Exchange Between Organisms And Their Environment Flashcards

Question

What are the features of exchange surfaces?

Answer 1

•Large surface area often achieved by folding •Thin so short diffusion distance •Steep concentration gradient •Maintained by a fresh supply of substances on one side (to maintain high concentration) •Rapid removal of substance on the other side (to maintain low concentration) - selectively permeable to allow selected materials to cross

Answer 2

``` -Alveoli in lungs: gas exchange (oxygen in / carbon dioxide out) •Gills in fish •Villi in small intestine •Hepatocytes in liver •Mesophyll tissue in leaf •Root hair cells ```

Answer 3

surface area for absorption of the products of digestion- microvilli further increase surface area of epithelial cells in small intestine and of hepatocytes in liver

Answer 4

* Removes excess glucose from blood to store as glycogen * Releases glucose back into blood when blood glucose levels are low * Removes excess amino acids from blood

Answer 5

Root hairs increase surface area for: •Uptake of water by osmosis •Uptake of mineral ions by active transport

Answer 6

A cell-surface membrane (in the same way,carbon dioxide from respiration diffuses out across their body surface- where a living cell is surrounded by a cell wall, this is no additional barrier to the diffusion of gases)

Answer 7

1- surface area of a sphere= 4X pi X r squared 2- surface area of the cell = 4 X 3.14 X (5X5) = 314 micrometers squared 3- volume of a sphere= 4/3 X pi X r cubed 4- volume of the cell = 4/3 X 3.14 X (5X5X5)= 523.33 micrometers cubed 5- SA: V ratio = 3.14/ 523.33= 0.6:1

Answer 8

- surface area/ thickness of cell-surface membrane - permeability of cell-surface membrane to particular substance - concentration gradient of substance inside/outside of cell - temperature

Answer 9

Rate of diffusion = area of diffusion surface X difference in conc ——————————————————— Thickness of surface over which diffusion takes place

Answer 10

Tracheal system

Answer 11

- insects have evolved an internal network of tubes called tracheae - the trachea are supported by strengthened rings to prevent them from collapsing - the trachea divide into smaller dead-end tubes called tracheoles - the tracheoles extend throughout all the body tissues of the insect - in this way, atmospheric air with the oxygen it contains is brought directly to the respiring tissues as there is a short diffusion pathway from a tracheole to any body cell

Answer 12

1- along a diffusion gradient 2- mass transport 3- the ends of tracheoles are filled with water

Answer 13

When cells are respiring, oxygen is used up and so its concentration towards the end of the tracheoles falls. This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheoles to the cells. Carbon dioxide is produced by cells during respiration; this creates a diffusion gradient in the opposite direction. This causes gaseous carbon dioxide to diffuse along the tracheoles and trachea from the cells to the atmosphere

Answer 14

Diffusion in air much faster than in water, respiratory gases are exchanged quickly by this method

Answer 15

The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases

Answer 16

- During periods of major activity, the muscle cells around the tracheoles respire and carry out anaerobic respiration, producing lactate which is soluble and lowers the water potential of the muscle cells. Water therefore moves into the cells from the tracheoles by osmosis - the water in the ends of the tracheoles decreases in volume and in doing so draws air further into them - this means the final diffusion pathway is in a gas rather than a liquid phase and therefore diffusion is more rapid = increases the rate at which air is moved into the tracheoles but leads to greater water evaporation

Answer 17

On the body surface

Answer 18

Water vapour can evaporate from insect; so most of the time, insects keep their spiracles closed to prevent this water loss. But periodically they do open the spiracles to allow gas exchange

Answer 19

- because it relies on diffusion to bring oxygen to the respiring tissues - if insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs

Answer 20

Gas exchange requires a thin, permeable surface with a large area and conserving water requires thick, waterproof surfaces with a small area

Answer 21

Fish have a waterproof (and therefore gas-tight) outer covering; being relatively large they have a small SA:vol ratio= like humans and insects they have evolved a specialised internal gas exchange- the gills

Answer 22

- The gills are located within the body of the fish, behind the head - they are made up of stacked gill filaments - perpendicular to the gill filaments are gill lamellae which increase the surface area of the gills - water is taken in through their mouth and forced over the gills out through an opening on each side of the body - the flow of water over the gill lamellae and the flow of blood within them are in opposite directions = counter-current flow

Answer 23

- the essential feature of the countercurrent exchange system is that blood and water flow over the gill lamellae in opposite directions meaning that: - blood that is already well loaded with oxygen meets water that has its maximum concentration of oxygen therefore diffusion of oxygen from water to the blood takes place - blood with little oxygen in it meets water which has had most, but not all of its oxygen removed. Again, diffusion of oxygen from the water to the blood takes place

Answer 24

A diffusion gradient for oxygen is maintained across the ENTIRE WIDTH of the gill lamellae. In this way, about 80% of the oxygen available in the water is absorbed into the blood of the fish

Answer 25

If the flow of water and blood was in the same direction (parallel flow) the diffusion gradient would only be maintained across part of the length of the gill lamellae and only about 50% of the available oxygen would be absorbed

Answer 26

- gill filaments and lamellae increase the surface area increasing rate of exchange of gases - lamella have lots of blood capillaries and thin epithelium increasing rate of diffusion- thin layer of cells= short diffusion pathway

Answer 27

Less energy is required because the flow does not have to be reversed (important as water is dense and difficult to move)

Answer 28

If an organism has a large volume e.g. hippo, its surface area is relatively small making it harder to lose heat from its body

Answer 29

If an organism is small e.g. mouse its relative surface area is large, so heat is lost more easily meaning smaller organisms need a relatively high metabolic rate in order to generate enough heat to stay warm

Answer 30

Animals with a compact shape have a small surface area relative to their volume, minimising heat loss from their surface- animals with a less compact shape (those that are a bit gangly or have sticky outy bits) have a larger surface area relative to their volume, increasing heat loss from their surface

Answer 31

1- animals with a high SA: volume ratio tend to lose more water as it evaporates from their surface. Some small desert mammals have kidney structure adaptions so that they produce less urine to compensate 2- to support their high metabolic rates, small malls living in cold regions need to eat large amounts of high energy goods such as seeds and nuts 3- smaller mammals may have thick layers of fur or hibernate when the weather gets very cold 4- larger organisms living in hot regions e.g. elephants and hippos find it hard to keep cool as their heat loss is relatively slow. Elephants have developed large flat ears to increase their surface area, allowing them to lose more heat - hippos spend much of their day in the water- behavioural adaption to help them lose heat

Answer 32

Some plant cells (plant cells with chloroplasts) photosynthesis

Answer 33

In respiration and vice versa- reducing gas exchange with the external air

Answer 34

The balance between rates of photosynthesis and respiration

Answer 35

mitochondria carrying out respiration and chloroplasts carrying out photosynthesis

Answer 36

The external air

Answer 37

Diffuses out of the cell

Answer 38

Oxygen diffuses into the leaf because it is constantly being used by cells during respiration; in the same way, carbon dioxide produced from respiration diffuses out

Answer 39

- no living cell is far from the external air and therefore, a source of oxygen and carbon dioxide - diffusion takes place in the gas phase (air) which makes it more rapid than if it were in water

Answer 40

Which simply diffuse in and out the leaves

Answer 41

The surface of the mesophyll cells in the leaf. Gases move in and out through special pores in the epidermis called stomata (occur mainly on underside of leaf) which can open to allow exchange of gases and close if the plant is losing too much water

Answer 42

Guard cells

Answer 43

1- many stomata (small pores), so no cell is far from a stomata and therefore the diffusion pathway is short 2- numerous interconnecting air spaces that occur throughout the mesophyll so that gases can readily come into contact with mesophyll cells 3- Large surface area of mesophyll cells for rapid diffusion

Answer 44

- insects may create mass air flow whereas plants never do - insects have a smaller SA: vol ratio than plants - insects have special structures (trachea) along which gases can diffuse, whereas plants do not - insects do not interchange gases between respiration and photosynthesis whereas plants do

Answer 45

Helps to control water loss by evaporation/ transpiration

Answer 46

Compromising the efficiency of their gas-exchange systems

Answer 47

- small SA: vol ratio to minimise the area over which water is lost - waterproof coverings over their body surfaces: a rigid outer skeleton of chitin that is covered with a waterproof cuticle - spiracles: if losing too much water they close their spiracles using their muscles - tiny hairs around spiracles to reduce evaporation

Answer 48

An internal network of tubes called tracheae that carry air containing oxygen directly to the tissues

Answer 49

Plants photosynthesis which requires a large SA for the capture of light

Answer 50

- waterproof waxy cuticle over parts of the leaves - stomata: stomata are usually kept open in the dah to allow gaseous exchange. Water enters the guard cells, making them turgid which opens the stomata pore. If the plant starts to become dehydrated, the guard cells lose water and become flaccid which closes the pore

Answer 51

Xerophytes

Answer 52

- thick waxy cuticles on leaves and stems to reduce evaporation - rolling up of leaves: protects the lower epidermis from the outside helps trap a region of still air within the rolled leaf. This region becomes saturated with water vapour and so has a very high water potential. There is no water potential gradient between the inside and outside of the leaf and therefore no water loss e.g. Marram grass - layer of ‘hairs’ on epidermis traps still,moist air next to the leaf surface. The water potential gradient between the inside and the outside of the leaves is reduced and therefore less water is lost through evaporation e.g. species of heather plant - reduced number of stomata = fewer pores for water to escape - reduced SA:volume ratio of the leaves e.g. pine needles as opposed to broad flat leaves considerably reduces rate of water loss (reduced evaporation)- this reduction in SA is balanced against the need for a sufficient area for photosynthesis to meet the requirements of the plant

Answer 53

Efficient gas exchange requires a thin, permeable surface with a large area. On land these features can lead to a considerable loss of water by evaporation

Answer 54

- Waterproof covering to the body | - Ability to close the openings of the gas exchange system (stomata and spiracles)

Answer 55

Almost all stomata are on the lower epidermis. This would be exposed to air currents that would reduce the water potential immediately outside the leaf. The water potential gradient would be increased and a lot of water vapour would be lost

Answer 56

Epithelium of the alveoli in the lungs

Answer 57

- relatively large organisms with a larger volume of living cells - they maintain a high body temperature which is related to them having metabolic and respiratory rates As a result, mammals have evolved specialised surfaces called lungs to ensure efficient has exchange between the air and their blood

Answer 58

- air is not dense enough to support and protect these delicate structures - the body as a whole would otherwise be a great deal of water and dry out

Answer 59

The ribcage

Answer 60

The muscles between them

Answer 61

A tidal stream of air, thereby ensuring that the air within them is constantly replenished

Answer 62

- lungs - trachea - bronchi - bronchioles - trachea

Answer 63

Pair of lobed structures made up of a series of highly branched tubules called bronchioles, which end in tiny air sacs called alveoli

Answer 64

Flexible airway supported by rings of cartilage that prevent the trachea collapsing as the air pressure inside falls when breathing in. The tracheal walls are made up of muscle lined with ciliated epithelium and goblet cells

Answer 65

Two divisions of the trachea, each leading to one lung. They are similar in structure to the trachea and, like the trachea, they also produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat. The larger bronchi are supported by cartilage but the amount of cartilage is reduced as the bronchi get smaller

Answer 66

Series of branching subdivisions of the bronchi. Their walls are made of muscle lined with epithelial cells. This muscle allows them to constrict so that they can control the flow of air in and out of the alveoli

Answer 67

Minute air-sacs with a diameter between 100-300 micrometers, at the end of the bronchioles. Between the alveoli there are some elastic and collagen fibres and the alveoli are lined with epithelium. The elastic fibres allow the alveoli to stretch as they fill with air when breathing in. They then spring back during breathing out in order to expel the carbon dioxide rich-air. The alveoli membrane is the gas exchange surface.

Answer 68

Oxygen in air moves through the nose, the trachea, the bronchi and bronchioles into the alveoli down a pressure gradient. Once in the alveoli, the oxygen diffuses across alveolar epithelium, then the capillary endothelium down a diffusion gradient ending up in the capillary itself

Answer 69

ciliated epithelium and goblet cells- goblet cells produce mucus that ‘traps’ particles of dirt and bacteria in the air breathed in. The cilia on these cells moves the debris up the trachea and into the stomach. The dirt/bacteria could possibly cause damage to the alveoli

Answer 70

Move air in and out

Answer 71

To maintain diffusion of gases across the alveolar epithelium, air is constantly moved in and out the lungs= ventilation

Answer 72

When the air pressure of the atmosphere is grater than the air pressure inside the lungs air is forced into the lungs

Answer 73

When the air pressure inside the lungs is greater than that of the atmosphere, air is forced out the lungs

Answer 74

- the diaphragm (sheet of muscle that separates the the thorax from the abdomen) - the intercostal muscles which lie between the ribs. There are 2 types of intercostal muscles: - internal intercostal muscles= whose contraction leads to exhalation - external intercostal muscles= whose contraction leads to inhalation

Answer 75

- the external intercostal muscles and diaphragm contract while the internal intercostal muscles relax - causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity (space where lungs are) - as the volume of the thoracic cavity increases the lung pressure decreases (to below atmospheric pressure) - as air moves down a pressure gradient, the air flows down the trachea into the lungs - inhalation is an active process so requires energy

Answer 76

1- the external intercostal muscles and diaphragm relax 2- the ribcage moves downwards and inwards and the diaphragm becomes curved again 3- the volume of the thoracic cavity decreases causing the air pressure to increase (above atmospheric pressure) 4- air is forced down the pressure gradient and out of the lungs 5- normal exhalation is a passive process so doesn’t require energy

Answer 77

The external intercostal muscles relax and the internal intercostal muscles contract, pulling the ribcage further down and inwards- during this time, the movement of the two sets of intercostal muscles is said to be antagonistic

Answer 78

Pulmonary ventilation= tidal volume X breathing rate | Check camera roll for units

Answer 79

And the internal medium (e.g. blood)

Answer 80

Thin, flat cells called the alveolar epithelium

Answer 81

1- there’s a huge number of alveoli in the lungs which means there’s a big surface area for exchanging oxygen and carbon dioxide 2- the alveolar are surrounded by a network of capillaries 3- oxygen diffuses out of the alveoli across the alveolar epithelium and the capillary endothelium (type of epithelium that forms the capillary wall) and into the haemoglobin in the blood 4- Carbon dioxide diffuses into the alveoli from the blood and is exhaled out

Answer 82

- red blood cells (erythrocytes) are slowed as they pass through pulmonary capillaries allowing more time for diffusion - the distance between the alveolar air and the erythrocytes is reduced as the erythrocytes are flattened against the capillary walls - alveoli have only a single layer of epithelial cells and the blood capillaries have only a single layer of endothelium cells therefore short diffusion pathway - alveoli and pulmonary capillaries have a very large total surface area - breathing movements constantly ventilate the lungs and the action of the heart constantly, circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of gases to be exchanged is maintained

Answer 83

- thin surface exchange- alveolar epithelium single layer of epithelial cells = short diffusion pathway which speeds up diffusion - large surface area= the large number of alveoli means there’s a large surface area for gas exchange - each alveolus is covered by a dense network of pulmonary blood capillaries= steep concentration gradient of oxygen and carbon dioxide between alveoli and capillaries which increases rate of diffusion- this is constantly maintained by the flow of blood and ventilation (blood capillaries have only a single layer of endothelial cells)

Answer 84

Volume of air in each breath- usually between 0.4dm^3 and 0.5dm^3 for adults

Answer 85

Number of breaths per minute- for a healthy person it’s about 15 breaths

Answer 86

Maximum volume of air that can be breathed out in 1 second

Answer 87

Maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in

Answer 88

Spirometer

Answer 89

- pulmonary tuberculosis (TB) - fibrosis - asthma - emphysema

Answer 90

- when someone becomes infected with TB, immune system cells build a wall around the bacteria in the lungs forming small, hard lumps known as tubercles - infected tissue within the tubercles dies and gaseous exchange surface is damaged so tidal volume is decreased - tuberculosis also causes fibrosis which further reduces the tidal volume - a reduced tidal volume means less air can be inhaled with each breath. In order to take in enough oxygen, patients have to breathe faster I.e. ventilation rate is increased - common symptoms include a persistent cough, coughing up blood and mucus, chest pains and shortness of breath and fatigue

Answer 91

- fibrosis is the formation of scar tissue in the lungs; this can be the result of an infection of exposure to substances like asbestos or dust - scar tissue is thicker and less elastic than normal lung tissue = lungs less able to expand so can’t hold as much air as normal = tidal volume decreased and so is forced vital capacity (FVC) - there’s a reduction in the rate of gaseous exchange- diffusion is slower across a thicker scarred membrane - symptoms of fibrosis in our shortness of breath, a dry cough, chest pain, fatigue and the weakness - fibrosis sufferers have a fast ventilation rate than normal (to get sufficient air into their lungs to oxygenate their blood)

Answer 92

- asthma is a respiratory condition where the airways become inflamed and irritated- the causes vary from case to case but it’s usually because of an allergic reaction to substances such as pollen and dust - during an asthma attack, the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced = constriction of the airways making it difficult for the sufferer to breathe properly. Air flow in and out of the lungs is severely reduced,so less oxygen enters the alveoli and moves into the blood. Reduced air flow means that forced expiratory volume is severely reduced I.e. less air can be breathed out in 1 second - symptoms include wheezing, a tight chest and shortness of breath. During an attack, the symptoms come on very suddenly- they can be relived by drugs (often in inhalers) which cause the muscle in the bronchioles to relax, opening up the airways

Answer 93

- emphysema is a lung disease caused by smoking or long-term exposure to air pollution- foreign particles in the smoke (or air) become trapped in the alveoli = causes inflammation which attracts phagocytes to the area- the phagocytes produces an enzyme that breaks down elastin (a protein found in the walls of the alveoli). Elastin is elastic and helps the alveoli to return to their normal shape after inhaling and exhaling air.loss of elastin means the alveoli can’t recoil to expel air as well (it remains trapped in the alveoli) - emphysema also leads to the destruction of the alveoli walls which reduces the surface area of the alveoli, so the rate of gaseous exchange decreases - symptoms of emphysema include shortness of breath and wheezing. People with emphysema have an increased ventilation rate as they try to increase the amount of air (containing oxygen) reaching their lungs

Answer 94

All of those lung diseases reduce the rate of gaseous exchange in the alveoli. Less oxygen is able to diffuse into the bloodstream, so the body cells receive less oxygen and the rate of aerobic respiration is reduced = less energy released and so sufferers often feel tired and weak

Answer 95

The human digestive system is made up of a long muscular tube and its associated glands- the glands produce enzymes that hydrolyse larger molecules into smaller ones ready for absorption. The digestive system is therefore an exchange surface through which food substances are absorbed

Answer 96

Process in which large molecules are hydrolysed by enzymes into small molecules which can be absorbed and assimilated

Answer 97

Carries food from the mouth to the stomach

Answer 98

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 that digest proteins

Answer 99

The ileum is a long muscular tube- food is further digested in the ileum by enzymes that are produced by its walls and by glands that pour their secretions into it. The inner walls of the ileum are folded into villi which gives them a large surface area- the surface area of these villi is further increased by millions of tiny projections called microvilli on the epithelial cell of each villus = adapts ileum for its purpose of absorbing the products of digestion into the bloodstream

Answer 100

Absorbs water- most of the water that is absorbed is water from the secretion of the many digestive glands

Answer 101

Final section of the intestines- the faeces are stored here before being periodically being removed via the anus in a process called egestion

Answer 102

Situated near the mouth- they pass their secretions via a duct into the mouth. These secretions contain the enzyme amylase which hydrolyses starch into maltose

Answer 103

Large gland situated below the stomach and produces a secretion called pancreatic juice- this secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch

Answer 104

1- physical breakdown | 2- chemical digestion

Answer 105

The cells and cell-surface membranes of the epithelial lining of the intestines

Answer 106

If the food is large, it is broken down into smaller pieces by means of structures such as the teeth; this not only makes it possible to ingest the food but provides a large surface area for chemical digestion. Food is churned up by muscles in the stomach wall and this also physically breaks it up

Answer 107

Can’t be absorbed from the gut into the blood

Answer 108

Chemical digestion hydrolyses large, insoluble molecules into smaller, soluble ones carried out by enzymes- enzymes are specific and so it follows that more than one enzyme is needed hydrolyse a large molecule. Usually, one enzyme hydrolyses a large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes

Answer 109

1- carbohydrases hydrolyse carbohydrates ultimately to monosaccharides 2- lipases hydrolyse lipids to fatty acids and glycerol 3- proteases hydrolyse proteins, ultimately to amino acids

Answer 110

1- saliva enters the mouth from the salivary glands and is thoroughly mixed with food during chewing. Saliva contains the enzyme salivary amylase which hydrolyses any starch present in the food into maltose by hydrolysing the alternate glycosidic bonds. It also contains mineral salts that help to maintain the PH at around neutral, as this is the optimum PH for amylase to work 2- the food is swallowed and enters the stomach, where the conditions are acidic, denaturing the amylase, preventing further hydrolysis of starch. 3- after a time,the food is passed to the small intestine where it mixes with the secretion from the pancreas, pancreatic juice. This pancreatic juice contains pancreatic amylase, which continues the hydrolysis of any remaining starch to maltose. Alkaline salts are produced by both the pancreas and the intestinal wall, to maintain the PH at around neutral, so that amylase can function. 4- muscles in the intestinal wall push the food along the ileum; its epithelial tissue produces the disaccharide maltase. Maltase is part of the cell-surface membranes of the epithelial cells, that line the ileum, so it is therefore referred to as a membrane-bound disaccharide. The maltase hydrolysis the maltose from the starch breakdown to a-glucose

Answer 111

1- sucrase (in lots of fruits) hydrolyses the single glycosidic bond in sucrose to give glucose and fructose 2- lactase hydrolyses the single glycosidic bond in the lactose molecule to give glucose and galactose

Answer 112

- Lipids are hydrolysed by enzymes called lipases - lipases are enzymes produced in the pancreas that hydrolyse the ester bond found in the triglycerides to form fatty acids and monoglycerides (glycerol molecule with a single fatty acid attached) - lipids are firstly split up into tiny droplets called micelles, by bile salts, which are produced by the liver- emulsification and increases the surface area of lipids, so that the action of lipases is speeded up

Answer 113

- Proteins (polypeptides) are large, molecules that are hydrolysed by a group of enzymes called peptidases (proteases) - endopeptidases: hydrolyse the amino acids in the central region of a protein molecule, forming a series of peptide molecules - exopeptidases: hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases - dipeptidases: hydrolyse the bond between the two amino acids of a dipeptide- dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum

Answer 114

Villi and microvilli increase surface area to speed up absorption of soluble molecules. As the food in the stomach has not yet been hydrolysed into soluble molecules they cannot be absorbed so villi and microvilli are unnecessary

Answer 115

Low water potential in the colon causes water to move from epithelial cells in the lumen of the colon creating watery stools

Answer 116

- ileum adapted to the function of absorbing the products of digestion - the wall of the ileum is folded and possess finger-like projections called villi- they have thin walls lined with epithelial cells on the other side of which is a rich network of blood capillaries - the villi considerably increase the surface area of the ileum and therefore accelerate the rate of absorption

Answer 117

At the interface between the lumen of the intestines (in effect the outside of the body)

Answer 118

- they increase surface area for diffusion - they are very thin walled, thus reducing the distance over which diffusion takes place - they contain muscle so are able to move. This helps to maintain diffusion gradients because their movement mixes the contents of the ileum; this ensures that as the products of digestion are absorbed from the food adjacent to the villi, new material rich in the products of digestion replaces it - well supplied with blood vessels so blood can carry away absorbed molecules and hence maintain a diffusion gradient - epithelial cells lining the villi possess microvilli- finger-like projections of the cell-surface membrane that further increase the surface area for absorption

Answer 119

Ileum epithelium into the bloodstream

Answer 120

- glucose is absorbed by active transport with sodium ions via a co-transporter protein; galactose is absorbed in the same way using the same co-transporter protein - fructose is absorbed via facilitated diffusion through a different transporter protein

Answer 121

- once formed during digestion, monoglycerides and fatty acids remain in association with the bile salts that initially emulsified the lipids droplets- structures formed called micelles - through the movement of material within the lumen of the ileum, the micelles come into contact with the epithelial cells lining the villi of the ileum - here the micelles break down, releasing the monoglycerides and fatty acids (as these are non-polar molecules they can easily diffuse across the cell-surface membrane into the epithelial cells - once inside the epithelial cells monoglycerides and fatty acids are transported to the ER where they are recombined to form triglycerides. Starting in the ER and continuing into the Golgi apparatus, the triglycerides associate with cholesterol and lipoproteins to form structures called chylomicrons (specialised particles adapted for the transport of lipids) - chylomicrons move out of the epithelial cells by exocytosis and they enter lymphatic capillaries called lacteals that are found at the centre of each villus. From here, the chylomicrons pass via lymphatic vessels into the blood system. The triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of the blood capillaries from where they diffuse into cells

Answer 122

- ER to re-synthesise triglycerides from monosaccharides and fatty acids - Golgi apparatus to form chylomicrons from triglycerides, cholesterol and lipoproteins - mitochondria to provide ATP required for co-transport of glucose and amino acid molecules

Answer 123

Globular protein in erythrocytes that readily combines with oxygen to transport it around the body- it comprises 4 polypeptide chains each containing an iron-containing haem group

Answer 124

unloading it under a different set of conditions

Answer 125

- primary structure= sequence of amino acids in the 4 polypeptide chains - secondary structure= in which each of these polypeptide chains is coiled into a helix - tertiary structure= in which each polypeptide chain is folded into a precise shape- an important factor in its ability to carry oxygen - quaternary structure= in which all 4 polypeptides are linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group, which contains a ferrous ion; each ferrous ion can combine with a single oxygen molecule making a total of 4 oxygen molecules that can be carried by a single haemoglobin molecule in humans

Answer 126

Loading or associating; in humans this takes place in the lungs = oxyheamoglobin - haemoglobin saturation depends on partial pressure of oxygen. Oxygen loads onto haemoglobin to form oxyhaemoglobin where there’s a high partial pressure of oxygen (oxygen enters blood capillaries at alveoli in lungs so alveoli have high partial pressure of oxygen)

Answer 127

Unloading or dissociating; in humans this takes place in the tissues

Answer 128

Take up oxygen more easily, but release it less easily

Answer 129

Take up oxygen less easily, but release it more easily

Answer 130

- readily associate with oxygen at the surface where gas exchange occurs - readily dissociate from oxygen at tissues requiring it - these two requirements may appear to contradict each other, but they are achieved by a remarkable property of haemoglobin- it changes its affinity (chemical attraction) for oxygen under certain conditions. It achieves this because its shape changes in the presence of certain chemicals, like carbon dioxide- in the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen = haemoglobin releases its oxygen

Answer 131

- each species produces a haemoglobin with a slightly different amino acid sequence - haemoglobin of each species therefore has a slightly different tertiary and quaternary structure and hence different oxygen binding properties - depending on its structure, haemoglobin molecules range from those that have a high affinity for oxygen to those that have a low affinity for oxygen

Answer 132

- different base sequences in DNA - different amino acid sequences - different tertiary/quaternary structure and shape - different affinities for oxygen

Answer 133

If all oxygen molecules were released, there would be none in reserve to supply tissues when they were more active

Answer 134

Carbon monoxide will gradually occupy all the binding sites on haemoglobin instead of oxygen. No oxygen will be carried to tissues such as the brain. These will cease to respire and to function, making the person lose consciousness

Answer 135

When haemoglobin is exposed to different partial pressures of oxygen, it does not bind the oxygen evenly. The graph of the relationship between between the saturation of haemoglobin with oxygen and the partial pressure of oxygen = oxygen dissociation curve

Answer 136

Check camera roll

Answer 137

1- shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bid to one of the sites on its four polypeptide subunits because they’re closely united. Therefore, at low oxygen concentrations, little oxygen binds to haemoglobin = gradient of curve is shallow initially 2- however, binding of this first 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 I.e. binding of first oxygen molecule induces the other subunits to bind to an oxygen molecule 3- it therefore takes a smaller increase in partial pressure of oxygen to bind to the second oxygen molecule than it did the first = positive cooperativity as binding of the first oxygen molecule makes binding of the second easier and so on= gradient of curve steepens 4- situation changes however after binding of the third oxygen molecule simply due to probability- with the majority of binding sites occupied, it is less likely that a single oxygen molecule will find an empty site to bind to = gradient of curve reduces and graph flattens off

Answer 138

1- the further to the left the curve, the greater is the affinity of haemoglobin for oxygen (so it loads oxygen readily but unloads it less easily) 2- the further to the right the curve, the lower is the affinity of haemoglobin for oxygen (so it loads oxygen less readily but unloads it more easily)

Answer 139

Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide- the greater the concentration of carbon dioxide (higher the partial pressure of carbon dioxide) the more readily haemoglobin releases its oxygen = Bohr effect

Answer 140

(To complicate matters, haemoglobin gives up its oxygen more readily at higher partial pressures of carbon dioxide= cunning way of getting more oxygen to cells during activity) 1- when cells respire they produce carbon dioxide which raises the partial pressure of carbon dioxide 2- this increases the rate of oxygen unloading (I.e the rate at which oxyhaemoglobin dissociates to form haemoglobin and oxygen) = dissociation curve ‘shifts’ to the right. The saturation of blood with oxygen is lower for a given partial pressure of oxygen meaning more oxygen is being released = BOHR EFFECT

Answer 141

- at the gas exchange-surface e.g. lungs, the concentration of carbon dioxide is low because it diffuses across the exchange surface and is excreted from the organism. The affinity of haemoglobin for oxygen is increased, which coupled with high concentrations of oxygen in the lungs, means that oxygen is readily loaded by haemoglobin. The reduced carbon dioxide concentration has ‘shifted’ the oxygen dissociation curve to the left - in rapidly respiring tissues e.g. muscles, the concentration of carbon dioxide is high= the affinity of haemoglobin for oxygen is reduced, which coupled with low concentrations of oxygen in the muscles means that oxygen is readily unloaded from the haemoglobin into the muscle cells = increased carbon dioxide concentration has shifted the oxygen dissociation curve to the right

Answer 142

1- organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen than our human haemoglobin = dissociation curve to the left of ours e.g animals living in depleted oxygen environment such as a lugworm (higher affinity for oxygen)- haemoglobin of the lugworm is fully loaded with oxygen even when there is little available in their environment 2- organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin = curve to the right of a human one e.g. active animal with a high respiratory rate living where there’s plenty of oxygen available such as a hawk

Answer 143

Check camera roll

Answer 144

Exercising muscles release heat, ‘shifting’ the curve to the right causing the haemoglobin to release more oxygen to fuel the muscular activity

Answer 145

Respiration produces carbon dioxide and this builds up in the burrows when the tide is out. If lungworm haemoglobin exhibited the Bohr effect, it would not be able to absorb oxygen when it was present in only very low concentrations in the burrow

Answer 146

Shifted to the right because this means that oxygen is more readily released to the tissues and so the haemoglobin supplies more oxygen to enable the muscles to respire rapidly

Answer 147

A- unloads more easily B- oxygen is more easily released from haemoglobin to the tissues = helps tissues respire more and so produce more heat which helps to maintain the body temperature of the mouse

Answer 148

Carbon dioxide is acidic and lowers PH causing haemoglobin to change shape

Answer 149

- all organisms exchange materials between themselves and their environment - in small organisms, this exchange takes laces over the surface of the body - but with increasing size, the SA:Vol ratio decreases to a point where the needs of an organism cannot be met by body surface alone = specialist exchange surface required (to absorb nutrients snd respiratory gases and remove excretory products) - transport system required to take materials from cells to exchange surfaces and from exchange surfaces to cells - as organisms have evolved into larger and more complex structures, the tissues and organs of which they are made have become more specialised and dependent upon one another = transport system all more essential

Answer 150

Large organisms require a transport system to take materials from exchange surfaces to cells that require them

Answer 151

1- SA:Vol ratio 2- how active the organism is lower the SA:vol ratio and more active the organism, the greater is the need for a specialised transport system with a pump

Answer 152

- suitable medium in which to carry materials e.g blood (this is normally a liquid based on water because water readily dissolves substances and can be moved around easily, but can be a gas such as aid breathed in and out of the lungs - form of mass transport in which the transport medium is moved around in bulk over large distances= more rapid than diffusion - a closed system of tubular vessels that contain transport medium and forms a branching network to distribute it to all parts of the organism - a mechanism for moving the transport medium within vessels- this requires a pressure difference between one part of the system and another - a mechanism to maintain the mass flow movement in one direction e.g. valves - a means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism - a mechanism for the mass flow of water or gases, for example intercostal muscles and diaphragm during breathing in animals

Answer 153

1- animals use muscular contraction, either of the body muscles or of a specialised pumping organ, such as the heart 2- plants rely on natural, passive processes such as the evaporation of water

Answer 154

- because when the blood is passed through the lungs, its pressure is reduced - if it were to pass immediately to the rest of the body, its low 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 - as a result, substances are delivered to the rest of the body quickly, which is necessary as mammals have a high body temperature and hence a high metabolic rate

Answer 155

Arteries, veins and capillaries (blood circulates through heart to arteries, arterioles, capillaries, venules, to veins, back to heart)

Answer 156

Two ‘loops’ in our body in which blood circulates-pulmonary circulation I.e. blood flow between heart and lungs is separate from systematic circulation- I.e. movement of blood from the heart through the rest of the body (excluding the lungs) then back to heart - pulmonary circulation= oxygenated blood - systemic circulation= deoxygenated blood

Answer 157

- open circulatory system - these systems include a pump (heart) and open-ended vessels - hemolymph is pumped out of the vessels into the body cavity where it bathes the tissues

Answer 158

- have a system of air tubes (trachea) that respiratory gases diffuse through to reach every cell in the body - BUT this limits the maximum body size of insects

Answer 159

Increases blood pressure and therefore the rate of blood flow to tissues

Answer 160

Check camera roll

Answer 161

Blood flows through the heart once in a complete circuit around the body Heart-> gills-> body-> heart

Answer 162

- closed double circulatory system - made up of 2 parts: pulmonary circulation and systemic circulation - blood travels twice through heart in one complete circuit around the body

Answer 163

- circulatory system in fish: - blood pressure reduced as blood passed through capillaries of gills - therefore flow is reduced through the rest of the body - oxygen and glucose not delivered as quickly to respiring tissues for aerobic respiration - fish however are less active than mammals and do not maintain their body temp = require less energy IN CONTRAST - double circulatory system in mammals: - lower blood pressure in pulmonary circulation to avoid damage to capillaries in lungs - heart increases blood pressure in systemic circulation so blood flows more quickly through body tissues - oxygen and glucose delivered quickly to respiring tissues for aerobic respiration - mammal more active than fish and maintain their body temp = require more energy from respiration

Answer 164

Left and right coronary arteries

Answer 165

Thought atmosphere contained more oxygen than today

Answer 166

Arteries (arterioles) capillaries (venules) and veins

Answer 167

- carry blood away from heart at high pressure - narrow lumen to maintain pressure - thick wall containing: - collagen (provide strength to withstand pressure) - elastic tissue (allows wall to stretch and recoil to maintain pressure) - smooth muscle (contract to constrict lumen to maintain pressure) - folded endothelium (squamous epithelium provide a smooth surface to reduce friction and folded to allow wall to stretch)

Answer 168

Aorta- distributes oxygenated blood to all parts of the body through systemic circulation

Answer 169

Pulmonary arteries, which take deoxygenated blood to the lungs

Answer 170

Arterioles- these form a network throughout the body. Blood is directed to different areas of demand in the body by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow full blood flow

Answer 171

- carry blood back to heart at low pressure - wide lumen to aid blood flow - very little elastic or muscle tissue (no need to stretch, recoil, restrict blood flow) - veins contain valves to prevent backflow of blood - blood flow through veins is aided by contraction of skeletal muscles surrounding them

Answer 172

Pulmonary veins which carry oxygenated blood to the heart from the lungs

Answer 173

1- pressure falls behind valves. Pockets fill and close the valve 2- pressure builds from the blood JG

Answer 174

- arterioles branch into capillaries, which are smallest of blood vessels - site of exchange (e.g. glucose,oxygen, carbon dioxide) between blood and cells via tissue fluid so they’re adapted for efficient diffusion - always found very near cells in exchange tissues e.g. alveoli in lungs = short diffusion pathway - walls consist of single layer of endothelium (squamous epithelium) = shortens diffusion pathway - large number of capillaries = increases SA for exchange- networks of capillaries in tissues called capillary beds

Answer 175

Increase in cross sectional area in arterioles and capillaries

Answer 176

- specialised tissue composed of: | Cells including erythrocytes, leukocytes, and platelets suspended in a liquid called plasma

Answer 177

- salts - nutrients e.g. glucose, amino acids, fatty acids - carbon dioxide (mainly as hydrogencarbonate ions) - waste products e.g. urea - plasma proteins e.g. immunoglobulins and albumin - hormones e.g. insulin

Answer 178

- fluid that bathes the cells formed from blood plasma - cells exchange materials with tissue fluid by diffusion or facilitated diffusion (take in oxygen and nutrients from it and release metabolic waste into it) - provides stable environment with the conditions cells need to function - composition of tissue fluid maintained as part of homeostasis (by maintaining composition of the blood) - unlike blood, does not contain erythrocytes or large proteins (too large to be pushed out of capillary walls)

Answer 179

- thin capillary walls composed of squamous epithelium= short diffusion distance - steep concentration gradient (cells use nutrients and produces waste, also blood flow) - capillary bed has large surface area for which exchange can occur= increases diffusion rate

Answer 180

Pressure filtration = formation of tissue fluid

Answer 181

1- due to high hydrostatic pressure (due to contraction of the muscle in the ventricle) at the artery end of the capillary bed 2- plasma containing dissolved substances is forced out of the capillary 3- through gaps (pores) in the capillary wall by ultrafiltration 4- forms tissue fluid

Answer 182

1- tissue fluid = no large proteins blood= contains large proteins 2- tissue fluid= some leukocytes but not erythrocytes or platelets blood= contains erythrocytes 3- tissue fluid= always low pressure blood= pressure variable

Answer 183

-once tissue fluid has exchanged metabolic materials with the cells it bathes, it is returned to circulatory system-most tissue fluid returns to blood plasma directly via capillaries and occurs as follows: 1- loss of tissue fluid from capillaries reduces hydrostatic pressure inside them 2- as a result, by the time the blood has reached the venous end of the capillary network, its hydrostatic pressure is usually lower than that of the tissue fluid outside of it 3- therefore tissue fluid forced back into capillaries by the higher hydrostatic pressure outside them 4- in addition, the plasma has lost water and still contains proteins = therefore has a lower water potential than tissue fluid 5- as a result, water leaves the tissues by osmosis down a water gradient - the tissue fluid has lost much of its oxygen and nutrients by diffusion into the cells that it bathed, but has gained carbon dioxide and waste materials to return

Answer 184

- a colourless fluid containing white blood cells, which bathes the tissues and drains through the lymphatic system into the bloodstream - lymph flows very slowly - lymph vessels contain semilunar valves and rely on contraction of skeletal muscles to ensure flow - lymph nodes are also found at intervals which contain macrophages (phagocytes) and lymphocytes - eventually returns to the blood in the subclavian veins

Answer 185

Less oxygen, more carbon dioxide and fewer nutrients

Answer 186

Capillaries cannot serve every single cell directly, so metabolic materials travel in tissue fluid which bathes the tissues

Answer 187

In the thoracic cavity behind the sternum (breastbone)

Answer 188

- left atrium - left ventricle - right atrium - right ventricle

Answer 189

Oxygenated = oxygenated blood-> body = systemic circuit

Answer 190

Deoxygenated = de-oxygenated blood-> lungs = pulmonary circuit

Answer 191

- problem with such a system is that blood has to pass through tiny capillaries in the lungs in order to present a large surface area for the exchange of gases - in doing so, there is a very large drop in pressure and so the blood flow to the rest of the body would be very slow - mammals therefore have a system in which the blood is returned to the heart to increase its pressure before it is distributed to the rest of the body

Answer 192

Circulatory system transporting nutrients, oxygen, waste materials, hormones and immune cells throughout the body continuously

Answer 193

Out of the heart, while also creating low pressure to bring it back in

Answer 194

Check camera roll

Answer 195

Pulmonary vein

Answer 196

Left atrioventricular valve

Answer 197

Aorta ❤️

Answer 198

Semi-lunar valve

Answer 199

Through the vena cava

Answer 200

Right atrioventricular valve

Answer 201

Semi-lunar valve

Answer 202

- right ventricle pumps deoxygenated blood only to the lungs - whereas left ventricle has a thick muscular wall enabling it to contract to create enough pressure to pump oxygenated blood to the rest of the body

Answer 203

Both ventricles contract together, pumping the same volume of blood

Answer 204

- blood always moves from a region of higher pressure to one of lower pressure - valves used to prevent any unwanted back-flow of blood - AV valves= between atria and ventricles - closure of these valves ensures that when the ventricles contract(ventricle pressure exceeds atrial pressure) blood within them moves to the aorta and pulmonary artery and aorta rather than back to the atria - semi-lunar valves= prevent back-flow of blood into the ventricles when the pressure within these vessels exceeds that in the ventricles - this arises when the elastic walls of the vessels recoil increasing the pressure within them and when ventricle walls relax reducing the pressure within the ventricles

Answer 205

- mixing of oxygenated and deoxygenated blood would result in only partially oxygenated blood reaching the tissues and lungs - this would mean the supply of oxygen to the tissues would be inadequate and there would be a reduced diffusion gradient in the lungs - limiting the rate of oxygen uptake

Answer 206

- the relative pressure of the heart chambers - if there’s higher pressure behind a valve, it’s forced open - but if pressure is higher in front of the valve, it’s forced shut - this means blood only flows one way through the heart

Answer 207

The coronary arteries, which branch off the aorta shortly after it leaves the heart

Answer 208

Ongoing sequence of contraction (systole) and relaxation (diastole) of the atria and the ventricles that keeps blood continuously circulating around the body

Answer 209

1- relaxation of the heart (diastole) 2- atrial systole 3- ventricular systole

Answer 210

- blood returns to the atria of the heart through the pulmonary vein (from the lungs) and the vena cava (from the body) - as the atria fill, the pressure in them rises - when this pressure exceeds that in the ventricles the AV valves open allowing the blood to pass into the ventricles - passage of blood aided by gravity - muscular walls of both atria and ventricles are relaxed at this stage - the relaxation of the ventricle walls causes them to recoil and reduces the pressure within the ventricle - this causes pressure to be lower than that in the aorta and pulmonary artery - so the semi-lunar valves in the aorta and pulmonary artery close - accompanied by the ‘dub’ sound of the heart

Answer 211

- contraction of atrial walls forces the remaining blood into the ventricles from the atria - throughout this stage, the muscles of the ventricle walls remain relaxed

Answer 212

- after a short delay to allow the ventricles to fill with blood, their walls contract simultaneously - this increases the blood pressure within them and forces shut the AV valves preventing back-flow of blood into the atria - the ‘lub’ sound of these valves closing is a characteristic of the heartbeat - with the AV valves closed, the pressure in the ventricles rises further - once it exceeds that in the aorta and the pulmonary artery, blood is forced from the ventricles into these vessels = semi-lunar valves open

Answer 213

In veins that occur throughout venous system

Answer 214

Ensure that when veins are squeezed during skeletal muscle contraction blood flows back towards the heart rather than away from it

Answer 215

Volume of blood pumped by one ventricle of the heart in one minute

Answer 216

Cardiac output= heart rate X stroke volume (volume of blood pumped out at each beat)

Answer 217

- the wall of an artery is made up of several layers - the endothelium (inner lining) is usually smooth and unbroken - if damage occurs to the endothelium e.g by high blood pressure, white blood cells and lipids (fat) from the blood clump together under the lining to form fatty streaks - over time, more white blood cells, lipids and connective tissue build up and harden to form a fibrous plaque called an atheroma - this plaque partially blocks the lumen of the artery and restricts blood flow which causes blood pressure to increase

Answer 218

The arteries have lots of atheroma in them which restricts blood flow to the heart muscle and can lead to myocardial infarction

Answer 219

Aneurysm and thrombosis (diseases that affect the arteries)

Answer 220

- atheroma plaques damage and weaken arteries and also narrow the arteries increasing blood pressure - when blood travels though a weakened artery at high pressure, it may push the inner layer of the artery through the outer elastic layer to form a balloon-like swelling (aneurysm) - this aneurysm may burst, causing a haemorrhage (bleeding)

Answer 221

- an atheroma plaque can rupture (burst through) the endothelium (inner lining of an artery) - this damages the artery wall and leaves a rough surface

Answer 222

A heart attack

Answer 223

- the heart is a muscle supplied with blood from the coronary arteries - this blood contains the oxygen needed by the heart muscle cells to carry out respiration - if a coronary artery becomes completely blocked e.g. by a blood clot, an area of the heart muscle will be totally cut off from its blood supply, receiving no oxygen - causing a myocardial infarction - heart attack can cause damage and death of the heart muscle - symptoms include pain in the chest and upper body, shortness of breath and sweating - if large areas of the heart are affected then complete heart failure can occur which is often fatal

Answer 224

- high blood cholesterol and poor diet - cigarette smoking - high blood pressure

Answer 225

- high blood cholesterol increases risk of cardiovascular disease - this is because cholesterol is one of the main constituents of the fatty deposits that form atheromas - atheromas can lead to increased blood pressure and blood clots - this could block the flow of blood to coronary arteries which could cause a myocardinal infarction - a diet in high saturated fat is associated with high blood cholesterol levels - a diet high in salt also increases the risk of cardiovascular disease because it increases the risk of high blood pressure

Answer 226

- both nicotine and carbon monoxide found in cigarette smoke increase the risk of cardiovascular disease - nicotine increases the risk of high blood pressure - carbon monoxide combines with haemoglobin and reduces the amount of oxygen available to the tissue - if heart muscle doesn’t receive sufficient oxygen it can lead to a myocardial infarction

Answer 227

- high blood pressure increases the risk of damage to the artery walls - damaged walls have an increased risk of atheroma formation causing a further increase in blood pressure - atheromas can also cause blood clots to form - a blood clot could block flow of blood to the heart muscle, possibly resulting in a myocardial infarction - so anything that increases blood pressure also increases the risk of cardiovascular disease e.g. being overweight, not exercising and excessive alcohol consumption

Answer 228

Having a genetic predisposition to coronary heart disease or having high blood pressure as a result of another condition

Answer 229

Check camera roll

Answer 230

- oxygen for respiration - carbon dioxide for photosynthesis - mineral ions and water - organic nutrients for respiration and growth

Answer 231

- large SA: V ratio due to many leaves - leaves are thin= short diffusion pathway - large SA for gaseous exchange - demand for energy from respiration in plants is typically lower than in animal cells

Answer 232

To transport water and products of photosynthesis large distances

Answer 233

- water absorbed in soils= needed all over plant - water and mineral ions= up stem in xylem - water lost= leaves - sugars= synthesised in leaves (source) - sugars move = down stem in phloem

Answer 234

Vascular tissues

Answer 235

- xylem tissue transports water and mineral ions in solution (these substances move up the plant from the roots to the leaves) - phloem tissue (and sieve tubes) transports organic substances like sugars (products of photosynthesis) also in solution both up and down the plant

Answer 236

A group of similar cells working together to perform a particular function

Answer 237

Transports the water and ions

Answer 238

- composed of elongated cells arranged end-to-end - dead cells that lack cytoplasm and nucleus - lignin deposited in cell walls to become impermeable (waterproof) and cell contents die - end walls break down to form a continuous narrow, hollow tube for the transport of water - contains pits (non-lignified areas of cellulose cell wall) to allow movement of water in/out of vessels

Answer 239

- humidity of atmosphere usually less than that of their air spaces next to the stomata - as a result there is a water potential gradient from the air spaces through the stomata to the air - provided the stomata are open, water vapour molecules diffuse out of the air spaces into the surrounding air - water lost by diffusion from the air spaces is replaced by water evaporating from the cell walls of the surrounding mesophyll cells

Answer 240

Evaporation of water from a plant’s surface, especially the leaves

Answer 241

Allow gaseous exchange for photosynthesis

Answer 242

Water also lost via transpiration

Answer 243

Guard cells go flaccid

Answer 244

Stomata close reducing water loss

Answer 245

Cohesion-tension

Answer 246

- water evaporates from mesophyll cells due to heat from the sun leading to transpiration - water molecules from hydrogen bonds between one another hence tend to stick together = cohesion - water forms a continuous, unbroken column across the mesophyll cells and down the xylem - as water evaporates from the mesophyll cells in the leaf into the air spaces beneath the stomata, more molecules of water are drawn up behind it as a result of this cohesion - a column of water is therefore pulled up the xylem as a result of this cohesion = transpiration pull - transpiration pull puts the xylem under tension, that is, there is a negative pressure within the xylem hence name cohesion-tension theory

Answer 247

Photosynthesis- plant needs to open its stomata to let in carbon dioxide so that it can synthesis glucose, but this also lets water out

Answer 248

- light - temperature - humidity - wind

Answer 249

The lighter it is the faster the transpiration rate I.e positive correlation between light intensity and transpiration rate because stomata open when it gets light to let in carbon dioxide for photosynthesis and when it’s dark stomata sure usually close so there’s little transpiration

Answer 250

- higher the temp the faster the transpiration rate | - increased evaporation and diffusion due to increased kinetic energy so increased water movement

Answer 251

- higher humidity will decrease rate of water loss as there will be a smaller water vapour potential gradient between the air spaces in the leaf and the air outside

Answer 252

Air moving outside the leaf will carry away water and maintain a high water vapour gradient so winder it is, the faster the transpiration rate

Answer 253

- change in diameter of tree trunks according to rate of transpiration- during the day when transpiration is at its greatest, there is more tension (negative pressure) in the xylem pulling the walls of the xylem vessels inwards and causes the trunk to shrink in diameter. At night, when transpiration is at its lowest, there is less tension in the xylem and so the diameter of the trunk increases - if a xylem vessel is broken and air enters it, the tree can no longer draw up water; the continuous column of water is broken and so the water molecules can no longer stick together - when a xylem vessel is broken, water does not leak out, as would be the case if it were under pressure. Instead, air is drawn in which is consistent with it being under tension

Answer 254

- solutes are dissolved substances which the phloem tissue transports round plants. Like xylem, phloem is formed from cells arranged in tubes - sieve tube elements and companion cells are important cell types in phloem tissue - sieve tube elements are living cells that form the tube for transporting solutes- they have no nucleus and few organelles so... - there’s a companion cell for each sieve tube element that carry out living functions for sieve cells e.g. providing the energy needed for active transport of solutes

Answer 255

Movement of solutes e.g sugars like sucrose from sources (e.g leaves where sugars synthesised so is at a high concentration) to sinks where they’re used up (e.g. other parts of the plants especially food storage organs so at lower concentration) - enzymes maintain a concentration gradient from the source to the sink by changing the solutes at the sink e.g. by breaking them down ensuring there’s always a lower concentration at the sink than the source e.g. in potatoes, sucrose is converted to starch in the sink areas

Answer 256

1- sugars are actively transported into the phloem from sources in the plant via companion cells 2- lowering the water potential in the siege tubes 3- so water moves by osmosis from the xylem into siege tubes 4- this increase in pressure causes mass movement towards the sinks e.g. the roots where sugars are stored

Answer 257

Active transport of sugars

Answer 258

- if a ring of bark (which includes the phloem, but not the xylem) is removed from a woody stem, a bulge forms above the ring. The fluid from the bulge has a higher concentration of sugars than the fluid from below the ring = evidence that there’s a downward flow of sugars - radioactive tracer such as radioactive carbon ^14C can be used to track the movement of organic substances in a plant - pressure in phloem can be investigated using aphids- they pierce the phloem, then their bodies are removed leaving the mouthparts behind, which allows the sap to flow out. The sap flows out quicker nearer the leaves than further down the stem = evidence there’s a pressure gradient - if a metabolic inhibitor (which stops ATP production) is put into the phloem, then translocation stops = evidence that active transport is involved

Answer 259

- sugar travels to many different sinks, not just the one with the highest water potential as the model suggests - the sieve plates would create a barrier to mass flow- a lot of pressure would be needed for the solutes to get through at a reasonable rate

Answer 260

1- can be done by supplying part of a plant (often a leaf) with an organic substance that has a radioactive label 2- radioactive carbon will then be incorporated into organic substances produced by leaf e.g. sugars produced by photosynthesis, which will then be moved around the plant by translocation 3- the movement of these substances can be tracked using a technique called autoradiography. To reveal where the radioactive tracer has spread to in the plant, the plant is killed e.g. by freezing it using liquid nitrogen and then the whole plant, or sections of it, is placed on photographic film- the radioactive substance is present wherever the film turns black - results demonstrate translocation of substances from source to sink over time e.g. autoradiography of plants killed at different times shows an overall movement of solutes e.g. products of photosynthesis from leaves towards roots

Answer 261

If squirrel strips away phloem around whole circumference of the branch it may not have sufficient sugars for its respiration to release enough energy for survival as none can reach it from other parts of the plant

Answer 262

If the branch has sufficient leaves to supply its own sugar needs from photosynthesis, rather than depending on supplies from elsewhere, it might survive for a little while at least

Answer 263

Unlikely that squirrels would strip bark from around a whole circumference of a large tree trunk and any intact phloem could still supply sufficient sugars to its roots to allow it to survive

Answer 264

- based on evolutionary relationships between organisms and their ancestors - classifies species into groups using shared characteristics derived from their ancestors - arranged in a hierarchy in which groups are contained within larger composite groups with no overlap

Answer 265

Mackerel have increased number of gill lamellae = larger surface area compared to plaice