Introduction to Biology Chapter 3 Notes: Cell Structure and Function
Mr. Grivensky/Mr. Rutkoski
3-1 Early Microscopes
In the 1600s, a Dutch glassmaker named Anton van Leeuwenhoek discovered that if he placed several magnifying lenses at the proper distances from each other he could greatly magnify small objects.
van Leeuwenhoek is given credit for creating the first microscopes
“Cell Theory Scientists”
Robert Hooke, an English physicist, at about the same time as Leeuwenhoek, was using a microscope to observe flowers, insects, and slices of cork. In 1665, Hooke published a book of his drawings and named the chambers he observed in plant samples, “cells”. He chose this name because they reminded him of the tiny rooms in a monastery, which are also called cells. Hooke believed that only plants were made up of cells, as did most scientists of his time and nearly 200 years later. In 1839, a German biologist, Theodor Schwann found that animal tissues also had cell-like structures which lead him to the conclusion that animals were made up of cells also.
..more “Cell Theory Scientists”
Around the same time as Schwann made his discovery, Robert Brown, a Scottish biologist had found that cells had a structure near the center. We now call this structure the nucleus. German biologist, Matthias Schleiden, suggested that the nucleus played a role in cell reproduction. In 1855, German physicist, Rudolf Virchow, studied cell reproduction further and proposed that animal and plant cells were produced by the division of existing cells.
The discoveries of these scientists are summarized in the cell theory. Cell Theory states that:
A. All living things are composed of cells B. Cells are the smallest working units of living things C. All cells come from preexisting cells by cell division
Compound light microscope Uses more than one lens to magnify objects Can magnify an image up to 1000 times These are what we use at Wyoming Area Cells and organisms can be studied while they are still alive
Electron Microscopes: TEM
Use magnets to focus a beam of electrons, much like a television The beam of electrons can be used to examine a sample Electron microscopes can magnify 1000x larger than a light microscope (100,000 times) Transmission Electron Microscope (TEM) Shines a beam of electrons through a sample, and then projects the image onto a fluorescent screen
Electron Microscopes: SEM
Scanning Electron Microscope (SEM) Uses a beam of electrons to scan the surface of a sample. The SEM collects the electrons that bounce off the sample, and forms an image on a television screen Both, TEMs and SEMs can only observe nonliving specimens. These specimens must be sliced very thin for use in a TEM, and the SEM only shows the outer surface of the specimen
SEM & TEM Photos
Scanning Probe Microscope
In the early 1980s, the scanning probe microscope was invented It does not use any lenses, and instead traces the surface of an object with a probe These microscopes have been used to photograph molecules and atoms.
3-2 Cell Boundaries
Every cell has a cell membrane along its boundary. The principal role of the cell membrane is to separate and protect the cell from its surroundings. The cell membrane is said to be selectively permeable
Selectively Permeable means that the cell membrane allows some substances through but denies passage to other substances
The cell membrane is composed of a phospholipid bilayer. A phospholipid has a polar end called the head and a nonpolar end called the tail. The polar heads group together on the outside of the lipid bilayer. The nonpolar heads group together on the inside of the bilayer because they avoid water. The lipid bilayer provides the cell membrane with a tough, flexible barrier that protects the cell from substances.
Found in plants, algae, and bacteria. Located outside the cell membrane. Helps to support and protect the cell. Made up of carbohydrates and protein. The principle carbohydrate is cellulose. Cellulose provide the cell with rigidity and strength.
Substances cross the cell membrane without the cell expending energy Examples1. Diffusion 2. Facilitated Diffusion 3. Osmosis
Diffusion is the process by which substances spread throughout a liquid or gas. In diffusion, substances move from regions of high concentration to regions of low concentration
Substances diffuse across the cell membrane through special channels in protein Example is glucose
The diffusion of water through a selectively permeable membrane
Hypertonic Solution: Solute concentration of solution higher than cell
More dissolved particles outside of cell than inside of cell Hyper = more (think hyperactive); Tonic = dissolved particles Water moves out of cell into solution Cell shrinks
Hypotonic Solution: Solute concentration of solution lower than cell
Less dissolved particles outside of cell than inside of cell Hypo = less, under (think hypodermic, hypothermia); Tonic = dissolved particles Water moves into cell from solution Cell expands (and may burst)
Isotonic Solution: Solute concentration of solution equal to that of cell
No net water movement
Requires energy The movement of substances against a concentration gradient Similar to a pump. Examples
1. Endocytosis 2. Phagocytosis 3. Exocytosis
3-3 Inside the Cell
There are two categories of organisms: prokaryotes and eukaryotes Prokaryotes- organisms that do not contain nuclei and membrane bound organelles (ex.bacteria) Eukaryotes- organisms that contain a nucleus and organelles
Control center of the cell Large and dense Contains nearly all of the cell’s DNA
Contains coded instructions for making proteins DNA wrapped around special proteins(histones) is known as chromatin Chromatin condenses to form chromosomes
Structures in the Nucleus
Nucleolus- small, dense region found in the nucleus; ribosomes are assembled here Nuclear envelope- two distinct membranes that contain many holes called nuclear pores
Structures of the Nucleus
Portion of the cell outside of the nucleus Fluid like material that contains organelles Organelles-small structure that performs a specialized function within the cell
Ribosomes Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum Golgi Apparatus Lysosomes Cytoskeleton
1. Microtubules 2. Microfilaments
Cilia Flagella Vacuoles Centrioles Plastids Mitochondria Chloroplast
Ribosomes Protein and RNA complex responsible for protein synthesis
Rough Endoplasmic Reticulum
Rough endoplasmic reticulum (RER) A network of interconnected membranes forming channels within the cell. Covered with ribosomes (causing the "rough" appearance) which are in the process of synthesizing proteins.
Smooth Endoplasmic Reticulum
Smooth endoplasmic reticulum (SER) A network of interconnected membranes forming channels within the cell. A site for synthesis and metabolism of lipids.
Golgi apparatus A series of stacked membranes. Vesicles (small membrane surrounded bags) carry materials from the RER to the Golgi apparatus. Vesicles move between the stacks while the proteins are "processed" to a mature form.
Lysosymes A membrane bound organelle that is responsible for degrading proteins and membranes in the cell, and also helps degrade materials ingested by the cell.
The cytoskeleton extends through out the cytoplasm. Composed of protein fibers called intermediate filaments, microtubules and microfilaments, the cytoskeleton maintains cell shape, allows the cell to move, and moves structures within the cell.
Cilia and Flagella
Plant cells do not have cilia and flagella. Both are anchored in the cytoplasm by centrioles and extend from the outside surface of the plasma membrane. Flagella are used to propel the cell. Cilia can be used to propel the cell, or move fluids past the cell.
Cilia and Flagella
Vacuoles Membrane surrounded "bags" that contain water and storage materials in plants.
A centriole is a short, barrel shaped ring composed of nine microtubules around an empty center. Centrioles are found only in animal cells. They are arranged in pairs that sit perpendicular to one another.
Plastids are a storage organelle unique to plant cells and some photosynthetic protists. They are not found in animal cells. Located in the cytoplasm, the plastids are used to store substances such as pigments and starches.
Mitochondria Surrounded by a double membrane with a series of folds called cristae. Functions in energy production through metabolism. Contains its own DNA.
Chloroplasts (plastids) Surrounded by a double membrane, containing stacked thylacoid membranes. Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars.