonic solutions are used (same osmolarity as inside the cell)
Isotonic solution: A solution that has the same salt concentration as cells and blood.
In medical procedures, isotonic solutions are commonly used as
1) Intravenously infused fluids in hospitalized patients.
2) Used to rinse wounds and skin abrasions
3) Saline eye drops
4) Packing donor organs for transport (frozen to slush)
5) During skin grafts, used to keep the damaged area moist
(normal saline is approx. 300 mOsm)
ß - Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)
Osmolarity of Potato or Yam Cores Lab
1.5 The Origin of Cells
∑ - Understandings:
∑ - Cells can only be formed by the division of pre-existing cells.
∑ - The first cells must have arisen from non-living material.
1) Production of carbon compounds such as amino acids and sugars. Miler and Urey’s experiment showed how this could happen by passing water vapour through Ammonia, methane, and hydrogen (early earth atmosphere). They added electricity to simulate lightning discharge. They found they could create amino acids and carbon compounds
2) Assembly of carbon compounds into polymers might have occurred at the deep-sea hydrothermal vents, which could have supplied the inorganic compounds such as iron sulphide and thermal energy for the assembly
3) Formation of membranes would be possible if phospholipids were some of the first polymers created. These phospholipids would naturally form vesicles allowing for a different environment to exist inside compared to the surrounding water
4) Development of a mechanism for inheritance would be needed in order for the organism to replicate and pass its DNA on to the next generation. Current organisms need enzymes to replicate DNA; however, enzymes are created by the genes on the DNA. A possible solution to this would be RNA being the first nucleic acid formed because it is self-replicating and can also act as a catalyst.
∑ - The origin of eukaryotic cells can be explained by the endosymbiotic theory.
Diagram is to the right -->
http://learn.genetics.utah.edu/content/cells/organelles/
Applications and skills:ß - Application: Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth.
Pasteur's Experiment
The steps of Pasteur's experiment are outlined below:
First, Pasteur prepared a nutrient broth similar to the broth one would use in soup.
Next, he placed equal amounts of the broth into two long-necked flasks. He left one flask with a straight neck. The other he bent to form an "S" shape.
Picture 1 to the right
Images courtesy William Harris
Then he boiled the broth in each flask to kill any living matter in the liquid. The sterile broths were then left to sit, at room temperature and exposed to the air, in their open-mouthed flasks.
Picture 2 to the right
Images courtesy William Harris
After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.
Picture 3 to right
Images courtesy William Harris
He concluded that germs in the air were able to fall unobstructed down the straight-necked flask and contaminate the broth. The other flask, however, trapped germs in its curved neck, preventing them from reaching the broth, which never changed color or became cloudy.
Picture 4 to the right
Images courtesy William Harris
Taken from http://science.howstuffworks.com/innovation/scientific-experiments/scientific-method5.htm.
1.3 Membrane structure
Understandings: ∑
∑ - Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
Hydrophilic and Hydrophobic Properties | |
|
∑ - Membrane proteins are diverse in terms of structure, position in the membrane and function.
Hormone binding sites (receptor proteins)
Proteins embedded in the membrane, which bind to specific hormones.
When the hormone binds, it causes the receptor protein to undergo a conformational change, which signals the cell to perform a function.
For example, insulin receptors.
Immobilized Enzymes
Integral proteins that catalyze specific chemical reactions.
Many of these enzymes catalyze metabolic reactions or are a part of a metabolic pathway, such as ATP Synthase in aerobic respiration.
Cell Adhesion
Proteins that form tight bonds between adjacent cells in tissues and organs.
For example, gap junctions.
Cell-to-cell communication
Receptors for neurotransmitters at synapses between two nerve cells.
Glycoproteins on the surface can also be used for cell identification purposes.
Channels for passive transport
Integral proteins that span the membrane and provide a passageway for molecules to move from an area of high concentration to low concentration.
Specific proteins are also used for facilitated diffusion.
Pumps for Active Transport
Proteins that use ATP to move substances from a low concentration to a high concentration across the membrane.
For example, Sodium/Potassium (Na+/K+) pumps and the proton (H+) pumps
∑ - Cholesterol is a component of animal cell membranes.
Applications and skills: ß
ß - Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.
ß - Skill: Drawing of the fluid mosaic model.
ß - Skill: Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model.
ß - Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model.
Davson and Danielli proposed a the theory that the lipid bilayer was coated on either side with a layer of globular proteins (as seen below)
Using your text, the web and the library analyze the evidence and the falsification of the Davson-Danielli model of the cell membrane by completing the analysis on page 26-27 in your text. Type your paragraph here.
IBWorld.me
IB Biology - Curriculum Notes
1.2 Ultrastructure of cells
∑ = Understandings:
The next two understandings point are basically asking to compare and contrast prokaryotes and eukaryotes (previous syllabus) but with a focus on compartmentalization. The following goes with the comparison in the table below.
∑ Prokaryotes have a simple cell structure without compartmentalization.
All prokaryotes have a cell membrane and a cell wall surrounding the outside membrane. The cell wall is made from peptidoglycan. The entire interior of the cell is filled with cytoplasm (not compartmentalized) as no membrane-bound nucleus is present.
∑ Eukaryotes have a compartmentalized cell structure.
Eukaryotes have a much more complicated cellular structure. The inside of the cell also contains cytoplasm but it is separated by compartments that allow for specialization. The compartments are membrane bound organelles such as the nucleus and the mitochondria. Some advantages of compartmentalization are
1) Enzymes that serve a specific function or catalyze a specific reaction can be concentrated within the compartment instead of being spread throughout the cytoplasm.
2) Ideal conditions or particular processes can be maintained within the compartments such as pH
3) Organelles with their content can be moved around the cell
4) Damaging substances such as digestive enzymes (lysosome) can be contained within their organelle.
Comparison between prokaryotic cells and eukaryotic cells
Prokaryotic Cells | Eukaryotic Cells |
Small - less than 10µm | Larger cells – greater than 10 µm |
DNA free within the cytoplasm | DNA contained within the nucleus |
DNA in a ring free of proteins (naked DNA) | DNA associated with proteins |
No membrane bound organelles | Membrane-bound organelles |
No mitochondria | Mitochondria present |
70s ribosomes | 80s ribosomes |
No internal compartmentalization to form organelles | Internal membranes that compartmentalize their functions |
Reproduction through binary fission | Reproduction through mitosis and meiosis |
∑ Electron microscopes have a much higher resolution than light microscopes.
∑ Prokaryotes divide by binary fission.
ß - Skill: Drawing of the ultrastructure of prokaryotic cells based on electron micrographs
Micrograph on the right
Applications and skills: ß
ß - Application: Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of the leaf.
Exocrine Gland Cells of the Pancreas
Here are the specific details of the functions of a eukaryotic animal cell
Ribosomes
Golgi Apparatus
Nucleus
Mitochondria
Rough endoplasmic reticulum (rER)
Lysosome
ß - Palisade Mesophyll cells carry out most of the photosynthesis in the leaf.
ß - Skill: Drawing of the ultrastructure of eukaryotic cells based on electron micrographs.
ß - Skill: Interpretation of electron micrographs to identify organelles and deduce the function of specialized cells.
Identify as many structures and organelles you can from the two micrographs below. Also, practice with the 3 micrographs in your book on page 25
Animal cell Plant Cell