OCR Gateway Science Biology A (J247) Revision Flashcards

Comprehensive vocabulary flashcards covering OCR Gateway Science Biology A (Topics B1-B4), including Higher Tier content and Required Practicals.

Resolution

The ability to distinguish two adjacent points as separate, determining the level of detail visible in an image.

Transmission Electron Microscope (TEM)

A microscope that passes a beam of electrons through an ultra-thin specimen to produce a 2D image of internal sub-cellular structures.

Scanning Electron Microscope (SEM)

A microscope where electrons bounce off the surface of a specimen to create 3D images of external structures.

Magnification Formula

$$\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}$$

Mitochondria

Double-membrane organelles where the inner membrane is folded into cristae; the site of aerobic respiration and ATP production.

Ribosomes

The site of protein synthesis (translation); eukaryotic cells contain 80S ribosomes while prokaryotic cells contain 70S ribosomes.

Plasmids

Small circular loops of extra DNA in prokaryotes that often carry antibiotic resistance genes and can be transferred between bacteria.

Peptidoglycan

The polymer that makes up the cell wall of prokaryotic organisms, distinct from the cellulose found in plant cell walls.

DNA (Deoxyribonucleic acid)

A double helix polymer made of nucleotide monomers consisting of a deoxyribose sugar, a phosphate group, and nitrogenous bases.

Complementary Base Pairing

The absolute rule where Adenine pairs with Thymine via 2 hydrogen bonds, and Guanine pairs with Cytosine via 3 hydrogen bonds.

Transcription

The Higher Tier process in the nucleus where DNA unwinds and RNA polymerase joins free RNA nucleotides to form a single-stranded mRNA molecule.

Translation

The Higher Tier process at the ribosome where tRNA molecules match anticodons to mRNA codons to build a polypeptide chain.

Induced Fit Model

The Higher Tier enzyme model where the active site slightly changes shape to mold around the substrate, straining bonds and lowering activation energy.

Enzyme Denaturation

The permanent change in an enzyme's active site shape due to extreme pH or temperatures above the optimum, preventing substrate binding.

Aerobic Respiration Equation

$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$$

Anaerobic Respiration (Animals)

The process of breaking down glucose into lactic acid without oxygen, yielding only $2\,ATP$ per glucose molecule.

Anaerobic Respiration (Plants and Yeast)

Often called fermentation; the process where glucose is converted into ethanol and carbon dioxide: $\text{Glucose} \rightarrow \text{Ethanol} + \text{Carbon dioxide}$.

ATP (Adenosine Triphosphate)

The universal energy currency of the cell, used for processes like active transport, muscle contraction, and cell division.

Photosynthesis Equation

$$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$

Inverse Square Law

The Higher Tier principle stating that light intensity is inversely proportional to the square of the distance: $\text{light intensity} \propto \frac{1}{d^2}$.

Diffusion

The passive net movement of particles from an area of high concentration to an area of low concentration down a gradient.

Osmosis

The net movement of water molecules from high water potential to low water potential across a partially permeable membrane.

Water Potential ($\psi$)

The tendency of water to move by osmosis; pure water has the highest value of $0\,kPa$.

Active Transport

The movement of substances against a concentration gradient using carrier proteins and energy in the form of ATP.

Mitosis

Part of the cell cycle where a nucleus divides into two identical nuclei, resulting in two genetically identical daughter cells.

Pluripotent

A property of embryonic stem cells meaning they can differentiate into any of the approximately 200 cell types in the human body.

Meristems

Regions of undifferentiated, actively dividing cells in plant root and shoot tips that allow for indefinite growth.

Double Circulation

A system where blood passes through the heart twice per circuit, consisting of the pulmonary and systemic circuits.

Xylem Vessels

Unidirectional tubes made of dead, lignified cells that transport water and inorganic minerals from roots to leaves.

Phloem

Living tissue composed of sieve tube elements and companion cells that transports sucrose and amino acids bidirectionally via translocation.

Stomata

Pores in the leaf epidermis surrounded by guard cells that regulate gas exchange and water loss.

Synapse

The junction between two neurones where neurotransmitters diffuse across a synaptic cleft to trigger a new electrical impulse.

Accommodation

The Higher Tier process involving the ciliary muscles and suspensory ligaments to change lens shape for focusing on near or distant objects.

Myopia

Short-sightedness occurring when the eyeball is too long or the lens is too curved, causing distant objects to focus in front of the retina.

Endocrine System

A coordination system using chemical messengers (hormones) secreted into the blood to produce slower, longer-lasting effects.

Negative Feedback

A homeostatic mechanism that detects a deviation from a set point and triggers a response to oppose and reverse the change.

FSH (Follicle-Stimulating Hormone)

A hormone from the pituitary gland that stimulates follicle maturation in the ovaries and the production of oestrogen.

Auxins

Plant hormones produced in growing tips that promote cell elongation in shoots and inhibit growth in roots.

Gibberellins

Plant hormones that promote stem elongation, break seed dormancy for germination, and stimulate fruit development.

Ethene

A gaseous plant hormone that promotes fruit ripening and the abscission (shedding) of leaves and flowers.

Homeostasis

The maintenance of a stable internal environment within narrow optimal ranges, such as core body temperature and blood glucose.

Glucagon

A Higher Tier hormone secreted by pancreas alpha cells when blood glucose is low, stimulating the breakdown of glycogen into glucose.

Nephron

The functional unit of the kidney consisting of the Bowman's capsule, proximal convoluted tubule, loop of Henle, and collecting duct.

ADH (Antidiuretic Hormone)

A hormone that increases the permeability of the kidney collecting ducts to water, resulting in more water reabsorption.

Saprotrophic

The mode of nutrition used by decomposers which involves secreting extracellular enzymes to digest dead organic matter before absorption.

Nitrogen Fixation

The conversion of atmospheric nitrogen gas ($N_2$) into nitrates or ammonium by bacteria, lightning, or industrial processes.

Mutualism

A symbiotic relationship between two different species where both organisms benefit from the interaction.

Biomass Transfer Efficiency

The percentage of biomass passed between trophic levels, calculated as: $\frac{\text{biomass at higher level}}{\text{biomass at lower level}} \times 100$.