Topic 4

Question 1

Ficks Law?

Answer 1

The rate of diffusion is proportional to =

(SA:V x difference in concentration) / Distance of diffusion pathway.

Question 2

mass flow?

Answer 2

the fast movement of a fluid due to a force. Hence it uses ATP

Question 3

Describe and explain the fluid mosaic model

Answer 3

The plasma membrane is a mosaic of phospholipids, cholesterol and proteins that move fluidly and freely in the membrane.
Phospholipid: a lipid made of glycerol, 2 fatty acid tails and a phosphate linked head. The head is hydrophilic hence faces outwards, the tail is hydrophobic hence faces inwards in the phospholipid bilayer.
Cholesterol: found along side phospholipids and minimises the effects of temperature on fluidity.
Membrane proteins: channel proteins, integral proteins
Glycoproteins: carbohydrates attached to proteins. only found on outer surface.
Glycolipids: carbohydrates attached to phospholipids, only found on outer membrane.

Question 4

What is a saturated and unsaturated fatty acid tail?

Answer 4

Saturated = single carbon bond
Unsaturated = double carbon bond. This causes a kink.
At cooler temperatures, the straight tails of the saturated fatty acids can pack tightly together, making a dense and fairly rigid membrane.

Question 5

What is passive transport?

Answer 5

movement of molecules that does not require ATP.

Diffusion: movement of particles in a liquid or gas down a concentration gradient.
Facilitated Diffusion: diffusion that takes place through protein channels, because the substances have a strong charge or are large molecules.
Osmosis: movement of solvent molecules down a concentration gradient. Water from a high to low concentration.

Question 6

What is active transport?

Answer 6

ATP provides the energy needed. It is hydrolised to provide an accessible supply of energy for biological processes.

Active transport is the movement of molecules up a concentration gradient.
Endocytosis: the movement of large molecules into cells through vesicle formation
Exocytosis: movement of large molecules out of cells through vesicle formation.

Question 7

Water potential equation?

Answer 7

Water potential = turgor pressure + osmotic potential.

Water potential: a measure of the potential for water to move out of a solution by osmosis.
Turgor pressure: a measure of the inward pressure exerted by the plant cell wall on the protoplasm of the cell as the cell contents expand and press outwards, a force which opposes the entry of water by osmosis.
Osmotic potential: a measure of the potential of a solution to cause water to move into the cell across a partially permeable membrane as a result of dissolves solutes.

Question 8

How is the human body adapted to have a fast rate of diffusion in their gas exchange system?

Answer 8

large SA; 600million alveoli = 100m2. Hence large surface area
Short Diffusion Pathway: 2 cell diffusion pathway of squamous alveolar epithelium and capillary epithelium.
High Concentration gradient: Good blood flow.
TIdal ventilation keeping gas diffusion concentration.

Question 9

How does ventilation in the lungs occur?

Answer 9

1. The diaphragm contracts and flattens
2. The external intercostal muscles contract pulling the ribs up and out.
3. The volume of the thorax increases
4. Hence pressure decreases causing air to enters the lungs down a pressure gradient.
5. The diaphragm relaxes and returns to dome shape.
6. External intercostal muscles relax. Ribs move down.
7. Volume of thorax decreases.
8. Hence pressure in thorax increases, causing air to leave lungs.

Question 10

Why is gas exchange more difficult for fish?

Answer 10

Gas exchange is more difficult because concentration of O2 is less than 1% in water. And water is more dense and viscous than air.

Question 11

How are fish adapted to have a fast rate of diffusion in their gas exchange system?

Answer 11

large SA: Thousands of filaments covered in thousands of lamellae.
Short Diffusion Pathway: Thin epithelial walls in lamellae pathway.
High Concentration Gradient: Countercurrent exchange; the water and blood flow in opposite directions. Hence more than 50% of the O2 in the water can diffuse in the blood. Gives a high concentration gradient.

Question 12

How does ventilation in Fish occur?

Answer 12

1. Mouth opens, causing volume in buccal cavity to increase
2. Hence pressure in buccal cavity decreases. The Opercular valve is closed.
3. Hence water flows through mouth and over gills.
4. The mouth closes, causing buccal volume to decrease.
5. Hence pressure in buccal cavity increases. The Opercular valve opens.
6. Hence water flows over gills and out through the opercular valve.

Water flows in one direction to conserve energy as water is dense and viscous hence it would take too much energy to reverse its flow.

Question 13

How are insects adapted to have a fast rate of diffusion in their gas exchange system?

Answer 13

large SA: Many spiracles
Short Diffusion pathway: Single cell for air to diffuse from tracheole directly into muscle cells.
High Concentration gradient: Low concentration of O2 in muscle cells due to aerobic respiration.

Question 14

How does ventilation in insects occur?

Answer 14

Small insects: Air enters the open spiracles and O2 diffuses down the trachea due to the steep concentration gradient from respiring muscle cells. This is enhanced b the air sacs which act as bellows.

Large Insects: Muscles relax abdomen increasing volume.
This decreases pressure causing air to move into the trachea through open spiracles.

Can open/close spiracles with sphincters. Hence controlling rate of gas exchange and minimising water loss. Spiracles open when the concentration of CO2 raises.

Question 15

How are plants adapted to have a fast rate of diffusion in their gas exchange system?

Answer 15

Large SA: Broad shape oaf leaves
Short Diffusion Pathway: Thin leaf. Spongy mesophyll provides air spaces hence rapid diffusion.
High concentration gradient: ventilated by the wind

Question 16

Ventilation in plants?

Answer 16

Respiration occurs constantly. Photosynthesis occurs during the day.
Stomata open to allow gas exchange.
Guard cells close the stomata when flaccid and open the stomata when turgid.
They balance the conflicting needs of water loss and need for gas exchange.

Question 17

Diagram of the human heart?

Answer 17

Diagram????

LHS is more muscular to generate more force to generate more pressure to pump the blood around the whole body.
Hear tissue is made of cardiac muscle, which does not tire.

Question 18

What do arteries do? What is their structure?

Answer 18

Carries blood? From heart to capillaries. Oxygenated except pulmonary artery.
Blood pressure? high
Structure? Thick muscle layer to withstand high pressure. Smooth endothelial interior to reduce friction. Elastic for stretch and recoil. Small lumen to maintain high pressure.
Valves? No. Blood is under enough pressure to prevent backflow

Question 19

What do capillaries do? What is their structure?

Answer 19

Carries blood? Arteries to veins. Oxygenated and deoxygenated.
Blood Pressure? low
Strucuture? One cell thick and permeable to allow substance exchange.
Very small lumen. Wide enough for one RBC.
Valves? No. Too Small

Question 20

What do veins do? What is their structure?

Answer 20

Carries blood? From capillaries to heart. Deoxygenated except pulmonary vein.
Blood Pressure? lowest
Structure? Little muscle and elastic tissue.
Very smooth endothelium to reduce friction.
Large lumen to reduce friction.
Valves? Yes. Low pressure hence needed to prevent backflow.

Question 21

Why is the circulatory system in humans double?

Answer 21

Circulatory system in humans is ‘double’ because blood is pumped twice in the heart before travelling around the whole body. . THis is advantageous because:
It maintains a higher pressure as blood is pumped twice.
Maintains a steeper concentration gradient by separating oxygenated and deoxygenated blood.

Question 22

What is the cardiac cycle?

Answer 22

Diastole:

• Atriums and ventricles relax.
• Heart fills with blood.
• Atrioventricular valves open.
• Semilunar valves close (DUH sound)

Atrial systole:

• Sinoatrial node (SAN) sends out a wave of electrical excitation. This causes the atria to contract.
• Hence blood flows into ventricles.
• Atrioventricular valves open.
• Semilunar valves closed.

Ventricular systole:

• Atrioventricular node(AVN) delays transmission. So the the atria can fully empty.
• AV valves shut (DUM sound)
• Wave of depolarisation passed from AVN to bundle of his.
• Depolarisation reaches purkinje fibres causes ventricles to contract.
• Semilunar valves are open so blood flows into arteries.

The cardiac cycle is myogenic. It can contract on its own without needing nerve impulses.

Question 23

Cardiac output equation?

Answer 23

Cardiac output (cm3.min-1) = heart rate (beats.min-1) x stroke volume (cm3.beat-1)

Question 24

Electrocardiogram?

Answer 24

THe Electrocardiogram records electrical activity of the heart. X axis = time. Y axis = millivolts. 
P = depolarisation from SAN
Q = purkinje fibre excitation
R = start of ventricular systole. 
S = ventricles fully contracted. 
T = ventricle relaxation.

Question 25

What is the structure of the blood?

Answer 25

Plasma: fluid of the blood. It transports: hormones, glucose, RBC, WBC, platelets, water, urea….

Thrombocytes (platelets): cell fragments involved in clotting.

Erythrocytes (RBC): transport oxygen. They are enucleated, contains haemoglobin, biconcave shape.

Leucocytes(WBC): immune response.

Question 26

How do blood clots occur?

Answer 26

Platelets clump forming a plug.
Clotting factors are released including thromboplastin which catalyses the conversion of plasma protein prothrombin into enzyme thrombin.
Thrombin catalyses the conversion of soluble fibrinogen into insoluble fibrin.
Fibrin forms a strong mesh strengthening plug.

Question 27

What are the types of white blood cells?

Answer 27

Basophils, neutrophil, eosinophils, monocytes, lymphocytes.

Question 28

What is atherosclerosis?

Answer 28

damage to an artery leads to low density lipoproteins accumulating within the wall of the arteries to form fatty plaques (atheroma) The atheroma can harden and calcify. This is atherosclerosis. These bulge into the lumen of the artery causing ti to narrow and results in reduced blood flow.

Question 29

What is haemoglobin?

Answer 29

Quaternary structure. ( 2 alpha, 2 beta = 4 polypeptide chains.)
Conjugated protein: prosthetic group = haem.

Haemoglobin transports O2. It associates with O2 when it has a high affinity at the gas exchange surface. It dissociates with O2 at respiring tissues when CO2 causes the shape of haemoglobin to change.

Question 30

Why is the fetal haemoglobin oxygen affinity curve shifted left?

Answer 30

Fetal hemoglobin has a higher affinity for O2 so its curve is shifted left. So O2 unloaded by mothers hemoglobin in placenta binds to fetal haemoglobin.
Myoglobin is found only in muscle cells, it has a higher affinity for O2. hence curve shifts left.

Question 31

Why does high CO2 cause the oxygen affinity curve to shift right?

Answer 31

Co2 reacts with water to form carbonic acid = lower PH.
Hence haemoglobin changes shape lowering its affinity for O2.
Curve shifts right s Hb dissociates at higher partial pressures of O2.

Question 32

What is tissue fluid? how is is formed?

Answer 32

The interchange of substances occurs through the formation and reabsorption of tissue fluid.
Tissue fluid is anything small enough to move through capillary walls. I.e plasma - large proteins.

FORMATION: Tissue fluid is formed at arterial end of capillary bed. Residual pressure from heartbeat forces tissue fluid out of capillary walls. This is pressure filtration. Hydrostatic pressure is greater than oncotic pressure.
REABSORPTION: at venue end of capillary bed, oncotic pressure is higher than hydrostatic pressure. Water moves in by osmosis, solutes move in by diffusion. Excess tissue fluid drains into the lymphatic system.

Question 33

What is the structure and function of the xylem?

Answer 33

The xylem is more central than the phloem.
It transports water and dissolved mineral ions UPWARDS.
Large cross sectional area (to transport large volumes of H2O)
Dead cells, continuous columns( low resistance to flow)
Wall strengthened with lignin (to prevent collapse)

Question 34

What is the strict and function of the phloem?

Answer 34

The phloem further out than the xylem.
Transports sugar and metabolites (cell sap) UPWARDS & DOWNWARDS
Sieve tube cells and few organelles (low resistance to flow)
Sieve plate - perforated walls (allows sap to flow)
Companion cells (active transport into sieve tube cells)

Question 35

how is water transported through the roots?

Answer 35

Water moves into root hair cells via osmosis across a semipermeable membrane down a water potential gradient.
Root pressure: a small pressure pushing water a short way up the xylem. It results when salts are actively secreted from the root cells to the xylem sap.
Symplastic pathway: water is moved through cytoplasm connected by plasmodesmata, down a water potential gradient. It moves through living cells via cytoplasm.
Apoplastic Pathway: water is transported through non-living gaps, down a water potential gradient.
Casparian Strip: blocks apoplastic pathway. It has a waxy substance called suberin which blocks water.

Question 36

How is water transported through the stem?

Answer 36

Cohesion tension theory:
Water evaporates from leaf via transportation.
Water moves out of xylem into spongy mesophyll layer by osmosis.
This creates a water potential gradient in the leaf, and water is drawn out of the xylem.
This creates tension, due to cohesion.
Water molecules form a continuous unbroken column from the mesophyll down to xylem and root. Water doesn’t flow backwards due to adhesion to xylem walls.

Question 37

What is cohesion?

Answer 37

water molecules attract other WATER molecules due to hydrogen bonding.

Question 38

What is adhesion?

Answer 38

water molecules attract other molecules and surfaces due to hydrogen bonding

Question 39

What is transpiration? Why does it occur?

Answer 39

The evaporation and diffusion of water out of the stomata. WHY?:
This requires kinetic energy, so keeps the leaf COOL
Supplies water, which is a reactant in PHOTOSYNTHESIS.
Mineral ions are carried in the water up the xylem vessels.
Keep cells turgid.

Question 40

What factors affect the rate of transpiration?

Answer 40

Increased temperature= Increased transpiration = molecule have more kinetic energy. So the particles move faster increasing the rate of evaporation and diffusion out of the stomata.

Increased humidity= decreased transpiration = shallower diffusion gradient of water vapour across the stomata.

Increased wind speed = increased transpiration =
blows water away maintaining a steep diffusion gradient of water vapour across the stomata.

Increased light intensity =
increased transpiration = opens the stomata which increases the rate of evaporation out of the leaf.

Question 41

Explain the mass flow hypothesis.

Answer 41

Transport of sucrose in plants occurs in the phloem from production sites in source cells to store sites called sink cells.
At source cells: sucrose is actively transported into the phloem vessels by companion cells. This decreases the water potential in the phloem.
Hence water moves from the xylem to the phloem by osmosis. THis increases the hydrostatic pressure in the phloem so water and dissolves solutes are forced downwards. (MASS FLOW)
At sinks: sucrose is transported from the phloem by diffusion or active transport in the root cells. This increase water potential in the root phloem.
Hence the xylem has a lower water potential that the phloem so water moves by osmosis from the phloem to the xylem. Water and its dissolved ions are moved up the xylem by tension.

Question 42

What is translocation?

Answer 42

Translocation: the transport of solutes in the phloem.

Question 43

Strengths of the mass flow hypothesis?

Answer 43

The concentration of sucrose is higher in the leaves (source) than roots (sink)
Companion cells contain mitochondria to produce ATP.
Downward flow in the phloem occurs in the day but not at night.
There is pressure within the sieve tubes, as shown by sap being released when they are cut.
Metabolic poisons/ lack of O2 inhibit translocation of sucrose in the phloem.
Increases in sucrose levels in the leaf are followed by increases in the phloem.

Question 44

Weaknesses of the mass flow hypothesis?

Answer 44

Sucrose is delivered at the same rate to all regions.
Not all solutes move at the same speed
The function of the sieve plates is unclear, as they would seem to hinder mass flow. ( function may be structural to prevent tubes from bursting under pressure)