Topic 4

Question 1

facilitated diffusion

Answer 1

passive transport of certain larger substances from a high to low concentration at channel proteins and carrier proteins without the use of energy until evenly distributed

Question 2

channel proteins

Answer 2

involved in facilitated diffusion, allows water soluble substances e.g. ions through

Question 3

carrier proteins

Answer 3

involved in facilitated diffusion and active transport allows medium sized molecules through e.g. glucose

Question 4

water potential equation

Answer 4

Water potential = turgor pressure + osmotic potential

ψ = P + π

Question 5

water potential

Answer 5

measure of the potential of water to move out of a solution by osmosis

Question 6

turgor pressure

Answer 6

inward pressure exerted by the cell wall on the protoplasm as a result of hydrostatic pressure from water entering cell by osmosis (usually positive)

Question 7

osmotic pressure

Answer 7

potential of a solution to cause water to move across the partially permeable membrane (always negative)

Question 8

lenticels

Answer 8

spongy tissue underneath bark which are site of gas exchange in woody stems and roots

Question 9

to open stomata

Answer 9

turgid guard cells

thin part of cellulose cell wall stretches more than thick part

Question 10

cardiac cycle (3)

Answer 10

1. Ventricular diastole (T):
   Ventricles are relaxed so blood enters atria and pressure rises
   When pressure in the atria is higher than in the ventricles, atrioventricular valves open allowing blood into the ventricles
2. Atrial systole (P):
   Atrial walls contract to force blood into ventricles
3. Ventricular systole (QRS):
   Ventricular walls contract increasing pressure
   Atrioventricular valves close preventing blood from re-entering atria
   When pressure in ventricles are higher than in the arteries, semi-lunar valves open and blood is forced out of the heart

Question 11

how is heart beat controlled (6)

Answer 11

Myogenic so no stimulation from the brain and generated from the heart

1. Sinoatrial node in right atrium generates action potential, depolarisation causes atria to contract
   (2. Non-conducting tissue called annulus fibrosus delays passage of impulse to ventricles)
2. Action potential is delayed by atrioventricular node
3. Passes down a group of fibres called purkinje fibres (collectively, Bundle of His) to stop atria contracting before ventricles start contracting
   (5. Bundle of His splits into two and carries impulses to Purkyne tissue)
4. Impulse reaches base of the ventricles so they start contracting from the bottom so there is no blood trapped at the bottom of the ventricles

Question 12

two types of white blood cells (leucocytes)

Answer 12

o Granulocytes contain granules and have lobed nuclei, non-specific immune response
o Agranulocytes do not contain granules (so do not take up stain) and have unlobed nuclei for specific immune response

Question 13

granulocytes

Answer 13

Neutrophils engulf and digest pathogens by phagocytosis

Eosinophils for developing immunity and against parasites, allergic reactions and inflammation

Basophils have two lobed nuclei and produce histamine in inflammation and allergic reactions

Question 14

agranulocytes

Answer 14

Monocytes move out of blood to form macrophages and engulf pathogens

Lymphocytes produce antibodies e.g. T cells and B cells

Question 15

forming blood clot and clotting cascade

Answer 15

• Plasma, blood cells and platelets flow out of a cut blood vessel
• Platelets break open when in contact with collagen fibres in skin, releasing serotonin and thromboplastin
- Serotonin: causes smooth muscle of blood vessel to contract to cut off blood flow
- Thromboplastin: enzyme which triggers cascade of events leading to clot formation

Blood clotting cascade: (requires vitamin K)
• Thromboplastin catalyses (soluble) prothrombin to (soluble) enzyme thrombin, requires Ca2+ ions
• Thrombin catalyses fibrinogen to become (insoluble) fibrin, forming a mesh of fibres that covers the wound
• More blood cells and platelets are trapped in the mesh forming a clot
• Proteins in the structure of platelets contract, making the clot tighter/ tougher, forming a scab

Question 16

how is artherosclerosis caused

Answer 16

o Caused by high blood pressure (strain on cells) and chemicals in tobacco smoke
o Inflammatory response occurs where white blood cells arrive at site
o Fibrous tissue and calcium salts deposit forming hardened plaque which hardens artery wall (less elastic)
o Narrowing of the lumen results in higher blood pressure so further damage is more likely

Question 17

factors that increase risk of artherosclerosis (6)

Answer 17

genetics, age (more time, higher bp), male (oestrogen reduces plaque building up), smoking, lack of exercise
stress

Question 18

transport of CO2

Answer 18

CO2 diffuses and dissolves into cytoplasm of RBC and reacts with water to form carbonic acid, dissociates releasing H+
CO2 + H2O + carbonic anhydrase H2CO3 H+ + HCO3-
chloride shift: HCO3- diffuse out and Cl- diffuse in from plasma

carried in haemoglobin to form carbaminohaemoglobin

Question 19

myoglobin

Answer 19

respiratory pigment globular protein found in muscle tissue with a higher affinity for O2 at low O2
only one subunit
dissociation curve is not S shaped

Question 20

function of tissue fluid

Answer 20

supplies oxygen/ glucose so respiration can occur

removes CO2/ urea so pH is controlled/ cells not poisoned

Question 21

compare lymph vessels and veins

Answer 21

both have valves and carry at low pressure

lymph vessels have faster flow than veins

Question 22

cambium

Answer 22

layer of unspecialised cells that divide to form the xylem and phloem

Question 23

schlerenchyma

Answer 23

strengthening tissue with thick lignified cell walls and empty lumen for structural support and do not have end plates

Question 24

parenchyma

Answer 24

provide support by acting as packing in stems and roots

Question 25

collenchyma

Answer 25

cells with areas of cellulose thickening which provide mechanical strength and support

Question 26

xylem structure (5)

Answer 26

- cellulose cell walls held by hydrogen bonds contain helical lignin that hold together microfibres to keep fibres parallel - mesh of microfibrils for structural support to withstand water pressure - large cross sectional area to transport large volumes - empty cells with no cytoplasm so low resistance - pits are holes on xylem walls that allows sideways movement

Question 27

symplastic pathway

Answer 27

through the cytoplasm and plasmodesma of the root cells by osmosis (via cell wall and cell membrane first)

Question 28

apoplastic pathway

Answer 28

through the permeable cell walls (faster) by diffusion but will stop at the impermeable Casparian strip so is forced upwards to the symplast pathway non-living

Question 29

translocation

Answer 29

Fructose (synthesised form GALP) + glucose = sucrose 1. Sucrose passes from the source into companion cells by facilitated diffusion 2. H+ ions pass from companion cells into the phloem by active transport 3. H+ ions diffuse into sieve elements and carries sucrose by co-transport which lowers water potential in the sieve tubes 4. Higher water potential in the xylem means water moves into the phloem by osmosis, increasing the hydrostatic pressure 5. Respiring cells have a low concentration of sucrose so sucrose enters which lowers water potential causing water to move in and lower the hydrostatic pressure in the sieve tubes 6. High hydrostatic pressure at the source and a low hydrostatic pressure at the sink 7. Mass flow of sucrose solution from source to sink 8. Sucrose actively transports by the companion cells out of the sieve tubes and into the sink cells