Comprehensive Science 8 Review Notes: Biology, Ecology, and Atomic Physics

Plant Transport System

• Xylem

  • Transports water and minerals from the roots to the leaves.

  • Moves substances upward through the plant.

  • Primary association: Xylem = Water.

• Phloem

  • Transports food (glucose) produced in the leaves to the rest of the plant.

  • Primary association: Phloem = Food.

Mendelian Genetics

• Key Genetics Terminology

  • Dominant Trait: Appears when at least one dominant allele is present.

  • Recessive Trait: Appears only when both alleles are recessive.

  • Carrier: Has one dominant and one recessive allele (represented as $Ee$).

• Punnett Square Analysis ($Tt \times Tt$)

  • Parent Cross setup: Monohybrid cross between two heterozygous parents ($Tt \times Tt$).

  • Offspring genotype combinations:

    • Top-Left Cell ($T \times T$): $TT$

    • Top-Right Cell ($T \times t$): $Tt$

    • Bottom-Left Cell ($t \times T$): $Tt$

    • Bottom-Right Cell ($t \times t$): $tt$

  • Genotypic Ratio: $1\,TT : 2\,Tt : 1\,tt$

  • Phenotypic Ratio: $3\,\text{Tall} : 1\,\text{Short}$

  • Probability Outcomes: The probability of producing short plants ($tt$) is $25\%$.

Classification of Living Things

• The Three Domains of Life

  • Archaea

    • Prokaryotic organisms lacking a nucleus.

    • Inhabit extreme environments such as hot springs and salt lakes.

  • Bacteria

    • Prokaryotic organisms lacking a nucleus.

    • Consists of common prokaryotes.

  • Eukarya

    • Eukaryotic organisms containing a nucleus.

    • Includes plants, animals, fungi, and protists.

• The Six Kingdoms of Life

  • Animalia: Multicellular consumers.

  • Plantae: Multicellular producers.

  • Fungi: Decomposers.

  • Protista: Mostly single-celled eukaryotes.

  • Eubacteria: Common bacteria.

  • Archaebacteria: Ancient bacteria living in extreme environments.

Cycles in Nature

• Water Cycle

  • Plants release water vapor into the atmosphere through transpiration.

  • Environmental impact: During periods of drought, less transpiration affects the water cycle.

• Carbon-Oxygen Cycle

  • Correct sequence of the cycle:

    1. Plants use carbon dioxide.

    2. Photosynthesis occurs.

    3. Plants release oxygen.

    4. Animals breathe oxygen and release carbon dioxide.

Photosynthesis and Cellular Respiration

• Photosynthesis Overview

  • Chemical Word Equation:         $\text{Carbon Dioxide} + \text{Water} + \text{Sunlight} \rightarrow \text{Glucose} + \text{Oxygen}$

  • Raw Materials (Reactants): Carbon dioxide, Water, and Sunlight (energy source).

  • Products: Glucose (food) and Oxygen.

  • Key Facts:

    • Occurs in the chloroplast.

    • Chlorophyll captures sunlight.

    • Plants make their own food.

• Comparison: Photosynthesis vs. Cellular Respiration

  • Photosynthesis:

    • Makes glucose.

    • Releases oxygen.

    • Occurs in chloroplast.

    • Stores energy.

    • Main organelle: Chloroplast.

  • Cellular Respiration:

    • Breaks down glucose.

    • Uses oxygen.

    • Occurs in mitochondrion.

    • Releases energy.

    • Main organelle: Mitochondrion.

Experimental Investigation of Photosynthesis

• Testing Water as a Requirement

  1. Use two similar plants.

  2. Give both plants sunlight.

  3. Water only one plant.

  4. Compare results.

• Testing Carbon Dioxide as a Requirement

  1. Use two similar plants.

  2. Give both plants sunlight.

  3. Remove carbon dioxide from one plant.

  4. Test leaves for starch afterward.

• Good Experimental Practice

  • Change only one variable.

  • Keep all other conditions the same.

  • Compare similar plants.

History of the Atomic Model and Key Scientists

• Timeline of Atomic Models

  1. Democritus: Proposed tiny indivisible particles called atoms.

  2. John Dalton: Formulated the first modern atomic theory; introduced the solid sphere model.

  3. J.J. Thomson: Discovered the electron; proposed the Plum Pudding Model.

  4. Ernest Rutherford: Conducted the Gold Foil Experiment; introduced the Nuclear Model.

  5. Niels Bohr: Proposed that electrons move in fixed energy levels.

  6. Modern Model: Electron cloud model.

• Scientists and Their Contributions

  • Democritus: Idea of atoms.

  • John Dalton: Modern atomic theory.

  • J.J. Thomson: Discovered the electron.

  • Ernest Rutherford: Discovered the nucleus.

  • Niels Bohr: Electron shells.

  • James Chadwick: Discovered the neutron.

Rutherford's Gold Foil Experiment

• Observation

  • Most alpha particles passed through the gold foil.

  • A few alpha particles were deflected.

• Conclusion

  • Most of the atoms are empty space.

  • The nucleus is small, dense, and positively charged.

Subatomic Particles, Atomic Number, and Mass Number

• Properties of Subatomic Particles

  • Proton ($p^+$):

    • Charge: $+1$

    • Location: Nucleus

    • Function: Determines the element.

  • Neutron ($n^0$):

    • Charge: $0$

    • Location: Nucleus

    • Function: Adds mass and stabilizes the nucleus.

  • Electron ($e^-$):

    • Charge: $-1$

    • Location: Electron shells

    • Function: Determines chemical behavior.

• Atomic Number and Mass Number

  • Atomic Number:

    • Equal to the number of protons.

    • Identifies the element.

  • Mass Number:

    • Formula:             $\text{Mass Number} = \text{Protons} + \text{Neutrons}$

• Element Example: Oxygen

  • Protons: $8$

  • Neutrons: $8$

  • Electrons: $8$

  • Atomic Number: $8$

  • Mass Number: $16$

• Identifying Elements

  • $6$ Protons: Carbon

  • $8$ Protons: Oxygen

  • $17$ Protons: Chlorine

  • Changing protons changes the element.

  • Changing neutrons creates isotopes.

Electron Arrangement and Chemical Behavior

• Electron Arrangement Structure

  • Example configuration: $2, 8, 1$

  • First shell: $2$ electrons

  • Second shell: $8$ electrons

  • Third shell: $1$ electron

• Chemical Behavior

  • One valence electron is easily lost.

  • Forms a positive ion.