3.6 Biology - Exchange

Features of Specialised Exchange ?

• Large SA:Vol ratio → increases diffusion rate

• Thin walls → shortens diffusion pathway

• Extensive blood supply → maintains concentration gradient

• Selectively Permeable → controls what is exchanged

How does gas exchange occur in insects

1. Air enters the tracheal system through open spiracles in the exoskeleton.

2. Air moves into tracheae and diffuses into tracheoles.

3. Oxygen dissolves in water in tracheal fluid and diffuses from tracheoles into body cells.

4. Carbon dioxide diffuses out of body cells into the tracheoles.

5. Air is then carried back to the spiracles via the tracheae and released from the body.

Components of digestion

• Salivary Glands → Contain amylase → (Starch to maltose)

• Oesophagus

• Stomach → digests foods (esp proteins), produces acid to destroy pathogens & has muscular walls

• Liver → produces bile salts → help digest lipids

• Pancreas → contains enzymes (lipase, exo & endopeptidase, amylase)

• Small Intestine (ileum) → microvilli increase SA & are thin to shorten diffusion pathway

• Large Intestine → absorbs water

• Rectum & Anus → Store and release faeces

Describe Inhalation

• External intercostal muscles contract and ribcage is pulled up and out

• Diaphragm contracts and flattens

• Thorax volume increases and pressure decreases so air is drawn in down pressure gradient

Describe Exhalation

• External intercostal muscles relax and ribcage moves down and out

• Diaphragm relaxes and becomes dome shaped

• Thorax volume decreases and pressure increases so air is forced out by elastic recoil in lungs

How do insects limit water loss?

• Exoskeleton is covered in waxy cuticle to prevent water loss

• Spiracles can close

• small sa:vol ratio where water can evaporate from

What are the adaptations for gills?

• Lamellae increase surface area

• Lamellae are thin → decrease diffusion pathway

• Gills have good blood supply → maintains conc. gradient

Describe counter-current flow system

• Blood and water flow in opposite directions

• So concentration gradient is maintained across whole length of lamellae

• As there is always more oxygen in water than in blood

How can plants limit water loss ?

• guard cells that open and close stomata (close at night when photosynthesis isnt occuring)

• waxy cuticle

How do xerophytes limit water loss ?

thick waxy cuticle → reduces water loss

rolled leaves → maintain humid air around stomata so shallower concentration gradient

hairy leaves → maintain humid air around stomata so shallower concentration gradient

stomata in sunken pits → maintain humid air around stomata so shallower concentration gradient

small leaf SA:Vol → reduces SA for evaporation

State the adaptations of the human gas exchange system

• Trachea → rings of cartilage to prevent collapsing, muscle can contract to control airflow & elastic fibres can stretch out and spring back

• Bronchi → produces mucus to trap dirt and cilia moves dirty mucus to throat

• Bronchioles → elastic fibres so can stretch out and spring back

Describe the role of micelles in the absorption of fats into the cells lining the ileum

• Micelles include bile salts and fatty acids

• They make the fatty acids more soluble

• They carry fatty acids to epithelial cell lining

• They maintain higher concentration of fatty acids than in cell

How is alveoli adapted for gas exchange?

(CO₂ diffuses out of blood in capillaries to alveoli and O₂ diffuses into blood from alveoli)

• many alveoli in lungs increase SA

• thin walls decrease diffusion pathway

• surrounded by a network of capillaries which maintains conc. gradient

what is digestion

physical → large food molecules are broken down into smaller molecules which increases SA for chemical digestion

chemical → large insoluble molecules are hydrolysed into small soluble molecules by enzymes

how are carbohydrates digested

• amylase (pancreas + salivary glands) hydrolyses starch into maltose

• maltase (small intestine) hydrolyses maltose into glucose

• (glucose passes into cytoplasm from lumen of gut via facilitated diffusion)

how are proteins digested

• endopeptidase hydrolyses peptide bonds between amino acids in the middle of polypeptide

• exopeptidase hydrolyses peptide bond between amino acids at the end of polypeptide

• dipeptidase hydrolyses peptide bond between two amino acids

how are lipids digested

• Lipids are emulsified by bile salts (produced in pancreas, stored in gall bladder)

• Many droplets of lipids increase SA and allow fast hydrolysis by lipase

• Lipase hydrolyses emulsified lipids into fatty acids and glycerol

describe the process of lipid absorption

• Micelles contain bile salts and fatty acids/monoglycerides

• Micelles make fatty acids/monoglycerides more soluble

• Fatty acids/monoglycerides absorbed into ileum by diffusion

• triglycerides reform in golgi and are packaged into chylomicrons for transport

• chylomicrons exit epithelial cell via exocytosis and enter bloodstream via lacteals

define tidal, vital, residual and total lung capacity

how do you calculate pulmonary ventilation rate (PVR)

• tidal volume → resting breathing rate

• vital capacity → the max volume you can inhale or exhale

• residual volume → the minimum volume in the lungs

• total lung capacity → max. volume of air u can fit in lungs

• PVR = breathing rate x tidal volume

• there is positive correlation between lung cancer deaths and cigarettes smoked per year

• however correlation doesnt mean causation

• data overlaps from 2500 to 3500 cigarettes smoked per year as lung cancer deaths doesnt increase

explain the oxyhaemoglobin dissociation curve

• At low pO₂ there is low affinity, e.g. in respiring cells where haemoglobin readily unloads oxygen

• At high pO₂ there is high affinity e.g. in lungs where haemoglobin loads to oxygen

what is the bohr effect

when high CO₂ causes the oxyhaemoglobin dissociation curve to shift to the right, meaning haemoglobin’s affinity for oxygen decreases as CO₂ slightly changes the shape of the Hb

(right=release)

why is it referred to as a closed double circulatory system

• closed = blood remains in vessels

• double = two circuits, one from heart to lungs and other from heart to body