Cell Theory

Cell Theory

• Unit 5: Cells in Action

Welcome to Class! Cell Theory

• Tuesday, January 14, 2024
• Agenda: Cell Theory
• Learning Objective: Students will be able to:
  • Use microscopes to identify differences in cells from different organisms
  • Describe the historical figures which lead to the development of the cell theory
  • Explain why cells are important in maintaining balance in the body

Question of the Day:

• How did scientists learn about cells?

Cell Theory

Robert Hooke (1665)

• Observed cork cells for the first time through a microscope.

Naming of "Cells"

• Hooke named them "cells" because they looked like the small rooms monks lived in at the monastery.

Anton van Leeuwenhoek

• Observed single-celled organisms swimming in pond water shortly after Hooke.
• He called them "animalcules."

Importance of Learning about Cells

• Since then, we've learned a lot more about cells and why they are important.
• Why it is important to learn about cells?
  • Genetics
  • Cancer
  • Cloning (Dolly)

Reasons to Follow Logic

• Avoid the idea “one person holds all knowledge” - we all can determine the truth for ourselves.
• Avoid cult-like followings or superstition - Jonestown Massacre of 1977.
• Keep companies accountable for illegally dumping carcinogens/harmful chemicals in water streams - DuPont.
• Avoid baseless accusations like how vaccines cause autism or how COVID vaccines are government surveillance monitors.
• Become informed citizens of our country to align in proper social political parties and VOTE FOR THE RIGHT PRESIDENT, OUR GENERAL RIGHTS, ETC.

The 3 Parts of Cell Theory:

• After many years of research about cells, cell theory was developed. There are 3 parts to the cell theory:
  • All living things are made of cells.
  • Cells are the smallest unit of life.
  • All cells come from pre-existing cells.
• Let's figure out what these three theories mean and how they came to be…

1. All Living Things are Made of Cells

• In 1838 Matthias Schleiden proposed that plants are made of cells.
• In 1839, Theodor Schwann added that animals are also made of cells.

How to Determine if Something is Living

• Have DNA
• Change over time
• Use materials and energy
• Grow and develop
• Respond to environment
• Reproduce
• Maintain homeostasis
• How do we know if something is LIVING or not?

2. Cells Are The Smallest Unit of Life

• Is there anything smaller than a cell?
  • Yes! Atoms are the smallest thing there is on our planet… but atoms are not alive.

Cell Size Variation

• Do larger animals have larger cells? Are elephant cells larger than mouse cells?
• Nope!
• Elephants just have MORE cells than mice.

3. All Cells Come From Pre-existing Cells

• In 1855 Rudolf Virchow came out with the theory that cells must come from other pre-existing (already living) cells.

Cell Origins

• Life can't just make itself on its own! You have to have cells to make new cells.
• People used to think if you left meat out on the counter maggots would grow from the meat.
• Now we know that the maggots come from flies that land on the meat and lay eggs.

Advancements Since Cell Theory

• What else have we learned about cells since the cell theory?
• There are different types of specialized cells.
• Cells have small compartments inside them called organelles that have specific functions.

Additional Cell Insights

• Cells are the smallest unit of life.
• Cells act as compartments to help organisms maintain homeostasis.
• There are two main types of cells:
  • Prokaryotic cells are cells without a nucleus. (ie. bacteria)
  • Eukaryotic cells are cells with a nucleus (ie. plant & animal cells)
  • [Archaea (a third branch, won’t learn about)]
• Cells contain organelles, which are specialized structures that help the cell carry out its functions.

Stem Cell Research

• Fundamentally, all cells (in one organism) have the same DNA, it just depends on which parts of the DNA are being expressed.
• This allows our body to have different specialized cells; the cells on our tongue are not the same cells as the skin on the bottom of our feet.
• Stem cells allow us to manipulate what type of cell we can make from our DNA. So whichever type you’re in need of, we can apply stem cell research to develop new kidney cells, heart cells, etc. But this is highly morally ambiguous and ethically controversial in many cases.

Relative Cell Size

• Most cells are about 1/10 the diameter of a human hair.
• Take a look at one strand of hair and try to imagine how small cells are!
• https://scaleofuniverse.com/

The Wacky History of Cell Theory

Normal Red Blood Cell vs. Sickle Cell Anemia

Structure of the Plasma Membrane

• Selective seal around the entire cell that only allows certain things to exit and enter. This is called a selectively-permeable membrane.
• Some molecules are small enough to pass through without assistance. Others need a channel or help getting across.
• Phospholipid bilayer contains many other proteins, like aquaporins and ion channels, etc. Also holds cholesterol.

Phospholipid Bilayer

• One side of the molecule is polar (attracted to charges) while the other half of the molecule is nonpolar (not attracted to charges).
• The polar side is attracted to molecules like water and the nonpolar side is attracted to fatty acids like oil.
• Phospholipids organize in a way to make a seal for the cell. Only certain things may enter and exit through proper channels.

Cell Membrane Components

• Diagram of phospholipid bilayer, hydrophobic tail, hydrophilic head, alpha-helix protein, glycolipid, globular protein, hydrophobic segment of alpha-helix protein, oligosaccharide side chain, cholesterol

Cholesterol's Role in Cells

• Our cells can respond to cold temperatures by adding more cholesterol to our phospholipid bilayer of our skin cells.
• As we live in colder climates, our body will learn to incorporate more cholesterol.
• Adding cholesterol further lowers our skin’s freezing point, so we won’t freeze to death as quickly. Those that have lived in colder climates naturally have more cholesterol in their skin cells.

Phagocytosis

• When the cell engulfs or “eats” another dead cell or larger molecule.
• This involves creating a separate “orb” for that larger cell to be engulfed.

Na+/K+ Pump & Diffusion

• Diagram of extracellular space, intracellular space, Na+ diffusion, Na+/K+ pump, K+ diffusion

Aquaporins - Water Channels

Cell Wall

• Plant cells have an additional Cell Wall around their plasma membrane. This is a key difference between animal cells versus plant cells.

Nucleus - The Brain of the Cell

• All cells house the same DNA (deoxyribonucleic acid) inside of an enclosed structure called the nucleus.
• Similar to the plasma membrane, the nucleus has a nuclear envelope that is selective to what enters and exits.
• Instructions are copied from the nucleus and sent out as messenger RNA (mRNA, ribonucleic acid) to be translated into proteins outside the nucleus.

Ribosomes - Translators of Messages

• The nucleus sends out mRNA as a template strand and the ribosomes read the template and synthesize specific proteins out of that message.
• Think of it like lego pieces. The instructions would be mRNA, you would be the ribosome and the last product of the lego figure (a starship, a flower) would be the end protein made.

Summary of mRNA translation into protein

• RNA polymerase, coding strand, template strand, bases used to make DNA (AGCT), bases used to make RNA (A, G, C, U), mRNA, ribosome, tRNA, newly born protein, amino acids, large subunit, small subunit, A site, P site

Mitochondrial DNA Fun Fact

• All mitochondrial DNA (there’s a separate storage of DNA in mitochondria) is EXCLUSIVELY passed down from egg cell AKA from your MOM!

Homework

• Reading Notes To prepare for class on Wed/Thurs, read and take notes on the Essay: Compartments & Cells (linked on google classroom).

Class Closing

• Homework:
  • Reading Notes
• Reminders: None

Molecular Movement

• Unit 5: Cells, Balance & Homeostasis

Welcome to Class! Molecular Movement

• Tuesday, January 21, 2025
• Agenda: Molecular Movement Reading,
• Cell Transport
• Practice & Exit
• Learning Objective: Students will be able to:
  • Identify examples of cellular transport
  • Define and provide examples of diffusion
  • Describe the difference between active and passive transport
  • Predict the ways that cells respond and direction of diffusion

Question of the Day:

• How do we maintain balance?

Homeostasis Maintained

• All of the examples we have been seeing and learning about this unit are examples of cells or organisms responding to their environment to maintain homeostasis (balance).
• All living organisms, from plants to bacteria to people, must regulate their internal environment to survive. This starts at the level of the cell, moving molecules across their cell membrane to take in what they need and get rid of what they don’t.

Cell Transport

Active vs. Passive Transport

• Active Transport requires energy.
  • Needs ATP energy and a protein.
• Passive Transport does NOT require energy.
  • Osmosis and Diffusion (Simple & Facilitated) are both examples of passive transport.

Diffusion Explained

• A “Concentration Gradient” refers to the gradual decrease in concentration of a substance.
• Because molecules constantly move and collide with one another, they will diffuse until they reach equilibrium.

What is Diffusion?

• Diffusion is the net (overall) movement of a substance down its concentration gradient.
  • Passive transport; no energy is required
  • Substances travel from [High] → [Low] naturally ● “ [___]” means concentration (ie. [Solute] = Solute concentration)

How Long Will Substances Diffuse?

• Molecules diffuse until they reach “equilibrium”.
• Equilibrium means that the net (overall) movement of molecules is zero.
• The substances have equal concentration on either side of a membrane.
• However, particles will continue to move!
• The particles shown would be moving and can cross over to the other side in equal amounts.
• Since there is no longer a concentration gradient to travel down, the overall movement is still zero as equilibrium has been reached.

Types of Diffusion: Simple vs. Facilitated

• Simple Diffusion
  • Passive transport (no energy required)
  • Directly through a cell membrane
  • Small, nonpolar molecules
• Facilitated Diffusion
  • Passive transport (no energy required)
  • Requires a membrane protein
  • Larger or charged molecules

Test Your Understanding of Diffusion

• Will the oxygen diffuse? In which direction?
• What type of diffusion would this be? Why?
• Simple Diffusion! (small, nonpolar)
• Cell Membrane, High [Oxygen], Low [Oxygen]

Diffusion of Oxygen through Alveoli of Lung

• Veins bring deoxygenated blood to the lungs. They have LOW oxygen concentrations.
• Alveoli are tiny air sacs that we breathe oxygenated air into. They have HIGH oxygen concentrations.
• We need SIMPLE DIFFUSION to occur to bring oxygen into our bloodstream (and to remove carbon dioxide).

Types of Diffusion: Osmosis

• Osmosis is the diffusion of water, typically through channel proteins called “aquaporins”.
  • Water diffuses from a high concentration of water to a low concentration of water.
  • Note: sometimes water can squeeze through a membrane (because it is so small), but typically move through aquaporin channels.

Relative Solutions

• For any cell in a liquid environment, we have relative terms based on the solute (salt) concentration and solvent (water) concentration in a cell.
• Since water moves in and out passively in a cell, there are different situations where the cell can shrivel or explode.
• Let’s go over these situations

Describing Solutions

• Hypertonic Solutions - solute outside is greater than solute inside the cell. Water leaves the cell to compensate. Cell shrivels up.
• Hypotonic Solution - solute outside is lower than solute inside the cell. Water moves into the cell. Cells start to expand and possibly explode.
• Isotonic Solutions: identical solute concentrations inside the cell and outside in the solution. Cell stays the same, while water still moves in and out, in equilibrium.

Visualizing Relative Solutions

• Diagrams of Hypertonic, Hypotonic, and Isotonic solutions with water movement.

• H2O travels out of the cell, causes cell to shrivel.

• H2O travels into the cell, causes cell to swell

• H2O travels in and out of the cell, cell stays the same

Solution Scenarios

• Determine what type of solution the cell would be in based on the percentages of water and solute in the container versus in the cell (with answers).

• Scenario 1:

  • Cell: 90% H2O, 10% solute
  • Solution: 65% H2O, 35% solute
  • Solution is hypertonic, water moves out, cell shrinks.

• Scenario 2:

  • Cell: 30% H2O, 10% glucose
  • Solution: 30% H2O, 10% glucose
  • Isotonic; the cell will stay the same size.

Factors Affecting RATE (speed) of Diffusion

• Distance
• Temperature
• Characteristics of Substance
• Difference in Concentration

Distance and Diffusion

• Proximity and location of different enzymes and other factors play a role in how quickly diffusion occurs.
• LONG distances = SLOW diffusion rates

Temperature & Diffusion Rate

• Influences distance/proximity inherently. How quickly the molecules move will impact transportation into and out of the cell.
• HIGH temperatures = FAST diffusion rates. More movement of molecules

Substance Characteristics & Diffusion Rate

• Size of the substance
• Polarity of the substance (partially charged or nonpolar)
• pH of the environment
• LARGE substances (with more mass) = SLOW diffusion rates
• Small, nonpolar substances = easier time traveling through membranes

Concentration Difference & Diffusion Rate

• By law of Entropy (disorder, chaos), all things follow this pattern of moving away from highly concentrated areas to low.
• Never the opposite, the opposite would be an example of active transport.
• LARGE difference in concentrations = FAST diffusion rates

Cell Transport Recap

Cell Transport - Purpose: Maintain Homeostasis

• Passive Transport
  • [High] -> [Low]
  • Down the concentration gradient
  • No energy
• Active Transport
  • [Low] -> [High]
  • Against the concentration gradient
  • Requires energy
• Simple Diffusion (No Protein)
  • Small, nonpolar molecules
    • Semipermeable Membrane OR
    • Go through the cell membrane directly OR spread out in a space without a cell membrane
  • Result after transport
    • Tranport of ANY substance down its concentration gradient.
    • Equilibrium
• Facilitated Diffusion (Yes Protein)
  • Larger molecules or ions or ionic compounds
    • Travel through a membrane protein
  • Semipermeable Membrane
    • Equilibrium
• Osmosis
  • Diffusion of water through a semi-permeable membrane
    • Water travel from an area of to an area of
  • Requires membrane protein
    • Semipermeable Membrane
  • Result after osmosis
    • -High [water] --> low [water]
    • -Low [solute]--> high [solute]
    • - Hypotonic --> hypertonic
    • Hypertonic solution - High [solute] in the solution
      • Net movement of water: Water leaves the cell. The cell shrinks
    • Hypotonic solution - Low [solute] in the solution
      • Net movement of water: Water enters the cell. The cell expands
    • Isotonic solution - Same [solute] in the solution vs. in the cell
      • No net movement of water. Equal amount of water move in/out of the cell Cell size remains the same

Class Closing

• Homework:
  • Finish Classwork
• Reminders:
  • Additional resources at end of slides

Solution Question Review Slides

Diffusion

Cell Transport Recap Cont.

• “Passive Transport” refers to any transport that does not use energy (ATP) to move the material, whereas “Active Transport” does use energy to move substances with the help of transport proteins.
• A “Concentration Gradient” refers to the gradual decrease in concentration of a substance.
• “Equilibrium” refers to a state of balance.
• “Diffusion” is the molecular movement from an area where molecules are more concentrated to an area where they are less concentrated.
  • “Osmosis” is one type of diffusion, specifically referring to the movement of water from an area of greater concentration to an area of lesser concentration. (Osmosis does NOT occur in an isotonic solution).
  • In “Facilitated Diffusion” proteins form channels that allow substances to move down their concentration gradient.

Mitosis

• Unit 6: Cells to Systems

Welcome to Class! Mitosis

• Friday, January 31, 2025
• Agenda: Growth & Development, Mitosis Notes
• Learning Objective: Students will be able to:
  • Explain growth and development in organisms
  • Propose solutions for constraints in cell division
  • Design an initial model for cell division using words and images in small groups

Question of the Day:

• How does a single cell develop into a body?

Unit 7: Cells to Systems - Growth & Homeostasis Topics:

• Mitosis
• Cell Cycle
• Development and Differentiation
• Stem Cells
• Body Systems
• Human Homeostasis
• Circulatory System & Heart Dissection
• Major Assessments:
  • Stem Cell Debate
  • Heart Dissection
  • Unit 7 Quiz

Growth & Development Defining

• Each of us began as a single cell, so one important question is: How did that single cell develop into a body with more than a trillion cells?
• We know cells are the building blocks of life, but how exactly do cells grow and develop into complex organisms?

Growth vs. Development

• "Growth" the increase in the size and mass of a particular organism over time.
• "Development" a process wherein a particular organism transforms itself from a single cell into a more complicated multicellular organism.

How Organisms Grow

• Organisms depend on the ability of their cells to reproduce (multiply) to grow and develop.
• But how does this happen?

Mitosis & The Cell Cycle

The Role of Mitosis

• Remember, In multicellular organisms, growth takes place primarily through an increase in the number of cells, not through an increase in the size of cells.