3. Organisms Exchange Substances With Their Environment Flashcards
1
Q
What’s the environment around the cells of multicellular organisms called
A
Tissue fluid
2
Q
4 examples of things needed to be interchanged between an organism and its environment
A
-Respiratory gases (oxygen and carbon dioxide)
-Nutrients (glucose, fatty acids, amino acids, vitamins and minerals)
-Excretory products (urea and carbon dioxide)
-Heat
3
Q
What are the 2 ways excretory products, nuterients and respitory products are exchanged
A
-passively (no metabolic energy required), by diffusion and osmosis
-actively (metabolic energy is required) by active transport
4
Q
What’s required for gas exchange to be effective
A
The exchange surfaces of an organism must be large compared to its volume
(Large surface area to volume ratio)
5
Q
Surface area of a sphere =
A
4 π r^2
6
Q
Volume of a sphere
A
4/3 π r^3
7
Q
How to calculate the surface area to volume ratio
A
Surface area / volume
Make sure volume is 1
Eg:
SA: = 0.6:1
8
Q
Features of specialised exchange surfaces
A
-Large surface area to volume ratio: increases the rate of change
-very thin = short diffusion distance pathway = materials cross exchange surface rapidly
-selectively permeable = allows selected materials to cross
-movement of the environmental medium (eg: air) to maintain a concentration gradient
-a transport system ensures movement of the internal medium (eg: blood) to maintain a diffusion gradient
9
Q
Diffusion equation
A
Diffusion ∝ (surface area x difference in concentration )
—————————————————————
.length of diffusion pathway
Diffusion is directly proportional to surface area and concentration difference
Diffusion is inversely proportional to length of diffusion pathway
10
Q
Why are specialised exchange surfaces located on the inside of an organism
A
They’re thin so are easily damaged and dehydrated
11
Q
Describe gas exchange in a single-celled organism
A
-single called organisms are small -> large surface area to volume ratio
-oxygen is absorbed by diffusion across a cell surface membrane
-CO2 from aerobic respiration diffuses out
Cell walls are no additional barrier to the diffusion of gases
12
Q
What types of organisms are insects
A
Terrestrial
13
Q
Describe the specialised exchange surface that insects have evolved for efficient gas exchange
A
tracheae:internal network of tubes, supported by strengthened rings to prevent them from collapsing
They divide into tracheoles: small dead-end tubes that extend throughout body tissue
Allows o2 to be brought directly to respiring tissues due to small diffusion pathway.
14
Q
What are the 3 ways respitory gases move in and out of the tracheal system
A
1) along a diffusion gradient
2) mass transport
3) ends of the tracheoles are filled with water
15
Q
How do gases enter and leave the tracheae
A
Through tiny pores called spiracles
-Found on the body surface which open and close by a valve
When open: water vapour evaporates from insect
When closed: prevents water loss
For most of the time, insects keep their spiracles closed
16
Q
What are the limitations of the tracheal system as a method of gas exchange
A
-relies mostly on diffusion to exchange gases between cells and environment
- for diffusion to be effective, the diffusion pathway needs to be short so insects are small sized. Length of diffusion pathway limits size of that insects attain.
17
Q
Describe the general structure of a fish and how does that relate to their exchange system
A
Have a waterproof and gas tight outer covering
Small surface area to volume ratio
Therfore:
Their body surface isn’t adequate to supply and remove respiratory gases so…
they’ve evolved specialised internal gas exchange surfaces
18
Q
Describe the structure of the gills
A
Located within the body, behind the head
Made up of gill filaments stacked up in a pile
Perpendicular to the filaments are gill lamellae, which increase surface area of gills
19
Q
Describe the ventilation of gills
A
Water is taken through mouth and forced over gills through an opening on each side of the body
Flow of water over the gill lamellae and flow of blood in opposite directions - counter current flow principle
Ensures maximum gas exchange is achieved
20
Q
Describe what the countercurrent exchange principle in fish means will happen
A
-oxygenated blood meets water with high oxygen concentration.
-deoxygenated blood meets water with low oxygen concentration.
So Diffusion of oxygen from water to blood takes place DOWN a concentration gradient
Diffusion gradient for oxygen is maintained across entire width of gill lamellae
21
Q
Compare the parallel flow and countercurrent flow in the gills of a fish
A
Countercurrent:
A diffusion gradient is maintained all the way across the gill lamellae. Almost all the oxygen from the water diffuses into the blood
Parallel:
A diffusion gradient is maintained for only half of the distance across the gill lamellae. Only 50% of oxygen in water diffuses into the blood
22
Q
How do respiratory gases move in & out of the tracheal system along a diffusion gradient ?
A
When cells respire, o2 is used up and so the conc. towards the ends of the tracheoles falls which creates a diffusion gradient. (Allows o2 to diffuse in)
CO2 is produced by respiring cells which creates a diffusion gradient in the opposite direction (allows co2 to diffuse out)
23
Q
How do respiratory gases move in & out of the tracheal system via mass transport ?
A
The contraction of muscle s in insects can squeeze the trachea enabling mass movement of air in and out
24
Q
How do respiratory gases move in & out of the tracheal system due to the end of the tracheoles being filled with water ?
A
During strenuous activity the muscle cells around the tracheoles respire anaerobically, producing lactate which is soluble and lowers the water potential of the muscle cells.
Water can therefore move from the tracheoles and into the cells by osmosis which decreases the volume of water in the tracheoles and allows air to be drawn further in
25
What are the 3 similarities of gas exchange between insects and plant leaf
-no livingcell is far from, the external air, so a source of oxygen and carbon dioxide
-diffusion takes place in air which makes it more rapid than if in water
-short fast diffusion pathway
26
Adaptions of leaf gas exchange for rapid diffusion
- **many stomata** and so no cell is far from a stoma so short diffusion pathway
- numerous **interconnecting air-spaces** that occur throughout the mesophyll so gases readily come in contact with mesophyll cells
- **large surface area** of mesophyll cells for rapid diffusion
27
Structure and function of stomata
-Minute pores mostly on the underside of leaves
-Each stoma is surrounded by a pair of guard cells which open and close the stoma pore to control rate of gas exchange and prevent water loss by evaporation
When guard.cell is turgid (swollen) - stomata is open
When guard cell is flaccid (shrunken) - stomata is closed
28
Do all plant cells photosynthesise
Plant cells respire all the time
But only plant cells with chloroplasts photosynthesise
And when conditions are right
29
What happens in the exchange of oxygen and carbon dioxide in plant cells when photosynthesis is NOT taking place, linked to respiration
When it’s dark, oxygen diffuses into the leaf because it’s constantly being used by cells during respiration. In the same way, carbon dioxide produced during respiration diffuses out
30
Compare blood circulation of fish and mammals
Fish:
Single circulation
2 chambers
One artery carrying blood away
Mammal:
Double circulation
4 chambers
Two arteries carrying blood away
31
What features of insects for efficient gas exchange conflicts with conserving water
Thin
Permeable surface
Large area
32
Why is it hard for terrestrial organisms like insects to conserve water
Water easily evaporated from their body surface so they can become dehydrated
33
What are the 3 adaptions insects have evolved to reduce water loss
-**small surface area to volume ratio**: minimises area over which water is lost
-**waterproof covering** over body surface: rigid exoskeleton of chitin covered with a waterproof cuticle
-**spiracles**: openings of tracheae at body surface which close to reduce water loss. But this conflicts with the need for oxygen and so occurs largely when insect is at rest
34
How do terrestrial plants limit water loss
-waterproof covering over parts of the leaves
-ability for guard cells to go flaccid and close stomata
-xerophtypes prevent water loss through transpiration
35
Leaf adaptions to prevent water loss in xerophytic conditions
-thick cuticle
-rolling up of leaves
-Hairy leaves
-stomata in pits or groves
-reduced surface area to volume ratio of leaves
36
Describe how a **thick cuticle** prevents water loss in plants
Forms a waterproof barrier
The thicker the cuticle, the less water can escape
37
Describe how **rolling up of leaves** prevents water loss in plants
Protects the lower epidermis that has most of the stomata on it from the outside by trapping air within the rolled leaf
becoming saturated with water vapour so has a high water potential.
There’s no water potential gradient between the inside and outside of the leaf so no water loss.
38
Describe how **hairy leaves** prevents water loss in plants
thick layer of hair especially on lower epidermis, traps still, moist air next to leaf surface.
Water potential gradient between the inside and the outside of the leaves is reduced so less water is lost by evaporation.
39
Describe how **stomata in pits or grooves** prevents water loss in plants
Trap still, moist air next to the leaf and reduce the water potential gradient
Eg: pine trees
40
Describe how **a reduced surface area to volume ratio of leaves** prevents water loss of plants
The smaller the surface area to volume ratio, the slower the rate of diffusion
Leaves that are small and roughly circular in cross-section have a reduced rate of water loss.
balanced against need for sufficient area for photosynthesis
41
How do all aerobic organism release energy
They require a constant supply of oxygen to release energy in form of ATP during respiration
42
Why does the volume of oxygen absorbed and volume of carbon dioxide released have to be large in mammals
-they’re large organisms with a **large volume of living cells**
-they **maintain a high body temp** which is **related to them having a high metabolic & respiratory rates**
So they’ve evolved specialised surfaces called lungs to ensure efficient gas exchange between sir and their blood
43
What’s the site of gas exchange in mammals
Lungs (epithelium of the alveoli)
44
Why are lungs located inside the body
-air isn’t dense enough to support and protect the delicate structures
-the body would lose a lot of water and dry out of not
45
What bony box protects the lungs
Rib cage
46
What are the main parts of the human gas-exchange system
-lungs
-trachea
-bronchi
-bronchioles
-alveoli
47
Describe the structure of the **lungs** in the human gas-exchange system
Pair of lobed structures made of a series of highly branched tubules called bronchioles which end in tiny air sacs called alveoli
48
Describe the structure of the **trachea** in the human gas-exchange system
**Flexible airway** that’s supported by **rings of cartilage** preventing trachea collapsing as the air pressure inside falls when breathing in. **Walls are made up of muscle, lined with ciliated epithelium and goblet cells**
49
Describe the structure and function of the **bronchi** in the human gas-exchange system
2 divisions of trachea, each leading to one lung.
Like the trachea, they **produce mucus to trap dirt particles** and have cilia that **move dirty mucus towards the throat**.
The larger bronchi are supported by cartilage.
50
Describe the structure and function of the **bronchioles** in the human gas-exchange system
**Series of branching subdivisions of the bronchi**.
Walls are made of muscle lined with epithelial cells allowing them to constrict so they can **control flow of air in and out of alveoli**
51
Describe the structure and function of the **alveoli** in the human gas-exchange system
Minute air-sacs at the end of bronchioles.
Lined with epithelium
Elastic fibres allow alveoli to stretch as they fill with air in inspiration
Spring back during expiration to remove carbon dioxide air.
**Alveolar membrane is the gas-exchange surface**
**Each alveolus has a network of pulmonary capillaries** around it, so narrow that red blood cells flatten against the thin capillary walls to squeeze through
52
Define process of ventilation / breathing
**Air is constantly moved in and out of the lungs** to **maintain diffusion of gases across the alveolar epithelium**
53
State the 2 processes in ventilation / breathing
**inspiration** - inhalation / breathing in
**expiration** - exhalation / breathing out
54
What 3 muscles control pressure changes in the lungs
**Diaphragm**- a sheet of muscle that separates the thorax from the abdomen
**Intercostal muscles** - lie between the ribs
- 2 sets:
-**internal intercostal muscles**: contraction leads to expiration
-**external intercostal muscles**: contraction leads to inspiration
55
Which of inspiration or expiration is an active process
Inspiration - requires energy
56
Describe process of inspiration
1) **external** intercostal muscles **contract** as **internal** intercostal muscles **relax**
2) ribs are pulled upwards and outwards, increasing volume of thorax
3) diaphragm muscles contract, so flattens, increasing volume of thorax
4) results in reduction of pressure in the lungs
5) atmospheric pressure is greater than pulmonary pressure in lungs so air is forced into lungs
57
Describe process of expiration
1) **internal** intercostal muscles contract as **external** intercostal muscles relax
2) ribs are pulled **downwards and inwards**, decreasing volume of thorax
3) diaphragm muscles relax, so is pushed up by contents of abdomen that were compressed during inspiration, decreasing volume of thorax
4) results in increase of pressure in the lungs
5) atmospheric pressure is lower than pulmonary pressure in lungs so air is forced out
58
What’s the main cause of air being forced out during normal quiet breathing
Recoil of the elastic tissue in the lungs
Only under strenuous activity like exercise do muscles play a major part
59
What’s the pulmonary ventilation rate and how is it calculated
Total volume of air moved into the lungs during one minute
Pulmonary ventilation rate (dm^3 min^-1) -
= tidal volume (dm^3) x breathing rate (min^-1)
Tidal: volume of air taken in at each breath when body is at rest. Usually 0.5dm^3
Breathing (ventilation) rate: number of breaths taken in 1 min. Usually 12-20
60
How is a constant supply of oxygen to the body ensured
A diffusion gradient is maintained at the alveolar surface
61
Why is the diffusion of gases between the alveoli and the blood very rapid
- red blood cells **slowed** as they pass through pulmonary capillaries = **more time for diffusion**
•the **distance** between the alveolar air & red blood cells is **reduced** as red blood cells are **flattened** against capillary walls
• the **walls** of both alveoli & capillaries are very **thin** = **very short diffusion distance**
• alveoli & pulmonary capillaries have **large total surface area**
• **breathing movements** constantly ventilates lungs, **action of the heart** constantly circulates blood around the alveoli.
Together, ensure steep concentration gradient is maintained
• **blood flow** through pulmonary capillaries maintains a **concentration gradient.**
62
What are the risk factors the increase the probability of getting lung disease
1) Smoking
2) air pollution
3) genetic make-up
4) infections
5) occupation eg: working with harmful chemicals, gases and dusts
63
Describe the human digestive system.
What’s it made up of?
How is it an exchange system through which food substances can be absorbed ?
Made up it a long muscular tube and it’s associated glands
These glands produce enzymes that hydrolyse large molecules into small ones ready for absorption
64
Describe the role of the œsophagus
Carries food from the mouth to the stomach
65
Describe the role of the stomach
The stomach is a **muscular sac** with an **inner layer** that **produces enzymes**.
Its role is to **store and digest food**, especially proteins
It **has glands that produce enzymes**which digest protein
66
What is the ileum (small intestine) and what’s its role
**Long muscular tube**.
**Food is digested by enzymes** that are **produced by its walls & by glands** that pour their secretions into it
Inner walls are folded into villi = large sa
sa of villi increased further by millions of tiny projections (microvilli) on the epithelial cells of each villus
**this adapts the ileum for its purpose of absorbing products of digestion into the bloodstream**
67
Describe the role of the large intestine
Absorbs water
Most of which is from the secretions of many digestive glands
68
Describe the role of the rectum
Final section of the intestines
**Faeces are stored here** before periodically being **removed via the anus** in a process called **egestion**
69
Describe the role of the salivary glands
Situated near the mouth
Pass their secretions via a duct into the mouth
Secretions contain amylase which hydrolyses starch into maltose
70
Describe the role of the pancreas
Large gland situated below stomach
Produces a secretion called pancreatic juice
Contains protease, lipase and amylase to hydrolyse proteins, lipids and starch
71
What are the 2 stages of digestion in humans
Physical breakdown
Chemical breakdown
72
Describe and explain process of physical breakdown
If the food is large it is broken down into smaller pieces by the teeth
Makes it **possible to ingest & provides a larger sa for chemical digestion**
Food is also physically broken down by being churned up by muscles in stomach wall
73
Describe and explain chemical digestion
Hydrolysis large insoluble molecules into smaller soluble ones
Carried out by enzymes which function by hydrolysis
Enzymes are specific so more than one is needed to hydrolyse a large molecule
74
Describe and explain the role of carbohydrases
Hydrolyse carbohydrates, ultimately to monosaccharides
75
Describe the role of lipases
Hydrolyse lipids (fats and oils) into glycerol and fatty acids
76
Describe the role of proteases
Hydrolyse proteins, ultimately to amino acids
77
Give the step by step process of starch digestion in humans
- **Saliva**enters the mouth from salivary glands & mixes thoroughly with food during chewing
- **Amylase** hydrolyses the alternate glycosidic bonds of the starch molecule producing **maltose**
- Food is swallowed, enters the stomach where conditions are acidic- **denatures** amylase & prevents further hydrolysis of the starch
- After a time, food is passed into small intestine where it mixes with pancreatic juice (containing **pancreatic amylase**)
- Allows hydrolysis of remaining starch to maltose to continue
- Muscles in the intestine wall push the food along the ileum. **Epithelial lining** produces disaccharide **maltase**
- Maltase hydrolyses the maltose into **a-glucose**
78
How is the pH of **salivary amylase** maintained at around neutral and why is this important ?
Contains mineral salts - help to maintain neutral pH which is the optimum pH for salivary amylase to work
79
How is the pH of **pancreatic amylase** maintained at around neutral and why is this important ?
Alkaline salts are produced by both the pancreas and the intestinal wall to maintain the pH at round neutral so the amylase can function
80
Why is maltase referred to as a **membrane-bound disaccharide**?
Not released into the lumen of the ileum but is part of the cell-surface membranes of the epithelial cells that line the ileum
81
What does the membrane-bound disaccharide **sucrase** hydrolyse ?
Hydrolyses the single glycosidic bond in the sucrose molecule.
Produces glucose and fructose
82
What does the membrane-bound disaccharide **lactase** hydrolyse ?
Hydrolyses the single glycosidic bond in the lactose molecule
Produces glucose and galactose
83
Describe the process of lipid digestion
- **split up into tiny droplets** called **micelles** by **bile salts** (produced by the liver)
- process is called **emulsification** (increases sa of lipids so that Lipase action is sped up)
- they can then be **hydrolysed by lipases** - (hydrolyse the ester bond in triglycerides to **form fatty acids & monoglycerides**)
84
Describe the process of protein digestion
Proteins are large complex molecules hydrolysed by a group of enzymes called **peptidases** (proteases)
3 types:
- endopeptidases
- exopeptidases
- dipeptidases
85
What is the role of **endopeptidases** in protein digestion
Hydrolyses the peptide bonds between amino acids in the central region of a protein forming a series of peptide molecules
86
What is the role of **exopeptidases** in protein digestion
Hydrolyses the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases
Release dipeptidases and single amino acids
87
What is the role of **dipeptidases** in protein digestion
Hydrolyses the bond between 2 amino acids of a dipeptide
Dipeptidases are membrane-bound, being part of the epithelial cells lining the ileum
88
Which properties of the **villi** increase the efficiency of absorption?
- increase SA for diffusion
- thin walled, reducing diffusion distance
- contain muscle so are able to move - maintains diffusion gradients
- well supplied with blood vessels, blood can carry away absorbed materials (maintains diffusion gradient)
- villi possess microvilli - further increase SA for absorption
89
Which methods are used to absorb amino acids and monosaccharides?
Diffusion and co-transport
90
How are triglycerides formed (from digestion products)
- Micelles come into contact with the epithelial cells lining the villi of the ileum and break down, releasing the monoglycerides and fatty acids.
- As these are non-polar they can diffuse across the cell-surface membrane into the epithelial cells
- they are then transported to the Endoplasmic Reticulum where they’re recombined to form triglycerides
91
How are the triglycerides absorbed once formed ? (from products of digestion)
- Starting in the Endoplasmic Reticulum and continuing in the Golgi apparatus the triglycerides **associate with cholesterol and lipoproteins** to **form structures called chylomicrons**(specially adapted for transport of lipids)
- Chylomicrons **move out of the epithelial cells by exocytosis** and **enter lymphatic capillaries** called **lacteals** and then into the **bloodstream via lymphatic vessels**
- The **triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries** where they **diffuse into cells**
92
Describe in detail the quaternary structure of haemoglobin
All **4 polypeptides** are linked to form **globular** molecule
Each polypeptide is associated with **haem group** containing a **ferrous ion (Fe2+)**
Each Fe2+ can combine with a single oxygen molecule(O2) making **x4 O2 molecules** that can be carried by a single haemoglobin molecule in humans
93
What is the name of the process by which haemoglobin **binds** with oxygen and where does it take place in humans ?
Loading/ associating
Takes place in lungs
94
What is the name of the process by which haemoglobin **releases** its oxygen and where does it take place in humans ?
Unloading/dissociation
Takes place in the tissues
95
Haemoglobins with a **high affinity** for oxygen…
take up oxygen more easily but release it less easily
(Opposite for haemoglobins with low affinity for oxygen)
96
To be efficient at transporting oxygen, haemoglobin must:
- readily associate with oxygen at the surface where gas exchange takes place
- readily dissociate form oxygen at those tissues requiring it
**achieved by ability to change affinity for oxygen under different conditions as a result of shape changes**
97
At the gas exchange surface, under which conditions is the affinity of oxygen optimal ?
High O2 concentration
Low CO2 concentration
98
At the respiring tissues, under which conditions is the affinity of oxygen optimal ?
Low O2 concentration
High CO2 concentration
99
What is oxygen dissociation curve measuring ?
The relationship between the saturation of haemoglobin with oxygen (%) and the partial pressure of oxygen (KPa)
100
Explain the shape of the oxygen dissociation curve (why is the gradient of the curve initially shallow?)
**Shape of the haemoglobin** molecule makes it **difficult for the 1st oxygen molecule to bind** to 1 of the sites on its 4 polypeptide subunits because they are **closely united.**
Therefore at low concentrations, little oxygen binds to the haemoglobin
101
Explain the shape of the oxygen dissociation curve (why does the gradient of the curve steepen?)
The binding of the 1st oxygen molecule changes the quaternary structure of the haemoglobin molecule, causing it to change shape
This change makes it easier for the other subunits to bind to an oxygen molecule
102
What does the term positive cooperativity refer to ?
There is a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind the first one. (Binding becomes easier)
103
Explain the shape of the oxygen dissociation curve (why does the gradient of the curve reduce and flatten off?)
After the binding of the 3rd oxygen molecule probability makes it harder for 4th to bind.
With majority of binding sites occupied, it is less likely that single oxygen molecule will find an empty site to bind to
104
The further to the right the oxygen dissociation curve is, the…
lower the affinity of haemoglobin for oxygen (loads less readily but unloads readily)
Opposite for a curve further to the left
105
What is the Bohr effect
Haemoglobin has a reduced affinity for oxygen in the presence of co2
The greater the co2 conc the more readily the haemoglobin releases its oxygen
106
What is the advantage of having a **low** co2 concentration at the gas-exchange surface (lungs)
At the lungs co2 diffuses across the exchange surface and is excreted from the organism.
The affinity for oxygen is increased, which, coupled with the high conc of oxygen in the lungs means that oxygen is readily associated with haemoglobin.
Oxygen dissociation curve is shifted to the left
107
What is the advantage of having a **high** co2 concentration at the respiring tissues
The affinity of haemoglobin for oxygen is reduced, which, coupled with the low conc of o2 in muscles, means that oxygen is readily dissociated from the haemoglobin to the muscle cells.
Oxygen dissociation curve is shifted to the right
108
How does the body ensure that there is always sufficient oxygen for respiring cells (step by step process of loading, transport and unloading of o2)
- At the gas-exchange surface **co2 is constantly being removed**
- The **pH is slightly raised** (due to the low conc of co2)
- The higher pH **changes the shape of haemoglobin** into one that **enables o2 to be readily loaded**
- **Shape increases the affinity of haemoglobin for o2** so it is not released while being transported in blood to tissues
- In the **tissues co2 is produced** by respiring cells
- CO2 is **acidic in solution so the pH of the blood** within the tissues is **lowered**
- Lower pH **changes shape of haemoglobin** into one with a **lower affinity for o2**
- Haemoglobin **releases its o2 into respiring tissues**
109
Why does the tissue being more active have an effect in the volume of o2 unloaded
The higher the rate of respiration -> more co2 produced -> lower the pH -> greater haemoglobin shape change -> more readily o2 is unloaded -> more o2 available for respiration
110
Whether or not there is a specialised transport medium and whether or not it is circulated by a pump depends on which 2 factors?
The surface area to volume ratio (SIZE)
How active the organism is (METABOLIC RATE)
(The lower the sa:v & the more active the organism is, the greater the need is for a specialised transport system with a pump)
111
Describe the circulatory system in mammals
Closed, double circulatory system
Blood is confined to vessels and passes twice through the heart for each complete circuit of the body
112
Why does the blood pass twice through the heart for each complete circuit of the body ?
Because when **blood is passed through the lungs**, it’s **pressure is reduced**.
**If it were to pass immediately to the rest of the body** its low blood pressure would make **circulation very slow**.
Blood is therefore **returned to the heart to boost its pressure** before being circulated to the rest of the tissues - **substances are delivered** to the rest of the body **quickly**, necessary as mammals have **high body temp and high rate of metabolism**
113
What is the atrium
Thin walled and elastic chamber - stretches as it collects the blood
114
What is the ventricle
Much thicker muscular walled chamber as it has to contract strongly to pump blood some distance, either to lungs or rest of body
115
What do the left and right pumps of the heart individually deal with
Left deals with oxygenated blood from lungs
Right deals with deoxygenated blood from body
116
What are the two valves in the chambers of the heart
The left atrioventricular (bicuspid) valve
The right atrioventricular (tricuspid) valve
117
What is the aorta
Connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs
118
What is the vena cava
Connected to the right atrium and brings deoxygenated blood back from tissues of the body (except the lungs)
119
What is the pulmonary artery
Connected to the right ventricle and carries deoxygnated blood to the lungs where it’s oxygen is replenished and co2 is removed.
120
What is the pulmonary vein
Connected to the left atrium and brings oxygenated blood back from the lungs
121
What happens if the coronary arteries (which branch off from the aorta) is blocked ?
Leads to myocardial infarction or a heart attack because an area of the heart muscle is deprived from blood and therefore oxygen also.
Muscle cells are therefore unable to respire aerobically and so die
122
Which factors can increase the risk of an individual suffering from cardiovascular disease ?
Smoking
High blood pressure
Blood cholesterol
Diet
123
How does smoking increase likelihood of suffering from heart disease
Carbon monoxide - combines easily & irreversibly with haemoglobin to form carboxyhemoglobin **reducing the oxygen carrying capacity of the blood**. Heart has to work harder and blood may be insufficient to supply the heart muscle during exercise = raised blood pressure or chest pain (angina) or in severe cases, heart attacks
Nicotine - stimulates production of adrenalin = increases heart rate and blood pressure - greater risk of heart disease/stroke. Also makes platelets ‘sticky’ - higher risk of thrombosis
124
How does high blood pressure increase risk of heart disease ?
As there is already a higher pressure in the arteries, heart has to work harder to pump blood into them- more prone to failure
Also more likely to develop an aneurysm and burst causing a haemorrhage.
To resist higher pressure the walls of the arteries tend to become thicker and harden restricting blood flow
125
Describe and explain the relaxation of the heart (diastole)
Blood returns to the atria of the heart through the pulmonary vein and vena cava.
**As atria fill pressure inside them rises** & when the this **pressure exceeds that in the ventricles** the **atrioventricular valves open** allowing the blood to **pass through to ventricles**.
At this stage the **muscular walls of both the atria and ventricle are relaxed** which causes them to **recoil and reduces pressure within ventricle**.
The ventricle pressure is lower and so the **semi-lunar valves in aorta and pulmonary artery close** producing the ‘dub’ sound of the heart beat.
126
Describe and explain the contraction of the atria (atrial systole)
The contraction of the atrial walls, along with the recoil of the relaxed ventricle walls, forces the remaining blood into the ventricles from the atria.
Throughout the muscles of the ventricle walls remain relaxed
127
Describe and explain the contraction of the ventricles (ventricular systole)
After a short delay to allow the ventricles to fill with blood their **walls contract simultaneously**.
**Increases the blood pressure within them**, forcing the **atrioventricular valves to shut**, preventing the backflow of blood into the atria, producing a ‘lub’ sound.
The closing of the valves **increases the pressure in the ventricles, forcing blood into the aorta and pulmonary artery**
128
What are valves and what are their roles
Valves in the cardiovascular system are designed so that they open whenever the difference in blood pressure either side of them favours the movement of blood in the required direction.
129
What are atrioventricular valves
Between left atrium and right atrium and ventricle.
These prevent back flow of blood when contraction of ventricles means that ventricular pressure exceeds atrial pressure. Closure of these valves ensures that when the ventricles contract blood within them moves to the aorta and pulmonary artery rather than back to the atria
130
What are semi-lunar valves
Found but the aorta and pulmonary artery.
Prevent backflow of blood into the ventricles when the pressure in these vessels exceeds that of the ventricles. This arises when the elastic walls of the vessels recoil increasing the pressure within them
131
What are pocket valves
In veins.
Ensures that when veins are squeezed blood flows back towards the heart rather than away from it
132
Describe structure of valves
Made up of a number of flaps of tough, but flexible, fibrous tissue which are cusp shaped.
133
Cardiac output (dm3min-1) =
Heart rate x stroke volume
(Stroke volume is the volume of blood pumped out at each beat)
134
What are the 4 different types of blood vessels and what are their functions?
Arteries : carry blood away from heart and into arterioles
Arterioles: smaller arteries that control blood flow frown arteries to capillaries
Capillaries: tiny vessels that link arterioles to veins
Veins : carry blood from capillaries back to heart
135
Describe the basic layered structure of arteries, arterioles and veins from outside in (all have the same)
**tough fibrous outer layer** - resists pressure changes
**muscle layer** - can contract and so control the flow of blood
**elastic layer** - helps to maintain blood pressure by stretching and springing back (recoiling)
**thin inner lining (endothelium)** - smooth to reduce friction and thin to allow diffusion
**lumen**- central cavity through which the blood flows
136
Describe the structure of the artery relative to its function
**thicker muscle layer than veins** - smaller arteries can be constructed and dilated in order to control the vol of blood passing through
**thicker elastic layer than veins** - important for blood pressure to remain high if it is to reach extremities of the body. stretching and recoiling action helps smooth pressure surges caused by the beating of the heart
**overall thickness of wall is great** - resists the vessel bursting under pressure
**there are no valves** - due to high pressure blood tends not to flow backwards
137
Describe the structure of the arteriole related to its function
**thicker muscle layer than in arteries** - contraction of this layer allows constriction of the lumen which restricts blood flow and so controls movement into capillaries
**thinner elastic layer than arteries** - blood pressure is lower
138
Describe the structure of the vein relative to its function
**thin muscle layer**- constriction & dilation can’t control blood flow to tissues
**thin elastic layer** - blood pressure is too low to create recoil action
**overall wall thickness is small** - pressure within is too low for risk of bursting. Also can be easily flattened aiding blood flow
**valves throughout** - ensure no backflow of blood which might otherwise occur due to low pressure
139
Describe the structure of the capillary related to its function
**walls consist mostly of lining layer** - short diffusion distance as thin = rapid diffusion
**numerous and highly branched** - large SA for exchange
**narrow diameter** - permeate tissues which means that no cell is far from a capillary
**narrow lumen** - red blood cells are squeezed flat, bringing them closer to cells supplying o2, reducing diffusion distance
**spaces between lining** - allow white blood cells to escape in order to deal with infections within tissues
140
What is tissue fluid
Supplies glucose, amino acids, fatty acids, ions in solution and o2 to the tissues.
Receives co2 and other waste materials form tissues
Provides a mostly constant environment for the cells it surrounds as it is formed from blood plasma whose composition is controlled by various homeostatic systems
141
In the case of the cytoplasmic route, water movement occurs because:
- Mesophyll cells lose water to the air spaces by evaporation due to heat supplied by the sun
- These cells now have a lower water potential and so water enters by osmosis from neighbouring cells
- The loss of water from these neighbouring cells lowers their water potential
- They in turn, take in water from their neighbours by osmosis
142
What is ultrafiltration
A type of filtration under pressure that removes tissue fluid from capillaries at the arterial end
- pressure is only enough to force small molecules out of the capillaries leaving all cells and proteins in the blood because they are too large to cross cell-surface membranes
143
Give the steps for the return of tissue fluid to the circulatory system
- The **loss of tissue fluid from capillaries reduces the hydrostatic pressure inside them**
- So, by the time the blood has **reached the venous end** of the capillary network, **hydrostatic pressure** is usually **lower than that of the tissue fluid outside** of it
- Therefore **tissue fluid is forced back into the capillaries**
- Also the plasma has lost water yet **plasma proteins remain in the capillaries lowering the water potential of the blood**
- **Water leaves tissue and enters blood by osmosis** down a water potential gradient
144
What happens to the tissue fluid that isn’t returned to the capillaries
Carried back by the lymphatic system (system of vessels that begin in the tissue)
These vessels drain their contents back into the bloodstream via 2 ducts that join veins close to the heart
145
How are the contents of the lymphatic system moved if not by the pumping of the heart?
Hydrostatic pressure of the tissue fluid that has left the capillaries
Contraction of body muscles that squeezes the lymph vessels
146
The movement of water up the stem occurs as follows:
- **Water evaporates from mesophyll cells** due to heat from sun, leading to **transpiration**
- Water molecules **form hydrogen bonds** between one another - **cohesion**
- Water forms a **continuous unbroken column across the mesophyll cells & down the xylem**
- As water evaporates from mesophyll cells in the leaf into the air spaces beneath the stomata, more molecules are drawn up behind it
- The **column of water** is therefore **pulled up the xylem** as a result of transpiration **(transpiration pull)**
- This puts the **xylem under tension**, creating a **negative pressure** in the xylem **(cohesion-tension theory)**
147
What evidence is there for the cohesion tension theory
**Change in diameter of tree trunks according to the rate of transpiration**- during day, when transpiration is at its greatest, there is more tension in xylem- pulls the walls of xylem vessels inwards and causes trunk to shrink in diameter
**If xylem vessel is broken and air enters the tree can no longer draw up water** as continuous column is broken and so no more cohesion
**When a xylem vessel is broken water does not leak out** as it would if under pressure. Instead air is drawn in (consistent with it being under tension)
148
Describe the structure of xylem vessels
Hollow, dead, thick walled tubes
No end walls
149
Is transpiration pull passive or active
Passive
150
Explain the steps to find the rate of water loss using a potometer
- A leafy shoot is cut under water. Don’t get water on leaves
- Potometer is filled completely with water, no air bubbles
- Using a rubber tube, the leafy shoot is fitted to the Potometer underwater
- The Potometer is removed form under water and joints are sealed with waterproof jelly
- An air bubble is introduced to capillary tube
- Distance moved by air bubble in given time is measured a number of times & mean is calculated
- Volume of water loss is calculated & plotted against time on graph
151
Describe the structure of the phloem and how is it adapted for mass transport
Made up of sieve tube elements
Walls are perforated to form sieve plates
Companion cells are associated with sieve tube elements (contain many mitochondria for production of ATP)
Few organelles to allow more room for mass flow
152
What are ‘sources’ and ‘sinks’
**Source** - site of production of sugars during photosynthesis
**Sink** - places where sugars produced during photosynthesis can be used directly or stored for future use
(Sinks can be found anywhere in plant, sometimes above a source. Therefore translocation in phloem can be in either direction)
153
What does mass-flow theory refer to
The mechanism of translocation
154
Give the steps in the 1st step of translocation: transfer of sucrose into sieve elements from photosynthesising tissue
- Sucrose is manufactured from the products if photosynthesis in cells with chloroplasts
- Sucrose diffuses **down a conc gradient** by **facilitated diffusion** from photosynthesising cells into companion cells
- Hydrogen ions are **actively transported** from companion cells into spaces within cell walls using **ATP**
- They then diffuse down a conc gradient through **carrier proteins** into sieve tube elements
- Sucrose molecules are transported along with the hydrogen ion - **co-transport**. Protein carriers are therefore known as **co-transport proteins**
155
Give the steps in the 2nd step of translocation: Mass flow of sucrose through sieve tube elements
sucrose has been actively transported into sieve tubes (as described in previous step)…
- This causes sieve tubes to have a lower **water potential**
- As the xylem has a much higher water potential, water moves from xylem into the sieve tubes **by osmosis** creating a **high hydrostatic pressure** within them
- At the sinks, sucrose is being used up for respiration or converted to starch for storage
- Sinks therefore have a low sucrose content and so sucrose is **actively transported** into them from sieve tubes, lowering water potential
- Due to lowered water potential, water also moves in from sieve tubes by osmosis
- Hydrostatic pressure if sieve tubes in this region is lowered
- Therefore there is a **mass flow** of sucrose solution down this **hydrostatic gradient** in sieve tubes
156
Is mass flow passive or active ?
While mass flow is passive it occurs as a result of the active transport of sugars.
Therefore the process as a whole is **active** which is why it’s affected by temperature and metabolic poisons
157
Give evidence supporting the mass flow theory
- there is pressure within sieve tubes, as shown by sap being released when cut
- conc of sucrose is higher in leaves (source) than in roots (sink)
- downward flow in the phloem occurs in daylight but ceases when leaves are shaded or at night
- increase in sucrose levels in the leaf followed by similar increases in sucrose levels in phloem a little later
- metabolic poisons and/or lack of oxygen inhibit translocation of sucrose in phloem
- companion cells contain many mitochondria and readily produce ATP
158
Give evidence questioning the mass flow theory
- function of sieve plates is unclear, as they would seem to hinder mass flow (suggested structural function)
- not all solutes move at same speed - they should do if movement is by mass flow
- sucrose is delivered at more or less the same rate to all regions rather than going more quickly to ones with lowest sucrose conc
159
Give the steps in the 3rd step of translocation: transfer of sucrose from sieve tube elements into storage or other sink cells
Sucrose is actively transported by companion cells out of the sieve tubes and into the sink cells
160
The observations made in ringing experiments suggest that removing the phloem around the stem has led to…
The sugars of the phloem accumulating above the ring, leading to swelling in this region
The interruption of flow of sugars to the region below the ring and the death of tissues in this region
**shows us that phloem rather than xylem is responsible for translocating sugars in plants**
161
What is a ringing experiment and how is it used ?
Woody stem cross section : layer of bark > layer of phloem > layer of xylem
Section of outer layers (bark and phloem) are removed around the complete circumference of the stem while it is still attached to rest of the plant.
After a period of time the region above the missing ring of tissue will swell.
Samples of the liquid accumulated in the swollen region are found to be rich in sugars and other dissolved substances.
Below the ring tissue withers and dies
162
What are tracer experiments and how are they used?
Radioactive isotopes are useful for tracing movement of substances in plants
Isotopes can radioactively label co2 for example.
If a plant is then grown in an atmosphere containing that substance the isotope will be incorporated into the sugars during photosynthesis.
These sugars can then be traced as they move within the plant using **autoradiography**
163
Explain how autoradiography is used in tracer experiments
Involves taking thin **cross sections** of the plant stem and placing them on a piece of **x-ray film.** The film **becomes black** where it has been exposed to the radiation produced by the radioactive isotope in the sugars.
Blackened regions are found to **correspond** to where the **phloem tissue** is in the stem.
The non-blackened regions of the film do not carry sugars which **shows that the phloem alone is responsible for their translocation**
164
State what assumption must be made if a Potometer is used to measure the rate of transpiration
That all water taken up is transpired
(Some can be used in respiration)
165
Explain why phloem pressure is reduced in the hottest part of the day (use understanding of transpiration and mass flow)
At the hottest part of the day, the rate of **water loss by transpiration is high.**
This creates **high tension in the xylem**.
Means that **less water is diffused from xylem by osmosis** because of **insufficient water potential gradient**
166
How is tissue fluid pushed out of the capillaries
Pumping of the heart creates hydrostatic pressure at the arterial ends of the capillaries - causes tissue fluid to move out
167
The combined effect of which 2 forces creates an overall pressure that pushes tissue fluid out of the capillaries ?
Hydrostatic pressure of the tissue fluid outside the capillaries which resists outward movement of liquid
Lower water potential of the blood, due to the plasma proteins that causes water to flow back into blood within capillaries
