Biology CLEP Weak Points

Spermatogenesis output

1 primary spermatocyte produces 4 sperm; continuous from puberty

Oogenesis output

1 primary oocyte produces 1 egg + polar bodies (unequal cytoplasm division)

What triggers ovulation?

LH surge

Corpus luteum

Empty follicle after ovulation; makes progesterone to maintain uterine lining

Role of hCG

Made by embryo; keeps corpus luteum alive in early pregnancy (detected by pregnancy tests)

Sertoli vs Leydig cells

Sertoli nourish sperm (respond to FSH); Leydig make testosterone (respond to LH)

Cortical reaction

Slow block to polyspermy; hardens the fertilization envelope

Fast block to polyspermy

Depolarization of the egg membrane right after sperm fusion

Order of early embryo stages

Zygote → cleavage → morula → blastula → gastrula → neurulation/organogenesis

Cleavage

Rapid mitotic divisions with no growth; cells get smaller

Blastocyst parts (mammals)

Inner cell mass (becomes embryo) + trophoblast (helps form placenta)

Gastrulation

Cells move in through the blastopore, forming the 3 germ layers

Protostome vs deuterostome

Protostome: blastopore becomes mouth (arthropods, mollusks). Deuterostome: blastopore becomes anus (echinoderms, chordates)

Ectoderm becomes

Epidermis, hair, nails, nervous system (brain, spinal cord), eye lens

Mesoderm becomes

Muscle, bone, blood, heart and vessels, kidneys, gonads, notochord

Endoderm becomes

Lining of digestive and respiratory tracts, liver, pancreas, thyroid, lungs

Neural tube forms from

Ectoderm, induced by the notochord (mesoderm)

Amnion

Fluid-filled sac that cushions the embryo

Chorion

Outer membrane for gas exchange; contributes to the placenta in mammals

Allantois

Stores waste; becomes umbilical blood vessels in mammals

Yolk sac

Provides nutrients; site of first blood cells

Induction

One group of cells signals another to change its developmental fate

Hox (homeotic) genes

Control body plan along the head-to-tail axis

Apoptosis in development

Programmed cell death, e.g., removes webbing between fingers

Determination vs differentiation

Determination = cell's fate is fixed; differentiation = cell actually specializes (comes after)

Heart chambers: fish, amphibian, bird/mammal

Fish 2; amphibian 3 (2 atria, 1 ventricle); birds and mammals 4

Blood path through mammal heart

Vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta

Which artery carries deoxygenated blood?

Pulmonary artery (arteries carry blood AWAY from the heart, not always oxygenated)

Heart's pacemaker

SA (sinoatrial) node

What controls breathing rate?

Medulla oblongata, responding mainly to blood CO2/pH

Inhalation mechanics

Diaphragm contracts → chest volume increases → pressure drops → air flows in

Countercurrent exchange in fish gills

Water and blood flow in opposite directions to maximize O2 uptake

Where does most digestion and absorption occur?

Small intestine (villi and microvilli)

Pepsin

Stomach enzyme that starts protein digestion; works at low pH

Bile

Made by the liver, stored in gallbladder; emulsifies fats (not an enzyme)

Large intestine main job

Absorbs water

Nephron steps in order

Glomerulus/Bowman's capsule (filtration) → proximal tubule (reabsorption) → loop of Henle (concentrates) → distal tubule → collecting duct

ADH effect

Increases water reabsorption in collecting duct → concentrated urine

Aldosterone effect

Increases Na+ reabsorption in the kidney

Ammonia vs urea vs uric acid

Ammonia: aquatic animals, most toxic. Urea: mammals, amphibians. Uric acid: birds, reptiles, insects (saves most water)

Resting membrane potential

About −70 mV

Depolarization vs repolarization

Depolarization: Na+ rushes in. Repolarization: K+ flows out

Saltatory conduction

Impulse jumps between nodes of Ranvier on myelinated axons → faster

Sympathetic vs parasympathetic

Sympathetic = fight or flight. Parasympathetic = rest and digest

Cerebellum function

Balance and coordination of movement

Insulin vs glucagon

Insulin (beta cells) lowers blood glucose; glucagon raises it

Steroid vs peptide hormone receptors

Steroid: receptor inside the cell. Peptide: receptor on cell surface → second messenger (cAMP)

B cells

Become plasma cells that make antibodies (humoral immunity)

Helper T cells

CD4 cells that activate B cells and cytotoxic T cells; target of HIV

Cytotoxic T cells

CD8 cells that kill infected body cells (cell-mediated immunity)

Basis of vaccines

Memory B and T cells → faster, stronger second response

Muscle contraction sequence

Ca2+ released → binds troponin → tropomyosin moves → myosin binds actin and pulls → ATP releases myosin

Griffith experiment

Showed bacteria can be transformed by material from dead cells

Avery, MacLeod, McCarty

Identified DNA as the transforming principle

Hershey-Chase experiment

Labeled DNA (32P) entered bacteria, protein (35S) didn't → DNA is genetic material

Chargaff's rules

A = T and G = C in DNA

Meselson-Stahl experiment

Proved DNA replication is semiconservative

Purines vs pyrimidines

Purines (A, G) have 2 rings; pyrimidines (C, T, U) have 1 ring

Which base pair is stronger?

G–C (3 hydrogen bonds) vs A–T (2)

Antiparallel

DNA strands run in opposite directions (5'→3' and 3'→5')

Helicase

Unzips the DNA double helix

Primase

Lays down a short RNA primer

DNA polymerase III

Adds nucleotides to the 3' end; builds only 5'→3'

Okazaki fragments

Short DNA pieces on the lagging strand

DNA ligase

Seals gaps between Okazaki fragments

Telomerase

Extends chromosome ends (telomeres); active in stem and cancer cells

RNA differs from DNA by

Ribose sugar, uracil instead of thymine, single-stranded

mRNA, tRNA, rRNA

mRNA carries the code; tRNA brings amino acids (has anticodon); rRNA forms the ribosome

Where does transcription start?

RNA polymerase binds the promoter (e.g., TATA box)

Eukaryotic mRNA processing

5' cap, poly-A tail, splicing (introns removed, exons kept)

Start codon

AUG (methionine)

Stop codons

UAA, UAG, UGA

Ribosome sites in order

A (tRNA enters) → P (peptide bond forms) → E (exit)

Silent mutation

Base change that codes for the same amino acid

Missense mutation

Base change that codes for a different amino acid (sickle-cell)

Nonsense mutation

Base change that creates an early stop codon

Frameshift mutation

Insertion/deletion not a multiple of 3; changes every codon after it

lac operon

Inducible: lactose binds repressor → genes turn ON

trp operon

Repressible: tryptophan activates repressor → genes turn OFF

Histone acetylation vs DNA methylation

Acetylation loosens DNA → more transcription. Methylation silences genes

Restriction enzymes

Cut DNA at specific sequences, often leaving sticky ends

Gel electrophoresis direction

DNA is negative → moves toward positive end; smaller fragments travel farther

PCR

Copies DNA: heat to separate → primers anneal → Taq polymerase extends

Reverse transcriptase

Retrovirus enzyme (HIV) that makes DNA from RNA

Conditions for natural selection

Variation, inheritance, overproduction, differential survival and reproduction

Biological fitness

Reproductive success — number of fertile offspring

Homologous structures

Same origin, different function (human arm, bat wing) → common ancestry/divergent evolution

Analogous structures

Same function, different origin (bird vs insect wing) → convergent evolution

Vestigial structure

Reduced, little-used structure (human appendix, whale pelvis)

Hardy-Weinberg equations

p + q = 1 and p² + 2pq + q² = 1

In Hardy-Weinberg, what is 2pq?

Frequency of heterozygotes (carriers)

Hardy-Weinberg conditions

Large population, random mating, no mutation, no gene flow, no natural selection

16% have recessive trait; what % are carriers?

q² = 0.16 → q = 0.4, p = 0.6 → 2pq = 0.48 (48%)

Only source of new alleles

Mutation

Genetic drift

Random allele frequency changes; strongest in small populations

Bottleneck effect

Population drastically reduced → loss of genetic diversity

Founder effect

Small group starts a new population with limited alleles

Directional selection

One extreme favored (antibiotic resistance, peppered moths)

Stabilizing selection

Intermediate favored (human birth weight)

Disruptive selection

Both extremes favored; can lead to speciation