Exchange Systems

Question 1

Why do organisms need to exchange substances with their environment?

Answer 1

• to take in oxygen and nutrients and remove carbon dioxide and urea
• to keep temperature and water levels constant by taking in/removing heat and water

Question 2

What is the relationship between surface area to volume ratio and size of the organism?

Answer 2

The larger the organism, the smaller the surface area to volume ratio. This is because larger organisms have higher metabolic rates and demands.

Question 3

What is metabolic rate and metabolic demand?

Answer 3

The metabolic rate is the amount of energy used by an organism in a period of time. The demand is how much oxygen and nutrients an organism needs to take in per day to maintain their metabolic rate.

Question 4

Why do larger organisms need specialised exchange systems?

Answer 4

They have higher metabolic demands so more efficient oxygen delivery is necessary, meaning more respiration is needed. Without specialised systems, not enough respiration takes place to produce this much oxygen.

Question 5

What are some differences between unicellular and multicellular organisms?

Answer 5

• unicellular have large SA:V to absorb enough substances but multicellular have small SA:V so cannot
• unicellular diffusion distance is short to get from environment to centre fast and multicellular distance is large so too slow to supply cells efficiently
• unicellular can exchange substances directly but multicellular need mass transport systems
• unicellular lose heat and water quickly so can’t survive in extremes but multicellular lose less heat so can survive in the cold but need adaptations in the heat

Question 6

What are some adaptations to maintain heat levels in cold environments?

Answer 6

Behavioural - small mammals with large SA:V lose heat easily so eat large amounts of high energy food (e.g. seeds and nuts) to maintain body temperature or hibernate
Physical - streamlined, compact body shape to create a smaller SA:V and smaller animals have thicker fur for insulation

Question 7

What are some adaptations to maintain heat levels in hot environments?

Answer 7

Behavioural - large organisms spend lots of time in water to help lose heat and some organisms are nocturnal, so they are active in cooler temps
Physical - Large organisms have large ears to increase SA:V and lose heat

Question 8

What are some adaptations to maintain water levels in hot environments?

Answer 8

Behaviour - organisms are nocturnal so are most active in cooler temps, to reduce water loss
Physical - small mammals have adapted kidneys which produce less urine to compensate for water lost through evaporation

Question 9

What features of the small intestine maximise the movement of substances through cells into the blood?

Answer 9

• folded internal walls called villi increase SA:V
• villi have thin walls to ensure short diffusion pathway
• villi have many capillaries to maintain concentration gradient as they constantly transport nutrients away
• villi contain muscles which mix the contents of the ileum so they have new material next to them, maintaining concentration gradient

Question 10

What are some adaptations of epithelial cells of the ileum for efficient digestion?

Answer 10

• microvilli increase surface area for diffusion
• many mitochondria to provide energy for active transport
• channel and carrier proteins for facilitated diffusion and active transport

Question 11

What enzyme do the salivary glands produce?

Answer 11

Amylase is used in the mouth to hydrolyse glycosidic bonds in starch to form maltose

Question 12

What enzyme does the pancreas produce?

Answer 12

Pancreatic amylase is used in the small intenstine to hydrolyse glycosidic bonds in starch to form maltose

Question 13

What enzyme does the small intestine produce for carbohydrate breakdown?

Answer 13

Membrane-bound disaccharides (maltase, sucrase and lactase) are found in the cell membrane of epithelial cells and they hydrolyse glycosidic bonds of disaccharides to form monosaccharides

Question 14

How are monosaccharides absorbed across the ileum epithelium?

Answer 14

They are transported across the epithelial cell membrane through specific transporter proteins. Glucose and galactose are actively transported using sodium ions through co-transporter proteins while fructose is absorbed by facilitated diffusion through another transporter protein.

Question 15

How are proteins digested in the stomach?

Answer 15

1. whole proteins are chewed and swallowed into the stomach
2. hydrochloric acid denatures proteins, unfolding their 3D structure to reveal the polypeptide chain
3. the enzyme, pepsin, breaks down the polypeptide chain into shorter polypeptides

Question 16

How are proteins digested in the small intestine?

Answer 16

1. peptidases continue enzyme digestion to form tripeptides, dipeptides and amino acids
2. tripeptides and dipeptides are further broken down into amino acids, which can be absorbed into the bloodstream

Question 17

What are the different types of peptidases?

Answer 17

• endopeptidases hydrolyse peptide bonds within a large protein to create smaller polypeptide chains and more terminal ends for exopeptidases to work on
• exopeptidases hydrolyse terminal ends of polypeptide chains to remove individual amino acids from the chain
• dipeptidases are a type of exopeptidase that hydrolyse the peptide bond in dipeptides to create two amino acids

Question 18

How are amino acids absorbed into the bloodstream?

Answer 18

They are absorbed through active transport with a sodium ion out of the ileum cells.

Question 19

What are lipases?

Answer 19

They are enzymes that hydrolyse the ester bonds in triglycerides to form fatty acids and monoglycerides. They are made in the pancreas and used in the small intenstine.

Question 20

What do bile salts do?

Answer 20

• They are produced by the liver, stored in the gall bladder and used in the small intestine.
• They help break down large fat globules through emulsification, which turns them into smaller droplets to increase their SA:V so lipases are more efficient.
• After hydrolysis, fatty acids and monoglycerides remain attached to the bile salts to form micelles which help in their absorption into the bloodstream.

Question 21

What is the process of the absorption of fatty acids and monoglycerides?

Answer 21

1. micelles endocytose into epithelial cells and break down so monoglycerides and fatty acids diffuse across the membrane thanks to their lipid-solubility
2. they are transported to the endoplasmic reticulum where they recombine into triglycerides
3. At the golgi, they bind to cholesterol and proteins to form chylomicrons
4. chylomicrons travel by vesicle to the cell membrane and exocytose from the epithelial cell into lymphatic capillaries called lacteals
5. lacteals transport chylomicrons away from the small intenstine to muscle tissues where triglycerides can be hydrolysed and fatty acids used by the tissues

Question 22

What is the structure of the gas exchange system of insects?

Answer 22

• they have air-filled pipes called tracheae
• they divide into smaller tubes called tracheoles which get smaller until penetrating individual body cells
• air enters the tracheae through pores on the exoskeleton called spiracles

Question 23

What are some adaptations of an insect’s gas exchange system?

Answer 23

• tracheoles have thin walls which shorten the diffusion distances of gases
• tracheoles are highly branched to increase surface area
• there is fluid at the end of the tracheae where it joins tissues as gas exchange from air to liquid is faster for diffusion
• muscles can pump air in/out to maintain concentration gradient of gases
• spiracles can close to prevent water loss

Question 24

How do insects ventilate?

Answer 24

They contract muscles to compress the tracheae and pump gases in/out of the body. Pumping raises pressure and forces air out of the spiracles to increase carbon dioxide removal at high respiration levels.

Question 25

What is the structure of the gas exchange system in fish?

Answer 25

- they have gills made out of many gill filaments attached to a gill arch to create a large surface area for water to flow over - gill filaments are covered in tiny folds called lamellae to increase surface area. They have many capillaries to maintain concentration gradient and are very thin to shorten diffusion distance - water flows over the lamellae in a countercurrent flow to the blood

Question 26

What is the difference between concurrent and countercurrent flow?

Answer 26

- in concurrent, water and blood flow in the same direction but in countercurrent, they are in opposites - in concurrent, concentration gradient will decrease because equilibrium will be reached as the blood and water will have the same amount of oxygen. In countercurrent, the concentration gradient is maintained so diffusion occurs for the full length of the lamellae

Question 27

What are some adaptations of the fish gas exchange system?

Answer 27

- thin lamellae epithelium shortens diffusion distance - many gill filaments/lamellae increases surface area - countercurrent flow maintains concentration gradient - many capillaries maintains concentration gradient - ventilation by operculum ensures constant fresh water to maintain concentration gradient

Question 28

How do fish ventilate?

Answer 28

1. fish takes in water via buccal cavity in mouth through pharynx over gills. Opeculum is closed 2. water enters cavity due to decreased pressure and increased volume 3. mouth closes and operculum opens, resulting in increased pressure and decreased volume 4. increased pressure forces water to leave via opercular openings

Question 29

What is the structure of the human gas exchange system?

Answer 29

- air flows through the mouth and nose, down the trachea - the trachea splits into two bronchi then smaller tubes called bronchioles - bronchioles lead to alveoli, which are surrounded by capillaries and this is the site of gas exchange - the diaphragm, ribs and intercostal muscles help move air in and out of the lungs - each lung is surrounded by a membrane and pleural cavity, which is filled with pleural fluid which lubricates lungs and helps them to expand

Question 30

What are some specialised features of the lungs?

Answer 30

- cartilage, in the trachea and bronchi, provides strength and holds the airway open to prevent the collapse of the airway - surfactant, on the surface of the lungs, is a phospholipid layer which maintains moisture and reduces surface tension to stop collapsing alveoli - smooth muscle lines the trachea to bronchioles and contracts to constrict the airways - goblet cells line the trachea to bronchioles and secrete mucus to trap dust and bacteria particles - ciliated epithelial cells which line the trachea to bronchioles beat regularly to waft mucus up airways to be removed in the mouth to keep airways clear and prevent infections - elastin lines all airways and alveoli and allow lung tissue to stretch when breathing in and recoil when breathing out to force air out - sqamous epithelium lines alveoli and gives a short diffusion distance for substances

Question 31

What are some adaptations of the lungs?

Answer 31

- alveolar epithelium and capillary epithelium are very thin to shorten diffusion distance - large number of alveoli increases surface area - large number of capillaries maintain concentration gradient - capillaries are very narrow so red blood cells are squeezed through one at a time, increasing time for diffusion and making sure they also uptake oxygen - constant ventilation of air maintains steep concentration gradient

Question 32

How do humans inhale and exhale?

Answer 32

Inhalation/inspiration: 1. diaphragm contracts and intercostal muscles contract to pull ribcage up and out 2. increases volume in thoracic cavity and reduces air pressure to make more space 3. air moves into the trachea (this process is active and requires energy) Exhalation/expiration: 1. diaphragm relaxes and intercostal muscles relax to pull ribcage in and down 2. decreases volume in thoracic cavity and increases air pressure to make less space 3. air is pushed out of the trachea (this process is passive and requires no energy)

Question 33

How does oxygen move from the alveoli to capillaries?

Answer 33

1. moves from alveoli 2. through alveolar epithelial cells (squamous) 3. through capillary endothelium 4. into red blood cells in the capillary

Question 34

What is ventilation rate, tidal volume and residual volume?

Answer 34

Ventilation rate - how many breaths per minute (about 40 for humans) Tidal volume - volume of air in each breath Residual volume - volume of air that remains in the lungs to make sure they never fully deflate

Question 35

What does a spirometer do?

Answer 35

- measures lung function - can be used to work out breathing rate, tidal volume and ventilation rate

Question 36

What is forced vital capacity?

Answer 36

It is the maximum volume of air it is possible to breathe forcefully out of the lungs

Question 37

How do lung diseases cause muscle weaknesses and tiredness?

Answer 37

- less oxygen diffuses into bloodstream - body cells receive less oxygen - rate of aerobic respiration is reduced - less energy is released - causes symptoms of tiredness or muscle weaknesses

Question 38

What are the two types of lung disease?

Answer 38

Restrictive diseases - make it difficult to fully breathe in, which reduces the forced vital capacity e.g. fibrosis Obstructive diseases - make it difficult to breathe out as airways are blocked, reducing FVC e.g. asthma

Question 39

What are some examples of lung diseases?

Answer 39

- Tuberculosis - caused by inhaling bacteria so macrophages build a wall around them in the alveoli, which damages the alveoli. This leads to a smaller surface area do diffusion rate is reduced as well as reduced elasticity so lungs can't hold as much air (=shortness of breath, coughing, fatigue) - Pulmonary fibrosis - scar tissue formed in lungs after infection. Thicker scar tissue reduces diffusion rate due to long diffusion distance and reduced elasticity means lungs can't hold as much air (=dry cough, shortness of breath, chest pain from higher heart rate, fatigue) - Asthma - airways inflamed due to allergic reaction so smooth muscle lining contracts and there is lots of mucus. Airway constrictions reduce air flow and oxygen diffusion rate (= wheezing, shortness of breath, tight chest) - Emphysema - foreign particles (e.g. from smoking) trapped in alveoli, causing inflammation so phagocytes produce enzymes that break down elastin. Damaged alveoli causes a smaller surface area and loss of elastin means alveoli can't recoil and less air is removed (= shortness of breath, wheezing)