Topic 2: Cells 2.1 Cell Theory

2.1.1 Outline the cell theory The cell theory states that: All living organisms are made of cells Cells are the smallest unit of life Cells only come from pre-existing cells Modern additions to the cell theory include: Cells contain information for growth, development and behavior Cells are the site for the chemical reactions of life (metabolism) (Not yet in the IB curriculum) bitesizebio.com/.../05/history-of-cell-biology/

2.1.2 Discuss the evidence for the cell theory All living things are made of cells: When living things are observed under the microscope they consistently appear to be composed of cells. Cells are the smallest unit of life. The cell is the smallest unit of organization that can show all the characteristics of living processes. Organelles often require the cooperation of other organelles for their successful function.

2. 1. 1 Outline the cell theory 2. 1 2.1.1 Outline the cell theory 2.1.2 Discuss the evidence for the cell theory Cells come only from other cells. Where do cells come from? Cells carry out a form of cell division to form new cells. This process of cell replication in eukaryotes is called mitosis and in prokaryotes is called binary fission. The parental cell divides to produce identical daughter cells. This aspect of cell theory suggests that all cells therefore have a common ancestor, the original ancestral cell form which all other cells have arisen by descent. (origin of cellular life). This relationship of common ancestor suggest that all organisms came from the very first cell.

2.1.3 State that unicellular organisms carryout all the functions of life One-celled organisms (unicellular organisms) are able to carryout all the functions of life The functions of life include: metabolism – respiration and excretion response – to a stimuli growth – increase in cell size reproduction – sexual or asexual homeostasis – maintain a stable internal environment nutrition – the source of food http://www.micrographia.com/specbiol/protis/homamoeb/amoe0100/amoeba23.jpg

2.1.4 Compare the relative size of molecules, cell membrane thickness, viruses, bacteria, organelles and cells using appropriate SI units • A micrometer (μm) is one millionth of a meter 10-6 m 1000μm = 1mm or • A nanometer (nm) is a billionth of a meter 10-9 m click4biology.info

2.1.4 Compare the relative size of molecules, cell membrane thickness, viruses, bacteria, organelles and cells using appropriate SI units Take this cool little interactive journey to get an idea for how small things really are. And this interesting video, narrated by Morgan Freeman, gives us a real feel for the scale of the universe and “micro-verse”.

magnification = size of the image (measured) / real size (scale bar) 2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications Magnification – the number of times larger the image (picture) is than the specimen If you are using a compound microscope and the eye piece magnification is 10x and the objective lens is 10x, than the image is magnified 100x http://www.bio12.com/ch16/IBExcretion/table4.GIF magnification = size of the image (measured) / real size (scale bar) real size (scale bar) = size of image (measured) / magnification

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnifications

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size Why are cells so small? Cells are small because it is easier to exchange materials between the cytoplasm and the environment If a cell is too large, diffusion becomes very difficult and inefficient Because the uptake of resources and the removal of waste must pass through the cell membrane it is important that it doesn't have to travel a long distance

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size Organisms have different ways to cope with surface area to volume ratio problems Flat worms increase surface area by being flat The villi in the intestines help with absorbing nutrients The alveoli in the lungs help with gas exchange by increasing the surface are to volume ratio Image of nudabranch: richard-seaman.com

2.1.7 State that multi-cellular organisms show emergent properties Definition – the whole is more than the sum of its parts An organism can do more than what each cell can do individually Example – the human brain

2.1.8 Explain that cells in multi-cellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others Every cell in your body contains the exact same genetic information. Why are the cells that make up your hair very different from the cells that make up your brain? Some information is expressed (turned on) and some is not expressed (turned off) In the nucleus the genetic information exists in two forms (euchromatin and heterochromatin) euchromatin is the part of the genetic information of the cell that is expressed heterochromatin is not expressed

2.1.8 Explain that cells in multi-cellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others Cells have an effect on their neighboring cells and determine what information will be expressed and what kind of cell it will be (through chemical gradients and positioning) www.ncbi.nlm.nih.gov

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways Stem cells are characterized in three ways: they are unspecialized and can be any type of cell they are self replicating (renew) They can continue to divide into new cells for a long period of time Sources of stem cells include: Embryos Umbilical cord Bone marrow

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways Controversy Against Embryonic stem (ES) cells are a source of controversy because the cells are obtained from fertilized embryos (for example, fertility treatments and the embryos are then discarded) For Stem cells may be a way to grow new cells and treat diseases like Alzheimer's, Parkinson's, Type I diabetes, etc...

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways Some terms Totipotent stem cells from embryos that can become any type of cell Pluripotent stem cells that can be any type of tissue Multipotent Stem cells (usually from the umbilical cord) that can become a limited type of different cells www.prayersforthepeople.com/id70.html

2.1.10 Outline one therapeutic use of stem cells Can be used for burn victims to “re-grow” skin The nucleus of a blastocyst cell is removed The nucleus of the patients cell (in this case, skin cell) is transplanted into the blastocyst cell The cells are then grown in a Petri dish and then transplanted back to the patient In some cases, the embryonic cell can be “genetically triggered” to produce the desired cell