3.3 Organisms Exhange Substances with their Environment

Question 1

Outline the role of surface area to volume ratio in organism and structures (eg. a cell)

Answer 1

• The amount of material an organism or structure needs to exchange depends on its volume and the amount of material it can exchange depends on its surface area

• As size increases, volume increases faster than surface area, so SA:V decreases. The amount of material needed to be exchanged increases by a lot and the amount it CAN exchange increases by a little

• Rate of heat loss depends on surface area to volume ratio

Question 2

When can surface area to volume ratio kill an organism

Answer 2

If the metabolic rate exceeds the rate of exchange of vital materials and wastes due to a low surface area to volume ratio, the organism will die

Question 3

Outline surface area to volume ratio in single-celled organisms

Answer 3

• Very large surface area
• Can rely on diffusion of substances in and out of
the cell to meet the organisms needs
• Fast rate of diffusion due to short diffusion
distances

Question 4

Outline surface area to volume ratio in multicellular organisms

Answer 4

• Smaller surface area to volume ratio
• Can’t rely on the diffusion of substances through
its surface to meet the organisms needs so larger
organisms have evolved exchange surfaces and
transport systems because:
1) SA:V is too low and can’t exchange enough substances to supply a large volume of organism through a relatively small outer surface area
2) Diffusion distances are too great

Question 5

Adaptations of exchange surfaces and transport systems in multicellular organisms

Answer 5

• Large surface area
• Good blood supply to maintain a concentration gradient
• Thin membranes
• Ventilation

Question 6

How does the rate of heat loss depends on surface area to volume ratio

Answer 6

A large surface area to volume ratio means more heats lost to surroundings so metabolic rate must increase to release heat from aerobic respiration to stay warm
- animals in hot environments may have
adaptations to increase surface area to lose
more heat

Question 7

How do you calculate surface area to volume ratio

Answer 7

Surface area
——————
Volume

Question 8

Identify the adaptations of single-celled organisms for gas exchange

Answer 8

• Large surface area to volume ratio
• Gas exchange can take place by diffusion across the thin membrane body surface so no gas exchange system is needed

Question 9

Identify the gas exchange system used by insects

Answer 9

The tracheal system

Question 10

Describe the tracheal system in insects

Answer 10

• A series of tubes that supply respiring cells directly with oxygen

• By pumping the abdomen, air is drawn in and out of the tracheae via pores in the surface called spiracles

• Oxygen diffuses down a concentration gradient towards the cells

• Tracheae branch off into trachioles which have thin, permeable walls that border repairing cells

• Oxygen diffuses in and carbon dioxide diffuses out down a concentration gradient through the spiracles

Question 11

Identify the adaptations of the tracheal system in insects for gas exchange

Answer 11

• Thin, permeable walls that border repairing cells
• Tracheae maintain a concentration gradient

Question 12

Identify the gas exchange system used by fish

Answer 12

Gills

Question 13

Explain why fish have gills

Answer 13

There’s a lower concentration of oxygen in water than air and the diffusion of oxygen and carbon dioxide is much slower so they have gas exchange organs called gills adapted to overcoming these problems

Question 14

Describe the function of gills in fish

Answer 14

• Fish open their mouths and allow water to flow through the gills and out via the operculum (gill cover)

Question 15

Identify the adaptations of the gills in fish for gas exchange

Answer 15

• Short diffusion pathway due to thin lamellae and one cell thick capillaries

• Large surface area due to many gill filaments, lamellae and large numbers of capillaries

• Maintenance of a concentration gradient due to the counter-current flow system, ventilation and large numbers of capillaries

Question 16

Outline the counter-current flow system in fish gills

Answer 16

• Blood flows through the lamellae in the opposite direction to the flow of water

• This maintains a favourable oxygen concentration gradient between water and blood across the entire length of the gill lamellae

• The concentration of oxygen in water is always higher than in the blood

• As much oxygen as possible diffuses from the water into the blood

Question 17

Identify the adaptations of the leaves of dicotyledonous plants for gas exchange

Answer 17

• Short diffusion distance due to thin leaves

• Short diffusion distance due to stomata (stoma) that are pores in the lower epidermis that allow diffusion of gases, so no cell is far from a stomata

• Large surface area due to air spaces in the spongey mesophyll as gases are exchanged with the atmosphere in the mesophyll layer of the leaf

Question 18

What adaptions are present in terrestrial insects that compromise opposing needs for efficient gas exchange and limitation of water loss and therefore desiccation

Answer 18

• Spiracles can close to prevent water loss

• Hairs around spiracles trap humid air, creating a low concentration gradient of water vapour reducing rate of diffusion of water vapour out of spiracles

• Air sacs around tracheae for extra oxygen supply if spiracles have to be closed for longer periods

Question 19

Identify the name for the drying out of a living organism

Answer 19

Desiccation

Question 20

How can water loss (transpiration) be controlled In dicotyledonous plants

Answer 20

• Waxy cuticle reduces evaporation
• Regulation of the opening and closing of stomata by guard cells

Question 21

Describe the process of the regulation of the opening and closing of stomata by guard cells

Answer 21

• When plants have enough water, guard cells are turgid which keeps stomata open

• When plants are dehydrated, guard cells pump out K+ ions to lower the water potential of the surrounding tissue, causing water to leave the guard cells by osmosis making them decrease in size as they become shrunken and stomata close
(Also close during the night to prevent water loss)

• Affected by light intensity, water availability and carbon dioxide concentration. Plants in dryer environments will have fewer stomata to help reduce water loss

Question 22

Define transpiration

Answer 22

The loss of water from a plant

Question 23

Where and why does most photosynthesis take place in a plant leaf

Answer 23

The palisade mesophyll cells, as they received the most sunlight and so contain lots of chloroplasts

Question 24

What’s the role of the upper epidermis

Answer 24

Protects internal tissues from mechanical damage and invasion of bacteria and fungi

Question 25

What’s a xerophyte

Answer 25

Plants living in and adapted to warm/dry/windy conditions

Question 26

What adaptions are present in xerophytic plants that compromise opposing needs for efficient gas exchange and limitation of water loss and therefore desiccation

Answer 26

• Stomata are sunk in pits and hair on the epidermis traps moist air, decreasing the concentration gradient of water vapour in and out of the leaf, slowing down water loss

• Curled leaves with stomata inside to protect moist air so it’s not blown away by the wind

• Less stomata, so fewer places for water to diffuse out

• Waxy, waterproof cuticle on the leaves and stem that prevents evaporation

Question 27

What’s the human gas exchange system

Answer 27

Lungs

Question 28

Describe the pathway air follows as its breathed in through the human gas exchange system

Answer 28

• Nasal cavity
• Pharynx
• Larynx
• Trachea
• Bronchus
• Bronchioles
• Alveoli

Question 29

Define ventilation

Answer 29

Movement of air into and out of the lungs

Question 30

Define gaseous exchange

Answer 30

Diffusion of oxygen from the air in the alveoli into the blood and of carbon dioxide from the blood into the air in the alveoli

Question 31

Define respiration

Answer 31

Chemical reaction to release energy in the form of ATP

Question 32

Describe the process of ventilation

Answer 32

• Initiated by changes in intrapulmonary air pressure in the lungs relative to atmospheric pressure, it’s split into inspiration and expiration

Question 33

Describe the process of inspiration in ventilation

Answer 33

• There’s a higher partial pressure of oxygen (pO2) in the atmosphere compared to the lungs so oxygen moves down the trachea, bronchi and bronchioles into the alveoli down a pressure gradient

• The internal intercostal muscles relax and the external intercostals contract to move the ribs and sternum upwards and outwards, while the diaphragm contracts, becoming flatter and increasing the volume of the thoracic cavity

• The pressure between pleural membranes is reduced which allows elastic pulmonary tissue to expand, increasing lung volume

• Pulmonary pressure falls below atmospheric pressure so movement of air into the lungs occurs due to a pressure gradient until lung pressure equals atmospheric pressure

• This is an active process that requires energy

Question 34

Describe the process of expiration in ventilation

Answer 34

• The external intercostals relax, causing the ribs and sternum to move downwards and inwards and the diaphragm relaxes decreasing the volume of the thoracic cavity

• The pressure between pleural membranes increases which compresses elastic pulmonary tissues, decreasing lung volume

• Pulmonary pressure is driven above atmospheric pressure, so atmospheric air is forced out of the lungs via respiratory passages until lung pressure equals the atmospheric pressure again

• This is a passive process that requires no energy

Question 35

Describe gas exchange at the alveoli

Answer 35

• Oxygen moves through the lungs down a pressure gradient, but moves down a concentration gradient into the capillaries

• Oxygen diffuses into the alveoli across the alveolar epithelium and the capilliary endothelium into the capillary down a concentration gradient into haemaglobin in the blood

• Red blood cells slow down in capillaries and are pressed against the capillary wall to allow more time for diffusion of gases, increase the surface area available of red blood cells and minimise oxygen diffusion distance

• Carbon dioxide diffuses into the alveoli from deoxygenated blood and is breathed out

Question 36

Identify adaptations of the alveoli

Answer 36

• Alveolar epithelium is one cell thick

• Large surface area for gas exchange due to many alveoli

• Rich blood supply from an extensive capillary network to maintain a favourable concentration gradient

• Ventilation also maintains a favourable concentration gradient

Question 37

Identify what most lung diseases do

Answer 37

• Decrease the rate of gas exchange in the alveoli so less oxygen’s able to enter the bloodstream and reach cells

• The rate of aerobic respiration reduced so less energy’s released and people feel weak and tired

Question 38

Outline digestion

Answer 38

• Defined as the hydrolysis of large, insoluble molecules into smaller, soluble molecules

• Large biological molecules are too large to cross cell membranes so can’t be absorbed directly into the blood

• Large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.

• This is done using a variety of different enzymes produced by specialised cells in the digestive system that are secreted into the gut to mix with food

Question 39

Outline the digestion of carbohydrates

Answer 39

• The hydrolysis of Glycosidic bonds by amylase enzymes and membrane-bound disaccharidases

• There’s no carbohydrate digestion in the stomach, it’s too acidic for salivary amylase and stomach enzymes only digest proteins

• Amylase hydrolyses starch into maltose, which is broken down by maltase. There are two types of amylase: Salivary amylase is produced by the salivary glands and Pancreatic amylase is produced by the pancreas and secreted into the small intestine in pancreatic juice.

• Membrane-bound disaccharidases are enzymes attached to the cell surface membrane of epithelial cells lining the ileum that hydrolyse disaccharides

Question 40

Descibe the absorption of monosaccharides

Answer 40

• Glucose and Galactose are absorbed by active transport with Na+ ions via a co-transporter protein

• Fructose is absorbed via a facilitated diffusion through a different transport protein

Question 41

Outline the digestion of lipids

Answer 41

• The hydrolysis of Ester bonds by lipase enzymes and the action of bile salts

• Triglycerides are broken into a monoglyceride and two fatty acids that are lipid soluble so can diffuse over cell surface membranes.
• Triglycerides can be reformed by the smooth endoplasmic reticulum

• Lipase enzymes are produced by the pancreas and secreted into the small intestine in pancreatic juice
• Bile salts (produced by the liver) lower surface tension between lipids and water so large drops of lipids split into smaller ones through emulsification which increases surface area for lipase enzymes to act on

Question 42

Describe the action of bile salts in lipid digestion

Answer 42

• Bile salts (produced by the liver) lower surface tension between lipids and water so large drops of lipids split into smaller ones through emulsification. This increases the surface area for lipase enzymes to act on.

• The products of lipid digestion (monoglyceride and fatty acids) then stick to the bile salts to form micelles.
• Micelles help move the monoglycerides and fatty acids to the epithelial cells and constantly break up and reform so they can release their monoglycerides and fatty acids, allowing them to be absorbed

Question 43

Describe the absorption of lipids

Answer 43

• The products of lipid digestion (monoglyceride and fatty acids) then stick to the bile salts to form micelles.

• Micelles help move the monoglycerides and fatty acids to the epithelial cells and constantly break up and reform so they can release their monoglycerides and fatty acids, allowing them to be absorbed

Question 44

Outline the digestion of proteins

Answer 44

• The hydrolysis of Peptide bonds by several proteases (endopeptidases, exopeptidases and membrane-bound dipeptidases) to form amino acids

• These proteases are very effective when working together e.g. endopeptidases expose more ends for exopeptidases to hydrolyse

• Endopeptidases hydrolyse peptide bonds within a protein

• Exopeptidases hydrolyse peptide bonds one bond from the end of a protein

• Membrane-bound dipeptidases hydrolyse bonds in dipeptides. They’re attached to the cell surface membrane of epithelial cells in the ileum

Question 45

Describe the absorption of proteins

Answer 45

Amino acids are absorbed via co-transport similarly to glucose/ galactose via an Na+ co-transporter protein where Na+ takes amino acids into the lumen as they diffuse

Question 46

Identify a type of endopeptidase and describe its role in the digestion of proteins

Answer 46

• Pepsin is the main gastric enzyme that digests proteins in the stomach

• Pepsin breaks bonds between amino acids in the central region of a protein, forming several peptide molecules

• Pepsinogen (‘pepsin maker’) is inactive pepsin; the acidic pH in the stomach activates pepsinogen into pepsin

Question 47

Identify and explain adaptations of the ileum

Answer 47

• Very Long
-Allows time for diffusion/active transport of
products of digestion

• Folded lining
-Millions of projections called Villi, which are
folded into Microvilli create a large surface area
for diffusion

• One cell thick epithelial wall
-Short diffusion distance
-Epithelial cells have lots of mitochondria for
active transport

• Rich blood supply in the Villi
-Maintains a concentration gradient

• Many membrane-bound enzymes
-Short diffusion distance for the products of
digestion into epithelial cells, increasing
absorption

Question 48

Define a mass transport system

Answer 48

The system that exists when organisms have a:

• Large SA:V because they can’t rely on simple diffusion of substances through its surface to meet the organisms needs

• A large activity of the organism (requires more substances at one time than smaller organisms

Question 49

Outline the structure and function of Haemaglobin

Answer 49

• A quaternary protein with 4 polypeptide chains, each associated with a ‘haem’ group containing a ferrous (Fe2+) ion

• Haemoglobin transports oxygen and each Haemoglobin can carry four O2 molecules and therefore 8 oxygen atoms as each Fe2+ can combine with a single oxygen

• Oxygen saturates haemoglobin to form oxyhaemoglobin. There are different types of haemaglobin depending on the animal, some can load oxygen better than others while some can unload oxygen better than others

Question 50

Explain oxygen loading

Answer 50

• Association refers to the loading of oxygen onto a haemaglobin molecule. Haemoglobin that can load oxygen very easily is referred to as having a high affinity (how well the oxygen is bound to haemoglobin)

• At the lungs, there’s a high partial pressure of oxygen and haemoglobin has a high affinity for oxygen and so becomes saturated with oxygen

Question 51

Explain oxygen unloading

Answer 51

• Dissociation refers to the unloading of oxygen from a haemoglobin molecule. Haemoglobin that can unload oxygen very easily is referred to as having a low affinity (how well the oxygen is bound to haemoglobin)

• At respiring tissues, there’s a low partial pressure of oxygen and haemoglobin has a low affinity for oxygen and becomes less saturated with oxygen

Question 52

Define partial pressure of oxygen

Answer 52

A measure of the concentration of oxygen present in tissues

Question 53

Define and identify the calculations for percentage saturation

Answer 53

• The amount of oxygen combined with the haemoglobin. It can be used to measure how oxygenated the blood is

• (Oxygenated haemoglobin ➗ maximum saturation) ✖️ 100

• (Number of binding sites occupied by O2 molecules ➗ Maximum number of binding sites) ✖️ 100

Question 54

Explain oxygen association and how this is represented

Answer 54

• Oxygen binds to Haemoglobin through co-operative binding. This means the binding of the first molecule of oxygen to haemoglobin changes its tertiary and quaternary structure to uncover another haem group, making it easier for subsequent oxygen molecules to bind to the haemoglobin.

• An oxygen dissociation curve is a graph that shows how oxygen is saturated onto haemaglobin molecules, represented by an ‘S shape’ or Sigmoid curve

Question 55

Explain oxygen dissociation curves shifting to the left

Answer 55

• If the curve shifts to the left, haemaglobin has a higher affinity with oxygen and so at the same partial pressure of oxygen there’s a greater percentage saturation of haemoglobin with oxygen. This means haemaglobin loads oxygen more readily and can be transported to respiring tissues

• Species that have an oxygen dissociation curve lying to the left live in environments where the environmental partial pressure of oxygen is low e.g. high altitude, bottom of a lake, human foetus

• Left shift, Low partial pressure of oxygen, aLtitude, bottom of Lakes

Question 56

Explain oxygen dissociation curves shifting to the right

Answer 56

• If the curve shifts to the right, haemaglobin has a lower affinity with oxygen and so at the same partial pressure of oxygen there’s a lower percentage saturation of haemoglobin with oxygen. This means haemoglobin unloads oxygen more readily at repairing tissues

• Species that have an oxygen dissociation curve lying to the right have a high metabolic rate and the curve is much steeper so haemoglobin will unload its oxygen much faster as the red blood cells pass into the tissue

• Right shift, respiring tissues, high metabolic rate

Question 57

Explain the Bohr effect

Answer 57

• Carbon dioxide decreases the pH of the tissue fluid surrounding the cells which alters the tertiary structure of haemoglobin

• This means that in the presence of carbon dioxide, the oxygen dissociation curve shifts to the right and affinity of haemoglobin for oxygen is reduced.

• Therefore at the same partial pressure of oxygen, the percentage saturation of haemoglobin is less and oxygen unloads more readily to respiring tissues

Question 58

State what the left atrium is

Answer 58

The chamber of the heart that holds oxygenated blood from the pulmonary vein

Question 59

State what the left ventricle is

Answer 59

• The chamber of the heart that holds oxygenated blood that is forced in from the atrium

• The left ventricle has a thicker muscular wall than the right ventricle as it contracts more forcefully to create a higher blood pressure as it must transport blood around the whole body

Question 60

State what the right atrium is

Answer 60

The chamber of the heart that holds deoxygenated blood from both vena cava (superior and inferior)

Question 61

State what the right ventricle is

Answer 61

The chamber of the heart that holds deoxygenated blood that is forced in from the atrium

Question 62

State what the aorta is

Answer 62

The artery that transports blood from the ventricle to the entire body

Question 63

State what the pulmonary vein is

Answer 63

The vein that carries oxygenated blood to the heart

Question 64

State what the pulmonary artery is

Answer 64

The artery that carries deoxygenated blood to the lungs

Question 65

State what the vena cava is

Answer 65

The vein that carries deoxygenated blood to the heart

Question 66

Outline valves

Answer 66

• To prevent back flow to make sure blood flows in one direction through the heart. Valves open when the pressure before them is higher than the pressure after them and close when the pressure after them is higher than the pressure before them

• The semilunar valves are the valves that separate the ventricles from the arteries and prevent back flow of blood into the ventricles

• The atrioventricular valves are the valves that separate the atria from the ventricles and prevent back flow of blood into the atria

• The bicuspid valve is the valve that separates the two chambers responsible for oxygenated blood (left atrium and left ventricle)

• The tricuspid valve is the valve that separates the two chambers responsible for deoxygenated blood (right atrium and right ventricle)

Question 67

Outline the coronary arteries

Answer 67

• Provide the heart muscle cells with oxygen and glucose for respiration

• If they become blocked, less blood reaches the heart muscle cells so less oxygen is available for respiration. This causes cells to die which leads to a myocardial infarction (heart attack)

Question 68

Define cardiac output and identify how it’s calculated

Answer 68

• The volume of blood pumped out of the left ventricle of the heart per minute (dm3min-1)

• Cardiac output = Stroke volume x heart rate

Question 69

Define stroke volume

Answer 69

The amount of blood pumped out of the left ventricle per beat

Question 70

Explain why a double circulatory system is required

Answer 70

Blood pumped out of the left ventricle must be at a high pressure to be transported around the whole body.
Blood pumped outbid the right ventricle must be at a lower pressure in order for the blood to become fully oxygenated