Section 3 - Organisms exchange substances with their environment: 6. Exchange Flashcards
What is exchange
The transfer of materials between the internal and external environments of an organism
What is passive exchange
Exchange that requires no metabolic energy (diffusion/osmosis)
What is active exchange
Exchange that requires metabolic energy (active transport)
What are the main factors that effect the rate of diffusion
- SA available for diffusion
- Diffusion pathway
- Permeability of membrane
- Concentration gradient
- Temperature
What are the common features of specialised exchange surfaces
- Large SA:Vol ratio (whilst still minimising water loss)
- Shot diffusion pathway
- Selectively permeable membranes
- Ventilation of the internal and environmental mediums (to maintain a concentration gradient)
What is the SA:Vol ratio
The available surface area for exchange per unit of volume
How do you calculate the SA:Vol ratio
SA / Vol
What is the relationship between diffusion and SA, Concentration gradient and diffusion pathway
Diffusion ∝ (SA x Conc. gradient) / (diffusion pathway)
What is the relationship between SA and Vol
SA ∝ Vol^⅔
How does gas exchange occur in single-celled organisms
Small size means SA:Vol ratio is large enough for exchange to occur by diffusion
What is the gas exchange system of an insect
Tracheal system
What are the main features of the tracheal system
- Spiracles
- Tracheae
- Air sacs
- Tracheoles (containing tracheal fluid)
What is the structure and function of spiricles
Small holes in the exoskeleton of insects that allow gas to enter and exit for exchange to occur
What is the structure and function of the tracheae (in the tracheal system)
Network of internal tubes that make up part of the tracheal system, with one main trachea in each side of the insect’s body
What is the structure and function of the tracheoles
Small divisions of the trachea within the tracheal system, that carry and remove air to/from individual cells within the body of the insect
What is the structure and function of the air sacs within the tracheal system
Muscles in the abdomen can contract, reducing the volume of theses sacs and increasing the pressure to force air out, ventilation the system
What is the function of the tracheole fluid
- During intense exercise, anaerobic respiration takes place, releasing Lactic acid
- This lactic acid is water soluble and reduces the water potential within the cells
- The tracheole fluid has a high water potential, so is then taken into the cells by osmosis
- This decreases the pressure within the tracheoles, so air is drawn in through the system, giving a greater oxygen supply, which is needed due to the intense exercise
What is the structure of the gas exchange system of a fish
Under the operculum, there are many gill arches that the water flows past, allowing exchange of oxygen and carbon dioxide to take place
What are the main features of a gill arch
- Gill bar
- Gill filaments
- Gill lamellae
- Gill rakers
What is the structure and function of the gill bar
A stiff bar of cartilage that the gill filaments attach to, supporting the structure of the gill arch
What is the structure and function of the gill filaments
Long projections off of the gill bar, increasing the surface area for gas exchange
What is the structure and function of the gill lamellea
Small disc like projections along and perpendicular to the gill filaments, with a large supply of blood flowing through them, to increase the surface area for diffusion
What is the structure and function of the gill rakers
Small, finger like protrusions and hairs along the gill bar to catch and trap any debris that may damage the structure of the gills are reduce the SA for exchange
What is the counter current flow principle
In the gills, the blood and the water flow in opposite directions, to allow a concentration gradient to be maintained the whole way across, as the blood with the highest oxygen concentration meets the water with the most oxygen concentration, and vice versa
Why is parallel flow unsuitable in the gills
An equilibrium would be reached, as the same section of blood flows along side the same section of water, until the concentrations of gases are the same, and no more exchange con occur
What is the structure of the gas exchange system of a plant
Stomata within the leaf allow air to enter and exit, directly reaching the cells so gas exchange can occur
How are leaves adapted for their function
- Stomata on the lower epidermis allow all cells do be close to the external air, to give a short diffusion pathway
- Numerous air spaces within the spongy mesophyll, increasing the available surface area for diffusion
- Waxy cuticle, to reduce water loss through the upper epidermis
How does light levels regulate the opening and closing of the stomata
- Increased light levels causes K to move into the cells
- K allows starch (insoluble) to be converted to malate (soluble)
- Water potential of the guard cells decrease, so water enters by osmosis
- Thicker cell wall on the inside means the stomata open when the guard cells expand
This means the stomata are open in light conditions, allowing for photosynthesis to occur
How does the plants water regulate the opening and closing of the stomata
If the plant has more water, it enters the guard cells by osmosis, causing them to expend, and due to the thicker cell wall on the inside, the stomata opens
This means that if the plant has more water, the stomata can open to allow for photosynthesis, as the water loss this causes won’t have a negative impact.
How do insects limit water loss
- Small SA:Vol ratio
- Waterproof covering: rigid exoskeleton
- Opening and closing of the spiracles
How does SA:Vol ratio effect waterloss
Larger SA:Vol ratio = More surface for gas exchange = more surface for water loss
A balance is needed where the SA:Vol ratio is large enough to allow for sufficient gas exchange, but small enough to limit water loss
What is a xerophyte
A plant adapted to live in dry, arid conditions
What is a hydrophyte
A plant adapted to live in water environments
What is a mesophyte
A plant adapted to live in average water conditions
What are the main adaptations of xerophytes to limit water loss
- Thick cuticle
- Rolling up leaves (lower epidermis on the inside)
- Hairy leaves
- Stomata in pits/grooves
- leaves with smaller SA:Vol ratio
How does rolling up leaves limit water loss for plants
Rolling up leaves with the stomata (lower epidermis) on the inside will trap a region of air, and once its water potential reaches that of the leaves, there will be no potential gradient, so water loss will stop.
How do hairy leaves reduce water loss
The hair traps a layer of air close to the surface of the leaf, so fresh air doesn’t blow directly next to the stomata, reducing the potential gradient, limiting water loss
How does having the stomata in pits/grooves limit water loss in plant
Still moist air is trapped next to the stomata, as air can’t flow directly over them, limiting the potential gradient and reducing water loss
Why do plants living on sand dunes require xerophyte adaptations despite their being adequate rainfall
- Rain quickly drains through the sand and out of reach of the roots before it can be absorbed, so water intake is limited
- High wind speeds in costal regions increase the water potential gradient in and out of the leaves, as it constantly brings fresh air with a low water potential along side the leaf, so water loss increases
What is the structure of the human gas exchange system
Air is forcibly ventilated in an internal system, mainly locate in the lungs, with alveoli giving a larger surface area to allow for gas exchange to occur
What are the main features of the human gas exchange system
- Lungs
- Trachea
- Bronchi
- Bronchioles
- Alveoli
What is the structure and function of the lungs
Pair of lobed structures containing many branches with an increased surface area, through which gas exchange can occur
What is the structure and function of the trachea (in human gas exchange system)
Flexible airway supported by rings of cartilage, to prevent collapse, and lined with ciliated epithelial cells and produce mucus to trap debris; transporting air to the lungs.
What is the structure and function of the bronchi
two divisions of the trachea that transport air to each lung, also supported by cartilage and lined with ciliated epithelial cells.
What is the structure and function of the bronchioles
A series of branching subdivisions of the bronchi, with walls made of muscle lined with epithelial cells, and they control the flow of air in and out of the alveoli
What is the structure and function of the alveoli
Small air sacs between 100μm and 300μm in diameter, at the end of the bronchioles, lined with epithelium, and are the site of gas exchange.
Between them are some collagen and elastic fibres that can stretch, allowing the volume of the lungs to expand as the alveoli fill with air
What are the muscles involved in ventilating the human gas exchange system
- Internal intercostal muscles (IIM)
- External intercostal muscles (EIM)
- Diaphragm
What are the stages of inspiration
- EIM contract and IIM relax
- Ribs pulled up and out, increasing thorax volume
- Diaphragm contracts, increasing lung volume
- Increased volume = Decreased pressure
- External air with higher pressure moves into the lungs
What are the stages of expiration
- IIM contract and EIM relax
- Ribs move down and in, decreasing thorax volume
- Diaphragm relaxes, decreasing lung volume
- Decreased volume = Increased pressure
- Air in the lungs move out into the external astrosphere, where the pressure is lower
What is the tidal volume
Volume of air taken in at each breath, when the body is at rest
(~0.5dm^3)
What is the breathing (ventilation) rate
Number of breaths taken in 1 minuet (12-20min^-1 for healthy adults)
What is the pulmonary ventilation rate
The total volume of air that is moved into the lungs in one minuet
(Tidal Vol. x Breathing rate)
What are the adaptations of the alveoli to be suited for gas exchange
- Small capillaries slow down blood as it passes through the alveoli, increasing time for diffusion
- Short diffusion pathway due to thin walls and thin capillary walls
- All alveoli together have a very large surface area for diffusion
- Well ventilated by the flow of blood and the movement of air, maintaining a concentration gradient
How is oxygen transported through the blood
Bound to the haemoglobin, by a reversable reaction, for form oxyhaemoglobin
How is CO2 transported through the blood
Dissolved in the blood plasma, increasing the acidity of the blood and therefore effecting enzyme action
What is physical digestion
Food is mechanically broken down into smaller pieces, increasing the SA for chemical digestion (eg. chewing)
What is chemical digestion
Hydrolysis of larger, insoluble molecules into smaller soluble molecules, by enzyme action
What is the function of the oesophagus in the digestive system
Carries food from the mouth to the stomach
What is the function of the Stomach in the digestive system
Muscular sac with inner layer that produces enzymes, kills microbes and churns food
What are the three sections of the small intestine
- Duodenum
- Jejunum
- Ileum
What is the function of the Duodenum in the digestive system
1) Where food is digested and broken down (chemical digestion), into the products that the body can use
What is the function of the Jejunum in the digestive system
2) Digestion and breakdown continues, but absorption of the products begins
What is the function of the Ileum in the digestive system
3) Long thin tube with folded inner layer (villi and microvilli to increase the SA), where most of the absorption takes place
What is the function of the Large intestine in the digestive system
Absorbs water
What is the function of the Rectum in the digestive system
Stores waste before being removed via the anus, in the process of egestion
What is the function of the salivary gland
Releases salivary amylase, catalysing the hydrolysis of starch into maltose
What is the function of the pancreas in the digestive system
Releases digestive enzymes (Proteases, Lipase and pancreatic amylase)
What is the process of the digestion of carbohydrates (starch)
- Food enters mouth
- Food mixes with saliva and is chewed
- Saliva contains salivary amylase and mineral salts (maintains neutral pH)
- The salivary amylase catalyses the breakdown of starch into maltose
- The mixture is swallowed and the salivary amylase is denatured by the stomach acid, so hydrolysis stops
- Mixture moves to the small intestine
- Pancreatic amylase and mineral salts are added (neutral pH)
- Pancreatic amylase breaks down starch into maltose
- Epithelial cells contain membrane bound disaccharidase, maltase, which breaks down maltose into ɑ-glucose
- ɑ-glucose is absorbed by the epithelial cells.
What enzyme catalyses the hydrolysis of starch into maltose
amylase
What enzyme catalyses the hydrolysis of maltose into ɑ-glucose
Maltase (a disaccharidase)
Why is it important that maltase is membrane bound, within the epithelial cells
They are released close the surface of absorption, so ɑ-glucoses produced by hydrolysis right next to where it is needed
What is the process of the digestion of lipids
- Food enters the mouth, is chewed, passes through the stomach and into the small intestine
- Bile salts emulsify the fats into micelles, to increase the SA
- Lipase is added from the pancreas, hydrolysing the ester bonds between the glycerol and fatty acid
- Releases 2 fatty acids and one monoglyceride, which are absorbed into the epithelial cells
What is the process of the digestion of proteins
- Food enters the mouth, is chewed, passes through the stomach and into the small intestine
- Polypeptide chains are hydrolysed by proteases
- Amino acids are released and are absorbed into the epithelial cells
What are the three types of proteases
- Endopeptidase (centre of chains)
- Exopeptidase (end of chains)
- Dipeptidase (In dipeptides)
What is the function of Endopeptidase
Hydrolyses the peptide bonds in the central region of chains, forming smaller polypeptide molecules
What is the function of Exopeptidase
Hydrolyses the bonds on the terminal amino acids, releasing dipeptides and single amino acids
What is the function of dipeptidase
Hydrolyses the peptide bond in a dipeptide, releasing individual amino acids (membrane bound)
How is the ileum adapted for absorbtion
- Large SA for diffusion (due to villi + microvilli)
- Thin walls give a short diffusion path
- Contains muscles to contract and move food through the lumen, maintaining a concentration gradient
- Good blood supply to maintain a concentration gradient
How are amino acids and monoglycerides absorbed
Once released by digestion, they are absorbed by diffusion and co-transport into the bloodstream.
How are triglycerides absorbed
- Lipid droplets are hydrolysed into monoglycerides and 2 fatty acids
- Bile salts emulsify the fats, forming micelles, with a larger SA
- Micelles move into the epithelial cells by diffusion
- Triglycerides are reformed in the endoplasmic reticulum
- Move through the Golgi to form a chylomicron (a lipoprotein)
- Leave the cells by exocytosis into the lacteal system
