1. Cell Structure and Function
Biology Ch. 3

2. 3.1 Cell Theory
In all branches of biology a key point to remember is that structure is related to function.
Cells are the smallest units of living matter that can carry out all life processes.
The invention and development of the compound microscope allowed for the discovery of cells.
Compound microscopes contain 2 or more lenses. Using more lenses increases the magnification.

3. Robert Hooke was the first to identify and name cells.
Used a compound microscope to examine thin slices of cork
He observed that cork is made of tiny hollow compartments
The compartments reminded him of small rooms so he named them cells.
What Hooke saw was the cell walls of the cork.

4. Robert Hooke Microscope Drawing of a plant cell as seen by

5. Anton van Leeuwenhoek
Used single lens microscopes that were much more powerful than Hooke’s
Became one of the first people to describe living cells observing single celled organisms in pond water.

6. Van Leeuwenhoek microscope
Microscopic life observed by van Leeuwenhoek

7. Matthias Schleiden
Used a compound microscope to study plant tissue
Proposed that plants were made of cells
Theodore Schwann
Observed similarities between plant and animal cells
Concluded that all animals are made of cells
Published the first statement of the cell theory:
All living things are made of cells and cell products
Rudolf Virchow
Stated that all cells come from preexisting cells

8. The Cell Theory
All organisms are made of cells
All existing cells are produced by other living cells
The cell is the most basic unit of life

9. Despite the variety of cells sizes and shapes in the body, all cells in the body share many characteristics.

10. Cells tend to be microscopic in size
Cells have similar building blocks
Cells are enclosed by a membrane that controls the movement of materials into and out of the cell.
The region inside the cell membrane is filled with cytoplasm.

11. Cytoplasm is a jellylike substance that contains the building blocks of the cells
Proteins, nucleic acids, minerals, & ions
Organelles are structures that perform processes in the cell.

12. Cells can be separated into 2 broad categories:
Prokaryotic
Do not have a nucleus or membrane bound organelles
DNA is suspended in the cytoplasm
Most are single celled

13. Eukaryotic
Have a nucleus and organelles
The nucleus contains the DNA
Can be multicellular or single celled

14. Additional handout
Prokaryotic cells
Believed to be the first cells
Two major forms
Archaebacteria
Eubacteria
Earth’s most abundant organisms
Wide range of environments and obtain energy in many ways

15. Eukaryotic cells
Larger
Genetic material contained in a membrane
Organelles

16. 3.2 Cell Organelles
Cytoskeleton
Network of proteins that form fibers that crisscross the entire cell
Microtubules: gives the cell its shape, acts as tracts for movement of organelles, and assists in cell division

17. Intermediate filaments: give the cell it’s strength
Microfilaments: enables the cell to move and divide and play an important role in muscle contraction

18. Cytoplasm
Fills the space between nucleus and membrane
Fluid portion is called cytosol and is mostly water
Location for many important chemical reactions

20. Nucleus
Contains the DNA of the cell
DNA contains the genes that have instructions for making proteins
Carefully protects the DNA and ensures that DNA is available at the proper times

21. The membrane consists of 2 layers and is called the nuclear envelope
Pores in the envelope allow larger materials to pass out of the nucleus
Contains the nucleolus which is the location where ribosomes are made

22. Endoplasmic Reticulum (ER)
Network of thin folded membranes
The numerous folds allow it to fit in the cell
Production of proteins and lipids
Ribosomes are located on the surface of the ER
Ribosomes link amino acids together to form proteins

23. Rough ER contains ribosomes and smooth ER does not
Smooth ER makes lipids
Proteins made on the ribosomes of ER are used on the cell membrane or are secreted
Proteins made on suspended ribosomes are used in chemical reactions.

24. Golgi Apparatus
Looks like layered stacks of membranes
Process, sort and deliver proteins
Contains enzymes that make changes to proteins
Packages proteins and stores them for later use

25. Vesicles
Small sacs that divide some materials from the rest of the cell
Transports materials throughout the cell
Protect proteins as they are transported to the Golgi apparatus
Function in storage, transport, and secretion.

26. Mitochondria
Supplies energy to the cell
Chemical reactions that convert the food you eat into usable energy
Have their own ribosomes and DNA

27. Vacuoles
Fluid filled sac used for storage
Plants contain a large central vacuole that contains a watery fluid that provides strength and support.

28. Lysosomes
Contains enzymes
Defend the cell from bacteria and viruses by engulfing them
Break down worn out or damaged cell parts
The enzymes form at the ER and the lysosomes form from the Golgi apparatus
Contains a membrane to keep the enzymes form destroying important parts of the cell.

29. Centrosome and Centrioles
The centrosome produces microtubules
Contains 2 small centrioles
Before the animal cell divides, the centrosome doubles and moves to opposite ends of the cell

30. Microtubules grow from each centrosome and form spindle fibers
These fibers help divide the DNA during cell division
Centrioles form cilia and flagella which assist in movement

32. Cell walls
Found in plants, algae, fungi, and bacteria
Rigid layer that surround the cell membrane
Provides protection, support, and shape to the cell
Contains channels for material to pass through

33. Composition varies depending on the organism:
Plants and algae – cellulose
Fungi – chitin
Bacteria - peptidoglycan

34. Chloroplasts
Carry out photosynthesis
Contain sacs called thylakoids that contain chlorophyll
Chlorophyll is the light absorbing molecule that gives plants their green color and plays a role in photosynthesis.
Have their own ribosomes and DNA
Plants do contain mitochondria along with chloroplasts which work together to capture and convert energy.

36. 3.3 Cell Membrane
The cell (plasma) membrane forms a boundary and controls the passage of materials.
The cell membrane consists of a double layer of phospholipids
A phospholipid contains 3 parts:
A phosphate group
Glycerol
2 fatty acid chains
The glycerol and phosphate groups form the “head” of the phospholipid
The fatty acids form the “tail”

37. The head of the phospholipid is polar
The head forms hydrogen bonds with water because water is also polar
The head is hydrophilic because it is attracted to water
The fatty acid tails are nonpolar and are repelled by water.
The tails are hydrophobic because they are repelled by water
The properties of polar heads and nonpolar tails cause the structure of the phospholipid bilayer.

39. Structures associated with the phospholipid bilayer
Cholesterol molecules provide strength
Proteins allow materials to pass through the membrane
Carbohydrates serve as identification tags

40. The fluid mosaic model is used to describe the arrangement of molecules that make up the cell membrane.
The cell membrane is flexible not rigid
The phospholipids move very easily
The membrane behaves like a fluid
Proteins stay in their positions
The variety of molecules embedded in the membrane resembles a mosaic

42. The cell membrane is selectively permeable which means it allows some, but not all, materials to cross.
The cell must be able to control the import and export of molecules and ions
Different molecules pass across the cell membrane in different ways
Small nonpolar molecules easily pass through the cell membrane
Small polar molecules are transported by proteins
Large molecules are moved by vesicles

43. Signal molecules allow communication with other cells
A receptor is a protein found on the cell membrane that detects a signal molecule and performs an action in response.
Receptors only bind to certain molecules
The molecule that a receptor binds to is called a ligand
There are 2 major types of receptors present in cells.
Intracellular
Membrane

44. Intracellular
Found inside the cell
Bind with molecules that are usually nonpolar and small such as hormones
Aldosterone in the kidneys is an example which helps to regulate blood pressure.

45. Membrane
Binds to molecules that cannot pass across the cell membrane
The receptor sends the message to the cell interior causing molecules inside the cell to respond

46. 3.4 Diffusion and Osmosis
Passive transport is the movement of molecules across the cell membrane without using energy.
Diffusion and osmosis are 2 types of passive transport.
Diffusion is the movement of molecules in a fluid or gas from a region of high concentration to a region of low concentration.
Concentration is the number of molecules of a substance

47. The concentration gradient is the difference in the amount of a substance from one location to another.
Molecules diffuse down their concentration gradient
Move from high to low concentration
In cells, substances such as small lipids and nonpolar molecules such as CO2 and O2 easily diffuse across the cell membrane
Diffusion occurs without the cell expelling any energy

48. Osmosis is the diffusion of water molecules
A higher concentration of dissolved particles will lower the concentration of water molecules.
A solution can be described as isotonic, hypertonic, or hypotonic.

49. Isotonic: solution has the same concentration of dissolved particles as the cell
Water molecules move in and out at an equal rate
Hypertonic: solution has a higher concentration of dissolved particles than the cell
Water concentration is higher inside the cell
Water flows out
Hypotonic: solution has a lower concentration of dissolved particles than the cell
Water concentration is higher outside the cell
Water flows in

51. Some molecules pass through the cell membrane through transport proteins.
This process is called facilitated diffusion
Even though transport proteins are used, it is still a type of passive transport.
Most transport proteins only allow certain ions and molecules to pass through.
Some transport proteins act as simple channels while others change shape to allow molecules to pass through.

53. 3.5 Active Transport, Endocytosis, and Exocytosis
Some transport proteins in cells move materials against the concentration gradient (low to high)
Transport proteins that move materials against the concentration gradient are called pumps
Transport against the concentration gradient across the cell membrane is called active transport
The transport proteins require chemical energy

54. All transport proteins span the entire cell membrane
Most transport proteins change shape when they bind to a molecule just like enzymes
There are different types of transport proteins:
Some bind to only one type of molecule
Some bind to two different types
Some bind to 2 types and move them both in the same direction
Some bind to 2 types and move them in opposite directions

55. Most transport proteins use ATP as the primary energy source
In nerve cells (neurons) the sodium-potassium pump uses ATP to move sodium and potassium to opposite sides of the cell membrane during a nerve impulse conduction.
The proton pump uses energy from ATP to move hydrogen ions (H+) out of the cell. This is used to power other active transport proteins.

56. Endocytosis is the process of taking large molecules into a cell by engulfing them in a vesicle.
A lysosome breaks down the vesicle once the molecule is inside the cell allowing the molecule to be released in the cell
Phagocytosis is a type of endocytosis where the cell membrane engulfs large particles.
Phagocytosis is common in the immune system

57. Exocytosis is the release of substances out of the cell by fusion with a vesicle
A vesicle forms around the material that is going to leave the cell
The vesicle moves to the cell surface and fuses with the cell membrane where it releases it contents.
This process occurs when a nerve impulse travels from one neuron to the next.