Chapter 6- Exchange Flashcards
Features of specialised exchange surfaces
-Large SA- increase SA:V -> increases exchange rate
-Thin- short diffusion pathway
-Selectively permeable- selected materials can cross- controls rate of movement
-Movement of external + internal mediums- maintains diffusion gradients
Surface area to volume ratio
Smaller organism- higher SA:V
As size increases - volume increases faster than SA- smaller SA:V - need specialised exchange organs/processes
Gas exchange in single-celled organisms
Small- large SA:V
Oxygen absorbed by diffusion across surface + CO2 from respiration diffuses out
3 ways respiratory gases move in/out of tracheal system in insects
- Along diffusion gradient (insect at rest)
-Oxygen used in respiration -> concentration falls -> diffusion gradient -> oxygen diffuses in -> CO2 produced - opposite direction gradient -> CO2 diffuses out - Mass transport (high activity)
-Contract abdominal muscles -> large volumes of air forced out (abdominal pumping) -> new air enters on relaxation -> speeds up exchange - Ends of tracheoles filled with water (high activity)
-Muscle cells in tracheoles respire anaerobically -> produces lactic acid which is soluble -> dissolves in cells + lowers their water potential -> water moves into cells by osmosis -> volume of air in tracheoles decrease -> draws air in
How are insects adapted for gas exchange?
Main structures: spiracles, tracheae, tracheoles, muscle cells
Spiracles = tiny pores, opened/closed by valves, prevents water loss
Limitation of insect gas exchange -> relies solely on diffusion, must have short diffusion pathway + insects must be small
Gas exchange in fish
Small SA:V
Have gills + each has a gill arch which has gill filaments which has lamellae
Blood + water flow in a counter current mechanism- maintains diffusion gradient across entire lamellae length -> max amount of diffusion
Adaptations for gas exchange in a leaf
Many stomata- no cell is far away- short diffusion pathway
Interconnecting air spaces- gases in contact with mesophyll cells
Large SA of mesophyll cells
How do stomata help with gas exchange?
Pores- mainly on underside of leaves
Each stoma surrounded by guard cells- open+close -> control rate of exchange + reduces water loss
How do insects limit water loss?
Small SA:V - minimises area
Waterproof coverings
Spiracles- close to reduce water lost- mostly when insects are at rest
How do plants limit water loss?
Waterproof covering over leaves
Thick cuticle- water can’t escape
Rolling up of leaves protects lower epidermis + traps air that has a high water potential so there’s no gradient for water to be lost
Hairy leaves + stomata in pits/grooves = traps still, moist air next to leaves -> reduces water potential gradient - less water loss
Reduced SA:V of leaves e.g. pine needles- reduces rate of water loss
Structure of the human gas exchange system
Lungs supported/protected by rib cage
Lungs = lobed structures
Trachea = flexible airway protected by cartilage rings, made of muscle
Bronchi = 2 divisions of trachea, produces mucus + has cilia, can by supported by cartilage
Alveoli = air-sacs at end of bronchioles, collagen + elastic fibres, lined with epithelium
Alveolar membrane = site of gas exchange
What are the two sets of intercostal muscles (muscles which lie between the ribs)?
Internal intercostal muscles (contraction -> expiration)
External intercostal muscles (contraction -> inspiration)
Process of inspiration (breathing in + active process)
External intercostal muscles contract + internal intercostal muscles relax
Ribs pulled up + out + diaphragm contracts -> increases thorax volume
Decreased pressure in lungs
Creates pressure gradient -> air drawn in
Process of expiration (breathing out + largely passive process)
External intercostal muscles relax + internal intercostal muscles contract
Ribs move down + in + diaphragm relaxes = decreases thorax volume
Increases pressure in lungs
Creates pressure gradient (pulmonary pressure is >) - air forced out
How are the lungs adapted for gas exchange?
-Total SA of alveoli = 70m^2
-Each alveolus lined with epithelial cells - vey thin
-Each alveoli has network of pulmonary capillaries - RBCs flattened against capillary walls which are a single cell thick
How is gas diffusion between alveoli + blood quick?
-RBCs slowed through pulmonary capillaries - more diffusion time
-RBCs flattened against capillary walls - distance reduced
-Alveoli + capillary walls = very thin -> short diffusion pathway
-Alveoli + pulmonary capillaries = v.large SA
-Breathing ventilates lungs, heart constantly circulates blood + blood flows -> maintains steep conc. gradient
What are the major parts of the digestive system?
-Oesophagus = carries food from mouth to stomach
-Stomach = produces enzymes + shortens/digests food
-Ileum = food further digested here, large SA, digestion products absorbed
-Large intestine = absorbs water
-Rectum = final section of intestine
-Salivary glands = near mouth, release secretions
-Pancreas = produces pancreatic juice containing enzymes
Purpose + process of physical breakdown of food
-Large food broken down mechanically
-Provides large SA for chemical digestion
Purpose of chemical digestion of food
Hydrolyses large, insoluble molecules -> small, soluble ones
Carbohydrate digestion
- Salivary amylase produces + hydrolyses starch to maltose
- Pancreas produces pancreatic juice -> contains pancreatic amylase which hydrolyses starch -> maltose
- Membrane-bound maltase hydrolyses maltose -> glucose (glycosidic bonds broken)
Lipid digestion
-Emulsification aids digestion
-Bile salts produced by liver + stored in gall bladder
-Large lipid droplets split into micelles by bile salts
-Increases lipids SA - increases lipase activity - increases rate of lipid digestion
-Lipases (in pancreatic juice) hydrolyses triglycerides into monoglycerides + fatty acids (breaks ester bonds)
-Micelles carry monoglycerides/fatty acids to epithelial cell membrane (maintains high conc. at lining helps for diffusion)
What are micelles?
Associations of bile salts, monoglycerides + fatty acids
Protein digestion
- Endopeptidases = hydrolyse central region of protein to form a series of peptide molecules
- Exopeptidases = progressively release dipeptides + single amino acids by hydrolysing peptide bonds on terminal amino acids
- Dipeptidases (membrane-bound) = break bonds between 2 amino acids of dipeptides
Structure of the ileum
Highly folded
Has villi - increase SA
Thin walls - lined with epithelial cells + other side has blood capillaries
Adaptations of the ileum
-Increase SA for diffusion
-Walls = very thin - short diffusion distance
-Contains muscle - maintains diffusion gradient (material rich food replaces old food)
-Blood vessels - carry away absorbed molecules - maintains gradient
-Epithelial cells on villi contain microvilli to increase SA
How are amino acids + monosaccharides absorbed in the ileum?
By diffusion + co-transport
How are triglycerides absorbed in the ileum?
- Micelles come into contact with epithelial cell membranes -> break down -> release monoglycerides + fatty acids
- MGs + FAs diffuse across phospholipid bilayer into epithelial cells
- MGs + FAs move to endoplasmic reticulum where they are recombined to form triglycerides
- Triglycerides move to Golgi apparatus -> associate with cholesterol + phospholipids to form chlyomicrons
- Chylomicrons move out of epithelial cells by exocytosis
- Chylomicrons enter lacteals + are transported away from intestines
What are chylomicrons?
Lipoproteins that are adapted for transporting dietary lipids from intestines to other parts of the body, made from triglycerides, phospholipids + cholesterol
