Exchange Flashcards
What kind of SA:V ratio do small organism have
A large one
Gas exchange in single celled organisms
Substances just diffuse across body surface
What features does insects have for gas exchange
- Trachea
- Tracheoles w/ water in the ends
- Spiracles
- Muscle fibre
What supports the trachea
Rings of cartilage so it doesn’t collapse
Why are do the tracheoles allow quick diffusion
Because they are directly next to cells allowing air to be directly brought to the respiring tissue
What 3 ways are gases moved in the insect tracheal system
- along a diffusion gradient
- mass transport
- the ends of the tracheoles are filled with water
How do gases move in the insect tracheal system along a diffusion gradient
- when cells are respiring, oxygen is used up decreasing its concentration at the ends of tracheoles -> this creates a diffusion gradient causing oxygen to diffuse from the atmosphere to the tracheoles
- carbon dioxide is produced in cells during respiration -> this creates a diffusion gradient in the opposite direction so it’s taken out into the atmosphere
How do gases move in the insect tracheal system by mass transport
The contraction of muscles in insects can squeeze the trachea -> this allows mass movements of air in and out of
How do gases move in the insect tracheal system due to tracheoles being water filled
- when insects undergo major activity, some anaerobic respiration takes places producing lactate
- this lactate is soluble and lowers the water potential of the muscle cells
- so water moves into cells from tracheoles by osmosis
- the water in tracheoles ends decreases in volume allowing more air to be drawn in
- this increases rate of air moved in but leads to greater water evaporation
What are spiracles
Pores on the body surface of an insect which open and close by a valve to let substances in and out of the
What are the limitations of the insect tracheal system
- relies mostly on diffusion for gas exchange
- and for diffusion to be effective the diffusion pathway must be short
- so insects have to be of a small size
Structure of the gills
They are made up of gill filaments which have gill lamellae at a right angle
-> these increase surface area
What is the countercurrent flow
The flow of water over the gill lamellae and the flow of blood within them are in opposite directions
Why is the countercurrent so important
- it means that the blood is already full of oxygen when it meets water which has its maximum concentration of water
-> therefore diffusion of oxygen from the water to the blood takes place - blood with little oxygen in it meets water which has had most of its oxygen removed
-> so diffusion of oxygen from the water to blood takes place
What is flow in the same direction called
Parallel flow
Why is countercurrent flow better than parallel flow
Parallel flow would mean the diffusion gradient would only be maintained across part of the length of the gill lamellae and only half the available oxygen would be absorbed by the blood
What adaptations do plant leaves have for gas exchange
- many stomata
- many air spaces throughout the mesophyll
- large SA of mesophyll cells for rapid diffusion
What do the stomata do
- each stoma is surrounded by guard cells which can open and close the stomata and so can control the rate of gas exchange and control water loss
What adaptations do insects have to reduce water loss
- small SA:V ratio
- waterproof cuticle
- spiracles -> can open and close
What are xerophytes
Plants that have many adaptations to limit water loss through transpiration
Adaptations of xerophytes
- thick cuticle -> waterproof barrier
- rolling up of leaves -> protects lower epidermis of stomata + traps moist air with high water potential so there’s no movement of water
- hairy leaves -> traps moist air so water potential gradient is decreased
- stomata in pits -> traps moist air
- small SA:V ratio
What do all aerobic organisms require a constant supply of and why
Oxygen to release energy in the form of ATP in respiration
What supports lungs
Ribcage
Why are lungs inside the body opposed to outside
- air isn’t dense enough to support and protect the delicate structures
- the body would lose a lot of water and dry out
Features of the lungs
- trachea
- tracheoles
- bronchi
- bronchioles
- alveoli
Structure of trachea
- supported by rings of cartilage that prevents it from collapsing as air pressure inside falls when breathing in
- tracheal walls are made up of muscle, lined with ciliated epithelium and goblet cells
Structure of bronchi
- 2 divisions of the trachea that each lead to one lung
- produce mucus to trap dirt
- have cilia to move mucus towards throat
- larger bronchi are supported by cartilage -> but amount decreases as bronchi gets smaller
Structure of bronchioles
- walls are made of muscles lined with epithelial cells
-> this muscles lets them construct so they can control the flow of air in and out of the alveoli
Structure of alveoli
- have collagen and elastic fibres between alveoli -> elastic fibres allow them to stretch as they fill with air and then spring back during exhalation to get rid of carbon dioxide rich air
- lined with epithelium
What is the scientific word for breathing
Ventilation
What is the other word for inhalation and what is it
Inspiration
- when the atmospheric pressure is greater than pulmonary pressure and air is forced into the lungs
What is the other word for exhalation and what is it
Expiration
- when pulmonary pressure is greater than atmospheric pressure and air is forced out of the lungs
What muscles cause pressure changes in lungs
- diaphragm
- intercostal muscles
What are the types of intercostal muscles
- internal intercostal muscles -> contract during expiration
- external intercostal muscles -> contract during inspiration
Process of inspiration
• The external intercostal muscles contract, while the internal intercostal muscles relax
• The ribs are pulled upwards and outwards, increasing the volume of the thorax
• The diaphragm muscles contract, causing it to flatten, which also increases the volume of the thorax
• The increased volume of the thorax results in reduction of pressure in the lungs
• Atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs
Process of expiration
• The internal intercostal muscles contract, while the external intercostal muscles relax
• The ribs move downwards and inwards, decreasing the volume of the thorax
• The diaphragm muscles relax and so it is pushed up again by the contents of the abdomen that were compressed during inspiration
The volume of the thorax is therefore further decreased
• The decreased volume of the thorax increases the pressure in the lungs
• The pulmonary pressure is now greater than that of the atmosphere, and so air is forced out of the lungs
What types of processes are inspiration and expiration
Inspiration is an active process (uses energy)
Expiration is a largely passive process (doesn’t require much energy)
What is the main cause of air being forced out during breathing
The recoil of elastic tissue
BUT under more strenuous conditions, various muscles start to play a major part
Why is diffusion of gases between the alveoli and blood very rapid
- RBCs are slowed as they pass through the pulmonary capillaries -> allowing more time for diffusion
- the distance between the alveolar air and RBCs is reduced as the RBCs are flattened against the capillary walls
- the walls of the alveoli and capillaries are very thin
- large SA of alveoli and pulmonary capillaries
- well ventilated + rich blood supply -> maintains steep concentration gradient
- blood flow through the pulmonary capillaries maintains a concentration gradient
Why is the diffusion pathway in alveoli short
Because the alveoli only have a single layer of epithelial cells and the blood capillaries only have one layer of cells
What is a correlation
When a change in one of two variables is reflected by a change in the other variable
Vital capacity
the maximum volume of air that can be inhaled or exhaled in a single breath.
Varies depending on gender, age, size as well as height
Tidal volume
the volume of air we breathe in and out at each breath at rest
Breathing rate
the number of breaths per minute, can be calculated from the spirometer trace by counting the number of peaks or troughs in a minute
What is digestion
the hydrolysis of large biological molecules into smaller molecules which can be absorbed across cell membranes
What enzymes digest carbohydrates
- Amylases in the mouth digest larger polymers
- Maltases in the ileum break down monosaccharides
- Sucrases and lactases break down the dissacharides sucrose and lactose
What enzymes digest lipids and how
- Lipases by hydrolysing the ester bond between the monoglycerides and fatty acid.
- Before being broken down in the ileum, lipids are emulsified into micelles by bile salts released by the liver
What does emulsification do
Emulsification increases the surface area and speeds up the chemical reaction
What enzymes digest proteins and what are the 3 types:
- Peptidases of which they are divided into 3 main groups:
• endopeptidases
• exopeptidases
• dipeptidases
What does an endopeptidase do
hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide
What does an exopeptidase do
hydrolyse bonds at ends/terminals of a polypeptides
What does a dipeptidase do
break dipeptides into individual amino acids
How are amino acids transported
Via co transport
How does the co transport of amino acids work
- Amino acids are absorbed by facilitated diffusion through specific carrier molecule in the surface membrane of epithelial cells.
- With each amino acid, one Na+ is also taken up, therefore amino acid absorption occurs via a process known as co-transport.
- A diffusion gradient for Na+ is maintained by their active transport through the base of epithelial cells where amino acids pass by facilitated diffusion.
Why can monoglycerides and fatty acids easily diffuse across the cell membrane
Because they are polar
Where do monoglycerides and fatty acids go once through the cell membrane
- into the epithelial cells lining the epithelium
- then are transported to the endoplasmic reticulum where they are reformed into triglycerides again
- then they leave the cells via vesicles into the lymph system
Where does lipid digestion occur
Only in the lumen of the small intestine
What happens in the stomach
Lipids are churned to turn them into a fatty liquid
What does bile contain
Bile salts
What is emulsification
When lipids are broken down (by binding to bile salts) into small droplets giving them a large SA
Where is lipase secreted from and to
From the pancreas to the small intestine
What do bile salts do
Bind to fat droplets and break them down into smaller fat droplets (emulsification)
What are micelles
Droplets that are smaller than fat droplets in emulsified lipids
How are micelles formed
When monoglycerides and fatty acids associate with bile salts and phospholipids
What does micelles do
Transport the poorly soluble monoglycerides and fatty acids to the surface of the epithelial cells where they can be absorbed
How do the micelles get the monoglycerides and fatty acids in the cell
- they are constantly breaking down and reforming producing a small pool of monoglycerides and fatty acids that are in solution
- only the freely dissolved monoglycerides and fatty acids can be absorbed -> not the micelles because they are non-polar
Where do short chain fatty acids diffuse into
Directly into the blood from the lumen of the small intestine via the epithelial cells
How do longer chain fatty acids diffuse into the blood
- monoglycerides and glycerol diffuse into the epithelial cells where they recombine to form triglycerides again
- these triglycerides are packed with cholesterol and phospholipids to form water soluble fat droplets called chylomicrons
- these are then transferred to a lymph vessel and then eventually into the blood system
How are chylomicrons transferred
By exocytosis
- when a small piece of cell surface membrane is wrapped around the lipid droplet and pinched off so that the fatty droplets are now wrapped in membrane as they enter the lymph vessels
Where are the triglycerides reformed in the epithelial cell
At the endoplasmic reticulum
What is a lacteal
A lymph vessel
How is a lipid droplet formed
By lipids being churned in the stomach and then emulsified by binding to bile salts from bile made in the liver and stored in the gallbladder
What happens after lipids are emulsified
The droplets are hydrolysed into fatty acids and glycerol by lipase from the pancreas in the small intestine
What is a chylomicrons
A water soluble fat droplet
Why are micelles used in lipid digestion
Because the components on their own are portly soluble and can’t move very well
Explain the sodium potassium pump
- not all available glucose can be absorbed because there’s no concentration gradient
- so sodium ions are actively transported out of epithelium cells into the lumen -> takes place in a protein carrier molecule in the surface membrane
- now there’s a higher concentration of sodium ions in the lumen of the intestine than inside the cells
- the sodium ions now diffuse back into the cells down a concentration gradient through a different type of protein carrier
- as the sodium ions go back they couple with glucose molecules which are carried with them
- the glucose passes into the blood by facilitated diffusion using another type of carrier
What powers the movement of glucose into cells
The sodium ion concentration gradient rather than ATP directly
-> this makes it an indirect rather than a direct form of active transport
Insect adaptations to limit water loss
- Spiracles
- Small SA:V ratio (of tracheal system not whole insect)
- Waterproof exoskeleton
Adaptations for quick diffusion in insects
- steel diffusion gradient
- large number of tracheoles -> increases SA
- short diffusion pathway
Why do fish need an exchange surface
Because they are waterproof and have a small SA:V ratio
Gas exchange surface features
- large SA:V ratio
- short diffusion distance
- maintained concentration gradient
Fick’s Law
Diffusion = SA x difference in conc / length of diffusion pathway
Adaptations in fish for efficient gas exchange
- large SA:V ratio created by many gill filaments cover in gill lamellae
- short diffusion pathway due to capillary network in lamellae and thin lamellae
- maintains concentration gradient by countercurrent flow
Countercurrent and what it does
When water flows over the gills in the opposite direction to the flow of blood in the capillaries
-> ensures that equilibrium isn’t reached
-> ensures that a diffusion gradient is maintained across the entire length of the gill lamellae
How do stomata reduce water floss
Close at night when photosynthesis wouldn’t be happening
What are xerophytic plants
Plants adapted to survive in environments with limited water
What is the compromise in xerophytes
They have structure features to allow efficient gas exchange whilst also limiting water loss
Xerophyte adaptations
- Curled leaves to trap moisture to maintain water potential
- hairs to trap moisture
- sunken stomata to trap moisture
- thicker cuticle to reduce evaporation
- longer root network to reach more water
What do carbohydrates need to be hydrolysed
2 enzymes
- amylases
- membrane-bound disaccharides
What produces amylase
The pancreas and salivary glands
What does amylase do
Hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds
Where does protein digestion start and end
Starts in stomach and ends in ileum where it’s fully digested
What are lipids digested by
Lipase and bile salts
Where is lipase produced
Páncreas
What does lipase do
Hydrolyses the ester bond in triglycerides to form monoglycerides and fatty acids
Where are bile salts produced
Liver
What do bile salts do
Emulsify lipids to form micelles -> increases SA for lipase to act on
What are the 2 stages of digestion of lipids
Physical: emulsification and micelle formation
Chemical: lipase
What is the physical stage of lipid digestion
- lipids bind to bile salts to be emulsified
- micelles provide larger SA for faster hydrolysis by lipase
What is the chemical stage of lipid digestion
- lipase hydrolyses lipids in glycerol and fatty acids (some monoglycerides)
What are micelles
Vesicles formed from fatty acids, monoglycerides and bile salts
Where are products of digestion absorbed
across the cells lining the ileum
What is the ileum wall covered in
Villi
-> which have thin walls surrounded by a network of capillaries
-> epithelial cells have even smaller microvilli
Why is active transport and co-transport required for glucose and amino acid absorption
Because there is usually more glucose in the epithelial cells
