Cells and Their Internal Structures

Define magnification, resolution, and contrast.

Three key terms for microscopy:

• Magnification — how much bigger the image appears compared to the actual object

• Resolution — ability to distinguish two close objects as separate. Higher resolution = sharper, more detailed image

• Contrast — difference in brightness between the object and background. Stains are often used to increase contrast

Differentiate between transmission electron microscopes (TEM) and scanning electron microscopes (SEM).

	TEM	SEM
Full name	Transmission Electron Microscope	Scanning Electron Microscope
How it works	Electrons pass through the specimen	Electrons scan the surface of the specimen
Image type	Flat 2D internal view	3D surface view
Best for	Internal organelle structure	Surface texture and shape

Identify the best type of microscope to use for different samples.

Situation	Best Microscope
Living cells or tissues	Light microscope
Internal organelle detail	TEM
3D surface of a virus or cell	SEM
Quick cheap observation	Light microscope
Highest possible resolution	Electron microscope

List and describe the structures that all cells have in common.

1. All living things are made of cells

2. The cell is the basic unit of life

3. All cells come from pre-existing cells

1. Cell membrane — controls what enters and exits the cell

2. DNA — genetic information that runs the cell

3. Ribosomes — make proteins

Explain the relationship between surface area and volume of a cell and how this explains why most cells are small.

• As a cell gets bigger its volume grows faster than its surface area

• This is a problem because nutrients and waste enter/exit through the surface (membrane)

• If the cell gets too big, the membrane can't keep up with the demands of the volume inside

Define and differentiate between the genome and proteome.

• Genome — the complete set of DNA in a cell. All of your genetic instructions. Every cell in your body has the same genome.

• Proteome — the complete set of proteins a cell produces. Different cells express different proteins even though they have the same genome.

Define cytosol and its function.

• Cytosol — the liquid component inside the cell that surrounds the organelles

• It's mostly water but also contains salts, sugars, proteins, and other molecules

• Together cytosol + organelles = cytoplasm

Diagram a bacterial cell illustrating the location and functions of the main structural components including the DNA, the nucleoid, ribosomes, plasmids, cell membrane, cell wall, capsule/glycocalyx, pili, and flagella.

Structure	Function
DNA/Nucleoid	Region where DNA is located — no membrane around it
Ribosomes	Make proteins
Plasmids	Small circular DNA separate from main DNA — often carry antibiotic resistance genes
Cell membrane	Controls what enters and exits
Cell wall	Rigid outer layer that gives shape and protection
Capsule/Glycocalyx	Sticky outer coat — helps bacteria attach to surfaces and evade immune system
Pili	Short hair-like projections — help bacteria attach to surfaces or other cells
Flagella	Long whip-like tail — used for movement

List the components of the cytoskeleton and explain their general functions.

Component	Size	Function
Microfilaments	Thinnest	Made of actin. Give cell shape, help with cell movement and division
Intermediate filaments	Medium	Provide mechanical strength and anchor organelles
Microtubules	Thickest	Made of tubulin. Cell shape, move organelles, form spindle fibers during cell division. Also make up cilia and flagella

List and describe the major eukaryotic organelles and explain the function of each.

Organelle	Function
Nucleus	Controls cell activity, stores DNA
Nucleolus	Inside nucleus, makes ribosomes
Ribosomes	Make proteins
Rough ER	Has ribosomes, makes and processes proteins
Smooth ER	No ribosomes, makes lipids, detoxifies drugs/alcohol
Golgi Apparatus	Packages and ships proteins to their destination
Mitochondria	Makes ATP (energy) — powerhouse of the cell
Lysosomes	Digest waste, old organelles, and foreign invaders
Vacuoles	Storage — large in plant cells, small in animal cells
Chloroplasts	Photosynthesis — only in plant cells
Cell wall	Rigid support — only in plant cells
Centrioles	Help organize cell division — only in animal cells

Differentiate between a prokaryotic cell and a eukaryotic cell based on structural/organelle differences.

Feature	Prokaryote	Eukaryote
Nucleus	No — DNA floats in nucleoid	Yes — DNA enclosed in nucleus
Membrane bound organelles	No	Yes
Size	Smaller	Larger
DNA shape	Circular	Linear chromosomes
Ribosomes	Yes (smaller)	Yes (larger)
Examples	Bacteria, archaea	Animals, plants, fungi, protists

Differentiate between a plant cell and animal cell based on structural/organelle differences.

Feature	Plant Cell	Animal Cell
Cell wall	Yes	No
Chloroplasts	Yes	No
Large central vacuole	Yes	No (small vacuoles)
Centrioles	No	Yes
Shape	Rigid, rectangular	Flexible, irregular

Diagram the process of making a protein such as insulin for secretion.

The endomembrane system is a series of organelles that work together to make, process, and ship proteins.

Organelles involved:
Nucleus → Rough ER → Smooth ER → Golgi → Vesicle → Cell membrane

The pathway using insulin as an example:

Step	What happens
Nucleus	DNA instructions for insulin are read and sent out as mRNA
Rough ER	Ribosomes on rough ER read mRNA and build the insulin protein
Smooth ER	Protein gets some initial processing
Golgi Apparatus	Insulin gets packaged, modified, and labeled for shipping
Vesicle	Insulin is wrapped in a membrane bubble for transport
Cell membrane	Vesicle fuses with membrane, insulin is released outside cell (exocytosis)