Chapter 6 - Gas Exchange

Question 1

How does a large surface area affect the rate if diffusion

Answer 1

organisms that have a large surface area relative to their volume so the diffusion of substances is fast

Question 2

How does a small SA:V affect rate of diffusion

Answer 2

organisms that have a small surface area relative to their volume so the diffusion of substances is slower.

Question 3

How to calculate the surface area of a cube

Answer 3

Length x width x 6

Question 4

How to calculate the volume (V) of a cube:

Answer 4

V = length x width x depth

Question 5

Why can’t substances diffuse directly across the cell membrane in multicellular organisms

Answer 5

• Cells are not in direct contact with the external environment.
• Diffusion distances between cells and their environment are large.
• Larger organisms have higher metabolic rates, so they need more oxygen and glucose.

Question 6

How are exchange surfaces specialised to allow materials to be transferred between cells and an organisms environment

Answer 6

• large surface area to provide a larger area across which substances can be exchanged
• thin walls to minimise diffuse distance
• an extensive blood supply or ventilation to maintain a steep concentration gradient
• being surrounded by selectively partially permeable membranes to control what substances are exchanged

Question 7

Why do insects need efficient systems for gas exchange

Answer 7

• To deliver oxygen to cells - This allows aerobic respiration to occur to release energy for cellular processes.
• To remove carbon dioxide from cells - The build up of carbon dioxide produced as a waste product of respiration reduces pH, which can denature enzymes.

Question 8

Main structures of an insects gas exchange system

Answer 8

Tracheae - These are air-filled tubes branching throughout the body.
Tracheoles - These are fine branches of tracheae that deliver gases to cells.
Spiracles - These are external openings of the tracheal system on the exoskeleton along the abdomen and thorax.

Question 9

How is the trachea adapted for gas exchange

Answer 9

Reinforced with spirals of chitin - This prevents collapsing.
Multiple tracheae - This increases surface area.

Question 10

How are the tracheoles adapted for gas exchange

Answer 10

Penetrate directly into tissues - This reduces the gas diffusion distance.
Thin walls - These reduce the gas diffusion distance.
Highly branched - This maximises the surface area.
Not reinforced with chitin - This allows gas exchange to occur.
Fluid at the ends of the tracheoles (tracheal fluid) - This allows oxygen to dissolve to aid diffusion and reduces water loss.

Question 11

How are the spiracles adapted for gas exchange

Answer 11

Open and close - This allows them to control gas exchange with the atmosphere and minimise water loss.

Question 12

How does gas exchange occur in an insect

Answer 12

1)Air enters the tracheal system through open spiracles.
2)Air moves into larger tracheae and diffuses into smaller tracheoles.
3)Tracheoles branch throughout the body, transporting air directly to cells.
4)Oxygen dissolves in water in tracheal fluid and diffuses down its concentration gradient from tracheoles into body cells.
5)Carbon dioxide diffuses down its concentration gradient out of body cells into the tracheoles.
6)Air is then carried back to the spiracles via the tracheae and released from the body.

Question 13

How is the concentration gradient maintained in insects

Answer 13

Cells using up oxygen for respiration - This keeps oxygen concentration low in cells.
Cells producing carbon dioxide in respiration - This keeps carbon dioxide concentration high in cells.
Continuous ventilation - Fresh air is supplied to the tracheal system via spiracles.

Question 14

Other ventilation mechanism insects use for gas exchange

Answer 14

• Mechanical active ventilation - This is when muscles around the tracheae contract and relax, changing the volume and pressure in the abdomen and squeezing the tracheae to pump air in and out of the spiracles.
• Wing muscles connected to sacs - These pump air to ventilate the tracheal system.
• Vibration of thoracic muscles - This pumps air to ventilate the tracheal system.

Question 15

Structure of gills

Answer 15

Gills are covered by an operculum flap.
Gills consist of stacked filaments containing gill lamellae.
Gill lamellae are surrounded by extensive blood vessels.

Question 16

Adaptation of the gills for efficient gas exchange

Answer 16

• The lamellae provide a large surface area.
• The lamellae membranes are thin to minimise diffusion distance.
• The gills have a rich blood supply to maintain steep diffusion gradients.
• The countercurrent flow of blood and water creates even steeper concentration gradients.
• Overlapping filament tips increase resistance, slowing water flow over gills and allowing more time for gas exchange.

Question 17

What happens in a countercurrent flow system

Answer 17

1) the blood and water flow over the lamellae in opposite directions
2) the blood constantly has less oxygen than the water
3) so when the oxygen rich blood meets water that is at is highest percentage of oxygen the oxygen will move down its concentration gradient into the blood as the blood will have less oxygen than the water
4) the oxygen poor blood returning from t body tissue will also meet oxygen poor water which had had most of its oxygen removed but the water will still have a higher concentration of oxygen so the oxygen will move down it’s concentration gradient
5) this countercurrent happens along the whole fish which maintains a steep concentration gradient across the entire gill

Question 18

Why can’t fish use parallel flow/ con counter current

Answer 18

As this oxygen in the blood and in the water will eventually reach equilibrium this reduces the concentration gradient so less oxygen is absorbed

Question 19

How do plants limit water loss in general

Answer 19

They have a waterproof waxy cuticle on their leaves.
They have guard cells that can close stomata when needed.

Question 20

What are xerophytes

Answer 20

plants adapted to living in dry environments with limited water availability.

Question 21

How are xerophytes adapted to minimise water loss

Answer 21

• Thick waxy cuticle - This reduces water loss through evaporation.
• Rolling or folding of leaves - This encloses the stomata on the lower surface to reduce air flow and the evaporation of water.
• Hairs on leaves - These trap moist air against the leaf surface to reduce the diffusion gradient of water vapour.
• Sunken stomata in pits - These reduce air flow and the evaporation of water.
• Small, needle-like leaves - These reduce the surface area across which water can be lost.
• Water storage organs - These conserve water for when it is in low supply.

Question 22

Structure and functions of a leaf

Answer 22

• Upper epidermis with waxy cuticle - This reduces water loss from the leaf surface.
  Air spaces
• Mesophyll cells - These are cells within the mesophyll tissue, located between the upper and lower epidermis.
• Stomata - These are small pores surrounded by guard cells on the underside of leaves that can open and close.
• Lower epidermis - This is the bottom layer of cells in a leaf that contains the stomata and guard cells.
• Vascular tissue (xylem and phloem) - This transports water and nutrients.

Question 23

Adaptions of structure of the leaf for gas exchange

Answer 23

Air spaces - These provide a network for gases to quickly diffuse in and out of the leaf and access photosynthesising cells.
Mesophyll cells - These are dispersed throughout the leaf, providing a large surface area across which gases can diffuse.
Stomata - These open when conditions are suitable for photosynthesis, allowing inward diffusion of carbon dioxide and outward diffusion of oxygen, and close to minimise water loss.

Question 24

How does air travel through a humans respiratory system

Answer 24

1) Air first enters the trachea.
2) Air travels into the two bronchi, with one bronchus going to each lung.
3) Air travels into smaller airways called bronchioles.
4) Air travels into clusters of air sacs called alveoli at the end of the bronchioles.

Question 25

How does the ciliated epithelium protect our airways against microbes

Answer 25

contains mainly goblet cells and ciliated epithelial cells:
- Goblet cells - These produce and secrete mucus that traps dust and microbes.
- Cilia on ciliated epithelial cells - These waft the mucus upward to the mouth so it can be swallowed.

Question 26

What is the trachea

Answer 26

A large tube that carries air from the throat down to the lungs.

Question 27

Adaptions of the trachea

Answer 27

1) Rings of cartilage keep the airway open.
2) Smooth muscle can contract or relax to constrict or dilate the airway and change airflow.
3) Elastic tissue contains elastic fibres with elastin that allows stretching and recoiling.
4) Lined with ciliated epithelial cells and goblet cells.

Question 28

What is the bronchi

Answer 28

two main branches extending from the trachea that carry air into each lung

Question 29

Adaptations of the bronchi

Answer 29

1) Reinforced with cartilage to keep the airway open.
2) Smooth muscle can contract or relax to constrict or dilate the airway and change airflow.
3) Elastic tissue contains elastic fibres with elastin that allows stretching and recoiling.
4) Lined with ciliated epithelial cells and goblet cells.

Question 30

What are the bronchioles

Answer 30

smaller airways branching from the bronchi that carry air to the alveoli.

Question 31

Adaptions of bronchioles

Answer 31

1) No cartilage, can change shape.
2) Smooth muscle can contract or relax to constrict or dilate the airway and change airflow.
3) Elastic tissue contains elastic fibres with elastin that allows stretching and recoiling.
4) Simple squamous epithelium (only larger bronchioles have a ciliated epithelium).

Question 32

How does the alveoli carry out gas exchange

Answer 32

1) Oxygen diffuses from the alveoli into the pulmonary capillaries where it binds to haemoglobin in red blood cells.
2) Carbon dioxide dissociates from haemoglobin and diffuses from the blood into the alveoli.

Question 33

Adaptations of the alveoli

Answer 33

1) Large surface area - This increases rate of gas exchange.
2) Partially permeable - This means that only certain gases can move across the wall.
3) Surrounded by dense network of capillaries - These bring blood close to air for gas exchange.
4) Ventilation of air and is one cell thick (as its wall consists of one layer of squamous epithelial cells) - This maintains steep diffusion gradient and rapid rate of diffusion
5) Elastic fibres - These allow stretching and recoiling.
(6) Collagen fibres - These contain strong collagen that prevents alveoli from bursting and limits overstretching.) - good for essays
7) Moist inner surface - This allows gases to dissolve, and lung surfactant helps alveoli remain inflated.

Question 34

What are the pulmonary blood vessels that are involved in the circulation of blood in the lungs

Answer 34

• The pulmonary artery - This delivers deoxygenated blood from heart to pulmonary capillaries.
• The pulmonary vein - This delivers oxygenated blood from capillaries to heart.
• The pulmonary capillaries - These are the site of gas exchange between blood and alveoli.

Question 35

Adaptions of the pulmonary capillaries for gas exchange

Answer 35

• Thin walls (one endothelial cell thick) - This maintains a short diffusion distance.
• Red blood cells pressed against capillary walls - This reduces diffusion distance.
• Large surface area - This increases diffusion speed.
• Movement of blood - This maintains steep diffusion gradient.
• Slow blood movement - This allows more time for diffusion.

Question 36

What happens during inspiration

Answer 36

1) The external intercostal muscles contract while the internal intercostal muscles relax, moving the ribcage up and out.
2) The volume of the thoracic cavity increases.
3)The diaphragm contracts and flattens, further increasing the volume of the thoracic cavity.
4) The lung pressure decreases below atmospheric pressure.
5) Air flows into the lungs down the pressure gradient.

Question 37

What happens during expiration

Answer 37

1) The external intercostal muscles relax while the internal intercostal muscles contract, moving the ribcage down and in.
2) The volume of the thoracic cavity decreases.
3) The diaphragm relaxes and unflattens, further decreasing the volume of the thoracic cavity.
4) The lung pressure increases above atmospheric pressure.
5) Air is forced out of the lungs down the pressure gradient.

Question 38

What are the two main ways the digestive system breaks down food and how does both processes work

Answer 38

• Physical digestion - The break down of large food pieces into smaller ones to increase the surface area for chemical digestion.
• Chemical digestion - Enzymes catalyse hydrolysis reactions that break bonds in large insoluble molecules to form smaller soluble molecules.

Question 39

Key components involved in digestion

Answer 39

• Salivary glands - These secrete saliva containing amylase.
• Oesophagus - This transports food to the stomach.
• Stomach - This digests food (especially proteins) and produces acid to destroy pathogens.
• Liver - This produces bile salts to aid lipid digestion.
• Pancreas - This secretes pancreatic juice containing enzymes (proteases, lipases, and amylases).
• Small intestine - This consists of three parts (you only need to know the final part, the ileum) that are the site of further digestion and absorption.
• Large intestine - This absorbs water and stores waste.
• Rectum - This stores faeces before removal via egestion through the anus.

Question 40

What is the order that food travels down your alimentary canal (the pathway food takes through the body)

Answer 40

Mouth ➔ oesophagus ➔ stomach ➔ small intestine ➔ large intestine ➔ rectum ➔ anus

Question 41

What do carbohydrases do

Answer 41

They break down large carbohydrates into smaller polysaccharides, disaccharides and monosaccharides

Question 42

Where are carbohydrases produced

Answer 42

salivary glands, the pancreas, and the epithelial cells lining the ileum.

Question 43

How does starch digestion occur

Answer 43

1) Salivary amylase breaks down starch into the disaccharide maltose in the mouth.
2) Acid in stomach denatures salivary amylase.
3) Pancreatic amylase continues starch digestion in small intestine.
4) The epithelial cells in the ileum lining produce maltase to break down maltose into α-glucose monomers.

Question 44

What does the lipases do

Answer 44

breaks down lipids into fatty acids and monoglycerides.

Question 45

What are lipase produced by

Answer 45

the pancreas and act in the small intestine.

Question 46

How does the digestion of lipids occur

Answer 46

1) Bile salts emulsify lipids into tiny droplets called micelles, increasing the surface area of the lipids.
2) Pancreatic lipase breaks down micelles into fatty acids and monoglycerides.

Question 47

What do protease do

Answer 47

break down proteins, polypeptides, or dipeptides into smaller units and eventually into amino acids

Question 48

What are the three types of protease and what do they do

Answer 48

-Endopeptidases - These hydrolyse internal peptide bonds in the middle of proteins to form shorter polypeptides, increasing the number of ends for other proteases to work on.
- Exopeptidases - These hydrolyse peptide bonds at the ends of polypeptides to remove terminal amino acids or dipeptides.
- Dipeptidase - These break down any remaining dipeptides into amino acids.

Question 49

What are the adaptions of the ileum (small intestine)

Answer 49

1) The walls are folded into villi to increase surface area.
2) Epithelial cells have microvilli to further increase surface area.
3) It has thin walls reduce diffusion distance.
4) It has an extensive capillary network and a good blood supply to maintain steep diffusion gradients.
5)Muscles in the ileum wall contract to mix content and bring new material into contact with villi.

Question 50

How are triglycerides absorbed into the bloodstream

Answer 50

1) Bile salts emulsify triglycerides into tiny droplets called micelles
2) Micelles are broken down to release fatty acids and monoglycerides.
3) As they are both non-polar, fatty acids and monoglycerides can diffuse into the epithelial cells that line the ileum.
4) Triglycerides reform inside the cells’ endoplasmic reticulum.
5) Triglycerides are packaged into chylomicrons for transport.
6) Chylomicrons are released from the epithelial cells by exocytosis into lacteals, which are lymphatic vessels in the villi.
7) Chylomicrons are transported via lymph vessels in the lymphatic system to the blood.