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Cellular Basis of Life, Homeostasis
Key Question: How are cell structures adapted to their functions?
The Discovery of the Cell
Early Microscopes
In the late 1500’s, eyeglass makers in Europe found that they could use several glass lenses together to make very small things easy to see
In 1665, Robert Hooke used a microscope to look at thin slices of cork from plants - he discovered “boxes” and named them cells
Cells - the basic unit of all forms of life
Around the same time, Anton van Leeuwenhoek used a single lens microscope to observe pond water and discovered a whole world of tiny, living organisms.
Cell Theory
A fundamental concept of biology that states that:
i. All living things are composed of cells
ii. Cells are the basic units of structure/function in living things
iii. New cells are produced from existing cells
Light Microscopes and Cell Stains
A light microscope lets light pass through an object
Its two lenses focus the light to form an image
Only work up to 1000 times magnification
Electron Microscopes
Used to study very small things such as DNA
Focus beams of electrons using magnetic fields to create an image
Can show things that are 1 billionth of a meter is size
2 types: Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM)
Two main kinds of cells:
Eukaryotes
Organisms whose cells contain a nucleus
Prokaryotes
Unicellular organisms that lack a nucleus
Nucleus
A structure that contains the cell’s genetic material in the form of DNA
Cell Organization
Cytoplasm
The fluid portion of the cell outside the nucleus
Organelles
A specialized structure that performs important cellular functions within a eukaryotic cell; “little organs”
Control center of the cell
Holds nearly all of the cell’s DNA
Surrounded by a nuclear envelope dotted with holes (nuclear pores)
Vacuoles and Vesicles
Vacuole
The cell organelle that stores materials such as water, salts, proteins, and carbohydrates
Found in both plant and animal cells
Vesicles
Membrane sacs that store and move materials between organelles as well as to and from the outside of the cell
Lysosome
The cell organelle that breaks down lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell
Found in animal cells and some special kinds of plant cells
Cytoskeleton
The network of protein filaments in a eukaryotic cell that gives the cell its shape and internal organization and is involved in movement
Contains two types of protein filaments:
Microfilaments - threadlike structures made up of a protein called actin
Microtubules - thin, hollow pipe made up of proteins known as tubulins
Ribosomes
Ribosome
A cell organelle consisting of RNA and protein found throughout the cytoplasm in a cell; the site of protein synthesis
Can be free floating in the cytoplasm or attached to the Rough ER
Endoplasmic Reticulum
The internal membrane system found in eukaryotic cells; the place where lipid components of the cell membrane are assembled
Rough ER - ribosomes on the surface make it “bumpy”
Smooth ER - no ribosomes on its surface
Golgi Apparatus
An organelle in cells that modifies, sorts, and packages proteins and other materials from the endoplasmic reticulum for storage in the cell or release outside the cell
Chloroplasts
Chloroplast
An organelle found in cells of plants and some other organisms that captures the energy from sunlight and converts it into chemical energy
Contain chlorophyll
Mitochondria
Cell organelles that convert the chemical energy stored in food into compounds that are more convenient for the cell to use; the “power plant” of the cell
Cell Walls
Jobs are to support, shape, and protect the cell
Most prokaryotes and many eukaryotes, such as plant cells, have cell walls
Animal cells do NOT have cell walls
Lipid Bilayer
A flexible double-layered sheet that makes up the cell membrane and forms a barrier between the cell and its surroundings
Protects the cell, regulates what enters/exits, allows for flexibility
ALL cells have cell membranes
Passive Transport
Every cell needs to be able to control what crosses its membrane
Cells want to balance fluid outside of the cell with fluid inside the cell
Diffusion
The process by which particles tend to move from an area where they are more concentrated to an area where they are less concentrated
Particles will ALWAYS move from high to low
Does NOT require energy from the cell - this is why it is a type of passive transport
Facilitated Diffusion
The process of diffusion in which molecules pass across the membrane through cell membrane channels
These act as short cuts for important molecules such as glucose
Does NOT require energy from the cell - passive transport
Osmosis
The diffusion of water through a selectively permeable membrane
Selectively permeable - some things can cross while others cannot
Many cells have water channel proteins (aquaporins) that allow water to pass right through
Osmotic Pressure
The pressure that must be applied to prevent osmotic movement across a selectively permeable membrane
Three Types:
Isotonic
Hypertonic
Hypotonic
Isotonic
The concentration is the same inside and outside the cell; water moves at the same rate in both directions
Hypertonic
The outside solution has a higher concentration than the solution inside the cell; movement of water molecules outside the cell causes it to shrink
Hypotonic
The outside solution has a lower concentration than the solution inside the cell; water molecules move into the cell causing it to swell
The movement of particles across the cell membrane using energy
Three major kinds:
Protein Pumps - chemical energy is used to pump ions across the cell membrane
Endocytosis - membrane forms a pocket around a particle outside the cell and brings the item into the cell
Exocytosis - vesicle inside the cell carries a particle to the cell membrane and forces the particle outside the cell
The Cell as an Organism
All living things have certain characteristics in common
They are all made of cells
They all have the same kinds of organelles
Homeostasis
The relatively constant internal physical and chemical conditions that organisms maintain
The cells of human beings and other many-celled organisms do not live on their own - they need other cells to survive
These cells have to communicate with one another to maintain homeostasis
Cell Specialization
Different kinds of cells have different jobs
Each cell only completes its own jobs to keep the organism alive
Cells
Tissue
A group of similar cells that perform a particular function
Organ
A group of tissues that work together to perform closely related functions
Organ System
A group of organs that work together to perform a specific function
Organism
Cells in large organisms use chemical signals to communicate
These signals can speed up or slow down the activities of the cell
Passed across cellular junctions - the meeting point between cells