Exchange & Transport 3.3 Flashcards
1
Q
Digestion and absorption (AO1)
During digestion, large biological molecules are ____________________ to smaller molecules that can be absorbed across cell membranes.
A
hydrolysed
2
Q
Digestion and absorption (AO1)
Amylase hydrolyses which bonds?
A
Glycosidic bonds
(in starch)
3
Q
Digestion and absorption (AO1)
Where is amylase produced in the body?
A
Salivary glands
Pancreas
4
Q
Digestion and absorption (AO1)
Starch is hydrolysed into which disaccharide
A
Maltose
5
Q
Digestion and absorption (AO1)
Where are disaccharidases (e.g. maltase) located?
A
Membrane-bound
(in the cell surface membrane of epithelial cells lining the ileum of the small intestine)
6
Q
Digestion and absorption (AO1)
Describe the complete digestion of starch by a mammal (4 marks).
A
1. Hydrolysis;
2. (Of) glycosidic bonds;
3. (Starch) to maltose by amylase;
4. (Maltose) to glucose by disaccharidase/maltase;
5. Membrane-bound (disaccharidase/maltase);
7
Q
Digestion and absorption (AO1)
What is the name of the process by which glucose and amino acids are absorbed into the blood via the ileum of the small intestine?
A
Co-transport
8
Q
Digestion and absorption (AO1)
Epithelial cells lining the ileum of mammals absorb glucose by co-transport with sodium ions. Explain how (3 marks).
A
1. Sodium ions actively transported from ileum cell into blood;
2. Forms concentration/diffusion gradient for sodium to enter cells from small intestine
(Sodium and glucose bind to co-transporter at different binding sites)
3. Glucose enters cell by facilitated diffusion along with sodium ions (co-transport);
4. Glucose then leaves epithelial cell and moves into blood via faciliated diffusion
9
Q
Digestion and absorption (AO1)
TRUE or FALSE
Active transport requires ATP
A
**TRUE **
10
Q
Digestion and absorption (AO1)
Describe and explain two features you would expect to find in a cell specialised for absorption (2 marks).
A
- Folded membrane/microvilli so large surface area (for absorption);
- Large number of co-transport/carrier/channel proteins so fast rate (of absorption)
- Large number of mitochondria so make (more) ATP (by aerobic respiration)
- Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);
11
Q
Digestion and absorption (AO1)
A
- (ATP to ADP + Pi ) releases energy;
- (energy) allows ions to be moved against a concentration gradient
OR
(energy) allows active transport of ions / Na+;
12
Q
Digestion and absorption (AO1)
Endopeptidases hydrolyse _____________ peptide bonds within the polypeptide chain.
A
internal
13
Q
Digestion and absorption (AO1)
Exopeptidases hydrolyse the peptide bonds at the ________________ ends of the polypeptide chain.
A
terminal
14
Q
Digestion and absorption (AO1)
Describe the role of enzymes in the digestion of proteins in a mammal (4 marks).
A
- Hydrolysis of peptide bonds;
- Endopeptidase act in the middle of protein/polypeptide
OR Endopeptidase produces short(er) polypeptides/ increase number of ends;
- Exopeptidases act at terminal end of protein/polypeptide
OR Exopeptidase produces dipeptides/amino acids;
- Dipeptidase acts on dipeptide/between two amino acids
OR Dipeptidase produces (single) amino acids;
15
Q
Digestion and absorption (AO1)
TRUE OR FALSE
Dipeptidases are produced in the stomach
A
FALSE
(They are membrane-bound enzymes located in the cell surface membrane of the ileum)
16
Q
Digestion and absorption (AO1)
The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how (2 marks).
A
- Exopeptidases hydrolyse peptide bonds at the terminal ends of a polypeptide/protein AND endopeptidases hydrolyse internal peptide bonds within a polypeptide/protein;
- (This produces) more ‘ends’ OR more surface area (for further hydrolysis);
17
Q
Digestion and absorption (AO1)
Describe the mechanism for the absorption of amino acids in the ileum (4 marks).
A
- Sodium ions actively transported from cell to blood
Accept ‘pumped’ for transported - Creating sodium ion concentration/diffusion gradient;
- Co-transport;
- Facilitated diffusion of amino acid
- Facilitated diffusion of amino acid into blood;
Note: these are the same steps as those involved in glucose absorption
18
Q
Digestion and absorption (AO1)
Endopeptidases and exopeptidases are involved in the hydrolysis of proteins. Name the other type of enzyme required for the complete hydrolysis of proteins to amino acids.
A
Dipeptidase(s);
19
Q
Digestion and absorption (AO2)
A
- No/less ATP produced OR No active transport;
- Sodium (ions) not moved (into/out of cell);
- No diffusion/concentration gradient for sodium (to move into cell with amino acid)
20
Q
Digestion and absorption (AO1)
Bile contains bile salts, which ____________ fat droplets
A
emulsify
21
Q
Digestion and absorption (AO1)
Describe two functions of bile salts.
A
1. Emulsify lipids/fats;
2. Increases surface area (of lipid/fat) for
increased/faster lipase activity;
3. Form micelles
22
Q
Digestion and absorption (AO1)
Emulsification increases the _____________ of the lipids for faster action of lipase enzymes.
A
surface area
23
Q
Digestion and absorption (AO1)
Lipases hydrolyse triglycerides into ____________
A
Glycerol &
(3) fatty acids
24
Q
Digestion and absorption (AO1)
Describe the hydrolysis reactions involved in the digestion of triglycerides (2 marks).
A
1. Breaking of ester bonds;
2. By addition of water;
(during condensation reaction)
25
# **Digestion and absorption (AO1)**
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (*5 marks*).
**1.** Micelles contain bile salts and fatty acids;
**2.** Make fatty acids (more) soluble (in water)
OR
Bring fatty acids to cell/lining (of the iluem)
OR
Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
**3.** Fatty acids absorbed by diffusion;
**4.** Triglycerides (re)formed (in cells);
*Accept chylomicrons form (in the Golgi apparatus)*
**5.** Vesicles move to cell membrane;
*Accept exocytosis for ‘vesicles move’*
26
# **Digestion and absorption (AO1)**
Explain the advantages of lipid droplets following emulsification.
1. Droplets increase surface areas (for lipase / enzyme action);
2. (So) faster hydrolysis / digestion (of triglycerides / lipids);
27
# **Digestion and absorption (AO1)**
Explain the advantage of micelle formation.
Micelles bring fatty acids and glycerol to membrane / to (intestinal epithelial) cell;
28
# **Digestion and absorption (AO1)**
Describe the role of micelles in the absorption of fats into the cells lining the ileum (*3 marks*).
1. Micelles include bile salts and fatty acids;
2. Make the fatty acids (more) soluble in water;
3. Bringfatty acids to cell/lining (of the ileum);
4. Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
5. Fatty acids (absorbed) by diffusion;
29
# **Digestion and absorption (AO1)**
What is the process by which fatty acids and glycerol enter the intestinal epithelial cell.
Diffusion
30
# **Surface area to volume ratio (AO1)**
As an organism gets ____________, the smaller the surface area : volume ratio.
larger
31
# **Surface area to volume ratio (AO1)**
The smaller the organism, the ____________ surface area : volume ratio.
larger
32
# **Surface area to volume ratio (AO1)**
Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake (*2 marks*).
**1.** Large(r) organisms have a small(er) surface area : volume (ratio);
OR
Small(er) organisms have a large(r) surface area:volume (ratio);
**2.** Provide a shorter diffusion pathway
OR
Faster diffusion;
33
# **Surface area to volume ratio (AO2)**
In large cells of U. marinum, most mitochondria are found close to the cell-surface membrane. In smaller cells, the mitochondria are distributed evenly throughout the cytoplasm.
Use this information and your knowledge of surface area to volume ratios to suggest an explanation for the position of mitochondria in large U. marinum cells (*2 marks*).
**1.** Large(r) cells have small(er) surface area to volume ratio;
**2.** Diffusion distance/pathway is long(er);
OR
(Takes) longer for oxygen to diffuse (to mitochondria)
OR
Less/no oxygen diffuses (to mitochondria)
34
# **Surface area to volume ratio (AO1)**
What adaptations to cells or specialised exchange surfaces enable a FASTER rate of diffusion?
1. Large surface area
2. Large concentration gradient
3. Short diffusion distance
35
# **Surface area to volume ratio (AO1)**
For smaller organsisms with a larger surface area : volume ratios, what is the main disadvantage?
heat loss
| (via the larger surface area)
36
# **Surface area to volume ratio (AO1)**
How do smaller organisms compensate for heat loss?
**increased** metabolic activity
e.g. **respiration**
37
# **Surface area to volume ratio (AO1)**
What is a by-product of increased respiration that allows smaller organisms to maintain an optimal body temperature?
heat
38
# **Surface area to volume ratio (AO2)**
Mammals such as a mouse and a horse are able to maintain a constant body temperature.
Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse.
**1.** Mouse is smaller so larg**er** surface area to volume ratio;
**2.** Fast**er** heat loss OR lose **more** heat easily (per gram/in relation to body size);
**3.** Fast**er** rate of respiration/metabolism releases heat;
39
# **Surface area to volume ratio (Maths)**
Complete Table 1. State your calculated volume and surface area : volume ratio to 2 significant figures.
40
# **Gas Exchange (AO1)**
How does oxygen enter a single-celled organism e.g. amoeba?
Simple diffusion
41
# **Gas Exchange (AO1)**
What adaptations does the single-celled single-celled amoeba have for a faster rate of gas exchange?
Large surface area to volume ratio;
Short diffusion distance;
42
# **Gas Exchange (AO1)**
Describe how gas exchange occurs in a single-celled organism **and** explain why this method cannot be used by large, multicellular organisms?
**1.** Diffusion across the cell surface membrane;
**2.** Larger organisms have a smaller surface area : volume ratio;
**3.** Diffusion pathway would be too long OR
Diffusion would be too slow;
43
# **Gas Exchange (AO2)**
Name the process by which oxygen reaches the cells inside the body of a tubifex worm shown below.
Simple diffusion
44
# **Gas Exchange (AO2)**
Using the information provided below, explain how two features of the body of the tubifex worm allow efficient gas exchange.
**1.** Thin/small so short diffusion pathway;
**2.** Flat/small so large surface area to volume ratio
45
# **Gas Exchange (AO1)**
Name of insect gas exchange system
the tracheal system
46
# **Gas Exchange (AO1)**
Location of gas exchange in the tracheal system
tracheoles
| Supply oxygen direct to tissues
47
# **Gas Exchange (AO1)**
Name the structure through which gases enter and leave the body of an insect.
spiracles
48
# **Gas Exchange (AO1)**
Adaptations of tracheoles for efficient gas exchange
**1.** **Highly branched** so provide a large surface area for faster rate of diffusion
**2.** Their **walls are thin** so there is short diffusion distance;
**3.** **Supply tissues** (e.g. muscle fibres) so diffusion is **direct into cells**
49
# **Gas Exchange (AO1)**
Describe how atmospheric oxygen reaches respiring cells in an insect
**1.** Oxygen enters the insect through spiracles and into the tracheae.
**2.** Spiracles close
**3.** Oxygen diffuses (down a conc gradient) through the tracheae into the tracheoles (where gas exchange occurs)
**4.** Oxygen is delivered directly to respiring tissues
50
# **Gas Exchange (AO1)**
Explain the movement of oxygen into the gas exchange system of an insect when it is at rest
(*3 marks*).
**1.** Oxygen used in (aerobic) respiration;
**2.** (so) oxygen (concentration) gradient (established);
**3.** (so) oxygen diffuses in;
51
# **Gas Exchange (AO1)**
Explain the role of abdominal pumping in insects during gas exchange?
Movement of the insect body by its muscles;
Increases pressure so forces carbon dioxide out
(spiracles open);
Maintains concentration gradient of carbon dioxide and oxygen;
52
# **Gas Exchange (AO1)**
Insects must balance minimising ___________ loss with efficient gas exchange.
water
53
# **Gas Exchange (AO1)**
Describe and explain how the insect gas exchange system limits water loss (*2 marks)*.
**1.** **Exoskeleton is impermeable to water** so reduces water loss.
**2.** **Spiracles close** to prevent water loss
**3.** **Small hairs around the spiracles**
54
# **Gas Exchange (AO1)**
Describe and explain how the structure of the insect gas exchange system provides cells with sufficient oxygen (*4 marks*).
**1.** Spiracles, tracheae, tracheoles;
**2.** Spiracles allow diffusion (of oxygen)
OR (Oxygen) diffusion through tracheae/tracheoles;
**3.** Tracheoles are highly branched so large surface area for exchange;
**4.** Tracheole walls thin so short diffusion distance (to cells)
**5.** Tracheole walls are permeable to oxygen/air;
55
# **Gas Exchange (AO1)**
F = Filament
G = Lamella(e)
56
# **Gas Exchange (AO1)**
Gills have many finger-like projections called gill ____________.
filaments
57
# **Gas Exchange (AO1)**
Each gill filament has many _____________
lamellae
| (singular lamella)
58
# **Gas Exchange (AO1)**
Lamellae contain ____________ and are the site of gas exchange.
capillaries
59
# **Gas Exchange (AO1)**
The capillaries bring ___________ blood to the lamellae.
deoxygenated
60
# **Gas Exchange (AO1)**
Site of gas exchange in fish gills
lamellae
| (singular lamella)
61
# **Gas Exchange (AO1)**
Explain two ways in which the structure of fish gills is adapted for efficient gas exchange.
**many gill filaments/lamellae** provide a large surface area;
lamellae have a **thin epithelium** for short diffusion distance (between water and blood)
62
# **Gas Exchange (AO1)**
Describe and explain the **counter current mechanism in fish gills**.
**1.** Water and **blood** flow in opposite directions;
**2.** Maintains diffusion/concentration gradient of oxygen
**3.** (Diffusion) along length of lamellae / filament / capillary;
63
# **Gas Exchange (AO1)**
Draw and label a cross section of leaf tissue
64
# **Gas Exchange (AO1)**
Why is the concentration of carbox dioxide low in the palisade mesophyll cell?
Used in photosynthesis
65
# **Gas Exchange (AO1)**
Through which structures does carbon dioxide enter the leaf.
stomata
| (Singular stoma)
66
# **Gas Exchange (AO1)**
What cells open and close the stomata?
guard cells
67
# **Gas Exchange (AO1)**
Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (3 marks).
**1.** Carbon dioxide enters via stomata;
**2.** (Stomata opened by) guard cells;
**3.** Diffuses through air spaces (in the spongy mesophyll layer);
**4.** **Down** diffusion/concentration gradient;
68
# **Gas Exchange (AO1)**
Describe and explain how the leaf is adapted for efficient gas exchange.
**1.** They are **flat** so have **larger surface area** to volume ratio
**2.** Contain **many stomata** which **allow air to move in and out** of the leaf
**3.** **Air spaces** in the spongy mesophyll so **short distance pathway**
(between air spaces the palisade mesophyll cells)
69
# **Gas Exchange (AO1)**
**TRUE or FALSE:**
Water is lost from the leaf via the stomata due to transpiration
TRUE
70
# **Gas Exchange (AO1)**
How do plants minimise water loss?
At night, the guard cells close the stomata so less transpiration;
Upper & lower surfaces have a waxy cuticle which increases diffusion distance / impermeable to water;
71
# **Gas Exchange (AO1)**
Group of plants adapted to live in dry conditions
Xerophytes
72
# **Gas Exchange (AO1)**
List the adaptations of xerophytes to dry conditions
Small leaves
Spines
Rolled leaves
Stomata in pits
Hairs
Thick waxy cuticle
73
# **Gas Exchange (AO1)**
How does a small leaf reduce water loss in xerophytes?
Smaller surface area so **reduced number of stomata**
74
# **Gas Exchange (AO1)**
How does a thick waxy cuticle reduce water loss in xerophytes?
Increased diffusion distance so reduces transpiration
75
# **Gas Exchange (AO1)**
How do spines reduce water loss in xerophytes?
Reduces the surface area : volume ratio
76
# **Gas Exchange (AO1)**
What features of a xerophyte **reduce the water potential gradient** by trapping water vapour?
Hairs;
Stomata in pits;
Rolled leaves;
77
# **Gas Exchange (AO2)**
Species B (no mark)
**1.** Smaller surface area so less evaporation ;
**2.** Thicker leaves so greater diffusion distance (for water);
**3.** Fewer stomata so less diffusion / evaporation (of water);
**4.** Smaller surface area to volume ratio so less evaporation.
78
# **Gas Exchange (AO2)**
Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly (*2 marks*).
**1.** Stomata close (to reduce water loss);
**2.** Less carbon dioxide (uptake) for less photosynthesis;
79
# **Gas Exchange (AO1)**
Describe the gross structure of the human gas exchange system (*2 marks*)
**1.** Named structures: trachea, bronchi, bronchioles, alveoli;
**2.** Above structures named in **correct order**
80
# **Gas Exchange (AO1)**
Site of gas exchange in human lungs
Alveolar epithelieum
81
# **Gas Exchange (AO1)**
Describe the pathway taken by an oxygen molecule from an alveolus to the blood (*2 marks*).
**1.** First across alveolar epithelium;
**2**. Then across endothelium of capillary;
82
# **Gas Exchange (AO1)**
What adaptation of the lungs provides a large surface area for rapid gas exchange?
Many alveoli
83
# **Gas Exchange (AO1)**
What adaptation of the lungs provides a short diffusion distance for rapid gas exchange?
Alveolar epithelium is single layer of cells / one cell thick
84
# **Gas Exchange (AO1)**
What adaptation of the lungs provides a large concentration for rapid gas exchange?
Alveoli have a good blood supply / surrounded by many capillaries;
Brings deoxygenated blood;
Concentration of oxygen in blood lower than alveoli;
85
# **Gas Exchange (AO1)**
Describe and explain features of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange.
*Mark in pairs*:
**1.** Single layer of cells / one cell thick
**2.** Reduces diffusion distance
OR
**3.** Permeable
**4.** Allows diffusion of oxygen/carbon dioxide
OR
**5.** Large surface area
**6.** Lots of membrane for diffusion of oxygen/carbon dioxide
86
# **Gas Exchange (AO1)**
Explain how one feature of an alveolus allows efficient gas exchange to occur
**1.** Single layer of cells / one cell thick;
**2.** Reduces the diffusion distance / creating a short diffusion pathway;
87
# **Gas Exchange (AO1)**
Ventilation is a result of the difference in ______________ between the lungs and the air outside the body.
pressure
88
# **Gas Exchange (AO1)**
Which muscles contract during inhalation (i.e. breathing in).
Diaphragm
**External** intercostal muscles
89
# **Gas Exchange (AO1)**
Which muscle contracts during exhalation (i.e. breathing out).
**Internal** intercostal muscle
90
# **Gas Exchange (AO1)**
Which muscles relax during exhalation (i.e. breathing out).
Diaphragm
**External** intercostal muscle
91
# **Gas Exchange (AO1)**
Describe the mechanism of breathing that causes air to **enter** the lungs (*3 marks*).
**1.** Diaphragm contract **AND** diaphragm flattens/pulled down;
**2.** **External** intercostal muscles contract **AND** ribcage pulled up/out;
**3.** Causes volume increase **AND** pressure decrease in **thoracic cavity**;
(to below atmospheric pressure)
92
# **Gas Exchange (AO1)**
Describe the mechanism of breathing that causes air to **exit** the lungs (*3 marks*).
**1.** Diaphragm (muscles) relaxes **AND** diaphragm moves up;
**2.** External intercostal muscles relax **AND** ribcage moves down/in;
*Accept internal intercostal muscles contract*
**3.** (Causes) volume decrease **AND** pressure increase in thoracic cavity (to above atmospheric pressure);
93
# **Gas Exchange (AO1)**
Interaction between internal and external intercostal muscles
Antagonistic
| *One contracts, the other relaxes*
94
# **Gas Exchange (Maths)**
Pulmonary ventilation rate =
(include units)
95
# **Gas Exchange (Maths)**
96
# **Gas Exchange (AO2)**
Tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting. The tidal volume in a person with emphysema is reduced compared with the tidal volume in a healthy person.
Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli (*3 marks*).
**1.** Less carbon dioxide exhaled/moves OR More carbon dioxide remains (in lung);
**2.** So reduced concentration **gradient**;
(between blood and alveoli)
**3.** Slower movement of carbon dioxide out of blood OR More carbon dioxide stays in blood;
97
# **Gas Exchange (AO2)**
What is a risk factor?
Environmental and genetic factors that can increase/ decrease the risk of developing a disease
98
# **Gas Exchange (AO2)**
Correlation does not mean _____________
causation
99
# **Gas Exchange (AO2)**
Risk factors for lung disease
Smoking
Air pollution
Risk alleles / genes
Infections
Occupation
100
# **Gas Exchange (AO3)**
Draw out a linear relationship
## Footnote
Look for a straight line / constant gradient
101
# **Gas Exchange (AO3)**
**Linear or non-linear:**
Non linear
102
# **Gas Exchange (AO3)**
**Linear or non-linear:**
There is a proportional Y increase as X increases
Linear
103
# **Gas Exchange (AO3)**
When to use a t test?
When comparing the **differences between two means** (e.g. control vs. treatment group)
104
# **Gas Exchange (AO3)**
Name of statistical test used to assess the strength of relationship between two continuous variables.
Correlation coefficient
105
# **Gas Exchange (AO3)**
A t-test produced a p value = 0.03.
What can you conclude?
**Significant** difference between means;
**LESS** than 5% probability the **DIFFERENCE** is due to chance
OR 3% probability the **DIFFERENCE** is due to chance
106
# **Gas Exchange (AO3)**
A t-test produced a p value > 0.11
What can you conclude?
**NO Significant** difference between means;
**MORE** than 5% probability the **DIFFERENCE** is due to chance
107
# **Gas Exchange (AO3)**
A t-test produced a p value = 0.001.
What can you conclude?
**HIGHLY Significant** difference between means;
**LESS** than 5% probability the **DIFFERENCE** is due to chance
OR 0.01% probability the **DIFFERENCE** is due to chance
108
# **Gas Exchange (AO3)**
A correlation coefficient produced a p value > 0.2.
What can you conclude?
**NO Significant correlation**
**MORE** than 5% probability the **CORRELATION** is due to chance
109
# **Gas Exchange (AO3)**
A correlation coefficient produced a p value < 0.045.
What can you conclude?
**Significant correlation**
**LESS** than 5% probability the **CORRELATION** is due to chance
110
# **Gas Exchange (AO3)**
A correlation coefficient produced a p value < 0.001.
What can you conclude?
**Highly significant correlation**
**LESS** than 5% probability the **CORRELATION** is due to chance
OR **LESS** than 0.1% probability the **CORRELATION** is due to chance
111
# **Gas Exchange (AO3)**
Researchers carried a correlation coefficient to assess the relationship between the concentration of carbon monoxide and the number of asthma attacks.
They found R = 0.50, with P <0.0001
Explain the meaning of the result of their calculations.
**1.** Positive correlation - as carbon monoxide increases, the number of asthma attacks increases;
**2.** P value of <0.0001 shows a highly significant correlation;
**3.** Less than a 5% probability this correlation is due to chance;
112
# **Gas Exchange (AO3)**
Write out an alternative hypothesis for an experiment that requires a t test.
e.g. there is a (significant) **difference between the mean** tidal volume between the control group (+placebo) and the treatment group (+new asthma drug)
| **Always use context of the question**
113
# **Gas Exchange (AO3)**
Write out a null hypothesis for an experiment that requires a t test.
e.g. there is a **NO** (significant) **difference between the mean** tidal volume between the control group (+placebo) and the treatment group (+new asthma drug)
| **Always use context of the question**
114
# **Gas Exchange (AO3)**
Write out a null hypothesis for an experiment that requires a correlation coefficient.
e.g. There is **no correlation** between exercise per day (mins) and the % of people with lung cancer
| **Always use context of the question**
115
# **Gas Exchange (AO2)**
*Mark in pairs, 1, and 2 OR 3. and 4.*
**1.** Water has low(er) oxygen partial pressure/concentration (than air);
**2.** So (system on outside) gives large surface area (in contact with water)
OR
So (system on outside) reduces diffusion distance (between water and blood);
**3.** Water is dense(r) (than air);
**4.** (So) water supports the systems/gills;
116
# **Gas Exchange (AO1)**
K = bronchiole and
L = artery/arteriole/vein/venule;
117
# **Gas Exchange (AO2)**
Particulate matter is solid particles and liquid particles suspended in air. Polluted air contains more particulate matter than clean air.
A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.
Explain why death of alveolar epithelium cells reduces gas exchange in human lungs (*3 marks*).
**1.** Reduced surface area;
**2.** Increased distance for diffusion;
**3.** Reduced **rate** of gas exchange;
118
# **Haemoglobin (AO1)**
**TRUE or FALSE**
The haemoglobins are a group of chemically similar molecules found in many different organisms.
TRUE
119
# **Haemoglobin (AO1)**
Haemoglobin is a protein with a _____________ structure.
quaternary
120
# **Haemoglobin (AO1)**
Haemoglobin in red blood cells transports _______ around the body.
oxygen
121
# **Haemoglobin (AO1)**
Haemoglobin has a quaternary structure with four [1] chains, each containing a [2] group.
[1] polypeptide
[2] haem
122
# **Haemoglobin (AO1)**
Each haem group contains an [1] ion which can associate with one [2] molecule.
[1] iron
[2] oxygen
123
# **Haemoglobin (AO1)**
oxygen + haemoglobin =
oxyhaemoglobin
124
# **Haemoglobin (AO1)**
Haemoglobin is a protein with a quaternary structure.
Explain the meaning of quaternary structure.
**More than one** polypeptide chain.
OR
**two or more** polypeptide chains
125
# **Haemoglobin (AO1)**
126
# **Haemoglobin (AO1)**
Draw out and fully annotate an oxygen dissociation curve
127
# **Haemoglobin (AO1)**
What type of mathematical curve is the oxygen dissociation curve?
sigmoid
| i.e. it is 'S' shaped = very steep gradient in the middle of curve
128
# **Haemoglobin (AO1)**
Haemoglobin has a high [1] for oxygen at a high partial pressure of oxygen therefore [2] occurs.
[1] affinity
[2] association
129
# **Haemoglobin (AO1)**
Haemoglobin has a [1] affinity for oxygen at a low partial pressure of oxygen and [2] occurs.
[1] low
[2] **dis**sociation
130
# **Haemoglobin (AO1)**
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why (*2 marks*).
**1.** Binding of first oxygen changes tertiary / quaternary structure of haemoglobin;
**2.** Uncovers second **binding site**
OR uncovers another iron / Fe / haem group to bind to;
131
# **Haemoglobin (AO1)**
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin (*3 marks*).
**1.** Decreases blood pH/increasing acidity;
**2.** Changes the tertiary/quatenary structure of haemoglobin
**3.** Decreases haemoglobin affinity for O2;
**4.** Increases/more oxygen dissociation/unloading
132
# **Haemoglobin (AO1)**
The Bohr effect shifts the oxygen dissociation curve in which direction?
to the **right**
133
# **Haemoglobin (AO1)**
Describe the advantage of the Bohr effect during intense exercise (*2 marks*).
**1.** Decreased haemoglobin affinity for oxygen;
**2.** Increases dissociation of oxygen;
**3.** More oxygen for aerobic respiration at the cells/tissues/muscles;
134
# **Haemoglobin (AO2)**
**d)**
**curve drawn to the right**, following the same pattern and **starting at Y = 0** and **finishing at the same percentage** saturation as original curve;
**e)**
**1.** During exercise
OR At low pO2 (in the tissues);
OR ‘high altitude’ or ‘lack of red blood cells’
**2.** More oxygen for respiration;
OR More aerobic respiration;
135
# **Haemoglobin (AO2)**
**1.** **Curve to the right so lower affinity** / % saturation of haemoglobin;
**2.** **Increased dissociation of oxgyen** (from haemoglobin)
**3.** **More oxygen to cells** / tissues / muscles;
**4.** For greater / more / **faster respiration**;
136
# **Haemoglobin (AO1)**
Explain a property of iron ions that enables these ions to carry out their role in red blood cells (*2 marks*).
**1.** charged/polar
OR part of haem(oglobin);
**2.** Binds to oxygen
OR Transports oxygen;
137
# **Haemoglobin (AO1)**
Shifting the oxygen dissociation curve **to the left** means that haemoglobin has a _________ affinity for oxygen.
higher
138
# **Haemoglobin (AO2)**
The oxygen dissociation curve of the foetus is to the left of that for its mother.
Explain the advantage of this for the foetus (*2 marks*).
**1.** Higher affinity at low / same partial pressure / pO2;
**2.** Oxygen moves from mother to fetus;
139
# **Haemoglobin (AO2)**
**1.** Binding of first oxygen changes tertiary / quaternary structure of haemoglobin;
**2.** Uncovers second **binding site**;
**3.** Allows more O2 to bind (easily) / greater saturation with O2;
140
# **Haemoglobin (AO2)**
**1.** Less (oxygen) loaded at high pO2 / lungs (compared with no CO)
OR Maximum Hb saturation is 50% (oxygen);
OR Accept ‘levels (off)’ OR ‘plateau at 50%’ for maximum
**2.** At low pO2 Hb has higher affinity (for oxygen);
**3.** Hb has more oxygen at low pO2
OR Hb unloads less oxygen at low pO2;
141
# **Haemoglobin (AO2)**
**1.** **Higher affinity** for oxygen (than haemoglobin)
OR Associates more readily;
**2.** Allows aerobic respiration when diving/at low(er) pO2;
OR provides oxygen when haemoglobin unloaded;
142
# **Haemoglobin (AO2)**
The oxygen dissociation curve of a mouse is to the right of the curve for a horse.
Suggest how this allows the mouse to have a higher metabolic rate than the horse (*2 marks*).
1. **Mouse haemoglobin** has a **lower** affinity for oxygen
2. **More oxygen can be dissociated** / released / unloaded (for metabolic reactions/respiration);
143
# **Haemoglobin (Maths)**
574
144
# **Haemoglobin (Maths)**
145
# **Haemoglobin (AO1)**
**TRUE or FALSE:**
Many animals are adapted to their environment by possessing different types of haemoglobin with different oxygen transport properties.
TRUE
| e.g. llama haemoglobin = high affinity for oxygen owing to high altitude
146
# **Mass Transport in Animals (AO1)**
Aorta - D;
Renal vein - G;
Vena cava - F;
147
# **Mass Transport in Animals (AO1)**
Name the blood vessels that carry blood to the heart muscle
coronary arteries
148
# **Mass Transport in Animals (AO1)**
Name the blood vessels that carry blood to the kidney
renal artery
149
# **Mass Transport in Animals (AO1)**
Name the blood vessel that carries deoxygenated blood to the lung
pulmonary artery
150
# **Mass Transport in Animals (AO1)**
Name the blood vessel that carries oxygenated blood to the left atrium
pulmonary vein
151
# **Mass Transport in Animals (AO1)**
Give the pathway a red blood cell takes when travelling in the human circulatory system **from a kidney to the lungs** (*3 marks*).
**1.** Renal vein;
**2.** Vena cava to right atrium;
**3.** Right ventricle to pulmonary artery;
152
# **Mass Transport in Animals (AO1)**
Name of valve that separates the atria from the ventricles on both sides of the heart
atrioventricular valve
(AV valve)
153
# **Mass Transport in Animals (AO1)**
Name of valve that separates the ventricles from the aorta (left side) and pulmonary artery (right side)
semi-lunar valve
154
# **Mass Transport in Animals (AO1)**
What side of the heart pumps oxygenated blood around the body?
LEFT
155
# **Mass Transport in Animals (AO1)**
In a healthy person, blood moves in one direction as it passes through the heart. Give two ways in which this is achieved (*2 marks*).
**1.** Pressure gradient moves blood from high to low pressure;
**2.** Valves prevent backflow;
156
# **Mass Transport in Animals (AO1)**
Explain how the atrioventricular valve maintains a unidirectional flow of blood (*2 marks*).
**1.** Pressure in atrium is higher than in ventricle **causing** valve to open;
**2.** Pressure in ventricle is higher than in atrium **causing** valve to close;
157
# **Mass Transport in Animals (AO1)**
What can you conclude from the appearance of valves in the image below about heart muscle activity and blood movement between:
**1.** ventricles and arteries?
**2.** atria and ventricles?
(ventricles and arteries)
1. Ventricle muscles relaxed
2. No backflow of blood into ventricles
(atria and ventricles)
3. Atria muscle contracted;
4. Blood pumped from atria into ventricles;
158
# **Mass Transport in Animals (AO1)**
Which blood vessel carries blood at the lowest blood pressure?
Vena cava
159
# **Mass Transport in Animals (AO2)**
**1.** Semi-lunar valves is closed;
**2.** Because pressure in aorta higher than in ventricle;
160
# **Mass Transport in Animals (AO2)**
Use the graph to explain why the AV valve is closed
Pressure in ventricle is **higher** than pressure in the atria
161
# **Mass Transport in Animals (AO2)**
Use the graph to explain why the semi-lunar valve is open
Pressure in ventricle is **higher** than pressure in the aorta
162
# **Mass Transport in Animals (AO1)**
Describe one way in which the graphs of cardiac cycles on the right and left ventricle would similar to and one way it would be different (*2 marks*).
(Similarity)
1. Peaks/contractions at the same/similar time
OR Same/similar pattern;
(Difference)
2. Lower pressures on the right hand side;
163
# **Mass Transport in Animals (AO2)**
164
# **Mass Transport in Animals (AO1)**
The maximum pressure in the ventricle is much higher than that in the atrium.
Explain what causes this (*2 marks*).
**1.** Ventricle has thick wall / more muscle;
**2.** So contractions are stronger / harder;
165
# **Mass Transport in Animals (AO1)**
**i)** C
**ii)** A
166
# **Mass Transport in Animals (AO1)**
167
# **Mass Transport in Animals (AO2)**
Some babies are born with a hole between the right and the left ventricles.
These babies are unable to get enough oxygen to their tissues. Suggest why (2 marks).
**1.** Blood flows from left ventricle to right ventricle/ mixing of oxygenated and deoxygenated blood;
**2.** Lower volume of oxygenated blood leaves left ventricle/flows into aorta
OR Lower pressure in blood leaving left ventricle/flowing into aorta
168
# **Mass Transport in Animals (AO1)**
Function of coronary arteries (*2 marks*)
**1.** Carry oxygen / glucose;
**2.** To heart muscle / cells / tissues.
169
# **Mass Transport in Animals (AO2)**
1. Ventricle pressure rises then blood starts to flow into aorta because pressure **causes** semilunar valve to open;
2. Ventricle pressure starts to fall so blood flow falls;
170
# **Mass Transport in Animals (AO1)**
Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta (*5 marks*).
**1.** Atria contract and this increases pressure
**2.** Atrium has higher pressure than ventricle causing atrioventricular valves to open;
**3.** Ventricle contract and this increases pressure
**4.** Ventricle has higher pressure than atrium causing atrioventricular valves to close;
**5.** Ventricle has higher pressure than aorta causing semilunar valve to open;
**6.** Higher pressure in aorta than ventricle (as ventricle relaxes) causing semilunar valve to close;
171
# **Mass Transport in Animals (Maths)**
Cardiac output equation
Cardiac output (CO) = stroke volume (SV) x heart rate (HR)
172
# **Mass Transport in Animals (Maths)**
Cardiac output unit
173
# **Mass Transport in Animals (Maths)**
What is stroke volume?
Volume of blood pumped out of the left ventricle during each cardiac cycle (cm^3)
174
# **Mass Transport in Animals (AO1)**
**TRUE or FALSE:**
The cardiac cycle describes the contraction and relaxation of both the atria and ventricles during each heart beat.
TRUE
175
# **Mass Transport in Animals (Maths)**
**TRUE or FALSE:**
Heart rate is the length of one cardiac cycle in seconds
FALSE
| Heart rate is the number of cardiac cycles / heart beats **per minute**
176
# **Mass Transport in Animals (Maths)**
Heart rate of 75 bpm and a cardiac output of 5175cm^3 min^-1 - what is the stroke volume?
69 cm^3
177
# **Mass Transport in Animals (Maths)**
One cardiac cycle of 0.7s, what is the heart rate?
60 / 0.7 = 85.7 or 86 bpm
178
# **Mass Transport in Animals (Maths)**
Use the below graph to determine the length of one cardiac cycle.
Peak to peak OR trough to trough
e.g.1.24 - 0.48 = 0.76s
179
# **Mass Transport in Animals (Maths)**
Use the below graph to determine stroke volume.
120 - 40 = 80cm^3
180
# **Mass Transport in Animals (Maths)**
Convert 770 milliseconds (ms) into seconds (s)
770 / 1000 = 0.77s
181
# **Mass Transport in Animals (Maths)**
Convert 3.5 seconds (s) into milliseconds (ms)
3.5 x 1000 = 3500ms
182
# **Mass Transport in Animals (Maths)**
8 beats in 800 ms
1 beat = 100 ms / 0.1s
Heart rate = 60 / 0.1 = 600bpm
CO = SV x HR
CO = 0.03 x 600 = 18cm^3 min^-1
183
# **Mass Transport in Animals (Maths)**
60 / 0.9 =
66.7 or 67 bpm
| One cardiac cycle or heart beat = 0.9 seconds
184
# **Mass Transport in Animals (AO1)**
Arteries have [1] muscle walls that can withstand [2].
[1] thick
[2] pressure
185
# **Mass Transport in Animals (AO1)**
Arteries contain [1] tissue to stretch when the ventricles contract and [2] when the ventricle relaxes. This recoil helps to [3] the high pressure.
[1] elastic
[2] recoil
[3] maintain
186
# **Mass Transport in Animals (AO1)**
Arteries have muscular walls that [1] to reduce the diameter of the [2]. This is vasoconstriction and allows changes in flow/pressure.
[1] contract
[2] lumen
187
# **Mass Transport in Animals (AO1)**
Describe one key feature and function of the endothelieum in arteries.
**Feature:** smooth
**Function:** reduces friction.
188
# **Mass Transport in Animals (AO1)**
What is the **only artery** that contains valves?
Aorta
| contains semi-lunar valve
189
# **Mass Transport in Animals (AO1)**
Explain **four ways** in which the structure of the aorta is related to its function.
**1.** Thick muscle withstands/resists high pressure
**2.** Elastic tissue stretches when ventricles contract OR recoils when ventricle relaxes;
**3.** Elastic tissue to allow stretching / recoil which maintains pressure;
**4.** Smooth endothelium reduces friction;
**5.** Wall contains fibrous protein withstands/resists high pressure OR stop bursting;;
**6.** Semi-lunar valve prevents backflow;
190
# **Mass Transport in Animals (AO1)**
Give two structural features of an **aorta wall** and explain how they are related to the function of an aorta
**1.** Thick muscle withstands/resists high pressure
**2.** Elastic tissue stretches when ventricles contract OR recoils when ventricle relaxes;
**3.** Elastic tissue to allow stretching / recoil which maintains pressure;
**4.** Smooth endothelium reduces friction;
**5.** Wall contains fibrous protein withstands/resists high pressure;
191
# **Mass Transport in Animals (AO1)**
Explain how an arteriole can reduce the blood flow into capillaries (*2 marks*).
**1.** Muscle contracts;
**2.** Constricts/narrows the lumen of the arteriole;
192
# **Mass Transport in Animals (AO1)**
Capillary walls are only one cell [1], which allows the short [2] pathway.
[1] thick
[2] diffusion
193
# **Mass Transport in Animals (AO1)**
The capillary wall is **permeable OR impermeable**
permeable
194
# **Mass Transport in Animals (AO1)**
Capillaries contain [1] which allow small biological molecules e.g. [2], to leave the blood vessel to be delivered to cells.
[1] fenestrations
[2] glucose / amino acids
195
# **Mass Transport in Animals (AO1)**
Capillaries have a [1] lumen which reduces flow rate giving more time for [2].
[1] narrow
[2] diffusion
196
# **Mass Transport in Animals (AO1)**
Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue.
**1.** Permeable capillary wall / membrane;
**2.** One cell thick, reduces diffusion distance;
**3.** Fenestrations, allows large molecules through;
**4.** Small diameter / narrow, gives a short diffusion distance;
**5.** Narrow lumen, reduces flow rate giving more time for diffusion;
**6.** Red blood cells in contact with wall / pass singly, gives short diffusion distance;
197
# **Mass Transport in Animals (AO1)**
Veins have [1] at intervals throughout to ensure no [2] of blood due to the low pressure.
[1] valves
[2] backflow
198
# **Mass Transport in Animals (AO1)**
Veins have wide [1] which provides reduced [2].
[1] lumen
[2] friction
199
# **Mass Transport in Animals (AO1)**
Explain how blood in the vein of a leg is returned to the heart (*4 marks*).
**1.** Muscles surrounding veins contract and press on walls of vein and squeezes blood along veins;
**2.** Valves prevent backflow
**3.** Wide lumen little resistance / friction
**4.** Low pressure in heart muscle after contraction;
**5.** Draws blood from veins into atria;
200
# **Mass Transport in Animals (AO1)**
130 bpm
201
# **Mass Transport in Animals (AO2)**
**1.** Aorta pressure is directly linked to ventricle pressure which is higher;
**2.** Aorta has elastic tissue;
**3.** So stretches and recoils;
202
# **Mass Transport in Animals (AO2)**
**1.** Many / more capillaries (than arterioles);
**2.** (Cross-sectional) area of capillaries greater (than of arterioles);
203
# **Mass Transport in Animals (AO1)**
Describe how tissue fluid is formed
**1.** High blood OR hydrostatic pressure;
**2.** Forces water / fluid out;
*(which contains glucose and amino acids)*
**3.** Large proteins remain in capillary;
204
# **Mass Transport in Animals (AO1)**
Describe how tissue fluid is returned to the circulatory system.
- Low water potential in capillary;
- Due to plasma proteins;
- Water enters capillary;
- By osmosis;
- Any fluid not returned is absorbed by lymphatic vessels;
205
# **Mass Transport in Animals (AO2)**
**Blood vessel:** vein;
**Explanation:** wide(r) lumen
OR thinner wall;
206
# **Mass Transport in Animals (AO1)**
Explain the role of the heart in the formation of tissue fluid (*2 marks*).
**1.** Contraction of ventricle(s) produces high blood OR hydrostatic pressure;
**2.** This forces water (and some dissolved substances e.g. glucose) out of capillaries;
207
# **Mass Transport in Animals (AO2)**
Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system.
Suggest how a blockage in the lymphatic system could cause lymphoedema (*1 mark*).
Excess tissue fluid cannot be (re)absorbed / builds up
208
# **Mass Transport in Animals (AO2)**
**1.** (Overall) outward pressure of 3.2 kPa;
**2.** Forces small molecules out of capillary;
209
# **Mass Transport in Animals (AO1)**
The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary.
Explain why (*1 mark*).
Loss of water / loss of fluid
(pushing against capillary lining).
210
# **Mass Transport in Animals (AO1)**
Endothelium
211
# **Mass Transport in Animals (AO1)**
Plasma
| Plasma = solution part of blood separate from red & white blood cells
212
# **Mass Transport in Animals (AO1)**
213
# **Mass Transport in Animals (AO1)**
0.4s
| When the pressure is higher in the aorta than the left ventricle
214
# **Mass Transport in Animals (AO1)**
*(describe)*
slow decrease in speed until reaches arterioles then rapid decrease;
*(explain)*
increase in total cross-sectional area of blood vessels / more friction (so blood flow decreases);
215
# **Mass Transport in Plants (AO1)**
Which plant tissue transports water and mineral ions up the stem into the leaves?
Xylem
216
# **Mass Transport in Plants (AO1)**
Describe the structures of the xylem
No cytoplasm and no organelles;
Long tubes with no end walls - forms a continuous tube;
Lignin cell walls;
Lateral pits in cell wall;
217
# **Mass Transport in Plants (AO1)**
Function of no cytoplasm and no organelles in xylem
No obstruction to flow of water
218
# **Mass Transport in Plants (AO1)**
Function of long tubes with no end walls in xylem
Allows continuous columns of water to form
219
# **Mass Transport in Plants (AO1)**
Function of lignin in xylem cell wall
Strengthens xylem;
Waterproofs xylem;
Prevents collapse of xylem under tension.
220
# **Mass Transport in Plants (AO1)**
Function of lateral pits in xylem cell wall
Allows lateral movement around blockages (in xylem)
221
# **Mass Transport in Plants (AO1)**
Explain how xylem tissue is adapted for its function (*4 marks*).
**1.** Long tubes with no end walls allow continuous columns of water to form;
**2.** No cytoplasm / no organelles to obstruct flow of water;
**3.** Lignin provides support / withstand tension / waterproofs the tissue;
**4.** Pits in walls allow lateral movement / get around blocked vessels;
222
# **Mass Transport in Plants (AO1)**
Theory the explains movement of water up the xylem
Cohesion tension
223
# **Mass Transport in Plants (AO1)**
Bond that enables 'cohesion' between water molecules
hydrogen
224
# **Mass Transport in Plants (AO1)**
What is tension?
A pulling force
225
# **Mass Transport in Plants (AO1)**
Describe the cohesion-tension theory of water transport in the xylem (*5 marks*).
**1.** **Water lost via stomata** due to **transpiration**
**2.** **Lowers water potential** of mesophyll / leaf cells;
**3.** **Water pulled up xylem** via tension (to replace water lost via transpiration);
**4.** Water molecules have **cohesion** so ‘stick’ together by **hydrogen bonds**;
**5.** Forming **continuous column of water** column;
**6.** **Adhesion** of water molecules to walls of xylem;
226
# **Mass Transport in Plants (AO1)**
Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.
Explain the importance of the xylem being kept open as a continuous tube (*3 marks*).
**1.** Transpiration creates tension (in column)
OR Water moves from xylem (into cells) creates tension
**2.** Form continuous column of water
OR (So) no barrier to (water) movement;
**3.** Cohesion from hydrogen bonds between (all) water (molecules)
227
# **Mass Transport in Plants (AO2)**
1. Stomata open;
2. Transpiration highest around mid-day as middle of day warmer (higher temperature) / lighter (higher light intensity);
3. Increased tension on column of water as greatest water potential gradient;
(this leads to negative pressure in xylem);
228
# **Mass Transport in Plants (Maths)**
229
# **Mass Transport in Plants (AO2)**
**1.** Initial and final mass
(of beaker and all contents);
Accept change in mass/weight
**2.** Number of (groups of) xylem vessels;
230
# **Mass Transport in Plants (AO2)**
**1.** Water is transpired (from leaves / stalk / celery / plant);
**2.** Water potential gradient/lower water potential creates tension / pulls up water
**3.** Hydrogen bonds / cohesion maintains column of water;
231
# **Mass Transport in Plants (AO2)**
Short diffusion pathway (to cells)
OR
It has a surface permeable (to water/ions into cells);
232
# **Mass Transport in Plants (AO1)**
Use your knowledge of leaf structure to explain why less water is lost through the upper surface of leaves than is lost through the lower surface (*2 marks*).
**1.** more stomata on the lower surface;
**2.** (thicker) waxy cuticle on the upper surface;
233
# **Mass Transport in Plants (AO1)**
Factors that affect transpiration
Temperature
Light intensity
Wind speed
Humidity
234
# **Mass Transport in Plants (AO1)**
Explain how increasing light intensity affects the rate of transpiration
1. More stomata open
2. Faster rate of transpiration;
235
# **Mass Transport in Plants (AO1)**
Explain how increasing temperature affects the rate of transpiration
1. Increases kinetic energy;
2. Water molecules diffuse faster;
3. Faster rate of transpiration;
236
# **Mass Transport in Plants (AO1)**
Explain how decreasing humidity affects the rate of transpiration
1. Less water vapour in the atmosphere
2. Increases the water potential gradient between atmosphere and mesophyll / air spaces
3. Faster rate of transpiration;
237
# **Mass Transport in Plants (AO1)**
Explain how increasing humidity affects the rate of transpiration
1. More water vapour in the atmosphere
2. Decreases the water potential gradient between atmosphere and mesophyll / air spaces
3. Slower rate of transpiration;
238
# **Mass Transport in Plants (AO1)**
Explain how increasing wind speed affects the rate of transpiration
1. Moves water vapour away from leaf
2. Increases the water potential gradient between atmosphere and mesophyll / air spaces
3. Faster rate of transpiration;
239
# **Mass Transport in Plants (AO2)**
Suggest an explanation for the difference in transpiration rate between conditions A and B (*2 marks*).
**1.** Removes water vapour;
**2.** Increases water potential gradient;
240
# **Mass Transport in Plants (AO2)**
Suggest an explanation for the difference in transpiration rate between conditions A and C (*2 marks*).
**1.** Increases kinetic energy so water molecules move faster;
**2.** Increases diffusion;
241
# **Mass Transport in Plants (AO2)**
Give one environmental factor that the student should have kept constant during this investigation.
Temperature /
Light intensity /
Wind speed /
Humidity
242
# **Mass Transport in Plants (AO2)**
The student cut the shoot and put it into the potometer under water. Explain why.
Prevent air entering the continuous water column;
243
# **Mass Transport in Plants (AO2)**
The student wanted to calculate the rate of water uptake by the shoot in cm^3 per minute. What measurements did she need to make?
1. Distance and time;
2. Radius / diameter / area
(of capillary tube);
244
# **Mass Transport in Plants (AO2)**
The student assumed that water uptake was equivalent to the rate of transpiration.
Give two reasons why this might not be a valid assumption.
1. Water used in photosynthesis
2. Apparatus not sealed / ’leaks’;
3. Water used to provide turgidity / support;
245
# **Mass Transport in Plants (AO2)**
The student measured the rate of water uptake three times.
Suggest how the reservoir allows repeat measurements to be made (*1 mark*).
Returns bubble (to start);
246
# **Mass Transport in Plants (Maths)**
The air bubble moved 7.5 mm in 15 minutes along the capillary tube in a potometer.
The diameter of the capillary tube was 1.0 mm.
Calculate the rate of water uptake by the shoot in this experiment.
Give your answer in mm^3 per hour.
The area of a circle is found using the formula, area = πr^2.
π x 0.5^2 x 7.5 = 5.89 mm^3 in 15 minutes
π x 0.5^2 x 7.5 = **23.56 mm^3 per hour**
247
# **Mass Transport in Plants (AO1)**
Which plant tissue transports sucrose and other organic molecules up AND down the stem to shoot tips and roots?
phloem
248
# **Mass Transport in Plants (AO1)**
Name the two specialised cells that make up the phloem
companion cells
sieve tube elements
249
# **Mass Transport in Plants (AO1)**
What is translocation?
The movement of organic molecules (e.g. sucrose) from sources such as leaf cells to sinks such as root hair cells.
250
# **Mass Transport in Plants (AO1)**
What hypothesis explains translocation in plants?
Mass flow hypothesis
251
# **Mass Transport in Plants (AO1)**
Describe the structure of the sieve tube elements.
No nucleus;
Few organelles;
Very little cytoplasm;
Connected to each other through sieve plates;
252
# **Mass Transport in Plants (AO1)**
Companion cells contain large numbers of which organelle.
Mitochondria
253
# **Mass Transport in Plants (AO1)**
Describe the transport of carbohydrates in plants (*5 marks*).
**1.** Sucrose is **actively transported** into the sieve tubes;
**2.** **by companion cells**;
**3.** This **lowers water potential** in sieve tubes and **water enters by osmosis** from xylem;
**4.** This produces **higher hydrostatic pressure** inside the sieve tubes at the source end of the phloem;
**5.** **Mass flow to respiring cells**; or storage tissue
**6.** Sucrose is moved into the sinks e.g. root tips or shoot tips by **active transport or facilitated diffusion**.
254
# **Mass Transport in Plants (AO1)**
Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube (*3 marks*).
**1.** Sucrose actively transported
(into phloem by companion cells);
**2.** Lowering water potential;
**3.** Water moves into phloem by osmosis (from xylem);
255
# **Mass Transport in Plants (AO1)**
Use the below diagram to suggest and explain one other way in which sieve cells are adapted for mass transport.
**1.** No / few organelles / very little cytoplasm
**2.** (So) easier / more flow
OR
**3.** Thick walls
**4.** Resist pressure.
256
# **Mass Transport in Plants (AO1)**
Using the below diagram to suggest and explain one other way in which companion cells are adapted for the transport of sugars between cells.
**1.** Mitochondria release energy / produce ATP / site of aerobic respiration;
**2.** For active transport
OR
**3.** Ribosomes / rough endoplasmic reticulum produce(s) proteins;
**4.** (Proteins) linked to transport e.g. carrier proteins.
257
# **Mass Transport in Plants (AO1)**
What is 'ringing'?
Removal of outer layer of bark that includes the phloem but leaves the xylem in tact.
258
# **Mass Transport in Plants (AO1)**
Draw a diagram that shows the result of ringing.
259
# **Mass Transport in Plants (AO1)**
After a ringing experiment, why does a bulge appear above where the phloem has been removed?
Bulge has a higher concentration of sugars than the fluid from below the ring;
This is because the sugars can’t move past the area where the bark has been removed;
This is evidence that there can be a downward flow of sugars (via mass flow)
260
# **Mass Transport in Plants (AO1)**
What molecule is radioactively labelled to test the mass flow hypothesis?
Carbon dioxide
261
# **Mass Transport in Plants (AO1)**
Describe how radioactively labelled carbon dioxide is used to test the mass flow hypothesis (*3 marks*)?
Leaf supplied with radioactive carbon dioxide;
Via photosynthesis, leaf converts carbon dioxide into the glucose, then sucrose;
Radioactivity enables tracing of organic molecules throughout the plant;
Autoradiography detects radiation;
262
# **Mass Transport in Plants (AO2)**
Leaf-chewers and insects that feed on xylem sap are active feeders; this means they use their jaw muscles to obtain their food.
In contrast, insects that feed on phloem sap are passive feeders; this means they do not use their jaw muscles to take up sap from phloem.
Explain why phloem feeders can take up sap without using their jaw muscles.
**1.** Active transport of sucrose into phloem via companion cells;
**2.** Lowers water potential and water enters by osmosis;
**3.** Contents of phloem vessel pushed into insect’s mouth by high pressure;
263
# **Mass Transport in Plants (AO2)**
PCMBS is a substance that inhibits the uptake of sucrose by plant cells.
Scientists investigated the effect of PCMBS on the rate of translocation in sugar beet. The figure below shows their results.
During their experiment, the scientists ensured that the rate of photosynthesis of their plants remained constant.
Explain why this was important.
**1.** Rate of photosynthesis related to rate of sucrose production;
**2.** Rate of translocation higher when sucrose concentration is higher.
264
# **Mass Transport in Plants (AO2)**
PCMBS is a substance that inhibits the uptake of sucrose by plant cells.
Scientists investigated the effect of PCMBS on the rate of translocation in sugar beet. The figure below shows their results.
The scientists concluded that some translocation must occur in the spaces in the cell walls.
Explain how the information in the figure above supports this conclusion.
**1.** Rate of translocation does not fall to zero / translocation still occurs after 120 minutes;
**2.** But sucrose no longer able to enter cytoplasm of phloem cells.
