Unit 2 Biology AS: Cell Structure, Reproduction, Development and Plant Biodiversity

A comprehensive set of vocabulary flashcards based on Unit 2 Biology AS material, covering cell ultrastructure, reproduction, protein synthesis, genetics, plant anatomy, and conservation strategies.

Cell theory

Concept stating all living organisms are made of cells, cells are the basic units of life, and cells arise from pre-existing cells.

Eukaryotic cell

A cell with a membrane-bound nucleus and organelles like animal and plant cells.

Prokaryotic cell

A cell without a nucleus or membrane-bound organelles, such as bacteria.

Ultrastructure

Detailed internal structure of a cell visible only under an electron microscope.

Magnification

How much larger the image is compared to the actual object.

Resolution

The ability to distinguish two close points as separate.

Nucleolus

Dense region inside the nucleus that synthesises ribosomal RNA.

Rough Endoplasmic Reticulum (rER)

Membrane-bound sacs with ribosomes attached that synthesise and process proteins for secretion or membrane use.

Smooth ER

Membrane-bound sacs without ribosomes involved in lipid synthesis and detoxification.

Mitochondria

Site of aerobic respiration and ATP production, featuring a double membrane, inner folds called cristae, and a matrix.

Golgi Apparatus

Stacks of flattened sacs (cisternae) with vesicles that modifies, packages, and transports proteins and lipids.

Lysosomes

Vesicles containing hydrolytic enzymes that digest old organelles, pathogens, and waste.

Centrioles

Cylindrical structures made of microtubules in animal cells involved in spindle formation during cell division.

Peptidoglycan (murein)

The material that makes up the cell wall of prokaryotic cells.

Plasmid

Small circular DNA molecule in prokaryotes, separate from main DNA, carrying genes for antibiotic resistance.

70S Ribosomes

The type of ribosomes found in prokaryotic cells, which are smaller than the 80S type in eukaryotes.

Locus

The specific, fixed position on a chromosome where a particular gene is located.

Independent Assortment

Occurs during Metaphase I when homologous chromosomes line up randomly at the equator, resulting in $2^n$ combinations.

Crossing Over

Process in Prophase I where non-sister chromatids of homologous chromosomes exchange segments at chiasmata to produce new allele combinations.

Acrosome

Part of the sperm cell containing enzymes to digest the zona pellucida during the acrosome reaction.

Zona pellucida

Thick glycoprotein layer surrounding the egg cell that protects it and blocks polyspermy.

Cortical granules

Organelles in the egg that fuse with the cell surface membrane and release enzymes by exocytosis to harden the zona pellucida.

Morula

A solid ball of undifferentiated totipotent cells formed during an early embryonic stage.

Blastocyst

A hollow structure with an inner cell mass of pluripotent cells that form the embryo.

Totipotent

Stem cells that can give rise to any cell type, including placental tissue such as extra-embryonic cells.

Pluripotent

Stem cells that can give rise to all body cells but not placental tissue.

DNA Methylation

The addition of methyl groups ($CH_3$) to cytosine bases in DNA, often at CpG sites, which inhibits transcription and silences genes.

Histone Acetylation

An epigenetic modification where DNA is loosely wrapped around histones, making it available for mRNA binding and gene activation.

Alternative Splicing

Post-transcriptional process where introns are removed and different combinations of exons are joined to produce multiple proteins from a single gene.

Polygenic Inheritance

Traits controlled by many genes where each gene contributes additively, resulting in continuous variation like height or skin colour.

Non-disjunction

Failure of homologous chromosomes or sister chromatids to separate properly, resulting in gametes with extra or missing chromosomes.

Proto-oncogenes

Genes that promote normal cell division which, when mutated, become oncogenes that promote uncontrolled division.

Cellulose

A polymer of $\beta$-glucose with straight unbranched chains joined by 1,4 glycosidic bonds, forming microfibrils for cell wall strength.

Starch

A polymer of $\alpha$-glucose consisting of helical amylose ($1,4$ bonds) and branched amylopectin ($1,4$ and $1,6$ bonds) for energy storage.

Lignin

A complex, non-carbohydrate polymer in xylem cell walls that adds rigidity, waterproofs the vessel, and provides mechanical support.

Xylem

Plant tissue made of dead, hollow, lignified cells that passively transports water and mineral ions via the transpiration stream.

Phloem

Living tissue containing sieve tube elements and companion cells used for the active transport of organic solutes like sucrose.

Sclerenchyma fibres

Dead, elongated cells with thick, lignified walls that provide mechanical strength but have no role in transport.

Endemism

An ecological state where a species is found only in one specific geographic location.

Heterozygosity index

A measure of genetic diversity within a population calculated as the proportion of heterozygotes.

Simpson's Index of Diversity ($D$)

A numerical measure of biodiversity that accounts for both species richness and evenness using the formula $D = 1 - \sum (\frac{n}{N})^2$.

Niche

The unique role of a species within an ecosystem, including its habitat, diet, behaviour, and abiotic tolerances.

Hardy-Weinberg Equation

Mathematical equations ($p + q = 1$ and $p^2 + 2pq + q^2 = 1$) used to determine if allele frequencies in a population are stable.

Allopatric Speciation

The formation of new species due to populations becoming geographically separated by physical barriers.

Sympatric Speciation

The formation of new species within the same geographical area due to reproductive barriers like behavior or timing.

In situ Conservation

Protection of species within their natural habitat, such as in national parks or wildlife reserves.

Ex situ Conservation

Protection of species outside their natural habitat, such as in zoos, seed banks, or botanic gardens.

Seed Bank

Facility where seeds are dried and stored in air-tight containers at $-18\,^{\circ}\text{C}$ to $-20\,^{\circ}\text{C}$ to preserve genetic diversity.

Cryopreservation

Storage of biological material in liquid nitrogen at $-196\,^{\circ}\text{C}$ to preserve viability indefinitely.

Micropropagation

The cultivation of plant cells or tissues in sterile lab conditions to produce genetically identical clones.