8 - Exchange with the environment

Question 1

What is Fick’s Law?

Answer 1

Rate of diffusion is proportional to: Surface area x concentration gradient divided by diffusion distance

Question 2

How are the alveoli adapted for gas exchange?

Answer 2

• Many alveoli, provide large surface area
• Walls of alveoli 1 cell thick, short diffusion distance
• Walls of capillary are 1 cell thick, short diffusion distance
• Capillary and alevoli walls are flattened cells, short diffusion distance
• Cell membrane permeable to gases
• Many blood capillaries, provide a large surface area and good circulation

Question 3

Describe breathing in humans?

Answer 3

Inspiration - external intercostal muscles contract, expands ribs up and out, diaphragm flattens; volumes increases, pressure decreases
Expiration - Intercostal muscles relax, volume decreases, pressure increases
During exercise the internal intercostal muscles and abdominal muscles force expiration

Question 4

Structure of trachea?

Answer 4

C shaped rings of cartilage, creates flexibility. Walls made of muscle and ciliated epithelium and goblet cells.

Question 5

Structure of bronchi?

Answer 5

Divisions of trachea with cartilage

Question 6

Structure of Bronchioles?

Answer 6

Walls made of muscles and lined with epithelial cells. Muscles allows control of air in and out.

Question 7

Structure of alveoli?

Answer 7

Folded walls to increase SA. Single cell thick. Flattened cells. Walls contain elastic fibre and collagen. Elasticity to stretch and recoil to help expel air.

Question 8

Describe the thorax?

Answer 8

Linned by two pleural membranes which secrete pleural fluid that reduces friction of moving lungs and attaches the lungs to the inside of the ribs by surface tension, so the lungs can move with the ribs.

Question 9

Pulmonary ventilation?

Answer 9

Total volume of air moved into lungs in a minute

Question 10

Tidal volume?

Answer 10

Volume of air taken in in a normal breath

Question 11

Ventilation rate?

Answer 11

Number of breaths taken in a minute

Question 12

Pulmonary ventilation rate (dm-3/min)?

Answer 12

Tidal volume (dm-3) x ventilation (min)

Question 13

Why is gas exchange difficult for fish?

Answer 13

Low oxygen content in water and water has a high density and requires a lot of energy to move across exchange surfaces.

Question 14

How are gills adapted for gas exchange?

Answer 14

• Filaments and secondary lamellae increase SA
• Thin epithelium decrease diffusion distance
• Counter-current flow maintains concentration gradient along the length of gill, so equilibrium is not reached early.

Question 15

Describe counter-current flow?

Answer 15

Water flows in opposite direction to blood across lamellae so difference in concentration is maintained so diffusion occurs across the entire length of the lamellae.

Question 16

Describe inspiration in fish

Answer 16

1. Mouth opens
2. Opercular valve shuts
3. Floor of mouth lowered
4. Increases volume
5. Water enters due to decreased pressure

Question 17

Expiration in fish

Answer 17

1. Mouth closes
2. Opercular valve opens
3. Floor raised causes decreased volume
4. increased pressure causes water to be forced over gills

Question 18

How is the trachea adapted in insects for gas exchange?

Answer 18

• Spiracles on underside of insect, openings of exoskeleton
• Low conc of oxygen in tissues, so oxygen diffuses down conc gradient from air
• Tracheoles heavily branched to increase SA
• Tracheoles branch deep into tissue, decreased diffusion distance
• Abdominal beating: contractions forcing air out of air sacs keeps air ventilating
• Spirales not always open to decrease water loss, are controlled by valves and only open when CO2 conc peaks, forcing them open
• Waterproof, waxy cuticle and tiny hairs around their spiracles which reduces water loss by evaporation

Question 19

How are leaves adapted for gas exchange?

Answer 19

• Mesophyll cells
• Leaves have large SA:V ratio (broad and flat)
• Large numbers of stomata provide large surface area
• Guard cells open stomata
• Leaves are thin, short diffusion distance

Question 20

How do plants reduce water loss?

Answer 20

• Thick waxy cuticle, increase diffusion distance
• Guard cells can close
• Spines - reduce SA
• Shrunken stomata and hairs, traps moist air increasing humidity and decreasing conc gradient
• Curled leaves, traps moist air increasing humidity and decreasing conc gradient

Question 21

Emphysema

Answer 21

Smoking
Inflammation of alveoli attracts phagocytes,
breaks down elastic tissue which reduces conc gradient

Question 22

Fibrosis

Answer 22

Scar tissue, thicker, less elastic, reduces expansion of lungs and therefore tidal volume is decreased
increase in diffusion distance and decrease in conc gradient

Question 23

TB

Answer 23

Bacteria transmitted by droplets, bacteria will wake and destroy the alveoli, reducing surface area
Tidal volume decreased

Question 24

Asthma

Answer 24

Smooth muscle in bronchioles contacts, mucus produced, narrows air way, less oxygen absorbed, less respiration
Lowers airflow
FEV lowered

Question 25

Digestion in mouth

Answer 25

Salivary amylase released
Chemical digestion - starch to maltose by maltase
Mechanical digestion - chewing
Saliva lubricates food for swallowing

Question 26

Digestion in osophagus

Answer 26

Food moves down by perisalsis

Question 27

Digestion in stomach

Answer 27

Pepsin released
Larger polypeptide chains broken down into smaller polypeptide chains, hydrolyse reactions
Pepsin is an endopeptidase
Juices secreted are called gastric juices
Low pH kills bacteria and is optimum for pepsin

Question 28

Digestion in small intestine (duodenum)

Answer 28

Amylase - Starch to maltose
Trypsin - small polypeptide to amino acid
Maltase - maltose to glucose
Lipase - lipids to fatty acids and glycerol
Enzymes in pancreatic juices
NaHCO3 released to neutralise stomach acid

Question 29

What happens in the ileum?

Answer 29

Absorption of glucose, amino acids, fatty acids and glycerol.
Many villi and micro villi speed it up

Question 30

Protein digestion

Answer 30

• Large protein broken down by pepsin into shorter polypeptides (endopeptidase)(Hydrogen bonds break the chain)(stomach)
• Trypsin breaks down shorter polypeptides into dipeptides (duodenum)(endo and exo peptidase)
• Di-peptides broken down into amino acids in the walls of the duodenum

Question 31

Lipid absorption?

Answer 31

Large fatty acids and glycerol diffuse across epithelial cells where they combine to form triglycerides, which packaged with phospholipids to make Chylomicrons which are absorbed by the laceal villus
Short fatty acids diffuse straight away

Question 32

Glucose digestion

Answer 32

Glucose and Na+ ions co-transported into epithelial cell
Na + ions diffuse into capillary
Glucose actively transported into capillary

Question 33

Amino Acid digestion

Answer 33

Amino acid diffuses into epithelial cell
Na + ion diffuses into capillary
Amino acid actively transported into capillary

Question 34

Volume and surface area?

Answer 34

Volume = Height * Length * Width
SA = Area of surface sides

Question 35

Size and shape?

Answer 35

Size - Smaller sized organisms have a larger surface area to volume ratio and therefore lose heat more quickly - higher metabolic rate due to this
Shape - Compact shape - small surface area to volume ration - minimised heat loss

Question 36

Lipid digestion?

Answer 36

Bile salts emulsify the lipids to increase their surface area for effective action of lipase - form small droplets
Lipase made in pancreas and secreted into the small intestine
Lipase breaks down lipids into monoglycerides and fatty acids
Monoglycerides and fatty acids combine with bile salts to produce micelles
Bile also helps neutralise stomach acid
Lipids absorbed in illeum

Question 37

Exopeptidases and endopeptidases?

Answer 37

Endopeptidases break peptide bonds internally in the polypeptide
Expeptodases break the bonds at the end and remove amino acids
Both working together increases surface area for exopeptodases