CSET Life Science: General Science Domain 3

Elements in living things

• Carbon (C) → backbone of most biological molecules

• Hydrogen (H) → found in water and organic molecules

• Oxygen (O) → important for cellular respiration

• Nitrogen (N) → found in proteins and DNA/RNA

• Phosphorus (P) → found in DNA, RNA, ATP, and cell membranes

• Sulfur (S) → found in some proteins

• CHONPS

Biomolecules

• Biomolecules = molecules made by living things.

• Carbohydrates → quick energy

• Lipids → long-term energy + cell membranes

• Proteins → structure + enzymes + many cell functions

• Nucleic acids → store genetic information (DNA & RNA)

Cell Theory

• All living things are made of one or more cells.

• The cell is the basic unit of life.

• All cells come from pre-existing cells.

Prokaryotes vs. Eukaryotes

• Prokaryotes

  • No nucleus

  • No membrane-bound organelles

  • Usually smaller and simpler

    • Example: bacteria

• Eukaryotes

  • Have a nucleus

  • Have membrane-bound organelles

  • Usually larger and more complex

    • Examples: plants, animals, fungi, protists

Organelles

• Nucleus → stores DNA; controls cell activities

• Ribosomes → make proteins

• Mitochondria → produce ATP/usable energy

• Cell membrane → controls what enters/leaves

• Cytoplasm → jelly-like fluid that fills the cell and holds organelles in place.

• Vacuole → store nutrients, water, and waste

• Lysosomes → break down waste/materials

• Golgi apparatus → modifies, sorts, packages proteins

• Endoplasmic reticulum (ER) → makes/transports proteins and lipids

Protein Synthesis

• Protein synthesis = process of making proteins from genetic information.

• DNA → RNA → Protein

• Transcription = DNA → mRNA

• Translation = mRNA → protein

• Ribosomes perform translation.

Mitosis vs. Meiosis

• Mitosis

  • Produces 2 identical diploid cells

  • Used for growth, repair, and replacing cells

  • 1 division

  • Daughter cells have the same chromosome number as the original cell

• Meiosis

  • Produces 4 genetically different haploid cells

  • Used to make gametes (sex cells)

  • 2 divisions

  • Daughter cells have half the chromosome number

Cell Differentiation

• The process where unspecialized cells become specialized for specific functions.

• Different cells have the same DNA, but express different genes.

• Specialized cells have structures suited to their functions.

  • Example:

    • muscle cells → specialized movement

    • nerve cells → specialized in transmitting signals.

Levels of Biological Organization

• Cell → basic unit of life

• Tissue → group of similar cells working together

• Organ → group of tissues working together

• Organ system → group of organs working together

• Organism → complete living thing

Plant Structures & Processes

• Plant Organs (The Main Structures)

  • Roots → absorb water and minerals from the soil; anchor the plant firmly in the ground.

  • Stem → supports the leaves and flowers; transports water, nutrients, and food between the roots and leaves.

  • Leaves → the main organ where photosynthesis takes place to create food for the plant.

• Transport Tissues (The Plant's Plumbing)

  • Xylem → microscopic tubes that transport water and minerals upward from the roots to the leaves.

  • Phloem → microscopic tubes that transport sugars and food throughout the entire plant.

• Leaf Anatomy & Gas Exchange (The Surface Level)

  • Cuticle → a waxy outer layer on the leaf surface that prevents water loss.

  • Stomata → microscopic openings or pores on leaves that allow gases (oxygen and carbon dioxide) to enter and exit.

  • Guard cells → pairs of cells that surround each stoma to control its opening and closing.

• Cellular Structures

  • Chloroplasts → the specific structures inside plant cells where photosynthesis takes place.

  • Chlorophyll → the green pigment inside chloroplasts that captures sunlight energy.

  • Cell wall → support/protection

Photosynthesis

• The process plants use to convert light energy → chemical energy (glucose).

• Occurs mainly in the chloroplasts.

• Chlorophyll absorbs light energy.

• Formula

  • CO₂ + H₂O + light → C₆H₁₂O₆ + O₂

Cellular Respiration

• The process cells use to break down glucose to make ATP energy.

• Occurs mainly in the mitochondria.

• Uses glucose + oxygen.

• Produces ATP + CO₂ + H₂O.

• ATP = main usable energy source for cells.

Homeostasis & Feedback

• Homeostasis refers to maintaining a stable internal environment despite outside changes.

• Negative feedback = reverses a change to restore stability.

  • Example: body temperature gets too high → sweating cools you down.

• Positive feedback = amplifies a change.

  • Example: Blood clotting → a clotting response activates more clotting factors → the clot grows.

Biotic vs. abiotic factors

• Biotic factors = living parts of an ecosystem.

  • Examples: plants, animals, bacteria, fungi

• Abiotic factors = nonliving parts of an ecosystem.

  • Examples: sunlight, temperature, water, soil, rocks, pH

Populations & Communities

• Population → all individuals of the same species living in the same area.

• Community → all the different populations/species living and interacting in an area.

• Ecosystem → community + abiotic factors.

Food webs

• Food chain → one pathway of energy flow.

• Food web → multiple interconnected food chains.

• Producer → makes its own food (usually plants/algae).

• Consumer → gets energy by eating other organisms.

• Decomposer → breaks down dead organisms and returns nutrients to the environment.

• Trophic levels:

  • Producer → Primary consumer → Secondary consumer → Tertiary consumer

    • Producer: Grass uses sunlight to make its own food through photosynthesis.

    • Primary consumer: Grasshopper eats the grass to get energy.

    • Secondary consumer: Frog eats the grasshopper for energy.

    • Tertiary consumer: Snake eats the frog as the top meat-eater in this chain.

      
      

  • Only about 10% of energy is transferred to the next trophic level.

    
    

DNA Structure & Function

• DNA → molecule that stores genetic information.

• Nucleotide → building block of DNA.

• Each nucleotide has: sugar + phosphate + nitrogen base.

• DNA has a double helix structure

  • Bases:

    • A → Adenine

    • T =→Thymine

    • C → Cytosine

    • G → Guanine

  • Base pairing: A ↔ T and C ↔ G

• Gene = section of DNA that contains instructions for a functional product, usually a protein.

Mutations & Variation

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  • Mutation → change in DNA sequence.

  • Mutations create genetic variation, which are differences in DNA/traits among individuals.

• Examples of mutations:

  • Substitution: one DNA base is replaced

  • Insertion: extra DNA bases are added

  • Deletion: DNA bases are removed

  • Frameshift: insertion/deletion shifts how codons are read

• Examples of genetic variation:

  • Different eye colors

  • Different blood types

• Examples of effects:

  • Harmful: mutation causes a genetic disorder

  • Beneficial: mutation provides resistance to a disease

  • Neutral: mutation has no noticeable effect

• Mutations can happen randomly or be caused by environmental factors.

• Variation is important for natural selection and evolution.

Genotype vs. Phenotype

• Genotype → an organism’s genetic makeup (alleles).

  • Example: BB, Bb, bb

• Phenotype → the observable trait.

  • Example: brown eyes, blue eyes

• Genotype influences phenotype

• Phenotype can also be affected by the environment.

• Examples:

  • Height

    • Genes influence potential height, but nutrition can affect actual height.

  • Skin color

    • Genetics influence pigmentation, while sun exposure can affect it.

Dominant/recessive traits

• Dominant allele → expressed when at least one copy is present.

  • B = dominant

• Recessive allele → expressed only when two copies are present.

  • b = recessive

• Homozygous = two same alleles

  • BB or bb

• Heterozygous = two different alleles

  • Bb

• Examples:

  • BB → dominant phenotype

  • Bb → dominant phenotype

  • bb → recessive phenotype

Sex Linked Traits

Males (XY): Are hemizygous and only have one X chromosome. A single recessive allele cannot be masked, so it is automatically expressed.

• X^BY (unaffected) , X^bY (has the condition)

Females (XX): Have two X chromosomes. They must be homozygous recessive to express the trait; if they are heterozygous, they are unaffected carriers.

• X^BX^B (Not a carrier), X^BX^b(carries but unaffected), X^bX^b (has condition)

Incomplete Dominance

• Incomplete dominance → neither allele is completely dominant.

• Heterozygous phenotype is a blend/intermediate of the two homozygous phenotypes.

• Example:

  • RR = red flowers

  • WW = white flowers

  • RW = pink flowers

Evidence for Evolution

• Fossils → show organisms from the past and changes over time.

• Homologous structures → similar structures due to common ancestry.

  • Example: human arm, bat wing, whale flipper.

• Vestigial structures → reduced structures with little/no current function.

  • Example: human tailbone.

• Embryology → similarities in early development can indicate common ancestry.

• Comparative DNA/proteins → more genetic similarity = more closely related.

• Biogeography → geographic distribution of organisms supports evolutionary relationships.

Common Ancestry

• Common ancestry → different species descended from a shared ancestral species.

• Species that share a more recent common ancestor are more closely related.

• Evolution causes populations to change over generations.

• Example

  • Humans and chimpanzees share a common ancestor.

  • Humans did not evolve directly from modern chimpanzees.

Speciation

• The formation of a new species.

• Usually happens when populations become reproductively isolated.

• Reproductive isolation = populations can no longer successfully mate and produce fertile offspring.

• A common cause is geographic isolation → populations are separated → evolve differently → eventually become different species.

• Example:

  • A population of birds gets separated onto different islands.

  • Each population experiences different environments and selection pressures.

    • Over many generations → they become genetically different → eventually cannot interbreed → new species.