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Transcript
Cells: Agriculture’s Building Blocks Original Power Point Created by: Andy Harrison Modified by GA Agriculture Education Curriculum Office July 2002 August 2008 Cells • All living organisms are composed of cells. • The ability to study cells was first made possible by the invention of the microscope. • An understanding of cells has allowed scientists to develop new products and technology. • Some animals are only single cell organisms, such as the amoeba, paramecia, and protozoa. August 2008 Cells • One-celled bacteria are important for cattle health and maintenance (ruminant digestion). • Other bacteria are important for converting atmospheric nitrogen to nitrogen for plant use. • In addition, some cells such as the one-celled phytoplankton are food for fish and whales. August 2008 Cell Characteristics • Animals and plants contain specialized cells, which vary in size and shape – Largest – ostrich egg – Smallest – some bacteria • Cell shape can be round, boxed, long, or string-like. • Other cells, such as amoebas, have the ability to change shape constantly. August 2008 Reproductive Cells • Reproduction begins in the cells. • Male & female reproductive organs produce cells that unite to form new organisms. • All eggs are single cells. August 2008 Cell Structure – Cell Wall • Plants have a cell wall, animals do not. • Cell wall provides cell shape and protects its contents • The cell wall is composed of cellulose which: – Makes cell walls rigid – Provides support for plant – Used to make paper August 2008 Cell Structure- Cell Membrane • Located inside the cell wall • Also known as the plasma membrane • All material going in and out of the cell must pass through this membrane • Membrance is semi-permeable; allows certain substances (small molecules and ions [charged molecules]) to pass through August 2008 Cell Structures- Cell Membrane • Allows water and nutrients into and out of the cell • Transports waste out of the cell • Membrane does this by a process called diffusion. – Diffusion: molecules pass through the membrane from a region of higher concentration to a region of lower concentration August 2008 Cell Structure- Cell Membrane • Osmosis is the process where water passes through a cell’s semi-permeable membrane from a higher concentration to a lower concentration – The less substance water has in it , the less concentrated – The more substance – more concentrated • Cells draw water inside their membranes to equalize the concentrations on each side of the membrane. August 2008 Cell Structure- Cell Membrane • Homeostasis: the ability of an organism to remain stable when conditions around it change • Turgid: cells filled with water so that they are taut (firm) • Turgor pressure: helps cells to retain their shape August 2008 Cell Structure- Nucleus • A relatively large structure – Eukaryotic cells – have nucleus – Prokaryotic – no true nucleus • The nucleus is made of: – Nucleic acids – Proteins – Enzymes August 2008 Cell Structure- Nucleus • Surrounded by a double-layer membrane – This membrane regulates movement of materials in and out of nucleus, just as the cell membrane regulated movement in and out of the cell itself. • Contains genetic code – Code is located in DNA (Deoxyribonucleic acid) – DNA arranged in threadlike strands called chromosomes – Genes: segments of the chromosome; site of the actual traits August 2008 Cell Structure- Cytoplasm • • • • Thick clear fluid surrounding nucleus Constantly moving Suspends other parts of cell Contains all essential materials for cell life process August 2008 Cell Structure- Organelles • Small structures located in cytoplasm – Mitochondria: peanut shaped; break down food and supply cell with energy • Cells requiring more energy (muscles) have a greater number of mitochondria – Vacuoles: storage compartments • Membrane that encloses water and other material • Stores cell waste August 2008 Cell Structure- Organelles – Microtubules: • • • • August 2008 Thin hollow tubes Composed of protein Function as the “bones” of the cell In animals, they aid in chromosome movement during cell division. Cell Structure- Organelles – Microfilaments: fine fiber-like structures made of proteins • Help the cell to move by oscillating back & forth – Ribosomes: organelle where protein molecules are assembled – Enzymes: not an organelle, but important compounds composed of proteins that regulate chemical processes in cell August 2008 Cell Structure- Organelles • Golgi apparatus: shaped like group of sacks bundled together. – Remove water from proteins and prepare it for transport • Lysosomes: digestive units of cells – Digest proteins, carbohydrates, and other molecules, including bacteria and worn out cell parts August 2008 Cell Structure- Organelles • Plastids: present in plants but NOT in animals • Three types: – Chloroplast: contains chlorophyll, converts sunlight energy to carbohydrates. – Leucoplast: provides storage for cells – Chromoplast: manufactures pigments that give fruits and leaves color August 2008 Cell Reproduction • All growth comes from cells increasing in number • When a cell reaches its maximum size, the cell divides to increase in number. • Original cell: parent cell • New cells: daughter cells August 2008 Mitosis • Process where the genetic code is duplicated and passed on to daughter cells. • The process is divided into phases: – Interphase – Prophase – Metaphase – Anaphase – Telophase August 2008 Interphase • Phase where cells are not actively dividing • Not actually part of mitosis • Cell begins to synthesize materials and transport them outside of the cell • Cell grows and reaches maximum size • DNA replicates and forms two sets of chromosomes August 2008 Prophase • First actual phase of mitosis • Chromatin appears in the form of distinct shorten rod-like structures – Chromatin is two strands called chromatids that are attached in middle by a centromere • Nuclear membrane begins to dissolve • Nucleus begins to disperse • In place of nucleus , a spindle is formed, – A spindle is football shaped and made of microtubules August 2008 Metaphase • Chromatids move toward center of spindle • When they reach the center, they connect themselves to the fibers of the spindle August 2008 Anaphase • Pairs of chromatids separate into an equal number of chromatids • Centromeres duplicate • Chromosomes move to opposite end of cell August 2008 Telophase • Chromosomes continue to migrate to the ends of the cell • Remains of the spindle disappear • New membranes are formed around the chromosomes – This forms two new nuclei August 2008 Cytokinesis • Divides the cytoplasm in cell • Separate process from mitosis • In animals, the separation point is the cleavage furrow in the center of the cell • In plants, they form a cell plate and grow outward until cells are separate August 2008