Biology - Chapter 6: 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.

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

• Small Intestine (ileum) → folded walls into villi increase SA & 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 gas exchange ?

• Exoskeleton is covered in waxy cuticle

• Spiracles can close

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 oxygen 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

• 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 so can stretch out and spring back

• Bronchi → produces mucus to trap dirt and cilia move 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