Introduction to Cells 1.1 Mr. McGee, IB Biology (HL)

By the end, you will understand: According to cell theory, living organisms are composed of cells. Organisms consisting of only one cell carry out all the 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 cell’s genome. The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development. It also makes stem cells suitable for therapeutic uses.

Cells A cell is defined as the smallest collection of matter that exhibits the characteristics of life. All living things are made of cells. Some living things consist entirely of one cell (unicellular), while others consist of many cells working together to form the entire organism (multicellular). All life’s processes have their basis at the cellular level. All cells share these characteristics: – An outer membrane, which separates the inside of the cell from the outside – Genetic material, which stores all instructions needed for cellular activities – Chemical reactions, which are catalyed by enzymes – Release of energy to power activities

Cell Theory: i.All organisms are composed of one or more cells. ii.Cells are the smallest units of life. iii.All cells come from pre-existing cells. Cell theory has arisen from hundreds of years of scientists wondering what makes up an organism. Pioneers: -Robert Hooke (1665) -First to see cells -Anton van Leeuwenhoek (1674) -Microscopic organisms -Matthias Schleiden (1837) -Plant cells -Theodor Schwann (1838) -Animal cells

Evidence for the Cell Theory Nothing smaller than a cell has been seen to exhibit all properties of life – Including cell organelles organelles and viruses (why)? Living tissues and organisms have been seen to consist of cells, using the microscope. – Cell membranes and nuclei were visible under the earliest light microscopes. Observation of tumor cells led to understanding of cell division. Cells must have originally developed from abiotic origins, but the anaerobic conditions necessary for that step no longer exist (we think).

With the development of microscopy, a new system of measurement was necessary for tiny things… All scientific measurements are taken in SI units of measurement (metric). – It grows by the power of 10. – Do you understand scientific notation?

Measurements Science uses the SI System of measurements, based on the powers of 10. SI UnitAbbrev.PrefixMetric Equivalent Scientific Notation Real-Life Examples Gigameter GmGiga-1,000,000,000m1.0 x 10 9 Our sun is just over 1Gm wide Megameter MmMega-1,000,000m1.0 x 10 6 The Earth is 13Mm wide Kilometer kmKilo-1,000m1.0 x 10 3 Just over half a mile long Meter m 1m1.0 x 10 0 A 2 nd graders height (3.3ft) Centimeter cmcenti-0.01m1.0 x 10 -2 About the length of a bug Millimeter mmmilli-0.001m1.0 x 10 -3 About the width of a pencil tip Micrometer µmmicro-0.000001m1.0 x 10 -6 Length of a bacterial cell Nanometer nmnano-0.000000001m1.0 x 10 -9 Thickness of cell membrane Picometer pmpico-0.000000000001m1.0 x 10 -12 About 1/10 the radius of a helium atom. Attometer amatto- 0.000000000000000001m 1.0 x 10 -18 Diameter of quarks, smallest length we’ve ever observed. Planck Length ℓPℓP - 0.000000000000000000000 00000000000001m 1.0 x 10 -35 Superstrings, quantum gravity – Tiniest length; cannot get any smaller

Relative size of things http://htwins.net/scale2/

Comparing relative sizes Molecules: 1 nm Cell membrane thickness: 10 nm Viruses: 100 nm (0.1 μm) Bacteria: 1 μm (1000 nm) Organelles: 10 μm Cells: 100 μm (0.1 mm) Remember that cells and other cellular components are three dimensional, even though microscopes can only focus on 2 dimensions, or one “layer” at a time. (Except SEM)

Preparing and Sketching Microscope Specimens Skills: Use a light microscope to investigate the structure of cells and tissues Draw cell structures as seen with the light microscope Calculate the magnification of drawings and the actual size of structures shown in drawings or in micrographs.

IB Biology Requirements for Sketches: Draw what you actually see, not what you think you should see. Label each drawing at the bottom, with the detailed name of the specimen, magnification, type of microscope as well as “wet mount” or “preserved” specimen noted. Drawings should take up approximately ¼ sheet of paper. Use a circle to indicate field of vision. (Tracing a petri dish works well) Label structures by writing the label to the side of the drawings horizontally, and drawing a line with a ruler to touch the structure you are labeling. Label with names of identifiable structures or descriptions. Indicate one cell if possible. Include a scale in your sketch with appropriate units. Make perfect circles and straight lines when needed!!!

KingdomWet mountPrepared slide Protista (single- celled organisms) Place one drop of compost tea and one drop of methylene blue stain. Gently mix with a toothpick. Place a clean cover slip on top of the specimen. Use a prepared slide of Ameoba or Plasmodium Alternatively, make an additional slide of compost tea and sketch a different organism. PlantaeUse a razor blade to slice a thin cross section of spinach leaf. Gently place on a slide and add a drop of water. Place a clean cover slip on top of the specimen. Alternatively, use a razor blade to cut out a thin section of green onion root Use a prepared slide of dicot leaf epidermis or lilac leaf paradermal section. AnimaliaGently scrape the inside of your cheek with a clean cotton swab. Rub the cotton swab over the slide. Add one drop of methlylene blue stain and mix with a toothpick. Place a clean cover slip on top of the specimen. Alternatively, make your own blood smear. See me for assistance. Use a prepared slide of human smooth, skeletal or cardiac muscle, or a human blood smear.

What are the properties of life? Nutrition, or a way to obtain the energy needed for growth Metabolism, or chemical reactions within the cell Growth, an irreversible increase in size Sensitivity, responding to changes in the environment Homeostasis, keeping inside conditions within tolerable limits Reproduction, producing offspring through dividing or exchanging genetic information Single celled organisms possess all these properties independently. Multicellular organisms have cells that possess these characteristics as well, but they cannot function independently of one another.

Exceptions to the Cell Theory Application: Question the cell theory using atypical examples including striated muscle. Discuss for each example: what makes it an exception to the cell theory? Is it still a cell?

Why Are Cells Small? Multicellular organisms don’t have bigger cells than unicellular organisms, they just have more. Cell size is limited by the surface area to volume ratio. – The rate at which cells consume resources and produce waste is a direct function of cell volume. – The rate at which cells exchange heat and materials with their environment is a direct function of surface area. – Therefore, cells need to have a high surface area to volume ratio in order to maintain the appropriate balance between metabolism and exchange. Cells must remain small to function effectively!

Multicellular Life Single celled organisms can only do so much. Multicellular organisms have emergent properties. This means that multicellularity conveys some advantages beyond those of a single cell. The whole is greater than the sum of the parts. https://www.youtube.com/watch?v=4U4N9MQXcgc

Differentiation Multicellular organisms have different types of cells that perform different functions. Different cell structures allow the cells to perform specialized functions. A group of cells that perform the same function are called a tissue. To reproduce, multicellular organisms must be able to make any type of cell from a single zygote. This works because all cells have the same complete genome. Cells differentiate, or become different in structure and function by expressing certain portions of the genetic code, and “turning off” other portions.

Stem Cells Stem cells are cells that have not been differentiated. They are “generic cells” that can divide and may differentiate into any type of cell. Embryos contain high proportions of stem cells because they are still growing and developing into the whole organism. At a very early stage, an embryo consists entirely of stem cells. Adults also have stem cells in bone marrow, liver and skin, contributing to the body’s immune system and its ability to repair itself.

Therapeutic uses of stem cells Because of their ability to divide quickly and to become any type of cell, stem cells have enormous potential in the regeneration of tissues and organs. It is theoretically possible to take stem cells and use them to re-grow or replace cells, tissues or entire organs by selectively “turning on” certain genes. This could benefit people with many diseases and conditions such as multiple sclerosis, Parkinson’s, Huntington’s, and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis (to name a few).

Introduction to Cells 1.1 Mr. McGee, IB Biology (HL)

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Introduction to Cells 1.1 Mr. McGee, IB Biology (HL)

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