Biology · Units 1–10 · Quick reference

General Biology

Grades 9–12+8 pages

Life and the scientific method, the chemistry of life, cells and transport, energy, cell division, heredity, DNA and biotechnology, variation and origins, classification, microbes, plants and animals, the human body and ecology.

1Study of life2Chemistry of life3Cells4Transport5Energy6Cell division7Mendel8Beyond Mendel9DNA10Gene expression11Biotech12Origins13Classification & microbes14Plants & animals15Human body16Ecology

1The Study of Life

Seven marks of living things

Made of one or more cells.
Uses energy (metabolism).
Grows and develops.
Responds to stimuli.
Reproduces.
Keeps a stable inside (homeostasis).
Carries inherited instructions in DNA.

Viruses reproduce only inside a living cell.

Independent variable: the one factor you change (x-axis)
Dependent variable: what you measure (y-axis)
Control group: gets no treatment; the baseline for comparison
Theory: a broad, well-tested explanation; strong or weak, always open to testing

Cells Make Great Reasons, Really Hard to Deny

Cells, Metabolism, Growth, Response, Reproduction, Homeostasis, DNA.

Levels of organization

molecule → cell → tissue → organ → organ system → organism
population → community → ecosystem → biosphere

Scientific method

Observe and ask a testable question.
Form a hypothesis (an if–then prediction).
Experiment: change one variable, keep the rest constant, repeat trials.
Analyze data (tables, graphs, averages).
Conclude and share; others repeat the test.

Name the variables Worked

Does fertilizer change bean height?

IV fertilizer; DV height; control none addedlight, water, soil constant

Microscope

Field of view shrinks by the same factor the power rises.

total magnification = ocular × objective

Estimate a cell size Worked

10× ocular, 40× objective → 400×
FOV at 40× is 4.5 mm, so at 400× it is 0.45 mm = 450 μm10× more power
9 cells span it → 450 μm9 = 50 μm each

2The Chemistry of Life

The four macromolecules
Molecule	Monomer	Job	Examples	Test
Carbohydrate	monosaccharide	quick energy, structure	glucose, starch, cellulose, glycogen	Benedict’s (sugar), iodine (starch)
Lipid	glycerol + fatty acids	stored energy, membranes	fats, oils, phospholipids, steroids	grease spot on brown paper
Protein	amino acid (20 kinds)	enzymes, structure, transport	hemoglobin, keratin, insulin	biuret (turns violet)
Nucleic acid	nucleotide	genetic information	DNA, RNA (ATP is a nucleotide)	—

Elements: carbs and lipids C, H, O; proteins add N (S); nucleic acids add N, P. Saturated fats (no C=C) are solid; unsaturated oils are liquid.

Water: why life depends on it

Polar: O slightly −, H slightly +.
Hydrogen bonds give cohesion (surface tension) and adhesion (climbing xylem).
High specific heat steadies temperatures.
Ice floats (less dense), so lakes freeze from the top.
Solvent: dissolves ions and polar molecules.

pH scale

0–14; below 7 acidic, 7 neutral, above 7 basic. Each step is a 10× change.

pH = −log[H⁺]

EXpH 3 is 10^{5 − 3} = 100× more acidic than pH 5. Buffers resist change (blood stays near 7.4).

Building and breaking

Dehydration synthesis links monomers and releases water (one H₂O per bond).
Hydrolysis adds water to split them.

EXC₆H₁₂O₆ + C₆H₁₂O₆ → C₁₂H₂₂O₁₁ + H₂O (glucose + glucose → maltose)

Enzymes

Protein catalysts: speed reactions by lowering activation energy; not used up.
The substrate fits the active site (lock and key; the site flexes to fit, induced fit).
Each has a best temperature and pH; heat or wrong pH denatures it (shape lost, job lost).
Lactase splits lactose.

A human enzyme works fastest near body temperature; above it the shape breaks down.

Enzymes end in -ase and never go to waste

Look for -ase, and remember an enzyme comes out of the reaction unchanged, ready to work again.

General BiologyBiology · Units 1–10 · continued

3Cells

Animal and plant cells (not to scale). Labels in the middle point to the part in each cell; color tags mark parts found in only one.

Cell theory

All living things are made of cells.
The cell is the basic unit of structure and function.
All cells come from existing cells (Virchow, 1855).

Hooke (1665), Schleiden, Schwann.

Pro = no

Prokaryotes have no nucleus; eukaryotes have a true one. (Traditional.)

Why cells stay small Worked

surface area ÷ volume falls as a cell grows
1 cm cube: SA = 6 cm², V = 1 cm³ → 6 : 1
2 cm cube: SA = 24 cm², V = 8 cm³ → 3 : 1half the ratio

Organelles at work
Part	Job
Nucleus	holds DNA; control center
Nucleolus	makes ribosome parts
Ribosome	builds proteins
Rough ER	ribosome-studded; makes and ships proteins
Smooth ER	makes lipids; detoxifies
Golgi apparatus	modifies, sorts and packages
Mitochondrion	cellular respiration: makes ATP
Lysosome	digests waste and worn parts
Vacuole	stores water and materials
Chloroplast	photosynthesis (plants, algae)
Cell membrane	controls what enters and leaves
Cell wall	rigid support (plants: cellulose)
Cytoskeleton	protein fibers: shape, movement

Two cell types
	Prokaryote	Eukaryote
Nucleus	no (DNA loop in cytoplasm)	yes
Membrane organelles	none	many
Size	1–5 μm	10–100 μm
Ribosomes	yes (small)	yes
Examples	bacteria, archaea	protists, fungi, plants, animals

The factory

Nucleus = front office, ribosomes = workers, ER = assembly line, Golgi = shipping dock, mitochondria = power plant, lysosomes = cleanup crew. (Traditional comparison.)

4Membranes & Transport

Passive transport runs down the concentration gradient; active transport pumps against it and uses ATP.

Water chases salt

Water moves toward more dissolved stuff: hyper outside, water leaves; hypo, water enters. (After the traditional “water follows salt.”)

Fluid mosaic: a phospholipid bilayer (water-loving heads out, water-fearing tails in) with proteins drifting in it
Selectively permeable: lets only some substances through

Osmosis and tonicity
Outside solution	Water moves	Animal cell	Plant cell
Hypotonic (less solute)	in	swells, may burst	firm (turgid): best
Isotonic (equal)	in = out	normal	limp (flaccid)
Hypertonic (more solute)	out	shrivels	plasmolysis: membrane pulls from wall

Ways across the membrane
Kind	Energy?	How
Diffusion	no	high → low (O₂, CO₂)
Facilitated diffusion	no	high → low via a channel or carrier (glucose)
Osmosis	no	water moves toward more solute
Active transport	ATP	low → high by a pump (Na⁺/K⁺)
Endo- / exocytosis	ATP	membrane folds in / vesicles fuse out

Potato in salt water Worked

mass 5.00 g → 4.60 g after 1 h

% change = 4.60 − 5.005.00 × 100 = −8.0 %lost water: solution was hypertonic

General BiologyBiology · Units 1–10 · continued

5Energy: Photosynthesis & Respiration

ATP: adenosine triphosphate; the cell’s energy “cash”; ATP → ADP + P releases energy
Autotroph: makes its own food (plants, algae)
Heterotroph: eats other organisms (animals, fungi)

The two processes run in opposite directions: the products of one are the reactants of the other.

Photosynthesis

In chloroplasts. Chlorophyll absorbs red and blue light and reflects green.

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

Photosynthesis in two stages
Stage	Where	In	Out
Light reactions	thylakoid membranes	light, H₂O	O₂, ATP, NADPH
Calvin cycle	stroma	CO₂, ATP, NADPH	sugar (G3P → glucose)

Rate goes up with…

more light, more CO₂, warmer temperature, until something else runs short (a limiting factor) or heat damages enzymes.

Cellular respiration

Aerobic (needs oxygen); mostly in mitochondria.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Go Keep Eating

Glycolysis → Krebs → Electron transport: the order the cell “eats” glucose.

Respiration in three stages
Stage	Where	Net ATP
Glycolysis	cytoplasm	2
Krebs (citric acid) cycle	mitochondrial matrix	2
Electron transport chain	inner membrane	≈ 26–34

Total: about 30–38 ATP per glucose. Oxygen is the final electron acceptor and becomes water.

Mass is conserved Worked

180.2 g glucose + 192.0 g O₂1 mol + 6 mol

→ 264.1 g CO₂ + 108.1 g H₂O: 372.2 g each side

Fermentation (no oxygen)
	Lactic acid	Alcoholic
Who	muscles, some bacteria (yogurt)	yeast (bread, brewing)
Products	lactic acid	ethanol + CO₂
ATP per glucose	2	2

6Cell Cycle, Mitosis & Meiosis

The cell cycle

G1: cell grows, does its job.
S: DNA is copied (synthesis).
G2: prepares to divide.
M: mitosis (nucleus divides), then cytokinesis (cytoplasm divides).

G1 + S + G2 = interphase (about 90 % of the cycle). Checkpoints stop a damaged cell; when they fail, cells divide out of control (cancer).

Meiosis I separates homologous pairs; meiosis II separates sister chromatids.

Mitosis vs meiosis
	Mitosis	Meiosis
Purpose	growth, repair	eggs and sperm
Divisions	1	2
Cells made	2 identical	4 different
Chromosomes	2n → 2n	2n → n
Crossing over	no	yes (prophase I)

Mitosis in a cell with 2n = 4 (blue = long pair, rust = short pair).

Mitosis step by step
Phase	What happens
Prophase	chromosomes condense; nuclear envelope breaks down; spindle forms
Metaphase	chromosomes line up at the middle
Anaphase	sister chromatids pulled to opposite poles
Telophase	two nuclei form; chromosomes unwind
Cytokinesis	animal: cell pinches (furrow); plant: cell plate forms

PMAT: Please Make Another Twin

Prophase, Metaphase, Anaphase, Telophase (PMAT is traditional; the sentence is new). Metaphase = Middle; Anaphase = Apart.

Chromatid: one of two identical copies joined at the centromere
Homologous pair: one chromosome from each parent, same genes
Diploid (2n): two sets; human body cells 46
Haploid (n): one set; human egg or sperm 23

Sources of variety in meiosis

Crossing over: homologs swap segments.
Independent assortment: pairs line up at random.
Random fertilization: any egg with any sperm.

Nondisjunction: chromosomes fail to separate (Down syndrome: three copies of chromosome 21).

Combinations Worked

human: n = 23 pairs, each lines up 2 ways

2²³ = 8,388,608 kinds of gametesbefore crossing over

General BiologyBiology · Units 1–10 · continued

7Mendelian Genetics

Gene: a stretch of DNA that codes for a trait
Allele: one version of a gene (B or b)
Dominant: shows with one copy (capital: B)
Recessive: shows only with two copies (bb)
Homozygous: two alike (BB, bb)
Heterozygous: two different (Bb), a hybrid
Genotype: the alleles (Bb)
Phenotype: the trait you see (black fur)

Bb × Bb

test cross: any bb pup means the parent was Bb

Mendel’s numbers Worked

F₂ seeds: 5474 round, 1850 wrinkled

54741850 = 2.96 : 1 ≈ 3 : 1what a Bb × Bb cross predicts

Dihybrid BbRr × BbRr: gametes BR, Br, bR, br; 9 : 3 : 3 : 1 (shaded: both dominant).

Probability rules

Multiply for independent events together; add for exclusive outcomes.

and: P(A) × P(B)

or: P(A) + P(B)

Mendel’s laws (1865)

Segregation: each parent passes on one of its two alleles.
Independent assortment: genes on different chromosomes sort separately.
Dominance: one allele can mask another.

Mendel, an Augustinian friar, counted about 28,000 pea plants.

Use the rules Worked

BbRr × BbRr: P(bbrr) = 14 × 14 = 116
Bb × Bb: P(shows dominant) = 14 + 12 = 34BB or Bb
four children of Bb × Bb, all bb: (14)⁴ = 1256each child is independent

Each child is a new coin toss

Earlier children never change the odds for the next one: three girls in a row still leave 12 for a boy.

8Beyond Mendel: Sex Linkage & Pedigrees

Non-Mendelian patterns
Pattern	What happens	Example
Incomplete dominance	blend in hybrids	red × white snapdragons → pink; F₂ 1 : 2 : 1
Codominance	both show fully	roan cattle (red and white hairs); AB blood
Multiple alleles	more than two alleles	ABO blood: Iᴬ, Iᴮ, i
Polygenic	many genes, a smooth range	height, skin color, eye color
Environment	conditions affect the trait	hydrangea color and soil pH

X-linked recessive pedigree: □ male, ○ female, shaded affected, dot carrier; rows are generations.

ABO blood types
Blood type	Genotypes	Antigen on red cells
A	IᴬIᴬ, Iᴬi	A
B	IᴮIᴮ, Iᴮi	B
AB	IᴬIᴮ	A and B
O	ii	none

Blood type cross Worked

Iᴬi × Iᴮi

¼ AB, ¼ A, ¼ B, ¼ Oall four from two parents

Sex chromosomes

22 pairs of autosomes + 1 pair of sex chromosomes.
Female XX; male XY. Every egg carries X; a sperm carries X or Y, so P(boy) = P(girl) = ½.

Reading a pedigree
Clue in the chart	Points to
Affected child, unaffected parents	recessive
Every affected child has an affected parent	dominant
Mostly males, via carrier mothers	X-linked recessive

Sex-linked (X-linked) trait: gene on the X chromosome; Y has no matching allele
Carrier: a female with one recessive allele (XᴴXʰ): unaffected but can pass it on

Carrier mother × normal father (shaded: affected).

Reading the square

Daughters: ½ carriers, none affected. Sons: ½ affected. Overall ¼.

Examples: red-green color blindness, hemophilia, Duchenne muscular dystrophy.

Sons get their X from Mom

A boy’s only X comes from his mother, so X-linked recessive traits show mostly in males and skip through carrier daughters.

General BiologyBiology · Units 1–10 · continued

9DNA & Replication

Finding the genetic material
Year	Who	Found
1928	Griffith	a “transforming principle” turned harmless bacteria deadly
1944	Avery, MacLeod, McCarty	the principle is DNA
1952	Hershey & Chase	virus DNA, not protein, enters cells
1952	Franklin (Photo 51)	X-ray pattern of a helix
1953	Watson & Crick	double-helix model

Replication

Helicase unzips the helix at the origin.
Primase lays a short RNA primer.
DNA polymerase adds matching nucleotides 5′→3′ and proofreads.
Leading strand: continuous; lagging strand: in Okazaki fragments joined by ligase.

Semiconservative: each new helix keeps one old strand and one new one.

A DNA ladder (untwisted). The rungs are base pairs; the rails are sugar and phosphate.

Apple in the Tree, Car in the Garage

A pairs with T, C pairs with G. (Traditional.)

Chargaff’s rule Worked

A sample is 30 % A

T = 30 %; G + C = 40 %, so G = 20 %, C = 20 %A = T, G = C

Nucleotide: phosphate + sugar (deoxyribose) + base
Purines: A, G (two rings)
Pyrimidines: C, T, U (one ring)
Antiparallel: one strand runs 5′→3′, its partner 3′→5′

Write the partner strand Worked

5′ ATG CCT AGA 3′

3′ TAC GGA TCT 5′A–T, G–C

DNA vs RNA
	DNA	RNA
Sugar	deoxyribose	ribose
Strands	2 (double helix)	1
Bases	A, T, G, C	A, U, G, C
Where	nucleus	nucleus and cytoplasm
Job	stores the code	carries it out (mRNA, tRNA, rRNA)

10Gene Expression & Mutations

The genetic code (mRNA codons). Find the first base at left, the second at top, the third at right.

DNA to protein Worked

template DNA: 3′ TAC CGA AGT ATT 5′
mRNA: 5′ AUG GCU UCA UAA 3′pair A→U, T→A, G→C, C→G
protein: Met – Ala – Ser – stopread the table

Kinds of mutations
Mutation	Change	Effect
Silent	base swap, same amino acid	none
Missense	base swap, new amino acid	sickle cell: GAG → GUG, Glu → Val
Nonsense	base swap makes a stop	short, broken protein
Frameshift	insert or delete 1–2 bases	every later codon changes (THE CAT → TEC AT…)
Chromosomal	deletion, duplication, inversion, translocation	many genes affected

The central dogma

Transcription (DNA → mRNA, in the nucleus), then translation (mRNA → protein, at a ribosome).

DNA → RNA → protein

Transcription

RNA polymerase binds a promoter and copies the template strand.
In eukaryotes the pre-mRNA is edited: introns cut out, exons joined, cap and tail added.

Translation

The ribosome reads mRNA three bases at a time (a codon).
Each tRNA has an anticodon that matches a codon (GCU ↔ CGA) and carries one amino acid.
Starts at AUG (Met); ends at a stop codon (UAA, UAG, UGA).

Copy, then Cook

Transcription = transcribe a copy of the recipe; Translation = turn it into the meal (protein).

Mutagen: raises the mutation rate: UV, X-rays, some chemicals
Repair: enzymes fix most errors; most mutations are neutral or damaging

General BiologyBiology · Units 1–10 · continued

11Biotechnology

Biotech tools
Tool	What it does	Used for
PCR (1983)	copies one DNA segment over and over	testing, forensics
Gel electrophoresis	sorts DNA fragments by size; small ones travel farthest	DNA fingerprints
Restriction enzyme	cuts DNA at a set sequence (EcoRI: GAATTC)	cutting and pasting genes
Recombinant DNA	a gene inserted into another organism	human insulin made by bacteria (since 1982)
CRISPR (2012)	guided enzyme edits a chosen DNA site	research, gene therapy
Sequencing	reads the order of bases	Human Genome Project (2003)

PCR doubling

Heat to separate strands (≈ 95 °C), cool so primers bind, let a heat-proof polymerase build (≈ 72 °C); repeat.

copies = 2ⁿ

EX30 cycles: 2³⁰ = 1,073,741,824 ≈ a billion copies

Reading a gel

DNA is negative, so it moves toward the + end.
Shorter fragments move farther.
Matching band patterns = matching DNA.

Bioethics

Every human life has worth at every stage, so treating a sick patient is a mercy, while making or destroying embryos for research treats persons as products.
Ask of any technique: what is it for, who bears the risk, and does it respect human life?

12Variation, Adaptation & Origins

Natural selection: the observable steps

Individuals vary.
Much variation is inherited.
More offspring are born than survive.
Those with helpful traits survive and reproduce more, so those traits become more common.

Selection sorts existing variation; it does not create new traits.

Adaptation: an inherited trait that helps survival and reproduction in an environment
Artificial selection: humans choose which animals or plants breed
Microevolution: small changes within a population, such as allele frequencies
Macroevolution: large-scale change, such as new body plans, proposed over long ages
Kind: in creation biology, an originally created group whose members can vary and sometimes interbreed (often near the family level)

Selection in numbers Worked

beetles 80 % green, 20 % brown; birds eat ½ of green, 110 of brown

left: 40 green, 18 brown per 100 → 4058 ≈ 69 % green, 31 % brownbrown rises

Observation vs. interpretation

Observed: variation, heredity, selection within populations, fossils in rock layers, similar bones and DNA.
Inferred about the unobserved past: who descended from whom, and when.
Darwin (Beagle, 1831–36) observed island variation; universal common descent was his inference.

The case for universal common descent, as each side presents it
Evidence offered for common descent	Open questions critics raise
fossil sequences (Tiktaalik, whale series)	Cambrian explosion: body plans appear suddenly
homology (arm, wing, flipper)	similarity can also reflect common design
molecular similarity; shared “broken” genes	“junk” DNA and vestigial claims often revised
biogeography; vestigial structures	origin of new genetic information; origin of life; timescales

Weigh it fairly

All agree variation and natural selection are real.
They differ on the age of the earth, the reach of natural processes, the origin of new kinds and of humans, and how to read Genesis.
State each view so its holders would agree: “He that is first in his own cause seemeth just; but his neighbour cometh and searcheth him” (Proverbs 18:17, KJV).

Observed by everyone
Example	What was observed
Galápagos finches (Grants, 1973–)	1977 drought: deeper beaks survived; average depth rose about 4 %. After 1983 rains smaller beaks were favored.
Peppered moths	dark moths common on sooty trees; light moths returned after clean-air laws
Antibiotic resistance	resistant bacteria survive a drug and multiply; finish every prescription

Views of origins, stated fairly
View	Its holders say
Young-earth creation	Genesis is history: six ordinary days thousands of years ago; created kinds vary within limits; a global Flood laid down most fossil-bearing rock
Old-earth creation	the earth is billions of years old, but God created distinct kinds by special acts
Intelligent design	some features (irreducible complexity, information in DNA) are best explained by an intelligent cause
Darwinian theory	all life descends from a common ancestor by natural processes, chiefly mutation and selection; theistic evolutionists see this as God’s method

See it, then say it

What you can see (variation, selection) is observation; what you say happened long ago is interpretation. Label which is which.

General BiologyBiology · Units 1–10 · continued

13Classification & Microbes

Three domains, six kingdoms
Domain	Kingdom	Cells	Wall	Food	Examples
Bacteria	Bacteria	prokaryote	peptidoglycan	auto / hetero	E. coli, Streptococcus
Archaea	Archaea	prokaryote	no peptidoglycan	auto / hetero	hot-spring, salt-lake microbes
Eukarya	Protista	eukaryote, mostly 1 cell	some	auto / hetero	amoeba, algae
Eukarya	Fungi	eukaryote, most many	chitin	hetero (absorb)	mushrooms, yeast, molds
Eukarya	Plantae	eukaryote, many	cellulose	auto	mosses, ferns, pines, flowers
Eukarya	Animalia	eukaryote, many	none	hetero (ingest)	sponges, insects, fish, people

Naming

Linnaeus (1735) sorted life into nested groups.
Binomial name: Genus species, italic, genus capitalized: Canis lupus, Homo sapiens.

Daring Kids Pack Crisp Oranges For Great Snacks

Ranks from broad to narrow: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Species: organisms that can interbreed and produce fertile offspring
Dichotomous key: two choices at each step lead to a name (needles in bundles → pine)

Bacteria vs viruses
	Bacteria	Viruses
Living cell?	yes	no; genes in a protein coat
Size	1–5 μm	20–300 nm
Reproduce	binary fission	only inside a host cell
Treated by	antibiotics	not antibiotics; vaccines prevent some
Helpful roles	decomposers, nitrogen fixers	research tools

Shapes: cocci (spheres), bacilli (rods), spirilla (spirals)
Lytic / lysogenic: virus bursts the cell now / hides in host DNA, activating later
Vaccine: a harmless form or part of a germ trains the immune system (Jenner, 1796)

Bacterial growth Worked

1 cell, doubling every 20 min, for 3 h

3 h = 9 doublings → 2⁹ = 512 cells

Protozoa: animal-like protists: amoeba, paramecium, Plasmodium (malaria)
Algae: plant-like: diatoms, kelp, Euglena
Molds: fungus-like: slime molds, potato blight

Fungi

Bodies of threadlike hyphae forming a mycelium; walls of chitin.
Absorb food: decomposers that recycle nutrients.
Reproduce by spores; yeast by budding.
Uses: bread and cheese, antibiotics (Fleming found penicillin in a mold, 1928); harms: athlete’s foot, crop rusts.

14Plants & Animals

Plant groups
Group	Vessels?	Seeds?	Examples
Nonvascular	no	no (spores)	mosses, liverworts
Seedless vascular	yes	no (spores)	ferns, horsetails
Gymnosperms	yes	naked, in cones	pines, firs, cycads
Angiosperms	yes	in fruit; flowers	grasses, oaks, roses

Xylem: carries water and minerals up from roots
Phloem: carries sugar from leaves to the rest of the plant
Stomata: leaf pores run by guard cells: CO₂ in, water vapor out
Transpiration: water loss from leaves; pulls water up

Xylem goes up, phloem flows food

Xylem lifts water up like a ladder; phloem moves food (sugar) wherever it is needed.

Two kinds of flowering plants
	Monocot	Dicot
Seed leaves	1	2
Leaf veins	parallel	net
Flower parts	threes	fours or fives
Examples	corn, lilies	beans, oaks

Flower parts

Male stamen = anther (pollen) + filament.
Female pistil = stigma + style + ovary (ovules).
Petals attract pollinators.

After fertilization the ovule becomes a seed, the ovary a fruit.

Vertebrate classes
Class	Traits
Fish	gills, fins, scales; ectotherm
Amphibians	moist skin; young in water
Reptiles	dry scales; shelled eggs on land
Birds	feathers, hollow bones, endotherm
Mammals	hair, milk, endotherm; most bear live young

Major animal phyla
Phylum	Key traits	Examples
Sponges	pores; no tissues	bath sponge
Cnidarians	stinging cells; radial	jellyfish, coral
Flatworms	flat; one gut opening	planaria
Roundworms	round; two-opening gut	hookworm
Mollusks	mantle; often a shell	snail, octopus
Annelids	segmented worms	earthworm
Arthropods	jointed legs; exoskeleton	insects, crabs
Echinoderms	spiny skin; tube feet	sea star
Chordates	notochord; nerve cord	fish to mammals

Every phylum but the chordates is invertebrate (no backbone). Symmetry: radial, bilateral or none.

Arthropod body count

Insects 6 legs (3 body parts), spiders 8 (2 parts), crustaceans 10+.

General BiologyBiology · Units 1–10 · continued

15The Human Body

11 organ systems
System	Main organs	Job
Skeletal	bones, joints	support, protect, make blood cells
Muscular	skeletal, smooth, heart muscle	movement, heat
Circulatory	heart, blood vessels, blood	carry O₂, food, wastes
Respiratory	nose, trachea, lungs (alveoli)	gas exchange
Digestive	mouth, stomach, intestines, liver	break down and absorb food
Excretory	kidneys, bladder, skin	remove wastes, balance water
Nervous	brain, spinal cord, nerves	sense, control, think
Endocrine	glands (pituitary, thyroid, pancreas)	hormone signals
Immune	white blood cells, lymph nodes	fight disease
Integumentary	skin, hair, nails	barrier, temperature
Reproductive	ovaries, testes	make eggs or sperm; continue the family

Homeostasis by negative feedback

A change triggers a response that reverses it.
Too hot → sweat; too cold → shiver.
Blood sugar high → pancreas releases insulin; low → glucagon.

Path of blood

body → right atrium → right ventricle → lungs → left atrium → left ventricle → aorta → body

Arteries carry blood away from the heart; veins return it; capillaries trade with cells.

A for Away

Arteries carry blood away from the heart; veins bring it back in. (Traditional.)

16Ecology & Stewardship

Biotic / abiotic: living parts / nonliving parts (water, light, soil)
Ecosystem: a community of species plus its nonliving setting
Niche: an organism’s role; habitat is where it lives

About 10 % of the energy at one level becomes the next level’s body; the rest is used for living or lost as heat.

The 10 % rule Worked

producers capture 50,000 kcal

herbivores 5,000 → carnivores 500 → top carnivores 50 kcal× 0.1 at each step

Ten percent, the rest is spent

About a tenth moves up each step, so chains seldom pass five links. Energy flows one way; matter cycles.

Dominion and care

Stewardship: measure and manage living resources wisely.
Bison fell to about a thousand by the late 1880s and recovered under protection and ranching; Duck Stamp sales (since 1934) fund wetland refuges.

Species interactions (+ helped, − harmed, 0 neither)
Relationship	Effect	Example
Mutualism	+ / +	bee and flower
Commensalism	+ / 0	barnacles on a whale
Parasitism	+ / −	tick on a dog
Predation	+ / −	owl and mouse
Competition	− / −	two plants for light

Water cycle

evaporation → condensation (clouds) → precipitation → runoff and groundwater → back to the sea; plants add transpiration.

“All the rivers run into the sea; yet the sea is not full” (Ecclesiastes 1:7, KJV).

Carbon cycle

Photosynthesis pulls CO₂ into sugar; respiration, decay and burning return it. Stores: oceans, rock, soil, fossil fuels.

Nitrogen cycle

Air is 78 % N₂, unusable by most organisms.
Fixation: soil and root-nodule bacteria (and lightning) make ammonia and nitrates.
Plants absorb nitrates; animals eat plants; decomposers return ammonia; denitrifying bacteria release N₂.

Unlimited resources give a J curve; limits bend it into an S that levels off at the carrying capacity K.

Trophic levels
Level	Gets energy from	Examples
Producer	sunlight (photosynthesis)	grass, algae, trees
Primary consumer	producers (herbivore)	rabbit, grasshopper, deer
Secondary consumer	herbivores	frog, snake, fox
Tertiary consumer	other carnivores	hawk, wolf
Decomposer	dead matter of every level	bacteria, fungi

Carrying capacity (K): the largest population the environment can support
Density-dependent: limits that grow with crowding: food, disease, predators
Density-independent: fire, flood, freeze
Succession: community change: primary (bare rock, lichens first) or secondary (soil remains)

Density and growth Worked

density = number ÷ area: 240 deer on 12 km² → 20 per km²

start 500; +120 born, −70 died → 50500 = 10 % growthadd immigrants, subtract emigrants

Mark and recapture Worked

mark 50 fish; later catch 40, of which 8 are marked

N = 50 × 408 = 250 fishmarked fraction matches