Substance exchange Flashcards
pulmonary ventilation rate (PVR)
PVR = tidal volume X breathing rate
tidal volume: normal volume of air displaced by the lungs at rest (cm3)
breathing rate: the number of breaths taken per minute (bpm)
Air is pulled into the lungs through the trachea:
the trachea divides into 2 bronchi, which further divide into bronchioles, until they terminate into alveoli.
when the volume of the lungs decreases,
the pressure increases, and causes air to be pushed out
when the volume of the lungs increases,
it decreases the pressure, causing air to be drawn in.
inhalation
external intercostal muscles contract, move ribs up
diaphragm contracts, flattens
lung volume increases
pressure in thoracic cavity decreases
movement of air into lungs
Exhalation
external intercostal muscles relax, move ribs down
diaphragm relaxes, moves up
lung volume decreases
pressure in thoracic cavity increases
movement of air out of the lungs
alveoli maxim gas exchange by:
- having a very large surface area
- being moist to aid diffusion of gases
- having a rich blood supply to maintain a concentration gradient
- the alveolar epithelium and capillaries are very thin, so the diffusion distance between air in alveoli and red blood cells in capillaries is short.
lung diseases decrease the surface area of the lungs, reducing
oxygen uptake
chronic obstructive pulmonary diseases (COPD) include:
- asthma: air pollution can result in asthma, causing airways to narrow
- bronchitis: a lung infection, causing inflammation of the linings, excess mucus production and coughs
- emphysema: phagocytes cross alveoli walls and break down proteins, causing alveoli to burst - reduces number o alveoli and number of capillaries, decreasing uptake of oxygen.
single-celled organism have a
large surface area to volume ration - can rely on diffusion for substance to move into and out of them.
mesophyll
- large, moist surfaces to absorb oxygen and carbon dioxide, facilitating diffusion
- air spaces between cells to allow gases to diffuse
- concentration gradient formed as gases are absorbed or released.
stomata
- allow gases to pass in and out of pores in the leaf surface
- gases diffuse due to concentration gradient between the inside and outside of the leaf
- stomata can close to reduce water loss
xerophytes
plants that grow in dry habitats (e.g. cacti, marram grass)a
adaptations to reduce water evaporation from leaves, whilst enabling gas exchange and photosynthesis, include:
- thicker cuticle
- reduced leaf surface area (e.g. spines or needles)
- sunken and fewer stomata
- rolled leaves.
spiracles (gas exchange in insects)
valves to allow air in and out by diffusion
terrestrial insects use
their spiracle valves to balance water loss and gas exchange
- in hot, dry conditions, water can be lost rapidly via evaporation from the spiracles. The valves close to reduce this.
adaptations of gills
- large surface area of lamellae and filaments when in water
- rich blood supply by mass flow to the gills
- concentration gradient of oxygen along the whole length of the lamellae by a countercurrent principle.
countercurrent principle
blood in the capillaries flows in the opposite direction to the water flowing over them.
by allowing the blood to flow in the opposite direction to the water,
an oxygen concentration gradient is maintained, where the oxygen concentration in the water is always high than in the blood.
- this maximises the amount of oxygen that can diffuse into the bloodstream and prevents oxygen diffusing back into the water again once the blood is oxygen rich.
during digestion, the addition of water molecules in hydrolysis reactions
breaks down large biological molecules into smaller molecules.
- these can be absorbed across cell membranes
digestion is a 2-step process in mammals:
- physical breakdown
- chemical digestion
physical breakdown
food is broken down into smaller pieces by teeth to increase the surface area available for enzyme action
chemical digestion
large, insoluble molecules are broken down into small, soluble ones by enzymes (hydrolases)
the 3 main types of hydrolases are:
carbohydrases, lipases and peptidases
carbohydrates are hydrolysed by…
amylases and membrane-bound disaccharides into lactose, glucose and other monosaccharides
lipids are hydrolysed by…
lipase (in association with bile salts) into fatty acids and monoglycerides
proteins are hydrolysed by…
exopeptidases, endopeptidases, and membrane-bound dipeptidases into amino acids.
exopeptidases hydrolyse
amino acids at the ends of the peptides, reducing them to amino acids
endopeptidases hydrolyse
peptide bonds in the central region of a protein, reducing it to a series of peptides.
bile is a greenish fluid produced by the liver. It doesn’t contain enzymes, but is made up of 2 important digestive chemicals:
- mineral salts: including sodium hydrogen carbonate - neutralise stomach hydrochloric acid to provide a neutral pH for small intestine enzymes
- bile salts - emulsify: (mechanically break down) lipids into tiny droplet increasing the surface area for lipases to act on.
Visking tubing is a cellulose tubing material that is partially permeable. It can be used to model the activity of enzymes in the ileum.
Visking tubing enables the effect of various factors, e.g. pH and temperature, on enzyme activity to be tested.
The products of digestion (e.g. amino acids, fatty acids, glycerol, and monosaccharides) must be absorbed by cells lining the ileum in the mammalian small intestine.
- amino acids and monosaccharides are absorbed using co-transport mechanisms
- micelles are involved in the absorption of lipids.
the ileum is adapted to maximise absorption:
- large surface area - 6m long and lined with 1mm long villi which increase SA. Villi are covered in cells which have projections called microvilli
- good blood supply to remove products of digestion and maintain a steep concentration gradient.
- thin walls so there is a short diffusion pathway
Amino acids and glucose are absorbed in the ileum through
co-transport
Co-transport in the ileum:
- sodium ions and glucose bind to a co-transporter protein in the cell-surface membrane of an epithelial cell.
- as the sodium ions move into the cell by facilitated diffusion, the glucose molecules are mainly carried through against a conc gradient.
- glucose and sodium ions pass through the cell and into the blood by facilitated diffusion (glucose) or active transport (sodium ions).
after digestion, fatty acids and monoglycerides, along with bile salts, form tiny round complexes called
micelles
micelles have a
hydrophobic centre but a hydrophilic outer layer which enables them to dissolve.
when a micelle reaches the ileum epithelium,
it breaks down, releasing the fatty acid and monoglycerides which can then diffuse through the epithelial cell surface membrane. The bile salts are reused.
In the epithelial cells, monoglycerides combine with fatty chains and glycerol molecules to reform
triglycerides.
These triglycerides package with cholesterol and phospholipids to form a water soluble fat droplet called a
chylomicron. This is then transferred by exocytosis to the lacteal.
monoglyceride
a molecule of glycerol attached to one fatty acid
what is the difference between the action of exopeptidases and endopeptidases?
exopeptidase hydrolyse amino acids from the ends of the peptide; endopeptidase hydrolyse peptide bonds in the central part of the protein or polypeptide.
mass transport
moves substances efficiently over the large distances between cells and exchange surfaces. This is important for larger organisms that can’t rely on simple diffusion.
many animals are adapted to their environment by possessing different types of oxygen-carrying proteins, such as
haemoglobin, with different oxygen transport properties.
red blood cells contain
haemoglobin to transport oxygen from the lungs to the cells.
the protein haemoglobin has a
quaternary structure, and it is made up of 4 polypeptide chains with haem groups.
oxygen loading
at the alveoli, when the first oxygen molecule binds to the first haem group the haemoglobin changes shape. This makes it easier to bind a further 3 oxygen molecules
oxygen unloading
at the tissues, oxygen dissociates from the haemoglobin due to low partial pressure of oxygen in the tissues. In high carbon dioxide concentrations, such as at the tissues, haemoglobin releases oxygen.
Bohr effect
The dissociation of oxyhaemoglobin is higher at the tissues, where the partial pressure of carbon dioxide is higher.
the heart is supplied with blood by the
coronary arteries.
the heart has 2 main arteries:
pulmonary artery (taking deoxygenated blood to lungs) and the aorta (sending oxygenated blood to the body)
the heart has 2 main veins:
pulmonary vein (receiving oxygenated blood from the lungs) and the vena cava (receiving deoxygenated blood from the body.
the kidneys are supplied with blood via the
renal artery and blood is taken away via the renal vein.
arteries
thick walls containing elastic tissues and smooth muscle tissue to maintain high pressures
arterioles
much smaller arteries that deliver blood to capillaries. Have thinner walls than armies and less elastic tissues.
veins
thin walls, containing less elastic and muscle tissue, and a larger lumen compared to arteries. Most contain valves.
capillaries
very small blood vessels, allow one red blood cell through at a time, low blood pressure, single layer of endothelial cells. Tissue fluid is formed around the body cells, bathing them in solutes. Tissue fluid drains into lymphatic vessels.
the human heart has 4 chambers of cardiac muscle:
2 atria dna 2 ventricles.
oxygenated blood is collected in the
left atrium, pushed into the left ventricle and then pumped through the aorta to the whole body.
deoxygenated blood returns from the body into the
right atrium and is pushed into the right ventricle, which pumps the blood to the lungs via the pulmonary artery.
plants transport water, sugar and mineral ions using 2 vessels:
xylem and phloem.
water and dissolved mineral salts are transported in the
xylem. this happens in 1 direction only - from roots to top of the plant
Phloem actively transports
organic molecules, such as sucrose from photosynthesis.
xylem transports water up the plant thanks to the
transpiration stream, as well as dissolved minerals to the tissues that need them. It is made of dead cells that form continuous tubes.
water moves from the soil into the root hair cells by
osmosis from a higher to a lower water potential, moving through the root tissues to the xylem vessel.
water evaporates from the leaves causing
tension, which pulls water molecules up the stem (cohesion-tension theory). This creates a continuous transpiration stream.
phloem is made up of
living cells that have sieve plates between them and the companion cells beside them, which provides metabolic support.
translocation
- plants transport sucrose and other substances from sources (e.g. leaf cells) to sink (cells that use or store substances)
- higher hydrostatic pressure is created at the source and lower hydrostatic pressure at the sink.
- this pressure gradient moves the phloem sap from source to sink. = mass flow hypothesis.
transpiration through xylem vessels can be measured using a
potometer
(potometer) the leaves can be exposed to different environment conditions to investigate the effect on transpiration, such as
temperature, light intensity and humidity.
(potometer) in these experiments, the rate at which the bubble moves in the capillary tube is assumed to correlate with
the rate of transpiration, as water evaporates from the stomata.
Other experiments include: (transpiration)
- ringing experiments -> woody stems have a layer of phloem cut from their circumference. The tissue below the cut dies and tissue above swells.
- tracer experiments -> using isotope 14C in carbon dioxide, the flow of sugars can be traced within the plant. These experiments show that sugars move around the plant only in phloem tissues.
