Biology- Unit 4

Question 1

Describe diffusion

Answer 1

The passive movement of small
Non-polar
Lipid-soluble molecules
Directly through phospholipid bilayer

Question 2

Describe facilitated diffusion

Answer 2

Requires channel proteins
Polar
Charged
Water-soluble molecules

Question 3

Describe osmosis

Answer 3

The movement of water molecules
From low solute conc to High solute conc
Through partially permeable membrane

Question 4

Describe active transport

Answer 4

Can transport all types of molecules
Through carrier proteins
Low conc. to high conc.
Requires ATP

Question 5

Describe endo and exocytosis

Answer 5

Transport large particles

Enclosed in vesicles

Question 6

What is turgor pressure?

Answer 6

Inward pressure caused by protoplasm expanding
Generates hydrostatic pressure
Generates reactive force pushing inwards
Prevents water from moving into a cell

Question 7

What is the relationship between water potential, osmotic pressure and turgor pressure?

Answer 7

Water potential= osmotic pressure + turgor pressure

Question 8

Describe exhalation

Answer 8

Intercostal muscles and diaphragm relax
Volume increases
Pressure decreases
Air diffuses out down pressure gradient

Question 9

How do insects intake oxygen?

Answer 9

Openings called spiracles
Oxygen diffuses down trachea
Trachea lined with rings of chitin so gas exchange doesn’t occur here
Oxygen diffuses into tracheoles

Question 10

How do fish intake oxygen?

Answer 10

Countercurrent exchange system
Water is pumped over gills covered in lamellae
Operculum (gill flap) closes
Floor of fish mouth is raised to increase pressure

Question 11

Describe the structure of the heart

Answer 11

Four chambers- atria, ventricles
Pulmonary vein
Pulmonary artery
Vena cava
Aorta
Atrioventricular valves- bicuspid, tricuspid
Semilunar valves- pulmonary/ aortic

Question 12

What is a single circulatory system?

Answer 12

System where blood is only pumped once

Question 13

What is a double circulatory system?

Answer 13

System where blood is pumped twice i.e heart to lung, heart to body

Question 14

What are the advantages of a double system?

Answer 14

Concentration gradient is maintained as oxy and deoxy blood don’t mix
Blood pressure in tissues is higher
Blood pressure in lungs is lower

Question 15

How does the heart contract?

Answer 15

Myogenic
1) Deopolarisation of senatorial node (SAN)
2) Depolarisation spreads through atria- causes atrial systole
Stimulates Atrioventricular node (AVN)
3) Slight delay for atrial diastole- AVN depolarises conductive fibres Bundle of His
5) Bundle of His splits into two branches- Purkyne fibres- causes ventricle systole

Question 16

What is the function of plasma?

Answer 16

Transports digested food products, nutrient molecules, hormones, excretory products

Question 17

What is the function of erythrocytes (RBC)?

Answer 17

Transport oxygen and some carbon dioxide

Adapted via their biconcave shape and lack of nucleus

Question 18

What is the function of leucocytes (WBC)?

Answer 18

Granulocytes-
Neutrophils (phagocytosis)
Basophils (inflammation)
Eosinophils (parasites)

Agranulocytes-
Monocytes
Lymphocytes

Question 19

What is the function of platelets?

Answer 19

Blood clotting

Question 20

Describe how blood clots

Answer 20

1) When a blood vessel is damages, platelets attach to exposed fibres
2) Platelets release thromboplastin- converts prothrombin into thrombin (Ca+ and vitamin K must be present)
3) Thrombin catalyses the conversion of fibrinogen into fibrin
4) Fibrin forms a network of fibres in which blood cells are trapped to form a clot

Question 21

Describe atherosclerosis

Answer 21

1) The endothelium is damages by high cholesterol, smoking, high BP
2) Increases risk of blood clotting in the artery, leads to inflammatory response, WBC move to artery
3) WBC, cholesterol, Ca salts and fibres build up and harden- plaque (atheroma)
4) Leads to narrowing of artery, increasing BP

Question 22

Describe how foetal haemoglobin is different to adult haem

Answer 22

Higher affinity for oxygen

Question 23

What is myoglobin?

Answer 23

Respiratory pigment with a higher affinity for oxygen than haemoglobin

Question 24

What is hydrostatic pressure?

Answer 24

Residual pressure from heartbeat

Higher at arterial end of capillary than venous end

Question 25

What is oncotic pressure?

Answer 25

Relatively constant | Higher at venous end than arterial end

Question 26

Describe the structure of the Xylem

Answer 26

Dead tissue with open ends Transport water and minerals Provide structural support Contain pits which enable water to move sideways Lignin enable the plant to remain flexible

Question 27

Describe the structure of the Phloem

Answer 27

Living cells Translocation- movement of nutrients to storage organs Sieve tubes to transport sugars Companion cells produce ATP for sieve cells

Question 28

What is the symplast pathway?

Answer 28

Moves through cytoplasm via plasmodesmata

Question 29

What is the apoplast pathway?

Answer 29

Moves through cells walls and intercellular spaces which are permeable

Question 30

Describe movement of water in the xylem

Answer 30

Cohesion-tension model 1) Water moves through root hair cells via osmosis 2) Water moves through xylem through either symplast of apoplast 3) Once the water reaches the Casparian strip (waterproof) it must travel via symplast 4) water reaches xylem, transpiration stream 5) Evaporation causes hydrostatic pressure, tension moves down column due to cohesion 7) Water evaporates from mesophyll cell walls

Question 31

What is cohesion?1

Answer 31

Attraction between molecules, water forms hydrogen bonds with other molecules of water

Question 32

What is adhesion?

Answer 32

Attraction between unlike molecules, water forms hydrogen bonds with mesophyll cells

Question 33

Describe movement in the phloem

Answer 33

Mass flow hypothesis 1) Sucrose is moved from source (high sugar conc.) to the sink (low sugar conc.) 2) Sucrose can be loaded into the phloem via the symplast or apoplast pathway 3) Sucrose is unloaded passively

Question 34

What factors affect the rate of transpiration?

Answer 34

Air movement Humidity Temperature Light intensity

Question 35

What are the strengths and weaknesses of the mass flow hypothesis?

Answer 35

Strengths- 1) Can use radioactive isotopes to track movement of sucrose through phloem 2) If steam is used to kill a ring of bark then movement stops in phloem 3) Aphids feed off phloem tubes- evidence of high hydrostatic pressure in phloem Weaknesses- 1) Doesn't explain bidirectional movement in sieve tubes 2) Doesn't explain how there is movement of different speeds in sieve tube 3) Doesn't explain presence of sieve plates 4) Doesn't explain how sieve and companion cells have to be alive for movement to occur.