Essential idea: The evolution of multicellular organisms allowed cell specialization and cell replacement. Nature of Science Looking for trends and discrepancies— although most organisms conform to cell theory, there are exceptions. (3.1) Ethical implications of research—research involving stem cells is growing in importance and raises ethical issues. (4.5) Outline Cell Theory Assessment Statement Outline Cell theory Cell Theory KEY CONCEPT Cells are the basic unit of life. Outline Cell Theory All living things are made of cells. Cells are the smallest unit of life. Existing cells have come from other cells. Outline Cell Theory How did the below scientist contribute to Cell Theory??? Evidence for Cell Theory Assessment State Discuss the evidence for Cell Theory Evidence for Cell Theory a. All living things are made of cells: When living things are observed under the microscope they consistently appear to be composed of cells. Evidence for Cell Theory b. Cells are the smallest unit of life. The cell is the smallest unit of organisation that can show all the characteristics of living processes, including: Metabolism Response Sensitivity Growth Reproduction Nutrition DNA Respire Organelles often require the cooperation of other organelles for their successful function. Evidence for Cell Theory c. Cells come only from other cells. o 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. o 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). o This relationship of common ancestor suggest that all organisms are related. Limitations of Cell Theory Questioning Cell Theory. Using atypical examples: Discuss problem in Cell Theory: • Striated Muscles Example • Giant Algae Example • Fungal Hyphae Example Functions of Life Assessment Statement State that unicellular organisms carry out all the function of life Functions of Life Organisms are able to carry out all the processes which are characteristic of living things such as: • a. metabolism which includes respiration the synthesis of ATP. • b. response to a change in the environment • c. homeostasis the maintenance and regulation of internal cell conditions. • d. growth which for a unicellular organism means an increase in cell size and volume. • e. reproduction which for the unicellular organism is largely asexual through cell division to form a clone. • f. nutrition which means either the synthesis of organic molecules or the absorption of organic matter. Relative Sizes Assessment Statements Compare relative sizes of molecules, cell membrane thickness, eukaryotes, viruses, bacteria and cells using the appropriate SI units Relative Sizes Relative sizes: 1. molecules (1nm). 2. cell membrane thickness (10nm). 3. virus (100nm). 4. bacteria (1um). 5. organelles (less 10um). 6. cells (<100 um). 7. generally plant cells are larger than animal cells. Relative Sizes • • • • • Molecules of Biological significance are around 1 nm in size where as the cell membrane is about ten times thicker at 10nm. Where as a virus is ten times larger again at around 100nm. where as a bacteria is ten times larger again at around 1 um. where as a eukaryotic animal cell is is ten time larger again at around 10 um. where as a eukaryotic plant cell is ten times larger again at around 100 um. Magnification Assessment Statement Calculate Linear Magnification of drawings and the actual size of specimens in images of know magnification Units used in magnification calculations Calculate Magnification of Specimen in Drawing Calculate Magnification = Length of specimen in drawing/ photo (measured) Actual length of specimen (estimated) Explain how you would estimate the size of cell A. 30 μm A Estimate the actual size of cell A. 30 μm A Use actual length and measured length to calculate Linear magnification Calculate Magnification = Length of specimen in drawing/ photo (measured) Actual length of specimen (estimated) 30 μm A Summary of Magnification Calculations Estimate Size of Amoeba in mm & μm a. mm μm. Calculate Magnification Actual length mm = Measure length in photo mm= Calculate Magnification = . . Length of specimen in drawing/ photo (measured) Actual length of specimen (estimated) Estimate the size of the Daphnia in mm & μm e. mm μm. Calculate Magnification Actual length mm = . Measure length in photo mm= Calculate Magnification = Length of specimen in drawing/ photo (measured) Actual length of specimen (estimated) . Calculate Actual size If a drawing of a cell has a magnification of 10X, and the length of the drawing is 20 mm. What is the actual length of the the cell? Actual length of specimen (estimated)= Calculate Magnification Length of specimen in drawing/ photo (measured) Actual length of specimen Magnification (estimated) Calculating Actual Length If the magnification of the drawing is 25Xwhat is the actual length of this drawing? Calculating Actual Size Calculating Actual Size Calculating Actual Size Cell Size Assessment Statement: • Explain the importance of the surface area to volume ratio as a factor of limiting cell size. Why are cells so small? Surface area to volume ratio • As cell size increases, volume increase faster than surface area • Surface area to volume ratio decrease as cell increases • Thus less cytoplasm has contact with plasma membrane to exchange material with its environment. Cell Size Cells need a large surface area to volume ratio for three reasons: 1. 2. 3. Get rid of waste more quickly Absorb materials from environment more quickly Get rid of internal heat and absorb heat from the environment more quickly. Cell Size Summary The smaller the cell the more easily it can get rid of waste to, and absorb nutrients from, its environment. LE 6-7 Surface area increases while Total volume remains constant Compare the Surface area of the solid box to the box made of a lot of small boxes 5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 150 750 Total volume (height x width x length X number of boxes) 1 125 125 Surface-to-volume ratio (surface area volume) 6 1.2 6 Surface Area to Volume Ratio The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings. Reason: as organisms get bigger their volume and surface area both get bigger, but not by the same amount. The volume increases as the cube but the area of the surface only increases by the square. Surface Area to Volume Ratio Conclusions: As the organism gets bigger its surface area : volume ratio decreases This rule is a limiting factor for cell size. As the cell gets bigger the ratio decreases If the ratio decreases the rate of exchange decreases Example: gas exchange of oxygen for respiration. A cell which respires aerobically demands oxygen for the process. Oxygen is obtained form the surrounding environment such as water or blood (depends on the cell). Oxygen diffuses across the cell membrane. More membrane more diffusion (Surface area= increases by the 2). Bigger cell (Volume = increases by the 3). However the ratio of surface area2 : volume 3 is decreasing Therefore the volume of oxygen obtained for each unit of cell volume is actually decreasing Cells must not get too big because they cannot obtain sufficient oxygen to satisfy the demands of the cell. why cells are small (reasoning): Size as a limiting Factors for cell because: A big cell needs more oxygen than a little cell Big cells need to have more oxygen diffusion across the cell membrane. But the big cell has relatively small surface area compared to its volume i.e. the surface area: volume ratio is small. What ever other benefits a cell might gain from being big, it cannot become larger than is limited by the rate of gas exchange. This reasoning can be applied to nutrients and to waste, anything that is exchanged across the cell surface. Try preparing a reason why size is a limiting factor for: Obtaining nutrient (glucose) Excretion of waste molecules ( urea, ammonia, carbon dioxide). Emergent Properties Assessment Statement: State that multicellular organisms show Emergent Properties Emergent Properties 'Emergent properties arise from the interaction of the component parts; the whole is greater than the sum of the parts'. Emergent Properties Emergence is the occurrence of unexpected characteristics or properties in a complex system. These properties emerge from the interaction of the ‘parts’ of the system. Remember that biology insists on a population thinking so that we know the interacting ‘parts’ vary in themselves and therefore their ‘emerging’ properties can only be generalized. Emergent Properties Multicellular and Differentiation Assessment Statement Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others. Multicellular and Differentiation Rather than all cells carrying out all functions, tissues and organs specialize to particular functions. These organs and systems are then integrated to give the whole organism (with its emergent properties). Differentiation: Cells within a multi-cellular organism specialize their function. Specialized cells have switched on particular genes (expressed) that correlate to these specialist functions. Multicellular and Differentiation These specific gene expressions produce particular shapes, functions and adaptations within a cell. Therefore a muscle cell will express muscle genes but NOT those genes which are for nerve cells. Multicellular and Differentiation What is the benefit of differentiation and specialization of tissues rather than all tissues carrying out all functions? In a multi cellular organism specialization is more efficient than the generalized plan when competing for a specific resource. Consider the role of water transport through the plant: In higher plants we have specialization to for a tubular system called the xylem. This is more efficient way of water transport than simply been passed by the mass movement of water from cell to cell. In the xylem water can be moved very efficiently from underground to the canopy of the highest trees at very little cost to the plant. If there is no specialized tissue for carrying water then the plant would rely on the movement of water by mass flow of diffusion which is very slow. The plant is therefore limited in size and therefore cannot compete with larger species. Multicellular and Differentiation Watch the below animation and then in your own words explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others http://outreach.mcb.harvard.edu/animations/preloaderStemCells.swf Multicellular and Differentiation Multicellular and Differentiation Stem Cells State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways What is a Stem Cell? Unspecialized cells Able to self-renew without differentiating for extended periods of time Ability to differentiate into specialized cells Embryonic and adult stem cells are derived from different sources. Human blastocyst showing inner cell mass and trophectoderm TIME 2001 Photo: Mr. J. Conaghan What is an Embryonic Stem Cell? Placenta cell Fusion of nuclei Stem cell First cell division Blastocyst (~5-6 days old): a “pre-embryo” ball of cells which has not implanted in the uterus. Only cells between the nuclei fusion and blastocyst stages are considered true stem cells. Stem cells are harvested from the inner cell mass. By the latter stages of development in the fetus, cells already have “decided” which tissues they are to become. Embryonic Stem Cells are Derived from Blastocysts Placenta cell Fusion of nuclei Stem cell First cell division Blastocyst (~5-6 days old) Stem cells are harvested from the inner cell mass. Undifferentiated stem cells are cultured (grown) in the laboratory. Adult Stem Cells Have two characteristics: They can make identical copies of themselves for the lifetime of the organism. • They can give rise to differentiated mature cells with specific morphologies (shapes and functions). • Adult stem cells are rare—and appear to help with homeostasis. Stem cells have been found in the brain and spinal cord, dental pulp, blood vessels, skeletal muscle, the digestive system, the cornea and retina, and the liver and Stem Cells A stem cell retains the capacity to divide and has the ability to differentiate along different pathways. A stem cell is able to divide but has NOT yet expressed genes to specialize to a particular function. Under the right conditions stem cells can be induced to express particular genes and differentiate into a particular type of cell. Embryonic Stem Cells Can Become Any Tissue in the Body Placenta cell Blastocyst Cultured laboratory stem cells Stem cell Scientific manipulations entice stem cells to become specialized tissues (blood, muscle, neuron, etc.). Blood cells Muscle cells Neuron (brain) cells Stems Cells Uses of Stem Cells Assessment Statement Outline one use of stem cells (6 Points) • Summarize. Question 3 Outline one therapeutic use of stem cells (6 points). Award [4 max] for any of the following general statements: stem cells are cells that retain the capacity to divide and have the ability to differentiate along different paths into all types of cells / are pluripotent / totipotent; stem cells are derived from blastocysts / human embryos, left over from IVF / placenta / umbilical cord / some adult tissues; new techniques / technologies rely on replacing diseased / dysfunctional cells with healthy / functioning ones; need to identify desired type of stem cell and grow in culture / special solutions / controlled conditions; develop biochemical solution that will cause cells to differentiate into desired cell type; develop means of implanting / integrating cells into patient’s own tissues so that they function with the body’s natural cells; danger of rejection of cells therefore need to suppress immune system; must make sure new cells do not become overgrown / develop into cancerous tumours; Award [2 max] for a specific example ie:  for type of cells and  for proposed use: eg retinal cells; replace dead cells in retina to cure presently incurable diseases such as glaucoma and macular degeneration; eg graft new skin cells; to treat serious burn victims; eg nerve tissue; help repair catastrophic spinal injuries / help victims of paralysisregain movement; What Diseases Could Be Impacted by Stem Cell Research? More than 100 million Americans suffer from diseases which might be alleviated by stem cell transplantation technologies. Examples include cardiovascular disease, autoimmune disease, diabetes, osteoporosis, cancer, Alzheimer’s disease and Parkinson’s disease. Stem cell treatment could potentially help patients with severe burns, spinal cord injuries, or birth defects. Types of Research • Transplantation • Therapeutic delivery systems • Developmental studies Science (2000) 287:1423. Uses of Stem Cells Non-Hodgkins Lymphoma is a cancerous disease of the lymphatic system. 1. patient requires heavy does of radiation and or chemotherapy. This will destroy health blood tissue as well as the diseased tissue. 2. Blood is filtered for the presence of peripheral stem cells. Cells in the general circulation that can still differentiate into different types of blood cell otherwise known as stem cells. 3. Bone marrow can be removed before treatment. 4. Chemotherapy supplies toxic drugs to kill the cancerous cells. 5. Radiation can be used to kill the cancerous cells. In time however the cancerous cells adapt to this treatment so that radiation and chemotherapy are often used together. 6. Post radiation/ chemotherapy means that the patients health blood tissues is also destroyed by the treatment. 7. Healthy stem cells or marrow cells can be transplanted back to produce blood cells again Animation of Stem Cells Watch the Below Animation and then address the sunsequent assessment statements : http://www.sumanasinc.com/webcontent/anim ations/content/stemcells.html Assessment Statements: State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways Outline one therapeutic use of stem cells.