organisms exchange substances with their environment

Question 1

Explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water.

Answer 1

• filaments/ lamellae= large SA
• large number of capillaries= maintain concentration gradient
• thin epithelium= short diffusion pathway
• pressure changes= bring in more water and to maintain gradient
• countercurrent= diffusion along whole length/ concentration gradient maintained/ blood always meets water with higher oxygen

Question 2

Describe and explain how fish maintain a flow of water over their gills.

Answer 2

1. mouth open, operculum shuts
2. floor of mouth lowered
3. water enters due to decreased pressure
4. mouth closes, operculum opens
5. floor raised results in increased pressure
6. increased pressure pushes water over gills

Question 3

Describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood.

Answer 3

1. alveoli= large SA
2. walls of alveoli are thin
3. thin capillary walls
4. cell membrane permeable to gases
5. many capillaries= large SA
6. cartilage rings keep airways open

Question 4

Describe how air is taken into the lungs.

Answer 4

contraction of muscles flattens diaphragm
contraction of intercostal muscles raises ribcage
increase in volume decreases pressure

Question 5

Describe the difference in the composition of gases in inhaled and exhaled air. Explain how these differences are caused.

Answer 5

1. inhaled air contains more oxygen than exhaled air
2. inhaled air contains less CO2 than exhaled air
3. inhaled air contains less water
4. relative amount of nitrogen also changes
5. respiration results in lower blood oxygen
6. oxygen enters blood
7. by diffusion
8. water vapour diffuses from moist surface

Question 6

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how.

Answer 6

1. sodium ions actively transport from the ileum to blood
2. maintains diffusion gradient for sodium to enter cells from gut
3. glucose enters by facilitated diffusion

Question 7

Describe how proteins are digested in the human gut.

Answer 7

1. hydrolysis of peptide bonds
2. endopeptidase break polypeptides into smaller peptide chains
3. exopeptidase remove terminal amino acids
4. dipeptidase hydrolyse dipeptides into small amino acids

Question 8

The epithelial cells that line the small intestine are adapted for the absorption of glucose. Explain how.

Answer 8

1. microvilli= large SA
2. many mitochondria produce ATP for active transport
3. carrier proteins for active transport
4. channel proteins for facilitated diffusion
5. co transport of sodium ion and glucose
6. membrane bound enzymes digest disaccharides to produce glucose

Question 9

Describe the role of the enzymes of the digestive system in the complete breakdown of starch.

Answer 9

1. amylase- starch to maltose
2. maltose to glucose
3. hydrolysis
4. of glycosidic bonds

Question 10

Describe the processes involved in the absorption of the products of starch digestion.

Answer 10

1. glucose moves in with sodium into epithelial cell
2. by carrier protein
3. sodium removed by active transport/ sodium potassium pump
4. into blood
5. maintaining low concentration of sodium in cell
6. glucose moves into blood
7. by facilitated diffusion

Question 11

Explain how tissue fluid is formed and how it may be returned to the circulatory system.

Answer 11

1. hydrostatic pressure of blood high at arterial end
2. water and soluble molecules pass out
3. proteins and large molecules stay
4. this lowers the water potential
5. water moves back into venous end of capillary
6. by osmosis
7. lymph system collects any excess tissue fluid
8. lymph returns to blood

Question 12

Gross structure of the heart

Answer 12

aorta
pulmonary artery
pulmonary vein
vena cava
atrium
ventricle

Question 13

structure and role of haemoglobin

Answer 13

1. quaternary structure
2. 2 alpha and beta proteins each containing a haem group
3. when oxygen binds to the haem groups it changes shape to make it easier for the next oxygen molecule to bind
4. first and fourth oxygen bind at high oxygen partial pressure

Question 14

the Bohr effect

Answer 14

the effects of carbon dioxide concentration on the dissociation of oxyhemoglobin
high CO2= low pH= low affinity of oxygen= more oxygen unloads = shift right

Question 15

common features of blood circulation in mammals

Answer 15

1. suitable medium (blood)
2. means of moving medium (heart)
3. mechanism to control flow around body (valve)
4. close system of vessels

Question 16

describe the cardiac cycle

Answer 16

atrial systole- aria contract, valves open and blood rushes into ventricles
ventricular systole 1st phase- valves close and ventricles is filled with blood
ventricular systole second phase- blood rushes through the pulmonary artery and aorta
ventricular diastole early- blood fills the atria
ventricular diastole late- all valves open and blood blood out passively

Question 17

describe lipid digestion

Answer 17

1. micelles contain bile salts and fatty acids/ monoglycerides
2. make fatty acids/ monoglycerides soluble
3. fatty acids/ monoglycerides absorbed by diffusion
4. triglycerides reformed in cells (Golgi modifies trig. and combines it with proteins to form vesicles)
5. vesicles move to cell membrane

Question 18

transpiration in xylem

Answer 18

• evaporation of water from plant surface
• evaporates from moist cell walls and builds up in spaces between cells in leafs
• stomata opens and moves through concentration gradient

Question 19

translocation in phloem

Answer 19

1. sucrose from photosynthesis actively transported to sieve tubes therefore low water potential
2. xylem has high water potential so water moves into sieve tubes via osmosis. this creates hydrostatic pressure
3. at sink, sucrose gets used up in respiration so actively transported from source to sink therefore low water potential creates pressure gradient pushing the solutes along

Question 20

cohesion theory

Answer 20

1. water evaporates from the cells and leaves of the plant once the stomata open
2. this creates a suction which pulls more water into the leaf
3. as water is cohesive due to hydrogen bonds when one molecule moves other tend to follow the column of the xylem and moves upwards
4. water enters through the roots

Question 21

ringing experiment and tracer

Answer 21

• phloem removed
• radioactive co2 given to plants
• no radioactive sucrose detected past the ringing point on stems
• radioactive tracers can also be used to track movement in plants

Question 22

tidal volume

Answer 22

volume of air we breathe in and out at each breath at rest

Question 23

breathing rate

Answer 23

number of breathes per minute