Module 3

Question 1

Cambium

Answer 1

• Lies in between xylem and phloem • Layer of meristem cells • Divide to produce new xylem and phloem

Question 2

Xylem

Answer 2

• Transports water and minerals within plant • Meristem cells produce small cells which elongate • Walls are reinforced with waterproof lignin • Ends of cells break down • This forms a long continuous tubes with a wide lumen • Provides support for the plant

Question 3

Phloem •

Answer 3

Transports products of photosynthesis within a plant • Structure consists of sieve tubes and companion cells • Meristem tissue produces cells that elongate and line up to form end to end tubes • Ends do not break down completely • Form sieve plates in between cells • Sieve plates allow for the movement of material up or down tube • Next to each sieve cell is companion cell, providing support
12

Question 4

Single Celled Organisms

Answer 4

Small, single celled organisms have a very large surface area to volume ratio ○ They are able to exchange gases, nutrients and waste across surface

Question 5

Multicellular Organism

Answer 5

○ Small surface area to volume ratio ○ Cells need more supplies ○ Outer surface not large enough to enable gases and nutrients to enter body fast enough to keep cells alive ○ Gases must travel greater distance to reach cells at centre of organism ○ Require specialised exchange surface ○ Transport systems help to move nutrients to all parts of the body

Question 6

Efficient Exchange Surface

Answer 6

Large surface • Provides more space for molecules to pass through • Often achieved by folding walls of membranes Thin barrier • Reduce diffusion distance • Often only one cell thick Maintain steep diffusion gradient • Fresh supply of molecules on one side, keeping concentration high • Removal of required molecules on other side keeps concentration low

Question 7

Components of the Mammalian Gaseous Exchange System

Answer 7

Airways • Larger airways allow sufficient flow of air • Divide into smaller airways, delivering air to alveoli • Strong airways withstand low and high pressure • Flexible • Able to stretch and recoil

Lungs • Air passes through trachea, bronchi and bronchioles • Each specifically adapted • Air reaches alveoli • These are specialised for gas exchange • Protected by ribs • Movement of ribs and diaphragm help in ventilation

Trachea and Bronchi • Bronchi and trachea very similar • Bronchi narrower than trachea • Walls consist of cartilage • Cartilage form C-shaped rings • Layers of loose tissue on inside of cartilage • Inner lining is ciliated epithelium

Bronchioles • Much narrower than bronchi • Smaller ones have no cartilage wall made from smooth muscle and elastic fibres • Smallest have clusters of alveoli at the ends

Question 8

Components of an efficient gaseous exchange surface:

Answer 8

Cartilage• Structural role • Supports trachea and bronchi • Holds them open • Prevents collapse when air pressure is low • Allows for movement

Question 9

Cilia

Answer 9

• Move in a synchronised pattern waft mucus up airway to back of throat • Mucus is then swallowed and bacteria killed in the acidic stomach

Question 10

Goblet cells

Answer 10

• Lie under epithelium • Secrete mucus • Mucus traps tiny particle sin the air • Traps bacteria and pollen, reducing the risk of infection

Question 11

Smooth Muscle

Answer 11

• Able to contract • Contraction arrows lumen, restricting air flow • This is important if harmful substances are present • Contraction involuntary

Question 12

Elastic Fibres

Answer 12

• Contraction of airways deforms elastic fibres in tissue • As smooth muscle relaxes, elastic fibres recoil to original size • Help to dilate airway

Question 13

Tidal Volume

Answer 13

• Volume of air moved in and out of lungs with each breath when at rest • It is approximately 500cm3 • Provides body with enough oxygen for its resting needs while removing enough carbon dioxide to maintain safe level

Question 14

Vital Capacity

Answer 14

• Largest volume of air that can be moved in and out of lungs in any one breath • Approximately 5dm3 • Varies from person to person • Regular exercise increases vital capacity

Question 15

Breathing rate

Answer 15

• Number of breaths per minute • Can be counted easily using a 60-second timer

Question 16

Oxygen uptake

Answer 16

• Measure of the volume of O2 inhaled per unit time • Can be recorded using a spirometer

Question 17

Spirometer

Answer 17

• Used to measure volumes of lung capacity • Consists of chamber filled with oxygen that floats in water • Patient breathes in, taking up oxygen, making the chamber sink • Breathing out pushes air into the chamber, causing it to float • Soda lime used to absorb CO2 that is exhaled • Volume of CO2 breathed out is same as oxygen uptake • Total reduction in volume is equal to oxygen uptake

Question 18

Bony fish gas exchange

Answer 18

• Use gills to absorb oxygen from surrounding water • Gills are also the site where carbon dioxide is released into the water • Most bony fish have 5 pairs of gills ○ The operculum is a bony plate covering the gills ○ Each gill has 2 rows of filaments ○ Each filament is folded into lamellae to increase their surface area • Blood capillaries circulate in the regions surrounding the gills

Question 19

Bony fish ventilation

Answer 19

• Fish use their mouths (buccal cavity) to generate waves of water that move over the gills • These movements are co-ordinated with movements of the opercula • This ensures that oxygenated water is continually flowing over the gills

Question 20

Insect gas exchange

Answer 20

Open circulatory system - no blood • ‘Tracheal system’ - airways that travel up and down the body • Trachea branch out as spiracles that open out into the air

• Therefore air circulates within the body in tiny vessels • Trachea also branch out inwards in tracheoles • This is where gas exchange occurs by diffusion

Question 21

Insect ventilation

Answer 21

• Larger insects can ventilate tracheal system by entire body movements • Moving the body squeezes and relaxes areas of the tracheal system - pumping air to circulate • Moving the wings can alter the volume of the thorax, changing air pressure in the thorax causing air to move in/out

Question 22

3 factors that affect need for a transport system

Answer 22

• Size ○ Several layers of cells make diffusion unfeasible ○ Only outer cells will access nutrients supplied by diffusion • Level of activity ○ Very active organisms need lots of energy and nutrients ○ Mammals need lots of energy • SA to Volume ratio ○ Larger animals have a low SA to v ratio ○ Surface area not large enough to supply cells with required oxygen

Question 23

• Single Circulatory System

Answer 23

○ Single circuit ○ Fish have this ○ Blood flow from – Heart – Gills – Body – Heart

Question 24

• Double Circulatory System

Answer 24

○ Mammals have this ○ Blood travels through the heart twice for one complete circuit
○ Pulmonary circulation carries blood to the lungs to pick up oxygen
○ Systemic circulation carries oxygenated blood round the body

○ Blood flows from: – Heart – Body – Heart – Lungs – Heart
○ This allows: – Blood pressure to be raised after passing through lungs – Blood flows more quickly to tissues – Provides required nutrients for respiration – Systemic circulation can have higher pressure than pulmonary

Question 25

Open Circulatory System

Answer 25

○ Insects have these ○ Blood (haemolymph) flows freely through body cavity ○ Oxygen diffuses into insects through spiracles (holes) ○ Spiracles attached to tracheoles which are ventilated by contraction of insect’s muscles

Question 26

Closed Circulatory System

Answer 26

○ Mammals have these ○ Blood closed at all times within vessels ○ Blood pumped by heart through vessels ○ Blood does not normally fill body cavities

Question 27

Arteries • Function

Answer 27

○ Blood pumped into arteries by the ventricles of heart ○ Arteries carry blood away from the heart ○ Blood travels to other part of body – E.g. lungs, muscles

Question 28

Arteries •Structure

Answer 28

○ Thick walls do not allow for diffusion of chemicals ○ Strong walls made of elastic fibre and muscle swell and contract as blood surges through them every time heart beats 82snaprevise.co.uk ○ Small Lumen ○ Blood is at high pressure ○ Therefore, arteries must be able to give under pressure ○ Blood is pumped through by the heart • Reason for structure ○ To keep blood pressure high and to be able to withstand high pressure

Question 29

Veins • Function

Answer 29

○ Veins bring blood back to the heart ○ The blood flows in only one direction ○ Veins do not pulse, the blood is helped back to the heart by muscles – In arms and legs, veins lie between muscles ○ When muscles contract, they squeeze the blood back to the heart ○ Valves only allow blood to be pumped one way

Question 30

Veins • Structure

Answer 30

○ Veins bring blood back to the heart ○ The blood flows in only one direction ○ Veins do not pulse, the blood is helped back to the heart by muscles – In arms and legs, veins lie between muscles ○ When muscles contract, they squeeze the blood back to the heart ○ Valves only allow blood to be pumped one way

Question 31

Capillaries • Function

Answer 31

○ Link between the arteries and veins ○ Diffusion into/out of the blood only occurs here

Question 32

Capillaries • Structure

Answer 32

○ Outer wall only one cell thin – allows diffusion of substances into/out of the blood in the capillaries ○ Steady blood flow ○ Small Lumen ○ Very thin – has to be small enough to fit between cells, so that it can bring blood to every cell in the body Reason for Structure ○ So that substances can easily diffuse into/out of the blood through the walls

Question 33

The Formation of Tissue Fluid from Plasma

Answer 33

1. Blood in the arteriolar end of the capillary has high hydrostatic pressure, meaning it has a high water potential. 2. Because it has a lot of water, it also has a lot of dissolved ions and small molecules like oxygen, glucose and amino acids 3. These molecules - including water - are small enough to be forced through the capillary lining because of this pressure 4. This is ultrafiltration 5. By the time blood arrives at the venous end of the capillary, the blood has lost some water and ions. It has a reduced hydrostatic pressure. 6. The proteins, which were too big to exit the capillary by ultrafiltration, are now at a higher concentration. They give the blood in the venous end of the capillary a high oncotic pressure, which draws back in water by osmosis, down the concentration gradient.

Question 34

Tissue Fluid

Answer 34

Tissue fluid is the fluid that surrounds individual cells and creates their environment. Tissue fluid homeostasis is a very important process and preserves constant characteristics that constitute the optimum environment for cells so they they function correctly. Tissue fluid is formed from blood plasma:

Question 35

fuction of lymph

Answer 35

no rbc no plasma proteins most wbc transports mainly lipid soluble substances

Question 36

tissue fluid

Answer 36

no rbc no plasma proteins lesst wbc provides nutrients to body cells and removes their waste products

Question 37

blood

Answer 37

has wbc rbc and plasma protins | transports mostly water soluble substances

Question 38

Nervous Control of the Cardiac Cycle

Answer 38

x • Sinoatrial node (SAN) sends signal across walls of both atria • Signal causes atria to contract • Signal reaches the AV node • Signal conducted down the purkinje fibres (specialised conducting tissue) • This signal causes the ventricles to contract from the bottom upwards • This occurs 55-80 times a minute

Question 39

Diastole

Answer 39

* Both atria and ventricles relaxed • Pressure decreased * Internal volume increases • Blood flows into heart from major veins • Blood flows into atria, then through open atrioventricular valves and into ventricles • ‘Filling phase’ • Atria and ventricles have blood inside of them

Question 40

Atrial Systole

Answer 40

• Both atria contract together (systole) • Small increase in pressure created by contraction helps to push blood from aorta into already partially full ventricles • Stretches walls of ventricles • Ensures that they are already full of blood • AV valves then shut

Question 41

Ventricular Systole

Answer 41

• Ventricles full of blood • Begin to contract • Pressure increases • Volume decreases • Contractions start at apex, pushing blood upwards towards arteries • Semilunar valves forced open • Blood pushes out of both ventricles and into the arteries • Semilunar valves shut

Question 42

ECG stands for electrocardiogram. It is a diagnostic tool used by doctors to:

Answer 42

• Assess heart rhythm • Diagnose cardiac arrhythmia • Diagnose myocardial infarction (heart attack) • Identify anatomical abnormalities in the heart, such as enlarged ventricular chambers or electrical interruptions

Question 43

Ectopic Heartbeat

Answer 43

Extra heartbeat where only atria or ventricles contract Premature ventricular contraction (PVC) looks like a v Premature atrial contraction (PAC) looks like an a

Question 44

when oxyhaemoglobin reaches a respiring cell

Answer 44

• Haemoglobin has higher affinity to CO2 than O2 • Hb dissociates with O2 and binds with CO2 instead • Thereby depositing oxygen in areas that are respiring a lot and getting rid of carbon dioxide which is a waste product that needs to be removed

Question 45

Haemoglobin dissociation curve is a ...

Answer 45

S-shaped curve

Question 46

at Low pO2 (eg respiring muscle)

Answer 46

○ Low partial pressure of Oxygen ○ Hb dissociates oxygen ○ Binds to CO2

Question 47

at High pO2 (eg lung capillaries)

Answer 47

High partial pressure of Oxygen ○ Due to CO2 concentration gradient across capillary wall, Hb that is bound to CO2 dissociates 89snaprevise.co.uk ○ Hb is now free to bind to O2 ○ First O2 molecule binds to haem group and these changes the overall shape of Hb making it easier for the other 3 molecules to bind

Question 48

how 85% of co2 is trasported

Answer 48

• CO2 in plasma diffuses into blood • Reacts with water by an enzyme called carbonic anhydrase to form carbonic acid (H2CO3) • Carbonic acid dissociates within the RBC to form hydrogen ion (H+) and bicarbonate ion (HCO3-) • Bicarbonate ion diffuses out of the cell and travels in the plasma • This is an exchange diffusion process where HCO3- is exchanged for chloride ions to maintain electrical gradient across the RBC plasma membrane • Hydrogen ion causes dissociation of oxyhaemoglobin to form four O2 molecules which diffuse out of the cell, and a deoxyhemoglobin molecule (HHb) which remains in the cell

Question 49

Young Root distribution of the vascular bundle

Answer 49

• Vascular bundle at centre • Large central core of xylem, often in an x shape • Phloem found in between x-shaped arms • Provides strength for roots • Bundle surrounded by endodermis and pericircle of meristem cells

Question 50

Stem

Answer 50

• Bundles found near outer edge of stem • Discrete in non-woody plants • Xylem found towards inside • Phloem on outside • Layer of cambium in-between • Layer of meristem cells

Question 51

Structure and Function of xylem

Answer 51

xylem • Xylem vessel elements • Long cells • Thick walls, impregnated by lignin • Cells die and contents decay • Leaves a long, hollow tube • Lignin strengthens and waterproofs walls • Lignin form patterns, allowing for flexibility • Bordered pit allow for water to pass in and out of xylem vessels

Question 52

Phloem • Sieve Tubes

Answer 52

• Sieve Tubes ○ Lined up end to end ○ Form a tube ○ Sugars dissolved into water, forming sap ○ Contains cross-walls, allowing sap to flow ○ Cross-walls are called sieve plates ○ 5/6 sided ○ Thin walls •

Question 53

Phloem Companion Cells

Answer 53

○ Lie between sieve tubes ○ Large nucleus, dense cytoplasm ○ Numerous mitochondria ○ Carry out metabolic processes needed by sieve tube elements ○ Cells linked by plasmodesmata ○ These gaps allow for the flow of minerals between cells

Question 54

Transpiration

Answer 54

the Loss of water by evaporation from aerial parts of the plant. Water enters the leaves through the xylem, passes through mesophyll cells by osmosis, and diffuses through air spaces in spongy layer. As water vapour collects, water vapour potential rises. When water vapour potential is higher inside the leaf, it diffuses out.

Question 55

Transpiration is an inevitable Consequence of Gaseous Exchange explain

Answer 55

Loss of water through transpiration is unavoidable. Plants exchange gases via stomata. During the day plants must take up carbon dioxide and release oxygen. The stomata must be open to allow this. This provides an easy route for water loss.

Question 56

Factors that Affect Transpiration

Answer 56

• Number of leaves Number and size of stomataPresence of cuticle Light Temperature • Relative Humidity• Air movement and wind Water availability

Question 57

• Number of leaves how it affects transpiration

Answer 57

○ More leaves means greater surface area ○ Greater area over which water can be lost

Question 58

Number and size of stomatahow it affects transpiration

Answer 58

○ Large stomata means water is lost more rapidly ○ If stomata are on the lower surface of the leaf, water loss is slower

Question 59

Presence of cuticle how it affects transpiration

Answer 59

○ Waxy cuticle reduces evaporation

Question 60

light how it affects transpiration

Answer 60

○ Light causes stomata to open ○ Allows gaseous exchange for photosynthesis

Question 61

Temperature how it affects transpiration

Answer 61

This will increase the rate of water loss in three ways: – Increases rate of evaporation from surface – Increase rate of diffusion through the stomata – Decreases relative water vapour potential in the air

Question 62

Relative Humidity how it affects transpiration

Answer 62

○ Higher humidity will decrease water loss ○ This will reduce the water vapour potential gradient between the air in the leaf and outside

Question 63

Air movement and wind how it affects transpiration

Answer 63

○ Moving air will carry water vapour away ○ This maintains a high water vapour potential gradient

Question 64

• Water availability how it affects transpiration

Answer 64

If there is low water availability, the plant cannot replace the lost water ○ Transpiration rates are therefore reduced

Question 65

Potometer

Answer 65

○ Can be used to estimate the rate of water loss ○ Only an estimate as it only measures the rate of water uptake ○ Gives an accurate estimate

Question 66

Set Up Potometer

Answer 66

○ Leafy shoot is placed in a glass tube full of water ○ Make sure there are no bubbles in the apparatus ○ The tube is raised out of the beaker ○ Movement of the meniscus and the end of the water column can then be measured ○ The distance travelled by the meniscus over a certain time period will give the rate of water uptake/loss

Question 67

Water Potential

Answer 67

• Water potential is a measure of the tendency of water molecules to diffuse from area to another • Cytoplasm of plant cells contains salts and sugars, reducing water potential ○ Water potential in plants is always negative

Question 68

○ Apoplast Pathway

Answer 68

– Cellulose walls have water-filled spaces between the cellulose molecules – Water can move through these spaces and between cells 96snaprevise.co.uk – Water does not pass through plasma membrane – Allows dissolved minerals and ions to be carried in the water

Question 69

○ Symplast Pathway

Answer 69

– Water enters cytoplasm through plasma membrane – Then passes through plasmodesmata from cell to the next – Once in the cytoplasm, water can move from cell to cell – Cytoplasm between cells is continuous and connected by one thin strand of cytoplasm through plasmodesmata

Question 70

○ Vacuolar Pathway

Answer 70

– Similar to symplast – Water is not just confined to the cytoplasm – It can pass through the vacuoles as well

Question 71

• Movement of water into Roots

Answer 71

○ Plant roots are surrounded by soil particles ○ Root hair cells use ATP to transport minerals from soil into the root ○ This reduces water potential of cell cytoplasm ○ Creates concentration gradient ○ Water is taken up across plasma membrane by osmosis

Question 72

Movement into Xylem

Answer 72

○ Movement of water across the root is driven by active process in the endodermis ○ Endodermis is layer of cells surrounding xylem – Contains granules of starch ○ Endodermis has waterproof Casparian strip in its walls ○ This blocks the apoplast pathway ○ Endodermis cells move minerals from the cortex into the xylem, decreasing water potential ○ Water moves through the endodermis cells into xylem by osmosis ○ This reduces water potential in cells just outside endodermis ○ Creates a water potential gradient ○ Water can move by the apoplast pathway, but must switch to the symplast at last minute to pass into xylem

Question 73

Movement up the Stem

Answer 73

○ Root Pressure – Action of moving nitrate ions into xylem drives water into xylem by osmosis – Pushes water up xylem – Can push water a few metres, but not to the top of a tree

Question 74

Transpiration Pull

Answer 74

○ Water is lost through transpiration at leaves ○ Water must be replaced ○ Water molecules are attracted to each other through cohesion ○ This forms a water column ○ As water molecules are lost through the stomata in leaves, the water chain is pulled up ○ This creates a transpiration stream ○ The pull of the water creates tension within the column ○ This tension is why xylem needs to be structurally strong and lignin is required

Question 75

Capillary Action

Answer 75

○ Water molecule also attracted to the sides of the xylem vessels ○ This is adhesion ○ Because xylem are narrow, these forces can pull water upwards

Question 76

• Role of the Casparian Strip

Answer 76

○ Blocks apoplast pathway between cortex and xylem ○ Ensures water and dissolved ions have to pass through the cell cytoplasm and membrane ○ Transporter proteins help to transport nitrate ions from cortex into xylem ○ This lowers water potential in xylem, creating a water potential gradient ○ Prevents water from flowing back into endodermal cells

Question 77

Xerophytes

Answer 77

(eg. cacti and marram grass) are plants that are specially adapted to survive higher temperatures by controlling transpiration. At higher temperature water molecule have greater kinetic energy: they move with more speed, increasing the rate of the diffusion through the stomata. This Increases the rate of evaporation from the spongy mesophyll to the air spaces. If the water loss is greater than the water uptake, the plant may suffer water stress, and the cells may lose turgidity.

Question 78

Small Leaves

Answer 78

Particularly needle shaped leaves ○ Reduces total surface area ○ Less water lost through transpiration

Question 79

Dense Spongy Mesophyll

Answer 79

○ Reduces cell surface area exposed to air inside leaves ○ Less water able to evaporate into leaf air spaces

Question 80

• Thicker Cuticle

Answer 80

○ Reduces evaporation

Question 81

Surface Hairs

Answer 81

○ Trap layer of air close to surface ○ Air can become saturated with water and reduce the diffusion of water vapour ○ Water vapour potential is reduced

Question 82

Pits ○

Answer 82

Pits contain stomata at the base ○ Trap air ○ Air can become saturated with water vapour

Question 83

• Rolled leaves

Answer 83

○ Lower epidermis not exposed to atmosphere ○ Air trapped ○ Air can become saturated with moisture ○ Eliminates water vapour potential gradient

Question 84

• Low Water Potential Inside Leaves

Answer 84

○ This is achieve by maintaining a high salt concentration in the cells ○ Low water potential reduces the evaporation of water from the cell surface ○ Reduces water potential gradient

Question 85

Hydrophytes (eg. water lilies)

Answer 85

are plants that are specially adapted to survive while submerged entirely or partially in wate

Question 86

• Large leaves

Answer 86

○ Contributes to plant’s ability to float ○ Increases total surface area ○ More water lost through transpiration

Question 87

air sacs in Spongy Mesophyll

Answer 87

○ Reduces density of leaves, promoting flotation

Question 88

Thinner Cuticle

Answer 88

○ Increases evaporation

Question 89

Lots of stomata

Answer 89

○ Increase transpiration and amount of water lost by evaporation per unit time

Question 90

• Stomata open most of the time

Answer 90

○ Release water through transpiration evaporation

Question 91

Translocation

Answer 91

is the transport of assimilates (sugars and chemicals made by plant cells) throughout the plantSugars are transported in the form of sucrose Translocation occurs in the phloem tissue. Sucrose is released into the phloem at sources and taken out of the phloem at sinks.

Question 92

How does sucrose enter the Phloem?

Answer 92

○ Loaded in by active process ○ Companion cells use ATP to transport hydrogen out of cells into cytoplasm ○ This establishes a diffusion gradient ○ Hydrogen ions diffuse back in through special cotransporter proteins ○ These allow hydrogen to bring sucrose molecule back in with them ○ Sucrose molecules build up in the companion cell ○ Diffuse into sieve tube elements through plasmodesmata

Question 93

• Source

Answer 93

○ Sucrose enters sieve tube element ○ Reduces water potential ○ Water molecules move in by osmosis ○ Increase hydrostatic pressure at the source

Question 94

Along the Phloem

Answer 94

○ Water enters at source ○ Moves down hydrostatic pressure gradient towards sink ○ Produces water flow ○ This carries sucrose and other assimilates along the phloem ○ This is called mass flow ○ Can occur both up and down a plant

Question 95

Sink

Answer 95

○ Sucrose used in cells surrounding phloem – May be converted to starch for storage – May be used in metabolic reactions ○ This reduces sucrose concentration ○ Sucrose molecules move out of the sieve tube elements ○ Water potential in sieve tube elements increases, so water moves out by osmosis ○ This reduces hydrostatic pressure at the sink

Question 96

evidence supporting the theory of translocation:

Answer 96

Use of Phloem ○ If radioactive carbon dioxide is supplied, it soon appears in the phloem ○ Ringing a tree results in sugars collecting above the ring • Use of ATP ○ Companion cells have many mitochondria ○ Translocation can be stopped by inhibiting ATP ○ Rate of flow of sugars is very high and some energy must be used to drive the flow • Mechanism ○ pH of companion cells is higher than surrounding cells ○ Concentration of sucrose is higher in the source than in the sink

Question 97

evidence contradicting the theory of translocation:

Answer 97

Evidence Against ○ Not all solutes in phloem move at the same rate ○ Sucrose is moved to all areas at the same rate, rather than quickly going to areas with lower concentrations ○ Role of sieve plates is unclear