Section 3: Organisms exchange substances with their enviroment Flashcards
What is metabolism
sum of all chemical reactions in the body
what is the relation between surface area to volume ratio and the size of an animal
As the size of an animal increases the surface area to volume ratio decreases
What are the three main uses of metabolism
muscle contraction and movement
building larger molecules from small ones
maintain body temperature
Name the key parts of a tracheal system in an insect
spiricales
Trachea
Chitin
Tracheoles
How is the insect gas exchange system adapted
- large number of tracheoles
- thin tracheole walls and short diffusion pathway ( spiricales —> tracheoles)
- steep concentration gradient as uses O2 and produces CO2
Do insects have a transport system
No
As oxygen needs to be transported directly to tissues which are undergoing respiration
Name the process by which carbon dioxide is removed from a single-cell organism
diffusion over the body surface
Explain why there is a conflict in terrestrial insects between gas exchange and conserving water
Gas exchange requires a thin permeable surface with a large surface area. Conserving water requires thick waterproof surfaces with a small area
Explain how the tracheal system limits the size of insects
because it relies on diffusion to bring oxygen to the respiring tissues. If insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs
How do insects prevent water loss
• Waterproof covering – The rigid outer skeleton (exoskeleton) made of chitin is covered by a waxy cuticle to reduce evaporation.
• Spiracles – Open and close to regulate water loss, especially when the insect is at rest.
• Internal gas exchange system – The tracheal system reduces the need for water loss through the surface by allowing direct gas exchange within the body.
What are the insects three methods of moving gas
- simple diffusion through spiricales - usage and production of O2 and CO2 provide conc gradient from tracheoles to outside
- mass transport - mass flow of air into tracheal system by closing spiracles and contracting and relaxing abdominal muscles pressure changes
- Anaerobic respiration and production of lactate
Describe anaerobic respiration in insects
anaerobic repiration produces lactate
lactate lowers water potential in cells
water moves from tracheoles to cells (osmosis)
tracheal fluid reducing draws more air to tracheoles
What is the exoskeleton of an insect made up of?
Polysaccharide chitin
What is on the surface of the exoskeleton and what do they lead to? ( relating to gas exchange system )
Spiricales lead to trachea which have tracheoles
What is the role of chitin rings? Where are they found?
In the insect gas exchange system, chitin rings in the tracheae prevent structural collapse. They are impermeable to gases, ensuring diffusion occurs only through the tracheoles.
Describe the structure of the fish gills
gills located behind head of fish
gill arch
made up of gill filaments
at right angles are gill lamellar which inc surface area
What are the adaptations of gill lamellae
Maintain concentration gradient: Generous supply of capillaries
Short diffusion pathway: Single layer of flattened cells/ thin membrane
High surface area
In relation to fish gills, describe what is meant by countercurrent flow
The movement of water and blood in opposite directions across gill lamellae
Outline why countercurrent flow is an effiecint means of exchanging gasses across the gills of fish
Because a steady diffusion gradient is maintained over the whole length of the gill lamellae. Therefore more oxygen diffuse from the water into the blood
Mackeral are active, fast-swimming dish whole plaice spend most of their lives moving slowly on the sea bed. suggest the differences in their gills
Mackerel have more gill lamellae / gill filaments / larger surface area compared to plaice
Water flow over fish gills is one way when’s the flow of air in and out of lungs is two-way suggest why one-way flow is an advantage to fish
Less energy is required because the flow does not have to be reversed ( important as water is dense and difficult to move)
Is an equilibrium ever reached between water oxygen concentration and gill oxygen concentration
No
countercurrent exchange system
What is the role of the operculum
hard boney flap-protection
What is the equation for photosynthesis?
6CO2 + 6H2O ——-> 6O2 + C6H12O6
chlorophyll and sunlight
Where does the oxygen go after photosynthesis?
Most diffuses out of the plant
Some is used for respiration
What are similarities between between plant and insect gas exchange
- No living cell is far from external air
- Diffusion takes place in the gas phase, which makes it more rapid than if it were in water
How are plants adapted for gaseous exchange
- many small pores called stomata, no cell is far from a stomata and therefore the diffusion pathway is short
- air spaces that occur throughout the mesothelioma so that gases can readily come in contact with mesophyll cells
- Large surface area of mesophyll cells for rapid diffusion
Explain the advantage of plants to be able to open and close stomata
Control water loss my evaporation and transpiration
What is the name of a plant adapted to dry conditions
Xerophytic
What is the name of a plant adapted to wet conditions
Hydrophytes
What are the adaptations of Xyerophiteg plants
Thick waxy cuticle
Sunken stomata to reduce air movement over stomata and create a humid microclimate
Hairy leaves
Curled leaves
Thick epidermis
What are the adaptations of Hydrophytes
Floating leaves
Thin waterproof waxy cuticle
Stomata located on the upper surface of the leaves
Reduced root system
Reduced veins in the leaves
How is the Waxy cuticle + Upper epidermis adapted for efficient gas exchange and water regulation?
Few or no chloroplasts, cells are transparent and waxy cuticle helps to reduce water loss
How is the palisade mesophyll tissue adapted for efficient gas exchange and water regulation?
Elongated for large surface area
Chloroplasts are close to surface to reduce diffusion distance
loads of chloroplasts
How is the air spaces and sponges mesophyll adapted for efficient gas exchange and water regulation?
air spaces increase surface area and maintain high concentration gradient for diffusion
State a modification shared by insects and plants to reduce water loss
Waterproof covering to the body
ability to close the openings of the gas-exchange system (stomata and spiracles)
Insects limit water loss by having a small SA:V ratio why isn’t this feasible for plants?
They photosynthesise
How does rolling up leaves help reduce water loss?
Water evaporating from the lead is trapped. The region rolled up becomes saturated with water vapour. There is no water potential gradient between the inside and outside of the lead and so water loss is considerably reduced.
Why would rolling up leaves not be an effective way to reduce water loss if the upper epidermis was on the inside?
Almost all stomata are on the lower epidermis. This would be exposed to air currents that would reduce the water potential immediately outside the lead. The water potential gradient would be increased and a lot of water vapour would be lost
Why are the lungs located on the inside of the body
air is not dense enough to support and protect the delicate structure
the body as a whole would otherwise lose a great deal of water and dry out
State two reasons why humans need to absorb large volumes of oxygen from the lungs
humans are large
have a high metabolic rate
high body temperature
List in correct sequence all the structures the air passes through on its journey from the gas-exchange surface of the lungs to the nose
Alveoli
bronchioles
bronchus
trachea
nose
Explain how the cells lining the trachea and bronchus protect the alveoli from damage
The cells produce mucus that traps particles of dirt and bacteria in the air breathed in. The cilia on these cells move this debris up the trachea and into the stomach. The dirt / bacteria could damage / cause infection in the alveoli
What happens during inspiration
External intercostal muscles contract, (while internal intercostal muscles relax)
The ribs are pulled upwards and outwards, increasing the volume of the thorax
The diagphram muscles contract, causing it to flatter, which also increases the volume of the thorax
The increased volume of the thorax decreases the pressure in the lungs
Air pressure from the atmosphere is now greater than pulmonary pressure, air is forced into the lungs
What happens in order to increase the volume of the thorax during inspiration
The ribs are pulled up and outwards
The diaphragm muscles contract causing it to flatten
What is happening when the external intercostal muscles contract
inspiration
What happens during expiration
Internal intercostal muscles contract, while external intercostal muscles relax
The ribs are pulled downward and inwards, decreasing the volume of the thorax
The diagphram muscles relax, which also decreases the volume of the thorax
The decreased volume of the thorax increases the pressure in the lungs
The pulmonary pressure s now greater than the atmosphere, air is forced out of the lungs
What is happening when the internal intercostal muscles contract
expiration
What is between alveoli
collagen and elastic fibres
How do you calculate the pulmonary ventilation rate
tidal volume x breathing rate
What is tidal volume and breathing rate
tidal volume = volume of air normally taken in at each breath when the body is at rest
breathing rate = number of breaths taken in 1 minute
What are the key features of alveoli for efficient gas exchange?
Lots of them to increase surface area: ration
Lined with thin epithelial cells, narrow capillary’s, only single layer of cells to decrease diffusion pathway
narrow capillaries to slow red blood cells as they pass through
constant ventilation and circulation maintains gradient
Why are the capillary’s narrow surrounding the alveolus?
Short diffusion pathway
Slows red blood cells as they pass through
What is the alveolus connective tissue made up of? and what is their role
Elastic fibres : allow stretch during ventilation, recoil on expiration to help expel carbon dioxide rich air
collegen : key protein, provides support, structure and scaffolding ( 15% of all lung tissue)
Why do alveolar cells release surfactant
surfactant is lipid and protein ans breaks up water molecules and reduces surface tension
alveoli walls are moist with water
What would happen if alveolar cells didnt have surfactant and only had water?
If just water lined the alveoli instead of surfactant, the surface tension would be very high. This would cause the alveoli to collapse and stick together, making it almost impossible to re-inflate them during breathing. Gas exchange would fail, leading to severe respiratory problems.
Name four lung diseases
Pulmonary tuberculosis ( TB )
Fibrosis
Asthma
Emphysema
What lung disease is caused by bacteria and what is the effect on lung function?
TB ( Pulmonary tuberculosis )
reduced surface area for gas exchange
How does fibrosis affect lung function?
thickens lung tissue making lungs less elastic and reducing tidal volume
What lung disease causes inflammation and constriction of the airways thus reducing air flow
Asthma
How does emphysema affect lung function.
Damage to alveoli, reducing surface area for gas exchange and elasticity
What are some common symptoms to various lung diseases?
Shortness of breath, fatigue, coughing, chest tightness or pain, wheezing
What are the major parts of the digestive system
Oesophagus
Stomach
Ileum
Large intestine
Rectum
Salivary glands
Pancreas
What are the two stages of digestion
Physical breakdown
Chemical breakdown
What is chemical digestion?
Chemical digestion hydrolyses large, insoluble molecules into smaller ones. Carried out by enzymes.
Describe the chemical digestion of carbohydrates
- Saliva containing salivary amylase starts hydrolysing starch to maltose
- This food is swallowed and the enzymes are denatured by the acidic conditions of the stomach
- The food mixes with pancreatic secretions in the small intestine
- Pancreatic amylase hydrolyse remaining starch to maltose
- Epithelial cells lining the ileum produce maltase that hydrolyse maltose into a-glucose
How is maltose digested and where
By maltase a membrane-bound disaccharide as it lines the epithelial cells in the ileum where it hydrolyses maltose into a glucose
How are lipids digested?
Bile salts break up lipids into tiny droplets called micelles. This process is called emulsification
Then hydrolysed by enzymes called lipases that break the ester bond
Describe protein digestion
Endopeptidase hydrolyse peptide bonds in central region
Exopeptidase hydrolyse peptide bonds at the terminal end of a polypeptide chain
Dipeptidase hydrolyse the bond between two amino acids
What is the final product of starch digestion
a glucose
List two structures that produce amylase
salivary glands and pancreas
Suggest why the stomach does not have villi or micro villi
Villi and micro villi increase surface area to speed up absorption of soluble molecules. As the food in the stomach has not been hydrolysed yet soluble molecules cannot be absorbed so villi are unnecessary
List three enzymes produced by the epithelium the ileum
Maltase
Sucrase
Lactase
List three organelles that you would expect to be numerous in an epithelial cell of the ileum and why
ER to re-synthesise triglycerides from monoglycerides and fatty acids
Golgi apparatus to form chylomicrons from triglycerides, cholesterol and lipoproteins
Mitochondria to provide ATP required for the co-transport of glucose and amino acid molecules
Name the chemicals that moves across epithelial cells with glucose during co-transport
Sodium ions
What increases absorption in the ileum
villi
high number of protein chanel’s and carrier proteins
How do will i increase absorption efficiency
Increase surface area for diffusion
Very thin walls
Contain muscle to move which maintains gradients
Well supplied with blood vessels
also possess microvilli
How are triglycerides absorbed
Triglycerides are hydrolysed by lipase which break the ester bond into monoglycerides and fatty acids
these are non-polar so diffuse easily into the epithelial cells
once in the epithelial cells they are transported to the ER where they are recombined into triglycerides
Then they go to the golgi where they associate with cholesterol and lipoproteins to from structures called chylomicrons
Chylomicrons move out of the epithelial cells by exocytosis to enter the lymphatic capillaries called lacteals
chylomicrons pass into blood system where they are hydrolysed by an enzyme insider to diffuse into cells
What are chylomicrons and where are they formed
Triglycerides associated with lipoproteins or cholesterol in the golgi apparatus of epithelial cells lining the ileum
Describe the structure of a haemoglobin
Four polypeptide chains linked together
Each polypeptide chain is associated with a haem group - which contains a Fe ion
Making a total of four O2 molecules that can be carried by a single haemoglobin molecule in humans
Explain how DNA leads to different haemoglobin molecules having different affinity’s for oxygen
Different base sequences in DNA - different amino acid sequences - different tertiary and quaternary structure - different affinities for oxygen
Why do the 2nd 3rd oxygen molecules bind more easily than the first and fourth
The shape of the haemoglobin makes it more difficult for the first oxygen to bind, after it has it changes the quaternary structure of the haemoglobin so the others can bind easier
In theory this should be true for the fourth oxygen molecule however the probability of it binding dramatically decreases when there’s only one possible binding sight
If the oxygen dissociation curve is to the left, the…
greater is the affinity of haemoglobin for oxygen
so it loads oxygen readily but unloads it less easily
If the affinity of haemoglobin for oxygen is very high what does this mean
Oxygen will load more readily and unload less easily
Curve to the left
If the curve the oxygen disassociation curve is to the right…
The lower is the the affinity of haemoglobin for oxygen
so it loads oxygen less readily but unloads very easily
The more active a tissue, the more O2 unloaded. Explain this
The higher the rate of respiration —> the more CO2 the tissues produce —> the lower the ph —> the greater the haemoglobin shape change —> the more readily O2 is unloaded —> the more O2 available for oxygen
In the presence of CO2 is haemoglobin affinity for oxygen high or low?
Low
When haemoglobin and oxygen bind what is it called
Oxyhaemoglobin
What is oxygen unloading and loading
When haemoglobin assosiates with oxygen the when Oxyhaemoglobin disassociates
If the ph is low then haemoglobin affinity for oxygen…
Decreases
because low ph indicates high CO2 levels which results in haemoglobin releasing O2 more readily in order to deliver O2 to respiring cells and tissues
Mammals have a ______, _____ circulatory system
closed, double
State the main advantage of the double circulation found in mammals
It increases blood pressure and therefore the rate of blood flow to the tissues
State two factors that make it more likely that an organism will have a circulatory pump such as the heart
Low surface area : volume ration
High metabolic rate
What valves separate the ventricle and atriums
left and right atrioventricular
Name the blood vessel that supplies the heart muscle with oxygenated blood
coronary artery
What major blood vessels carry oxygenated blood?
Aorta
Pulmonary vein
What major blood vessels carry deoxygenated blood?
Vena Cava
Pulmonary artery
What part of the heart does the aorta feed into
The left ventricle
What is the structural differences between the two types of chambers of the heart
Atrium are thin-walled and elastic that stretches
Ventricles are much thicker muscular wall as it had to contract strongly to pump blood around whole body or lungs
What blood vessel takes oxygenated blood from the lungs to the heart
Pulmonary vein
What does the vena cava do
Connected to the right atrium and brings deoxygenated blood from the organs and tissues to the heart and lungs
List the correct sequence of four main blood vessels and four heart chambers that a red blood cell passes through on its journey from the lungs
Pulmonary vein
Left atrium
Left ventricle
Aorta
Vena Cava
Right atrium
Right ventricule
Pulmonary artery
Suggest why it is important to prevent mixing of the blood in the two sides of the heart
Then there would be only partially oxygenated blood delivered to tissues, gradient wouldn’t be strong enough, inadequate oxygen supplied
What is myocardial infarction
a heart attack by blood clot in coronary artery
What is the relaxation of the heart
Diastole
Describe the cardiac cycle
- Diastole : atria filling with blood, atria and ventricle relaxed
- Atrial systole : blood from atria into ventricles, atria muscle contracts and ventricle relaxed
- Ventricular systole : Blood from ventricles to arteries, ventricle muscle contracted, atria relaxed
What happens during ventricular systole
Ventricles contract
atrioventricular valves are shut due to high ventricular pressure over atria pressure
semi lunar valves open once ventricular pressure exceeds aorta and pulmonary artery pressure
blood is forced into these vessels
What is Cardiac output and how do you calculate it
CO : volume of blood pumped by the heart in 1 minute
CO = Stroke volume x heart rate
What are the benefits of increased cardiac output?
Supply oxygen thus glucose to muscles faster
Remove CO2 and lactate from muscles faster
Remove heat away from muscles
What do the atrioventricular valves do
prevent back flow of blood when contraction of ventricles means that ventricular pressure exceeds arterial pressure.
Name the chamber in the heart that produces the greatest pressure
Left ventricle
After a period of training the heart rate is often decreased when at rest yet the cardiac output is unchanged. suggest an explanation for this
The heart muscles have gotten stronger so stroke volume has increased
Name the four types of blood vessels
Arteries : carry blood away from the heart
Arterioles : smaller arteries that control blood flow from arteries to capillaries
Capillaries : tiny vessels that link arterioles to veins
Veins : carry blood from capillaries back to the heart
How is the structure of an artery related to it’s function?
Muscle layer is thick compared to veins : can control volume of blood by constriction and dilation
Elastic layer is relatively thick compared to veins : stretching and recoiling to control blood pressure
Overall thickness of wall : vessel wont burst under high pressure
No valves : blood under high pressure not needed
What blood vessel carry blood under high pressure
Arteries
How is arterioles structure related to its function
Muscle layer is thicker than arteries : constriction of the lumen to control blood pressure as it goes into capillaries
Elastic layer thinner than arteries : blood pressure is lower
How is the structure of veins related to their function
Thin muscle layer, elastic layer and overall wall : low blood pressure
Valves : ensure the blood doesn’t flow backwards
How is capillaries structure related to their function
Thin : short diffusion distance
Narrow diameter : permeate tissues
Humours and highly branched : high SA
Lumen is narrow : shorter diffusion distance brings them close to wall
There are spaces between the lining cells : allows WBC to escape to deal with infection
Why do capillaries have spaces between the lining cells
So WBC can escape to deal with infections
Describe how tissue fluid is formed
- high blood / hydrostatic pressure at arterioles end
- Forces water out
- Large proteins remain in capillary
Describe how tissue fluid is returned to the circulatory system
- low water potential in capillary
- due to plasma proteins
- water enters capillary / blood by osmosis
Describe how tissue fluid is formed and how it is returned to the circulatory system. (6 marks)
Formation
1. high blood / hydrostatic pressure at arterioles end
2. Forces water out
3. Large proteins remain in capillary
Return
1. low water potential in capillary
2. due to plasma proteins
3. water enters capillary / blood by osmosis
What factors effect transpiration
Temperature : more sun = more Ek = more evaporation
Wind : water removed from leaf surface creating water potential gradient
Humidity : more moisture in air = less water potential gradient
Light : more light = more photosynthesis = stomata open = more evaporation
What is Transpiration Pull in Xylem?
Transpiration pull is the process by which water is drawn up the xylem vessels due to the loss of water through the stomata on the leaves. As water evaporates from the leaves, it creates a negative pressure that pulls water up from the roots, keeping the plant hydrated
Describe how water moves across the cells of a leaf?
Mesophyll cells lose water to the air spaces by evaporation due to heal supplied by the sun
these cells now have a lower water potential so water enters by osmosis from neighbouring cells
the loss of water from these neighbouring cells lowers there water potential
they, in turn, take in water form their neighbours by osmosis
Explain how water moves from the roots to the leaves.
• Water evaporates from mesophyll cells due to heat from the sun, causing transpiration.
• Cohesion (hydrogen bonding between water molecules) creates a continuous water column in the xylem.
• As water evaporates from mesophyll cells into air spaces, more water is drawn up due to cohesion.
• This transpiration pull moves water up the xylem.
• The pull creates tension (negative pressure) in the xylem, explaining the cohesion-tension theory.
What evidence supported the cohesion-tension theory in the xylem vessel?
Change in diameter of tree trunks according to the rate of transpiration
If xylem vessel is broken and air enters it tree can no longer draw up water
when xylem vessel broken water does not leak out
How is sucrose transferred into sieve elements from photosynthesising tissue?
- Facilitated diffusion of sucrose from the photosynthesising cells into companion cells
- Hydrogen ions actively transported from companion cells into the spaces of the cell wall
- The hydrogen ions then diffuse down a concentration gradient through carrier proteins into the sieve tube elements
- Sucrose molecules are transported along with the hydrogen in a process known as co-transport. The protein carriers are therefore known as co-transporter proteins.
When describing translocation or the transport of carbs the marking point is often just 1. Sucrose actively transported into phloem (cell);
OR
Sucrose is co-transported/moved with H+ into
phloem (cell);
Describe translocation.
Mass Flow theory
Source:
• Solutes actively loaded into phloem from companion cells.
• Lowers water potential, so water enters by osmosis.
• Creates high pressure at the source.
Sink:
• Solutes removed for respiration or storage (as starch).
• Water follows by osmosis.
• Lower pressure at the sink.
• Pressure gradient drives solute flow from source to sink
What is the structure of the phloem
Sieve cells
companion cells - provide ATP for active transport of organic substances
Seive plates
The cohesion-tension theory explains how water moves up the xylem into plants against gravity. Describe it.
- Transpiration – Water evaporates from mesophyll cells into air spaces and exits via stomata.
- Tension (Negative Pressure) – Water loss creates tension in the xylem, pulling more water up.
- Cohesion – Hydrogen bonds between water molecules create a continuous column of water.
- Adhesion – Water molecules stick to xylem walls, aiding upward movement.
- Water Uptake – Water is drawn in from roots to replace lost water.
This process is passive and relies on solar energy driving transpiration
Name the main polymer that forms the plant cell wall and the main polymer that forms the fungal cell wall.
Plant cell wall: cellulose
Fungal cell wall: chitin
Describe the transport of carbohydrates in plants. 5 marks
- Sucrose actively transported into phloem (cell);
OR
Sucrose is co-transported/moved with H+ into
phloem (cell); - (By) companion/transfer cells;
- Lowers water potential (in phloem) and water
enters (from xylem) by osmosis; - ((Produces) high(er) (hydrostatic) pressure;
OR
(Produces hydrostatic) pressure gradient; - Mass flow to respiring cells
OR - Mass flow to storage tissue/organ;
Unloaded/removed (from phloem) by active
transport;
What disaccharide is glucose converted into following photosynthesis and why?
The disaccharide sucrose
Sucrose is less reactive than glucose and is less likely to react with other molecules
What role do aphids play in proving the mass flow hypothesis?
Aphids feed on phloem sap. If their bodies are removed, the sap continues to flow from their mouthparts, showing that the contents of the phloem are under pressure and move due to mass flow.
Description of Transpiration (Max 3 marks)
• Water evaporates from the surface of mesophyll cells into air spaces in the leaf.
• Water diffuses out of the leaf through the stomata down a water potential gradient. • This creates a tension (negative pressure) that pulls water up the xylem from the roots via the transpiration stream. • Water molecules stick together due to cohesion, forming a continuous column in the xylem. • Adhesion between water molecules and xylem walls helps maintain the column.
Factors Affecting the Rate of Transpiration (Max 3 marks)
• Light intensity: More light leads to more open stomata, increasing transpiration.
• Temperature: Higher temperature increases evaporation and diffusion rates, raising transpiration. • Humidity: Higher humidity lowers the water potential gradient, reducing transpiration. • Wind speed: Higher wind speed removes moist air around the leaf, increasing transpiration. • Water availability: Low soil water content reduces water uptake, decreasing transpiration.
Suggest one advantage to a bacterium of secreting an extra cellular protease in its natural environment. Explain your answer.
- To digest protein;
- (So) they can absorb amino acids for growth/reproduction/protein synthesis/synthesis of named cell component;
OR
(So) they can destroy a toxic substance/proteins
Describe the action of membrane-bound dipeptidase and explain their importance. 2 marks
- Hydrolyse (peptide bonds) to release amino
- acids;
Amino acids can cross (cell) membrane;
OR
Dipeptides cannot cross (cell) membrane;
OR
Maintain concentration gradient of amino acids
for absorption;
OR
Ensure (nearly) maximum yield from protein
breakdown
Give three environmental variables that should be controlled when growing the plants before and experiment.
- Concentration of mineral ion/named mineral
ion in soil; - Soil pH;
- Temperature;
- Light intensity/wavelength/duration;
- Distance between seeds/plants;
- Volume of water given;
- CO2 concentration;
- Humidity;
A scientist is carrying out an experiment with leaves in water. Why does he need to ensure the temperature stays constant? And why does he shake the lead discs?
- (Maintain temperature) so that the rate of
diffusion (of ions out of cells) remains constant
OR - (Maintain temperature) so no change in fluidity
of phospholipids/kinetic energy of
phospholipids;
OR
(Maintain temperature) so no change in
shape/structure/denaturation of membrane
proteins;
(Shaking) So all surfaces of the leaf discs are
exposed (to water)/so all submerged;
OR
To maintain diffusion/concentration gradient
(for ions out of leaf discs);
Describe how phagocytosis of a virus leads to presentation of its antigens. 3 marks
- Phagosome/vesicle fuses with lysosome;
- (Virus) destroyed by lysozymes/hydrolytic
enzymes; - Peptides/antigen (from virus) are displayed on
the cell membrane;
Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen. 3 marks
- Helper T cell/TH cell binds to the antigen (on
the antigen-presenting cell/phagocyte);
This helper T/TH cell stimulates a specific B
cell;
- Helper T cell/TH cell binds to the antigen (on
- B cell clones
OR - B cell divides by mitosis;
(Forms) plasma cells that release antibodies;
State three comparisons of genetic diversity that the scientists use in order to generate Phylogenetic Classification. 3 marks
The (base) sequence of DNA;
The (base) sequence of mRNA;
The amino acid sequence (of proteins);
Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. 6 marks
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles/named cell
structure can be observed
OR
greater detail in organelles/named cell structure
can be observed; - TEM view only dead/dehydrated specimens and
optical (can) view live specimens; - TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming
preparation; - TEM focuses using magnets and optical uses
(glass) lenses;
