Organisms exchange substances with their environment Flashcards
What is the importance of surface area to volume ratio in living organisms of different sizes?
Organisms like the tape worm with a large surface area to volume ratio can use diffusion alone to sustain life as it supplies their cells with enough oxygen to allow them to carry out active transport and produce ATP.
In organisms with more then 2 layers of cells, they need a range of tissues to provide support and strength so the body gets thicker and increases the volume. Surface area doesn’t increase as much.
What happens as an organism gets larger?
The lower the surface area to volume ratio.
Why is the alveoli beneficial?
Allows more effective exchange of carbon dioxide and oxygen between alveoli an blood capillaries by increasing the surface area to volume ratio.
Maintenance of a steep concentration gradient is critical to ensure that the oxygen continues to diffuse from a higher concentration in the alveoli to a lower concentration in the capillaries.
Alveoli is lined by squamous epithelium which is a single layer of flattened cells. This reduces the diffusion distance which increases the rate of diffusion.
How do epithelial cells increase surface area to volume ratio?
They line the villi in the ileum (small intestine) an possess large numbers of microvilli which act to increase the surface area to volume ratio and enable faster absorption of the products of digestion.
What is Fick’s law?
Law of diffusion, which governs the diffusion of a gas across a membrane and is dependent of 3 properties.
rate of diffusion is directly proportional to:
surface area x concentration gradient/ thickness of membrane
What happens in active insects?
The concentration of lactic acid increases in muscle cells.
Water is drawn into cells by osmosis to bring air closer to muscle cells.
What happens in resting insects?
The ends of the tracheoles fill with water so membranes are permeable.
What happens in a bony fish?
Deoxygenated blood is pumped by the heart towards the 4 pairs of gills that are covered by a operculum. Blood flows along the gill arch, structural unit which bears the primary lamellae (gill filament). Filaments are thin (short diffusion pathway) and surface is faded (increases surface area) into secondary lamellae.
Water flows under and over gill filaments and oxygen is removed by blood in capillaries. Capillaries carry blood in opposite direction so it’s a counter-current system.
What’s an amoeba?
A single celled organism that belong to the protoctista kingdom. They have a large surface area to volume ratio. Gas exchange surface is cell membrane so gas exchange occurs across the entire length of the surface by simple diffusion.
What is an open circulatory system?
Blood doesn’t remain within the blood vessels at all times eg insects.
gas exchange in insects
spiracle - tracheae - tracheoles - tracheal fluid
Spiracles allow diffusion of o2
Tracheoles are highly branched so large surface area
Tracheole walls thin so short diffusion distance
Spiracles can close so no water loss
What is a single circulatory system?
Blood flows through the heart once for each circuit of the body.
Counter current flow
The mechanism by which fluids flow in the opposite direction to eachother. Ensures there is a higher concentration of oxygen in water than capillaries.
Why is loss of water vapour by transpiration an unavoidable phenomena?
In the day the stomata opens to allow carbon dioxide to diffuse into the plant so it can be fixed in the light-dependent reactions of photosynthesis.
Gas exchange in the leaf of a dicotyledonous plant
Intracellular air spaces exist between the spongy cells of the mesophyll layer as these cells are branched. This allows CO2 to diffuse through the spongy mesophyll and up to the little spaces found in the small separation between the palisade cells. From here, CO2 diffuses into the abundance of chloroplasts that are located near the cell wall for photosynthesis. The 02 produced by photosynthesis and any water vapour lost through transpiration can diffuse through the air spaces in the opposite direction then through the substomatal chambers and out the leaf.
What is transpiration?
The loss of water vapour from a plant, through the stomata of the leaves.
What does the opening and closing of the stomata allow?
The diffusion of CO2 and regulation of the loss of water vapour by transpiration.
Alveoli features
Has a large surface area.
Has a moist lining gases will dissolve in.
The epithelial cells lining the alveoli are thin and squamous (reduces diffusion distance) and can fit closely together to form tissues.
Alveoli walls are in close contact with a dense capillary network.
As soon as oxygen diffuses from the alveoli into the red blood cells, this newly oxygenated blood is carried away and deoxygenated blood takes its place.
How does O2 and CO2 move through the hydrophobic tails in the phospholipid bilayer?
Simple diffusion
The rate of simple diffusion will be increased when there is…
A large surface area
A high temperature
A small diffusing molecule
A short diffusion pathway
A steep concentration gradient
The mechanism of inhalation (at rest)
Following stimulation by the phrenic nerve, the diaphragm contracts and moves in a downwards direction.
The external intercostal muscles contract which acts to move the ribcage up and out.
This increases the volume of the thoracic cavity and therefore decreases the pressure.
This creates a pressure gradient between the atmosphere and alveolus, generating a flow of air from the higher pressure in the atmosphere and into the gas exchange system to the nose or mouth.
Air inflates the lungs as it flows along the trachea, the bronchi and the bronchioles before reaching the alveoli for gas exchange.
What interaction do internal and external intercostal muscles display?
Antagonistic
The mechanism of exhalation (at rest)
CO2 diffuses from the blood capillaries and into the alveoli before being expelled via exhalation. If this does not happen there would be an increase in the concentration of H+ ions and a decrease in pH, which causes enzymes to denature.
What happens during digestion?
Large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.
What do salivary and pancreatic and amylase do?
Hydrolyse dietary starch into disaccharides which are then hydrolysed by membrane-bound disaccharides like maltase into glucose.
What is peristalsis?
The movement of food along the oesophagus to the stomach (contraction of muscles in the walls of the stomach)
What is pepsin?
The endopeptidase found in the stomach that breaks the peptide bonds of non terminal amino acids
What is an endopeptidase?
An enzyme that breaks the peptide bonds of nonterminal amino acids.
Exopeptidases
Enzymes that break down peptide bonds from end pieces of terminal amino acids and can break down proteins in monomers
Dipeptidases
Breaks dipeptides into individual amino acids. These enzymes are secreted in the small intestine by enterocytes
Ileum
Found after the duodenum and jejunum it’s 2-4m long and its main function is the absorption of vitamin B12, bile salts and any products of digestion not absorbed in the jejunum.
The walls are highly folded where each fold has villi which increase surface area for absorption of digestion products.
Epithelial cells that line the villi have microvilli.
Monosaccharides are absorbed by the cells lining the ileum using co-transport proteins.
Formation of micelles is critical for the absorption of monosaccharides and fatty acids in the eneterocytes of the ileum
Haemoglobin dissociation curve
Sigmoid shape
At a low pp02 the Haemoglobin doesn’t associate readily with the 02 molecules as the haem groups are in the central of the haemoglobin molecule. As the pp02 increases, 1 o2 molecule will enter the haemoglobin and bind to 1 haem group.
Binding changes the haemoglobin molecules shape so it’s easier to further bind 02
(Conformational change- demonstrates cooperative nature of binding)
Structure of haemoglobin
Quarternary and has 4 polypeptides chains 2 a-globin and 2 b-globin on the outside of each chain is a haem group with Fe2+.
Is haemoglobin globular?
Yes
What does affinity mean?
A strong attraction (haem group has a high affinity for o2.
Haems group high affinity for 02 at the lungs
Allows haemoglobin to LOAD with 4 o2 molecules.
Oxygen + haemoglobin = oxyhaemoglobin
The binding of o2 is reversible so oxyhaemoglobin is able to unload the o2 when it reaches the respiring tissues
What does an increase of CO2 do?
Reduces the affinity of haemoglobin for 02.
What does a pH change do?
The carbonic acid dissociates into H+ ions which remain in the cytoplasm of the cell and decrease the pH of the cytoplasm and the increased acidity O2 alters the tertiary structure of the haemoglobin and decreases the affinity of haemoglobin for oxygen.
Dissociation curve
Moved downwards and right (Bohr Shift)
What circulatory system do mammals have?
A double, closed circulatory system where blood passes through the heart twice per cycle of the body.
Function of pulmonary artery
Carries blood into the pulmonary circulation which is the system of blood vessels that forms a closed circuit between the heart and lungs.
What branches of the pulmonary artery?
Artérioles which leads to a dense network of capillaries which is connected pulmonary vein by venules.
Systematic circulation
The circuit of blood vessels supplying oxygenated blood to, and returning deoxygenated blood from the tissues of the body.
The double circulatory system allows a heart to pump blood into the systematic circulation at a higher pressure than the blood that is pumped into the pulmonary circulation.
Function of the vena cava?
Carries deoxygenated blood to the heart from the respiring cells of the lower body.
Function of the left AV valve?
Prevents backflow of blood from the left ventricle to right atrium.
Function of right atrium
Contacts to pump blood into the right ventricle.
Function of septum
Allows oxygenated and deoxygenated blood to mix.
Blood pumped in pulmonary circulation contains some o2. Reduces steep conc gradient between blood capillaries and alveoli to decrease rate of diffusion.
Function of aorta artery?
Carries oxygenated blood from heart to rest of the body.
What is the human heart made out of?
Cardiac muscle which is myogenic in nature as it can initiate its own contraction
Why is left ventricles wall thicker then right ventricles?
Thick walls to contract with force as needed for higher pressure.
What is stroke volume?
Volume of blood ejected from the left ventricle per heart beat.
EDV-ESV (end-diastolic volume - end-systolic volume)
Cardiac output= stroke volume x heart rate
Systole
The phase of the heartbeat when the heart muscle contracts.
Ventricular systole
Contraction of ventricle walls pumps blood upwards into the arteries.
Diastole
Following systole, all 4 chambers of the heart relax and elastic recoil causes an increase in volume to allow blood to flow in from the veins.
Atrial systole
Contraction of the atrial walls pumps the blood into the ventricles.
Why do valves open and close?
Pressure changes
Why is atrial pressure at its highest point low?
It has thin walls so they cannot generate as much force when they contract.
What happens when atrial pressure is higher then ventricular pressure>
AV valves are open to allow blood to flow from atria to ventricles.
What are vascular tissues?
Xylem and phloem
Lignification
The deposition of lignin into the walls of xylem cells during development. Waterproofs the xylem and contents and end walls decay.
Is xylem tissue dead or alive?
Dead
Why is xylem hollow?
Allows water and minerals to flow without being impeded.
Function of lignin in xylem?
Strengthens walls and prevents vessel collapsing so they remain open. Deposited in a spiral which allows xylem to stretch and stem to bend.
Bordered pits
Lignification is not complete which leaves gaps in the cell walls.
Pits in 2 adjacent xylem vessels are aligned to allow water to leave one vessel and pass into the next vessel and out the xylem.
Capillary action
Forces of attraction can pull water up the sides of the vessel.
Root pressure
Can move water a few metres up the xylem by mass flow
Transpiration pull
Water loss in transpiration is replaced by water moving up the xylem
Cohesion
Attraction between 2 molecules due to hydrogen bonds
Tension
A pulling force that allows water to be pulled up in one continuous column
Adhesion
The attraction between water molecules and the xylem walls.
Movement of water through the leaf
Step1: water moves from xylem into spongy mesophyll cells via osmosis.
Step2: water evaporates to form water vapour. Water vapour potential in air space increases so vapour will diffuse out the stomata in transpiration.
What does the phloem transport?
Sucrose which dissolves in water to form cell sap.
And amino acids.
Sieve tube elements
Cells lined up end on end to form sieve tubes. At the end are perforated cross walls called sieve plates which allow cell sap to move from one sieve tube element to another
Sinks
Structures which need the assimilates and can be below or above leaves
Companion cells
Carry out active processes needed to load assimilates into sieve tubes.
Dense cytoplasm with an abundance of mitochondria.
Plasmodesmata
Thin strands of cytoplasm that link contents of adjacent cells eg companion cells and sieve tube elements to allow flow of assimilates between cells
