Comprehensive Biology Review – UPCAT 2012

A set of question-and-answer flashcards covering cell biology, genetics, chemistry of life, photosynthesis, evolution, ecology, taxonomy, anatomy, and physiology topics from the UPCAT 2012 Biology review. Use them to self-test key facts, definitions, and conceptual relationships across the breadth of the lecture notes.

Which organelle contains the genetic information that directs all cellular activities?

The nucleus (containing chromatin/DNA).

What cell structure is a network of membrane-enclosed spaces involved in protein manufacture and studded with ribosomes?

The rough endoplasmic reticulum (RER).

What freely-floating cytoplasmic structures are responsible for protein synthesis?

Ribosomes.

Which organelle controls the transfer of substances into and out of a cell?

The plasma (cell) membrane.

Which organelle is the primary site of lipid synthesis and detoxification?

The smooth endoplasmic reticulum (SER).

What part of the cytoskeleton reinforces cell shape and aids in cell movement?

Microtubules.

Which organelle modifies, sorts, and packages proteins for secretion or delivery to other organelles?

The Golgi apparatus (Golgi complex).

Phagocytic cells contain an abundance of which digestive organelles?

Lysosomes.

The organelle that produces ATP by aerobic respiration is the .

Mitochondrion.

What cellular structure is involved in the production of ribosomal subunits?

The nucleolus.

A rigid coat of cellulose, chloroplasts, and a large central vacuole indicate that a cell is a(n) __ cell.

Plant (eukaryotic) cell.

Prokaryotes lack which major membrane-bound structure found in eukaryotes?

A nucleus.

During which phase of the cell cycle does a cell grow and increase in size?

G1 phase.

DNA replication occurs in which specific phase of interphase?

S phase.

In which cell-cycle phase are microtubules necessary for division produced?

G2 phase.

What is the non-dividing phase that some cells enter permanently, leaving the cycle?

G0 phase.

What is the main difference between homologous chromosomes and sister chromatids?

Homologous chromosomes are a maternal and paternal pair with the same genes; sister chromatids are identical copies of the same chromosome formed after DNA replication.

Name the point of attachment between sister chromatids.

Centromere.

Mitosis yields daughter cells that are genetically to the parent cell.

Two; identical (diploid).

Meiosis yields daughter cells that are genetically and _ in ploidy.

Four; unique; haploid.

Where does meiosis occur in humans?

In the gonads – testes (spermatogenesis) and ovaries (oogenesis).

What happens to the four meiotic products in males versus females?

All four become functional sperm in males; in females, only one becomes an ovum while three form polar bodies.

Define allele.

An alternative form of a gene found at the same locus on homologous chromosomes.

How are dominant and recessive alleles symbolized in genetics problems?

Dominant = uppercase letter (e.g., A); recessive = lowercase letter (e.g., a).

Differentiate genotype from phenotype.

Genotype is an organism’s genetic makeup (allele combination); phenotype is the observable trait expressed.

State Mendel’s Law of Segregation.

Two alleles for each gene separate during gamete formation, so each gamete carries only one allele for each gene.

State Mendel’s Law of Independent Assortment.

Alleles of genes on different chromosomes assort independently during gamete formation.

If yellow seed color (Y) is dominant over green (y), what are the phenotypes of F1 offspring from YY × yy?

All F1 plants are yellow (genotype Yy).

In a Yy × Yy cross, what fraction of offspring are identical to the green parent (yy)?

1⁄4 (25%).

Define incomplete dominance and give a classic phenotypic ratio for F2.

Heterozygote shows an intermediate phenotype; F2 ratio = 1:2:1 (dominant : intermediate : recessive).

Define codominance and give a human blood-type example.

Both alleles are fully expressed in the heterozygote; e.g., IA IB yields type AB blood.

What blood types are possible from two type O parents?

Only type O (genotype ii).

A normal female (XX) and a hemophiliac male (XhY) mate. What fraction of their sons will have hemophilia?

0% – all sons receive the father’s Y and the mother’s normal X.

In X-linked recessive inheritance, why are affected girls rare for lethal traits?

They must inherit two mutant X chromosomes; girls with two lethal alleles often do not survive to term.

Lipids are unique among the major biomolecules because they are __.

Not composed of repeating monomeric subunits.

Polysaccharides such as chitin, cellulose, starch, and glycogen are classified as __.

Carbohydrates.

Proteins may serve in structure, movement, transport, and as __ (biological catalysts).

Enzymes.

Nucleic acids primarily function to __.

Store, transmit, and express hereditary information.

A DNA sample with 23% adenine has what percent cytosine?

27% cytosine (and 27% guanine).

DNA replication is described as __ because each daughter molecule contains one original and one new strand.

Semi-conservative.

Transcription occurs in the __, whereas translation occurs on __.

Nucleus; ribosomes (cytoplasm or rough ER).

What three-nucleotide mRNA units specify individual amino acids?

Codons.

Why does an enzyme-substrate reaction rate level off at high substrate concentrations?

Enzymes become saturated; all active sites are occupied.

How can the maximum rate of an enzyme-catalyzed reaction be increased further?

Add more enzyme molecules.

Why do enzymes from thermophiles show optimal activity at much higher temperatures than human enzymes?

Their protein structures have evolved increased thermal stability; denaturation occurs at higher temperatures.

Light-dependent reactions of photosynthesis occur before or after CO₂ fixation?

Before – they provide ATP/NADPH for the Calvin cycle.

What effect does increasing light intensity have on the rate of photosynthesis until saturation?

Rate increases proportionally until it plateaus when another factor (e.g., CO₂) becomes limiting.

Which modern domain includes organisms with circular chromosomes, flagella, histone-associated DNA, but no nuclear envelope or peptidoglycan?

Archaea.

What feature is shared by fungi and animals but not plants?

Heterotrophic nutrition (lack of photosynthesis) and storage of energy as glycogen/chitin cell walls.

Echinoderms and chordates uniquely share which embryological trait?

Deuterostome development (blastopore becomes anus).

Reptiles, birds, and mammals uniquely share possession of a(n) __ egg.

Amniotic.

Forelimbs of human, cat, whale, and bat are examples of structures produced by evolution.

Homologous; divergent.

List one piece of evidence supporting the endosymbiotic origin of mitochondria.

Mitochondria possess their own circular DNA similar to bacterial DNA.

Lemurs, chimpanzees, and humans share which three higher taxonomic categories?

Class (Mammalia), Phylum (Chordata), Kingdom (Animalia).

Which plant group has vascular tissue but reproduces with spores, not seeds?

Ferns (seedless vascular plants).

Why are organisms at the end of a food chain few in number?

Energy losses at each trophic level leave insufficient energy to sustain large populations of top consumers.

Why does the fact that xylem vessels are dead aid in water transport?

Dead, hollow vessels provide an uninterrupted, low-resistance pathway for one-way water movement via transpiration pull.

Woody stems increase in diameter primarily through the activity of which tissue?

Vascular cambium (secondary growth).

Why is a biconcave shape advantageous for an erythrocyte?

It increases surface area for gas exchange and allows flexibility in capillaries.

Placing onion epidermal cells in a saturated sugar solution causes what phenomenon?

Plasmolysis (water leaves the cell via osmosis, cytoplasm shrinks from the wall).

Minerals present at higher concentrations inside an alga than in pond water must be taken up by __.

Active transport.

Identify the transport mechanism that moves molecules down a concentration gradient without energy and without a membrane.

Simple diffusion (mechanism A).

Identify the mechanism that requires a membrane but no energy and moves down the gradient.

Facilitated diffusion (mechanism B).

Identify the mechanism that moves substances against a gradient and requires energy.

Active transport (mechanism C).

Which stomach tissue layer comes into direct contact with food and secretes gastric juice?

Mucosal epithelium of the stomach lining.

What leaf feature greatly reduces stomatal density on the upper epidermis and why is this beneficial?

Fewer stomata on the upper surface reduce water loss by transpiration while still allowing gas exchange on the lower surface.

Countercurrent heat exchange in bird or heron legs prevents heat loss by ensuring what blood-flow pattern?

Warm arterial blood transfers heat to returning venous blood, conserving core body heat.

A drop of blood travelling from the intestines to the brain will NOT pass through which heart chamber?

The right ventricle.

If two type AB individuals reproduce, what blood phenotypes can their children have?

Type A, type B, or type AB (no type O).

A type A mother and type B father cannot produce offspring with which blood type?

Type O, unless both are heterozygous (IAi × IBi can give type O); if both are homozygous IAIA × IBIB, type O is impossible.

On a pedigree, a trait that skips generations and affects males more often suggests which inheritance pattern?

X-linked recessive.

On a pedigree, a trait that appears in every generation and affects both sexes equally suggests __ inheritance.

Autosomal dominant.

Which cellular phase is characterized by chromosome alignment at the cell’s equatorial plate?

Metaphase (mitosis or meiosis).

During which meiotic phase does crossing-over (genetic recombination) typically occur?

Prophase I.

Give two reasons why ATP yield is higher in aerobic than in anaerobic respiration.

Presence of oxygen allows complete oxidation of glucose via the Krebs cycle and oxidative phosphorylation; NADH and FADH₂ donate electrons to the ETC, generating more ATP.

Explain why increasing CO₂ concentration initially raises the rate of photosynthesis.

CO₂ is a raw material for the Calvin cycle; higher availability increases carboxylation until RuBisCO or light becomes limiting.

Arrange these photosynthesis events chronologically: Light strikes chlorophyll, water is split, O₂ released, ATP/NADPH drive Calvin cycle.

1) Light strikes chlorophyll; 2) Water is split; 3) O₂ released; 4) ATP/NADPH drive Calvin cycle (CO₂ → glucose).

Which evolutionary pattern produces analogous structures such as wings in birds and insects?

Convergent evolution.

Name the vascular tissue that conducts organic nutrients in two directions in plants.

Phloem.

Why does water flow in only one direction through xylem but food can move both ways in phloem?

Xylem flow is driven by transpiration pull; phloem flow depends on pressure gradients that can exist source-to-sink in either direction.

Which heart valve prevents back-flow of blood from the left ventricle to the left atrium?

The bicuspid (mitral) valve.

What is the function of stomata in leaves?

Regulate gas exchange (CO₂ uptake, O₂ release) and control water loss via transpiration.

Name one adaptation of leaves that maximizes light capture.

Flat, thin lamina with broad surface area; or alternate/spiral arrangement to avoid self-shading.