Happy Hump Day! Quickwrite: What do you remember about cells from 8th grade! Types, organelles, functions, etc….

Cells Topic 1

1.1 Cell Theory

Scientists first became aware of cells as the basic building blocks of life in the 1600’s Made possible by the invention of the microscope Robert Hooke first coined the term “cell” after observing cork in 1655 Anton Van Leeuwenhoek first observed living cells in pond water in 1674

Cell Theory Modern scientists follow the cell theory, which was proposed by Rudolf Virchow in 1855 The cell theory consists of three components: All living organisms are composed of cells Cells are the smallest unit of life All cells come from pre-existing cells

Supporting Evidence for the Cell Theory: While cells may be composed of smaller parts called organelles, the cell itself is the smallest unit of life that can show all the characteristics of living processes (e.g metabolism and reproduction) The division of cells to create new cells has been observed with microscopes

Supporting Evidence for the Cell Theory: Experiments refuting Spontaneous Generation also provided evidence.

Exceptions: Exceptions to the cell theory: don’t follow the usual cell model Muscle Cells Long fibers that have more than one nucleus (organelle where DNA is located) per cell

Fungal Hyphae Fungal cells are long strands called hyphae that together form dense networks called mycelium The hyphae are multinucleated and have cell walls composed of chitin (normal cell walls are composed of cellulose)

Other exceptions Unicellular organisms are considered possible exceptions because they are larger in size than the cells of multicellular organisms Some tissues/organs contain large amounts of non-cellular material: The eye is filled with a liquid called the vitreous humour Bone is primarily composed of mineral deposits

As mentioned previously, all cells, even those that are simple unicellular organisms (i.e. bacteria) carry out the basic functions of life. These basic functions are: Metabolism – breaking down glucose and other nutrients in order to make ATP (the most basic unit of cellular energy) Response to outside stimuli Homeostasis – maintenance of a stable internal environment

Growth – in the case of cells this means an increase in size and volume Reproduction - cell division to create two cells from one Nutrition – for cells this refers either to the synthesis of organic molecules (e.g. plants creating glucose) or the absorption of organic matter (fungi absorbing nutrients from decaying organisms)

How small or large are cells? Relative sizes of microscopic objects: Molecules – 1 nm Cell Membrane thickness – 10 nm Viruses – 100 nm Bacteria – 1 um Organelles – up to 10 um Most cells – up to 100 um It should be noted that the above measurements are taken in two dimensions yet cells and their components are three dimensional

Microscopes Calculating Size: It is important to know how to calculate the actual size of an object based on it’s size in a drawing or a picture taken from a microscope The actual size of the object = measured length (using a ruler)/magnification In the case of the image to the right: Actual size = 60mm/10 = 6 mm 6 mm X 1,000 um = 6,000 um Magnification is 10 X Measured length is 60 mm

Calculating magnification If the image/drawing is given to you from another source (e.g. the IB Test) and you need to calculate the magnification you can do so by using the scale bar that will be found in the picture and by reversing the equation to: Magnification = measured length/actual length (based on scale bar)

Surface Area and Volume As the size of a structure increases (e.g. a cell), it’s surface area to volume ratio decreases: This causes problems with growing cells in that metabolic process, which occur inside the cell, depend upon the materials that the cell membrane allows to enter and leave the cell Once the ratio reaches a point at which the cell’s volume is more than can be supported by the surface area of the cell, the cell must divide

Emergent Properties Multicellular organisms show emergent properties Emergent properties arise from the interaction of component parts In other words, the whole is greater than the sum of it’s parts The human eye is an excellent example of this:

Stem Cells Cells in multicellular organisms begin as stem cells that are capable of expressing any of the genes they contain and therefore performing any function for the organism that they are a part of These stem cells will eventually differentiate to carry out specialized functions for the organism This is done by “shutting off” certain genes while allowing others to be expressed (“stay on”)

Differentiated Cells Examples of cells that have become differentiated for specific purposes include red blood cells, skin cells, brain cells, muscle cells, and kidney cells

Stem Cells Stem cells are a major topic of modern day scientific research Because they are undifferentiated they can be used to replace any type of body cell needed For instance, in 2005, stem cells were used to restore the insulation tissue of neurons (brain cells) in lab rats, resulting in subsequent improvements in their mobility

Human Stem Cells In humans, an example of the successful use of stem cells is the treatment of Non-Hodgkins Lymphoma (a type of cancer that destroys the lymphatic system) Cancer treatment such as radiation and chemotherapy can destroy healthy red blood cells along with the cancerous lymphatic cells Stem cells injected into patients can differentiate to become healthy red blood Stem Cell Animation: http://www.dnalc.org/stemcells.html

Stem Cells Stem cell research can be quite controversial, however, due to the ethical questions as to how to obtain them Most commonly, stem cells are obtained from embryos This can be of major concern for those who feel that a life is being destroyed in order to obtain the stem cells

Stem Cells Research is being conducted in order to find other sources of stem cells (e.g. bone marrow) Therapuetic Cloning has been developed to use already differentiated cells from a living person to create stem cells: Take a healthy cell from patient Insert the nucleus of the healthy cell (containing the patient’s DNA) with an egg cell that has had it’s nucleus removed

Egg cell divides multiple times to form a blastocyst (hollow ball of cells) composed of totipotent cells (capable of being pushed to differentiate into any type of cell) Totipotent cells are pushed to differentiate Newly developed cells are injected into patient