topic 3 (exchange and transport systems)

Describe the relationship between size and surface area to volume ratio in organisms

as size increases, surface area to volume ratio decreases

Explain how the counter-current principle allows efficient uptake in the fish exchange system

• blood and water flow in apposite directions

• diffusion gradient is maintained across the whole lamella/gill filament

• oxygen concentration always higher in water

Describe the mechanism that causes lungs to fill with air

• the external intercostal muscles and diaphragm contract

• leading to the the ribs moving up and outwards, while the diaphragm moves downwards

• increase of volume in the thoracic cavity, decrease in pressure

• so air moves down a pressure gradient

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

• alveolar epithelium

• capillary endothelium

Explain one feature of an alveolus that allows efficient gas exchange to occur

• One cell thick → short diffusion pathway

Describe the gross structure of the human gas exchange system and how we breathe in and out (6 marks)

• trachea, bronchi, bronchioles, alveoli

• inspiration, occurs when diaphragm and external intercostal muscles contract

• leading to increased volume and decreased pressure in the thoracic cavity

• air moves down a pressure concentration gradient, so moves into lungs

• expiration, diaphragm and external intercostal muscles relax

• leading to decreased volume, and increased volume in the thoracic cavity, so moves out of lungs

Explain three ways an insect’s tracheal system is adapted for efficient gas exchange

• highly branched → large surface area for diffusion and gas exchange to occur

• tracheoles have thin walls → short diffusion pathway

• trachea provides tubes full of air → so fast diffusion into insect tissues

• fluid in end of the tracheoles that move out during exercise → so larger surface area for diffusion

• body can be moved by muscles to move air → maintains diffusion gradient

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels

• lipids (monoglycerides and fatty acid) combine with bile salts to from micelles

• move the monoglycerides and fatty acids to the cell lining

• lipids diffuse via simple diffusion as lipid soluble

• triglycerides reformed

• vesicles move to cell membrane

Explain how the movement of NA+ out of the cell allows the absorption of glucose into the cell lining in the ileum

• cotransport

• NA+ and glucose bind to cotransport protein

• use NA+ concentration gradient, low concentration of NA+ in the cell

• ATP required from respiration

Describe the role of enzymes in digestion of proteins

• endopeptidases → hydrolyse the peptide bonds in the middle of the protein

• Exopeptidases → hydrolyse the peptide bonds at the ends of the proteins

• Dipeptidases → hydrolyse the peptide bonds between dipeptides, producing single amino acids

What is the function of coronary arteries

• delivers oxygenated blood to the heart muscles

Explain one advantage of the capillaries being narrow

• short pathway

• large surface area

• fast exchange/ diffusion

Describe how tissue fluid is formed

• small molecules forced out of the capillary, due to high hydrostatic pressure in the arteriole end

• leading to lower water potential in the venule end of the capillary bed

• so water moves via osmosis from the tissue fluid back into the capillary

• excess tissue fluid drained through the lymphatic system

Give the pathway of blood from the kidney to the lungs

• via the renal vein

• vena cava to the right atrium

• right ventricle to the pulmonary artery

Describe the advantage of the Bohr effect during exercise

• increases dissociation of oxygen

• for aerobic respiration of muscles

Describe the effect of increasing CO2 concentration on the dissociation of oxyhaemoglobin

• increased CO2 leads to increased dissociation

• decreasing blood pH

Binding of one molecule of oxygen to haemoglobin makes it easier for a second O2 to bind

• due to change in tertiary structure of haemoglobin

• uncovers second binding site

Describe the cohesion-tension theory of water transport in the xylem

• water lost from leaf via evaporation of water

• lowers water potential in mesophyll

• water pulled up xylem

• water molecules cohere together by hydrogen bonds

• forming water column

• adhesion of water to walls of xylem

Describe the mass flow hypothesis for the mechanism of translocation in plants

• sucrose actively transported into phloem

• by companion cell

• lowering the water potential of sieve cell

• water enters phloem via osmosis

• increasing pressure, moves from source to sink

• sugar stored or used at sink, so higher water potential increases, water moves back into the xylem via osmosis