Diffusion of WATER ONLY through a selectively permeable membrane. Water moves toward more solute. No ATP needed.
Remember
Water follows solute
Water moves where there's more dissolved stuff
Tonicity
Solution
Water Moves
Animal Cell
Plant Cell
Hypotonic
INTO cell
Swells/bursts
Turgid ✅
Hypertonic
OUT of cell
Shrinks
Plasmolysis
Isotonic
Both ways equally
Normal
Normal
Memory TrickHypo = less solute outside. Hyper = more solute outside. Iso = equal.
⚖️
Homeostasis & Feedback Loops
Maintaining balance
⭐ Test Topic
▼
What Is Homeostasis?
The ability to maintain a stable internal environment despite external changes. Body constantly adjusts temperature, blood sugar, pH, and water balance.
Feedback Types
Negative Feedback
Counteracts change — restores set point
Most common. Ex: temperature, blood sugar
Positive Feedback
Amplifies change — pushes further
Rare. Ex: childbirth contractions
⚠️ Confusion"Negative" doesn't mean bad! It MAINTAINS balance by opposing change.
Cytoplasm divides. Completes cell division. Two daughter cells formed.
Cut
⚠️ Tricky ones! Spindle fibers DISAPPEAR in Telophase. Nuclear envelope BREAKS DOWN in Prophase. Sister chromatids separate in ANAPHASE. Chromosomes condense in PROPHASE.
Interphase Stages — Correct Order
G1 (FIRST)
Cell grows and carries out normal cell functions
S Phase (SECOND)
DNA is duplicated (replicated)
G2 (THIRD)
Chromatid fibers packaged into chromosomes. Cell prepares for division.
Order: G1 → S → G2 The cell spends 90% of its life in interphase!
Sexual vs Asexual Reproduction
Feature
Asexual
Sexual
Parents needed
ONE
TWO
Offspring genetics
Identical (clones)
Unique (genetically different)
Speed
Faster
Slower
Adaptation
Poor (no diversity)
Good (diversity helps adapt)
Who uses it
Most single-celled organisms
Most multicellular organisms
Involves
Mitosis
Meiosis — union of sex cells (egg & sperm)
Example
Budding, binary fission
Humans, most animals
⚠️ Budding = ASEXUAL not sexual! Also: asexual does NOT allow adaptation to environmental changes — that's a disadvantage.
Diffusion — Factors That Affect Rate
Factor
Effect on Rate
Greater distance to travel
SLOWER diffusion rate
Dense solvents
DECREASE the rate
Molecule size (small nonpolar)
Pass through membrane EASIER
Higher concentration
INCREASE diffusion rate
Higher temperature
FASTER diffusion
Energy requirement
Does NOT require energy (passive)
Small NONPOLAR molecules cross membranes most easily (O₂, CO₂). Large or polar molecules need help (facilitated diffusion).
Osmosis — Tonicity Deep Dive
Remember: compare solute concentration OUTSIDE vs INSIDE the cell.
Solution Type
Solute Outside vs Inside
Water Moves
Cell Result
Hypertonic
MORE solute outside
OUT of cell
Cell shrinks/crenates
Hypotonic
LESS solute outside
INTO cell
Cell swells/bursts
Isotonic
EQUAL solute both sides
Both ways equally
No change
⚠️ Tricky Example! Cell: 40% water 60% solute / Solution: 60% water 40% solute → Solution has LESS solute → HYPOTONIC → water moves IN. The cell has more solute so water rushes in!
Turgor Pressure
Water pressure inside plant cells — critical for plant structure and staying upright
Plants in hypotonic solution become turgid = healthy & firm
Protein Channel
Structure that helps LARGE molecules cross the membrane
Used in facilitated diffusion — NOT active transport
Homeostasis — Advanced Concepts
Endotherm
Generates heat INTERNALLY (warm-blooded)
Humans, mammals, birds
Ectotherm
Generates heat EXTERNALLY (cold-blooded)
Reptiles, fish, amphibians
Shivering
Muscle contractions that generate HEAT
This INCREASES body temperature
ATP
Cellular respiration converts glucose into ATP
ATP = the energy currency of cells
What Increases vs Decreases Body Temperature
Increases Temp 🔺
Decreases Temp 🔻
Shivering (muscle contractions → heat)
Sweating
Exercising
Standing in a pool
Raising air temperature
Lowering air temperature
Adding clothing
Removing clothing
Cell Cycle — Key Facts
Brain cells
TRUE: Some cells like brain cells (neurons) never reproduce
Human chromosomes
Humans have 46 chromosomes (23 pairs)
Sister chromatids
Held together by CENTROMERES (not centrioles!)
Centrioles
Organelle that creates spindle fibers (in animal cells)
Chromosome
Entire structure containing DNA that carries genetic info
Apoptosis
Programmed cell death — controlled self-destruction
⚠️ Centromere vs Centriole! CENTROMERES hold sister chromatids together. CENTRIOLES create spindle fibers. These are completely different structures!
📝
Science Test Review — Cell Cycle, Diffusion & Homeostasis
Common test topics & tricky questions
⭐ Test Prep
▼
True/False Traps to Know
❌ FALSE
Some cells like brain cells never reproduce
TRUE — neurons rarely divide, but the statement is testing if you know exceptions exist
✅ TRUE
Humans have 46 chromosomes
23 pairs — one set from each parent
✅ TRUE
Reproductive cells do NOT undergo the mitotic phase
Sex cells use MEIOSIS, not mitosis
❌ FALSE
Sister chromatids are held together by CENTRIOLES
CENTROMERES hold sister chromatids. Centrioles make spindle fibers — totally different!
Centromere vs Centriole — The #1 Confusion
CENTROMERE
Holds sister chromatids together
Found on the chromosome itself
CENTRIOLE
Organelle that creates spindle fibers
Found in animal cells only. Helps pull chromosomes apart.
CHROMOSOME
The entire structure containing DNA
Carries genetic information. Humans have 46.
CHROMATID
One half of a replicated chromosome
Two sister chromatids = one duplicated chromosome
Cell Cycle Checkpoints
Checkpoint
What It Checks
When
G1 Checkpoint
Is DNA damaged? Is the cell big enough?
Before DNA replication
G2 Checkpoint
Was DNA replicated properly?
Before mitosis begins
M Checkpoint (Spindle Assembly)
Are all chromosomes aligned at equator?
During metaphase
⚠️ Common Mix-Up"Check for DNA damage" = G1. "Check DNA replicated properly" = G2. "Spindle assembly / chromosome alignment" = M checkpoint.
Cell Cycle Regulators
Positive Regulators
Allow the cell cycle to move FORWARD
Example: Cyclin proteins — rise and fall to signal progression
Negative Regulators
STOP or slow the cell cycle
Example: P53 — initiates apoptosis if DNA is too damaged
Cyclin
Proteins that rise and fall to control cell cycle phases
P53
Negative regulator — triggers apoptosis when DNA is damaged
Key FactRegulators are made of PROTEINS. Uncontrolled cell growth = Cancer. A clump of cancer cells = Tumor.
Diffusion — Factors That Affect Rate
Factor
Effect on Diffusion Rate
Greater distance
SLOWER — more ground to cover
Dense solvent
DECREASES rate — harder to move through
Molecule size
Small NONPOLAR molecules cross easiest
Higher concentration
INCREASES rate — steeper gradient
Higher temperature
FASTER — more kinetic energy
Energy needed?
NO — diffusion is passive
Key Terms
Protein Channel = Facilitated Diffusion
Large molecules use protein channels to cross — still no energy. Low concentration = fewer molecules. High concentration = more molecules crowded. Concentration gradient = difference between two areas.
Osmosis & Tonicity — The Tricky One
Scenario
Solution Type
Water Moves
Cell: 40% water 60% solute | Solution: 60% water 40% solute
HYPOTONIC (less solute outside)
INTO cell — cell swells
Cell: 60% water 40% solute | Solution: 60% water 40% solute
ISOTONIC (equal solutes)
Both ways equally
Cell: 60% water 40% solute | Solution: 40% water 60% solute
HYPERTONIC (more solute outside)
OUT of cell — cell shrinks
⚠️ RememberWater follows solute. More solute OUTSIDE = hypertonic = water leaves cell. Less solute outside = hypotonic = water enters cell. TURGOR PRESSURE = critical for plant structure — plants in hypotonic solutions become turgid and stand upright.
Homeostasis Extended
Ectotherm
Generates heat EXTERNALLY (from environment)
Ex: reptiles, fish — cold-blooded
Endotherm
Generates heat INTERNALLY (from metabolism)
Ex: mammals, birds — warm-blooded
Shivering
Muscle contractions generate HEAT
Negative feedback — warms body back to set point
Turgor Pressure
Water pressure inside plant cells keeping them rigid
Plants wilt when they lose turgor pressure
ATP
Cellular respiration converts glucose INTO ATP
ATP = energy currency of the cell
Solute
A substance that can be dissolved within a solvent
Salt dissolved in water: salt = solute, water = solvent
Increases Body Temp
Raising air temp, Shivering, Exercising, Adding clothing
Chromosomes at opposite poles, spindle fibers disappear, nuclear envelopes reform
Two nuclei forming
Cytokinesis
Cytoplasm splits into two daughter cells, completes division
Done!
⚠️ Interphase Order: G1 → S Phase → G2 G1 = cell grows. S Phase = DNA duplicated. G2 = chromatid fibers packaged into chromosomes, prepares for division. Cell spends 90% of its life in Interphase!
Asexual vs Sexual Reproduction
Feature
Asexual
Sexual
Parents needed
1
2
Offspring
Genetically IDENTICAL
Genetically DIFFERENT
Speed
Faster
Slower
Adaptation?
No — no genetic diversity
Yes — genetic variation helps adaptation
Who does it?
Most single-celled organisms
Most multicellular organisms
Example
Budding, binary fission
Union of egg & sperm
⚠️ Budding = ASEXUAL not sexual! Sexual reproduction combines genetic material from TWO parents producing genetically different offspring.
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⚙️
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Parts & functions
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Diffusion
Concentration gradient
🌊
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Tonicity & water
⚖️
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Feedback & balance
🔁
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G1, S, G2, M phases
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PMAT & cell division
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📐 Math
Circumference & Area of Circles
⭕
Key Formulas
The two most important formulas
⭐ Must Know
▼
Circumference
Formula 1 (using diameter)
C = π × d
d = diameter (all the way across)
Formula 2 (using radius)
C = 2 × π × r
r = radius (center to edge)
Memory Trick
Cherry Pie Delicious
C = π × d
Area
Formula
A = π × r²
r = radius, squared means × itself
Steps
1. Find radius → 2. Square it → 3. Multiply by π
Memory Trick
Apple Pies are Round
A = π × r²
🔢
Key Terms
Radius, diameter, pi, and more
▼
Vocabulary
Term
Definition
Tip
Radius (r)
Distance from center to edge
Half the diameter
Diameter (d)
Distance all the way across
d = 2r
Pi (π)
≈ 3.14 (or 22/7)
Never-ending number
Circumference
Distance around the circle
Like the perimeter
Area
Space inside the circle
Measured in units²
⚠️ Common MistakeArea uses r² (radius squared). Circumference uses d or r but does NOT square them!
🧮
Example Problems
Step-by-step walkthroughs
▼
Circumference Example
A circle has a diameter of 10 cm. Find the circumference.
Step 1
Write formula: C = π × d
Step 2
Plug in: C = 3.14 × 10
Step 3
Solve: C = 31.4 cm
Area Example
A circle has a radius of 5 cm. Find the area.
Step 1
Write formula: A = π × r²
Step 2
Square r: 5² = 25
Step 3
Multiply: 3.14 × 25 = 78.5 cm²
Finding Radius from Diameter
If you're given the diameter but need radius: divide by 2
Example
d = 14 → r = 14 ÷ 2 = 7
✏️ Math Quiz
Circles — Circumference & Area
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📖 ELA
Uglies by Scott Westerfeld
📖
Book Overview
Setting, premise & themes
⭐ Start Here
▼
Basic Info
Author
Scott Westerfeld
Genre
Dystopian / Sci-Fi / YA
Setting
Future city, ~300 years from now
Series
Book 1 of the Uglies series
The Premise
In this future society, everyone is considered "ugly" until they turn 16. At 16, everyone gets a surgery to become "pretty" — perfectly beautiful by society's standards. The story follows Tally Youngblood as she questions whether beauty and conformity are worth the cost.
Key IdeaThe surgery doesn't just change looks — it changes how people think, making them shallow and easy to control.
Major Themes
Beauty & Conformity
Society forces everyone to look the same — is that freedom or control?
Identity
Who are you when society erases what makes you different?
Government Control
The Specials use beauty as a tool to keep people obedient
Friendship & Loyalty
Tally must choose between her friend Shay and becoming Pretty
👥
Main Characters
Who's who in Uglies
▼
Characters
Tally Youngblood
Main character. Almost 16, desperate to become Pretty. Grows into a rebel when she learns the truth.
Shay
Tally's best friend. Refuses the surgery and runs away to the Smoke.
David
Leader's son in the Smoke. Grew up never having the surgery. Falls for Tally.
Dr. Cable
Leader of Special Circumstances. The main antagonist — manipulates Tally.
Peris
Tally's childhood best friend. Already turned Pretty at the start of the book.
The Smoke
Not a person — a hidden community of runaways who refused the surgery.
📝
Plot Summary
Key events chapter by chapter
▼
Story Arc
Part
What Happens
Beginning
Tally is an Ugly, 3 months from surgery. Her friend Peris already turned Pretty. She sneaks into New Pretty Town.
Rising Action
Tally meets Shay, who doesn't want the surgery. Shay runs away to "the Smoke" — a hidden rebel settlement.
Conflict
Dr. Cable blackmails Tally — find the Smoke or never become Pretty. Tally agrees and follows Shay's coded directions.
Climax
Tally arrives at the Smoke, discovers the surgery also brain-damages people. She accidentally triggers a tracker.
Resolution
Special Circumstances raids the Smoke. To save David's parents, Tally turns herself in to get the surgery.
💡
Literary Devices
Figurative language & techniques
▼
Key Techniques
Device
Definition
Example from Uglies
Dystopia
A seemingly perfect society with dark underlying control
Everyone becomes "pretty" but loses free thought
Symbolism
Objects/ideas representing something deeper
Surgery = conformity and loss of identity
Foreshadowing
Hints at future events
Shay's resistance hints at the rebellion to come
Irony
Opposite of what's expected
"Pretty" surgery makes people ugly on the inside
Conflict
Internal and external struggle
Tally torn between fitting in and doing what's right
✏️ ELA Quiz
Uglies by Scott Westerfeld
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🌍 Social Studies
The Cold War
🌐
What Was the Cold War?
Overview & causes
⭐ Start Here
▼
Quick Overview
The Cold War was a period of political tension between the United States and the Soviet Union (USSR) from roughly 1947 to 1991. It was called "cold" because the two superpowers never directly fought each other — instead they competed through proxy wars, arms races, and propaganda.
USA Side
Democracy & Capitalism
NATO alliance. Leader of the "free world."
USSR Side
Communism
Warsaw Pact alliance. Controlled Eastern Europe.
Duration
1947–1991 (~44 years)
Why "Cold"?
No direct military combat between USA & USSR
Main Causes
Cause
Explanation
Ideological Differences
USA (democracy/capitalism) vs USSR (communism) — totally opposite systems
Post-WWII Power Vacuum
After WW2, USA and USSR emerged as the two superpowers
Soviet Expansion
USSR took control of Eastern European countries after WW2
Atomic Bomb
USA had nuclear weapons first — USSR feared this and raced to catch up
🔑
Key Events
Timeline of major moments
▼
Timeline
Year
Event
Why It Matters
1947
Truman Doctrine
USA pledges to stop the spread of communism
1949
USSR gets atomic bomb
Now both sides have nukes — arms race begins
1950–53
Korean War
USA vs communist North Korea — first proxy war
1957
Sputnik launched
USSR first in space — space race begins
1961
Berlin Wall built
Divides communist East and democratic West Berlin
1962
Cuban Missile Crisis
Closest the world came to nuclear war
1969
Moon Landing
USA wins the space race
1989
Berlin Wall falls
Symbol of Cold War ending
1991
USSR dissolves
Cold War officially ends — USA wins
⚛️
Key Concepts
Terms you need to know
▼
Vocabulary
Term
Definition
Containment
US policy to stop communism from spreading to new countries
Arms Race
USA & USSR competing to build more/better nuclear weapons
Proxy War
Two superpowers support opposite sides in another country's war
Iron Curtain
Imaginary line dividing communist Eastern Europe from the West
MAD
Mutually Assured Destruction — both sides would be destroyed in nuclear war
Space Race
USA vs USSR competing to achieve space milestones first
NATO
US-led military alliance of Western democratic nations
Warsaw Pact
Soviet-led military alliance of communist nations
⚠️ RememberMAD = neither side dares to launch nukes first because both would be destroyed. This actually kept the peace!
🏁
How It Ended
The fall of the Soviet Union
▼
Why the USSR Collapsed
Economic Failure
Communism couldn't keep up with the cost of the arms race
Gorbachev's Reforms
Glasnost (openness) and Perestroika (restructuring) loosened control
Berlin Wall Falls 1989
Symbol that communist control was crumbling
1991
USSR officially breaks apart into 15 separate countries
✏️ Social Studies Quiz
The Cold War
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