Exchange Flashcards
What is surface area to volume ratio?
- the amount of surface area per unit volume of an object
- generally, the larger an object is, the smaller the ratio
Why do we need exchange?
- cells need to take in oxygen for aerobic respiration
- they need to take in nutrients like glucose and amino acids
- need to excrete waste products like urea and CO2
Exchange in single celled organisms
- they are able to obtain sufficient substances like glucose and oxygen through diffusion across their cell surface membrane
- this is because they are very small, which makes for a short diffusion pathway to the cell centre
- the also have a large SA:V
Why can’t multicellular organisms exchange easily?
- they can’t obtain sufficient oxygen and nutrients by diffusion across their outer membrane
- this is because many cells are deep within the body so there is a large distance between them and the outer environment
- diffusion would happen far too slowly to maintain metabolic activity
Large organisms and surface area
- large organisms have a small surface area to volume ratio
- this makes it difficult to supply enough substances the large volume of cells inside an organism with a relatively small surface area
How do multicellular organisms obtain sufficient oxygen?
- multicellular organisms need to greatly increase the surface area of gas exchange surfaces without significantly increasing their volume
- therefore large organisms develop specialised exchange organs (e.g. lungs or gills)
What is the SA:V like for animals living in colder environments?
- these animals need to conserve heat
- therefore, they would have a more compact shape, giving them a smaller SA:V to reduce loss of heat
- for example, polar bears
What is the SA:V like for animals living in hotter environments?
- have a less compact, sometimes flattened shape which gives them a large SA:V
- this increases heat loss
- for example, an elephant’s ears
Why do smaller organisms need a higher metabolic rate?
- they have a large SA:V ration, so lose heat quickly
- they need a relatively high metabolic rate to release enough heat in order to maintain their body temperature.
- small animals with a compact shape lose less heat, though, because they have a smaller SA:V ratio
FISH - oxygen and gas exchange in water
- Water contains far less oxygen than air
- This is because oxygen is not very soluble in water
- Therefore, oxygen diffuses more slowly through water than air
- water is far more dense than air, so harder to move over gas exchange surfaces
- This is why fish evolved the specialised gas exchange surface gills
FISH - What protective structure goes over the gill?
Operculum
FISH - What route does the water take through the fish?
Water enters the mouth, flows over the gills and exits under the operculum. It only moves in this direction.
FISH - gill arches
A bony structure supports many gill filaments.
Usually 4 per gill.
FISH - gill filaments
Supported by the bony structure of gill arches and increases surface area for gas exchange.
FISH - gill lamellae
On the surface of every gill filament, which increases surface area for gas exchange even more.
Good blood supply (lots of capillaries) to maintain gradient and a thin layer of cells for short diffusion pathway.
FISH - counter-current system
- Blood enters the lamellae at a lower oxygen concentration, as it has just arrives from the fish’s body.
- In the opposite direction, water with a higher concentration of oxygen, which diffuses into the lamellae into the bloodstream.
- This means a diffusion gradient for oxygen is maintained along the whole length of the gill
- This whole process is to maximise how much oxygen diffuses into the blood.
PLANTS - recap leaf structure
- Waxy cuticle - prevents the evaporation of water from the leaf surface
- Upper epidermis cells - transparent to let light through for photosynthesis.
- Palisade mesophyll cells - column shaped and contain many chloroplasts.
- Spongy mesophyll cells - irregularly shaped and are surrounded by air spaces which let gases diffuse through the leaf.
- Lower epidermis cells - layer of cells on the lower side of the leaf.
- Stomata - pores that open to allow the gases to pass in and out of the leaf.
PLANTS - how does diffusion and the gradient work for plants?
- Gases move into a leaf by diffusion through open stomata.
- Inside the air spaces, the concentration of carbon dioxide falls as it is used up for photosynthesis.
- Therefore, there is a lower concentration of carbon dioxide inside the air spaces than outside the leaf, which creates a gradient
- Carbon dioxide diffuses down this gradient through the open stomata and into the leaf.
PLANTS - why don’t they need a ventilation system?
- Their leaves are highly exposed to the environment.
- The air surrounding them is constantly being replaced as a result of the wind, which maintains a diffusion gradient.
PLANTS - LEAF ADAPTATIONS FOR EXCHANGE - the stomata
- many stomata for shorter diffusion distance as no mesophyll cell is far from a stoma so increases rate of diffusion
- Stomata can open (turgid guard cells) and close (flaccid guard cells) to reduce water loss. They are kept open during the day to reduce gaseous exchange, and closed at night when photosynthesis doesn’t occur so CO2 is not needed
PLANTS - LEAF ADAPTATIONS FOR EXCHANGE - air spaces in the mesophyll
- many interconnecting air spaces is the mesophyll (e.g. spongy mesophyll)
- the irregular shapes of mesophyll cells gives them a large surface area for rapid diffusion
PLANTS - LIMITING WATER LOSS - waxy cuticle
Prevents evaporation from the leaf surface.
PLANTS - xerophyte adaptations
- Thick waxy cuticle - reduces evaporation from the leaf surface.
- Fewer stomata - so less water can evaporate out.
- Hairs on leaves - traps water molecules around the leaf which reduced the diffusion gradient for water molecules between the inside and outside of the leaf.
- Curled leaves - this means the stomata are on the inside. Water molecules will accumulate around the stomata instead of being blow away by the wind, which reduce the diffusion gradient for water molecules between the inside and outside of the leaf.
- Sunken stomata - the stomata are in pits. Water molecules will accumulate in these pits, which reduces the water molecules’ gradient between the inside and outside of the leaf.
PLANT - what is a xerophyte?
Plants that are especially adapted to living in dry environments.
PLANTS - guard cells
- Become turgid = stoma opens
- Become flaccid = stoma closes
- Have chloroplasts
- inner cell walls are thicker and more rigid than the outer cell walls
- Absorption of water = expands and becomes more turgid
- Loss of water = becomes more flaccid
HUMANS - why is gas exchange necessary?
- Humans need to get oxygen into the blood for respiration
- In turn, we need to get rid of the carbon dioxide released by respiration
- Therefore, the breathing and gas exchange system is necessary
HUMANS - gas exchange system simplified
1) As you breathe in, air enters the trachea
2) The trachea spilts info two bronchi - a bronchus leading to each lung
3) These bronchi each branch of into small tubes called bronchioles
4) The bronchioles end in small air sacs called alveoli.
For this, the ribcage, intercostal muscles and diaphragm all work to move air in and out of the body
HUMANS - what is ventilation?
Breathing in (inspiration) and out (expiration)
HUMANS - inspiration
- The external intercostal and the diaphragm muscles contract - this makes it an active process as ATP is required for muscle contraction.
- This causes the ribcage to move upwards and outwards. The diaphragm contracts and flattens, which increases the volume of the thoracic cavity.
- As the volume of the thoracic cavity increases, the lung pressure decreases so that it is lower than the atmospheric pressure.
- This creates a pressure gradient between the atmosphere (higher pressure) and the lungs (lower pressure).
- Therefore, for inspiration, air moves down the pressure gradient into the lungs.
HUMANS - expiration
- The external intercostal and diaphragm muscles relax.
- The ribcage moves downwards and inwards and the diaphragm becomes curved again.
- The volume of the thoracic cavity decreases, causing the air pressure in the lungs to increase to above atmospheric pressure, which creates a pressure gradient.
- Air is forced down the pressure gradient and out of the lung.
- Therefore, normal expiration is a passive process as it doesn’t require energy.
- HOWEVER expiration can be forced, in which the external intercostal muscles relax and internal intercostal muscles contract, which pulls the ribcage further down and in. Therefore, the movement of the two sets of intercostal muscles is considered antagonistic.
HUMANS - alveoli adaptations
- Huge number - this means there is a large SA, which increases rate of diffusion and therefore gas exchange
- Capillaries - the alveoli are covered by a network of capillaries (which are flattened against the alveoli for a short diffusion pathway). The blood cells moves slowly through them, allowing time for diffusion.
- Thin walls/alveolar epithelium - gives a short diffusion pathway.
- Good ventilation - circulation of blood through the capillaries ensure a steep concentration gradient for O2 and CO2 between the alveoli and the blood.
- Surfacant (above spec) - a substance that consists of phospholipids that reduces the surface tension of the water. This prevents the alveoli from sticking together, reducing the amount of effort needed to breathe in and inflate the lungs.
HUMANS - the process of diffusion with the alveoli
- O2 diffuses out of the alveoli
- It goes across the alveolar epithelium and the capillary endothelium and into the haemoglobin, where it binds to create oxyhaemoglobin.
- CO2 diffuses into the alveoli from the blood and is breathed out.
HUMANS - pulmonary ventilation rate equation
Pulmonary ventilation rate (dm3 min-1) = tidal volume (dm3 min-1) x breathing rate (bpm)
HUMANS - what is PVR?
Pulmonary ventilation rate is a measure of how much air moves into the lungs in one minute.
HUMANS - what is tidal volume?
The volume of air in each breath.
HUMANS - what is ventilation rate?
The number of breaths per minute. In other words, breathing rate.
HUMANS - spirometry
- A simple test with a spirometer that is used to help diagnose and monitor certain lung conditions by measuring various aspects of breathing.
- Used to measure forced expiratory volume (FEV)
- Used to measure forced vital capacity (FVC)
- Can be used to diagnose lung diseases.
HUMANS - what is FEV?
Forces expiratory volume - the maximum volume of air that can be breathed out in one second.
HUMANS - what is FVC?
Forced vital capacity - the maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in.
Cause vs correlation?
A correlation occurs when a change in one variable is reflected in the other, while a cause can only be shown by evidence of one variable leading directly to a change in the other.
What are the features of exchange surfaces?
- Large SA:V - increases rate of exchange
- Thin - for a short diffusion pathway
- Transport system (e.g. blood) - ensures move of internal medium and maintains gradient.
-
Movement of the environmental medium (e.g. air) - maintains concentration gradient.
Selectively permeable - allows only selected materials to cross the membrane
INSECTS - what are tracheae?
A network of microscopic air-filled pipes used for gas exchange.
INSECTS - what are tracheoles?
The tracheae branch of into these tracheoles which have thin permeable walls and transport oxygen directly to the cells.
INSECTS - what are spiracles?
Pores on the insects surface where air moves into the insect.
INSECTS - what route does gas take (think gradients)?
DIFFUSION GRADIENT - there is a higher concentration of oxygen outside the body than inside, resulting in a gradient.
1. The respiratory gases diffuse down the gradient and into the spiracles.
2. It continues down the concentration gradient into the tracheae.
3. It continues into the tracheoles, which deliver the gas directly to the tissues.
4. Now respiration can occur, CO2 is produced, which naturally results in an increased concentration. This creates a gradient between the insects tracheoles and the external environment/outside. Therefore, the CO2 moves down this gradient and out of the insect.
INSECTS - when is abdominal pumping used?
- Larger insects use rhythmic contractions of the abdominal muscles or squeeze the trachea.
- This enables mass movements of air in and out of the tracheal system.
- This results in more effective respiration.
INSECTS - why are the ends of tracheoles water filled?
- during a period of intense activity, anaerobic respiration occurs, resulting in lactate (the ion that makes lactic acid) as a byproduct inside the cells.
- the lactate is soluble , so dissolves into water, which lowers the water potential of the cells.
- therefore, the water at the water-filled ends of the tracheoles moves into the cells by osmosis.
- this decreases in volume of water in the tracheoles increases rate of diffusion, as oxygen moves through air more easily than water.
- however, it does result in water loss, as there is a higher rate of evaporation.
INSECTS - how is water loss limited in insects?
- tracheal system increases the SA for gas exchange BUT also for water loss
- Hairs around spiracles - catch water to reduce gradient.
- Spiracles - can close.
- Waterproof covering - reduces water loss.
DIGESTION - what is physical digestion?
When large food molecules are broken down into small pieces by the teeth.
This allows for ingestion and provides a large SA for chemical digestion.
DIGESTION COMPONENTS - mouth
Teeth and tongue physically break up the food to increase the SA for chemical digestion.
DIGESTION COMPONENTS - salivary glands
Secretes saliva, containing water to dissolve soluble substances.
Mucus for lubrication.
Amylase for hydrolysing carbohydrates.
DIGESTION COMPONENTS - oesophagus
Muscular tube that connects the mouth to the stomach.
DIGESTION COMPONENTS - stomach
Where food is stored for up to a few hours.
Stomach acid is present to kill ingested bacteria.
Some protease enzymes are found (the low pH is their optimum pH).
DIGESTION COMPONENTS - pancreas
Produces many digestive enzymes, which are secreted through the pancreatic duct and into the small intestine.
DIGESTION COMPONENTS - liver
The liver secretes bile, which is stored in the gall bladder.
The bile has a high pH/is alkaline to neutralise the stomach acid and emulsify lipids.
DIGESTION COMPONENTS - duodenum
The first part of the small intestine where most of the digestion takes place.
DIGESTION COMPONENTS - ileum
The last part of the small intestine where the final digestion takes place.
Main site of absorption of food molecules.
Contains numerous membrane-bound maltase, sucrase and lactase enzymes.
DIGESTION COMPONENTS - large intestine
Water is absorbed here to form semi-solid faeces.
DIGESTION COMPONENTS - rectum
Faeces are stored here before being removed via the anus in a process called egestion.
DIGESTION - what is chemical digestion?
When large food molecules are broken down by hydrolysis (with the catalysing of specific enzymes) reactions into small molecules, which can be absorbed from the gut into the blood and transported around the body for cells’ use.
ABSORPTION OF CARBOHYDRATES - look at booklet (transport across cell membranes)
Go on!
DIGESTION OF CARBOHYDRATES - disaccharides and membrane-bound disaccharidases
- Maltase - maltose = glucose + glucose
- Sucrase - sucrose = glucose + fructose
- Lactase - lactose = glucose + galactose
- These enzymes are found attached to cell membranes of epithelial cells lining the ileum, which is why they are known as membrane-bound disaccharidases.
DIGESTION OF CARBOHYDRATES - digestion of starch
Starch is first digested into maltose by amylase.
It is then digested into alpha-glucose by maltase.
The enzymes work by hydrolysing the glycosidic bonds between alpha-glucose monomers.
DIGESTION OF PROTEINS - what are the monomers that make up proteins?
Amino acids
DIGESTION OF PROTEINS - what bond does a condensation reaction between two amino acids form?
Peptide bond.
Two amino acids joined together form a dipeptide, while many amino acids join to form a polypeptide.
DIGESTION OF PROTEINS - draw a dipeptide
DIGESTION OF PROTEINS - what are the three important enzymes for hydrolysis of proteins?
- endopeptidases
- exopeptidases
- membrane-bound dipeptidases
These are all proteases.
DIGESTION OF PROTEINS - where are peptidases made?
Pancreas
DIGESTION OF PROTEINS - endopeptidases
- enzymes that hydrolysis the peptide bonds within a protein
- they digest large polypeptide chains into a large number of shorter chains.
- mainly released and used in the small intestine, with the exception of pepsin (which is release by the cells lining the stomach and only works in acidic conditions).
DIGESTION OF PROTEINS - exopeptidases
- enzymes that hydrolyse the peptide bonds at the ends of proteins, removing a single amino acid from the end.
DIGESTION OF PROTEINS - how do endo- and exopeptidases work together?
- the work of endopeptidases means there are more shorter polypeptide chains for the exopeptidases to work on.
DIGESTION OF PROTEINS - where are they found and what do membrane-bound dipeptidases do?
- separate two amino acids in a dipeptide by hydrolysing the peptide bond.
- often found in the cell surface membrane of epithelial cells in the small intestine so are termed as membrane-bound.
- a type of exopeptidase
DIGESTION OF PROTEINS - absorption of proteins
Back to the co-transporters and such like with carbohydrates. Look over it again.
DIGESTION OF LIPIDS - what are lipids made up of?
Triglycerides and phospholipids.
Triglycerides are formed from the condensation of one molecule of glycerol and three molecules of fatty acid.
DIGESTION OF LIPIDS - what is the bond between two lipids called?
Ester bond
DIGESTION OF LIPIDS - what are lipids broken down into and how during digestion?
They are broken down into/hydrolyse into monoglycerides and fatty acids.
This reaction is catalysed by lipase enzymes, which are made in the pancreas and work in the small intestine.
DIGESTION OF LIPIDS - the role of bile
- after a fatty meal, bile is release into the small intestine where it emulsifies lipids.
- this means it causes larger lipid droplets to form smaller lipid droplets, which have a higher SA in total than a single large lipid droplet.
- this makes it easier for lipase to work.
- once lipids have been digested by lipase enzymes, which hydrolyse the ester bonds to make monoglycerides and fatty acids, the monoglycerides and fatty acids associate with bile salts, forming tiny structures called micelles.
DIGESTION OF LIPIDS - micelles
- the monoglycerides and fatty acids associated with with bile salts to form micelles
- micelles break up and reform at the epithelium
- monoglycerides and fatty acids move across by simple diffusion
DIGESTION OF LIPIDS - absorption of the products of lipid digestion
- The micelles move towards the epithelium.
- The micelles constantly break and reform at the epithelium, so they release monoglycerides and fatty acids. These smaller molecules can now pass across the cell membranes of the epithelium cells by simple diffusion, as they are lipid soluble. Therefore, they are absorbed.
- Once inside the epithelium cell, the monoglycerides are reformed into triglycerides in the smooth endoplasmic reticulum.
- The Golgi apparatus packages the triglycerides with cholesterol and proteins to form structures called chylomicrons.
- These chylomicrons are exported from the cell by exocytosis.
- Then chylomicrons are absorbed by lacteals in the villi, after which they move through the lymphatic system and eventually into the bloodstream.
