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A LEVEL BIOLOGY: 25 Mark essays

Terms in this set (16)

The importance of shapes fitting together in cells and organisms
*Enzyme properties and digestion
*Antigens, antibodies, B cells & T cells

*Structure of DNA
*DNA replication
*Transcription and translation
*Restriction enzymes

*Muscle contraction
*Action potentials and synaptic transmission
*Control of blood glucose concentration
How bacteria can affect the lives of humans and other organisms
*Pathogens
*Resistance to antibiotics

*Carbon cycle
*Nitrogen cycle
*Eutrophication

*Use of bacterial enzymes (restriction endonuclease, DNA polymerase for PCR)
*Use of bacterial plasmids
The importance of receptors in living organisms
*Immune system (receptor proteins in T-cells, primary response, secondary response)

*Nerve Impulses (Action potentials, pacinian corpuscle, synapses, thermoreceptors, light receptors)

*Survival and response (tropisms, auxins, kineses, taxis)

*Homeostasis (temperature, pH, glucose)

*Control of heart rate (baroreceptors, chemoreceptors)
The importance of movement in living organisms
*DNA replication

*Gas exchange (single celled, insects, fish, plant, human)

*Evolution/speciation (species isolated, sympatric speciation, allele freq changes, physical barrier)

*Mass transport (water in plants, mammalian circulation, haemoglobin)

*Protein synthesis (transcription, translation)

*Meiosis (2 nuclear divisions)

*Transport across membranes (active transport, cotransport, osmosis, diffusion)
The causes of disease in humans
*Pathogens (bacteria, viruses, fungi, damage cells, produce toxins, viruses replicate inside host cells, MRSA)

*Lifestyle (smoking, pollution, cancer, heart disease, radiation asthma, emphysema)

*HIV (AIDs, replicated inside T-cells, no cure)

*Genetics (non-functional enzymes, cell cycle, gene mutations, proto-oncogenes, tumour suppressor genes)
Polymers have different structures and functions. Describe how structures are related to functions.
*Storage molecules (Control of blood glucose, glycogen, starch)

*Informational molecules (enzymes, RNA, Antibodies, DNA)

*Structural molecules (cellulose, structural proteins, keratin, collagen
The importance to humans of the control of growth, reproduction and development, including themselves.
*Genetics- prediction of inherited conditions (Hardy-Weinberg principle, Chi squared test, sex linkage, multiple alleles, epistasis, ratios, chances of inheriting particular phenotypes, autosomal linkage)

*Succession (primary succession, pioneer species, thin soil, diversity, secondary succession, already soil layer, preventing succession to preserve ecosystem, conservation)

*Pathogens and antibiotic resistance (Aseptic techniques to prevent contamination of microbe cultures, immunity, vaccines

*Human influence on biodiversity (Conservation, fertilisers, eutrophication, farming practices)

*Selective breeding and farming practices (pest control, more for human consumption, productivity, efficiency)

*Regulation of gene expression, mitosis, cancer (mutations in proto-oncogenes, tumour suppressor genes, gene therapy, radiotherapy)
The importance of responses to changes in the external and internal environment of an organism.
*Immune response (cellular- phagocytes, T cells, primary/secondary, humoral- antibodies, B-cells)

*Transpiration (humidity, water potentials, mesophyll cells, xylem, transpiration pull)

*Adaptation and selection (abiotic conditions, niches, biotic conditions)

*Control of heart rate (chemoreceptors, baroreceptors)

*Homeostasis (temperature, glucose, negative feeback)

*Responses to stimuli, plants and tropisms (phototropism, gravitropism, IAA controls)
Cells are easy to distinguish by their shape. How are the shapes of cells related to their function?
*Red Blood Cells; biconcave for increased SA, move through capillaries easily, no nucleus

*Neurones; Dendrites make synaptic connection to other neurones, axon carries nerve impulses over long distances, mylelin sheath faster transmission

*Muscle cells; elongated with rows of sarcomeres lead to conctraction in entire length, force generated in a particular direction

*Sperm Cells; beating tail and streamlined to help sperm move and find egg cell, enzymes to digest into egg cell

*Leaf cell; palisade mesophyll are elongated, packed side by side, absorbs as much light as possible, root hair cells increase SA for water absorption, leaf hair cells trap air to reduce water lost by transpiration

*Bacterial cell; rotating flagellum, flagellum moves bacteria
Cycles in Biology
*Nitrogen Cycle
-Nitrogen Fixation (nitrogen gas into organic compounds using nitrogen-fixing bacteria)
-Ammonification (organic compounds into ammonia using saprobionts)
-Nitrification (nitrites into nitrates using nitifying bacteria)
-Denitfication (nitrates into gas using denitrifying bacteria)

*Phosphorous Cycle
-Phosphate rocks eroded into oceans
-Plants take up water from lakes
-Animals feed on plants
-Waste excreted from animals
-Waste deposited into rocks

*Krebs Cycle (respiration)
-Breaks down pyruvate to CO2
-Produces hydrogen for oxidative phosphorylation
-Regenerates 4C molecule using acetylcoenzyme A

*Calvin Cycle (Light independent photosynthesis)
-In Stoma
-RuBP combined with CO2 using rubisco to produced GP
-GP splits ATP, takes hydrogen from NADPH to produce TP which goes on to produce glucose
-TP regenerated to RuBP using ATP

*Cell Cycle
-Interphase (DNA replication, ATP increases)
-Prophase (chromosomes condense, centrioles move to ends, nuclear envelope breaks down)
-Metaphase (chromosomes attach to spindle, line up in middle)
-Anaphase (chromatids to opposite poles, centromere divides)
-Telophase (chromatids uncoil, nuclear envelope forms, cytoplasm divides)

*Cardiac Cycle
1. Ventricles relax, atria contract
-blood to ventricles
-Increased pressure
-SL valve shut
-AV valve open
2. Ventricles contract, Atria relax
-ventricles high pressure
-Ventricles low volume
-SL open

3. Ventricles relax, atria relax
-SL valve shut
-High pressure in vena cava
-Atria fill
-Atria pressure high
-AV open
Rising temperatures may result in physiological and ecological effects on organisms.
Describe and explain these effects.
*Effect on gas exchange
-Increased evaporation
-More rapid uptake of ions by plants
-Decreased affinity for oxygen of haemoglobin

*Effect on proteins
-Increased rate of enzyme activity
-10 degree C rise= increase enzyme action by 75%
-Increased effect on growth and activity
-Increased rate photosynthesis with small increases in temperature
-Discruption of photosynthesis with large increases in temperature
-Increased rate of denaturing of tertiary structure

*Effect on transpiration
-Increased rate of water loss- wilting/dehydration
-Reduced stomatal opening may affect photosynthesis- consequences of drought
-Increased capacity of air to absorb more water
-Increase in air temp warms water inside leaves quickly causing faster evaporation
-Evaporation and diffusion are faster

*Effect on food webs
-changes to niches and communities
-Earlier springs= earlier nesting for 28 migratory bird species on E. coast of US
-16/23 butterfly species in California shifted migration timing
-Decline in sea ice= less algae= less zoo plankton= less cod= less seals= less polar bears
-Irreversible changes when threshold is passed
-World's oceans reached 17 degrees C= highest ever

*Effect on growth and reproduction
-Spread of pathogens, parasites, diseases
-Effect on human health
-Weeds, pests, fungi compete with crops for light, water, nutrients

*Effect on agriculture
-Higher temperatures= more rain
-Higher temperatures= more drought
-Impacts on crop yields (some increase/some decrease)
-Farmers move crop locations
-Threatens livestock- reduce fertility, increase disease, reduce milk production, reduce forage
Describe how inorganic ions are used in living organisms.
*Action Potentials
-In resting potential, concentration of sodium ions outside membrane is high, potassium is low. Sodium pumped out, potassium pumped in to produce electro-chemical gradient
-High stimulus produces positive charge of +40mV, causing channels to change shape and sodium ions move into axon
-Once +40mV is reached, sodium ions close, potassium ions open
-Overshoot of gradient when more potassium pumped out (repolarisation)

*Nitrogen Cycle
-Plants take up nitrogen as nitrate ions- absorbed by active transport
-Nitrate ions leach through soil
-Nitrogen fixation (gas into compounds)
-Ammonification (ammonia into ammonium ions)
-Nitrification (ammonium ions into nitrite ions, nitrite ions into nitrate ions)
-Denitrification (nitrates into gas)

*Fertilisers and plant growth
-Artificial fertilisers contain nitrogen, phosphorous, potassium
-Nitrogen essential in amino acids, ATP, DNA nucleotides
-Where nitrate ions are available, plants develop earlier, grow taller, greater leaf area, more photosynthesis
-Cheaper food due to increased productivity

*Role of H+ in respiration
-Oxidation of TP (removal of H+)
-Production of NADH, FADH

*Role of H+ in photosynthesis
-Photolysis splits water into H+ ions and OH+ ions
-Chemiosmotic theory (H+ pumped from stroma into thylakoid membrane, ATP formed)
-GP/TP formation in light independent reaction
-Produces starch, cellulose, lipids etc.

*Hydrogen, pH and Enzymes
-pH= hydrogen ion concentration
-pH= -log10(H+)
-Extreme change= denaturation
-Alters charges on amino acids tat make up active site of enzyme
-Tertiary structure may change so substrate no longer binds to active site of enzyme
-pH fluctuations usually small- more likely to reduce activity than denature it.
Importance of water and water regulation in living organisms.
*Solvent
-Secretion of substances e.g. hormones
-Allows transport of nutrients e.g. glucose and amino acids in blood, sucrose in phloem
-Removal of excretory products e.g. ammonia and urea

*Metabolic reactions
-Hydrolysis (addition of water in breakdown of molecules e.g. protein to amino acids)
-Condensation reactions (water released when combining molecules)
-Digestion and absorption
-Respiration- water is product, final electron acceptor
-Photosynthesis- photolysis- splitting water to replace electrons and provide protons

*Cells and Support
-Transpiration brings nutrients
-Water not easily compressed
-High specific tension (xylem, walk on surface)
-Pressure against rigid cell wall- remain upright
-Buoyency for aquatic organisms

*Exchange
-Insects- ends of tracheoles in contact with cells, contact water to dissolve gases

*Temperature regulations
-High spec. heat capacity
-Reduces temp. fluctuations in organisms
-Minimises increase in temperature
-Evaporate sweat to cool down
The Importance of ATP in living organisms.
*Muscle Contraction
-Head of mysosin changes angle, moves actin along and releases ADP
-ATP fixes to myosin head, causing it to detach from actin
-Hydrolysis of ATP to ADP by ATPase provides energy for myosin head to resume normal position
-During muscle relaxation, ATP provides energy for calcium ions to be actively transported back to ER

*Respiration
-Glycolysis- Phosphorylation of glucose to GP using ATP, Oxidation of TP to pyruvate, producing ATP
-Krebs Cycle- ATP produced in o-r reactions
-Oxidative Phos- synthesis of ATP down transfer chain, catalysed by ATP synthase

*Photosynthesis
-Energy/ATP produced through electron transfer chain
-Protons through chloroplast membranes catalysed by ATP synthase embedded in membranes
-Hydrolysis of ATP from light-dep reaction provides energy for light-indep reaction
-ATP and NADPH used to reduce GP to TP

*Blood Glucose concentration- 2nd Messenger Model
-Raises glucose levels when too low
1. Adrenaline approaches transmembrane protein
2. Adrenaline fuses to receptor causing it to change shape, activating adenyl cyclase
3. Activated adenyl cyclase converts ATP to cAMP
4. cAMP activates protein kinase
5. Active protein kinase converts glycogen to glucose

*Active Transport of Ions
-Sodium ions into descending limb, out of ascending limb in nephron to control water
-Sodium ions into, potassium ions out of axon in action potential
-Sodium ions out of, potassium ions into resting potential
-AP travels through tubules, tubules in contact with sarcoplasmic reticulum which has actively transported calcium ions from cytoplasm of muscle

*Protein Synthesis
-5 ATP molecules required for addition of a single amino acid to a polypeptide chain
-2x ATP for amino acid activation, 2x ATP for peptide bond, 1x ATP for error correction
The Importance of proteins in the control of processes and responses in organisms.
*DNA
-DNA codes for proteins
-Proteins responsible for expressing information in DNA
-DNA wrapped around proteins called histones- DNA and histones covered in tags to form epigenome which determines shape of DNA-histone complex- controls which genes are switched on/off using methylation and acetylation

*Haemoglobin
• Globular protein with a quarternary structure
• Largest component of red blood cells
• Loads, transports and unloads oxygen
• Oxygen binding to first site makes other bindings easier
• Its evolution and small mutations in its structure can produce anaemia and other severe pathologies

*Immunology
• Antibodies are blood proteins produced in response to and counteracting a specific antigen.
• Complementary primary structure enables binding
• Lysozymes involved in phagocytosis to ingest pathogen
• Lymphocytes produce antibodies.
• Vaccines contain small quantities of weakened antigen- antibodies and memory cells produced

*Across Membranes
• Embedded proteins in membranes
• Act as antigens to allow them to be recognised
• Glycoproteins in fluid-mosaic model allow communication between cells
• Carrier proteins in Facilitated diffusion- Once a specific molecule collides with the Carrier Protein, it 'flip flops' carrying the molecule to the other side of the membrane. The Carrier Proteins involved in Active Transport are Complementary to the molecule they transport.
• Channel proteins in facilitated diffusion provide pores though which these molecules can diffuse

*Enzymes in Respiration
• acetate combines with coenzyme A in the link reaction to produce acetyl coenzyme A
• acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a six-carbon molecule that enters the Krebs cycle
• Synthesis of ATP by passage of protons across inner mitochondrial membranes and is catalysed by ATP synthase embedded in these membranes (chemiosomotic theory)

*Enzymes in Photosynthesis
• passage of protons across chloroplast membranes and is catalysed by ATP synthase embedded in these membranes(chemiosomotic theory)
• carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP). This reaction is catalysed by the enzyme rubisco
Hydrogen Bonds and their importance in living organisms.
*Gene Technology
•Restriction enzymes cut bacterial DNA and vectors at same sequence to produce same sticky ends by breaking hydrogen bonds
•PCR- strands heated to 95 degrees C for 2 mins to break hydrogen bonds

*DNA, Nucleic Acids
•H-bonds between complementary nucleotide base pairs
•2 H-bonds between A and T, 3 H-bonds between C and G
•Hydrogen bonds responsible for stability of DNA double helix structure
•Each bond weak, together strong
•Internal and external hydrogen bonds stabilise DNA molecule
•External bonds with surrounding water

*Enzymes
•Increasing or decreasing the concentration of hydrogen ions in a solution (changes pH)- altering tertiary structure
•When substrate and enzyme collide, hydrogen bonds hold substrate and enzyme together
•Denatured at high temperatures because H-bonds break which holds tertiary structure together
•H-bonds determine shape of enzymes in tertiary structure- responsible for complementary structures.

*Proteins, starch and cellulose
•Hydrogen bonds between chains of cellulose form microfibrils
•Microfibrils give cellulose mechanical strength and chemical stability
•Microfibrils held together form macrofibrils
•Prevent cells from bursting- make cell turgid

*Water and Cohesion tension
•Hydrogen bonds within water give it high stability so large amount of energy needed to raise temperature of water
•Cohesion holds hydrogen bonds together to create surface tension on water
•Water boatmen
•Transpiration pull up xylem.
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