science

all topics

biology-DNA structure (nucleotides, bases A,T,C,G)

DNA is a double-stranded helix made of repeating nucleotides, each containing a phosphate, deoxyribose sugar, and a base (A, T, C, or G). The strands are held together by complementary base pairing: A pairs with T, and C pairs with G via hydrogen bonds.

Nat

Chromosomes & DNA Location

chromosomes and DNA are primarily located within the nucleus of eukaryotic cells. Humans have 46 chromosomes (23 pairs)

DNA Replication

• Process of copying DNA

• Happens before cell division

• Steps:

1. DNA unzips

2. Complementary bases pair (A-T, C-G)

3. Two identical DNA molecules form

Result: 2 identical DNA strands

Genes & Proteins

• A gene = section of DNA

• Genes code for proteins

• Proteins determine traits (e.g., eye color, enzymes)

Mitosis vs Meiosis

Feature	Mitosis	Meiosis
Purpose	Growth & repair	Gamete formation
Cells produced	2	4
Genetically identical?	Yes	No
Chromosome number	Same (46)	Half (23)

Diploid vs Haploid

• Diploid (2n) = 46 chromosomes

  • Body cells

• Haploid (n) = 23 chromosomes

  • Sex cells (sperm/egg)

chemistry- Atomic Structure

Atoms are made of:

Particle	Charge	Location
Proton	+	Nucleus
Neutron	0	Nucleus
Electron	–	Electron cloud

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Atomic Number

• Number of protons

• Identifies the element

• Example:

  • Carbon = 6 protons → atomic number = 6

Electron Configuration

• Shows how electrons are arranged in shells

• Example:

  • 2, 8, 8 (for first 20 elements rule)

Ionic vs Covalent Bonding

Ionic Bonding

• Transfer of electrons

• Metal + non-metal

• Forms ions

Example:

• Na⁺ + Cl⁻ → NaCl

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Covalent Bonding

• Sharing of electrons

• Non-metal + non-metal

Example:

• H₂O

Identifying Bond Types

• Metal + non-metal → Ionic

• Non-metal + non-metal → Covalent

Writing Chemical Formulas

Ionic Compounds:

• Balance charges so total = 0

Example:

• Mg²⁺ + Cl⁻ → MgCl₂

Formation of Ionic Compounds

1. Metal loses electrons → positive ion

2. Non-metal gains electrons → negative ion

3. Opposite charges attract → compound forms

Ion Charges (Common)

Group	Charge
Group 1	+1
Group 2	+2
Group 6	–2
Group 7	–1

earth and science-light years

• A light year is a distance, not time

• It is how far light travels in one year

• ≈ 9.46 trillion km

Used to measure huge distances in space

Doppler Effect

• Change in wavelength/frequency due to movement

In space:

• Red shift → object moving away

• Blue shift → object moving toward

Parallax

• Apparent shift in position of a nearby star when viewed from different points

Used to measure distances to nearby stars

Big Bang Theory

• The universe began from a hot, dense point

• It has been expanding ever since

Expanding Universe

• Galaxies are moving away from each other

• The farther away they are, the faster they move away

Hubble’s Observations

• Edwin Hubble observed:

  • Galaxies show red shift

  • More distant galaxies = greater red shift

Conclusion: Universe is expanding

Evidence for the Big Bang

• Red shift (galaxies moving away)

• Cosmic microwave background radiation

• Abundance of light elements (hydrogen, helium)

Motion & Forces-Speed vs Velocity

• Speed = how fast something moves (no direction)

• Velocity = speed with direction

Speed Calculation

Speed= Time

Distance​

Units: m/s

Acceleration

• Change in velocity over time

Acceleration=Change in velocity

Time

Units

• Speed → m/s

• Acceleration → m/s²

Speed-Time Graphs

• Flat line → constant speed

• Upward slope → acceleration

• Downward slope → deceleration

• At 0 → object is stopped

Describing Motion from Graphs

• Steep slope → faster acceleration

• Horizontal line → steady motion

• Curve → changing acceleration

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Forces Affecting Motion

Main forces:

• Gravity → pulls objects downward

• Friction → opposes motion

• Air resistance → slows objects moving through air

• Applied force → push or pull

Newton’s First Law

• Objects stay at rest or move at constant velocity unless acted on by a force

Quick Memory Tips

• Light year = distance, not time

• Red shift = moving away

• Speed = no direction, velocity = direction

• Acceleration = change in speed

• A-T, C-G (DNA pairing)

• PMAT (mitosis stages: Prophase, Metaphase, Anaphase, Telophase)

• Ionic = transfer, Covalent = share

• Diploid = double, Haploid = half