Physiology Flashcards
Why can single cells not be larger than 100um?
Any larger and the surface area to volume ratio would not facilitate the speed of diffusion necessary to support the reactions needed for life
How can organisms larger than 100um survive?
They are multicellular and have specialised exchange systems
How does SA:V ratio relate to heat exchange?
Smaller SA:V means better insulation and less heat loss, larger SA:V means faster heat loss
What are the two ways materials move over large distance inside multicellular organisms?
Diffusion and Mass Flow
How do solutes move in diffusion?
In a random direction due to thermal energy
Why is diffusion referred to as a passive process?
Diffusion does not require any energy other than the thermal energy of its surroundings
How does a large concentration gradient affect diffusion?
Net diffusion will occur from an area of higher concentration to an area of lower concentration
What is mass flow?
When a fluid moves in a particular direction due to a force. Mass flow always requires a source of energy to pump the fluid and is independent of concentration differences
How are sea sponges adapted for exchange?
They increase their SA:V ratio by being hollow with very thin walls
How are tapeworms adapted for exchange?
They have flattened bodies which increases their SA:V ratio while also decreasing diffusion distance
How are earthworms adapted for exchange?
They are too thick for diffusion so they developed a rudimentary circulatory system containing haemoglobin to carry gas between the body surface and underlying tissues
What is the function of the exoskeleton of insects?
It is waterproof to prevent drying out but it also prevents gas exchange.
How do insects exchange gas through their exoskeleton?
Through openings in the exoskeleton called spiracles
Where do the spiracles in an insect exoskeleton lead to?
A network of tubes called tracheae which branch into tracheoles that carry air into the cells
What are the tracheae and tracheoles in insect circulatory systems held open by?
A polysaccharide called Chitin
What occurs in the insect circulatory system when at rest?
Water diffuses out of its cells into the ends of the tracheoles which reduces SA in contact with cells and reduces rate of diffusion
What occurs in insect circulatory system when flying?
Their muscles produce lactic acid which lowers he water potential in the cells so water diffuses by osmosis from the tracheoles into the muscle cells, which makes diffusion of oxygen faster for respiration
How do some larger insect circulatory systems differ from normal?
They ventilate their tracheal system by using muscles to squeeze the trachea and suck air in and out to increase gas exchange rate. They also have hairs around their spiracles to reduce water loss or can close their spiracles when inactive
What is the composition of gills in a fish’s circulatory system?
Gills are composed of thousands of filaments which are covered in feathery lamellae which are only a few cells thick and contain blood capillaries to give the structure a large SA and short diffusion path. Gills are covered in muscular flaps called opercula
How do gills work?
Water flows over the filaments and lamellae and oxygen can diffuse down the concentration gradient across a short distance while co2 diffuses the opposite way
Why does a fish suffocate if taken out of water?
The gills are so thin that if a fish is taken out of water they collapse and the fish suffocates
How does ventilation in fish differ from in humans and why?
It is not tidal, it is one way. This is necessary because water is denser and more viscous than air so it would take too much energy to change momentum every breath.
What is Ficks Law?
Rate of Diffusion:
((Surface area)*(Concentration difference))/distance
Explain the process of inspiration in fish
- Mouth open
- Muscles in mouth contract lowering the floor of the mouth and the opercula contract pushing it outwards
- which increases the volume of the buccal and opercular cavity
- decreases pressure of water inside buccal cavity lower than outside pressure
- outside pressure causes opercular valve to close
- water flows in through the open mouth and over the gills from high to low pressure
Explain expiration in fish
- mouth closes
- mouth and opercula relax, raising floor of buccal cavity
- decreases volume of buccal cavity
- increases pressure inside buccal cavity above outside pressure
- pressure difference forces opercula valves open
- water flows out over the gills and through the opercula valve from high to low pressure
What is a counter current system?
Blood flows toward the front of the fish while water flows toward the back to ensure a higher concentration gradient
What type of circulatory system do humans have?
A double circulatory system with a 4 chambered heart.
What are each side of the human circulatory system called and what do they do?
Right side pumps blood to the lungs and is called the pulmonary circulation. Left side pumps blood to the rest of the body and is called the systemic circulation.
What is the series of blood vessels blood circulates through as it circulates the body?
Heart -> Aorta -> Arteries -> Arterioles -> Capillaries -> Venules -> Veins -> Vena Cava -> Heart
What is the purpose of blood vessels?
To deliver blood to capillary beds where substances are exchanged between cells and blood.
Explain how arteries are adapted to their function
Arteries carry blood from the heart to every tissue in the body by branching out into smaller vessels. They have thick walls composed mainly of elastic tissue to allow the artery to expand without bursting from high pressure of blood from the heart.
How are Arterioles adapted to their function?
Arterioles are the smallest arteries, and carry blood to one capillary bed each. They have thinner walls composed of mainly smooth muscle tissue to regulate blood flow to the capillary bed by vasodilation or vasoconstriction.
How is vasodilation and vasoconstriction in the Arterioles controlled?
They happen constantly under the involuntary control of the medulla in the brain.
How are capillaries adapted to their function?
Capillaries are where the transported substances enter and leave the blood. They have one cell thick walls and there are a vast number of them, giving them a short diffusion path and a high SA:V ratio to aid diffusion between cells and blood.
How are veins adapted to their function of carrying blood from tissues to the heart?
Venules collect blood from capillary beds and feeds into larger veins. The blood has lost all pressure in the capillary beds so it is moving slowly through the veins so they do not need thick walls and have large lumen instead to reduce resistance to flow. They also have semi lunar valves to stop blood back flow.
How is blood carried up from the legs through veins if there is low pressure?
Contractions of the leg and abdominal muscles force blood up
How does cross sectional area of the vessels vary as they branch smaller and smaller?
The cross sectional area increases due to the increasing number of them as they branch out
How does the velocity of blood flow change as it flows through smaller vessels?
As blood reaches capillaries, the velocity decreases to give more time for and improve diffusion
How does pressure change as blood flows through he body?
Blood pressure decreases the further the blood is from the heart.
Through what are substances transferred from blood to cells?
Tissue fluid which surrounds all cells
Explain the process through which tissue fluid is formed
Pressure Filtration; At the arterial end of the capillary bed the blood pressure is still high so blood plasma is forced out of the permeable walls, but not cells or proteins because they are too big.
What are the four methods of transport across a cell membrane and what do they transport from the blood to tissue fluid?
- Gases and lipid soluble substances by lipid diffusion
- Water by osmosis
- Ions by facilitated diffusion
- glucose and amino acids by active transport
What occurs at the venous end of the capillary bed?
Blood and tissue fluid have the same pressure, so tissue fluid diffuses back into the blood, bringing water and solutes back into the water.
What happens to the excess tissue fluid which does not return to the blood?
It drains into lymph vessels, forming lymph.
How is movement of lymph in the lymphatic system stimulated?
Through muscular contraction much like veins, and semi lunar valves.
What is the lymphatic system?
A network of lymph vessels running along side blood vessels that lead toward the heart where lymph drains back into the blood.
What are the three fu cations of the lymphatic system?
- To drain excess fluid
- absorbs fats into the small intestine via the lacteals in the villi
- Part of the immune system, lymph nodes are the location of white blood vessels.
What is plasma?
The liquid part of blood. Contains dissolved glucose, amino acids, salts, vitamins, and suspended proteins and fats.
What is Serum?
Purified blood plasma without blood clotting proteins.
What is tissue fluid?
Solution surrounding cells which is like blood plasma without as many proteins
What is lymph?
Solution inside lymph vessels, which is similar to tissue fluid but with more fats
How is oxygen carried in the blood?
Oxygen is carried by red blood cells by binding to a protein called haemoglobin
What is the composition of haemoglobin?
4 polypeptide chains with a haem prosthetic group at the centre of each chain
How does oxygen bind to haemoglobin?
Each haem group contains an iron atom which an oxygen atom can bind with
How many oxygen atoms can bind to each haemoglobin?
4
What is the chemical sign for deoxygenated haemoglobin?
Hb
What is the chemical formula for oxygenated haemoglobin?
Hb(O2)4
What shape does an oxygen dissociation curve have?
An s shape
How do human foetuses obtain oxygen and how do their haemoglobin differ from adults?
Through placenta. In placenta the mother and foetuses capillary beds are intertwined and feral haemoglobin has a higher affinity for oxygen at lower partial pressures.
Where is a foetuses oxygen dissociation curve in relation to an adults?
It is shifted upwards due to a higher affinity for oxygen at lower partial pressures
How does lugworm haemoglobin differ from adult humans?
It has a higher affinity for oxygen as the oxygen concentration in their burrows can fall very low
How does a lugworm oxygen dissociation curve differ from an adult human?
It shifts up.
How does mouse haemoglobin differ from humans?
It has a lower affinity for oxygen because they have a high metabolic rate due to rapid heat loss, so they need more oxygen to be supplied to their muscles at all times.
How do mouse oxygen dissociation curves differ from humans?
It is shifted down
What is the purpose of chloroplasts?
They are where photosynthesis takes place
Where are chloroplasts found?
Only in photosynthetic organisms
What is the space between the thylakoid membrane and the inner membrane of a chloroplast called?
Storms
Where is chlorophyll found?
Inside the thylakoid membrane
What is a vacuole?
Membrane bound sacs containing water or dilute solutions of salts and other solutes. Plant cells usually have permanent vacuoles filled with cell sap to help with rigidity
What is the cell wall?
A thick layer outside the cell that is permeable to solutes made of cellulose and other polysaccharides. They have channels called plasmodesmata which link the cytoplasm of adjacent cells
What is starch made of?
Amylose and Amylopectin.
What is the shape of starch and why?
A helix held together by hydrogen bonds because amylose is poly(1-4) glucose.
Starch is insoluble, what does that mean in terms of water potentials?
It does not change the water potential of other cells and does not cause cells to take up water by osmosis.
What is amylopectin made of and what significance does that have?
96% Poly(1-4) and 4% Poly (1-6) Glucose. This gives it a more open molecular structure with more ends and is thus faster to break down than amylose by amylase
What is glycogen?
The animal storage polysaccharide, similar to amylopectin but with 9% Poly(1-6) branches instead of 4%. This allows it to be quickly mobilised.
What does mobilisation mean in terms of glycogen?
Breaking down of glycogen into glucose for energy
What is glycogen broken down by?
Phosphorylase
What is cellulose used for and what is it made of?
It is found in plants as it is the main component of cell walls. It is poly(1-4) BETA glucose.
If cellulose is formed with a different isomer of glucose to glycogen and starch, what does that mean for its structure?
Beta glucose has a different position of the hydroxyl group on C1 so alternating glucose molecules are inverted, which means it is rigid and forms straight chains
What are micro fibrils?
Hundreds of cellulose chains linked together by hydrogen bonds
What are the properties of microfibrils?
They are very strong and rigid and give structure to young plants
What can beta glycosidic bonds be broken down by?
Cellulase
What are the main gas exchange surfaces in plants?
The spongy mesophyll cells in the leaves
How do the spongey mesophyll cells aid in gas exchange?
They give leaves a large internal surface area, so a higher overall SA:V Ratio
Through what do gases enter leaves?
Stomata
Where are stomata usually found?
Underside of leaves
What are guard cells?
Cells which enclose stomata that can close the stomata to avoid water loss
How are plants adapted to reduce water loss?
- The upper surface of the leaf is covered in a water proof cuticle, made of lipids secreted by the upper epidermal cells.
- Sub-stomatal airspace remains moist to reduce water concentration gradient for less evaporation
- Guard cells can close stomata to stop water loss
What is the potential problem of guard cells closing stomata for too long to reduce water loss?
This also stops gas exchange and consequently photosynthesis, so plants could die if closed for too long.
How is the palisade layer adapted for photosynthesis?
Thin cytoplasm densely packed with chloroplasts which can move around on the cytoskeleton to areas of greatest light intensity. The cells are closely packed together in rows to maximise light collection (but spongy layer still has chloroplasts in case any is missed)
What is evaporation from leaves called?
Transpiration
What is water transported through plants by?
Xylem vessels. Dead cells joined together to from long empty tubes made of lignin
What are the different tissues in the root?
- Epidermis
- Cortex
- Endodermis
- Pericycle
- Vascular Tissue
What is special about the epidermis of roots?
They have many long extensions called root hairs which increase the surface area
What is the cortex of the root?
A thick layer of packing cells often containing stored starch
What is the endodermis of the root?
A single layer of cells containing a water proof layer called the casparian stripes prevent movement of water between cells
What is the Pericycle layer of the root?
A layer of undifferentiated meristematic growing cells
What is the vascular tissue of a root?
Contains the xylem and phloem cells which are continuous with the stem vascular bundles.
What is the symplast pathway?
It consists of the living cytoplasms of the cells in the root. Water is absorbed into root hairs through the rest of the root to the xylem down a water potential gradient, via the plasmodesmata connecting the cell walls.
What is the apoplast pathway?
Diffusion (not osmosis due to no membranes) of water through cell walls. Ends at the endodermis due to the casparian strip so the water crosses the membrane and joins the symplast to reach the xylem
What is root pressure?
A force that pushes water up the xylem which is caused by The uptake of water by osmosis and can be measure by putting a manometer over a cut stem.
What is guttation?
Where water is forced out of the ends of leaves due to root pressure
Through what method does water move through the stem and why?
Mass flow, because xylem is made of dead cells so osmosis can not occur.
What is the driving force for the mass flow in the stem?
Transpiration; it causes low pressure in the leaves so water is sucked up to replace it.
What is the name of the mechanism of pulling water up a stem?
Cohesion-Tension Mechanism
How does the water column not break under the stretching force of being sucked up the stem?
Water gas a high tensile strength due to the tendency of water molecules to stick together by hydrogen bonding (cohesion)
How water moves through the leaves?
Diffuses down the water potential gradient to the leaf from a branching system of vessels called leaf veins, using both symplast and apoplast pathways
What happens after water has diffused into the spongey layer of leaves?
Water evaporates from the spongy cells into the sub stomata air space and diffuses out through the stomata.
Why do guard cells have chloroplasts?
So they can photosynthesise and produce ATP and use that to drive active transport ion pumps to open or close their stoma
How do guard cells use active transport ion pumps to open their stoma?
The guard cells pump ions into the cell which lowers their water potential so water enters by osmosis. The cells become turgid and bend apart so the stoma opens
How do guard cells close the stoma?
They use active transport ion pumps to pump ions out of the cell raising the water potential so water leaves by osmosis. The cells become flaccid and straighten out closing the stoma
Explain the entire mechanism of water movement in plants
Energy from the sun causes water to evaporate from spongy cells and diffuse from leaves, lowering the water potential in leaves so water diffuses from xylem to leaves, which lowers the pressure in the xylem so water is sucked up by the cohesion tension mechanism, which decreases the water potential in the root xylem so water diffuses from root cells to xylem, which decreases the water potential in the root cells so water diffuses into the roots from the soil by osmosis.
What is the rate of transpiration measured by?
A potometer
What does a potometer do?
Measures the rate of uptake of water in a cut stem
How does temperature affect the rate of transpiration?
High Temp increases the rate of evaporation of water from the surface of spongy cells because it increases the kinetic energy of the water molecules. The raises the water potential in the sub stomatal air space and molecules are moving faster so transpiration increases
How does humidity affect transpiration?
High humidity means a higher water potential in the air surrounding the stomata so a lower water potential gradient between the sub stomatal air and the air outside so less evaporation so less transpiration.
How does air movement affect the rate of transpiration?
Wind blows away saturated air around stomata, replacing it with dry air, increasing the water potential gradient so higher rate of transpiration
How does light affect the rate of transpiration?
Light stimulates plants to open their stomata to allow gas exchange for photosynthesis, so water is also lost which increases the rate of transpiration
