Biology Module 2 Flashcards

Comprehensively covers cell structure, biochemistry, enzymes, membranes, cell division, and stem cells according to OCR Biology Module 2 specifications.

Plasmodesmata

A channel within the plant cell wall that allows for exchanging substances with adjacent cells.

Plasma membrane

Found in animal, plant, and prokaryotic cells; made of lipids and proteins; regulates movement of substances in and out of the cell and contains receptor sites.

Nucleolus

A structure within the nucleus responsible for making ribosomes.

Lysosome

An organelle surrounded by a membrane containing digestive enzymes used to digest invading cells or break down worn out cell components (apoptosis).

Ribosome

The site of protein synthesis, composed of proteins and RNA; not surrounded by a membrane.

RER (Rough Endoplasmic Reticulum)

A system of membranes enclosing fluid-filled space with a surface covered in ribosomes; functions to fold and process proteins.

SER (Smooth Endoplasmic Reticulum)

A system of membranes similar to RER but without ribosomes; functions to synthesise and process lipids.

Golgi apparatus

Fluid-filled, membrane-bound flattened sacs that process and package proteins and lipids, and produce lysosomes.

Matrix

The fluid inside a mitochondrion containing enzymes involved in respiration.

Thylakoid membranes

Membranes inside chloroplasts stacked to form grana, which are linked by lamellae.

Stroma

The fluid inside a chloroplast where photosynthesis takes place.

Centriole

Hollow cylinders made of microtubules involved in the separation of chromosomes during cell division.

Cilia

Tiny hair-like structures on the cell surface with a "9 + 2" arrangement of microtubules used to move substances along the cell surface or act as sensory organelles.

Endosymbiotic theory

States that mitochondria and chloroplasts originated from free-living prokaryotic cells engulfed by a larger eukaryotic cell, evidenced by their 70S ribosomes and circular DNA.

Cytoskeleton

A network of protein fibers providing mechanical strength, shape, and support for the cell, and enabling movement of organelles and the whole cell.

Peptidoglycan (murein)

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

Resolution

The ability to distinguish between two points that are close together.

Laser Scanning Confocal Microscope (LSCM)

A type of light microscope using laser beams and fluorescent dye to scan specimens at different depths and generate 3D images.

Transmission Electron Microscope (TEM)

Uses electromagnets to focus a beam of electrons through a thin specimen to show internal ultrastructure with a resolution of around $0.1\,nm$.

Scanning Electron Microscope (SEM)

Uses a beam of electrons scanned across a specimen to gather surface detail and create 3D images with a resolution of $1\text{--}10\,nm$.

Eyepiece graticule

A scale fitted onto the microscope eyepiece that has numbers but no units; must be calibrated against a stage micrometer.

Stage micrometer

A slide with accurate units used to work out the value of the eyepiece graticule divisions at a particular magnification.

Differential staining

The use of multiple stains to distinguish between different structures or cell types within one sample, such as the Gram stain or Acid-fast stain.

Specific heat capacity

The amount of energy needed to raise the temperature of $1\,kg$ of a substance by $1\,{}^\circ C$.

Latent heat of vaporization

The amount of energy needed to change $1\,kg$ of a liquid into a gas without changing its temperature.

Condensation reaction

A reaction that joins monomers together to form polymers, releasing a molecule of water and forming a chemical bond.

Hydrolysis reaction

A reaction that breaks polymers down into monomers by using water to break chemical bonds.

$\alpha$-glucose

A hexose monosaccharide where the hydroxyl group (OH) on carbon 1 is below the plane of the ring.

$\beta$-glucose

A hexose monosaccharide where the hydroxyl group (OH) on carbon 1 is above the plane of the ring.

Amylose

A component of starch made of $\alpha$-glucose joined by 1–4 glycosidic bonds, forming a coiled helix structure.

Glycogen

The main energy storage molecule in animals and fungi, made of $\alpha$-glucose with 1–4 and many 1–6 glycosidic bonds for rapid energy release.

Cellulose

A polysaccharide made of $\beta$-glucose with alternate monomers flipped $180\,{}^\circ$, forming straight chains and microfibrils for plant cell wall strength.

Triglyceride

A lipid molecule composed of one glycerol molecule and three fatty acids joined by ester bonds.

Phospholipid

An amphipathic lipid consisting of one glycerol, two fatty acids, and a phosphate group, forming the basis of all cell membranes.

Primary structure

The specific sequence of amino acids in a polypeptide chain held by peptide bonds.

Secondary structure

The folding of a polypeptide chain into an $\alpha$-helix or $\beta$-pleated sheet due to hydrogen bonds.

Tertiary structure

The further folding of a protein into a 3D shape stabilized by hydrogen bonds, ionic bonds, disulphide bonds, and hydrophobic interactions.

Quaternary structure

The arrangement of multiple polypeptide subunits joined together, such as in haemoglobin.

Conjugated protein

A globular protein that contains a non-protein prosthetic group, such as the haem group in haemoglobin.

Collagen

A fibrous protein consisting of three polypeptide chains wound into a triple helix, providing strength in skin, tendons, and bones.

Nucleotide

A monomer consisting of a pentose sugar, a phosphate group, and a nitrogenous base; elements include C, H, N, O, and P.

Purine

A type of nitrogenous base containing two carbon-nitrogen rings joined together, specifically Adenine (A) and Guanine (G).

Pyrimidine

A type of nitrogenous base containing one carbon-nitrogen ring, specifically Cytosine (C), Thymine (T), and Uracil (U).

Phosphodiester bond

The bond formed between the phosphate group of one nucleotide and the sugar of another in a condensation reaction.

ATP (Adenosine triphosphate)

A phosphorylated nucleotide with three phosphate groups that acts as an immediate energy source for cellular processes.

DNA Helicase

The enzyme that travels along the DNA molecule, breaking hydrogen bonds to separate strands during replication.

DNA Polymerase

The enzyme that forms phosphodiester bonds between nucleotides to build the sugar-phosphate backbone in the $5' \rightarrow 3'$ direction.

Semi-conservative replication

The method of DNA replication where each new DNA molecule contains one original parent strand and one newly-synthesised strand.

Meselson–Stahl experiment

Provided evidence for semi-conservative replication by using heavy (${}^{15}N$) and light (${}^{14}N$) nitrogen isotopes and centrifugation.

Degenerate code

The feature of the genetic code where more than one codon can code for the same amino acid, reducing the effect of mutations.

Transcription

The process in the nucleus where a section of DNA is copied into mRNA by RNA polymerase.

Translation

The process at the ribosome where the mRNA sequence is used to assemble a polypeptide chain with the help of tRNA.

Catalase

An intracellular enzyme that breaks down toxic hydrogen peroxide into water and oxygen ($H_2O_2 \rightarrow H_2O + O_2$).

Induced-fit hypothesis

A model where the active site is flexible and changes shape slightly to wrap around the substrate more closely to lower activation energy.

Temperature coefficient ($Q_{10}$)

A measure of how much the rate of a reaction changes when temperature increases by $10\,{}^\circ C$; for enzymes, it is typically around 2.

Cofactor

A non-protein substance, such as the inorganic chloride ion ($Cl^-$) for amylase, that helps an enzyme function properly.

Coenzyme

A small organic molecule, often derived from vitamins, that temporarily binds to the active site and acts as a carrier during reactions.

Competitive inhibitor

A molecule with a similar shape to the substrate that binds to the active site, preventing the substrate from binding.

Non-competitive inhibitor

A molecule that binds to an allosteric site, changing the enzyme's tertiary structure and active site shape regardless of substrate concentration.

Compartmentalisation

The separation of organelles from the cytoplasm by membranes to allow selective movement and control metabolic reactions.

Fluid Mosaic Model

Describes the membrane as a dynamic phospholipid bilayer with proteins scattered throughout it like a mosaic.

Facilitated diffusion

The passive movement of polar or large molecules down a concentration gradient through specific channel or carrier proteins.

Active transport

The movement of substances against their concentration gradient using carrier proteins and ATP.

Water potential ($\Psi$)

A measure of the tendency of water to diffuse in or out of a solution, measured in $kPa$; pure water is $0\,kPa$.

Plasmolysis

The condition in plant cells where the cytoplasm shrinks and the cell membrane pulls away from the cell wall due to water loss in a hypertonic solution.

Interphase

The stage of the cell cycle consisting of $G_1$, $S$ (DNA replication), and $G_2$ phases, where the cell grows and prepares for division.

Centromere

The region where two sister chromatids are joined together and where spindle fibres attach.

Mitotic Index

The ratio of the number of cells in mitosis to the total number of cells in a sample.

Homologous chromosomes

A pair of chromosomes that have the same genes at the same loci but may have different alleles.

Crossing over

The exchange of DNA between non-sister chromatids of homologous chromosomes during Prophase I of meiosis.

Independent assortment

The random orientation and separation of homologous chromosome pairs in Metaphase I, contributing to genetic variation.

Stem cell

An undifferentiated cell capable of dividing by mitosis and differentiating into specialised cell types.

Pluripotent

Stem cells that can differentiate into any body cell type but cannot form extra-embryonic tissues like the placenta.

Meristem

Found in plant root and shoot tips, containing stem cells that can differentiate into xylem vessel elements or phloem sieve tubes.

Budding

A form of asexual reproduction in yeast where a genetically identical daughter cell grows as a bud on the parent cell surface.

Binary fission

The process of asexual reproduction in prokaryotes where the circular DNA replicates and the cell divides into two clones.