3. Organisms Exchange Substances With Their Environment Flashcards
What’s the environment around the cells of multicellular organisms called
Tissue fluid
4 examples of things needed to be interchanged between an organism and its environment
-Respiratory gases (oxygen and carbon dioxide)
-Nutrients (glucose, fatty acids, amino acids, vitamins and minerals)
-Excretory products (urea and carbon dioxide)
-Heat
What are the 2 ways excretory products, nuterients and respitory products are exchanged
-passively (no metabolic energy required), by diffusion and osmosis
-actively (metabolic energy is required) by active transport
What’s required for gas exchange to be effective
The exchange surfaces of an organism must be large compared to its volume
(Large surface area to volume ratio)
What features have organisms evolved to enable more efficient diffusion?
- a flattened shape so that no cell is ever far from the surface (eg: a leaf)
- specialised exchange surfaces with large areas to increase the surface area to volume ratio (eg: lungs in mammals, gills of fish)
Surface area of a sphere =
4 π r^2
Volume of a sphere
4/3 π r^3
How to calculate the surface area to volume ratio
Surface area / volume
Make sure volume is 1
Eg:
SA: = 0.6:1
Features of specialised exchange surfaces
-Large surface area to volume ratio: increases the rate of change
-very thin = short diffusion distance pathway = materials cross exchange surface rapidly
-selectively permeable = allows selected materials to cross
-movement of the environmental medium (eg: air) to maintain a concentration gradient
-a transport system ensures movement of the internal medium (eg: blood) to maintain a diffusion gradient
Diffusion equation
Diffusion ∝ (surface area x difference in concentration )
—————————————————————
.length of diffusion pathway
Diffusion is directly proportional to surface area and concentration difference
Diffusion is inversely proportional to length of diffusion pathway
Why are specialised exchange surfaces located on the inside of an organism
They’re thin so are easily damaged and dehydrated
Describe gas exchange in a single-celled organism
-single called organisms are small -> large surface area to volume ratio
-oxygen is absorbed by diffusion across a cell surface membrane
-CO2 from aerobic respiration diffuses out
Cell walls are no additional barrier to the diffusion of gases
What types of organisms are insects
Terrestrial
Describe the specialised exchange surface that insects have evolved for efficient gas exchange
tracheae:internal network of tubes, supported by strengthened rings to prevent them from collapsing
They divide into tracheoles: small dead-end tubes that extend throughout body tissue
Allows o2 to be brought directly to respiring tissues due to small diffusion pathway.
What are the 3 ways respitory gases move in and out of the tracheal system
1) along a diffusion gradient
2) mass transport
3) ends of the tracheoles are filled with water
How do gases enter and leave the tracheae
Through tiny pores called spiracles
-Found on the body surface which open and close by a valve
When open: water vapour evaporates from insect
When closed: prevents water loss
For most of the time, insects keep their spiracles closed
What are the limitations of the tracheal system as a method of gas exchange
-relies mostly on diffusion to exchange gases between cells and environment
- for diffusion to be effective, the diffusion pathway needs to be short so insects are small sized. Length of diffusion pathway limits size of that insects attain.
Describe the general structure of a fish and how does that relate to their exchange system
Have a waterproof and gas tight outer covering
Small surface area to volume ratio
Therfore:
Their body surface isn’t adequate to supply and remove respiratory gases so…
they’ve evolved specialised internal gas exchange surfaces
Describe the structure of the gills
Located within the body, behind the head
Made up of gill filaments stacked up in a pile
Perpendicular to the filaments are gill lamellae, which increase surface area of gills
Describe the ventilation of gills
Water is taken through mouth and forced over gills through an opening on each side of the body
Flow of water over the gill lamellae and flow of blood in opposite directions - counter current flow principle
Ensures maximum gas exchange is achieved
Describe what the countercurrent exchange principle in fish means will happen
-oxygenated blood meets water with high oxygen concentration.
-deoxygenated blood meets water with low oxygen concentration.
So Diffusion of oxygen from water to blood takes place DOWN a concentration gradient
Diffusion gradient for oxygen is maintained across entire width of gill lamellae
Compare the parallel flow and countercurrent flow in the gills of a fish
Countercurrent:
A diffusion gradient is maintained all the way across the gill lamellae. Almost all the oxygen from the water diffuses into the blood
Parallel:
A diffusion gradient is maintained for only half of the distance across the gill lamellae. Only 50% of oxygen in water diffuses into the blood
How do respiratory gases move in & out of the tracheal system along a diffusion gradient ?
When cells respire, o2 is used up and so the conc. towards the ends of the tracheoles falls which creates a diffusion gradient. (Allows o2 to diffuse in)
CO2 is produced by respiring cells which creates a diffusion gradient in the opposite direction (allows co2 to diffuse out)
How do respiratory gases move in & out of the tracheal system via mass transport ?
The contraction of muscle s in insects can squeeze the trachea enabling mass movement of air in and out
How do respiratory gases move in & out of the tracheal system due to the end of the tracheoles being filled with water ?
During strenuous activity the muscle cells around the tracheoles respire anaerobically, producing lactate which is soluble and lowers the water potential of the muscle cells.
Water can therefore move from the tracheoles and into the cells by osmosis which decreases the volume of water in the tracheoles and allows air to be drawn further in
What are the 3 similarities of gas exchange between insects and plant leaf
-no livingcell is far from, the external air, so a source of oxygen and carbon dioxide
-diffusion takes place in air which makes it more rapid than if in water
-short fast diffusion pathway
Adaptions of leaf gas exchange for rapid diffusion
- many stomata and so no cell is far from a stoma so short diffusion pathway
- numerous interconnecting air-spaces that occur throughout the mesophyll so gases readily come in contact with mesophyll cells
- large surface area of mesophyll cells for rapid diffusion
Structure and function of stomata
-Minute pores mostly on the underside of leaves
-Each stoma is surrounded by a pair of guard cells which open and close the stoma pore to control rate of gas exchange and prevent water loss by evaporation
When guard.cell is turgid (swollen) - stomata is open
When guard cell is flaccid (shrunken) - stomata is closed
Do all plant cells photosynthesise
Plant cells respire all the time
But only plant cells with chloroplasts photosynthesise
And when conditions are right
How is the diffusion gradient in and out of leaves maintained
By mitochondria carrying out respiration and chloroplasts carrying out photosynthesis
In fish how is a steep diffusion gradient for oxygen maintained
Brining oxygen constantly to the exchange surface by ventilation and carrying it away from the surface by mass transport in the blood
What happens in the exchange of oxygen and carbon dioxide in plant cells when photosynthesis is NOT taking place, linked to respiration
When it’s dark, oxygen diffuses into the leaf because it’s constantly being used by cells during respiration. In the same way, carbon dioxide produced during respiration diffuses out
Compare blood circulation of fish and mammals
Fish:
Single circulation
2 chambers
One artery carrying blood away
Mammal:
Double circulation
4 chambers
Two arteries carrying blood away
What features of insects for efficient gas exchange conflicts with conserving water
Thin
Permeable surface
Large area
Why is it hard for terrestrial organisms like insects to conserve water
Water easily evaporated from their body surface so they can become dehydrated
What are the 3 adaptions insects have evolved to reduce water loss
-small surface area to volume ratio: minimises area over which water is lost
-waterproof covering over body surface: rigid exoskeleton of chitin covered with a waterproof cuticle
-spiracles: openings of tracheae at body surface which close to reduce water loss. But this conflicts with the need for oxygen and so occurs largely when insect is at rest
How do terrestrial plants limit water loss
-waterproof covering over parts of the leaves
-ability for guard cells to go flaccid and close stomata
-xerophtypes prevent water loss through transpiration
Leaf adaptions to prevent water loss in xerophytic conditions
-thick cuticle
-rolling up of leaves
-Hairy leaves
-stomata in pits or groves
-reduced surface area to volume ratio of leaves
Describe how a thick cuticle prevents water loss in plants
Forms a waterproof barrier
The thicker the cuticle, the less water can escape
Describe how rolling up of leaves prevents water loss in plants
Protects the lower epidermis that has most of the stomata on it from the outside by trapping air within the rolled leaf
becoming saturated with water vapour so has a high water potential.
There’s no water potential gradient between the inside and outside of the leaf so no water loss.
Describe how hairy leaves prevents water loss in plants
thick layer of hair especially on lower epidermis, traps still, moist air next to leaf surface.
Water potential gradient between the inside and the outside of the leaves is reduced so less water is lost by evaporation.
Describe how stomata in pits or grooves prevents water loss in plants
Trap still, moist air next to the leaf and reduce the water potential gradient
Eg: pine trees
Describe how a reduced surface area to volume ratio of leaves prevents water loss of plants
The smaller the surface area to volume ratio, the slower the rate of diffusion
Leaves that are small and roughly circular in cross-section have a reduced rate of water loss.
balanced against need for sufficient area for photosynthesis
How do all aerobic organism release energy
They require a constant supply of oxygen to release energy in form of ATP during respiration
Why does the volume of oxygen absorbed and volume of carbon dioxide released have to be large in mammals
-they’re large organisms with a large volume of living cells
-they maintain a high body temp which is related to them having a high metabolic & respiratory rates
So they’ve evolved specialised surfaces called lungs to ensure efficient gas exchange between sir and their blood
What’s the site of gas exchange in mammals
Lungs (epithelium of the alveoli)
Why are lungs located inside the body
-air isn’t dense enough to support and protect the delicate structures
-the body would lose a lot of water and dry out of not
What bony box protects the lungs
Rib cage
What are the main parts of the human gas-exchange system
-lungs
-trachea
-bronchi
-bronchioles
-alveoli
Describe the structure of the lungs in the human gas-exchange system
Pair of lobed structures made of a series of highly branched tubules called bronchioles which end in tiny air sacs called alveoli
Describe the structure of the trachea in the human gas-exchange system
Flexible airway that’s supported by rings of cartilage preventing trachea collapsing as the air pressure inside falls when breathing in. Walls are made up of muscle, lined with ciliated epithelium and goblet cells
Describe the structure and function of the bronchi in the human gas-exchange system
2 divisions of trachea, each leading to one lung.
Like the trachea, they produce mucus to trap dirt particles and have cilia that move dirty mucus towards the throat.
The larger bronchi are supported by cartilage.
Describe the structure and function of the bronchioles in the human gas-exchange system
Series of branching subdivisions of the bronchi.
Walls are made of muscle lined with epithelial cells allowing them to constrict so they can control flow of air in and out of alveoli
Describe the structure and function of the alveoli in the human gas-exchange system
Minute air-sacs at the end of bronchioles.
Lined with epithelium
Elastic fibres allow alveoli to stretch as they fill with air in inspiration
Spring back during expiration to remove carbon dioxide air.
Alveolar membrane is the gas-exchange surface
Each alveolus has a network of pulmonary capillaries around it, so narrow that red blood cells flatten against the thin capillary walls to squeeze through
Define process of ventilation / breathing
Air is constantly moved in and out of the lungs to maintain diffusion of gases across the alveolar epithelium
State the 2 processes in ventilation / breathing
inspiration - inhalation / breathing in
expiration - exhalation / breathing out
What 3 muscles control pressure changes in the lungs
Diaphragm- a sheet of muscle that separates the thorax from the abdomen
Intercostal muscles - lie between the ribs
- 2 sets:
-internal intercostal muscles: contraction leads to expiration
-external intercostal muscles: contraction leads to inspiration
Which of inspiration or expiration is an active process
Inspiration - requires energy
Describe process of inspiration
1) external intercostal muscles contract as internal intercostal muscles relax
2) ribs are pulled upwards and outwards, increasing volume of thorax
3) diaphragm muscles contract, so flattens, increasing volume of thorax
4) results in reduction of pressure in the lungs
5) atmospheric pressure is greater than pulmonary pressure in lungs so air is forced into lungs
Describe process of expiration
1) internal intercostal muscles contract as external intercostal muscles relax
2) ribs are pulled downwards and inwards, decreasing volume of thorax
3) diaphragm muscles relax, so is pushed up by contents of abdomen that were compressed during inspiration, decreasing volume of thorax
4) results in increase of pressure in the lungs
5) atmospheric pressure is lower than pulmonary pressure in lungs so air is forced out
What’s the main cause of air being forced out during normal quiet breathing
Recoil of the elastic tissue in the lungs
Only under strenuous activity like exercise do muscles play a major part
What’s the pulmonary ventilation rate and how is it calculated
Total volume of air moved into the lungs during one minute
Pulmonary ventilation rate (dm^3 min^-1) -
= tidal volume (dm^3) x breathing rate (min^-1)
Tidal: volume of air taken in at each breath when body is at rest. Usually 0.5dm^3
Breathing (ventilation) rate: number of breaths taken in 1 min. Usually 12-20
How is a constant supply of oxygen to the body ensured
A diffusion gradient is maintained at the alveolar surface
Why is the diffusion of gases between the alveoli and the blood very rapid
- red blood cells slowed as they pass through pulmonary capillaries = more time for diffusion
•the distance between the alveolar air & red blood cells is reduced as red blood cells are flattened against capillary walls
• the walls of both alveoli & capillaries are very thin = very short diffusion distance
• alveoli & pulmonary capillaries have large total surface area
• breathing movements constantly ventilates lungs, action of the heart constantly circulates blood around the alveoli.
Together, ensure steep concentration gradient is maintained
• blood flow through pulmonary capillaries maintains a concentration gradient.
What are the risk factors the increase the probability of getting lung disease
1) Smoking
2) air pollution
3) genetic make-up
4) infections
5) occupation eg: working with harmful chemicals, gases and dusts
Describe the human digestive system.
What’s it made up of?
How is it an exchange system through which food substances can be absorbed ?
Made up it a long muscular tube and it’s associated glands
These glands produce enzymes that hydrolyse large molecules into small ones ready for absorption
Describe the role of the œsophagus
Carries food from the mouth to the stomach
Describe the role of the stomach
The stomach is a muscular sac with an inner layer that produces enzymes.
Its role is to store and digest food, especially proteins
It has glands that produce enzymeswhich digest protein
