Chem + Bio

🧪 Iodine Clock Reaction

• The iodine clock reaction is a classic chemical kinetics experiment used to study reaction rates.

• It involves mixing two clear solutions that suddenly change color (usually to blue-black) after a measurable delay.

• This delay time depends on concentration, temperature, and catalysts, allowing investigation of how these factors affect rate.

• Typically, hydrogen peroxide reacts with iodide ions and thiosulfate ions in acidic conditions.

• The color change occurs when all the thiosulfate is used up, and iodine produced in the reaction reacts with starch, forming a blue complex.

⚙ Rate (Concepts)

• Rate of reaction = how quickly reactants turn into products.

• Measured by:

  
  

  • Disappearance of reactants (e.g., loss of mass, decrease in concentration)

  • Formation of products (e.g., gas volume, color change, precipitate).

  
  

• Formula:

  \text{Rate} = \frac{\text{Change in quantity}}{\text{Change in time}}

• Factors affecting rate:

  
  

  1. Temperature – higher temperature = faster particles, more collisions.

  2. Concentration – more particles in the same space, more collisions.

  3. Surface Area – smaller particles = larger area for reaction.

  4. Catalysts – lower activation energy without being used up.

  
  

🧾 Word Equations

• Word equations show the reactants and products in a chemical reaction using words, not symbols.

• Structure:

  Reactants → Products

• Example:

  Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen

• Word equations do not show quantities or chemical formulas, but they clearly identify what reacts and what forms.

⚛ Reactants, Products, and Arrows

• Reactants: Substances that start the reaction (on the left side of the arrow).

• Products: Substances that are formed (on the right side).

• The arrow (→) means “yields” or “produces.”

• Sometimes reversible reactions use a double arrow (⇌) to show that both directions occur.

• Example:

  \text{Calcium carbonate} \rightarrow \text{Calcium oxide} + \text{Carbon dioxide}

🧮 Intro to Chemical Formulae

• A chemical formula shows which elements and how many atoms of each are in a compound.

• Subscripts show the number of atoms:

  
  

  • H_2O = 2 hydrogen atoms + 1 oxygen atom.

  
  

• Capital letters start a new element symbol.

• Compounds always have fixed ratios of atoms.

• Example:

  
  

  • CO_2 (carbon dioxide): 1 C, 2 O

  • NaCl (sodium chloride): 1 Na, 1 Cl

  
  

🔥 Signs of a Chemical Reaction

Observable signs include:

1. Color change (e.g., blue to colorless)

2. Gas production (bubbling, fizzing)

3. Temperature change (heat absorbed or released)

4. Light emission (glow, flame)

5. Formation of a precipitate (solid forms in a liquid)

• These changes show new substances are formed with different properties from the original materials.

🌱 Reproduction (Overview)

• Reproduction = the process of making new organisms.

• Two main types: asexual and sexual.

• Ensures the continuity of life.

• Sexual reproduction involves gametes (sperm + egg) and genetic variation.

• Asexual reproduction involves one parent and produces identical offspring (clones).

💞 Sexual Reproduction

• Involves two parents producing male and female gametes.

• Fertilization: The fusion of sperm and egg nuclei to form a zygote.

• The zygote develops into an embryo, then a baby.

• Leads to genetic variation since offspring inherit genes from both parents.

• Example in plants: pollen (male) fertilizes the ovule (female).

🌿 Asexual Reproduction

• Involves only one parent; no gametes or fertilization.

• Offspring are genetically identical (clones).

• Common in plants and simple organisms (e.g., bacteria, fungi).

• Examples:

  
  

  • Potato tubers, strawberry runners, budding in yeast.

  
  

• Advantage: fast reproduction.

• Disadvantage: no variation — less adaptability.

👩‍⚕ Female Reproductive System

Main organs:

• Ovaries – produce eggs (ova) and hormones (oestrogen, progesterone).

• Oviducts (Fallopian tubes) – site of fertilization; transport egg to uterus.

• Uterus (womb) – where the embryo implants and grows.

• Cervix – narrow opening to the uterus.

• Vagina – receives sperm and serves as the birth canal.

👨‍⚕ Male Reproductive System

Main organs:

• Testes – produce sperm and testosterone.

• Epididymis – stores and matures sperm.

• Sperm duct (vas deferens) – carries sperm from testes.

• Prostate gland & seminal vesicles – add fluids to make semen.

• Penis – delivers sperm into the female reproductive system.

🩸 Menstrual Cycle

• The menstrual cycle prepares the female body for pregnancy every month (≈28 days).

  Phases:

1. Menstrual phase (days 1–5) – uterus lining breaks down (bleeding).

2. Follicular phase (days 6–13) – oestrogen rebuilds the uterine lining; egg matures.

3. Ovulation (day 14) – egg released from ovary.

4. Luteal phase (days 15–28) – progesterone maintains the lining; if no fertilization, hormone levels drop and the cycle restarts.