Exchange and Transport Flashcards
Explain the counter current system and how it acts as an adaptation for gas exchange
(3 marks)
The counter current system means the water flowing over the gills flow in the opposite to the blood in the capillaries.
This functions as an adaptation for gas exchange because it maintains a diffusion gradient along the whole length of the capillary. This means that diffusion of oxygen into the blood take places along the whole length of the gill.
Describe and explain features that are xerophytic in nature
(3 marks)
Sunken stomata which trap water vapour reducing the water potential gradients between the inside of the lead and the outside.
Hairs surrounding the stomata which trap water vapour reducing the water potential gradients between the inside of the lead and the outside.
Thich waxy cuticle which reduces evaporation.
Small surface area which reduces the number of stomata.
Densely packed cells within the leaf which reduces evaporation of water from the surface of these cells.
Describe and explain how the paralysis of the diaphragm can lead to reduced lung function
(3 marks)
The diaphragm will not contract which means there is no increase in volume in the thoracic cavity. This means that less air move into the lungs because the pressure gradient is not as steep.
Explain how asthma may lead to serious health conditions
(3 marks)
There is reduced airflow into the lungs.
As a result less oxygen is absorbed and less carbon dioxide is removed.
This means there is a lack of oxygen available for aerobic respiration.
Explain how the lungs are adapted to allow the rapid exchange of oxygen
(5 marks)
The lungs have many alveoli which are folded which creates a large surface area.
The alveoli are surrounded by many capillaries so there is a good blood supply.
The blood coming into the lungs has a higher concentration of carbon dioxide so the concentration gradient is maintained between the alveoli.
The walls of the alveoli are only one cell thick so there is a short diffusion pathway.
Ventilation maintains a concentration gradient so the air breathed in always has a higher concentration of oxygen compared to the air inside the lungs.
These features all increase the rate of diffusion.
Describe and explain the mechanism by which air is taken into the lungs
(5 marks)
The diaphragm and external intercostals contract.
This increases the volume of the thoracic cavity.
This results in a decrease in the pressure inside the lungs compared to the atmospheric pressure.
This forces air into the lungs down the pressure gradient.
Air travels through the trachea into the bronchi, then into bronchioles and then reaches the alveoli.
Explain why the walls of the alveoli contain elastic fibres
(2 marks)
It allows stretch and recoil.
They stretch so the alveoli do not burst during inhalation so there is a rapid expulsion of air from the lungs.
Describe how a large lipid droplet is absorbed into the blood stream
(5 marks)
The large lipid droplet is mixed with bile salts, which emulsifies the lipid which increases the surface area.
Lipase digests the lipid into fatty acids, monoglycerides and glycerol.
The fatty acids then diffuse into the epithelial cell through the phospholipid bilayer.
They then recombine in the smooth endoplasmic reticulum to reform triglycerides.
They are packed into chylomicrons. The chylomicrons are then transported into lacteals which distribute into the bloodstream.
Explain why the dipeptidases are important in protein digestion
(2 marks)
They hydrolyse peptide bond to produce amino acids
Dipeptides cannot cross the cell surface membrane as they are too large.
Describe the structure of haemoglobin and explain how it transports oxygen around the body
(6 marks)
STRUCTURE
- a protein with a quaternary structure
- made up of 4 polypeptides
- contains 4 haem groups
- each haem group contains and iron ion
TRANSPORT OF OXYGEN
- oxygen binds to haemoglobin in areas of high pp02
- haemoglobin changes shape after the first oxygen molecule binds
- oxygen unloads from haemoglobin in areas of low pp02.
- unloading takes place in the tissues as they have a lower pp02 due to aerobic respiration
Describe two functions of valves in the mammalian circulatory system
(2 marks)
Valves prevent the backflow of blood and ensure blood flows in one direction.
They maintain blood pressure
Describe and explain how the structure of capillaries enable them to function efficiently as exchange surfaces
(4 marks)
- Permeable wall
- Thin walls meaning a short diffusion pathway
- Narrow diameter which gives a large SA to volume ratio
- Narrow lumen which reduces blood flow rate and allows more time for diffusion
- Red blood cells are in contact with the capillary wall which gives a short diffusion pathway
Describe how sugar is transported from the lower leaves of the plant to the growing leaf buds at the top of the plant
(5 marks)
- active transport of sucrose from leaf into the phloem by companion cells.
- this causes the water potential to decrease in the phloem and so water enters by osmosis
- Water entry results in high hydrostatic pressure
- mass flow upwards to leaf buds down the pressure gradient
- at the leaves sugars are actively unloaded which lowers the water potential of the surrounding cells
- water moves out of the sieve tube by osmosis and hydrostatic pressure in the phloem decreases
- water leaving the phloem at the sink end maintains the pressure gradient.
Do the measurements taken from a potometer represent the true rate of transpiration in a plant?
(3 marks)
A potometer is used to measure water uptake and not transpiration.
Water is used in hydrolyses reactions and photosynthesis.
Water is produced in condensation reactions and respiration
