Biology AS OCR Unit 1 Module 2

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Biology AS OCR Unit 1 Module 2

OCR Biology Module 2 AS Unit 1

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Why do multicellular organisms need specialised exchange surfaces?
They have a small surface area to volume ration and so can't diffuse in everything they need as it can't get everywhere.
Why can single celled organisms simply diffuse in all of their nutrients and oxygen?
They have a small surface area to volume ratio and so the diffused substances reach everywhere.
What features make for a good exchange surface?
Large surface area  - folding walls and membranesThin barrier to reduce diffusion distanceFresh supply of molecules on one sideRemoval of required molecules maintaining gradient
What sized surface area is best for the lungs?
Large surface area provides more space for molecules to pass through.
What kind of barrier is best suited for the lungs?
The plasma membrane surrounding the thin cytoplasm of the cells form the barrier to exchange.Barrier PERMEABLE to oxygen and carbon dioxide
How thick is the alveolus wall?
One cell thick
How thick is the capillary wall?
One cell thick
What type of cells do both walls consist of?
Squamous cells - meaning flattened or very thing
Why are the capillaries so narrow?
So erythrocytes are squeezed against the wall making them closer to the alveoli and reducing rate of blood flow.
What is the total diffusion distance for the carbon dioxide to diffuse against?
2 flattened cells thick - less than 1um
How does the thin layer of moisture in the alveoli help diffusion?
Gasses absorbed by moisture making it easier for substances to diffuse into capillaries.
Why must the lungs produce a surfactant?
Moisture of the lungs evaporates when we breathe out and without the surfactant to reduce cohesive forces between water molecules the alveoli would collapse.
Outline the steps of inspiration
Diaphragm contracts to become flatter, External intercostal muscles contract to raise ribs,Volume of chest cavity increasesPressure in chest cavity drops below atmospheric pressureAir moves into lungs
Outline the steps of expiration
Diaphragm relaxes and is pushed up,External intercostal muscles relax, ribs fall,Volume of chest cavity decreases,Pressure in lungs increases and rises above atmospheric pressure,Air moves out of lungs
What can be found in the bronchioles?
Larger may have some cartilage - not muchSmooth muscleBlood vesselsLoose tissue with elastic fibresCiliated epitheliumGoblet cell
What can be found in the trachea?
CartilageSmooth muscleElastic fibresSmall blood vesselsCiliated epithelium with goblet cellsMucus secreting glands
Describe the route of air from the mouth to the lungs.
Mouth -> Trachea -> Bronchi -> Bronchioles -> Alveoli 
What is the role of cartilage?
Support trachea and bronchi -> hold openPrevents collapsing during low air pressureC-Ring for flexibility allowing movement without constriction of airway.Expands during swallowing
What is the role of smooth muscle?
Can contract to constrict airway and narrow lumenContraction of smooth muscle involuntaryi.e Asthma -> harmful substances in air
What is the role of elastic fibres?
As smooth muscle relaxes elastic fibres recoil to their original shape and size -> dilates airway
What is the role of goblet cells and glandular tissue?
Secrete mucus to trap tiny particles from the air.Trapping bacteria -> removed to reduce risk of infection
What is the role of ciliated epithelium?
Have numerous tiny, hair like structures called cilia,Cilia wave in sync to waft mucus up the airway to be swallowed.
Define Tidal Volume
Volume of air moved in and out of the lungs with each breath at rest. Approximately 0.5dm^3
Define Vital Capacity
Largest volume of air that can be moved in and out of the lungs in one breath. Approximately 5dm^3
Inspiratory Reserve + Expiratory reserve = Vital capacity
What is a spirometer and how does it work?
Consists of a chamber filled with O2 floating on water.Person breathes in medical-grade O2 through tube and exhales CO2 absorbed by soda lime.Breathing in moves chamber down whilst breathing out pushes chamber up.Different breathing rates affect results.
How does size affect the need for transport systems in multicellular organisms?
Organism has several layers of cells then diffusion will mean oxygen and nutrients only reach outer cells and inner cells are deprived.
How does surface area to volume ration (SA:V) affect the need for transport systems in multicellular organisms?
To allow animals to grow to a large size, they need a range of tissues and structural support which decreases SA:V ratio. The large the SA:V ratio the easier it is for diffusion to get to all the cells, but the smaller it is the harder it is as they are bigger and diffusion can't reach internal cells.
How does level of activity affect the need for transport systems in multicellular organisms?
High levels of activity require larger levels of energy.This energy can only be gained by quick good supplies of oxygen and energy which cannot be attained through simple diffusion to cells without a transport system.
What is meant by a single circulatory system? Who would have one?
There is only one system that transfers blood around the body. This occurs in fish.
       /\      ------>      Heart      ----->      |       |    Tissue       <--------      Gills   \/
What is meant by a double circulatory system? Who would have one?
One circuit carries blood to the lungs from the heart and back (Pulmonary system) and the other circuit carries blood from the heart to the tissues and back (systemic system) This occurs in mammals.
               \/<-----------    /\     /\     -----------> \/     Tissue                    Heart                     Lungs                    \/ -------------> /\        /\ <---------------\/
What is meant by the term open circulatory system? Where would this be present?
Blood fluid circulates through the body cavity, tissues and organs bathed directly in blood.Movement of muscles help circulate blood.Muscular pumping organ like heart pumps blood towards head by peristalsis (muscles contract in gut to squeeze blood up)Open ended tubes to direct blood.
INSECTS i.e Locust
What is meant by the term closed circulatory system?Where would this be present?
Blood stays in blood vessels.Tissue fluid bathes tissues and cells.Heart pumps blood at high pressure.
Present in fish.
heart -> arteries -> gills -> veins -> body tissue -> veins -> heart
What are the external features of the heart?
Dark red muscle - very firm around ventriclesCoronary arteries lie over surface to take oxygenated blood to the heart muscle itself.
What are the internal features of the heart?
Four chambersTwo atria at the topTwo ventricles at the bottomVena Cava brings in deoxygenated blood from tissuePulmonary Vein oxygenated blood from lungs into left atriumVentricular septum separates ventriclesAV septum separates atria from ventricles
In descending order name the thickest walls
Atria - least thickRight ventricle - thicker than atriaLeft ventricle - thickest (can be 2-3x thicker than right)
Why are the atria walls relatively thin?
They only have  to pump blood through the bicuspid and tricuspid valves into the ventricles rather than a great distance.
Why is the right ventricle wall thicker than the atria but thinner than the left ventricle wall?
Needs to pump the blood to the lungs so further than the atria but not as far as the left ventricle.
Why is the left ventricle wall so thick?
Blood pumped out through the Aorta and needs sufficient pressure to overcome resistance of system circulation.
Summarise the definition of the cardiac cycle
The sequence of events in one heartbeat
What is Diastole?
The filling phase; during which both the atria and ventricles are relaxed.Blood flows through into the atria and the opened ventricles
What is atrial systole?
The heart beats when the atria contract (right and left together)This small pressure increases pushes blood into the ventricles stretching the walls.Blood fills the AV flaps causing them to snap shit, prevent blood back into atria.
What is ventricular systole?
All four valves are shut, walls of ventricles contract.Raises pressure in ventricles,Contraction starts at apex pushing blood upwards pushing semi-lunar valves open and blood out of the heart.Ventricles relax.
How do the AV Valves open and close?
Blood pressure from atria push valves open.Blood pressure from ventricles push blood upward into valve pockets and keeps them closed.
How do the semilunar valves open and close?
Blood pressure from the ventricles becomes greater than pressure down from outside heart.Ventricles finish contraction and blood pressure becomes less than pressure from out of heart and blood starting to flow back push back semilunar valves, forcing shut.
What is the term used to describe tissue which can initiate its own contraction?
How does the heartbeat start?
The sinoatrial node in the top right atrium, a small patch of tissue, generates a wave of electrical excitation at regular intervals. 
This spreads across the atria.
Where does this wave of excitation go next?
As it cannot pass through the atrioventricular septumit passes to the atrioventricular node. This causes a delay in contractions which allows for blood to enter into the ventricles before the valves close.
How does the wave of excitation from the AV node cause the ventricles to contract?
It passes through the septum by the purkinje tissue which is a special conducting tissue running down the ventricular septum to the apex.The wave then spreads up from the apex cause the ventricles to contract upward.
What does Wave P of an ECG show?
Atrial systole
What does QRS show on an ECG show?
Ventricular systole
What does wave T show on an ECG?
Describe from in to out the layers of an artery
LumenEndotheliumElastic fibreSmooth muscleCollagen fibres
Describe from in to out the layers of a capillary
Describe from in to out the layers of a vein
LumenEndotheliumElastic fibresSmooth muscleCollagen fibres
What is the function of an artery?
Carry blood away from the heart at a high pressure.
What are the features of an artery?
Small lumen for high pressureRelatively thick wall for high pressureElastic fibres to stretch and recoil to maintain high pressureSmooth muscle can constrict to limit bloodEndothelium is folded and can unfold to stretch
What are the function of a vein?
Carry blood back to the heart and at low pressure
What are the features of a vein?
Relatively large lumen to ease blood flowWalls have thinner layers of everythingContain valves to help the blood flow back to the heart and prevent wrong direction of flow.Vein can be flattened by skeletal muscle which causes pressure forcing blood to move in correct direction.
What is the function of a capillary?
Very thin walls easy exchange of substances between blood and cells via tissue fluid.
What is the features of a capillary
Consist of single layer of squamous epithelial cells.Very narrow lumen - same as that of erythrocyte (7um)Erythrocytes must squeeze through capillariesReduces diffusion distance
Where is blood found?
Blood is held in the heart and in blood vessels
Where is tissue fluid?
Bathing the cells of individual tissues
Where is lymph found?
Held within the lymphatic system
What is blood?
Liquid which consists of blood cells in a watery fluid called plasma.
What does plasma contain?
Many solutes including oxygen, carbon dioxide, salts, glucose, fatty acids, amino acids, hormones and plasma proteins.
As well as cells such as erythrocytes, leukocytes, and platelets.
What is tissue fluid?
Like blood but does not contain the many of the cells or plasma proteins.
What is the role of tissue fluid?
Carry oxygen and nutrients from the blood to the cells and carbon dioxide and waste products back.
How is tissue fluid formed?
Arteries branch into smaller arterioles before branching in to capillaries. These eventually link up to the smaller version of veins known as venules.
Arterial end of capillaries have a high blood pressure due to contraction of the heart muscle (Hydrostatic pressure) This pushes the blood fluid out of the cappilaries through tiny gaps.
What remains in the blood when tissue fluid is formed?
red blood cellsplasma proteins
platelets and most of the white blood cells
Why do they not leave the capillaries?
They are too large to escape
Why does tissue fluid not enter into the blood at the arterial end of a capillary?
The arterial end has lots of solutes in the blood but due to the to the high hydrostatic pressure cause by the heart the blood fluid still leaves the capillaries.
How does the tissue fluid return to the blood at the venal end of a capillary?
The tissue fluid has a higher water potential than the blood and this causes a water potential. Where it cold not return to the blood before due to hydrostatic pressure, this is weaker at the venal end and the water potential force is therefore greater.
How is lymph formed?
Some tissue fluid is drained away into the lymphatic system which starts in the tissues and drain the excess into larger vessels -> rejoining at the chest cavity.
What is the difference between lymph fluid and tissue fluid?
Tissue fluid has less O2 and neutrients.Lymph fluid contains many lymphocytes produced by lymph nodes.
What are lymph nodes?
Swellings found at intervals through the lymphatic system.
What is found in each Haemoglobin subunit? How many subuints are there?
A polypeptide chain and a haem group.
What does each haem group contain?
A single iron atom - Fe2+
How many oxygen molecules can each haemoglobin hold?
What is the process of releasing oxygen?
The amount of oxygen is measured by the relative pressure that it contributes to a mixture of gas. What is this measured in and what is it called?
It is referred to as partial pressure or oxygen tension ad is measured in units of pressure (kPa)
Why is it difficult for haemoglobin to pick up oxygen at low pressures?
The haem group that attracts oxygen are in the centre of the haemoglobin molecule.
What is the change that allows for oxygen to diffuse more readily into haemoglobin molecules and why does this occure? 
It is called the conformational change and happens when eventually one oxygen molecule associates with a haem group causing a slight change in shape
When does it become difficult for the furth oxygen molecule to diffuse and associate?
On the final haem group as there is a high concentration and so association curve levels off as saturation approaches 100%
What type of affinity does a mammalian foetus have for oxygen?
Higher affinity than that of an adult
Why do foetuses have such a high affinity for oxygen?
Then need to pick up oxygen from the places adult haemoglobin dissociate.They must absorb oxygen from fluid in the blood -> lowers oxygen tension causing maternal haemoglobin to release oxygen.
What is the Bohr effect/shift?
Refers to the change in shape of the oxyhaemoglobin curve when carbon dioxide is present -> causes oxyhaemoglobin to relase oxygen more readily
What does carbon dioxide make when it combines with water in the blood?
Weak carbonic acid (catalysed by carbonic anhydrase)
What is the function of carbonic anhydrase and whaat is it?
To catalyse the reaction between carbon dioxide and water to form carbonic acid . It is an enzyme.
What is produced when carbonic acid dissociates?
Hydrogen ions and hydrocarbonate ions.                            _  H+ and HCO3
Where do the hydrocarbonate ions go and what takes their place and why?
They move into the plasma from the red blood cell.A chloride shift occurs when Cl- ions from the plasma move into the red blood cells to maintain the charge.
What happens with the hydrogen ions?
They move into the haemoglobin, to reduce acidity of red blood cells. This produces haemoglobinic acid.
What is the buffer in this movement and what is its function?
The haemoglobin is acting as a buffer. A buffer is a compound that maintain a constant pH
From left to right name the lines on a dissociation curve .
FetalNormalHigh CO2
Why do multicellular plants need a transport system?
As plants become larger and more complex transport systems become essential in the supply of nutrients and to remove waste from individual cells.
What is the problem between leaves and roots?
Leaves can make sugars but cannot obtain water from the air whilst roots can absorb water from the soil easily but cannot absorb sugars.
What substances move in the xylem and in which direction?
Water and soluble minerals travel UPWARDS in xylem tissue.
Xy like fly -> Up
What substances move in the phloem and in which direction?
Sugars travel UP or DOWN in phloem tissue.
Phlo - em like throw em -> can go up or down
Where are the phloem and xylem found?
In vascular tissue, in vascular bundles.Other tissue is also found here to give strength and support to plant.
Where is the vascular bundle found in a young root?
At the centre.The xylem has a central core usually X Shaped.Phloem can usually be seen between these arms.
What can be found around the vascular bundle?
Where can the layer of meristem cells be found and what is this layer called?
Just inside the endodermis and it is called the pericycle
Where are the vascular bundles found in the stem?
Near the outer edge of the stem
How does their layout differ in non-woody and woody plants?
Non-woody -> bundles are seperate and discreteWoody -> Young stems are separate but become continuous in older stems
What is fund between the xylem and phloem in a stem?
The cambium
What is the cambium?Where is the cortex?Where is the medulla?
A layer of meristem cells which divide to produce new xylem and phloem
The cortex can be found on the outer rim of the phloem
The medulla is found in the innermost part of a stem
What is distinct about a dicotyledon leaf?
Has branching network of veins that get smaller as they spread from the midrib.
Define Phloem
A plant transport tissue which carries the products of photosynthesis to the rest of the plant. It consists of sieve tube elements and companion cells.
What is the most obvious features of xylem in dicotyledons\.
The xylem vessel.Long cells with thick walls impregnated by ligninLignin waterproofs walls of the cell.Cell dies and their end walls and contents decay
What are some more effects of lignification
Lignin thickening forms patterns in the cell wall preventing vessel from being too rigid and allows flexibility
Lignification is not complete everywhere leaving pits.
How is the xylem adapted to fulfil its function?
Pits for sideways/adjacent movementLignin thickening forms patterns- flexibilityNo cell contents or organellesLigning prevents walls collapsingNo end wallsNarrow tubes effective capillary action
What two types of cell does phloem tissue contain?
Sieve tube elements and companion cells
What are the features of sieve tube elements?
Not true cells very little cytoplasm + no nucleusTransports sugars (sucrose)Have sieve plates to allow sap to flowVery thin walls5 or 6 sided
What are the features of companion cells?
Large nucleus _ dense cytoplasmLots of mitochondria for ATPCarry out metabolic processes for sieve tubeCytoplasm between the two linked via plasmodesmata
Define transpiration
The loss of water by evaporation from the aerial parts of a plant.
(The loss of water vapour from the upper parts of a plant particularly the leaves)
What are the stages of transpiration?
What enters the leaves in the xylem -> passes to the mesophyll cells by osmosisWater evaporates from the surface of mesophyll cells formin water vapour.Spongy mesophyll cells have large air spaces helping water vapour diffuse through leaf tissue.Water vapour potential rises in these spaces.Once potential in leaf is higher than outside water begins to diffuse out.Open stomata provide easy route out.Stomata open during day for gaseous exchange
What three processes are involved in transpiration?
Osmosis from xylem to mesophyll cellsEvaporation from surface of mesophyll into intercellular spacesDiffusion of water vapour from intercellular spaces out via stomata
Why is the transpiration stream useful?
Water required forPhotosynthesisTo enable cells to grow and elongateCells turgidCarry useful minerals up plantEvaporation keeps plant cool
What 8 features effects the rate of transpiration?
Number of leavesNumber, size position of stomataPresence of cuticleLightTemperatureRelative humidityAir movement or windWater availability
How does the number of leaves affect water loss by transpiration?
A plant with more leaves has larger surface area over which water can be lost
How does the stomata affect water loss by transpiration?
Large stomata -> water vapor lost more quicklyLower down on surface -> water vapour loss is slowLarge number > high water loss
How does the presence of cuticle affect water loss by transpiration?
Waxy cuticle reduces evaporation from leaf surface
How does temperature affect the water loss due to transpiration?
Increase rate of evaporation from cell surface raising water potential in leafIncreases rate of diffusion through stomata -> kinetic energyDecrease relative water vapour in air more rapid diffusion of water out of leaf
How does the relative humidity affect water loss due to transpiration?
Higher humidity decreases rate of water loss as smaller water potential gradient
How does air movement/wind affect the water loss due to transpiration?
Carries evaporated water away maintaining steep water vapour potential gradient.
How does water availability affect the water loss due to transpiration?
Little water in soil means plant cannot replace water loss.Water loss in plants is reduced when stomata are closed or plants shed leaves in winter
How is water loss measured in transpiration?
By a potometer to estimate rate of water loss.Water lost by the leaf is replaced by water from capillary tube, the meniscus (curved water bubble) movement can be measured
What is cohesion?
The attraction of water molecules for one another