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Level Biology Curriculum.
An ultimate Guide to Exam Study
Guide 2025/2026.
Magnigication - ansThe number of times larger an image appears compared to the size of the object Magnification calculation - ansObjective lens x eyepiece lens Image size / actual size Using stage graticule - ans1) insert eyepiece graticule into x10 eyepiece
- place stage graticule on microscope stage and bring into focus using low power objective (total mag=40)
- align eyepiece graticule and stage graticule. Check value of one eyepiece division at this mag
- 1mm = 40 eyepiece divisions
- each eyepiece divison 1000/40 = 25
- use x10 objective Lens on microscope and focus on stage graticule
- align then both
- 100 eyepiece divisions now correspond 1mm
- 1000/100 = 10 Nucleus - ansControl centre of cell Stores organisms genome Transmits genetic information Nuclear envelope - ansSeparates contents of nucleus from the rest of the cell Nucleolus - ansFound inside the nucleus and produces ribosomes RER - ansRibosomes attached Large surface area SER - ansSynthesis cholesterol Synthesis lipids/phospholipids Synthesis steroids hormones Golgi apparatus - ansStack membrane bound flattened scad Processes and packages proteins Mitochondria - ansSite of ATP production during aerobic respiration Fluid filled matrix Folded into cristae Chloroplasts - ansSite of photo synthesis Plant cells Stacks flattened membranes ( thylakoids ) Vacuole - ansFilled with water and solutes Maintain cell stabilityv Lysosomes - ansEngulf old organelles and foreign matter then digest Formed from Golgi apparatus Cilia - ansBeat and move mucus Ribosomes - ansSynthesise proteins Small spherical Attached to RER Centrioles - ansCell organelle that aids in cell division in animal cells only Formation cilia
Level Biology Curriculum.
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Two bundles mucrotubules right angle Cytoskeleton - ansA network of fibers that holds the cell together, helps the cell to keep its shape, and aids in movement Cellulose cell wall - ansThe rigid cell wall which surrounds plant cells. How insulin is made - ans1) mRNA copy of instructions for insulin made in nucleus
- mRNA leaves nucleus through nuclear pore
- mRNA attached to a ribosome on RER leads to assemble protein (insulin)
- insulin molecules pinched off in vesicles travel towards Golgi apparatus
- vesicles fuse with Golgi apparatus
- process and package insulin molecules ready for release
- insulin pinched off in vesicles move towards plasma membrane
- vesicles fuses
- exocytosis Similarities of Prokaryotes and Eukaryotes - ansPlasma membrane Cytoplasm Ribosomes DNA RNA Differences of Prokaryotes and Eukaryotes - ansSmaller Less developed cytoskeleton No nucleus No membrane bound organelles Peptidoglycan Smaller ribosomes Naked dna Flagella Pili binary fission - ansA form of asexual reproduction in which one cell divides to form two identical cells. covalent bond - ansA chemical bond that involves sharing a pair of electrons between atoms in a molecule condensation reaction - ansTwo molecules join with the removal of water hydrolysis reaction - ansTwo molecules split by addition of water hydrogen bond - ansWeak interaction Slightly negative and slightly positive charge water as a liquid - ansprovide habitats major component of tissues in living organisms medium for chemical reactions effective transport medium density of water - ansmore dense as it gets colder up until 4 degrees then due to polarity will become less dense stable environment insulate bodies of water
Level Biology Curriculum.
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Guide 2025/2026.
Polysaccharide examples - ansamylose, amylopectin, glycogen Amylose - anscoils into spiral alpha glucose molecules 1 - 4 glycosidic bonds less soluble unbranched Amylopectin - anscoils into spiral shape alpha glucose molecules 1 - 4 and 1-6 glycosidic bonds branched glycogen - ansin mammals smaller chains, less tendency to coil 1 - 4 and 1-6 glycosidic bonds branched more compacted (easier to snip off) Cellulose - ansplant cell walls long chains 15,000 beta glucose molecules condensation reaction glycosidic bonds second molecule turned 180 degrees microfibrils - ans60-70 cellulose cell walls joined 10 - 30 nm in diameter bundle in to macrofribrils embedded in pectins plant cell wall structure and function - anscellulose macrofibrils run in all directions glycosidic and hydrogen bonds provide high tensile strength hard to digest fully permeable can be reinforced with other substances bacteria cell wall - anspeptidoglycan exoskeleton cell walls - anschitin lipids - ansgroup of substances soluble in alcohol rather than water examples of lipids - anstriglycerides, phospholipids, steroids Trigylcerides - ansglycerol + 3 fatty acids condensation reaction ester bonds Saturated triglycerides - ansNo double bonds Tend to be solid at room temp unsaturated triglycerides - ansdouble bonds liquid at room temp Phosopholipids - ansphosphate + two fatty acids condensation reaction
Level Biology Curriculum.
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hydrophilic head hydrophobic tail micelle phospholipid bilayer (cholesterol) Cholesterol - anssteroid alcohol lipid 4 carbon based rings hydrophobic molecule regulates fluidity of membrane amino acids - ansN-C-C amino group r group carboxyl group dipeptide - ansTwo amino acids bonded together peptide bond (polypeptide) primary structure - anssequence of amino acids hydrogen bonds secondary structure - ansEither an alpha helix or a beta-pleated sheet. hydrogen bond tertiary structure - ansprecise shape supercoiled or spherical hydrogen bonds ionic bonds disulfide bonds quaternary structure - ansResults from two or more polypeptide subunits. hydrogen bonds ionic bonds disulfide bonds fibrous proteins - ansregular, repetitive sequences amino acids insoluble form fibres structural function fibrous proteins examples - anscollagen (mechanical strength) keratin (strong eg. hair, nails, horns) elastin (skin stretch around bones) globular proteins - ansspherical shape hydrophobic R groups turned inwards hydrophilic R groups turned outwards soluble specific shapes roles as enzymes, hormones, haemoglobin) globular protein examples - anshaemoglobin
Level Biology Curriculum.
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bases with a single-ring structure antiparallel sugar-phosphate backbone - ans5 end is where phosphate group attached to 5th carbon of deoxyribose (left) 3 end is where phosphate group is attached to 3rd carbon of deoxyribose (right) very stable semi-conservative replication - ansin each new DNA double helix, one strand is from the original molecule, and one strand is new DNA replication steps - ans1) helix unwinds
- helicase enzyme unzips
- free phosphorylated nucleotides in nucleoplasm bonded to exposed bases
- dna polymerase catalyses addition new nucleotide bases in 5 and 3 direction to single strands of dna using it as a template
- leading strand is synthesised continuously and the lagging strand is in fragments
- later joined by ligase
- hydrolysis activated nucleotides to release extra phosphate makes phosphodiester bond RNA - ansribose uracil single strand shorter chain mRNA, tRNA, rRNA genetic code - ansuniversal: all organisms have same triplet DNA bases code for same amino acids degenerate: for all amino acids there are more than one base triplet non-overlapping: read starting at fixed point in groups of three bases transcription - ans1) gene unwinds and unzips
- H bonds between complementary nucleotide bases break
- RNA polymerase catalyses the formation of temporary H bonds between complementary nucleotides and unpaired bases (A-U)
- the length RNA complementary to template strand of gene is produced, coding strand
- mRNA passes out the nucleus through envelope and attaches to ribosome Translation - ans1) tRNA brings amino acids and find their place when anticodon binds by temp H bonds to complementary codon on mRNA molecule
- ribosome moves along length mRNA when two amino acids adjacent peptide bond forms
- energy in form ATP needed for polypeptide synthesis
- after assembled mRNA breaks down and can be recycled into new lengths
- chaperone proteins fold protein into 3D shape Active site of an enzyme - ansthe region of an enzyme that attaches to a substrate Intracellular enzymes - answork inside the cell where they control cell metabolism (eg respiration). catabolic: metabolites broken down into smaller anabolic: synthesise larger molecules
Level Biology Curriculum.
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Extracellular enzymes - ansenzymes that act outside of the cell in which they are produced amylase trypsin prosthetic group - ansA non-protein, but organic, molecule (such as vitamin) that is covalently bound to an enzyme as part of the active site. eg. zinc + carbonic anhydrase Cofactors - ansAny nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis coenzyme - ansorganic cofactor B folic acid B B B lock and key hypothesis - ansThe idea that enzymes are specifically shaped to fit only one type of substrate induced fit hypothesis - ansTheory of enzyme catalysis which states that the partial binding of a substrate to an enzyme alters the structure of the enzyme so that its active site becomes complementary to the structure of the substrate, enabling binding. Enzymes and temperature - ansgain KE increase collisions ES complexes increase optimum vibration break H bonds breaks tertiary structure denatured Rate of reaction equation - ans1 / time taken to reach end point temperature coefficient (Q10) - ansa measure of how much the rate of a reaction increases with a 10 °C temperature increase. enzymes and PH - ansH bonds hold structures like alpha helix in place as H+ increases the positive charges are attracted to the negative charges so replace the H bonds work at narrow range PH buffers - ansresists changes in PH can donate or accept H+ eg. haemoglobin Enzymes and substrate concentration - ansincreased substrate conc leads to increased ROR substrate conc limiting factor all enzymes present at max rate so no longer limiting factor all active sites activated enzymes and enzyme concentration - ansenzyme concentration is limiting factor
Level Biology Curriculum.
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facilitated diffusion - ansmovement of molecules from an area of high concentration to low across a partially permeable membrane via protein channels or carriers does NOT involve ATP molecules in facilitated diffusion - anssmall polar molecules / ions = protein channels large molecules / glucose = carrier protein maintaining concentration gradients - ansO2 diffusing into cytoplasm of respiring cells then diffusing into mitochondria for aerobic respiration CO2 diffusing into palisade cell of plant leaf will then diffuse into chloroplasts for photosynthesis factors affecting diffusion - anstemperature diffusion distance surface area size of diffusing molecule concentration gradient Osmosis - ansmovement of water molecules from an area of high to low concentration through a partially permeable membrane water potential - ansthe tendency for water molecules to diffuse from one region to another pure water has highest wp more solute = lower wp equal = no net osmosis Cytolysis - ansanimal cell swells and bursts if a lot of water molecules enter as the plasma membrane breaks Crenated - ansanimal cell shrivels due to loss of water turgid - ansplant cell swells and contents push against cell wall to resist any further swelling and helps support Plasmolysed - ansplant cell loses water and shrinks so membrane pulls away from cell wall tissues are flaccid active transport - ansmovement of substances from a low to high concentration across a cell membrane using ATP and carrier proteins bulk transport - anstransport large molecules that are too large to pass through plasma membrane requires ATP Endocytosis - ansbulk transport into the cell phagocytosis pinoendocytosis Exocytosis - ansbulk transport out of the cell synapses Temperature and permeability - anstemperature drops:
- saturated fatty acids compress
- unsaturated fatty acids maintain fluidity
- cholesterol acts as buffer to prevent reduction in fluidity
Level Biology Curriculum.
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temperature increases:
- phospholipids get more KE
- move in random way gains fluidity
- some enzymes drift sideways
- cholesterol acts as buffer cell cycle - ansG1: growth, increase in size make sure cell ready for S phase G0: resting phase apoptosis, differentiation, senescence S phase: synthesis committed to completing cell cycle DNA replicates active in all cells duplicated first G2: ensure cell ready for mitosis stimulate proteins that make chromosomes condense M: prophase metaphase anaphase telophase cytokenesis Mitosis - ansasexual reproduction growth tissue repair genetically identical diploid prophase - ansChromosomes become visible, nuclear envelop dissolves, spindle forms metaphase - ansChromosomes line up in the middle of the cell attached by centromeres anaphase - ansPhase of mitosis in which the chromosomes separate and move to opposite ends of the cell telophase - ansthe separated chromosomes reach the poles and new nuclear envelope forms cell now contains two nuclei genetically identical Cytokinesis - ansdivision of the cytoplasm
Level Biology Curriculum.
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cells close together form continuous sheets receive nutrients by diffusion and tissue fluid short cell cycles divide 2/3 times projection, absorption, filtration, excretion, secretion connective tissue - ansmatrix containing proteins and polysaccharides separates living cells within tissue and enables it to withstand forces blood, bone, cartilage, tendons, skin Cartilage - ansimmature cells = chondroblasts mature = chondrocytes hyaline cartilage covers end of long bones form c shape in trachea fibrous cartilage occurs in discs between vertebrae elastic cartilage makes up outer ear and epiglottis muscle tissue - answell vascularised contain myofilaments made up of proteins actin and myosin allows muscles to contract types of muscle tissue - ansskeletal, cardiac, smooth epidermal tissue - ansFlattened cells Lack chloroplasts and form protective covering over leaves, stems and roots Waxy cuticle vascular tissue - ansxylem phloem meristematic tissue - anscontains stem cells derived from cell differentiation found in cambium no chloroplasts thin cell walls no large vacuole Organs - ansA structure consisting of several tissues adapted as a group to perform specific functions. Tissues - ansGroups of cells with a common structure and function. human organ systems - ans stem cells - ansundifferentiated cells can become any cell pluripotent able to express all genes can divide by mitosis sources of stem cells - ansembryonic stem cells umbilical-cord blood adult stem cells induced pluripotent stem cells stem cell uses - ansbone-marrow transplants drug research
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development biology repair damaged tissues replacement lost tissues cells need to take in things like - anso2 & glucose cells need to excrete - answaste products like Co2 and urea exchange of substances depend on - ansSA:V ratio single celled organism - anssubstances diffuse directly in or out of cell due to small distance multicellular organism - ansbig distance, higher metabolic rate, small Sa:v ratio LARGE SA - anslong hairs so large SA helps increase absorption of water and mineral ions THIN - anseach alveolus made from single layer of alveolar epithelium, decrease the distance Good blood supply and ventilation - ansalveoli (air constantly replace) and fish gills (fresh water passes over) large capillary network. Maintain conc grad In fish gas exchanged between - ansblood and water as u breathe in air enters - ansTrachea Trachea splits into - ans2 bronchi, one bronchus leading to each lung each bronchus branches off into - anssmaller tubes called bronchioles the bronchioles end in small air sacs called - ansalveoli goblet cells - anssecrets mucus and traps microorganisms and dust particles in inhaled air stopping them from reaching alveoli cilia - ansbeat the mucus upward away from alveoli towards the throat where it is swallowed prevents lung infection elastic fibres - ansbreathing in, inflate and stretch, breathing out recoil smooth muscle - ansdiameter controlled, relax wider, contract smaller rings of cartilage - ansstrong, flexible, prevent trachea and bronchi from collapsing trachea - ansc shaped cartilage, smooth muscle, elastic fibres, goblet cells, ciliated epithelium bronchi - anssmaller pieces of cartilage, smooth muscle, elastic fibres, goblet cells, ciliated epithelium larger bronchiole - anssmooth muscle, elastic fibres, goblet cells, ciliated epithelium smaller bronchiole - anssmooth muscle, elastic fibres, ciliated epithelium smallest bronchioles - anselastic fibres alveoli - anselastic fibres Inspiration step 1 (IS1) - ansexternal intercostal and diaphragm muscle contract IS2 - ansCauses ribcage to move upwards and outwards and diaphragm to flatten, increasing volume of thorax IS3 - ansas vol increases , lung pressure decreases causes - ansair to flow into lungs ES1 - ansexternal intercostal and diaphragm muscles relax ES2 - ansribcage moves downwards and inwards and diaphragm becomes curved again ES3 - ansAs thorax vol decrease, lung pressure increases (greater than atmosphere) causes - ansair out of lungs inspiration is - ansan active process needs energy expiration - anspassive process Tidal volume - ansvolume air in each breath
Level Biology Curriculum.
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dissect gas exchange system in insects - anshumanely killed, fixed to dissection board exoskeleton - anshard protective structure developed outside the body to examine tracheae - anscut and remove a piece of exoskeleton use a syringe - ansfill abdomen with saline solution, should see network of very thin silvery- grey tubes these are the tracheae, look silver filled with air examine trachea under light microscope - ansuse wet mount, trachea silver or grey but should see rings of chitin in walls of trachea, for support fish circ system - ansheart pumps blood to gills to pick up o2 and the to the rest of the body to deliver o2 in a single circuit mammals - ansright side of heart pumps blood to lungs to pick up o2, from lungs, it travels to left side of heart which pumps to the rest of the body , blood returns to heart enters thru right closed circulatory system - ansblood enclosed in blood vessels heart pumps blood into - ansarteries arteries branch out into - ansmillions of capillaries o2 and glucose diffuse from blood into - ansCapillaries into body cells but bloods stays inside the blood vessels as it circulates veins take - ansblood back to heart open circulatory system - ansblood isn't enclosed in blood vessels, flows freely in the blood cavity heart is - anssegemented Heart contracts in a - answave. It starts - ansfrom the back pumping into a single main artery. Artery opens up - ansin body cavity blood flows around insect - ansorgans blood makes it way back into the heart thru - ansseries of valves circ system in insects supplies cell with - ansnutrients but doesn't supply oxygen though, this is done by system of tubes called the tracheal system Arteries - ansthick and muscular walls stretch and recoil, helps maintain the high pressure all artery carry oxygenated blood except - anspulmonary artery arterioles (smaller than arteries) - anssmooth muscle (expand and contract controlling blood flow) like arteries but less elastic tissue capillaries - anslarge sa:v and one cell thick, glucose and o2 exchanged venules - anssmall vessels that gather blood from the capillaries into the veins Veins - anscarry blood to the heart under low pressure, wider lumen, little elastic tissue all veins carry deoxygenated blood except - anspulmonary vein Tissue fluid - ansThe fluid surrounding the cells and tissues Unlike blood tissue fluid doesn't contain - ansrbcs or big proteins in a capillary bed - anssubstances move out of capillaries into tissue fluid by pressure filtration at start of capillary bed near the artery - anshydrostatic pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid. Difference in hydrostatic pressure - ansforces fluid out of the capillaries and into the spaces around the cells forming tissue fluid
Level Biology Curriculum.
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As fluid leaves - anshp reduces in capillaries so hp much lower at the venue end of the capillary bed oncotic pressure - ansgenerated by plasma proteins in capillaries which lower the water potential. Venule end - answater potential lower in capillaries than tissue fluid, some water reenters capillaries from tissue fluid via osmosis not all tissue fluid reenters capillaries - anssome excess tissue fluid returned to blood via lymphatic system smallest lymph vessels are the - ansLymph capillaries excess tissue fluid passes into - anslymph vessels Once inside lymph vessels tissue fluid is now known as - anslymph valves in lymph vessels stop - anslymph going backwards lymph gradually moves - anstowards the main lymph vessels in the thorax and returned to the blood near the heart thorax - anschest cavity RBCs - ansIn blood, no tf or lymph bc rbcs too big to get through capillary walls into tissue fluid WBCs - ansIn blood, very few in ft, in lymph. Only enter ft when infection platelets - ansin blood, only present in tissue fluid if the capillaries are damaged proteins - ansin blood, very few in tf and in lymph only most plasma proteins too big to get through capillary walls water - ansin all 3, tf and lymph have higher water potential than blood dissolved solutes - ansin all 3 and can move freely between them Av valves link - ansatria to ventricles SV link - ansventricles to the pulmonary artery and aorta Av and Sv prevent - ansblood flowing in the wrong way valves - ansonly open one way, whether valves open or closed depends on - ansrelative pressure of heart chambers higher pressure in front of a valve - ansforced shut higher pressure behind valve - ansforced open heart dissection equipment - anspig or cow heart, dissecting tray, a scalpel, an apron and lab gloves external examination - anstry identify 4 main vessels feel inside vessels to help you Arteries are .... veins... - ansthick and rubbery, thinner internal examination - anscut and look inside each ventricle, measure thickness, cut atria and note whether thinner or thicker than ventricle walls, find Av and Sv valves and look at their structure. Draw a sketch
- ventricles relax and atria contract 1 - ansventricles are relaxed , atria contract vol decrease and pressure increase.
- ventricles relax and atria contract 2 - ansThis pushes blood into ventricles through the AV valves
- ventricles relax and atria contract 3 - ansThis causes slight increase in ventricular pressure and volume
Level Biology Curriculum.
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bigger wave - ansmore electrical energy and stronger contraction Tachycardia - ansfast heart rate more than 100bpm bradycardia - ansslow heart rate (less than 60 bpm) ectopic heartbeat - ansextra heartbeat due to earlier contraction of atria or ventricles fibrillation - ansreally irregular heartbeat, atria or ventricles completely lose their rhythm and stop contracting properly, can cause fainting or even death HB - ansquaternary structure, 4 polypeptides, each chain one haem group with Fe2+, high affinity for o Haemoglobin equation - ansHb + 4O2 = HbO how does oxygen leave oxyhb - ansdissociate pO2 - ansmeasure of O2 conc pCO2 - ansmeasure of Co2 conc oxygen loads onto HB - ansto form oxyhb when high pO oxyhb unloads its oxygen - anslower pO o2 enters blood capillaries - ansat alveoli in the lungs, high po2 so o2 loaded when cells respire use up o2 - anslowers po2 unloads o when pO2 high eg lungs - anshigh affinity for o2 and will readily combine with oxygen so high saturation when pO2 low eg respiring tissue - anslow affinity for o2 release o2 rather than combine, so has low saturation of o fetus gets oxygen from its mother's blood across - ansplacenta By the time mother's blood reaches the placenta - ansits oxygen saturation had decreased for fetus to get enough oxygen to survive its hb - anshas to have higher affinity for oxygen (so takes up enough) if hb had same affinity for o2 as adult hb its blood - answouldn't be saturated enough most of co2 from respiring tissues diffuse into - ansRbcs to react with water to form carbonic acid, catalysed by enzyme carbonic anhydrase, rest of co2 around 10 percent binds directly to hb carbonic acid dissociates - ansH2CO3 = H + HCO increase in H+ ions causes - ansoxyhb to unload its oxygen so Hb can take up the H+ ions, forms a compound called haemoglobinic acid, this process stops H+ ions increasing cell acidity HCO3- ions - ansDiffuse out of the red blood cells and are transported in the blood plasma. to compensate for loss HCO3- from rbcs - anscl- ions diffuse into rbcs, this is called chloride shift, maintains balance of charge between rbc and the plasma when blood reaches the lungs the low pCO2 causes - anssome of the HCO3- and H+ recombine into Co2 and water CO2 diffuses into alveoli and is - ansbreathed out plants need substances like - answater, minerals and sugar plants need to get rid of - answaste substances like animals, plants are multicellular so - anslarge SA:V ratio, high metabolic rate, direct diffusion too slow xylem tissue transport - answater and mineral ions
Level Biology Curriculum.
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xylem tissue substances move only - ansup phloem tissue - anstransport sugars phloem tissue substances move - ansup and down the plant xylem and phloem make up - ansvascular system vascular system - anscollection of specialised tissues (like xylem and phloem) in some plants that transports mineral nutrients up from the roots and brings sugars down from the leaves In roots - ansxylem in centre surrounded by phloem for support for the root as it pushes thru the soil in stem - ansxylem and phloem are near the outside to provide a sort of scaffolding that reduces bending in a leaf - ansxylem and phloem make up network of veins which support thin leaves transverse crossections cut at - ansright angle to its length longitudinal cross sections - anstaken along the length of the structure xylem vessels - anslong tube like structure formed from vessel elements xylem vessel have no - ansend walls the cells are - ansdead so no cytoplasm they have lignin which is a - answoody substance to help support xylem vessels and stop them from collapsing inwards lignin can be deposited through different ways eg - ansspiral or distinct rings amount of lignin increases - ansas cell gets older water and ions move out of the vessel through - anssmall pits of the walls where there is no lignin phloem tissue transports - anssolutes like xylem phloem is formed from cells arranged in - anstubes but unlike xylem phloem is purely a - anstransport tissue not used for support phloem tissue contains - ansPhloem fibres, phloem parenchyma, sieve tube elements and companion cells. sieve tube elements - ansliving cells transporting solutes, joined end to end to form sieve tubes, sieve parts are end walls allowing solutes to move thru what is unusual about sieve tube elements - anseventhough living cells no nucleus, thin layer of cytoplasm and few organelles How is cytoplasm connected in STE - anscytoplasm of adjacent cells is connected through the holes in the sieve plates companion cells - ansThe lack of nucleus and other organelles in STE means can't survive on own so need cc to carry out living function eg. provide energy for active transport Dissecting plant stems 1 - ansuse scalpel to cut cross-section, cut section thinly as possible Dissecting plant stems 2 - ansuse tweezers to place cut sections in water until you come to use them. Stops them from drying out Dissecting plant stems 3 - anstransfer each section to a dish containing a stain and leave for one minute eg. toluidine blue O (TBO) - ansstains lignin in walls of xylem vessels blue green, let you see the position of the xylem vessels and examine their structure Dissecting plant stems 4 - ansrinse of the sections in water and mount each one onto a slide
