Chapter 7: Cell Structure
Section 1: Introduction to Cells
I. Cells – the smallest unit of life; all living
things are made of one or more cells
A. Robert Hooke – English monk in 1665; observed
cork under a microscope & saw “little boxes”.
Named these “boxes” cells after the rooms
monks lived in.
B. Anton van Leeuwenhoek – Dutch 1673; first to
observe living cells; invented 1st working
microscope
II. Cell Theory
A. Evidence for Cell Theory:
1. Matthias Schleiden – proposed all plants are
made of cells
2. Theodor Schwann – proposed all animals are
made of cells
3. Rudolf Virchow – proposed all cells come from
other (preexisting) cells
B. Three Components of cell theory:
1. All living things are made of one or more cells.
2. Cells are the basic unit of structure & function
in an organism.
3. Cells only come from the reproduction of
other living cells.
C. Modern Cell Theory also includes:
A. Energy flow occurs within cells
B. Heredity information (DNA) is passed on from
cell to cell
C. All cells have the same basic chemical
composition
III. Cell Diversity
A. Looking at cells
1. Size – range from microscopic to visible with
naked eye.
• Limited by a cell’s surface area-to-volume
ratio
• If cell is too large, it takes too long for
materials to travel through it
2. Shape – spheres, cubes, flat, have extensions
(branched), smooth or rough surfaces.
Examples of Cell Shapes
IV. Cell Features
A. Internal Organization = how the inside is
divided into regions/areas for specific
functions.
1. Cell Membrane – cell’s outer boundary
2. Cytoplasm – fluid cytosol & any cellular
structures suspended in cytosol
3. Nucleus – cellular structure that houses DNA
4. Organelles – membrane-bound cellular
structures that carry out specific functions in a
cell
B. Types of Cells
1. Eukaryotes – cells with membrane-bound
organelles & nucleus
2. Prokaryotes – lack membrane-bound
organelles & nucleus
Section 2: Inside the Eukaryotic Cell
I. Cell Membrane – outer layer that surrounds
the cell that allows nutrients & wastes in and
out of the cell
A. Selectively Permeable – some materials are
allowed through, either in or out of the cell
B. Made of
.
1. Due to the make up of the cell membrane, only
certain materials can pass through it.
II. Cytoplasm – gelatin-like aqueous fluid
(cytosol) & the organelles suspended in it
1. Vesicle – small, spherical membrane sac that
transports proteins
III. Directing Cell Activity
A. Nucleus – “brain” of the cell; directs all cell
activities, cell division, & the making of
proteins (DNA is stored here)
1. Nuclear Envelope – double membrane around
nucleus; has pores (holes) that allow certain
molecules in or out
2. Nucleolus – spherical area inside the nucleus
that makes RNA & ribosome parts.
B. Ribosomes – made of RNA & proteins
1. Makes proteins
2. Can find them floating free in the cytoplasm
(“free”) or attached to the E.R. (bound).
IV. Protein Processing Organelles
A. Endoplasmic Reticulum – system of
internal membranes
1. Rough E.R. – covered with ribosomes; aids
ribosomes in making proteins & transporting
them by making vesicles; makes new cell
membranes
2. Smooth E.R. – not covered with ribosomes;
makes steroids, breaks down toxins, regulates
calcium levels, moves materials around cell
B. Golgi Apparatus – system of flattened
membranes
1. Modifies, packages, and secretes different
molecules in vesicles.
2. Assists E.R. in modifying proteins that are
leaving the cell.
V. Energy Production Organelle
A. Mitochondria – “power house of the cell”
1. Makes ATP! Breaks down food in cellular
respiration
2. Has a 2nd, inner membrane that has folds
called cristae.
3. Has its own DNA.
VI. Other Organelles
A. Lysosomes – contains enzymes that digests
proteins, DNA/RNA, old organelles,
bacteria, etc.
B. Vacuoles – can help maintain water
concentrations, store food, etc.
C. Cillia & Flagella – both help move the cell
1. Cillia are tiny hairlike projections.
2. Flagella is a single long whip-like tail
VII. Framework of the Cell
A. Cytoskeleton – web of protein fibers that
supports the cell & its organelles
1. Microfilaments – long thin fibers of the
protein actin; pulls the membrane in & out in
some places
2. Microtubules – thick hollow fibers of the
protein tubulin; molecules move through it
3. Intermediate Fibers – moderately thick &
anchors organelles in place
B. Centrioles
1. Made of microtubules
2. Helps the cell divide
3. Found in animal cells and most protists
VIII. Plant Cells – have some organelles not present
in animal cells
A. Cell Wall – rigid, inorganic layer surrounding
the cell membrane; made of cellulose &
other carbohydrates
B. Central Vacuoles
1. Fluid-filled organelles that store water, ions,
enzymes, & wastes
2. Can take up 90% of the space/volume of a cell
C. Chloroplasts
1. Have two membranes & their own DNA
2. Absorb sun light & converts it to food
(photosynthesis)
Plant Cell
Animal Cell
Section 3: From Cell to Organism
I. Diversity in Cells
A. Prokaryotes – cells that lack membranebound organelles & nucleus
1. Vary in shape, how they obtain food & use
energy, makeup of the cell wall, & how they
move.
2. Flagella
3. Pili – short, thick outgrowths; attach
prokaryote to surfaces or other cells
Prokaryote Cell
B. Eukaryotes – cells with membrane-bound
organelles & nucleus
1. Animal vs. Plant Cells
Animal Cells
Plant Cells
Lysosomes
Flagella
Central Vacuole
Cell Wall
Vesicles
Centrioles
Chloroplast
2. Eukaryote cells vary in internal makeup so that
cells can become specialized for certain functions
i.
Muscle cells use large amount of energy, so they
contain many mitochondria!
II. Levels of Organization
Cells  Tissues  Organs  Organ System  Organism
A. Tissues – group of cells that have similar structures &
functions
1. Muscle tissue, bone tissue, vascular tissue in plants
B. Organs – different tissues arranged together to
perform a specific function
1. Heart, lung, leaf
C. Organ System – group of organs that work together
to perform a set of functions, or a major body
function
1. Circulatory system, shoot systems of plants
D. Organism – interaction of all organ systems to carry
out all life processes
1. Human, Oak tree
Levels of Organization
III. Body Types
A. Unicellular – entire body of an organism is
one cell
B. Colonial – cells that live as a connected group
but do not depend on each other for survival
C. Multicellular – cells are specialized to
perform one or a few functions of life
1. Differentiation – process by which cells develop
specialized forms & functions
2. Life depends on the interaction of all the cells!
Unicellular, Colonial, & Multicellular