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chapter 4...

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4.1- Multicellular and cell specialization Unicellular organisms:        

Single celled Prokaryotes One cell carries out all functions to sustain life Functions are carried out by different organelles within cell Microscopic size- large surface area to volume Short lifespan due to energetically expensive workload Mostly assexual, clonal reproduction- duplicate Whole organism is involved in reproduction

Multicellular organisms:        

Many cells Eukaryotes Cells are specialized to perform specific functions required by the organism Functions are carried out at cellular, tissue, organ system levels Macroscopic size- increasing number of cells allows increased body size Long lifespan as work is efficiently divided between specialized cells Mostly sexual reproduction Cells specialized for production will reproduce (gametes).

What does cell specialization mean?  

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A single cell is produced as a result from the fusion of gamete cells(ovum and sperm) Gametes fuse together to form a single cell-zygote which contains all the genetic information required to develop into a fully functional multicellular organism. Then zygote develops by cell division into an embryo A process which occurs after cell division where the newly formed cells are structurally modified so that they can perform their function effectively and efficiently Something which is designed to do a particular job

Examples     

Red blood cells: Transports oxygen-changes some of the content of the cell Muscle cells: allows movement- change number of particular organelles. Nerve cells: contraction and relaxation of muscle tissues help in movement Ciliated epithelium cells-white blood cells: provides protection/defence Bone cells Cartilage cells: provides strength and support.

What is differentiation?  

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Process by which unspecialized cells(stem cells) become specialized cells. Differentiation occurs many times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of tissues and cell types. is how generic embryonic cells become specialized cells. This occurs through a process called gene expression. Gene expression is the specific combination of genes that are turned on or off (expressed or repressed), and this is what dictates how a cell function Embryonic (stem cells) originate in the blastula and make up the primary germ layers( ectoderm-mesoderm-endoderm) that differentiate to form specialized cells, tissues and organs in animals.

Primary germ layers: - Mesoderm(middle layer):   

Cardiac muscle + skeletal muscle cells Tubule cell of the kidney+ red blood cell Smooth muscle (In gut)

- Endoderm(internal layer): 

Lung+ thyroid+ pancreatic cells

- Ectoderm(external layer): 

Skin cells of epidermis+ neuron cell+ pigment cell

Gene expression:  

Gene expression is the process in which the information stored in genes is used to build the different structures in a cell. Gene expression determines how a cell will differentiate and function

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In specialized cells only some genes are active or expressed E.g. in developing red blood cells, the genes for hemoglobin are expressed

Advantages of Multicellularity:     

Energy efficient because specialized cells have own tasks Multicellular organisms have longer lifespans because they are more energetic Less vulnerable to short term changes in their environment Grow larger the unicellular organisms Increased size and specialization of limb means multicellular organisms are more mobile therefore more efficient at locating resources and avoiding predators

Disadvantages of Multicellularity:    

More cells means more energy is required for survival Cells cannot function independently, they are dependent on whole organisms More energy is required for reproduction, must have a partner to reproduce Populations take longer to evolve and to adapt

Cell function Exchange Transport Strength/ support Protection/ defense Photosynthesis Movement Communication

Cell specialization Plant cell Root hair Companion cell Fibers (xylem, phloem) Epidermal cells Mesophyll

Animal cell Gut epithelium cells Red blood cell Bone, cartilage cell White blood cells Muscle cells Nerve cells

Young cell-cell division-cell growth-cell specialization- mature cell (unlikely or unable to divide again)...