1 Cells and The Cell Theory IB Bio Topic 2 Cell Theory 1. Living organisms are composed of cells. 2. Cells are the smallest unit of life. 3. All cells come from pre-existing cells. (no spontaneous generation) Evidence • When living things are observed under the microscope they consistently appear to be composed of cells. • Cells carry out cell division to form new cells: Mitosis Pg. 78: Cell Theory • Viruses are not made up of cells. • Where did the first cells come from? • Mitochondria and chloroplasts contain their own DNA. Humongous fungus among us - Armillaria bulbosa is among the oldest and largest living things on Earth. - Single fertilized spore. - Vegetative growth using Hyphae http://www.crystalfalls.org/humongou.htm Exceptions • Cell Theory Exceptions: – Muscle cells are multinucleated (have many nuclei) – Fungi- are very large with many nuclei & a continuous cytoplasm. • Viruses reproduce via host’s cell division (Mitosis.) Pg. 78: Cell Theory
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Cells and The Cell Theory
IB Bio Topic 2
Cell Theory
1. Living organisms are composed of cells.
2. Cells are the smallest unit of life.
3. All cells come from pre-existing cells. (no spontaneous generation)
Evidence• When living things are observed under the microscope they consistently appear to be composed of cells.
• Cells carry out cell division to form new cells: Mitosis
Pg. 78: Cell Theory
• Viruses are not made up of cells.
• Where did the first cells come from?
• Mitochondria and chloroplasts contain their own DNA.
Humongous fungus among us- Armillaria bulbosa
is among the oldest and largest living things on Earth.
- Single fertilized spore.
- Vegetative growth using Hyphae
http://www.crystalfalls.org/humongou.htm
Exceptions
• Cell Theory Exceptions: – Muscle cells are multinucleated (have many nuclei)
– Fungi- are very large with many nuclei & a continuous cytoplasm.
• Viruses reproduce via host’s cell division (Mitosis.)
Pg. 78: Cell Theory
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Unicellular organisms carry out all the life functions
• Unicellular organisms evolved some 3-4 BYA• They were the dominant life form until 600 MYA• Life Functions:
1. Heavy does of radiation &/or chemotherapy to destroy diseased tissue (healthy blood tissue)2. Blood is filtered for the presence of peripheral stem cells (Cells that can still differentiate into different types of blood cells).
Stem Cell Use: Non-Hodgkins Lymphoma3. Bone marrow removed.
4. Healthy stem cells transplanted back to produce healthy blood cells again.
Animals� Do notDo not contain a cell wallcontain a cell wall
��Do notDo not contain contain chloroplastschloroplasts
��Have small vacuolesHave small vacuoles
��Generally have spherical Generally have spherical shape.shape.
��Contain centriolesContain centrioles
��CiliaCilia
Membrane structure & proteins
• The fluid mosaic model of the plasma membrane.
Phospholipids
• Hydrophilic molecules are attracted to water.
• Hydrophobic molecules are not attracted to water but have an affinity for one another.
• Stability provided by hydrophobic tails in the center & hydrophilic heads & surrounding water.
Simple Diffusion
The movement of particles from an area of high [ ] to an area of low [ ] through the spaces in the
phospholipid bilayer.
Facilitated DiffusionThe diffusion of particles that are unable to pass through the spaces in the phospholipidbilayer.
Channel proteins control this movement of particles but not the direction of flow. Still H���� L
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Specificity of these proteins for each molecule.
Ex: Voltage-gated channels have channel proteins for Na & K in neuron membranes.
Osmosis• The plasma membranes are usually
freely permeable to water.
• Solvents are liquids in which particles dissolve.
• Solutes are the particles that dissolve.
• The diffusion of water is due to the concentration of solutes.
Osmosis• Therefore osmosis is the diffusion of water from an area of low solute [ ] to an area of high solute [ ] across the plasma membrane.
The attraction is between the H2O & the solute particles.
Types of SolutionsHypertonic: A hypertonic solution contains a greater [ ] of solutes than the inside of the membrane.
Tap water is hypertonic to distilled water.
Types of Solutions
Hypotonic: A hypotonic solution contains a smaller [ ] of solutes than the inside of the membrane.
Types of Solutions
Isotonic: Isotonic is the term used when there is an equal concentration of solutes.
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Active Transport Across Membranes
• Active transport involves transport using ATP (energy) by the cell.
• Active transport moves from low [ ] to
high [ ] against a concentration gradient.
Active Transport Across Membranes
Phagocytosis
Phagocytosis is a process in which a cell engulfs undissolved, large particles by flowing around them and enclosing them in a vacuole.There are 2 ways this can be done.
Endocytosis and Exocytosis
1. Endocytosis is when the surface membrane encloses materials and allows them inside.
2. Exocytosis is when the surface membrane encloses materials and allows them outside.
Pinocytosis “cell drinking”�The process in
which liquids or very small particles from the surrounding medium are taken into a cell.
Exocytosis Vs. Endocytosis
• Process of exporting molecules from a cell by fusion of vesicles with the cell membrane.
• Vesicle usually budded from the ER or Golgi.
• Used by secretorycells to export products.
• Process of importing molecules into a cell by forming vesicles derived from the plasma membrane.
• Used by cells to incorporate extracellular substances.
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Active Transport Across Membranes Active Transport Across Membranes
Topic 2.5 Cell division Cellular Division
•• Consists of two Consists of two
processes:processes:
1. Nuclear division1. Nuclear division
2. Cytoplasmic division2. Cytoplasmic division
Nuclear division
•• The process of nuclear The process of nuclear
division is called division is called mitosismitosis
•• The division of the entire cell The division of the entire cell
is called is called mitotic cell divisionmitotic cell division
Mitosis•• An orderly series of complex An orderly series of complex changes in the nucleus.changes in the nucleus.
•• Involves an exact duplicate of the Involves an exact duplicate of the complete set of chromosomes and complete set of chromosomes and the separation of these the separation of these chromosomes into chromosomes into two identical two identical sets.sets.
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The Cell Cyclein Eukaryotes
The Cell Cycle• The cell cycle describes the major phases of activity in the division of a cell.
• The length of the cell cycle depends on the particular function of the cell.
• Ex: bacterial cells can divide every 30 minutes.
• Skin cells divide about every 12 hours.
• Liver cells every 2 years.
• Muscle cells never divide at all after maturing.
• The total length of a cell cycle varies depending on the specialised function of a cell.
• Interphase is the longest phase which itself occurs in three stages.
• G1 The cell performs its normal differentiated function. Protein synthesis/ mitochondria replication/ chloroplast replication.
• S DNA replication. At this point the mass of DNA in the cell has doubled.
• G2 Preparation for cell division
The Cell Cycle• Phases of mitosis (PMAT) • Cytokinesis: division of the cytoplasm to form two daughter cells.
Metaphase•• The doubleThe double--stranded stranded
chromosomes line up in the chromosomes line up in the middlemiddle of the cell.of the cell.
•• This creates the This creates the metaphase metaphase plate.plate.
Anaphase•• The doubleThe double--stranded stranded
chromosomes break at the chromosomes break at the centromere and divide into singlecentromere and divide into single--stranded sister chromosomes.stranded sister chromosomes.
•• The sister chromosomes move to The sister chromosomes move to oppositeopposite poles with the aid of poles with the aid of shortening spindle fibers.shortening spindle fibers.
Telophase•• Last phase of mitosis.Last phase of mitosis.
•• Chromosomes reach the poles & uncoil.Chromosomes reach the poles & uncoil.
• Re-formation of nuclear membranes & &
nucleolus.nucleolus.
•• Results in 2 Results in 2 diploiddiploid daughter cells that are daughter cells that are
the exact replica of the parent cell. the exact replica of the parent cell.
Cytokinesis•• Known as cytoplasmic division.Known as cytoplasmic division.
•• Here the cytoplasm of the cell is Here the cytoplasm of the cell is divided into two daughter cells, divided into two daughter cells, each containing one newly each containing one newly formed nuclei with an identical set formed nuclei with an identical set of chromosomes.of chromosomes.
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Mitosis in Plants
•• Plant cell division differs from animal cell division Plant cell division differs from animal cell division
in in twotwo ways:ways:
1. Most plants 1. Most plants do notdo not have Centrioleshave Centrioles
2. Plants have a rigid cell wall which prevents the 2. Plants have a rigid cell wall which prevents the
cell membrane from pinching in. cell membrane from pinching in.
Instead, a Instead, a cell platecell plate forms which divides the cell in forms which divides the cell in