exchange Flashcards
why do organisms need exchange 2
- living organisms need to exchange materials like oxygen, glucose, excretory products like urea, and heat with their environment
- exchange occurs across plasma membranes
what does the rate at which substances diffuse across an organism depend on
surface area to volume ratio
how does SA:V ratio affect rate of diffusion 3
- high SA:V = these organisms have a large surface area relative to their volume so the diffusion of substances is fast
- low SA:V = these organisms have a small surface area relative to their volume so the diffusion of substances is lower
- smaller organisms have a higher SA:V while larger organisms have a lower SA:V
formula for the surface area of a cube
length x width x 6
formula for the volume of a cube
length x width x depth
how do substances diffuse in a single celled organism
directly across the cell membrane
why cant substances diffuse directly across the cell membrane in multicellular organisms 4
- cells aren’t in direct contact with the external environment
- diffusion distances between cells and their environment are large
- larger organisms have higher metabolic rates, so they need more oxygen and glucose
- to solve this problem, multicellular organisms have evolved specialised exchange surfaces
key features of specialised exchange surfaces 4
- large surface area = larger area across which substances can be exchanged
- thin walls = minimise diffusion distance
- extensive blood supply/ ventilation = maintains steep concentration gradient
- surrounded by selectively permeable plasma membranes = controls what substances are exchanged
why do insects need gas exchange
insects have high oxygen demands but their tough chitinous external skeleton prevents direct gas exchange
why do insects need efficient systems for exchanging gases 2
- deliver oxygen to cells = allows aerobic respiration to occur to release energy for cellular processes
- remove carbon dioxide from cells = buildup of carbon dioxide produced as a waste product of respiration reduces pH, which can denature enzymes
insect gas exchange systems have adapted to balance two conflicting needs, 3
- maximising gas exchange efficiency
- minimising water loss
- the exoskeleton is covered with a waterproof cuticle to help prevent water loss, but the insect gas exchange system itself has additional methods to prevent excess water loss while still being effective at gas exchange
structures of the insect gas exchange system 4
- open respiratory system comprised of tubular structures that transport air
- tracheae = air-filled tubes branching throughout the body
- tracheoles = fine branches of tracheae delivering gases to cells
- spiracles = external openings of the tracheal system on the exoskeleton along the abdomen and thorax
adaptations of the tracheae 2
- reinforced with spirals of chitin = prevents collapsing
- multiple tracheae = increases surface area
adaptations of the tracheoles 5
- penetrate directly into tissues = reduces gas diffusion distance
- thin walls = reduce gas diffusion distance
- highly branched = maximises surface area
- not reinforced with chitin = allows gas exchange to occur
- fluid at the ends of the tracheoles (tracheal fluid) = allows oxygen to dissolve to aid diffusion and reduces water loss
adaptation of the spiracles
open and close = allows them to control gas exchange with the atmosphere and minimise water loss
stages of gas exchange in insects 6
- air enters the tracheal system through open spiracles
- air moves into larger tracheae and diffuses into smaller tracheoles
- tracheoles branch throughout the body, transporting air directly to cells
- oxygen dissolves in water in tracheal fluid and diffuses down its concentration gradient from tracheoles into body cells
- carbon dioxide diffuses down its concentration gradient out of body cells into the tracheoles
- air is then carried back to the spiracles via the tracheae and released from the body
how are the concentration gradients between the tissues and air in the tracheal system maintained 3
- cells using up oxygen for respiration = keeps oxygen concentration low in cells
- cells producing carbon dioxide in respiration = keeps carbon dioxide concentration high in cells
- continuous ventilation = fresh air is supplied to the tracheal system via spiracles
what are the additional ventilation mechanisms that drive air through the tracheal system (particularly active insects) 5
- mechanical active ventilation = when muscles around the tracheae contract and relax, changing the volume and pressure in the abdomen and squeezing the tracheae to pump air in/out of the spiracles
- tracheal fluid = this moves out into tissues during exercise to increase the diffusion rate and surface area for gas exchange
- enlarged collapsible tracheae, or accessory sacs and air reservoirs = inflate or deflate to ventilate the tracheal system and can increase the volume of air moved through the system
- wing muscles connected to sacs = pump air to ventilate the tracheal system
- vibration of thoracic muscles = pump air to ventilate the tracheal system
whats lactate accumulation
lactate levels in the tissues increase due to activity
how does lactate accumulation affect the rate of gas exchange 3
- lactate accumulation reduces the water potential in tracheal fluid at the end of tracheoles
- water leaves the trachea via osmosis
- higher surface area exposed for gas exchange
respiratory systems in bony fish
- large, active, bony fish have high oxygen needs
- these needs exceed simple diffusion across the body surface, which is also covered with scaly skin preventing gas exchange
- bony fish have evolved specialised respiratory systems to meet the challenges of extracting oxygen from water
what are some of these challenges 3
- water is denser and more viscous than air, resulting in slower diffusion of oxygen
- water has less oxygen than air
- bony fish are very active so have high oxygen demands
function of gills
allow bony fish to efficiently take up oxygen from water and remove carbon dioxide
structure of the gills 3
- gills are covered by an operculum flap
- gills consist of stacked filaments containing gill lamellae
- gill lamellae are surrounded by extensive blood vessels
adaptations of the gills for efficient gas exchange 5
- lamellae provides large surface area
- the lamellae membranes are thin to minimise diffusion distance
- the gills have a rich blood supply to maintain a steep diffusion gradient
- the countercurrent flow of blood and water creates even steeper concentration gradients
- overlapping filament tips increase resistance, slowing water flow over gills and allowing more time for gas exchange
what do the gills allow
countercurrent flow of blood and water, more efficient than a parallel flow
what happens in a countercurrent flow system 4
- blood and water flow over the lamellae in opposite directions
- this means that the oxygen-rich blood meets water that is at its most oxygen rich when it first moves across the gills, maximising diffusion of oxygen into the blood
- oxygen-poor blood returning from body tissues meets oxygen-reduced water that has had most of its oxygen removed, still allowing diffusion of oxygen into the blood
- this maintains a steep concentration gradient across the entire gill
what happens in a parallel flow system and compare to countercurrent exchange systems 2
- blood and water flow in the same directions
- countercurrent exchange systems enable more efficient gas transfer than parallel flow, because parallel flow reduces the concentration gradient so less oxygen can be absorbed
what does a large surface area means in plants
loss of water in plants
how can plants limit water loss 2
- waterproof waxy cuticle on their leaves
- guard cells that can close stomata when needed
what are xerophytes 2
- plants adapted to living in dry environments with limited water availability
- without adaptations they would dry out and die
adaptations of xerophytes 6
- thick waxy cuticle = reduces water loss through evaporation
- rolling/folding of leaves = encloses the stomata on the lower surface to reduce air flow and evaporation of water
- hairs on leaves = trap moist air against the leaf surface to reduce diffusion gradient of water vapour
- sunken stomata in pits= reduce air flow and evaporation of water
- small, needle-like leaves= reduce surface area across which water can be lost
- water storage organs= conserve water for when its in low supply
structures of a typical leaf 6
- upper epidermis with waxy cuticle = reduces water loss from leaf surface
- air spaces = interconnecting spaces that run through the mesophyll layer
- mesophyll cells = cells within the mesophyll tissue, located between upper and lower epidermis
- stomata = small pores surrounded by guard cells on the underside of leaves that can open and close
- lower epidermis= bottom layer of cells containing stomata and guard cells
- vascular tissue, xylem and phloem = transports water and nutrients
adaptations of leaf structures for gas exchange 3
- air spaces= provide network for gases to quickly diffuse in and out of the leaf and access photosynthesising cells
- mesophyll cells= dispersed throughout the leaf, provides large surface area across which gases can diffuse
- stomata= these open when conditions are suitable for photosynthesis, allowing inward diffusion of co2 and outward diffusion of oxygen, and close to minimise water loss
intro to the gas exchange system 3
- consists of the lungs and air passages
- system allows oxygen to enter the blood and co2 to leave the blood through gas exchange surfaces called alveoli
- lungs are located inside the chest in the thorax, protected by the ribcage
whys the gas exchange system located inside the body 2
- air isnt dense enough to support and protect these delicate structures
- body would otherwise lose water and dry out
how does air travel in the body 4
- air first enters the trachea
- air travels into the 2 bronchi, with one bronchus going to each lung
- air travels into smaller airways called bronchioles
- air travels into clusters of air sacs called alveoli at the end of the bronchioles
whats the ciliated epithelium
tissue located throughout most of the airways
what does the ciliated epithelium consist of 2
- goblet cells = produce and secrete mucus that traps dust and microbes
- cilia on ciliated epithelium cells = these waft the mucus upward to the mouth so it can be swallowed
whats the trachea
large tube that carries air from the throat down to the lungs
adaptations of the trachea 4
- rings of cartilage keep the airway open
- smooth muscle can contract or relax to constrict or dilate the airway and change airflow
- elastic tissue contains elastic fibres with elastin that allows stretching and recoiling
- lined with ciliated epithelial cells and goblet cells
what are the bronchi
two main branches extending from the trachea that carry air into each lung
adaptations of the bronchi 4
- no cartilage, can change shape
- smooth muscle can contract or relax to constrict/dilate the airway and change airflow
- elastic tissue contains elastic fibres with elastin that allows stretching and recoiling
- simple squamous epithelium, only larger bronchioles have a ciliated epithelium
what are alveoli 3
- tiny air sacs clustered at the ends of the bronchioles
- surrounded by a network of capillaries so gases can be exchanged between the air in the alveoli and the blood
- gas exchange occurs across the alveolar membrane of alveoli
how does the alveoli carry out gas exchange 2
- oxygen diffuses from the alveoli into the pulmonary capillaries where it binds to haemoglobin in red blood cells
- co2 dissociates from haemoglobin and diffuses from the blood into the alveoli
adaptations of alveoli for gas exchange 8
- wall consists of one layer of squamous epithelial cells = allows rapid diffusion
- large surface area = increases rate of gas exchange
- partially permeable = only certain gases can move across the wall
- surrounded by dense network of capillaries = bring blood close to air for gas exchange
- ventilation of air = maintains steep diffusion gradient
- elastic fibres = allow stretching and recoiling
- collagen fibres = contain strong collagen that prevents alveoli from bursting and limits overstretching
- moist inner surface = allows gases to dissolve, and lung surfactant helps alveoli remain inflate
what are pulmonary blood vessels
involved in the circulation of lungs
what do pulmonary blood vessels include 3
- pulmonary artery= delivers deoxygenated blood from heart to pulmonary capillaries
- pulmonary vein= delivers oxygenated blood from capillaries to the heart
- pulmonary capillaries= site of gas exchange between blood and alveoli
adaptations of the pulmonary capillaries for gas exchange 5
- thin walls (one endothelial cell thick)= maintains short diffusion distance
- red blood cells pressed against capillary walls= reduces diffusion distance
- large surface area= increases diffusion speed
- movement of blood= maintains steep diffusion gradient
- slow blood movement= allows more time to diffusion
whats ventilation 3
- constant movement of air into and out of the lungs
- consists of inspiration (breathing in) and expiration (breathing out)
- allows air to enter and leave the lungs, providing body with oxygen and removing carbon dioxide
muscles involved in ventilation 3
- ribcage is made up of bones called ribs that enclose the thorax = cavity where the lungs are located (thoracic activity)
- in mammals, ventilation is controlled by specific muscles. when the muscles attached to the ribcage contract and relax, they move the ribs to change the volume of thoracic cavity
- this affects the pressure in the lungs and controls ventilation
what are the 3 sets of muscles that act on the ribcage
- diaphragm= sheet of muscle that moves the ribcage up and out when it contracts
- external intercostal muscles= found between ribs and pull the ribcage up and out when they contract
- internal intercostal muscles= found between the ribs but pull the ribcage down and in when they contract
explain external and internal intercostal muscles 2
- opposite effects on the ribcage
- expand the ribcage during inspiration, while internal muscles shrink it during expiration
what’s inspiration
active process requiring energy for muscle contraction
what’s the process of inspiration 5
- the external intercostal muscles contract while the internal intercostal muscles relax, moving the ribcage up and out
- volume of the thoracic activity increases
- diaphragm contracts and flattens, further increasing the volume of the thoracic cavity
- lung pressure decreases below atmospheric pressure
- air flows into the lungs down the pressure gradient
whats expiration 2
- normal expiration at rest is a passive process so it doesnt require energy
- however, expiration can be forced by contracting the internal intercostal muscles to actively pull the ribcage down and in, forcing more air out
whats the process of expiration 5
- external intercostal muscles relax, moving the ribcage down and in
- volume of the thoracic cavity decreases
- diaphragm relaxes and unflattens, further decreasing the volume of the thoracic cavity
- lung pressure increases above atmospheric pressure
- air is forced out of the lungs down pressure gradient
what else happens during expiration 2
- elastic fibres in the alveoli also shrink and recoil back to their original shape when the thoracic cavity volume decreases
- increases the pulmonary pressure and helps to push air out of the lungs
whats physical digestion
break down of large food pieces into smaller ones to increase the surface area for chemical digestion
whats chemical digestion
enzymes catalyse hydrolysis reactions that break bonds in large insoluble molecules to form smaller soluble molecules
role of salivary glands in digestion
secrete saliva containing amylase
role of oesophagus in digestion
transports food to the stomach
role of stomach in digestion
digests food (especially proteins) and produces acid to destroy pathogens
role of liver in digestion
produces bile salts to aid lipid digestion
role of pancreas in digestion
secretes pancreatic juice containing enzymes (proteases, lipases and amylases)
role of small intestine in digestion
ileum is the site of further digestion and absorption
role of large intestine in digestion
absorbs water and stores waste
role of rectum in digestion
stores feces before removal via egestion through the anus
what order does food travel through the alimentary canal
mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus
what does the human digestive system consist of 2
- alimentary canal, which is the pathway food takes through the body
- and some associated accessory glands
what are digestive enzymes 2
- involved in chemical digestion
- this is where enzymes catalyse hydrolysis reactions that break bonds in large insoluble food molecules to form smaller soluble molecules, which can be absorbed in the bloodstream
3 main types of digestive enzymes
- carbohydrases
- lipases
- proteases
roles of enzymes in digesting carbs 2
- carbohydrases break down large carbs into smaller polysaccharides, disaccharides and monosaccharides
- carbohydrases are produced by the salivary glands, the pancreas and the epithelial cells lining the ileum
process of starch digestion 4
- salivary amylase breaks down starch into the disaccharide maltose in the mouth
- acid in the stomach denatures salivary amylase
- pancreatic amylase continues starch digestion in the small intestine
- epithelial cells in the ileum lining produce maltase to break down maltose into alpha glucose monomers
how are other disaccharides hydrolysed by specific disaccharidases enzymes 3
- sucrose hydrolysed to glucose and fructose by sucrase
- lactose hydrolysed to glucose and galactose by lactase
- some membrane bound disaccharidases, like maltase, are bound to epithelial cells that line the ileum
role of enzymes in digesting lipids
