AS Biology Unit 2 Model Answers Flashcards
Gas exchange in plants
During respiration oxygen diffuses into the plant when the stomata are open
Carbon dioxide diffuses out of the plant
During photosynthesis carbon dioxide diffuses into the plant and oxygen diffuses out
In the mesophyll layer the plant has numerous interconnecting air spaces to aid gaseous diffusion
Gases do not have to be dissolved in water for diffusion through the stomata
Stomata can close to conserve water
When this happens no gas exchange can occur through the stomata
What are the features of specialised exchange surfaces?
Large surface area to volume ratio
Thin so shorter diffusion pathway
Partially permeable
Movement of environmental medium to maintain a concentration gradient
Movement of internal medium to maintain a concentration gradient
How have large organisms evolved to be efficient at diffusion?
A flattened shape
So that no cell is ever far from the surface
Specialised exchange surfaces with large areas
To increase the surface area to volume ratio
E.g. Lung or gills
Gas exchange in insects
Air enters through the spiracles
And passes along the tracheae
There is a diffusion gradient in the tracheolus
Causing oxygen to diffuse into cells
Ventilation ( movement of muscles ) replaces air in the tracheae maintaining a concentration gradient
Spiracles are able to close
How do respiratory gases move in and out of the tracheal system?
Down a concentration gradient (air moving in has high oxygen content, at the tissues the oxygen content is low as cells are using up oxygen in respiration)
Ventilation by the movement of muscles in the abdomen creates mass air movement
Why fish gils are efficient at diffusion of oxygen
Numerous gill filaments with numerous lamallae
To increase surface area
Thin / squamous epithelium cells of gill and capillaries
So short diffusion pathway
Gills are well supplied with numerous small capillaries
This also increases the surface area
Steep concentration gradient maintained by countercurrent flow
Oxygen diffuses into blood along the whole length of the gill
Constant circulation of blood always takes blood high in oxygen away
Constant ventilation always increases oxygen content at gas exchange surfaces
What else happens when spiracles close?
Conserve water
What causes the spiracles to open?
The build up of carbon dioxide
Due to insects not having a blood system what happens to the oxygen?
The oxygen diffuses straight into the tissues from the tracheolus
What is the relationship between an organisms size and its surface are to volume ratio?
The bigger the organism, the smaller the ratio therefore the slower the rate of diffusion across the exchange surface
How insects are adapted to conserve water?
Small surface area to volume ratio
Waterproof coverings on body surfaces
Ability to close spiracles
How insects are adapted to increase gas exchange
Numerous spiracles to increase surface area
Short diffusion pathway as air in tracheoles connects direct to tissues (no blood)
Many numerous tracheoles to increase surface area
Concentration gradient maintained by ventilation and the removal of oxygen by respiring tissues
Gas exchange in fish
Water enters through the mouth
And is forced across the gill filaments
The water flows on an opposite direction to the blood in the gill lamallae- this is countercurrent flow
This produces a concentration gradient
To promote the diffusion if oxygen from the water into the blood along the whole length of the gill
Water passes out through the operculum
How plants are adapted to increase gas exchange
Numerous stomata increase surface area
Diffusion takes place in gas phase
No living cell is far from external air ( long, thin, flat shape of leaves)
Air spaces in spongy mesophyll
Sort diffusion pathway
Concentration gradient maintained by photosynthesis and respiration
Structure of haemoglobin
Primary structure consists of 4 polypeptide chains built up of amino acids
Secondary structure consists of these chains coiled into the alpha helix connected with hydrogen bonds
Tertiary structure provides the 4 chains with specific globular shapes with further bonding
Quaternary structure - 4 chains are linked together to form a spherical molecule
Each polypeptide is associated with a haem group containing iron (II) ions
Oxygen dissociation curves
Further to the left, greater affinity for oxygen ( takes it up readily but releases it less readily)
Further to the right; lower affinity for oxygen (takes up less readily but releases it more easily)
Low oxygen environments include…
High altitude Underwater Burrows In the uterus This also applies to myoglobin which has a high affinity for oxygen that haemoglobin does
Effects of carbon dioxide concentration
Greater concentration of carbon dioxide, the more readily haemoglobin releases its oxygen (Bohr effect)
Oxygen dissociation curve shifts to the right
Explain why haemoglobin unloads oxygen
Carbon dioxide level increase
pH becomes lower so is more acidic
Haemoglobin changes shape ( ionic bonds are changed
More oxygen is dissociated
Loading, transport and unloading of oxygen
Carbon dioxide is constantly removed at the gas exchange surfaces
pH is higher due to low level of carbon dioxide
Haemoglobin loads oxygen more readily
Haemoglobin has a high affinity in this state so does not release oxygen during transport
Carbon dioxide is acidic in solution so pH is lower
Shape of haemoglobin changes into one with a lower affinity for oxygen
Haemoglobin releases its oxygen into respiring tissue
Roles of haemoglobin
Readily associated with oxygen at surface where gas exchange takes place as it has a high affinity here
Readily dissociate from oxygen at respiring tissues as it has a lower affinity here
Explain the advantage of the curve being to the left in an organism in a low oxygen environment
High percentage saturation of haemoglobin with oxygen
At low ppO2⃣
Explain the advantage of the curve being to the right in an organism with a high level of activity/ high metabolic rate/ high exercise
Haemoglobin has a lower affinity for oxygen
So releases oxygen more readily to respiring tissue
Why do cells have to have oxygen to respire
To produce ATP to provide energy for processes such as active transport, muscle contraction etc
The most active cells will respire the most and therefore need the most oxygen
Explain how root pressure and cohesion-tension are responsible for the movement of water in xylem vessels
Salts are actively transported into the xylem
This causes the xylem to have a more negative water potential
Water enters the xylem by osmosis
Evaporation of water from the stomata causes transpiration pull
This lowers the water potential of the mesophyll
Water molecules cohere due to hydrogen bonding
And adhere to xylem walls
This pulls water up the xylem
Arteriole structure and function
Structure - thick muscle layer which contracts and relaxes
Function - reduces / controls blood pressure and flow into the capillaries
Artery structure and function
Structure - thick elastic layer, which stretches and recoils
Function- maintains a high blood pressure which is created by heart contraction
Structure - narrow lumen
Function - maintain high blood pressure
Structure - thick walls
Functions - prevents damage caused by high pressure
Capillaries structure and function
Rate of diffusion ( oxygen, carbon dioxide and glucose ) is increased
Structure - Numerous and branched, surface area is large
Structure - Thin endothelium, diffusion pathway is short
Structure - Narrow lumen so rbc is same size as lumen so passage of blood is slow, allows more time for diffusion to occur
Function - efficient gaseous diffusion
Constant circulation of blood maintains a steep concentration gradient
Vein structure and functions
Structure - Muscle layer is thin as their constriction and dilation does not control blood flow
Structure - Elastic layer is thin as pressure is low
Structure - Wall thickness is small as pressure is low, must be collapsible so can be squeezed by body muscles
Structure - Valves present to prevent back flow
The body makes more tissue fluid over a day that it can reabsorb. What happens to the excess
The excess is drained by the lymph vessels
Accumulation of fluid may lead to tissue swelling (oedema)
Formation, reabsorption and drainage of tissue fluid
High hydrostatic pressure at the arteriole end of the capillary
Forces water out through the thin capillary walls into tissue
Plasma proteins are too large too pass through the capillary wall
So they become more concentrated in the blood
This makes the water potential inside the capillary more negative
Compared to the less negative tissues
Water moves back into the capillary by osmosis
Along a water potential gradient
The hydrostatic force outside the capillary also helps to push water back in
Why a person experiencing high blood pressure may get swelling?
Hydrostatic pressure of the blood is high so more water is forced out of arteriole end of capillary
Some tissue fluid accumulates as not all of it can be reabsorbed
Why a starving person may get swelling
Fewer plasma proteins in the blood
So concentration gradient is not as steep and inside of capillary is less negative
Therefore less water can be reabsorb into the capillary by osmosis
Features of binomial system
Universal system
Generic names indicates the genus the organism belongs to
Specific names denotes the particular species
Gravity pulls tissue fluid down so it tends to accumulate in ankles and feet then…
Feet have very few lymph vessels
Contraction of body muscles surrounding the lymph vessels squeeze the lymph back to the chest where it can be drained and eventually excreted
Use cohesion-tension theory to explain why the presence of an air bubble in a xylem vessel blacks the movement of water
The presence of the air bubble breaks the continuous column of water And prevents cohesion of water molecules Water in the xylem is under tension Due to transpiration from leaves The air bubble inhibits this tension
Explain how active transport of mineral ions into xylem vessels results in water entering and being moved up the tissue
The water potential in the xylem is made more negative
By the active transport of ions into the xylem
This establishes a water potential gradient
So water moves from an area with less negative water potential to an area with a mo negative water potential
By osmosis
This increases pressure in the xylem
Explain how after enters a plant root from the soil and travels through to the endodermis
Water enter root hair cells
By osmosis
As the active uptake of ions into the roots create a water potential gradient
I.e. the root has a moe negative water potential
Water moves through the root cortex
Via the cell walls - the apoplastic pathway or via the cell cytoplasm - the symplastic pathway
Using Fick’s law to explain how the structural adaptation of xerophytes reduce the rate of water diffusion
Ficks law states that the rate of diffusion is proportional to the surface area times the concentration gradient divided by the length of the diffusion pathway
Xerophytes have a reduced number of stomata
This decreases the surface area
These plants also have a waxy cuticle
This increases the length of the diffusion pathway
These features mean that the water potential gradient is reduced
So less water is lost it the atmosphere
Factors affecting transpiration
Light - stomata open in the light for photosynthesis therefore an increase in light intensity increases transpiration rate
Temperature - increase in temperature increases kinetic energy and decreases the water potential of the air therefore increases transpiration rate
Humidity - increase of water molecules in air decreases the water potential gradient therefore an increase in humidity decreases transpiration rate
Air movement - an increase in air movement increases the rate of diffusion if water molecules out of the stomata and therefore increases transpiration rate
What can a potometer for?
To calculate rate of transpiration by measuring the uptake of water on a mm or cm scale over a set amount of time
Why cut the shoot and connect to the potometer under the water
To prevent air entering, to maintain a continuous water column
What measurements would have taken in order to calculate rate of water uptake in cm^3 min^-1
Time
Distance moved in cm
Radius/ diameter of capillary tube
Explain how evaporation of water from the leaves causes the water to move upwards
The water potential in the mesophyll becomes more negative
Water moves out of the xylem by osmosis
And is evaporated from the open stomata
This creates a transpiration pull
Caused by cohesion of the water molecules to each other
And adhesion to the xylem wall
