Edexcel International A-Level Biology I Unit 7 Respiration, Muscles and the Internal Environment I Primrose Kitten

CHEMIOSMOSIS

The flow of protons [hydrogen ions] through ATP synthase channels, creating an electrochemical force that is enough to produce ATP. It occurs in the cristae of the mitochondria and in the thylakoid membranes of chloroplasts during photosynthesis. It also occurs in the cell surface membranes of prokaryotes.

ATP SYNTHASE

A channel protein and enzyme which spans the thylakoid membranes or cristae of mitochondria. Hydrogen ions move through the channels within ATP synthase down an electrochemical gradient. The ATP synthase protein spins as the protons pass through and the active site accepts ADP and a phosphate ion to produce ATP, during chemiosmosis.

AEROBIC RESPIRATION

A sequence of enzyme controlled chemical reactions which requires oxygen and produces carbon dioxide, water and much ATP.

ANAEROBIC RESPIRATION

A sequence of enzyme controlled chemical reactions which take place in the absence of oxygen and produces lactate [in animals] or ethanol and carbon dioxide [in plants and fungi]. Only a small quantity of ATP is formed in both cases.

CRISTAE

The highly folded inner membranes of the mitochondria where the electron carriers and enzymes are found during oxidative phosphorylation.

MATRIX

The interior solution in the mitochondria. It contains lipids, and enzymes involved in the Krebs cycle. Mitochondrial DNA and 70S ribosomes allow the production of some mitochondrial proteins.

GLYCOLYSIS

A sequence of chemical reactions where the six carbon glucose molecule is split into two 3-carbon molecules of pyruvate. This process is oxygen independent and occurs in the cell cytoplasm.

LINK REACTION

This occurs in the matrix of the mitochondria where the 3-carbon pyruvate molecules enter a series of reactions which lead to the formation of a 2-carbon molecule called acetyl coenzyme A.

KREBS CYCLE

This occurs in the matrix of the mitochondria and is oxygen dependent. Acetyl coenzyme A is introduced into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD [which are used in oxidative phosphorylation]

OXIDATIVE PHOSPHORYLATION

This takes place on the inner mitochondrial membranes. Electrons [associated with reduced NAD and FAD] flow along the electron transport chain, providing energy for the active transport of hydrogen ions. ADP is phosphorylated to ATP during chemiosmosis.

OXIDATION

A chemical reaction in which hydrogen atoms or electrons are lost or oxygen atoms are gained.

REDUCTION

A chemical reaction in which hydrogen atoms or electrons are gained or oxygen atoms are lost.

NAD

Nicotinamide adenine dinucleotide [NAD] is a coenzyme and a hydrogen carrier molecule. The nicotinamide part accepts a pair of hydrogen atoms and becomes reduced. It is oxidised when it loses the hydrogen atoms. NAD is an important molecule involved in all stages of respiration.

FAD

Flavin adenine dinucleotide [FAD]. This acts as a hydrogen carrier and is tightly bound to a dehydrogenase enzyme embedded in the inner mitochondrial membrane. FAD does not pump hydrogen ions into the intermembrane space but instead, returns them to the matrix.

COENZYME A

This id often referred to as CoA. It carries the 2-carbon acetyl group made from pyruvate in the link reaction to the Krebs cycle. CoA also carries acetyl groups made from beta oxidation of fatty acids and some amino acids to the Krebs cycle.

DEHYDROGENASE

An enzyme involved in the removal of hydrogen atoms from a substrate molecule. Usually associated with a coenzyme.

SUBSTRATE-LEVEL PHOSPHORYLATION

Formation of ATP directly from ADP and Pi during glycolysis and the Krebs Cycle when one molecule is converted to another. It contrasts with ATP formed by oxidative phosphorylation.

PYRUVATE

A three carbon molecule. A 6-carbon molecule of glucose is split into two 3-carbon molecules of pyruvate during glycolysis in the cell cytoplasm.

DECARBOXYLATION

The removal of carbon dioxide from a substrate molecule in the link reaction and the Krebs cycle.

NADH-COENZYME Q REDUCTASE

A dehydrogenase enzyme that catalyses the oxidation of reduced NAD so that NAD can be recycled for reuse in the link reaction and the Krebs cycle.

LACTATE

A product of anaerobic respiration in muscle cells of animals. Pyruvate acts as a hydrogen acceptor from reduced NAD to form lactate. Lactate dehydrogenase catalyses the reduction of pyruvate to lactate and the oxidation of NAD.

ETHANAL

A metabolite formed during anaerobic respiration in plant and fungi cells. Pyruvate is decarboxylated by the enzyme pyruvate decarboxylase to form ethanal.

ETHANOL

A product of anaerobic respiration in plant and fungi cells. Ethanal accepts hydrogen atoms from reduced NAD by the enzyme ethanol dehydrogenase. Ethanal is reduced to ethanol and NAD is oxidised .

RESPIRATORY QUOTIENT [RQ]

This is the ratio of carbon dioxide produced by a respiring organism to the oxygen consumed in a given period of time. As it is a ratio, there are no units required. RQ values tell us what type of respiratory substrate is being metabolised and what type of respiration. RQ glucose = 1.0; RQ protein = 0.9; RQ triglycerides = 0.7; during anaerobic respiration, the RQ will be infinity.

ATPASE

An enzyme that catalyses the hydrolysis of ATP into ADP and a free phosphate ion, thereby releasing energy for use in other biochemical reactions.

ELECTROCHEMICAL GRADIENT

The difference in the charge and chemical concentration across the plasma membrane due to its selective permeability. An electrochemical gradient determines the direction an ion moves by diffusion or active transport across a membrane.

BETA OXIDATION

Fatty acid molecules are broken down in a series of reactions each generating a molecule of acetyl CoA. This continues until the fatty acid chain has been broken down. Acetyl CoA molecules can then enter the Krebs Cycle for oxidation. Beta oxidation takes place in the mitochondria of eukaryotes and the cytosol in prokaryotes.

RESPIROMETER

A device used to measure the rate of respiration of a living organism or tissue by measuring the rate of oxygen uptake or rate of carbon dioxide production.

TENDON

Connective tissue consisting of densely packed collagen and elastic fibres. Tendons connect muscle to bone.

LIGAMENT

Fibrous connective tissue which connects bones to bones

SYNOVIAL JOINT

A type of joint typically found between bones that move against each other such as shoulder, hip and knee. It has a joint cavity filled with synovial fluid.

SYNOVIAL FLUID

A viscous fluid found in the cavities of synovial joints. Reduces friction between the articular cartilage of synovial joints during movement. Synovial fluid also acts as a shock absorber. The fluid transports oxygen and nutrients and removes carbon dioxide and waste products from chondrocytes in the surrounding cartilage.

SYNOVIAL MEMBRANE

Secretes synovial fluid

FIBROUS CAPSULE

An envelop which surrounds a synovial joint

CARTILAGE

Absorbs synovial fluid. Acts as a shock absorber

EXTENSOR

A muscle whose contraction extends or straightens a limb.

FLEXOR

A muscle whose contraction bends a limb.

PATELLA

Knee cap

FEMUR

Thigh bone

TIBIA

Shin bone

BALL AND SOCKET JOINT

[Spheroid joint]. A type of synovial joint where the round head of the femur/humerus [ball] rests in the cup-like acetabulum [socket] of the pelvis or glenoid fossa [socket] of the shoulder blade. This enables the joint to move in many directions.

HINGE JOINT

A type of synovial joint where a convex surface fits into a concave surface e.g. elbow; knee. This allows motion in one plane only.

PIVOT JOINT

[Rotary or trochoid joint]. A type of synovial joint where one bone fits into a ring shaped concave surface and allows rotation around a single axis e.g. between the cranium and atlas vertebra which allows 'yes' 'no' movements; wrist joint which allows the hand to be turned up and down.

GLIDING JOINT

[Plane or arthrodial joint] Type of synovial joint where two flat surfaces slide over one another e.g. articulating surfaces between neighbouring vertebrae.

ANTAGONISTIC

A description of structures or chemicals in the body which perform opposite actions to each other e.g. biceps and triceps muscles.

STRIATED MUSCLE

Skeletal or voluntary muscle. Makes up the bulk of body muscle in vertebrates. Attached to bones by tendons. Under conscious control.

SMOOTH MUSCLE

Non striated or involuntary muscle. Not under conscious control. Found in the walls of blood vessels, the gut, the iris of the eye.

CARDIAC MUSCLE

Found exclusively in the heart. Myogenic. Cardiac muscle cells appear striated under the microscope with many mitochondria. Cardiac muscle cells are connected by intercalated discs.

MYOFIBRIL

Skeletal muscle consists of muscle fibres bundled together. Each muscle fibre contains many myofibrils, which are the contractile elements of the muscle. Each myofibril is made up of two types of protein filament: thin actin and thick myosin.

ACTIN

A thin type of protein filament found in a myofibril. Consists of two strands twisted around each other.

MYOSIN

A thick type of protein filament found in a myofibril. A molecule of myosin consists of a long rod shaped region with a bulbous head.

SARCOMERE

The section of a myofibril between two Z lines.

SARCOPLASM

The cytoplasm of a muscle fibre. The sarcoplasm contains a large concentration of mitochondria and endoplasmic reticulum.

SARCOLEMMA

The membrane which surrounds a muscle fibre.

SARCOPLASMIC RETICULUM

A membrane bound structure found within a muscle fibres, similar to the endoplasmic reticulum in other cells. The main function of the sarcoplasmic reticulum is to store calcium ions.

I BAND

Isotropic band. A light region consisting of thin actin filaments within a sarcomere. The I band becomes narrower when a myofibril contracts.

A BAND

Anisotropic band. A dark region consisting of overlapping thin actin and thicker myosin filaments. The A band remains the same width when a myofibril contracts.

Z LINE

A dark line which traverses the middle of each I band. The section of the myofibril between two Z lines is known as a sarcomere.

H ZONE

A lighter region which occurs in the centre of the darker A band of a myofibril. The H zone consists only of myosin filament. The H zone becomes narrower during contraction of the myofibril.

TROPOMYOSIN

A protein which forms a fibrous strand wrapped around an actin filament.

TROPONIN

A globular protein which binds to tropomyosin and can reversibly attach to calcium ions.

SLOW TWITCH FIBRES

These type of muscle fibres contract less rapidly and fatigue slowly. They provide less powerful contractions but over a long period of time. These type of muscle fibres are adapted to endurance work. They possess a large store of myoglobin, a rich blood supply and numerous mitochondria to produce ATP.

FAST TWITCH FIBRES

These type of muscle fibres contract rapidly, fatigue rapidly and produce powerful contractions over a short period of time. They are adapted for intense exercise e.g. weight lifting. They possess thicker and more numerous myosin filaments; a high concentration of glycogen; high concencentrations of enzymes involved in anaerobic respiration to provide ATP quickly; a store of phosphocreatine.

NEUROMUSCULAR JUNCTION

A specialised synapse where the end of a motor neurone meets a skeletal muscle fibre. Unlike nerve synapses, the postsynaptic membrane at a neuromuscular junction is folded to increase the surface area to allow more postsynaptic receptors to be present. In a neuromuscular junction a single impulse will always cause a contraction, unlike a nerve synapse.

MYOGLOBIN

A pigment found in muscles which acts as an emergency store of oxygen for aerobic respiration. Myoglobin has a high affinity for oxygen and will only release oxygen when the surrounding concentration [partial pressure] of oxygen is very low.

SLIDING FILAMENT THEORY

A theory to explain how the thin actin and thick myosin filaments can slide past one another to shorten the myofibrils during muscle contraction.

PHOSPHOCREATINE [PCr]

Sometimes referred to a creatine phosphate. Phosphocreatine is a chemical stored in muscle fibres which acts as a reserve supply of phosphate to convert ADP to ATP. No lactate is produced in this process so it does not lead to muscle fatigue. Phosphocreatine stores in muscle fibres are limited and will run out in a few seconds. The system provides only enough extra ATP for short bursts of activity. The phosphocreatine store is replenished using phosphate from ATP when the muscle is relaxed.

TRANSVERSE [T] TUBULES

Extensions of the sarcolemma which traverse [run across ] each muscle fibre and between myofibrils. They are involved in the uptake and release of calcium ions in the sarcoplasm, which in turn controls ATPase activity.

BASAL METABOLIC RATE

The rate at which the body uses energy while at rest to maintain vital functions such as breathing; keeping warm.

CARDIAC OUTPUT

"The volume of blood pumped by one ventricle of the heart in one minute. It is usually measured in dm3 min-1.

HEART RATE

The number of times the heart beats in one minute. Measured as beats per minute.

STROKE VOLUME

The volume of blood pumped out from the left ventricle during each systolic heart contraction. Measured in mL

ELECTROCARDIOGRAPHY [ECG]

A process which monitors the electrical activity of heart muscle cells to detect heart activity and identify certain problems with the heart.

P WAVE

A distinct wave observed on an electrocardiogram [ECG] caused by depolarisation of the atria, resulting in their contraction.

QRS COMPLEX

A distinct area observed on an ECG trace resulting from the depolarisation of the ventricles and their subsequent contraction.

T WAVE

A distinct wave observed on an electrocardiogram [ECG] caused by re-polarisation [recovery] of the ventricles, resulting in their relaxation.

SINOATRIAL NODE [SAN]

Referred to as the 'pacemaker' of the heart. A distinct group of cells in the wall of the right atrium of the heart. The initial stimulus for contraction originates here. The SAN controls and coordinates the contraction of the heart.

ATRIOVENTRICULAR NODE [AVN]

A group of cells which lie between the atria of the heart. After a short delay, the AVN conveys a wave of electrical excitation between the ventricles along Purkyne fibres.

PURKYNE FIBRES

A series of specialised muscle fibres located in the inner ventricular walls [septum] which collectively make up the bundle of His. The bundle of His conducts the wave of excitation from the AVN, through the atrioventricular septum to the base of the ventricles. The ventricles then contract quickly from the apex upwards.

BUNDLE OF HIS

A collection of Purkyne fibres located in the inner ventricular walls, which convey a wave of electrical excitation from the AVN to the apex of the ventricles.

MEDULLA OBLONGATA

A region of the brain and part of the autonomic nervous system. It contains control centres for heart rate; breathing rate and blood flow rate.

CHEMORECEPTOR

A type of receptor which responds to chemicals e.g. blood carbon dioxide concentration.

OSMORECEPTOR

A type of sensory receptor which detects concentration of body fluids.

BARORECEPTOR

A type of sensory receptor which detects blood pressure.

CAROTID ARTERIES

Main arteries which supply blood from the heart to the head. Chemoreceptors located in the walls of the carotid arteries are sensitive to the pH of the blood resulting from changes in blood carbon dioxide concentration.

SYMPATHETIC NERVOUS SYSTEM

Part of the autonomic [involuntary/subconscious] nervous system which carries nerve impulses to glands, smooth muscle and cardiac muscle. Sympathetic nervous system deals with 'flight or fight' responses.

PARASYMPATHETIC NERVOUS SYSTEM

Part of the autonomic [involuntary/subconscious] nervous system which carries nerve impulses to glands, smooth muscle and cardiac muscle. Parasympathetic nervous system deals with the 'rest and digest' system.

TACHYCARDIA

A condition which results in a rapid heart rate with a resting heart rate of more than 100 beats per minute.

BRADYCARDIA

A condition which results in a slow heart rate of less than 60 beats per minute

FIBRILLATION

A condition where the heart rate is rapid, irregular and has lost its rhythm. Severe fibrillation can be life threatening and increase the chances of strokes. Fibrillation can be treated in various ways: with drugs; pacemaker; electric shock treatment; catheter ablation.

ECTOPIC HEARTBEAT

A condition which results when the heart can beat too early followed by a pause or beats too late. This is common and requires no treatment.

VAGUS NERVE

A parasympathetic nerve from the cardiovascular control centre in the medulla, which carries nerve impulses to the SAN to decrease heart rate.

NEGATIVE FEEDBACK

Type of control mechanism in which a change from the normal value of a physiological factor is detected and a response is made that restores the value to the norm. e.g. control of blood glucose level

POSITIVE FEEDBACK

Type of control mechanism in which a change from the normal value of a physiological factor is detected and a response is made that moves the value further from the set point e.g. release of oxytocin and uterine contractions.

TRACHEA

A wide flexible tube in the human respiratory system. Known as the windpipe. Contains C-shaped rings of cartilage to provide 'scaffolding' to keep the tube open. The tracheal walls are made up of smooth muscle, lined with ciliated epithelial cells that contain goblet cells which secrete mucus.

BRONCHUS

[plural bronchi]. Bronchi are two divisions of the trachea, each leading to one lung. They are similar in structure to the trachea although they have a smaller diameter and thinner walls. The bronchi have complete rings of cartilage to support them.

BRONCHIOLES

These are numerous, thin, narrow branches of the bronchi. They do not have cartilage rings. The walls are lined with smooth muscle so that larger bronchioles can control the flow of air in and out of the alveoli [air sacs]. Smaller bronchioles have no goblet cells or cilia on their epithelium.

ALVEOLI

[singular alveolus]. Known as air sacs. Arranged in groups at the end of the smallest bronchioles. The alveoli are lined with a single layer of epithelium [which acts as a gas exchange surface] but there is also an extracellular matrix of collagen and elastic fibres between the alveoli. The elastic fibres allow the alveoli to expand during inspiration and recoil during expiration.

PULMONARY VEINS

These transfer oxygenated blood from the lungs to the left atrium of the heart.