Unit 2 - San Francisco de Paula, Science Department.
Topic 1 Cells 1.1 Introduction to cells IB Biology SFP - Mark Polko Nature of science Looking for trends and discrepanciesalthough most organisms conform to cell theory, there are exceptions. (3.1) Ethical implications of researchresearch involving stem cells is growing in importance and raises ethical issues. (4.5) Understandings: According to the cell theory, living organisms are composed of cells. Organisms consisting of only one cell carry out all functions of life in that cell. Surface area to volume ratio is important in the limitation of cell size. 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 cells 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. IB Biology SFP - Mark Polko 2 Applications and skills Application: Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae. Application: Investigation of functions of life in Parameciumand one named photosynthetic unicellular organism. Application: Use of stem cells to treat Stargardts disease and one other named condition.
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 adults own tissues. 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) Essential idea: Eukaryotes have a much more complex cell structure than 3 prokaryotes. IB Biology SFP - Mark Polko Introduction The cell is the basic unit of live, so everything that is alive is made out of at least one cell. Cells carry out the essential processes of life, so they are self contained units of structure and function. It is difficult to imagine the size of cells as almost all are invisible to the
naked eye. They vary in size from 100m (a tenth of a millimeter) to 1m (a thousanth of a millimeter). Just visible IB Biology SFP - Mark Polko 4 Introduction IB Biology SFP - Mark Polko 5 The Scale of the Universe IB Biology SFP - Mark Polko 6
Introduction The cell is the basic unit of matter, so everything that is alive is made up out of at least one cell. The first observations of cells were reported about 300 years ago when microscopes were invented. (Off course a Dutch invention). The microscopes we use in the lab are compount light microscopes, you can magnify objects up to 1000x their size. There are also electron microscopes, they can maggnify up to 100 000x. IB Biology SFP - Mark Polko 7 Introduction The features of cells Although cells vary much in size and shape they all have some features in
common: - Every living cell is surrounded by a membrane, which separates the cells contents from is surroundings. - Cells contain genetic material which stores all of te instructions needed for the cells activities (including reproduction) - Many of these activities are chemical reactions, catalyzed (speeded up) by enzymes produced inside the cell. - Cells have their own energy release system that powers all of the cells activities. So again, remember that cells can be thought of as the smallest living structures, nothing smaller can survive.
IB Biology SFP - Mark Polko LINK 8 Introduction Uni and multicellular organisms There are some organisms which are made up of one one cell, actually most are. Those organisms are called unicelular organisms. Do you know any examples? The most commonly known are: - Amoeba (eukaryoptic) - Bacteria like E. coli (prokariotic) - Some algae (eukaryotic) Examples of multicellular organisms are all animals and plants. IB Biology SFP - Mark Polko
9 Activity Take some time to read the exceptions to the cell theory on page 3 of your book. Make a short summary in your notebook. And search on the internet for an exception to the cell theory which you explain in class. IB Biology SFP - Mark Polko 10 Introduction The functions of life All organisms exist either in a unicellular or a multicellular form. And all organisms carry out all functions of life. These functions
include: - Metabolism. Includes all chemical reactions which occur in an organism. - Growth. Growth may be limited but is always evident in one way or another. - Reproduction. Involved hereditary molecules that can be passed on to offspring. - Response. Response to the environment is imperative to the survival of the organism. - Homeostasis. Refers to maintaining a constant internal environment, like temperature or acid-base levels. - Nutrition. Is all about providing a constant source of IB Biology SFP - Mark Polko 11 Introduction
Limitation on cell size The size of a cell is limited by its need to exchange materials with its environment. If a cell becomes too large, its diffusion distance becomes too long to be efficient and its surface to volume ratio becomes too small to allow the necessary exchange. The surface area is larger than the volume. The surface are is smaller than the volume. Surface to volume ratio = 6:1 Surface to volume ratio = 0,6:1 IB Biology SFP - Mark Polko 12 The rate with which a cell produces heat/waste and consumes
resources (food/oxygen) is directly proportional to its volume. However, since the uptake of resources and the removal of heat/waste goes via the cell membrane, the rate of uptake/removal is proportional to its surface area. The surface area is larger than the volume. Surface to volume ratio = 6:1 The surface are is smaller than the volume. Surface to volume ratio = 0,6:1 So a volume of 1cm3 has a surface area of 6 cm2 in the small cube, and a volume of 1cm3 in the big cube only of 0.6cm2, so a tenth the amount. IB Biology SFP - Mark Polko
13 ome statements regarding surface area to volume ratio: - as size increases both surface area and volume increase, but volume increases more - ratio of surface area to volume decreases as size of cell increases - rate of metabolism is a function of its mass to volume ratio - surface area limits/affects the rate at which substances can enter (or leave) the cell. - volume determines the rate at which material is produced/used - oxygen/nutrients/substances will take too long to diffuse into/out of the centre of the cell if it is too big - excretory products would take too long to be eliminated - heat will take too long to be eliminated example of cell adaptation to increase the ratio of surface area:volume e.g. root hair cell; IB Biology SFP - Mark Polko
14 Ways of dealing with volume surface area ratios. Increasing the surface area is the best way to facilitate a proper diffusion of substances through the cell membrane. Cells do that by: - Having protruding extensions For example the epithelium of the gut has small extensions to increase the surface area and facilitate the absorption of substances in the blood. - Flattening the cells. This makes the diffusion distance much smaller, like
the muscle cells on the image. Link to image IB Biology SFP - Mark Polko 15 Check out this animation to understand the concept a bit better LINK IB Biology SFP - Mark Polko 16 Multicellular organisms Multicellular organisms have properties that emerge from the interaction of their cellular components.
Unicellular organisms can live in colonies (see page 10) but for an organisms to be considered multicellular when they are composed of a mass of cells fused together. IB Biology SFP - Mark Polko 17 Activity Read page 10 and 11 of your book on emergent properties. Explain in class about the Caenorhabditis elegans. Do you know any other examples of emergent properties in multicellular organisms? IB Biology SFP - Mark Polko 18 Emergent properties
are those where the whole is more than the sum of their parts. A termite can not live alone, only with the cooperation of thousands they can survive. LINK The same counts for the neuron, millions are needed to make the brain operational. Link to image The levels of life can also be considered emergent properties. Each level emerges form a level below.
Organelles cooperate to form cells, cells to form tissues, tissues to form organs, organs to form organ systems, organs systems to form the organism. Link to image IB Biology SFP - Mark Polko 19 Emergent properties are those where the whole is more than the sum of their parts. Multicellular organisms show emergent properties. This means that the organism can achieve more than the sum of what each cell could achieve individually. This is caused by the fact that cells
interact, allowing them to perform tasks together that they not achieve, even in part, if they were alone. IB Biology SFP - Mark Polko 20 Cell differentiation Different cells perform different functions, a red blood cell carries oxygen, a muscle cell contracts and a nerve cell send impulses. A group of cells with the same function is called a tissue. Cells duplicate by the process of mitosis. As you have learned before, mitosis ends with two exact copies of the mother cell. Remember that your life has started as just one first cell, the zygote. That cell divided, copying the same DNA over and over again to the multicellular creature you are today. So each cell in your body contains exactly the same genetic
information (with the exception of tiny mutations here and there). Still, each tissue has its own function. The development of cells in different ways to carry out specific functions is called differentiation. So clearly your brain is different from your skin, how is this possible? Cell division IB Biology SFP - Mark Polko 21 Gene expression Cells differentiate by expression of some of their genes and not others. The genes which are not expressed by the cell, remain present in the nucleus but are packed away so tightly that they cannot be accessed. Euchromatin is light grey when viewed with an EM,
and heterochromatin is dark grey. Euchromatin often represents the genes that are used (transcribed), while heterochromatin tends to contain the inactive genes. Link to image IB Biology SFP - Mark Polko 22 Gene expression There are 220 different types of cells in your body but all of them have a different function. So when the cells in your eyes need to
make pigment to give the it is its colour, the genes with the information of that pigment will be translated into proteins. If new skin cells need to be made after an injury, the genes with the information to construct them will be translated and new cells are made. So there are 25 000 genes in all your cells, but only some are used. Just like the books in a library, all information is there, nut you only read what you need to know. LINK IB Biology SFP - Mark Polko 23 Stem cells In the early 19th century the name Stem cells was give to a zygote, as
the zygote is the beginning of all other cells of the organism. Stem cells are the cells of an organism that are not specialised for any function. They can multiply actively maintaining that state, and are able to transform into any of the 220 cell types that an adult has (heart, nerve, kidney, etc). Tha capacity of stem cells to divide and differentiate along different pathways is necessary in embrionic development. It also makes stem cells suitable for therapeutic uses. All animals and vegetables possess stem cells in maturity (they can be
obtained from tissues such as bone marrow, the umbilical cord or the liver), but they are abundant in embryos and fetuses. Stem cells were first isolated in 1998 Link to image LINK IB Biology SFP - Mark Polko 24 Stem cells Stem cells are most valuable to science and lots of research is done with the. This is mainly because of their two key properties. Stem cells are different from normal cells in two
ways: 1. Stem cells are undifferentiated. This means that they have not yet specialised into a certain type of cell. As a result, all (or most) of their genes can still be expressed. With the right manipulation, stem cells can become any other type of cell in a lab. 2. Stem cells are self-sustaining. They can divide again and again and replicate for long periods of time to produce new types of cells. They can be used for the growth of new tissue which has been damaged or lost. Theoretically, you could make a stem cell replicate and then differentiate into liver cells and grow a new liver this way. VIDEO IB Biology SFP - Mark Polko 25
Stem cell research In reality, research has only been going on since about 1998 when a group led by Dr. James Thomson at the University of Wisconsin developed a technique to isolate and grow the cells. In some countries, stem cell research is restricted by legal measures. In Denmark, Spain, Sweden and the UK, stem cell research is allowed using cells from embryos less than 14 days old but only Denmark and the UK allow the creation of embryos for research purposes. Research regulations per European country IB Biology SFP - Mark Polko 26 Stem cell research TOK
Non therapeutic use of The therapeutic use of stem cells is stem cells sometimes referred to as cell therapy. In cell therapy, cells that do not work well are replaced with healthy, functioning cells. The most common example of cell therapy is a bone marrow transplant. This technique has been used for more than 40 years. Cells in the bone marrow produce blood cells. People with leukaemia can receive a transplant of healthy, functioning bone marrow which may cure their disease. Here are some examples for stem cell therapy uses: - Brain damage - Deafness - Cancer - Spinal cord injuries
- Heart damage - Blindness - Etc. VIDEO IB Biology SFP - Mark Polko 27 Stem cell research e of stem cells to treat Stargardts disease and one other named condit So far stem cells have not been used often to treat diseases, but lots of research is going on in the area. If you come across something in the news, please discuss it in class! Here are two examples from your book, one which uses embryonic stem cells, the other adult stem cells. Introduction video
Stargardt disease The full name of the disease is Stardgardts Maculas Dystrophy. This genetic disease starts with children between 6 amd 12. It is due to the recessive mutation of a gene called ABCA4. The membrane proteins used for active transport in the retina (we see this later in this topic) malfunctions and the photoreceptive cells in the retina degenerate. Vision become worse and blindness is the outcome. IB Biology SFP - Mark Polko 28 Stem cell research e of stem cells to treat Stargardts disease and one other named condit The treatment Embryonic stem cells have been manipulated to develop into retina cells. First. Like usually, this was done with mice. The mice responded
well, the cells were accepted and no cancers developed. The vision of the mice improvred. So human trials began in 2010. 50 000 retina cells were injected in her eye and succesfully attached, her vision improved in the 4,5 month trial. Still more trials are needed but the scientific world is optimistic. IB Biology SFP - Mark Polko 29 Stem cell research e of stem cells to treat Stargardts disease and one other named condit Leucemia Leucemia is a type of cancer, in this case one which affects the bloodcells. As with alll cancers the cells divide without control and can even start to invade other tissues (metastasis) and become malignant.
Leucemia involves the production of abnormaly large amounts of white blloodcells. To cure leucemia the badly deviding cells in the bone marrow creating these large amount of white bloodcells must be destroyed. This is usually done with chemo therapy (administration of strong and agressive medicines). But after, healthy cells must be present again to continue producing normal cells. LINK IB Biology SFP - Mark Polko 30 Stem cell research e of stem cells to treat Stargardts disease and one other named condit Leucemia The following procedure is used to cure the effects of the chemotherapy:
Stem cells are isolated and stored for later use. Stem cells are taken from the bone marrow The stem cells are returned to the body The patients undergoes IB Biologychemotheraphy SFP - Mark Polko 31 Sources of stem cells
Sources of stem cells and the ethics of using them. Read through page 15 and 16 and have a class discussion about the ethics of the use of stem cells IB Biology SFP - Mark Polko 32 Topic 1 Cells 1.1 Introduction to cells IB Biology SFP - Mark Polko
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