Biology: Microscopes, Cells, and the Cell Cycle

Microscopes

Essential tools for observing cells and other tiny specimens.

Total Magnification

Ocular lens magnification × objective lens magnification (E.g. Ocular Lens 5X × Objective Lens 10X = 50X).

Common magnifications for classroom microscopes

Include 40x (low power), 100x (medium power), and 400x (high power), using a 10x ocular lens.

Field of View (FOV)

The visible area through the microscope; as magnification increases, the FOV becomes smaller, but more detail becomes visible.

FOV Formula

HP FOV × HP Magnification = LP FOV × LP Magnification.

Actual Cell Size

FOV (mm) ÷ # Specimens across.

Ocular Lens/Eyepiece

Contains a lens to magnify the image (usually 10x magnification).

Body Tube

Connects the eyepiece to the objective lenses and ensures correct alignment.

Arm

Connects the body tube to the base and is used for carrying the microscope.

Base

Supports the microscope's weight and contains electronics and the light source.

Lamp/Light Source/Illuminator

Sends light upwards through the hole in the stage onto the specimen.

Revolving/Rotating Nose Piece

Objective lenses are attached to it; rotating allows switching between lenses.

Objective Lenses

Further magnify the image (e.g., 4x, 10x, 40x).

Coarse Adjustment Knob

Used to help put the specimen in focus, primarily under low power.

Fine Adjustment Knob

Used for exact focusing, especially under higher power; both knobs move the stage up and down.

Stage

Where the slide containing the specimen is placed; it has a hole for light to pass through.

Stage Clips

Secure the slide on the stage.

Condenser Lens

Located under the stage, it focuses light from the illuminator through the stage hole onto the specimen.

Cells

The fundamental units of life, with various structures and functions.

Cell Theory

All living organisms are composed of one or more cells; the cell is the most basic unit of life; all cells arise from pre-existing, living cells.

Vesicle

Stores and transports substances throughout the cell.

Mitochondria

"The powerhouse of the cell," supplying energy by converting sugar into useful energy.

Lysosomes

The "clean-up system," responsible for digestion and breaking down bacteria and damaged organelles.

Rough Endoplasmic Reticulum

Carries material and is associated with making proteins; has ribosomes attached.

Ribosomes

Sites where proteins are assembled; can be attached to the rough ER or free in the cytoplasm.

Smooth Endoplasmic Reticulum

Produces fats and oils; does not have ribosomes.

Golgi Apparatus

Receives, modifies, sorts, and packages proteins for delivery inside and outside the cell.

Cytoskeleton

An internal network of fibres that helps maintain the cell's shape.

Centriole

Involved in cell division; found only in animal cells.

Chloroplasts

Contain chlorophyll, enabling plants to use sunlight for photosynthesis (converting CO2 and water into sugar and O2); found only in plant cells. They contain thylakoids (sacs of chlorophyll) stacked into grana.

Cell Wall

Provides strength, protection, support, and structure to plant cells; found only in plant cells.

Cell Membrane

Forms a protective barrier around the cell, allowing some substances to move through it via diffusion; made of lipids.

Cytoplasm

Jelly-like substance that fills the cell and suspends organelles, allowing nutrients and organelles to move within the cell.

Nucleus

Control center of the cell, determining growth and reproduction; typically found near the center of the cell and surrounded by the nuclear envelope.

Nuclear Envelope/Membrane

Surrounds the nucleus and contains pores for material transport.

Nucleolus

Small, dense area within the nucleus that contains most of the cell's DNA and manufactures ribosome parts.

Chromatin

Granular substance in the nucleus where DNA is bound; condenses to form chromosomes during cell division.

Vacuole

Stores wastes and other substances; in plants, a large central vacuole stores water.

Cell Division

Helps with growth, repair of tissues, and replacing old or damaged cells; prevents cells from becoming too large to function.

DNA

Long and must be packed tightly to fit in the nucleus.

Chromosomes

Before division, chromatin coils further into chromosomes.

Sister Chromatids

Each chromosome copies itself to form sister chromatids, joined at a point called the centromere.

Interphase

90% of cell life; includes G1 Phase, S Phase, and G2 Phase.

G1 Phase

The Cell grows and does normal jobs.

S Phase

DNA and proteins are copied.

G2 Phase

Prepares organelles and structures for division.

Mitotic Phase (M Phase)

Includes Mitosis (nuclear division) and Cytokinesis (cytoplasm division).

Prophase

Chromosomes become visible; centrioles move to opposite ends; spindle fibres form; the nuclear membrane breaks down.

Metaphase

Chromosomes line up in the middle; each attaches to spindle fibres at the centromere.

Anaphase

Sister chromatids separate and move to opposite poles.

Telophase

Chromatids reach the poles; new nuclear membranes and nucleoli form; the cell starts to split.

Cytokinesis

In animal cells, a ring tightens at the center, forming a cleavage furrow that splits the cell; in plant cells, vesicles create a cell plate that becomes the new wall.

Apoptosis

Programmed cell death; normal and necessary

Cancer

Cells ignore apoptosis and divide uncontrollably

Normal cells

Stick together, self-destruct when damaged

Cancer cells

Don't stick, divide endlessly, and move to other areas

Benign Tumour

Non-cancerous, doesn't spread

Malignant Tumour

Cancerous, invades nearby tissue

Metastatic Tumour

Spread to other body parts via blood or lymph

Inherited mutations

Genetic changes that can lead to cancer (e.g. BRCA genes)

Carcinogens

Substances that can lead to cancer (e.g. tobacco smoke, UV radiation)

Viruses

Infectious agents that can cause cancer (e.g. HPV, Hepatitis B/C)

Detection & Risk

~45% of men and ~40% of women in Canada will develop cancer

Early detection

Improves survival (e.g. colonoscopy for colon cancer)

Surgery

Physical removal of tumour

Chemotherapy

Cytotoxic drugs that stop mitosis (e.g. Taxol blocks spindle)

Radiation

Gamma/X-ray beams damage DNA in cancer cells

Stem Cells

Unspecialized cells that can become other cell types

Differentiation

Process where stem cell becomes specialized cell (e.g. red blood cell)

Embryonic stem cells

Found in embryos/placenta, can become any type (~200)

Adult stem cells

Found in skin, blood, and bone; help with repair

Regeneration in Humans

The liver can regenerate up to 75%; children <12 can regrow fingertips

Epithelial Tissue

Covers surfaces, lines organs (e.g. skin, intestine lining)

Connective Tissue

Supports/connects (e.g. bone, fat, blood)

Muscle Tissue

Enables movement (Skeletal, Smooth, Cardiac)

Nervous Tissue

Transmits signals using electrochemical impulses

Meristematic Tissue

Stem cells for growth (root tips, shoots)

Xylem

Moves water/minerals (dead cells)

Phloem

Moves sugar (alive cells)