Bio MYCTs

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Enzymes in Biotechnology Anthony Wu

It is:

- Industrial and commercial applications of biology

- Usually involves enzymes, GE and micro-organisms

Enzymes as industrial catalysts:

- Advantages:

Highly specific Efficient in small amounts Work at normal temperature & pressure

- Microorganisms > animals/plants to produce enzymes

Higher growth rates & more enzyme per body mass More economical use low cost substrates Easily genetically engineered Some can grow at extreme temp & pH fully functional at these conditions

Enzyme immobilization:

- Advantages:

Reusable Product is enzyme free (not contaminated)

Cost-effective

- Disadvantages:

Not as efficient as isolated- Procedure:

Prepare sodium alginate (2g) and distilled water (50cm3) mixture Prepare calcium chloride (1.4g) and distilled water (100cm3) mixture Mix together enzyme and sodium alginate solution Add drop by drop the mixture to the calcium chloride solution

Immobilised whole-cell enzymes (bacteria culture):

- Advantages:

Good when enzymes are expensive Good when enzymes are difficult/tedious to obtain Stable

- Disadvantages:

Much substrate used by bacteria for growth rather than conversion

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Optimum conditions to produce product may not be optimum conditions forbacteria growth

Immobilised cell-free enzymes (secreted by microorganisms):

- Advantages:

Easy to obtain in bulk No wasteful side reactions

- Disadvantages:

Some may be tedious to extractIndustrial uses of enzymes:

Dairy - Cheese manufacture to coagulate milk proteins - Rennin

Brewing - Reduce win/beer cloudiness

- Breakdown of starch to glucose for fermentation by yeast

- Protease

- Amylase

Food - Produce fructose syrup from glucose

- Fruit juice increase volume of extracted juice, remove

cloudiness from pectin

- Pre-digestion of baby food

- Meat tenderisation breakdown tough collagen & tissue

- Glucose isomerase

- Cellulase, hemicellulose

- Pectinase

- Trypsin

- Bromelain

- Papain- Ficin

Textile - Remove starch from fibres - Amylase

Forestry

& paper

- Remove lignin from pulverised wood

- Partial breakdown of starch smooth paper

- Ligninase

- Amylase

Medicine - Remove blood clots in wounds - Trypsin

Properties of enzymes:

Work on specific substrates

Remain unchanged at end of reaction reusable Biological catalysts Work best at optimum pH & temp Gets denatured at high temperatures

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Biotechnology Anthony Wu

Fuelling the future:

BiofuelsFeeding the world:

Natural pesticide More productivity

o Prevent diseaseso Drought resistant

GM foodRevolutionising industry:

Cleaner, greener, more efficient Using enzymes

o Plastico Fermentationo Pasteurisationo Meat tenderisation, cleaning

Gathering information:

Genome sequencingo

Human Genome Project (HGP) DNA computing

Making copies:

Biological materials Stem cells tissue Clone organisms (Dolly the sheep)

Environment care:

Biofuels renewable Bioindicators Clean oils pills

Diagnosing & treating illnesses:

Prosthetics Genetic screening

o Customise treatment Vaccines from microorganisms

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Chemicals of Life Anthony Wu

Biological Molecules:

- Large complex molecules produced by living organisms

Carbohydrates:

- Made of elements: C, H, O

- General formula: CX(H2O)X

- 1g yields 16 kJ of energy

- 3 types:

Monosaccharides (C6H12O6)o Glucoseo Fructoseo Galactose

Disaccharideso Sucrose (cane sugar)o Lactose (milk sugar)o Maltose (malt sugar)

Polysaccharideso Functions:

Energy storage Ideally:

Compact & inert Mobilised quickly when food is unavailable

Starch & glycogen: Large & insoluble in water Foldable into compact shapes Easily converted to sugars by hydrolysis

Structural support Cellulose plants Chitin fungi

o Formed though enzyme-mediated dehydration synthesiso Also called glycans, differing in:

Nature of recurring monosaccharides Length of their chains Degree of branching

- Dehydration synthesis/condensation reaction:

Formation of complex molecule from the bonding of 2 simpler molecules withthe removal of a molecule of water

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E.g.: Glucose + Fructose Sucrose + Water Glycosidic bond between monomers

- Hydrolysis:

Opposite of dehydration synthesis:o Sucrose + Water Glucose + Fructose

- Function:

Source of energy Form supporting structures (cellulose, chitin) Formation of nucleic acids (DNA & RNA) Synthesize lubricants (mucus, etc.) Produce nectar in flowers to attract insects for pollination

- Benedicts test:

For reducing sugars (All monosaccharides and disaccharides except sucrose) Add equal volume of benedicts solution and sample. Shake. Heat solution in

boiling water bath

Positive test: coloured precipitate observed:o Green (less) Yellow Orange Red Brick-red (more)

Negative test: Solution remains blue

- Iodine test:

For starch Add a few drops of iodine solution to unknown sample Positive test: Blue-black mixture observed Negative test: Mixture remains yellowish-brown

Lipids:

- Made of elements: C, H, O

- No fixed molecular formula/ratio

- Much more H than O


- Types:

Animal & vegetable fatso Triglyceride:

3 fatty acids + 1 glycerol molecule Formation dehydration synthesis

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Breakdown Hydrolysis Forms ester bonds between glycerol & fatty acids

Phospholipidso Constituent of cell membranes

Steroids (e.g.: cholesterol) Saturated fats:

o No double bonds present in fatty acid chaino Found in animals (pork, beef etc.)

Monounsaturated fats:o Presence of 1 double bond in fatty acid chaino Examples (Olive oil, peanut oil, avocado, salmon, mackerel, trout etc.)

Polyunsaturated fats:o Presence of 2 or more double bonds in fatty acid chaino Found in many nuts (Sunflower oil, corn oil, soybean oil, almonds,

cashews, walnuts, macadamia)

- Function:

Source & store of energy Insulating material prevent heat loss Solvent for fat-soluble vitamins (Vitamin A, D, E, K) & hormones (sex hormones

etc.) Constituent of cell membranes (phospholipids) Restrict water loss from skin surface Production of sex and growth hormones from cholesterol

- Overconsumption:

Increase in blood levels of cholesterol Excess cholesterol deposits on inner walls of arteries atherosclerosis High blood pressure & blood clot formation blockage in coronary arteries

heart attack

- Ethanol-emulsion test:

For all lipids Add 2cm3 of ethanol to a drop of sample oil. Shake thoroughly Add 2cm3 of water to mixture and shake. Positive test: White milky emulsion formed & heat is evolved Negative test: No emulsion observed

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Proteins:

- Made of elements: C, H, O, N, (sometimes S & P)

- Basic unit = amino acid

- Dehydration synthesis forms larger structures dipeptides, oligopeptides, polypeptides

etc.


- Structure:

Amino group + R group + Carboxyl group R groups:

Group Characteristics Names Example

Non-polar Hydrophobic Ala, Val, Leu, Ile, Pro,

Phe, Trp, Met

Leu: CH2CH(CH3)2

Polar Hydrophilic Gly, Ser, Thr, Cys, Tyr,

Asn, Gln

Thr: CH(OH)CH3

Acidic Negatively charged Asp, Glu Asp: CH2COOH

Basic Positively charged Lys, Arg, His Lys: (CH2)4NH3+

Linkages peptide bonds- Sources:

Animalo Meat, eggs, milk, seafood, liver

Planto Peas, beans, nuts

- Function:

Synthesis of protoplasm (i.e.: nucleus, cytoplasm, cell membrane) repair andgrowth of body cells

Synthesis of enzymes and some hormones (e.g.: insulin)

Formation of antibodies to combat diseases Source of energy

- Types:

Globular proteinso Transport protein haemoglobin (transport of oxygen from lungs to

body), membrane pumps (transport molecules across cell membranes)

o Enzymes speed up rate of chemical reactionso Antibodies destroy invading bacteria (immunity)

Structural proteins

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o Collagen (component of bone, tendon, teeth, skin)o Keratin (hair & nails)

- Biuret test:

Add 1cm3 of sodium hydroxide solution to 2cm3 of protein solution. Shakethoroughly

Add copper sulphate solution to mixture, drop by drop, shaking after each drop Positive test: Violet/purple colouration is observed Negative test: solution remains blue

Summary of molecules:

Class Monomer Polymer

Carbohydrate Monosaccharides (e.g.: Glucose etc.) Polysaccharide (e.g.: starch etc.)

Lipids Fatty acids; Glycerol NA

Proteins Amino acids Protein (e.g.: Haemoglobin etc.)

Nuclei Acids Nucleotides DNA, RNA

Water:

- 70-80% of cells made of water

- Universal solventmost common medium of chemical reactions (e.g.: hydrolyticreactions of digestion)

- Transporting agent for digested food substances, hormones & excretory products from

one part of the body to another

- Essential component of lubricant (e.g.: in joints, blood & digestive juices)

- Raw material for photosynthesis

- Temperature-regulation excess body heat removed through evaporation

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Photosynthesis & Leaf Structure Anthony Wu

Structure of typical leaf:

- 3 Parts:

Leaf blade (Lamina) Leaf stalk (Petiole) Leaf veins

- 2 types:

Simple leaf Compound leaf

- Characteristics:

Lamina:o Large flat surface

Increase surface area & maximise exposure to sunlighto Thin

Allow carbon dioxide to reach inner cells rapidly Enables sunlight to reach all mesophyll cells

Petiole:o Hold leaf away from stem

Absorb maximum sunlighto Continues into leaf bladeo

Sessile leaves

no petiole Veins:

o Carry water and mineral salts to cells in laminao Carry manufactured food from leaf blade to others parts of the planto Dicotyledonous plants network veins, lateral rootso Monocotyledonous Parallel veins, fibrous roots

- Internal structure:

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Epidermis:o Thin, waxy cuticle layer reduces water losso Single layer of closely packed cellso Keeps leafs shapeo Reduces evaporation from the leaf, preventing bacteria and fungi from

getting in

o Focuses light on mesophyll layers Mesophyll:

o Below epidermiso Site of photosynthesiso Split into 2 regions:

Palisade tissue Long, contain many chloroplasts Chloroplasts absorbs suns energy to make carbohydrates

from carbon dioxide and water

Spongy tissue Irregularly shaped

Loosely arranged to created air spaces among them allow rapid diffusion of carbon dioxide

Also contains chloroplastso

Chloroplasts: Oval shaped containing chlorophyll Grana:

Stacks of membranes or thylakoids Light dependent reactions sited here

Stroma: Enzymes for light independent stage here

Stomata:o Found in epidermis (more on lower in most dicots)o Consists of a pair of guard cells surrounding a stomatal poreo Guard cells bean-shaped, contain chloroplastso Regulation:

During sunlight hours, potassium ions enter guard cellsdecrease water potential

Water enters guard cells via osmosis Guard cells swell and become turgid (one side has thicker

cellulose cell wall) pore opens

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At night, potassium ions leave guard cells water potentialincreases

Water leaves guard cells Guard cells become flaccid pore closes

o Regulation controls water losso Entry of carbon dioxide into leaf:

CO2 used up during photosynthesis concentration decreases Diffusion gradient exists CO2 diffuses through stomata into

system of air space in leaf

CO2 dissolved in thin film of water on mesophyll layer cells diffuse into solution of cells

o Water from xylem leaf Water and dissolved mineral salts diffuse from cell to cell of

mesophyll cells after exiting veins

Photosynthesis:

- Definition:

Light energy absorbed by chlorophyll and transformed into chemical energyused in the synthesis of carbohydrates from water and carbon dioxide. Oxygen Is

liberated in the process exact phrasing

- Importance:

Converts light energy from sun to chemical energy stored in carbohydrates Carbohydrates, proteins, fats form other organic compounds fills food

requirements

Energy in coal, petroleum & natural gas comes from sun via photosynthesis Purifies air by removing carbon dioxide and releasing oxygen

- Heterotrophs:

Unable to make own food feed on other organisms Completely dependant on photoautotrophs for food & oxygen

- Conditions:

Chlorophyll Light Carbon dioxide Water Temperature (enzymes light independent)

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- Light dependent stage:

Energy from sun absorbed by chlorophyll and converted to chemical energy Light energy splits water molecules to oxygen & hydrogen 12H2O (photolysis) 6O2 + 24H

- Light independent stage:

Hydrogen used to reduce carbon dioxide to carbohydrates (glucose) Light dependent stage provide energy 6CO2 (energy) C6H12O6 + H2O

- Equations:

Carbon dioxide + Water (chlorophyll, light) Glucose + Oxygen 6CO2 + 12H2O (chlorophyll, light) C6H12O6 + 6H2O + 6O2

- Limiting factors:

Any factor that directly affects a process if its quantity is changed Photosynthesis:

o Concentration of CO2 (most important under normal environmentalconditions)

o Light intensityo Temperature

- Glucose:

Used in tissue respiration to provide energy for cellular activities

Make cellulose cell walls Excess converted to sucrose, transported to storage organs as starch or other

forms

In large amounts, temporarily stored as starch in leaves In darkness, photosynthesis stops and starch is reconverted by enzymes to

simple sugars

Fats formed from glucose Reacts with nitrates & other mineral salts to form amino acids, which combine to

form proteins

Excess amino acids stored as proteins build new protoplasm in leaves or growingplant parts

- Enzymes used:

StarchMaltose diastase Maltose Glucosemaltase Proteins Peptones pepsin Peptones Amino acids erepsin Fats Fatty acids and glycerol lipase

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Respiration Anthony Wu

Cellular respiration

Definition:

- Oxidation of food substances releases energy

- Occurs in living cells energy released in the form ATP (Adenosine Triphosphate)

- 3 stages:

Glycolysiso Occurs at cytosol of cello Input: Glucose + 2ATPo Output: 4ATP + 2NADH + 2H2O + 2 pyruvate

Krebs Cycle/tricarboxylic cycle/citric acid cycleo Occurs at mitochondrial matrixo Input: Pyruvateo Output: 2ATP + 8NADH + 2FADH2 + 6CO2

Oxidative phosphorylationo Occurs on inner membrane of mitochondriao Input: 10NADH + 2FADH2o Output: 34ATP + H2O

Energy:

- Uses Synthesis:

o Formation of new substances for growth, development & repair Transport:

o Active transporto Movement of materials across cell membranes

Movement:o Muscular contractions

Electrochemical activity:o Generation of nerve impulses

Heat production:o Maintain constant body temperature (warm-blooded animals)

Adenosine Triphosphate (ATP):

- Universal energy currency

- Constantly recycled

- Contains a lot of chemical energy

- Takes part in many metabolic reactions

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- Delivers energy in small amounts to drive individual reactions

- Involved in exergonic and endergonic reactions

- Formation:

Respiration & photosynthesis- ATP-ADP cycle:

ATP ADP & P + energy to do worko Active transporto Building moleculeso Muscle contractiono Working of neurons

Aerobic respiration:

- Respiration in presence of oxygen- Releases lots of energy

- Takes place in mitochondria of cells

- Equation:

Glucose + oxygen Carbon dioxide + water + lots of energy C6H12O6 + 6O2 6CO2 + 6H2O + lots of energy

Anaerobic respiration:

- Respiration in absence of oxygen- Releases a small amount of energy

- Yeast cells anaerobic respiration:

Ethanol & carbon dioxide produced fermentationo Used in wine making, bread making

Glucose Carbon dioxide + ethanol + small amount of energy C6H12O6 2CO2 + 2C2H5OH + small amount of energy

- Anaerobic respiration less efficient than aerobic:

Small amount of energy produced Lactic acid & ethanol produced

o Harmful to organisms if accumulatedo Contains much unused energy

Lactic acid can be converted back to sugar to be used for respiration Yeast cannot metabolise ethanol

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- Anaerobic respiration in muscles:

Muscular activity lack of oxygen in muscles Respiration not complete Lactic acid (CH3CHOHCOOH) built up Only first stage of respiration occurs (i.e. Glycolysis) 2ATP produced Accumulation of lactic acid muscle fatigue After rest [Cori cycle]:

o Lactic acid transported to livero Some oxidised to produce energy convert remaining lactic acid to

glucose

o Glucose transported to muscles for use Oxygen debt occurs

o Amount of oxygen required to oxidise the lactic acid produced in musclesduring anaerobic respiration

Glucose Lactic acid + small amount of energy C6H12O6 2CH3CHOHCOOH + 4H + small amount of energy

Respiration Photosynthesis

Energy liberated Energy stored in carbohydrate molecules

O2 used, CO2 & H2O released CO2 & H2O used, O2 given offCatabolic process, breakdown of glucose Anabolic process ; glucose is formed

Occurs all the time Occurs in presence of sunlight and chlorophyll

Results loss of dry mass Results gain of dry mass

External respiration

Inspiration:

- Process in which air is taken into the body- Principle:

Thoracic cavity expands Lungs expand to fill up enlarged space Expansion = lungs air pressure < atmospheric pressure Air rushes into lungs

- Breathing movements:

External intercostal muscles contract internal intercostal muscles relax Ribs swing upwards & outwards Sternum moves up and away from vertebral column

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^ Increases dorso-ventral diameter & breadth of thorax Diaphragm contracts & flattens ^ Enlarges thoracic cavity Volume of thorax increases air pressure decreases air enters lungs

Expiration:

- Process in which air is given out from the body

- Principle:

Thoracic cavity contracts Lungs contract Contraction = lungs air pressure > atmospheric pressure Air rushes out of lungs

- Breathing movements:

External intercostal muscles relax internal intercostal muscles contract Ribs lowered Sternum moves back near vertebral column Diaphragm relaxes & arches upwards ^ Decreases thoracic cavity Volume of thorax decreases air pressure increases air forced out of lungs

Lungs:- Organ dedicated to the exchange of gases between man and the environment

- 2 lungs present

- Located in the chest cavity

- Path of air to lungs:

Nasal passageso Air enters through nose/moutho Breathing through nose

Dust & foreign particles trapped by hair in nostril & mucus onmucous membrane

Air warmed and moistened Harmful chemicals detected by sensory cells in mucous membrane

Pharynxo Air passes into pharynx from nasal passage

Larynx [voice box]o Extends to chest cavityo Supported by C-shaped rings of cartilage

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Tracheao Air passes to trachea through an opening, the glottiso Divides into left and right bronchuso Supported by C-shaped rings of cartilageo Epithelium lining bears gland cells

Secretes mucus trap dust particles & bacteria Bear cilia sweep dust particles into pharynx

Bronchio Left bronchus divides into 2 bronchial tubeso Right bronchus divides into 3 bronchial tubeso Supported by C-shaped rings of cartilageo Epithelium lining bears gland cells

Secretes mucus trap dust particles & bacteria Bear cilia sweep dust particles into pharynx

Bronchioleso Ends in cluster of alveoli

Alveolio Thin, moist and well vascularised wallso Site of gaseous exchangeo Indicates large surface area for gaseous exchange

- Other structures:

Ribso Supports chest wallo Front attached to sternum (chest bone)o Back attached to vertebral column (backbone)o 12 pairs of ribs, first 10 attached to sternum

Intercostal muscleso External and internal muscles between ribso One set contracts, other set relaxeso Moving up and down change volume of thoracic cavity

- Gaseous exchange:

Air entering lungs more oxygen, less carbon dioxide Blood entering lungs less oxygen, more carbon dioxide ^ Diffusion gradient present, maintained by

o Continuous flow of blood through blood capillarieso Continuous flow of air through alveoli

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Membrane separating blood capillaries from alveolar air permeable to bothgases

Oxygen:o Dissolves in moisture lining alveolar walls

Why? To prevent formation of air bubble could cause strokeo Dissolved oxygen diffuses into bloodo Combines with haemoglobin to form oxyhaemoglobin

Haemoglobin contains porphyrin ring structure (heme group) withferrous iron (Fe

2+) covalently binded, which reversibly binds O2

Hb + 4O2 HbO8 Carbon dioxide:

o H2O + CO2 H2CO3 H+ + HCO3-o When CO2 concentration is low, carbonic anhydrase catalyse reaction in

which hydrogen carbonates converted to carbon dioxide and water

o % transported: Dissolved in plasma (7%) Bound to haemoglobin (23%) Dissolved as bicarbonate in plasma (70%)

o Diffuses out of blood into alveolar cavitieso Water evaporates from walls of alveoli

Inspired air Expired air

21% oxygen 16% oxygen

0.03% carbon dioxide 4% carbon dioxide

78% nitrogen 78% nitrogen

Water vapour variable Water vapour saturated

Temperature variable Body temperature (~37o)

Dust particles may be present Dust particles absent

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Gills:

- Countercurrent mechanism:

Water flows in opposite direction to blood Concentration gradient of oxygen is maintained Diffusion is more efficient and fast

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Plants Anthony Wu

Transport in plants

Xylem:

- Vascular tissue that transports water & mineral salts

- From roots to leaves of the plants

- Provides mechanical support to the plants

- Xylem cells dead at functional maturity

No protoplasm, hollow provide unimpeded flow of water No complete end walls water can flow easily from one cell to the next

- Lignin deposited on cell wall

Hard & rigid to provide support & prevent collapse

Phloem:- Vascular tissue that transports sugars and other food substances

- From photosynthesizing/storage regions to other plant parts

- Photosynthesizing & storage regions high amount of sugars

Photosynthesizing parts glucose Transport sugar sucrose Storage sugar starch

- Made of sieve tubes cells stacked upon one another

Degenerate protoplasm (lost nucleus & most organelle & almost all centralvacuole) provide unimpeded flow of sugars

Sieve plates with sieve pores between cells to allow flow of substances- Companion cell associated with each sieve tube cell

Dense cytoplasm (lots of mitochondria)- Provide energy for sieve tube to survive & carry out active transport

Monocotyledons vs. Dicotyledons:

- Based on no. of cotyledons found in seeds

Seed leaves Veins in

leaves

Vascular bundles Flower parts

Monocots (e.g.: maize,

orchids, rice, garlic, onion)

One cotyledon Parallel Scattered Multiples of threes

Dicots (e.g.: rose, hibiscus,

magnolia, apple, avocado)

Two cotyledons Netlike Arranged in ring Multiples of fours

and fives

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Stems:

- Epidermis

Outer layer (waterproof)- Cortex

Stores food & provides plant support Made of parenchyma cells

- Pith

Stores food & provides plant supportMade of parenchyma cells

- Phloem + Xylem = Vascular bundle

Monocots Dicots

Arrangement of vascular bundle Scattered about in cortex Arranged in a ring

Cambium (produces xylem & phloem cells) Absent Present

Pith Absent Present

Roots:

- Casparian strip

Controls entry of substances into xylem Waterproof

- Pericycle

Gives rise to branch roots- Endodermis

Delineates a boundary for the stele- Casparian strip + Pericycle + Endodermis = Stele

Monocots Dicots

Arrangement of tissue Xylem & Phloem arrangedalternate with each other in a ring

Xylem found in the middle in a 4-5 prongedstar shape with phloem arranged alternatingly

Central Pith Present Absent

Leaves:

- refer to leaves notes -

Monocots Dicots

Mesophyll layer No differences 2 distinct regions palisade & spongy

Stomata Both sides Only underside

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Path of water & minerals:

- Water around soil particles root hairs xylem of roots xylem of leaves

- Proof xylem transports water:

If leaf shoot kept in dyed water is cut, only xylem is stained Plant only wilts when xylem is removed, not phloem Mineral ions found in xylem sap

- Water from soil Root hairs:

Water enters plant through epidermal extensions (root hairs) at piliferous layer Layer of dilute salt solution around root hair cells Water enters root hair cell by osmosis due to presence of potential gradient Ions enter root hair cell via diffusion & active transport lower water potential Root hair cells increase surface area to volume ratio for efficient absorption Root hair cell contains a lot of mitochondria provide ATP for active transport

- Root hairs Xylem:

Water must move through cells to reach xylem Moves cell to cell through cortex, endodermis & Pericycle by osmosis to reach

xylem

Mineral ions move via diffusion

3 paths:o Apoplastic (continuum of cell walls)o Symplastic (continuum of cytosol through plasmodesmata)o Transmembrane (from vacuole to vacuole through cell wall)

Casparian strip (waterproof)o Water & dissolved ions cannot pass through apoplastically, only

symplastically or transmembrane

o Acts as selective sentry, controlling transport of certain materials- Xylem Leaves (3 ways):

Root pressure:o Root cells pump ions into xylem actively decreases xylem water

potential

o Water enters by osmosis, pushes xylem sap upwardso Only useful for small plants, ineffective in large trees

Capillary action:o In narrow vessels, water moves up by capillary action because of

Adhesive forces between water molecules & walls of vessel

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Cohesive forces between water moleculeso Why? Water has high surface tension strong hydrogen bondso Only up to 3m, ineffective in large trees

Transpiration pull:o Loss of water vapour from aerial parts of plant (esp. leaves)o Main factor that transports water to leaveso Steps:

Water leaves mesophyll cells to form a layer of moisture aroundthe cells

Moisture evaporatesmoves into intercellular air spaces Water vapour escapes by diffusion via stomata Evaporation causes mesophyll to become try Mesophyll cells absorb water from neighbouring cells absorb

from xylem

Results in suction force pulling column of water up xylem vessels(cohesive & adhesive forces)

Effective for over 100mPath of food substances:

- Process is active requires ATP

- Proof phloem transports food: Carbohydrates exudes from cut phloem Removal of phloem accumulation of sugars Radioactive tracing using 14CO2 Material in feeding aphids stylets are sugars

- Translocation:

Transport of manufactured food substances Bidirectional Much controversy on mechanism for translocation

- Mass Flow Hypothesis

Source = Photosynthetic organ capable of producing sugar Sink = Organ that stores/consumes sugar Loading sugars into source decreased water potential water enters by

osmosis

Created high pressure at sources compared to sink sap flow towards sink Sugars in sink increased water potential water leaves to xylem by osmosis

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Summary: Sugars move from source to sink, water recycled from xylem Experimental evidence:

o Aphids along phloem severed at styleto Closer to source sugar exuded out faster

Limitations:o Does not explain existence of sieve plate impedes flow of sugars

Transpiration:

- Importance:

Draw water & minerals up from roots stem leaveso Water used in photosynthesiso Water keeps plant cells turgid keeps leaves spread out to trap sunlight

Evaporation cools plant loss of latent heat of vaporisation- Measuring:

Use potometero Measures distance air bubble moves over time

- Excessive transpiration

Transpiration rate > absorption ratemesophyll cells lose turgor wilting Wilting decreases exposed surface area to sun

o Advantages: Flaccid guard cells Closed stomata reduce transpirationrate

o Disadvantages: Insufficient H2O & lack of CO2 reduced photosynthesisrate

- Factors affecting transpiration:

Cuticle:o Thick

Waterproof cuticle makes it harder for water to pass through Transpiration rate decreases

o Thin Thinner layer makes it easier for water to pass through Transpiration rate increases

Stomata:o Closed

Closed stomata prevents water vapour from escaping Transpiration rate decreases

o Open Larger opening enable water to transpire easily Transpiration rate increases

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Boundary layer of air:o Thick

Slow diffusion of water vapour lower concentration gradient Transpiration rate decreases

o Thin Water vapour diffuses faster higher concentration gradient Transpiration rate increases

Humidity:o High

High humidity decreased concentration gradient Transpiration rate decreases

o Low Low humidity increased concentration gradient Transpiration rate increases

Temperature:o Low

Low temperatures air holds less water Reduces concentration gradient Transpiration rate decreases

o High

High temperatures

air holds more water Increases concentration gradient Transpiration rate increases

Light:o Dark

Stomata close in dark lack of photosynthesis Transpiration rate decreases

o Bright Stomata open in light photosynthesis Transpiration rate increases

Wind:o Weak

Weak/no wind cannot move boundary layer created by watervapour

Transpiration rate decreaseso Strong

Strong wind moves boundary layer created by water vapour Transpiration rate increases

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Plant adaptations:

- Xerophytes:

Adapted to survive in environments with little water Reduce rate of transpiration

o Thick cuticle forms waxy barrier preventing water loss E.g.: Most cacti

o Absence of true leaves limits water loss to stems only (fewer stomata) E.g.: Most cacti

o Reduction of surface area to volume ratio of leaves limits transpirationarea

E.g.: Pineo Sunken stomata moist air trapped there lengthens diffusion pathway

reduces evaporation & transpiration rate

E.g.: Sorghum Storage of water

o Succulent leaves & stems stores water E.g.: Bryophyllum, most cacti

o Extensive root system allows for efficient absorption of water over widearea

E.g.: Most succulent plants

- Hydrophytes:

Adapted to survive wholly/partially submerged in water Obtain oxygen & water

o Location of stomata floating plants only have on upper surface of leaf,absent in submerged plants oxygen directly absorbed through

diffusion

E.g.: Water lilieso Cuticle absent in submerged plants, only at floating plants top surface

E.g.: Hydrilla thin cuticle, Water lilies top surface only (thick)o Presence of xylem redundant, water can easily diffuse directly, flexible

stems might snap in strong current

E.g.: Absent in Hydrillao Presence of aeration (aerenchyma) Large air spaces between leaf cells

for buoyancy for plants to get more sun

E.g.: All floating plantso Root system Reduced root system, used for anchorage only

E.g.: Most hydrophytes

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