✅6 - Exchange Flashcards
What are the features of specialised exchange surfaces?
A large surface area to volume ratio
Very thin so that diffusion distance is short
Selectively permeable to allow selected materials to cross
Movement of environmental medium to maintain a gradient
A transport system to ensure movement of internal medium
What is Fick’s law?
Diffusion ∝ Surface area x difference in concentration / length of diffusion pathway
How does gas exchange occur in single celled organisms?
Oxygen is absorbed by diffusion across body surface, Carbon Dioxide diffuses out
What are tracheae?
An internal network of tubes in insects, supported by strengthened rings
What are tracheoles?
Smaller, dead end tubes which the tracheae divide into
How do gases move in and out of the tracheal system?
Along a diffusion gradient
Mass transport
The water in the ends of the tracheoles
How do gases move in and out of the tracheal system by diffusion?
When cells respire, O2 at the ends of tracheoles used up, creates diffusion gradient and O2 diffuses in and along tracheae. CO2 creates gradient int he opposite direction
How do gases move in and out of the tracheal system by mass transport?
The contraction of muscles of insect squeeze tracheae enabling mass movement of air in and out
How does water in the ends of tracheoles enable movement of gases in and out?
In periods of activity, muscle cells respire and produce lactate, which lowers water potential of muscle cells. Water moves into the cells and the volume of tracheoles decreases, drawing air into them
What are the limitations of the tracheal system?
Relies mostly on diffusion
Diffusion pathway must be short
What are fish gills made up of?
A gill bar, gill filaments and lamellae
What is countercurrent flow?
The flow of water over the gill lamellae and the flow of blood within them are in opposite directions
What does countercurrent flow allow?
Maximum gas exchange
What does the arrangement of blood vessels in countercurrent flow allow?
Blood that is already well loaded with oxygen meets water which has its maximum concentration of oxygen, so diffusion takes place
Blood with little oxygen meets water which has most, but not all its oxygen removed. Again, diffusion takes place from blood to water
What is maintained across the lamellae?
A diffusion gradient for oxygen uptake
How much of the oxygen in the water is taken up by blood?
80%
How is gas exchange in plants similar to in insects?
No living cell is far from the external air
Diffusion takes place in the gas phase (air) which makes it more rapid than in water
How are leaves adapted for rapid diffusion?
Many stomata and so no cell is far from one, short diffusion pathway
Numerous interconnecting air spaces throughout the mesophyll so that gases can come into contact with them
Large surface area of mesophyll cells for rapid diffusion
What are stomata?
Minute pores that occur mainly on the underside of leaves and that can open and close to control the rate of gas exchange
What controls the opening and closing of the stomata?
Guard cells
Why is it important to open and close the stomata?
To prevent water loss
What adaptions do insects have to conserve water loss?
Small surface area to volume ratio
Waterproof coverings
Spiracles
Why can plants not have a small surface area to volume ratio?
Because photosynthesis requires a large surface area
What are xerophytes?
Plants which have evolved with adaptions against water loss through transpiration
What are adaptions of plants to prevent water loss?
A thick cuticle Rolling up of leaves Hairy leaves Stomata in pits or grooves Reduced surface area to volume ratio of leaves
How does a thick cuticle prevent water loss?
The thicker the cuticle, the less water can escape through it, eg holly leaves
How does rolling up leaves prevent water loss?
Most leaves have stomata on lower epidermis, so rolling protects lower epidermis from outside, helping to trap a region of still, warm air within. This region becomes saturated with water vapour and so there is no water potential gradient
How does having hairy leaves prevent water loss?
A thick layer of hairs traps still, moist air next to the leaf surface and the water potential gradient is reduced, so less water is lost
How does having stomata in pits or grooves prevent water loss?
Traps still, moist air close to the leaf to reduce water potential gradient
How does reduced surface area to volume ratio of leaves prevent water loss?
By having leaves that are small and roughly circular in cross section, eg pine needles, water loss is reduced
Why does the volume of oxygen absorbed and carbon dioxide removed need to be large in mammals?
They are relatively large organisms with a large volume of living cells
They maintain a high body temperature which is related to them having high metabolic and respiratory rates
Why are the lungs located inside the body?
Air is not dense enough to support or protect them
The body as a whole would otherwise lose a great deal of water and dry out
What are the main parts of the human gas exchange system?
Lungs Trachea Bronchi Bronchioles Alveoli
How are is the trachea supported?
By rings of cartilage
What dot he bronchi and trachea produce?
Mucus, to trap dirt particles and they have cilia to move the dirt laden mucus towards the throat
Why do alveoli have elastic fibres?
To allow them to stretch
What does contraction of the internal intercostals lead to?
Expiration
What does contraction of the external intercostals lead to?
Inspiration
What is the process of inspiration?
External intercostals contract, internals relax
Ribs pulled upwards and outwards, volume increases
Diaphragm contracts and flattens, increases volume
Pressure reduced, air drawn in
What is the process of expiration?
Internal intercostals contract, externals relax
Ribs move downwards and outwards, volume decreases
Diaphragm relaxes, pushed up, volume decreased
Pressure increased, air forced out
Where is the site of gas exchange in mammals?
The epithelium of the alveoli
How many alveoli are in each lung?
300 million
Why is diffusion of gases between alveoli and blood very rapid?
Red blood cells slowed as they pass through pulmonary capillaries
Distance between alveolar air and RBCs decreased as RBCs flattened against capillary walls
Walls of capillary and alveoli very thin
Large total surface area
Breathing constantly ventilates lungs, heart constantly pumps blood, steep concentration gradient
What are the main parts of the digestive system?
Oesophagus Stomach Ileum Large intestine Rectum
What role does the stomach play in digestion?
Muscular sac with inner later that produces enzymes. Stores and digests food, especially proteins. Has glands that produce enzymes to digest protein
What role does the ileum play in digestion?
Long muscular tube, food further digested by enzymes produced in the walls and glands. Inner walls folded into villi then microvilli, large surface area
What role does the large intestine play in digestion?
Absorbs water, most of water is from the secretions of digestive glands
What do the salivary glands produce?
Amylase, which hydrolyses starch to maltose
What does the pancreas produce?
Pancreatic juice, contains proteases, lipases and amylase
What are the two stages of digestion?
Physical breakdown
Chemical digestion
What is physical breakdown?
When food is large and broken down into smaller pieces by structures such as the teeth, increasing surface area
What is chemical digestions
Hydrolyses large, insoluble molecules into smaller, soluble ones, carried out by enzymes
What does amylase do?
Hydrolyses alternate glycosidic bonds in starch to produce disaccharides of maltose
What breaks down maltose?
Maltase
What is maltase produced by?
The lining of the ileum
What does salivary amylase do?
Hydrolyses starch into maltose and contains salts that help to maintain pH around neutral
When is amylase denatured?
When it enters the stomach and conditions are acidic
What is produced by the pancreas and intestinal wall?
Alkaline salts to maintain the pH at around neutral so that amylase can fucntion
What are membrane-bound disaccharidases?
Maltase that is not released into the lumen of the ileum but instead part of the cell surface membrane of epithelial cells
What is sucrase?
Hydrolyses single glycosidic bonds in the sucrose molecule
What is lactase?
Hydrolyses single glycosidic bonds in lactose
Where are lipases produced?
The pancreas
What do lipases do?
Hydrolyse the ester bonds found in triglycerides to form fatty acids and monoglycerides
What are lipids first broken own into?
Micelles
What are lipids broken down into micelles by?
Bile salts produced by the liver
What is the process of breaking lipids down into micelles called?
Emulsification
What are endopeptidases?
Hydrolyse the peptide bonds between amino acids in the central region of the protein, forming a series of peptide molecules
What are exopeptidases?
Hydrolyse peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases, release dipeptides and single amino acids
What are dipeptidases?
Hydrolyse the bond between two amino acids of a dipeptide
How do villi increase efficiency of absorption?
Increase surface area for diffusion
Very thin walls, reduced distance
Contain muscle so can move, helps maintain diffusion gradient as movement mixes contents of ileum
Well supplied with blood vessels so can carry away absorbed molecules and maintain diffusion gradient
Microvilli
What are the processes of absorbing amino acids and monosaccharides?
Co-transport and diffusion
How are micelles absorbed?
They come into contact with the epithelial cells lining the villi and break down, releasing monoglycerides and fatty acids, which diffuse across the cell membrane
What happens when monoglycerides and fatty acids have been absorbed?
They are transported to the endoplasmic reticulum where they are recombined to form triglycerides, then associating with cholesterol and lipoproteins in the golgi to form chylomicrons
What are chylomicrons?
Special particles adapted for the transport of lipids
What happens to the cylomicrons?
They move out of the epithelial cell by exocytosis and enter lymphatic capillaries called lacteals at the centre of each villus
How are triglycerides transported into cells by chylomicrons?
They pass into the blood stream and the triglycerides are hydroysed by an enzyme in the endothelial cells of blood capillaries where they diffuse into cells
