AQA A level biology - Essay Plans

The importance of cycles in biology

• the cardiac cycle

  • ensures blood is moved in the right direction so that respiring muscles always have oxygen available

    • if didnt happen blood would travel around the body incorrectly leading to muscles dying as cant respire

• nitrogen cycle

  • returns nitrates and ammonium ions to the soil so they can be taken up by plants to form new biomass, allowing for increased plant growth which increases biodiversity and the amount of food present for herbivores and their predators

• calvin cycle

  • produces hexose sugars,lipids and amino acids which can be used for growth, storage or structural support in the cell

    • linked to an increase in productivity, more seed and spore production so more population growth.

• krebs cycle

  • produces ATP and FADH and NADH which can then be used in oxidative phosphorylation

The uses and importance of ATP in organisms

• Active transport

  • active process so it requires ATP when the molecule binds to the carrier protein the hydrolysis of ATP phosphorylates the carrier protein so changes shape carrying molecule across the cell surface membrane

• Muscle contraction

  • ATP hydrolysis on myosin heads causes them to bind and moves the actin molecules inward over myosin and the attachment of a new ATP to each myosin head causes them to detach from the actin and returns the muscle to it original shape

• Respiration

  • ATP is formed in respiration but its also used to start off glycolysis by phosphorylating glucose without it respiration wouldnt occur

• Photosynthesis

  • ATP is used to form TP and reform rubisco in the light dependent reaction and without it hexose sugars, lipids and amino acids wouldnt be formed

The causes of variation and its biological importance

• speciation

  • sympatric or allopatric

• new combinations of alleles

  • homologous chromosomes associate together and the chiasmata forms and parts are exchanged

  • independent segregation

  • mutations

  • random fertilisation

• natural selection

  • antigenic variability - if a mutation occurs in a gene that codes for an antigen, the shape of it will change so immunity lost. gives advantageous allele ect.

• haemoglobin

  • different alleles have different genes coding for haemoglobin giving them different structures

  • Hb has different affinity for oxygen at diffrent partial pressures so O2 will binds when not readily available

  • O2 terminal electron acceptor so allows for ATP synthesis

How the structure of proteins is related to their function

• structure of proteins

• enzymes

  • active site complementary to form ES complexes

  • induced fit model

• transport proteins

  • transmembrane proteins that form channels or carry molecules to pass them throught the membrane by …

  • important as if not right shape dont transport proteins

    • CFTR mutated protein leads to cystic fibrosis

• antibodies

  • antibody antigen complex

  • agglutination

• strutural proteins

  • provide structural support to cell esp larger ones to prevent them collapsing in on themselve

    • found in muscles to prevent them moving outside the range of motion

    • if malformed, dont provide structure can lead to thing like hypermobility

The importance of energy transfers which take place inside living organisms

1) Photosynthesis

- ATP synthesised in LDR needed in LIR - processes

- GP --> TP - used to produce glucose & regenerate RUBP

2) Action potential & resting potential generation

- Na+ / K+ pump cotransport utilises energy from ATP

- process of maintaining a resting potential

- process of action potential formation

3.) Respiration

- ATP needed for phosphorylation of glucose in glycolysis

- process of glycolysis

- production of ATP by Krebs & O.P required for metabolic processes

4.) Muscle contraction

- ATP hydrolysis provides energy

- process: Ca2+ from sarcolemma, binds with troponin, changing its shape, moving tropomyosin revealing actin binding sites, A-M cross bridges, ATP hydrolysed, power stroke, myosin head changes shape, pulls actin filament over myosin shortening sarcomere

The importance of osmosis in living organisms

• osmoregulation

  • water reabsorption at DCT and CD ensures that not too much fluid is lost in urine

  • Loop of Henle maintains the Na+ ion gradient

  • ADH affects permeability of walls so affects water reabsorption

• Translocation

  • Process, importance: transport of essential solutes to where they're needed

  • Link on hydrotropism's in plants - ensures plants take up as much water as possible for photosynthesis

• Water potential gradients & osmosis

  • Importance of osmosis - plasma membrane structure - diffusion of polar water molecules

  • plant cells & osmosis - turgor pressure - maintaining structure

• Formation of tissue fluid

  • supplies oxygen, glucose and amino acids to cells

• Important in hydrolysis reactions as provides water to split molecules

  • useful in respiration

Importance of enzymes in plants and animals

• Rubisco in calvin cycle

  • carbon fixation of CO2 and ribulose biphosphate to produce a 6c molecule that quickly breaksdown

• Methyltransferase and histone acetylase in gene expression

  • catalyses the addition of a methyl group to teh C5 of a guanine residue which results in the silencing of a gene

    • link to cancer

• DNA replication

  • DNA helicase and DNA polymerase

• Acetyl cholinesterase in synapses

• ATP synthase in respiration

  • electrons produced in the oxidation of rNAD and rFAD are passed down a series of electron carriers on the mitochondrial membranes where they loose energy

  • some used to move H+ into inner membrane space whcih less pass back throguh by ATP synthase and energy used ADP + Pi → ATP

• Phosphorylase

  • ADH binds to receptors in the collecting duct which activates phosphorylase which stimulates vesicles containing aquaporins to move and fuse with csm which increases permeability

Importance of nitrogen containing compounds in biological systems

• DNA technologies

  • the human insulin gene is inserted into a plasmid vector by using same REN which allows the bacterium to produce human insulin

• Nitrogen cycle

  • n fixing bacteria reduce N2 into NH4-

  • oxidise them into NO2 then NO3

  • saphrobionts hydrloyse n containing compounds into amino acids via extracellular digestion

  • further broken down by deamination and NH3 released into soil

• ATP

  • nucleotide - describe structure

  • muscle contraction-

    • Ca2+ diffuse into myofibrils causing movement of tropomyosin allowing myosin heads to bind

    • ATP hydrloyses on myosin heads causing them to bind and moves actin molecules over myosin

    • new ATP attaches causing detach and muscle now relaxed

• Protein synthesis

  • tRNA contains nitrogenous bases, some are paired with others forming H bonds

  • important as results in the production of a functional polypeptide

  • without it proteins not synthesised so things like enzymes and antibodies wont be produced

How the shapes of cells are related to their function?

• palisade mesophyll cells

  • elongates cells which allows them to absorb lots of light

  • air spaces to maintain concentration gradients of gases

  • lots of chlorophyll

• bacterial cells

  • flagellum so can move to host and infect them allowinf them to reproduce

    • Vibrio cholerae which cause cholera which aids in it binding to and colonising the intestinal lining

• sperm cells

  • tail to move

  • lyzosymes so can hydrolyse egg and fuse forming a zygote

• red blood cells

  • no nucleus biconcave

• muscle cells

  • multinucelated

  • surrounded by sarcolemma

  • sarcoplasm with many mitochondria

  • many myofibrils that run parallel to each other which are surrounded by sarcoplasmic reticulum with Ca2+

Importance of inorganic ions

• H+

  • bohr shift

  • pH for enzymes

  • respiration

  • photosynthesis

• NPK

  • fertilisers

• PO43-

  • DNA

  • RNA

  • Phospholipids

  • Released by weathering and saphrobionts

• Na+ and K+

  • co transport

  • action potentials

    • maintain resting potential, refractory period and VG channels

• Na+ and Cl-

  • osmoregulation

• digestion

• fe2+

  • haem group

• Nitrogen

  • amino acids

  • DNA

  • ATP

The importance of how the structures of different polymers are related to their function

• polypeptide

  • how they are formed

  • antibody and immunity

  • enzymes

• Polysaccharides

  • glycogen

    • respiration how its broken down via glygogenolysis

    • slow and fast twitch muscle fibres

  • cellulose

    • link to cell wall and structural support in turgidity

• polynucleotide

  • DNA replication

    • codes for proteins

Explain how formed via condensation reactions form them

The causes of disease in humans

• bacteria

  • structure

  • antibiotics → natural selection

  • produce toxins which damage host cell by things like breaking downcell wall and inactivating enzymes

• virus

  • viral structure

  • HIV

• Genetic diseases

  • how they occur

    • CFTR, BRCA, KRAS

• Life style

  • bad diet

    • build up of plaque in coronary arteries

    • myocardial infarction

The importance of how CO2 may affect organisms directly or indirectly

• bohr shift

  • muscles respire increases co2 conc hb has reduced affinity so unloaded

• increases blood ph

  • detected by baroreceptors and heart response

  • if not protein can be denatured

    • affects enzymes

• increased LIR of photosynthesis

  • increased growth

• carbon cycle

  • most things require carbon so it needs to be recycled and most recycled as co2

  • absorbed by producers to make carbs

  • some dissolves in sea and converted into calcium carbonate in marine animals to make shells

  • co2 returned back via weathering of limestone and respiration

The importance of using DNA in science and technology

• transcription

  • important as forms mRNA so genes can be expressed and at a controlled rate

    • if not controlled leads to lots of proteins being produce

      • lead to things like cancer when too many cyclins produce such as cyclin D1

• translation

  • forms proteins with a specific primary structure

    • if not leads to non-functional proteins

• mutations - natural selection and cancers

  • genetic counselling and therapy

• genetic fingerprinting - VNTR

  • VNTR are non coding sections of DNA where a specific base sequence is repeated many times

  • they occur in lots of places in the genome and can be used as a comparison between two individuals as they mutated often so only close relative will have similar VNTRS

    • around half from each parent

• DNA replication

• Gene tech → mass production of insulin

  • isolate genes using REN

  • insert insulin gene into vector with marker gene

  • transfer recombinant vector to target DNA by encouraging cells to take up recombinant DNA

  • identify using marker gene

  • clone the bacteria with the marker gene on large scale to produce lots of protein to be extracted

How bacteria can affect the lives of humans and other organisms

• saphrobionts

  • found in soil and water and hydrloyse dead organic tissue into inorganic ions which can be taken up by plants to form new biomass

• DNA tech → plasmid vector

  • plamid vector from bacteria

    • mass production from insulin

• Antibiotic resistance

  • caused due to natural selection leads to increase of disease and fatality due to it as less people can fight it

• PCR

  • thermus aquaticus produces Taq polymerase which is a heat resistant enzyme

the importance of shapes fitting together in cells and organisms

• haemoglobin

  • oxygen binds so can be released at respiring cells

    • if not, heart not recieve so die and MI

• receptors

  • insulin and glucagon

    • cAMP activation

  • neurotransmitters at cholinergic synapses and neuromuscular junctions

  • collecting duct and DCT

• enzymes

  • induced fit

  • link to respiration and photosynthesis

• antibodies in the immune response

importance of different types of relationships and interactions between organisms

• succession

  • pioneer species makes area less hostile

• GE of crops

  • leads to antibiotic resistance if alleles passed on

• myocorrhizae

  • form symbiotic relationships with fungi and plants

• pathogens

  • HIV

    • use host cell to replicate

• nutrient cycle

  • nitrogen fixing bacteria found in the root nodules of legume plants

    • help legume plants absorb nitrates and ammonium ions whilst legume provides bacteria (rhizobia) with carbohydrates and amino acids

importance of responses to changes in external and internal environment of organisms

• body temperature

  • must be carefully controlled by feedback loops due to enzyme controlled reactions

• blood pressure and ph

  • chemo and baro receptors

  • pH can affect proteins

    • enzymes and transport proteins

• maintaining BGC

  • too high water moves out cells

    • leads to issues with sight due to osmotic lysis of lens

• taxes and kineses

  • taxes is directional response to or from a stimulus

  • kinese is a simple response by an animal to a change in stimulus by changing rate of movement in a random direction

    • allow organisms to move to an area with conditions they are better adapted to and to avoid predator

the importance of receptors

• synapses

  • cholinergic and neuromuscular

    • myasthenia gravis is autoimune diseases where antibodies destroy acetylcholine receptors at the neuromuscular junction leading to muscle weakness

• control of blood glucose

  • insulin and glucagon

    • 2nd messenger for cAMP activation

• Control of heart rate

• Pacinian corpusle

  • they are mechanoreceptors that convert mechanical stimuli into electrical signals that may invoke an action potential

importance of movement

• synapses

  • myasthenia gravis

  • if neurotransmitters dont diffuse action potential not happen on post synaptic neurone

• movement of tropomyosin on actin

  • uncovers myosin head binding sites so myosin can bind forming actomyosin bridge

• movement of substances

• DNA replication

  • mRNA produced from DNA which carry the protein info to the cytoplasm where it then associated with a ribosome

    • transcription

      • if didnt happen proteins wouldnt be made

• mutations

• electron transport chain

  • forms ATP in LDR and krebs cycle

• Transpiration

  • movement of water throught the xylem

the ways in which water and regulation of water content are important to organisms

• transpiration

  • water lost by transpiration which lowers WP of mesophyll cells so water pulled up xylem by osmosis causing tension as H2O molecules stick together by H bonding forming continuous columns of water and adhesion of water molecules to walls of xylem prevents it moving back down

    • helps maintain structural support oif plant and regulate temperature so cells remain turgid

• osmoregulation

• osmosis

• formation of tissue fluid (can be linked to osmosis

  • oedema due to hypertension

    • leads to restriction of movement and pain due to increased fluid retention

• translocation

  • sucrose AT into sieve tube by companion cells which lowers water potential drawing water in from the xylem leading to a high hydrostatic pressure due to vol increase which causes mass movement downwards towards sink where sucrose is removed and used for respiration, stored or to produce ATP

    • important as without water moving in by osmosis no high HP so no mass movement downwards

• properties of water

  • metabolite so involved in reactions

  • polar molecule so acts as universal solvent

  • high heat capacity so reduces fluctuiations in temperature which makes it important for marine life

  • high latent heat of vapourisation so provides a cooling effect when smal amount evapourate

  • strong cohesion supports colums on water which produces surface tension where water meets air

    • this supports small animals such as pond skaters allowing them to exist on the surface of the water

how nucleotides, molecules dervied from nucleotides and nucleic acids are important in keeping organisms alive

• DNA and RNA structure

• RISC, miRNA and siRNA

• tRNA

  • translation and formation of proteins

• mRNA

  • transcription

• Gene technology

  • mass producing insulin

importance of diffusion in organisms

• photosynthesis

  • CO2 diffuses in LIR

• Respiration

  • O2 is terminal electron acceptor and movement of H+ in innermembrane space

• action potential

• IAA in plant roots and shoots

• synapses

• muscle contraction

importance of bonding and bonds in organisms

• protein structrure

  • primary → peptide bonds

  • secondary → H bonds

  • tertiary → ionic, hydrogen and disulfide bridges, hydrophobic and hydrophilic interactions, h bonds

  • quaternary - disulfide bridges

• DNA

  • phosphodiester bonds

  • h bondss

• Transpiration

  • H bonds

• Carbs

  • glycosidic bonds

• esters

  • phospholipids and triglycerides

importance of DNA as an information carrying molecules and its use in gene tech nologies

• structure of DNA

• DNA in genetic diseases

  • how they are caused

  • genetic therapy

    • germline and somatic

• Cancer formation

  • amino acid structure altered so information altered so diff polypeptide

    • cyclins incorrectly formed then cell cycle not correctly done so cancer

• DNA probes for cancer screening

  • specific to a base sequence of DNA so wil bind to its complementary sequence

    • can be used to see how people will respond to drugs

      • breast cancer caused by a mutation in HER2 proto oncogene can only be treated with herception