THE CELL
History of Cell Theory- Robert Hooke 1665
Noticed cork cells- said they looked like “small rooms” in the monastery, named them “cells”.
Late 1600s, Leewenhoek, using the first microscope that he developed, observed pond water,
milk, tooth scrapings, and found living organisms.
The Cell Theory
1838 Matthias Schleiden studied plant tissues, found cells
1839 Theodore Schwann studied animal tissues, found cells
1855 Rudolf Virchow- cells arise from pre- existing cells
Needed a theory to unify study of cells- “The Cell Theory”
1. All living organisms are made of 1 or more cells.
2. Cells are the basic units of structure.
3. Cells arise from existing cells. They pass genetic information to daughter cells.
Basic Cell Types
1. Prokaryotic Cells- few organelles, no nucleus.
2. Eukaryotic Cells- many specialized organelles, have a nucleus.
Organelles- specialized structures that perform functions for the cell
Nucleus- central organelle with DNA
The Plasma Membrane:
Important for homeostasis-keeping a balance in the internal environment
Selective permeability- allows some molecules in and blocks other molecules from entering.
Composed of a phospholipid bilayer, with hydrophobic and hydrophilic components.
“Heads” made of glycerol and phosphate love the water/hydrophilic/ polar
“Tails” made of fatty acids do not like the water/hydrophobic/ non-polar
Transport mechanisms:
Passive transport- uses no ATP, goes with the concentration gradient (high to low is the natural
flow), where movement of particles is distributed from areas of high concentration to areas of
low concentration.
Diffusion- usually gases, CO2 and O2
Osmosis- movement of water only from areas of high concentration to low
concentration.
Factors affecting the rate of Diffusion/Osmosis
1. Temperature- goes faster when temperature increases
2. Pressure- goes faster when pressure is increased
3. Increased concentration of substance
Facilitated diffusion:
Requires no energy in the form of ATP, but uses a transport protein in the
plasma membrane for entry, can “hitch a ride” with water molecules.
Active Transport- uses ATP
Used when going against the concentration gradient, or moving large molecules
Sodium-Potassium Pump: moves 3 Na+ out for every 2 K+ into the cell
Endocytosis and exocytosis- using the plasma membrane to form a vesicle
around a molecule to bring it in, or send it out.
Cellular Organelles:
Nucleus- membrane bound central organelle that houses DNA
Mitochondria- organelle where cellular respiration occurs, makes ATP, has own DNA and
ribosomes.
Endoplasmic Reticulum- Rough- has ribosomes, proteins made here are sent to the rest of the
cell.
Endoplasmic reticulum- Smooth- synthesizes some lipids and hormones
Golgi Apparatus- modifies and packages proteins that come from the rough E. R.
Vesicles- small membrane bound storage
Vacuoles- membrane bound storage of water- large in plant cells
Ribosomes- synthesize proteins
Nucleolus- small component of the nucleus that makes ribosomes
Lysosomes- filled with hydrolytic enzymes, digest antigen, and old cellular debris
Centrioles- made of microtubules, function during cell division, close to the nucleus
Chloroplasts- in plant cells, site of photosynthesis, have own DNA and ribosomes.
Cell Wall- in plant cells, thick rigid and made of cellulose, help with plant structure
Cilia and Flagella- used for movement, attached to cell membrane
Plasma membrane- helps with homeostasis, present in all cells.