Introduction to Cells Assignment

Introduction to Cells Cell Theory Outline the three components of the cell theory All living things are composed of cells (or cell products) 1. …………………………………………………………………………………………………………………………………………………... The cell is the smallest unit of life 2. …………………………………………………………………………………………………………………………………………………... Cells only arise from pre-existing cells 3. …………………………………………………………………………………………………………………………………………………... Describe the features of the following cell types that challenge the concepts of the cell theory Striated Muscle Fibres: • Muscle fibres form from fused muscle cells and hence are long and have multiple nuclei ………………………………………………………………………………………………………………………………………………….......... • Challenges idea that cells always function as autonomous units ………………………………………………………………………………………………………………………………………………….......... Giant Algae: • Certain species of unicellular algae may grow to very large sizes (e.g. > 7 cm in length) ………………………………………………………………………………………………………………………………………………….......... • Challenges idea that cells are microscopic and larger organisms are composed of many cells ………………………………………………………………………………………………………………………………………………….......... Aseptate Fungal Hyphae: • Filamentous hyphae that are not partitioned (aseptate) will have a continuous cytoplasm ………………………………………………………………………………………………………………………………………………….......... • Challenges the idea that living structures are always composed of discrete cells ………………………………………………………………………………………………………………………………………………….......... List the functions of life Metabolism – Living things undertake essential chemical reactions M ……………………………………………………………………………………………… Reproduction – Living things produce offspring (sexual / asexual) R ……………………………………………………………………………………………… Sensitivity – Living things are responsive to stimuli S ……………………………………………………………………………………………… Homeostasis – Living things maintain a stable internal environment H ……………………………………………………………………………………………… Excretion – Living things require the removal of waste products E ……………………………………………………………………………………………… Nutrition – Living things exchange materials with the environment N ……………………………………………………………………………………………… Growth – Living things can move and change shape or size G ……………………………………………………………………………………………… Hint: Mr Sheng Compare the metabolic functions of Paramecium and Chlorella Paramecium Chlorella • Mode of nutrition is heterotrophic ………………………………………………………………………… ………………………………………………………………………… • Paramecium engulf food (via phagocytosis) and ………………………………………………………………………… ………………………………………………………………………… absorbs essential gases via diffusion ………………………………………………………………………… • Solids are removed via an anal pore, while liquids ………………………………………………………………………… are pumped out via vacuoles ………………………………………………………………………… • Mode of nutrition is autotrophic • Chlorella contain chlorophyll for photosynthesis • All essential materials are both absorbed and ………………………………………………………………………… eliminated via passive diffusion ………………………………………………………………………… ………………………………………………………………………… Cell Size Explain the importance of surface area to volume ratio as a factor limiting cell size • The rate of metabolism of a cell is a function of its mass / volume ………………………………………………………………………………………………………………………………………………….......... • The rate of material exchange between a cell and its environment is a function of surface area ………………………………………………………………………………………………………………………………………………….......... • As a cell grows, its volume increases faster than its surface area – meaning metabolic rate eventually ………………………………………………………………………………………………………………………………………………….......... exceeds rate of exchange ………………………………………………………………………………………………………………………………………………….......... • Hence cell sizes are limited in order to maintain a viable SA:Vol ratio (energy requirements cannot ………………………………………………………………………………………………………………………………………………….......... exceed rate of intake) ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... List three adaptations of cells that may function to maximise the surface area to volume ratio Cells may adopt an elongated or flattened shape to increase SA:Vol ratio (e.g. bacillus) 1. …………………………………………………………………………………………………………………………………………………... Cells may possess cellular extensions (e.g. root hairs) or folds to plasma membrane (e.g. microvilli) 2. …………………………………………………………………………………………………………………………………………………... Cells may reduce effective cell volume by including large central vacuoles (e.g. plant cells) 3. …………………………………………………………………………………………………………………………………………………... Suggest, with a reason, the location of the following cell within the human body Intestine (digestive tract) Location: …………………………………………………………………………………………………………………… Has microvilli to increase surface area (allows for more material absorption) Reason: …...………………………………………………………………………………………………………………… ……………...…………………………………………………………………………………………………………………… Magnification Compare the advantages and disadvantages of using light microscopes and electron microscopes Light Microscope Advantages Electron Microscope Can view living specimens Higher magnification …………………………………………………………… …………………………………………………………… Can view in natural colours Higher resolution …………………………………………………………… …………………………………………………………… Disadvantages Can only view dead specimens Lower magnification …………………………………………………………… …………………………………………………………… Views in monochrome (or use false colour) Lower resolution …………………………………………………………… …………………………………………………………… Identify the difference between a transmission electron micrograph and a scanning electron micrograph Transmission electron microscopy (TEM) generates cross-sections through a specimen (internal image) ………………………………………………………………………………………………………………………………………………….......... Scanning electron microscopy (SEM) generates a surface rendering of a specimen (external image) ………………………………………………………………………………………………………………………………………………….......... Calculate the actual size of the following image (width = 11 cm) ×86 Working: Actual = Image ÷ Magnification ……………………………………………………....... Image Size = ~11 cm ……………………………………………………....... Magnification = 86 ……………………………………………………....... Actual = 11 ÷ 86 = 0.128 cm ……………………………………………………....... Actual = 1.28 mm ……………………………………………………....... ……………………………………………………....... ……………………………………………………....... Calculate the linear magnification and actual size of the following image Working: Scale width = 2.2 cm (image) …………………………………………………………………… Parasite width = 7.2 cm (image) …………………………………………………………………… Magnification = Image ÷ Actual …………………………………………………………………… Magnification = 22000 ÷ 50 = 440 …………………………………………………………………… Actual = Image ÷ Magnification …………………………………………………………………… Actual Size = 7.2 ÷ 440 = 0.0163 cm …………………………………………………………………… 50μm Actual Size = 163 micrometres …………………………………………………………………… Cell Specialisation Outline, with an example, the organisation of cells in a multicellular organism • Cells of the same type may group together to form tissues (neurons form nerve tissue) ………………………………………………………………………………………………………………………………………………….......... • Different tissues interact to form functional organs (heart composed of nerve and cardiac muscle tissue) ………………………………………………………………………………………………………………………………………………….......... • Organs combine to form organ systems (e.g. heart and blood vessels form the cardiovascular system) ………………………………………………………………………………………………………………………………………………….......... Define emergent properties in relation to multicellular organisms An emergent property is a function present in a multicellular organism that is not present in any of its ………………………………………………………………………………………………………………………………………………….......... individual component cells / Emergent properties arise from the interaction of individual cells to produce ………………………………………………………………………………………………………………………………………………….......... new functions in multicellular aggregates / An example is increased antibiotic resistance seen in biofilms ………………………………………………………………………………………………………………………………………………….......... Explain how cells differentiate through selective gene expression All cells of an organism contain an identical genome (the entire set of genetic instructions for that organism) ………………………………………………………………………………………………………………………………………………….......... Differentiation involves the expression of some genes and not others in a cell's genome ………………………………………………………………………………………………………………………………………………….......... The activation of certain genes by chemical signals will cause a cell to develop differently from other cells ………………………………………………………………………………………………………………………………………………….......... Differentiation through selective gene expression causes different cell types to become more specialised ………………………………………………………………………………………………………………………………………………….......... and distinct as they mature ………………………………………………………………………………………………………………………………………………….......... Describe how genes may be packaged within eukaryotic cells • DNA in eukaryotes is packaged with proteins (histones) within the nucleus to form chromatin ………………………………………………………………………………………………………………………………………………….......... • Active genes are loosely packaged in an expanded and accessible form called euchromatin ………………………………………………………………………………………………………………………………………………….......... • Inactive genes are usually tightly packaged in a more condensed form called heterochromatin ………………………………………………………………………………………………………………………………………………….......... • Packaging of chromatin varies between cells according to which genes are active and inactive ………………………………………………………………………………………………………………………………………………….......... Stem Cells State the two key qualities of stem cells Self-renewal: Stem cells are capable of continuous cell division 1. …………………………………………………………………………………………………………………………………………………... Potency: Stem cells are capable of differentiation (are effectively unspecialised precursors) 2. …………………………………………………………………………………………………………………………………………………... Differentiate between pluripotent, multipotent and unipotent stem cells (with examples) Can form any cell type AND form extra-embryonic structures (can form new organisms) Totipotent: ………………..……………………………………………………………,,……………………………………………….......... E.g. blastocyst ………………………………………………………………………………………………………………………………………………….......... Can form any cell type (but can’t form extra-embryonic structures like the placenta) Pluripotent: ………………..…………………………………………………………………………………………………………….......... E.g. embryonic stem cells ………………………………………………………………………………………………………………………………………………….......... Can differentiate into closely related cell types Multipotent: …….……………………………………………………………………………………………………………………….......... E.g. hematopoeitic stem cells (in bone marrow) form a variety of blood cells ………………………………………………………………………………………………………………………………………………….......... Can divide but not differentiate Unipotent: ……….……………………………………………………………………………………………………………………….......... E.g. muscle cells can self-replicate ………………………………………………………………………………………………………………………………………………….......... Outline the therapeutic use of stem cells • Stem cells can be used to replace damaged / diseased cells with healthy ones ……………………………………………………………………………………………………………… • Stem cells can be harvested from embryos, umbilical cord blood or certain ……………………………………………………………………………………………………………… Harvest adult tissues (e.g. bone marrow) ……………………………………………………………………………………………………………… • Biochemical solutions are used to trigger the differentiation of stem cells ……………………………………………………………………………………………………………… Differentiate • Cells are surgically implanted into patient's own tissue and the host immune ……………………………………………………………………………………………………………… system is suppressed to prevent rejection of cells ……………………………………………………………………………………………………………… • New cells must be monitored to ensure they do not become cancerous ……………………………………………………………………………………………………………… Implant Describe the use of stem cells to treat Stargardt’s disease • Stargardt’s disease is caused by a gene mutation that impairs photoreceptor cells in the retina ………………………………………………………………………………………………………………………………………………….......... • This leads to genetically inherited macular degeneration (resulting in blindness) ………………………………………………………………………………………………………………………………………………….......... • May be treated by replacing damaged retinal cells with healthy ones (derived from stem cells) ………………………………………………………………………………………………………………………………………………….......... List three other therapeutic examples of stem cells Replace dead nerve cells in individuals with Parkinson’s disease (death of dopamine-secreting neurons) 1. …………………………………………………………………………………………………………………………………………………... Replace bone marrow in individuals with leukemia (cancer of the blood) 2. …………………………………………………………………………………………………………………………………………………... Replace pancreatic beta cells in individuals with type I diabetes (can’t regulate blood sugar levels) 3. …………………………………………………………………………………………………………………………………………………... Compare the implications of stem cell therapy using cells derived from different sources Growth Potential Tumour Risk Embryo High High Cord Blood High Lower Adult Tissue Low Low Harvesting Disadvantages Can be generated Requires the destruction artificially by SCNT of an embryo Easily obtained and Cells must be stored stored / preserved from birth at high cost Difficult to obtain / May be limited in scope invasive to extract of application Outline how stem cells may be artificially derived Involves the creation of embryos via therapeutic cloning (fusing a diploid nucleus with an enucleated SCNT: ……………………………………………………………………………………………………………………………………….......... egg cell and then stimulating with an electric current to promote division) ………………………………………………………………………………………………………………………………………………….......... Excess embryos are created by this process, raising ethical concerns about destruction of embryos ………………………………………………………………………………………………………………………………………………….......... Induce a change in the gene expression profile of a cell in order to transform it Nuclear Reprogramming: ………………………………………………………………………………………………………….......... into a different cell type (involves the use of oncogenic retroviruses, increasing risk of cancer) …………………………………………………………………………………………………………………………………………………..........