AQA A Level Biology: Organisms Topic 3 : Exchange Substances with their Environment

Comprehensive vocabulary flashcards covering gas exchange, digestion, and mass transport in animals and plants.

Surface area to volume ratio (SA:V)

A measurement determining the efficiency of substance exchange; as an organism gets larger, this ratio typically decreases.

Metabolic rate

The total energy an organism consumes over a specific duration, often measured via oxygen consumption during aerobic respiration to regenerate $ATP$.

Spiracles

Small surface pores in insects that open and close to facilitate gas diffusion while managing moisture levels.

Tracheoles

The fine, highly branched internal tubes in insects where gas exchange occurs directly with the tissues due to their thin walls and large surface area.

Abdominal pumping

The contraction of muscles in an insect's abdomen that alters internal pressure to move air through the tracheal system.

Counter current flow

A mechanism in fish gills where blood and water move in opposite directions, ensuring a constant oxygen concentration gradient across the entire length of the lamellae.

Xerophyte

A specialized plant, such as a cactus, possessing structural adaptations like rolled leaves or thick cuticles to survive in arid environments by reducing water loss.

Alveolar epithelium

The extremely thin, one-cell thick layer in human lungs that provides a short diffusion distance for $O_2$ and $CO_2$.

Antagonistic muscle action

The process in ventilation where the internal and external intercostal muscles perform opposing contraction and relaxation to move the ribcage.

Forced Vital Capacity (FVC)

The maximum volume of air that can be forcefully exhaled from the lungs in a single breath.

Amylase

An enzyme produced by the salivary glands and pancreas that hydrolyses starch into the disaccharide maltose.

Bile salts

Substances produced by the liver that emulsify lipids into smaller droplets to provide a larger surface area for lipase activity.

Micelles

Structures formed after lipid digestion that transport monoglycerides and fatty acids to the ileum lining for absorption.

Endopeptidases

Proteolytic enzymes that hydrolyse internal peptide bonds within a polypeptide chain.

Co-transport

A mechanism where sodium ions ($Na^+$) and glucose or amino acids are moved into epithelial cells together via carrier proteins.

Haemoglobin

A quaternary protein with four Haem groups containing $Fe^{2+}$ ions, responsible for transporting oxygen as oxyhaemoglobin.

Cooperative binding

The process where the binding of the first oxygen molecule alters the tertiary and quaternary structure of haemoglobin, making it easier for subsequent oxygen molecules to bind.

Bohr effect

The physiological phenomenon where increased $CO_2$ concentration reduces haemoglobin's affinity for oxygen, shifting the dissociation curve to the right.

Atrial systole

The phase of the cardiac cycle where the atria contract, increasing pressure and forcing blood through the atrioventricular valves into the ventricles.

Cardiac output

The volume of blood pumped by the heart per minute, calculated as $stroke \times volume \times heart \times rate$.

Tissue fluid

The watery liquid containing glucose, amino acids, and oxygen that bathes the cells, formed by hydrostatic pressure at the arteriole end of capillaries.

Cohesion-tension theory

The theory explaining water transport in the xylem as a continuous column pulled upward by transpiration and hydrogen bonding between water molecules.

Mass flow hypothesis

The movement of organic solutes in the phloem from source to sink driven by a hydrostatic pressure gradient.

Potometer

An apparatus used to estimate the rate of transpiration by measuring the distance an air bubble moves in a capillary tube over time using the formula \text{Volume} = \text{distance} \times \text{\textpi}r^2.