Biology: ALL 6 markers and long answer recall

Compare the structure and properties of triglycerides and phospholipids

Structure:

Triglycerides

• one glycerol attached to 3 fatty acid tails

• ester bonds between the fatty acids and glycerol

Phospholipids

• one glycerol, 2 fatty acid chains, one phosphate group

• phosphate group is hydrophilic - fatty acids tails are hydrophobic

• ester bonds

Properties:

Triglycerides

• energy storage

• insoluble in water so don’t affect water potential of cell

Phospholipids

• bilayer of cell membranes

• centre of bilayer is hydrophobic water

• soluble substances can’t pass through

Compare the structures and functions of starch, glycogen and cellulose

Starch

• polysaccharide of alpha glucose

• mixture of amylose and amylopectin - amylose is long, unbranded chains

• amylose coils, making it compact so good for storage

• amylopectin is long and branched

• amylopectin’s side branches are easily hydrolysed (by breaking glycosidic bonds) to release glucose quickly

Glycogen

• polysaccharide of alpha glucose

• very highly branched (more so than amylopectin)

• so stored glucose can be released quickly

• also compact so good for storage

Cellulose

• polysaccharide of beta glucose

• long, unbranched, straight chains

• cellulose chains linked by hydrogen bonds to form strong fibres called microfibrils

• so cellulose provides structural support for cells (plant cell walls)

How do you test for reducing and non-reducing sugars?

(all monosaccharides are reducing sugars, and some disaccharides - maltose and lactose)

Reducing sugars

- heat sample with Benedict’s reagent

- sample stays blue = no reducing sugar present

- sample forms green, yellow, orange, brick red ppt = reducing sugar present

Non-reducing sugars

- if stays blue with Benedict’s

- heat a new sample with dilute hydrochloric acid, then add sodium hydrogencarbonate (neutralises)

- heat sample with Benedict’s reagent

- sample stays blue = no non-reducing sugar present

- sample forms green, yellow, orange, brick red ppt = non-reducing sugar present

Describe the steps of an emulsion test

• add ethanol to sample

• shake

• add to water

• milky white emulsion = lipid

What is the structure of a protein?

Primary

• the sequence of amino acids

Secondary

• hydrogen bonds form between the amino acids

• coils into alpha helix, or folds into beta pleated sheet

Tertiary

• hydrogen bonds, ionic bonds and disulfide bridges form

• forming a 3D tertiary structure

Quaternary

• more than one polypeptide chain

What factors affect enzyme activity?

1. Temperature

• temp increase = rate increase, more kinetic energy, molecules move faster, more frequent collisions with enzyme active site

• up to a certain temp, if temp too high bonds can break in active site, changing its shape so enzyme is denatured

2. pH

• above and below optimum pH, ionic and hydrogen bonds holding enzyme’s tertiary structure in place are disrupted

• enzyme becomes denatured and active site changes shape

3. Substrate concentration

• higher substrate conc = faster reaction as collision between substrate and enzyme active site more likely

• up to a saturation point, where all active sites are occupied

4. Enzyme concentration

• more enzyme molecules = more likely collision with substrate and form ES complex

• but if amount of substrate is limited reach a point where adding more enzyme has no further effect

Compare the structure of DNA and RNA

Similarities

• both polynucleotides

• both have phosphodiester bonds

• both contain phosphate group and nitrogenous bases

Differences

• DNA is double stranded, RNA is single stranded

• DNA has a deoxyribose sugar, RNA has a ribose sugar

• DNA has bases A,T,G,C, RNA has bases A,U,G,C

• DNA is longer, RNA is shorter

Describe the structure of ATP, and enzymes involved in forming and breaking it

Structure:

• adenine, ribose sugar and 3 phosphate groups

ATP hydrolysed into ADP + Pi by ATP hydrolase (in hydrolysis reaction)

ATP formed by ADP + Pi by ATP synthase, in a condensation reaction

Describe and explain the useful properties of water

1. Metabolite: for condensation and hydrolysis reactions

2. Solvent: water is polar so ions dissolve for chemical reactions and transport

3. High latent heat of vaporisation: cooling effect for organisms (little water loss= lots of heat loss)

4. High specific heat capacity: buffer changes in temperature (to maintain stable internal conditions for enzyme function and makes water a good habitat)

5. Cohesive: allows water to flow in a column, and provides surface tension for pond skaters

Describe the importance of named inorganic ions

P

Iron ions:

• key component of haemoglobin - iron ion is what oxygen binds to

Hydrogen ions:

• H+ ions determine pH, more H+ = lower pH

• enzyme-controlled reactions are all affected by pH

Sodium ions:

• cotransport of glucose and amino acids

Phosphate ions:

• DNA, RNA, ATP all require phosphate ions to be made (phosphate group)

Describe the structure of a prokaryotic cell

• cytoplasm - contains small 70s ribosomes

• cell membrane

• cell wall - supports cell, made of meurin

• flagellum - allows movement

• circular DNA - not attached to any histones

• plasmids - small loops of DNA that can be passed between prokaryotes

• some have a capsule - protects from attack by immune system cells

Describe the process of binary fission

1. Circular DNA and plasmids replicate

2. DNA moves to opposite poles and cytoplasm divides

3. New cell walls form and two daughter cells are produced (one copy of circular DNA each, can have varied number of plasmids)

Describe viral replication for HIV

• attachment protein attaches to receptor protein on cell surface membrane of helper T cell (host)

• capsid released into cell, uncoats and releases RNA into cell cytoplasm

• reverse transcriptase makes a complementary DNA strand form the viral RNA

• double stranded DNA made and inserted into human DNA

• host cell enzymes used to make viral proteins

• viral proteins assembled into new viruses which are released from cell to infect others

Compare optical/light microscopes and electron microscopes

Optical:

• use light to form an image

• lower resolution - as light has longer wavelength (res of 0.2um)

• lower magnification (x1500)

Electron:

• use electrons to form an image

• higher resolution - as light has shorter wavelength (res of 0.0002um)

• higher magnification (x1,500,000)

• produce black and white images

Compare transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs)

TEMs:

• electrons transmitted through specimen

• denser parts absorb more electrons and appear darker

• can see internal structure of organelles

• give high resolution images

• can only be used on thin specimen

• require a vacuum so can only use non-living specimen

SEMs:

• scan a beam of electrons across the specimen

• images show the surface of the specimen and can be 3D

• can be used on thick specimen

• but give lower resolution images than TEMs

• can only use non-living specimen

How do you prepare a microscope slide?

1. Pipette a small drop of water onto the centre of a slide

2. Use tweezers to place a thin section of specimen on top of water drop

3. Add a drop of stain

4. Add a cover slip - avoid air bubbles as will obstruct view

Describe how to use ultracentrifugation to obtain a sample of nuclei

1. Homogenise tissue to break open cells

2. Filter to remove cell debris

3. Cold solution to prevent enzyme activity

4. Isotonic solution to keep same water potential to

prevent osmosis

5. Buffered solution to stop enzymes

denaturing

6. Centrifuge at low speed so nuclei in

pellet at bottom (discard supernatant)

What are the stages of mitosis?

1. Interphase

• DNA and organelles are replicated, ATP content is increased

2. Prophase

• chromosomes condense, getting shorter and fatter

• centrioles move to opposite ends of the cell forming spindle fibres

• nuclear envelope breaks down

3. Metaphase

• chromosomes line up in middle of cell and attach to spindle fibres by their centromere

4. Anaphase

• centromeres divide, separating each pair of sister chromatids

• spindles contract, pulling chromatids to opposite poles

• makes the chromatids appear V shaped

5. Telophase

• chromatids uncoil at the opposite poles

• nuclear envelope forms so there are now 2 nuclei

• cytoplasm divides (cytokinesis)

• there are now two daughter cells that are genetically identical

Describe the 3 separate stages of interphase

G1 - Gap phase 1

• cell grows and new organelles and proteins are made

S - Synthesis

• cell replicates its DNA, ready to divide by mitosis

G2 - Gap phase 2

• cell keeps growing and proteins needed for cell division are made

What is the formula for mitotic index?

Mitotic index = number of cells with visible chromosomes / total number of cells observed

How do you set up an optical microscope?

• clip the prepared slide onto the stage

• Select the lowest powered objective lens

• Use the coarse adjustment knob to bring the stage up to just below the objective lens

• Look down the eyepiece (containing ocular lens) and use coarse adjustment knob to move stage down until image roughly in focus

• Adjust focus with fine adjustment knob until have a clear image

Describe the stages of co-transport

• sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium-potassium pump

• creates a sodium concentration gradient (higher conc of sodium ions in lumen of ileum than cell)

• this causes sodium ions to diffuse from lumen of ileum into epithelial cells (down conc gradient) via sodium-glucose co-transporter proteins

• co-transporter carries glucose into cell with sodium, so glucose conc in cell increases

• glucose diffuses out of cell into blood through a protein channel by facilitated diffusion

Describe the differences between active and passive immunity

Active immunity

• requires exposure to antigen

• takes a while for protection to develop

• memory cells are produced

• protection is long term because antibodies are produced

Passive immunity

• doesn’t require exposure to antigen

• protection is immediate

• memory cells aren’t produced

• protection is short term because antibodies given are broken down

Describe the steps of a direct ELISA test

(testing for antigens in a patients blood sample)

• antigens from patient blood sample are bound to the inside of a well

• a detection antibody with an enzyme attached, that is complementary to the antigen is added

• if antigen is present it is immobilised on surface of well and detection antibody will bind to it

• well is washed out to remove any unbound antibody

• substrate solution is added, if detection antibody is present enzyme reacts with substrate to give a colour change (positive result)

Describe the steps of an indirect ELISA test

(testing for antibodies in a patients blood sample, uses 2 different antibodies)

• pathogen antigen is bound to bottom of well in a well plate

• sample of patient’s blood plasma added

• if there are any pathogen specific antibodies in the plasma these will bind to the antigen on the well

• well is washed out to remove any unbound antibody

• a secondary antibody with a specific enzyme attached is added

• the secondary antibody can bind to the pathogen specific antibody, well is washed out again

• if there’s no primary antibody in the sample, all of the secondary antibody will be washed away

• a solution containing substrate to the enzyme is added, colour change if antibodies are present in the blood plasma

Describe gas exchange in fish

• each gill is made of thin plates called gill filaments

• gill filaments are covered in lots of lamallae

• lamallae have lots of blood capillaries and a thin surface layer of cells

• these adaptations give a large surface area for gas exchange and a thin pathway so it can happen quickly

• blood flows through the lamallae in one direction and water flows over in the opposite direction - this is the countercurrent system

• means that water with high oxygen concentration always flows over blood with lower oxygen concentration, to maintain a steep diffusion gradient

Describe gas exchange in insects

spiracles —> trachea —> trachioles

• spiracles are pores on the surface of the insect

• abdominal muscles can contract to draw oxygen into the trachea down a concentration gradient, move air in and out of spiracles

• trachioles have thin, permeable walls and branch off

Describe the adaptations of xerophytic plants

• stomata sunk in pits so trap water vapour, reducing concentration gradient between leaf and air to reduce evaporation

• layers of hairs on epidermis so trap water vapour around stomata

• curled leaves with stomata inside so protect from wind (reduce diffusion and evaporation)

• reduced number of stomata so fewer places for water to escape

• thicker waxy cuticle on leaves and stems to reduce evaporation

Describe how we breathe in and out

Breathing in:

• external intercostal muscles contract

• diaphragm contracts and flattens

• rib cage moves up and out

• increasing volume of thoracic cavity

• and decreasing lung pressure, so air flows into lungs down a pressure gradient

Breathing out:

• external intercostal muscles relax

• diaphragm relaxes and becomes dome-shaped

• rib cage moves down and in

• volume of thoracic cavity decreases

• air pressure increases, forcing air out of lungs down pressure gradient

What is the partial pressure of oxygen like at different parts of the body?

Alveoli in lungs:

• high oxygen concentration

• High pO2

• High affinity for oxygen

• Oxygen loads

Respiring tissues

• low oxygen concentration

• Low pO2

• Low affinity for oxygen

• Oxygen unloads

Compare the different adaptations of arteries, arterioles and veins

Arteries

• thick, muscular walls

• with elastic tissue to stretch and recoil as the heart beats

• helps to maintain high pressure

• inner lining (endothelium) is folded allowing artery to stretch

• narrower lumen

Arterioles

• mainly circular muscle

• contract to restrict the blood flow or relax to allow full blood flow

Veins

• wider lumen

• carry blood under lower pressure

• very little elastic or muscle tissue

• contain valves to stop backflow of blood

How is tissue fluid formed?

• at start of capillary (arteriole end), hydrostatic pressure is higher than in tissue fluid

• forcing fluid out of capillaries into spaces around cells, forming tissue fluid

• as fluid leaves, hydrostatic pressure reduces in capillaries, so hydrostatic pressure is lower in the venule end

• due to fluid loss and increasing concentration of plasma proteins (which don’t leave capillary) water potential at venule end is lower than water potential of tissue fluid

• means some water reenters capillaries from tissue fluid by osmosis

• any excess tissue fluid is drained into lymphatic system

Describe the cardiac cycle

1. Ventricles relax, atria contract

• decreasing volume and increasing pressure of atria, pushing blood into ventricles

2. Ventricles contract, atria relax

• increasing ventricle pressure

• ventricle pressure becomes higher than atria, forcing AV valves shut to prevent backflow

• pressure in ventricles higher than in aorta and pulmonary artery so SL valve forced open, and blood moves out

3. Ventricles relax, atria relax

• higher pressure in pulmonary artery and aorta closes SL valve to prevent backflow

• blood returns to heart and atria fill again, cycle repeats

Cardiac output equation?

cardiac output = stroke volume x heart rate

Describe transpiration

• water evaporates from the leaf

• creating tension which pulls more water into leaf

• water molecules are cohesive, so stick together and form a continuous column of water

Describe the mass flow hypothesis (translocation)

1. Source

• sucrose is actively transported from companion cells into sieve tubes of phloem

• which lowers water potential inside phloem sieve tubes, so water enters the sieve tubes by osmosis form xylem and companion cells

• creates high hydrostatic pressure in sieve tubes at source end of phloem

2. Sink

• at sink end sucrose is removed from phloem to be used

• increasing water potential inside sieve tubes, so water also leaves by osmosis

• lowers pressure inside sieve tubes

3. Flow

• results in a pressure gradient from source to sink

• which pushes sucrose towards the sink

• higher concentration of sucrose at the source = higher rate of translocation

Compare mRNA and tRNA

mRNA:

• single stranded

• contains codons

• longer strand

tRNA:

• single stranded

• clover shaped

• contains anticodons

• has an amino acid binding site

Describe transcription

• hydrogen bonds between two DNA strands are broken by DNA helicase

• one of the strands is used as a template to make an mRNA copy

• free floating RNA nucleotides align with the exposed bases on the template

• by complementary base pairing (A-U, G-C)

• RNA nucleotides joined together by RNA polymerase

• mRNA detaches from the DNA when a stop signal is reached

Describe translation

• ribosome attaches to mRNA

• tRNA brings a specific amino acid to it

• ATP provides energy for bond to form between amino acid and tRNA molecule

• tRNA has an anticodon that’s complementary to the codon on the mRNA and a second tRNA molecule attaches in the same way

• the amino acids attached to the tRNA molecules are joined by peptide bonds

• using ATP

• process continues to produce a polypeptide chain until a stop signal is reached on the mRNA

Describe meiosis

1. DNA unravels and replicates so there are 2 copies of each chromosome, called chromatids

2. DNA condenses, 2 sister chromatids joined by a centromere

3. Meiosis I (1st division) - the chromosomes arrange themselves in homologous pairs

4. The homologous pairs separate

5. Meiosis II (2nd division) - the sister chromatids are separated (centromere divides)

6. Four genetically different haploid cells are produced

Explain what leads to genetic variation during meiosis?

Crossing over of chromatids

• homologous chromosomes pair up and bits of chromatid swap over

• the chromatids still contain the same genes but have a different combination of alleles

Independent segregation of chromosomes

• it is completely random which chromosome from each pair ends up in which daughter cell

Compare mitosis and meiosis

Mitosis

• produces cells with same number of chromosomes as the parent cell

• daughter cells are genetically identical

• produces 2 daughter cells

Meiosis

• produces cells with half the number of chromosomes as parent cell

• daughter cells are genetically different

• produces 4 daughter cells

What are the properties of ATP that make it a good energy source?

• ATP stores or releases only a small, manageable amount of energy at a time so no energy is wasted as heat

• It’s a small, soluble molecule so can be easily transported around the cell

• Easily broken down

• Can be quickly remade

• Can make other molecules more reactive by transferring one of its phosphate groups (phosphorylation)

• ATP can’t pass out of the cell

Describe the Calvin cycle

• CO2 combines with ribulose bisphosphate, catalysed by enzyme rubisco

• Gives an unstable 6C compound which breaks down into 2x glycerate 3-phosphate

• ATP provides energy to reduce GP (3C compound) to triose phosphate (3C)

• Requires H+ ions from reduced NADP

• Some triose phosphate is converted into useful organic compounds and some continues to regenerate RuBP

What are the products of glycolysis and where do they go?

• 2 reduced NAD - go to oxidative phosphorylation

• 2 pyruvate - actively transported into mitochondrial matrix for use in link reaction

• 2 ATP (net gain) - used for energy

What are the products of the link reaction and where do they go?

• 2 acetylcoenzyme A - go to Kreb cycle

• 2 CO2 - released as a waste product

• 2 reduced NAD - goes to oxidative phosphorylation

What are the steps of the Kreb cycle?

• acetylcoA combined with a 4C molecule to form citrate (6C)

• citrate is converted to a 5C compound, decarboxylation removing CO2

• dehydrogenation also occurs, H is used to reduce NAD

• 5C molecule converted to 4C molecule, decarboxylation and dehydrogenation produce one molecule of FAD and 2 reduced NAD

• ATP produced by ADP + Pi

Describe the processes that occur in the nitrogen cycle

Nitrogen fixation

• nitrogen gas in atmosphere converted to nitrogen-containing compounds

• carried out by bacteria

Ammonification

• nitrogen compounds from dead organisms are turned into ammonia

• by saprobionts

• which goes in to form ammonium ions

Nitrification

• ammonium ions in the soil changed into nitrogen compounds that can be used by plants

• nitrifying bacteria

• ammonium ions —> nitrites —> nitrates

Denitrification

• nitrates in the soil are converted into nitrogen gas

• by denitrifying bacteria

• happens under anaerobic conditions

Describe the phosphorus cycle

1. Phosphate ions in rocks are released into the soil by weathering

2. Phosphate ions taken into plants by roots. Mycorrhizae increase rate phosphorus can be assimilated

3. Phosphate ions transferred through food chain

4. Phosphate ions are lost from animals in waste products

5. When plants and animals die, saprobionts are involved in the breakdown, releasing phosphate ions into soil

6. Weathering of rocks also releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, eg algae, and passed along food chain to birds

7. Waste produced by sea birds is known as guano and contains a high proportion of phosphate ions. Guano returns a significant amount of phosphate ions to soils, often used as a natural fertiliser

Describe the process of eutrophication

1. Mineral ions leached from fertilised fields stimulate rapid growth of algae in ponds and rivers

2. Large amounts of algae block light from reaching plants below

3. Eventually the plants die because unable to photosynthesise enough

4. Bacteria feed on dead plant matter. The increased number of bacteria reduce the oxygen concentration in the water by carrying out aerobic respiration

5. Fish and other aquatic organisms die because there isn’t enough dissolved oxygen

Compare rods and cones

Rods

• mainly located in peripheral parts of retina

• black and white

• many rods join to one bipolar neurone

• high sensitivity to light

• low visual acuity

Cones

• mainly located in the fovea

• colour

• one cone joins to one bipolar neurone

• low sensitivity to light

• high visual acuity

Describe the response to high and low blood pressure

High blood pressure

• baroreceptors detect and send impulses along sensory neurones to medulla

• medulla sends impulses along parasympathetic neurones

• which secrete acetylcholine, which binds to receptors on SAN

• causes heart rate to slow down to reduce blood pressure

Low blood pressure

• baroreceptors detect and send impulses along sensory neurones to medulla

• medulla sends impulses along sympathetic neurones

• these secrete noradrenaline which binds to receptors on SAN

• causes heart rate to speed up to increase blood pressure

Explain the factors that affect speed of conduction of action potentials

1. Myelination

   • between Schwann cells are nodes of Ranvier where sodium ions are concentrated

   • in a myelinated neurone depolarisation only happens at nodes of Ranvier, so impulses jump quickly from node to node

   • in a non-myelinated neurone depolarisation occurs along whole length of axon

   • this is slower than saltatory conduction

2. Axon diameter

• action potentials conducted quicker along axons with bigger diameters

• because there’s less resistance to flow of ions in cytoplasm

• with less resistance, depolarisation reaches other parts of neurone cell membrane quicker

3. Temperature

• speed of conduction increases as temperature increases

• because ions diffuse faster

• only increases up to certain point, after which proteins denature and speed decreases

Compare spatial and temporal summation

Spatial summation

• two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone

• a small amount of neurotransmitter from each neurone can be enough to reach threshold altogether and trigger an action potential

• if some neurones release an inhibitory neurotransmitter the total effect might be no action potential

Temporal summation

• where two or more nerve impulses arrive in quick succession from the same presynaptic neurone

• makes action potential more likely because more neurotransmitter is released into synaptic cleft

Explain the process of muscle contraction

• arrival of an action potential

• depolarises the sarcolemma

• depolarisation spreads down T tubules to sarcoplasmic reticulum

• Ca 2+ ions released into sarcoplasm

• calcium ions bind to protein attached to tropomyosin causing protein to change shape

• pulls the attached tropomyosin out of the actin-myosin binding site on actin filament

• this exposes the binding site which allows the myosin head to bind

• forms an actin-myosin cross bridge

• hydrolysis of ATP releases energy for myosin head to bend

• pulls actin filament along in a rowing action

• another ATP molecule provides energy to break actin-myosin cross bridge so myosin head detaches from actin filament after it’s moved

• myosin head then returns to starting position

What is a summary of glycogenesis, glycogenolysis and gluconeogenesis?

Glycogenesis

• converts glucose to glycogen

• activated by insulin

• inhibited by adrenaline

Glycogenolysis

• converts glycogen to glucose

• activated by glucagon and adrenaline

Gluconeogenesis

• converts glycerol/amino acids to glucose

• activated by glucagon

Describe what happens when blood water content is too low (dehydration)

• water content of blood drops so water potential drops

• this is detected by osmoreceptors in the hypothalamus

• the posterior pituitary gland is stimulated to release more ADH into the blood

• more ADH means that the DCT and collecting duct are more permeable, so more water is re absorbed into the blood by osmosis