3.3 Organisms Exchange with their Environment

Question 1

surface area of a cube, cuboid and cylinder

Answer 1

cube (ll) * 6 sides
cuboid 2(lwlh*hw)
cylinder 2PiR + 2PiR~H

Question 2

3 adaptations of the tracheal system of an insect

Answer 2

1- tracheoles branched to increase surface area
2 - tracheoles have thin walls to reduce diffusion pathway
3 - in stages of movement, fluid is forced out the ends to allow for rapid diffusion

Question 3

3 adaptations of a xerophyte to prevent water loss

Answer 3

1 - sunken stomata to trap water vapour to reduce water potential gradient
2 - small/needle shaped to reduce surface area for water to be lost across
3 - waxy cuticle/waterproof which is impermeable to gases

Question 4

why is the metabolic rate higher in smaller organisms

Answer 4

the larger the surface area to volume ratio, the more heat loss, the more respiration needed to produce the heat lost

Question 5

how is the alveolar endothelium adapted

Answer 5

one cell thick epithelial layer to ensure short diffusion pathway
branched to increase surface area
very close to capillaries to ensure short diffusion distance and steep concentration gradient
moist lining so gases can easily dissolve across

Question 6

how is the atria different to ventricles

Answer 6

ventricles have thicker muscular walls to contract with enough force to provide the necessary pressure

Question 7

explain how air movement affects transpiration rate

Answer 7

a good airflow removes water vapour from the air so the concentration gradient between the leaf and air is maintained which increases water loss

Question 8

explain how humidity affects transpiration rate

Answer 8

causes less transpiration because if air is saturated with water vapour, the concentration gradient is weaker so less water is lost

Question 9

explain how light intensity affects transpiration rate

Answer 9

higher intensity causes more transpiration because the guard cells become turgid so the stomata open allowing water to be lost

Question 10

explain how temperature affects the rate of transpiration

Answer 10

the higher the temperature, the more transpiration occurs as particles have more kinetic energy so diffusion occurs faster

Question 11

define the hydrostatic pressure

Answer 11

the residual pressure from the heart beating which is created when blood is forced through the capillaries

Question 12

define oncotic pressure

Answer 12

the movement of fluid out of the capillaries which causes the water potential of the capillaries to decrease

Question 13

describe the process of tissue fluid formation

Answer 13

there is a high hydrostatic pressure at the arterial end of the capillary and the HSP inside is higher than that in the tissue fluid
this difference in pressure forces water and other small molecules out of the capillary to form tissue fluid
this causes the HSP in the capillary to decrease as water leaves it
the WP at the venue end is lower than the tissue fluid due to a loss of fluid and proteins remaining
some tissue fluid returns to the capillary from the venule end via osmosis
excess TF is drained into the lymphatic system

Question 14

explain a closed, double circulatory system

Answer 14

blood is confined to the vessels and passes twice through the heart for each complete circuit of the body

Question 15

simply, describe the journey of blood through the circulatory system

Answer 15

deoxygenated blood to the vena cava to the right atrium
out the right ventricle via the pulmonary artery to the lungs
oxygenated blood via the pulmonary vein from the lungs into the left atrium
out the left ventricle via the aorta to the body

Question 16

define myocardial infarction

Answer 16

when the coronary arteries are blocked so an area of the heart gets no blood so no oxygen can be used for respiration and the cells begin to die

Question 17

explain how the structure of an arteriole is related to its function

Answer 17

a tough fibrous outer layer resists pressure changes
a muscle layer which contracts to control and reduce blood flow
an elastic layer which recoils to maintain blood pressure
a thin endothelium which is smooth to reduce friction and thin for a short diffusion pathway

Question 18

explain how the structure of an artery is related to its function

Answer 18

a relatively thick muscle layer which constricts and dilates to control blood flow and thus the blood pressure
a comparatively thick elastic layer which stretches and recoils to help maintain high pressure
a large thickness which resists the vessel from bursting from pressure
no valves because the high pressure prevents blood from flowing backwards

Question 19

explain how the structure of a vein is related to its function

Answer 19

thin muscle layer because blood doesn’t flow to tissues so contraction/dilation isn’t necessary
thin elastic layer because they have a low blood pressure
small thickness because they have a low pressure
valves because the low pressure means blood might flow backwards

Question 20

explain the process of the movement of water across the cells of a leaf

Answer 20

mesophyll cells lose water to the air spaces by evaporation
the cells now have a lower WP so water enters them by osmosis from neighbouring cells
this lowers their water potential which, in turn, draws in more water from neighbouring cells by osmosis

Question 21

explain the process of transpiration

Answer 21

water evaporates from the mesophyll cells
due to cohesion, water molecules form hydrogen bonds between one another
due to adhesion, the water molecules form a continuous, unbroken stream down the xylem
more water is drawn up behind the stream as it evaporates
due to tension, the column of water is pulled up the xylem

Question 22

explain how a xylem vessel is adapted to its function

Answer 22

made of dead cells so water can move through unaffected
lignification which supports and strengthens the structure
no end walls so water can move in an unbroken and continuous tube

Question 23

what are bordered pits

Answer 23

cavities in the lignified walls for water to flow between vessels

Question 24

define a source and a sink

Answer 24

a source is a site of production of sugars
a sink is where the sugars will be used or stored for future use

Question 25

explain the mechanism of translocation

Answer 25

sucrose is made from the products of photosynthesis and diffuses down the CG by facilitated diffusion into the companion cells
H+ ions are actively transported from companion cells into spaces within cell walls
the ions then diffuse down the gradient into sieve tube elements
the sieve tubes have a lower WP so water moves from the xylem into sieve tubes by osmosis, creating a higher hydrostatic pressure
at the sink, sucrose is used so more is drawn in via active transport causing the hydrostatic pressure to decrease and increase at the source
as a result, a mass flow of sucrose occurs down the hydrostatic pressure gradient at STEs.

Question 26

what are companion cells responsible for

Answer 26

supporting sieve elements by carrying out respiration/metabolism

Question 27

describe the structural differences between companion cells and sieve tube elements

Answer 27

companion cells have a dense cytoplasm with lots of mitochondria and large nuclei but sieve tubes have little cytoplasm, no nucleus and ribosomes

Question 28

where are the atrioventricular valves and what is there function

Answer 28

between the left atrium and ventricle + between the right set
they prevent back flow by closing when contraction of the ventricles means ventricular pressure exceeds atrial pressure
this ensures that blood moves to the aorta and pulmonary artery instead of the atria

Question 29

where are the semi lunar valves and what is their role

Answer 29

they are in the aorta and pulmonary artery
they close to prevent back flow into ventricles when the pressure in vessels is higher than that in the ventricles
this occurs when the elastic walls of the vessels recoil and their pressure increases and when the ventricular walls relax to decrease their pressure

Question 30

define cardiac output

Answer 30

the volume of blood is pumped by one ventricle of the heart in one minute

Question 31

define stroke volume

Answer 31

the volume of blood pumped out at each beat

Question 32

how is the structure of the capillary related to its function

Answer 32

the walls consist mostly of the lining layer so there is a short diffusion pathway for a quick rate
they are numerous and highly branched which increases the surface area for exchange
narrow diameter so they can permeate tissues and ensure a short diffusion pathway to all cells
narrow lumen so they are close to cells for a short DP
there are spaces between the endothelial cells to allow white blood cells to escape in order to deal with infections

Question 33

state the equation for cardiac output

Answer 33

CO = Heart Rate * Stroke Volume

Question 34

explain the events in diastole

Answer 34

muscles in the heart relax
atrioventricular valves open because the atrial pressure has increased
blood therefore flows into ventricles
the atria are filled with blood
semi lunar valves remain shut as ventricular pressure is lower than the arteries

Question 35

describe atrial systole

Answer 35

atria walls contract
atrioventricular valves are open still
this forces the remaining blood into the ventricles from the atria
semilunar valves are shut

Question 36

describe ventricular systole

Answer 36

ventricles contract
av valves shut because the ventricular pressure has increased
semi lunar valves then open and blood is forced into the arteries

Question 37

describe the relationship between the position of the dissociation curve and oxygen affinity

Answer 37

the further the left the curve, the greater the affinity because oxygen was associated at lower partial pressures. the further the right the curve, the lower the affinity because oxygen was only associated at relatively high partial pressures.

Question 38

explain the Bohr effect of carbon dioxide on haemoglobin

Answer 38

the higher the rate of respiration the more carbon dioxide is produced by tissues
the large amount of carbon dioxide lowers the pH
the lower the pH the greater the HmG shape change
oxygen is thus more readily unloaded
so there is more oxygen available for respiration

Question 39

describe the structure of haemoglobin

Answer 39

proteins with a quaternary structure, each polypeptide chain is associated with a haem group that contains an Fe2+ ion which can combine with a single oxygen molecule

Question 40

state the site of association and dissociation

Answer 40

associating in the lungs where hmg binds with oxygen
dissociating in tissues where hmg releases oxygen

Question 41

what does a high and low affinity mean

Answer 41

high affinity means easy association and that it’s harder to dissociate
low affinity means easy dissociation and that it’s harder to associate

Question 42

explain the sigmoid shape of the oxyhemoglobin dissociation curve

Answer 42

1- the gradient is shallow because at low partial pressures oxygen, little oxygen can bind. this is because the hmg shape makes it difficult for the first oxygen molecule to bind to a haem group
2- after the first binding, the quaternary structure/shape changes which makes it easier for other fe2+ ions to bind. this means it takes a smaller increase in partial pressure oxygen for the second oxygen to bind than the first. the gradient steepens.
3- after the third binding, due to probability it is harder for the 4th molecule to bind because it is less likely to find an unoccupied site. the gradient reduces and flattens.

Question 43

describe the process of absorption of triglycerides

Answer 43

micelles come into contact with the epithelial cells lining the villi
this causes the break down of micelles to release monoglycerides and fatty acids
these are non polar so can easily diffuse across the cell surface membrane into epithelial cells

Question 44

define emulsification

Answer 44

when large lipid globules are broken down into several small lipid globules

Question 45

explain how hydrolysis of lipids occurs

Answer 45

lipase breaks down lipids via hydrolysis creating monoglycerides and fatty acids
these attach with bile to form micelles which carry fatty acids and monoglycerides into the intestinal endothelium via endocytosis
cholesterol is added across the molecule
micelles release the acids and MGs so they diffuse across the membrane into the cell due to non-polarity

Question 46

describe the 4 steps to carbohydrate digestion

Answer 46

1- salivary amylase hydrolyses starch in the mouth into maltose
2- this is swallowed into the stomach where acid denatures amylase and prevents any further hydrolysis of starch
3- once passed into the small intestine, pancreatic amylase continues hydrolysis of starch into maltose
4- when at the ileum, the epithelial lining produces maltase to hydrolyse maltose into alpha glucose

Question 47

explain the adaptations of villi for their function

Answer 47

they increase surface area for diffusion
very thin endothelial cells to reduce DP
muscular so can mix contents to maintain a CG
good supply of blood to maintain gradient
microvilli further increase SA for diffusion

Question 48

what does the smooth muscle in bronchi do

Answer 48

dilates when more air is needed and constrict when less air is needed

Question 49

describe the features of the alveoli

Answer 49

numerous to increase SA
thin walls to reduce diffusion pathway
extensive capillary network to maintain a steep CG

Question 50

what happens if guard cells become flaccid

Answer 50

stomata close so no more water can be lost through them

Question 51

describe what happens to diffusion when an insect is anaerobically respiring

Answer 51

there is a quicker rate because the production of lactate lowers the WP in muscle cells so water at the trachiole ends is drawn into respiring muscle by osmosis. this allows for quicker diffusion of gases.

Question 52

state the structure of a gill

Answer 52

there is a series of gills on each side
each gill arch is attacked to two stacks of filaments
there are rows of lamellae on the surface of each filament
the lamellae surface has a single layer of flattened cells covering the network of capillaries

Question 53

describe and explain the structure of leaves of dicotyledonous plants

Answer 53

they have a waterproof cuticle to reduce water loss
the upper epidermis is full of tightly packed cells
the palisade mesophyll has elongated cells with chloroplasts
the spongy mesophyll provides air spaces for carbon dioxide to diffuse into cellls quickly
stomata and guard cells control water loss and are thin for a short DP
carbon dioxide is quickly used to maintain the CG

Question 54

describe what happens when the guard cells are turgid

Answer 54

the stoma remain open to allow air to enter

Question 55

describe the need for a specialised system of gas exchange

Answer 55

a supply of oxygen is needed for aerobic respiration to produce ATP for biochemical processes
remove of carbon dioxide is necessary because accumulation alters the pH in cells

Question 56

describe how the tracheal system of insects is specialised for their function

Answer 56

a spiracle which is often closed to prevent water loss
trachea walls have rings of cartilage to prevent collapsing when breathing pressure changes
as oxygen is used quickly by respiring tissues, a CG is maintained so more is drawn into the spiracles

Question 57

describe how more active insects supply themselves with more oxygen

Answer 57

they close their spiracle and use muscles to create movement for ventilation which creates a mass flow of air into the trachea

Question 58

describe and explain the method of using a potomètre

Answer 58

1- cut the plant shoot under water (to prevent air entering)
2- place the shoot in the tube and set up apparatus necessary
3- make sure the tube is airtight using vaseline to seal any gaps (if air enters it will affect readings)
4- dry the leaves of the shoot (moisture affects rate)
5- remove the capillary from the water beaker to allow a single air bubble then put it back
6- set up your environmental factor and allow the plant to adapt
7- record the starting location of the air bubble and leave for a time period
8- then record the end location of the bubble
9- change your investigation factor and reset the bubble by opening the tap, repeat

Question 59

how would you provide the airflow, humidity, light intensity and temperature for the photometer experiment

Answer 59

a fan, spray water in a plastic bag and wrap around the plant, change the distance of the light source from the plant and use the room temperature