Exchange - Yr 1 Flashcards
Surface area: volume ratio
The important relationship between the surface area of a biological unit such as a cell or a whole animal, and its overall volume, which affects many aspects of its biochemistry. As the size of the unit increases, its surface area grows relatively more slowly than its volume.
Exchange surface
Surfaces across which substances could be transferred. To allow exchange to be efficient, surfaces will often have a large surface area:volume ratio, be very thin and selectively permeable. There will also often be movement of the environmental medium and a transport system to ensure the movement of the internal medium.
Concentration gradient
The difference between the concentration of a gas or substance inside and outside of the cell. The steeper the concentration gradient, the faster the rate of diffusion.
Tracheae
A large internal network of tubes in insects with supported rings to prevent them collapsing.
Tracheoles
These tubes extend from the tracheae and extend throughout all the body tissues of the insect to allow atmospheric air to be brought directly to respiring tissues.
Spiracle
Tiny pores that allow gases to enter and leave the tracheae (and water vapour to leave as well). They are opened and closed by a valve.
Gill
Located within the body of the fish, behind the head.
Gill filaments
Make up the gills of a fish – they are stacked up in a pile.
Gill lamellae
At right angle to gill filaments, which increase the surface area of the gills.
Countercurrent flow
Describes how the flow of water over the fill lamellae and the flow of blood within them are in opposite directions. Allows a diffusion gradient to be maintained all the way across the gill lamellae.
Stomata
Minute pores that occur mainly on the leaves, especially on the underside. They allow gaseous exchange (and water vapour to leave as well). They are opened and closed by guard cells.
Guard cells
Control the opening and closing of stomata.
Spongy mesophyll
Tissue in the leaf, which has large air spaces so gases can readily come into contact with mesophyll cells and large surface area of mesophyll cells for rapid diffusion.
Xerophyte
Plants which have a restricted supply of water which have evolved a range of adaptations to limit water loss through transpiration.
Lungs
A pair of lobe structures made up of a series of highly branched tubules called bronchioles, which end in tiny air sacs called alveoli.
Ventilation
The process in which air is constantly moved in and out of the lungs to maintain diffusion of gases across the alveolar epithelium. Also known as breathing.
Trachea
A flexible airway that is supported by rings of cartilage which prevent it collapsing as the air pressure inside falls when breathing in. Its walls are made up of muscle, lined with ciliated epithelium and goblet cells.
Bronchi
Two divisions of the trachea each leading to one lung. Amount of cartilage reduces as they get smaller. Also produce mucus to trap dirt particles and cilia that move this towards the throat.
Bronchioles
A series of branching subdivisions of the bronchi whose walls are made up of muscle (which constricts to control the flow of air in and out of the alveoli) lined with epithelial cells.
Alveoli
Minute air-sacs with a diameter of between 100µm and 300µm at the end of the bronchioles. They are lined with epithelium. Between the alveoli there are some collagen and elastic fibres.
Inspiration
An active process when external intercostal muscles contract, internal intercostal muscles relax, ribs are pulled upwards and outwards and the diaphragm muscles contract causing it to flatten, increasing the volume of the thorax, which reduces the pressure.
Expiration
A largely passive process when external intercostal muscles relax, internal intercostal muscles contract, ribs move downwards and inwards and the diaphragm muscles relax, decreasing the volume of the thorax, which increases the pressure.
Diaphragm
A sheet of muscle that separates the thorax from the abdomen.
Rib cage
the bony frame formed by the ribs round the chest
Intercostal muscles
Lie between the ribs. Two sets – internal whose contraction leads to expiration and external whose contraction leads to inspiration.
Enzyme
A protein that acts as a catalyst and so lowers the activation energy needed for a reaction.
Absorption
Movement of digested food molecules through the wall of the intestine into the blood or lymph
Oesophagus
Muscular tube which carries food from the mouth to the stomach
Stomach
A muscular sac with an inner layer that produces enzymes. Its role is so store and digest food, especially proteins.
Ileum
A long muscular tube where food is further digested. Enzymes are produced by its walls and by glands that pour their secretions into it. Inner walls are folded into villi which gives them a large surface area. Where products of digestion are absorbed into the bloodstream.
Large intestine
Where water is absorbed.
Rectum
The final section of the intestines where the faeces is stored before being egested by the anus.
Salivary glands
Situated near the mouth. They pass their secretions via a duct into the mouth which contain salivary amylase which hydrolyses starch into maltose.
Pancreas
A large gland situated below the stomach. It produces a secretion called pancreatic juice, which contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch.
Hydrolysis
How digestive enzymes function – the splitting up of molecules by adding water to the chemical bonds that hold them together.
Carbohydrases
Type of digestive enzyme which hydrolyse carbohydrates, ultimately to monosaccharides.
Lipases
Type of digestive enzyme which hydrolyse lipids (fats and oils) into glycerol and fatty acids.
Proteases
Type of digestive enzyme which hydrolyse proteins, ultimately into amino acids.
Salivary amylase
Produced by the salivary glands and released into the mouth and starts hydrolysing starch in food to maltose.
Pancreatic amylase
Produced by the pancreas and released into the small intestine where it continues the hydrolysis of starch to maltose.
Maltase
Produced by the epithelial lining and is a membrane-bound disaccharidase which breaks down maltose into glucose.
Membrane-bound disaccharidase
An enzyme which is not released into the lumen of the ileum but is part of the cell-surface membranes of the epithelial cells that line the ileum. E.g. maltase
Sucrase
Produced by the epithelial lining and is a membrane-bound disaccharidase which breaks down sucrose into the monosaccharides glucose and fructose.
Lactase
Produced by the epithelial lining and is a membrane-bound disaccharidase which breaks down lactose into the monosaccharides glucose and galactose.
Bile salt
Produced by the liver and split up lipids into tiny droplets called micelles.
Emulsification
The process by which lipids are split up into tiny droplets called micelles by bile salts, which are produced by the liver. It increases the surface area of the lipids so that the action of lipases is sped up.
Micelles
Tiny structures (4-7nm in diameter) formed when monoglycerides and fatty acids remain in association with the bile salts that initially emulsified the lipid droplets. They break down as they come into contact with the epithelial cells lining the villi of the ileum and release the monoglycerides and fatty acids which diffuse across the cell membrane into the epithelial cells.
Chylomicrons
A structure formed when triglycerides associate with cholesterol and lipoproteins, which are adapted for the transport of lipids. Start forming in the endoplasmic reticulum and continuing in the Golgi apparatus.
Lacteals
Lymphatic capillaries that are found in the centre of each villus, where chylomicrons pass into and then enter the bloodstream.
Exocytosis
The outward bulk transport of materials through the cell-surface membrane. How chylomicrons move out of the epithelial cells by this process.
Endopeptidases
A type of protease which hydrolyses the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules.
Exopeptidases
A type of protease which hydrolyses the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. They progressively release dipeptides and single amino acids.
Dipeptidases
A type of protease which hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum.
Lumen
The cavity of the intestines
Villi
Folded finger-like projections of the ileum wall, about 1mm long, which are increase the surface area of the ileum and therefore accelerate the rate of absorption.
Microvilli
Tiny finger-like projections from the cell-surface membrane of some animal cells.
