6.Exchange between organisms and their environment Flashcards
For an effective exchange…
the exchange surface of the organism must be large compared with their volume.
Name features of specialised exchange surfaces
- large SA:V ratio
- short diffusion pathway
- selectively permeable (to allow selected materials across)
- a transport system to maintain a diffusion gradient
What is Fick’s Law
Rate of diffusion α (surface area x concentration) / distance
Describe gas exchange in single-celled organisms
They have large SA:V meaning oxygen can just diffuses across their body surface
What are tracheae (i)
Internal network of tubes inside an insect
What are tracheoles
Smaller dead end tubes that are sub branches of tracheae
Name three ways gases move in and out the tracheal system
- along a diffusion gradient
- mass transport (abdominal pumping)
- through water or gas phase at end of tracheoles
Describe how gases move in and out the tracheal system along a diffusion gradient
- when cells are respiring oxygen is used up so concentration gradient is created
- causes oxygen to diffuse from atmosphere into and along the tracheal system
- when cells are respiring carbon dioxide is produces so concentration gradient is created
- carbon dioxide diffuses along and out the tracheal system
Describe how gases move in and out the tracheal system via mass transport
- abdominal pumping is the contraction of muscles in insects
- squeezes the trachea enabling mass movements of air in and out
- speeds up gas exchange
Describe how gases move in and out the tracheal system at the end of the tracheoles
- during periods of high activity muscles cells around the tracheoles respire anaerobically
- this produces lactate which is soluble and lowers the water potential of the muscle cells
- the water therefore moves via osmosis into the cells
- this causes air to be drawn in as it decreases the pressure
- also means the final diffusion pathway is gas rather than liquid phase and therefore more rapid
What are spiracles
Tiny pores that gases enter and leave the tracheal system. Mainly stay closed to reduce water loss
What is a limit of the tracheal system
Relies on diffusion meaning for it to be effective the diffusion pathway needs to be short. This limits the size the insects can attain.
Describe the structure of gills
- made up of gill filaments, stacked
- gill lamellae are at right angles to the gill filaments
What is a countercurrent system
a mechanism by which the efficiency of exchange between two substances is increased by having them flow in opposite directions
Countercurrent flow means that…
- blood already well loaded with oxygen meets water with max concentration so diffusion still takes place
- blood with little oxygen meets water with little oxygen but diffusion can still take place
Name 2 ways gas exchange in plants is similar to that of insects
- no living cell is far from external air and therefore a source of Co2 and oxygen
- diffusion takes place in a gas phase which makes it more rapid (compared to a liquid phase)
What adaptations for gas exchange do leaves show
- many stomata, no cell is far from stomata and therefore diffusion pathway is short
- numerous interconnecting air spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
- large SA:V ratio means rapid diffusion
What are stomata
- minute pores that occur mainly on leaves
- each stoma is surrounded by a pair of guard cells
- they control rate of gas exchange as they can open and close the stomatal pore
- they are important in controlling water loss
- close at times when water loss would be excessive
What problem do plants and insects have
The opposing needs of an efficient gas-exchange system and the requirement to conserve water
Describe the ways insects are adapted to reduce water loss
- small SA:V ratio to minimise the area over which water can be lost
- waterproof coverings over their body surfaces, insects have outer skeleton of waterproof chitin
- spiracles are the opening of the tracheae at the body surface which can be closed to reduce water loss
Describe the ways plants are adapted to reduce water loss
- waterproof covering
- ability to close stomata
What are xerophytes
Plants that are adapted to living in areas where water is in short supply
Name the ways xerophytes have evolved to reduce water loss
- a thick cuticle
- rolling up of leaves
- hairy leaves
- stomata in grooves or pits
- reduced SA:V of leaves
Describe how rolling of leaves reduces water loss
- causes air to be trapped in a region around the lower epidermis (where most stoma are found)
- this region becomes saturated with water vapour causing a high water potential
- there is no water potential gradient
- no water is lost from the leaf.
Describe how hairy leaves reduces water loss
- traps moist air near leaf surface
- water potential gradient between inside and outside is reduced
- less water is lost by evaporation
What is inspiration
- inhaling
- when air pressure is greater than the air pressure inside the lungs
What is expiration
- exhaling
- when air pressure in the lungs is greater than that of the atmosphere
What are the three muscles that cause pressure changes within the lungs
- diaphragm
- internal intercostal muscles
- external intercostal muscles
Which intercostal muscle is responsible for expiration
Internal intercostal muscles
Which intercostal muscle is responsible for inspiration
External intercostal muscles
What happens during inspiration
- external intercostal muscles contract
- internal intercostal muscles relax
- ribs move outwards, increasing the volume of the thorax
- diaphragm muscles contract causing it to flatten, increasing the volume of the thorax
- reduces pressure
- atmospheric pressure is now greater than pulmonary
- air is forced into the lungs
What happens during expiration
- internal intercostal muscles contract
- external intercostal muscles relax
- ribs move inwards, decreasing the volume of the thorax
- diaphragm relax contract causing it to be pushed up by the abdomen, decreasing the volume of the thorax
- increases pressure
- atmospheric pressure is now lower than pulmonary
- air is forced out the lungs
Name the main parts of the human gas exchange system
- lungs
- trachea
- bronchi
- bronchioles
- alveoli
What is the trachea
- flexible airway
- supported by rings of cartilage
- prevents the trachea from collapsing when pressure falls when breathing in
- walls are made of muscle
What are the bronchi
- two divisions of the trachea, each leading to one lung
- similar structure to trachea
- like trachea, also produce mucus
What are bronchioles
- branching subdivisions of the bronchi
- muscle lined which allows them to constrict so they can control air flow in and out of the alveoli
What are alveoli
- small air sacs at the end of bronchioles
- between the alveoli there are some collagen and elastic fibres
- elastic fibres allow the alveoli to stretch as they fill with air when breathing out
- lined with epithelium cells
What is the site of gas exchange in mammals
Alveoli
Describe reasons why the diffusion of gases between the alveoli and the blood will be very rapid
- red blood cells are slowed as the pass through pulmonary capillaries, allowing more time for diffusion
- short diffusion distance, both alveoli and capillaries wall are 1 cell thick
- alveoli and pulmonary capillaries have a very large total surface area
- ventilation of lungs and blood due to constant breathing and blood circulation, maintains concentration gradient
Name the major parts of the digestive system
- oesophagus
- stomach
- ileum
- large intestine
- rectum
- salivary glands
- pancreas
What is the ileum
- a long muscular wall
- inner walls are folded into villi (large SA)
- micro villi on epithelial cells of each villus
- function is too absorb the products of digestion into the bloodstream
What is the pancreas
Large gland that secrets pancreatic juice. The secretion contains proteases, lipase and amylase
What are the two stages of digestion
- physical breakdown
- chemical digestion
What is physical breakdown
Food is broken down into smaller pieces by structures such as the teeth. Provides a larger surface area for chemical digestion
Name three important digestive enzymes
- carbohydrase
- lipases
- proteases
Where is amylase produced
Mouth and pancreas
What does amylase do
Hydrolyses the alternate glyosidic bonds of the starch molecule to produce disaccharide maltose
Where is maltase produced
Lining of the ileum
What does maltase do
Hydrolyses glyosidic bonds in maltose, producing the monosaccharide alpha glucose
Describe the steps of starch hydrolysis (mouth)
- food enters mouth and is mixed with saliva
- saliva contains salivary amylase and salts to keep pH around 7 (optimal pH for salivary amylase)
Describe the steps of starch hydrolysis (stomach)
- food enters stomach
- acid denatures the amylase stopping hydrolysis of starch
Describe the steps of starch hydrolysis (small intestine)
- food passes into small intestine where it mixes with pancreatic juice
- pancreatic juice contains pancreatic amylase which hydrolyses the remaining starch to maltose
- alkaline salts maintain the pH so amylase can function (~pH 7)
What are alkaline salts produced by
- the pancreas
- intestinal wall
Describe the steps of starch hydrolysis (ileum)
- muscle in intestine wall push food along the ileum
- epithelial wall produces disaccharidase maltase
- maltase is not released into the lumen of the ileum but is part of the cell surface membrane (membrane bound disaccharidase
- maltase hydrolyses the maltose into alpha glucose
What is different about the disaccharidase in the ileum compared to amylase
- not released into the ileum
- is part of the cell-surface membrane
- therefore known as membrane-bound disaccharidase
Describe how sucrose and lactose are hydrolysed
- sucrase or lactase hydrolyses the single glyosidic bond in the sucrose or lactose
- produces the monosaccharides glucose + fructose and glucose + galactose
Where are lipases produced and found
- produced in the pancreas
- act in the stomach
What do lipases do
Hydrolyse the ester bond in triglycerides to form fatty acids and monoglycerides
What are micelles
Tiny droplets of bile salts associated with monoglycerides and fatty acids
Describe emulsification
Where lipids are split into micelles by bile salts which increases the SA of lipids so the action of lipases speed up
Name 3 types of peptidases
- endopeptidases
- exopeptidases
- dipeptidases
What do endopeptidases do
Hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
What do exopeptidases do
Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. This releases dipeptides and single amino acids
What do dipeptidases do
Hydrolyse the peptide bond between the two amino acids of a dipeptide. These are membrane-bound, part of the epithelial cells lining the ileum
Name enzymes produced by the epithelium
- maltase
- lactase
- sucrase
- dipeptidases
Where do endopeptidases work
Stomach
Where do exopeptidases work
Small intestine (duodenum)
What is the function of the ileum
Absorb the products of digestion
Describe how villi increase the rate of absorption
- increase the surface area for diffusion
- they contain muscle so are able to move. The movement mixes the contents of the ileum which maintains concentration gradient
- thin wall, reduces diffusion distance
- well supplied with blood to maintain concentration gradient
- posses microvilli to further increase SA for diffusion
By what mechanisms are amino acids and monosaccharides absorbed
Co-transport
Describe the role of micelles in the absorption of triglycerides
- monoglycerides and fatty acids remain associated with bile salts, these are known as micelles
- they come in contact with epithelial cells lining the villi of the ileum
- this causes them to break down releasing the monoglycerides and fatty acids
- here they passively diffuse across the cell surface membrane of the epithelial cells
By what mechanism are triglycerides absorbed
Passive diffusion as they are non-polar molecules (so lipid soluble
What happens when monoglycerides and fatty acids are absorbed by the epithelial cells of the ileum
- they are transported to the endoplasmic reticulum
- recombined to form triglycerides
- they then are transported to the Golgi apparatus where they associate with cholesterol and lipoproteins to form chylomicrons
- chylomicrons move out the epithelial cells by exocytosis where they enter lymphatic capillaries (lacteals) found at the centre of each villus
- here they pass into the blood system
- triglyceride in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries from where they diffuse into cells
