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A2 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Photosynthesis- light dependent

A
  1. Light is absorbed by the photosystems, causing photoionisation, e- is lost
  2. Electrons are passed down a decreasing energy gradient along the electron carriers
  3. This provides the energy to actively transport protons through the membrane to the thylakoid disk
  4. H+ flow back down pH gradient through ATP synthase
  5. ADP is phosphorylated to ATP when proton passes though its active site
  6. Water is split in photolysis, releasing H+/e- and O2
  7. The e- released replaces the electron lost from the photosystem and the proton is involved in creating the pH gradient
  8. The electron from the electron transfer chain joins with the proton from the pH gradient to form a hydrogen molecule
  9. Hydrogen reduces NADP to NADPH
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2
Q

Photosynthesis - Light Independent Reaction

A
  1. Ribulose Bisphosphate (5C) is carboxylated with CO2 by an enzyme called rubisco into a temporary unstable 6 carbon molecule
  2. 6 Carbon molecules splits into 2 x glycerate-3-phosphate (GP)
  3. ATP is hydrolysed to ADP to provide energy and NADPH is oxidised to provide H+/e-. These products are used in the conversion of GP to triose phosphate
  4. 83% of TP is recycled back into RuBP via the hydrolysis of ATP. The other 17% is used to make organic hexose sugars (e.g. glucose)
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3
Q

Respiration- glycolysis

A
  1. ATP is hydrolysed to allow the phosphorylation of glucose to two triose phosphate molecules
  2. TP is oxidised, losing protons to reduce NAD to NADH
  3. 2 ADP molecules are phosphorylated into ATP to dephosphorylate the TP into pyruvate
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4
Q

Respiration - Link Step

A
  1. Pyruvate is oxidised and decarboxylated to acetate, reducing 2 NAD to 2 NADH
  2. This acetate then reacts with coenzyme A, producing acetyl coenzyme A (ACoA)
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5
Q

Respiration - Krebs Cycle

A
  1. ACoA combines with a 4C molecule to form a 6C molecule
  2. In a series of reactions this 6C molecule loses CO2 and a hydrogen to give a 4C molecule and an ATP molecule from phosphorylation
  3. 3 NADHs and 1 FADH are also produced
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6
Q

Respiration - Oxidative Phosphorylation

A
  1. NADH is re-oxidised, donating protons and electrons to an electron carrier molecule
  2. Electron energises the ECM sufficiently to actively transport a proton into the inner membrane space
  3. Electron is transferred along an electron transfer chain down a decreasing energy gradient, reducing the carrier accepting the electron and oxidising the carrier losing the electron
  4. Protons build up in the intermembrane space, generating a pH gradient
  5. Protons flow via diffusion via ATP synthase, allowing the phosphorylation of ADP to ATP as the proton passes through the active site
  6. Oxygen acts as the final electron acceptor, joining with protons and electrons
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7
Q

Reflex Arc

A 
Stimulus
Receptor
Sensory neurone
Relay neurone (through spinal cord)
Motor neurone
Effector
Response
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8
Q

Control of Heart Rate

A
  1. Wave of excitation spreads out from the Sinoatrial node across the atria, causing them to contract and blood to move into the ventricles
  2. Wave reaches the atrioventricular node which lies between the atria
  3. Delay between the SAN and AVN allows atrial systole
  4. AVN conveys a wave of excitation between the ventricles to the bundle of His
  5. Wave is passed to the purkinje fibres which stimulate ventricles to contract
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9
Q

Phototropism in Flowering Plants

A
  1. Cells in tip of shoot produce IAA, which is transported evenly down the shoot
  2. Light causes the movement of IAA from the light side to the shaded side
  3. Greater concentration of IAA in the shaded side than the light side
  4. IAA causes elongation of shoot cells, to shaded side elongates faster than the light side
  5. Shoot tip bends towards the light
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10
Q

Gravitropism in Flowering Plants

A
  1. Cells in root tip produce IAA, which is transported evenly along the root
  2. Gravity influences the movement of IAA from the upper side to the lower side
  3. Greater concentration on the lower side than the upper side
  4. IAA inhibits cell elongation in root cells, so the upper side elongates faster than the lower side
  5. Root tip bends downwards, towards gravity
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11
Q

Passage of an Action Potential

A
  1. Resting Membrane Potential -
    Conc. of Na+ ions is higher outside the axon than inside due to the action of the Na/K pump
    Conc. of K+ ions is higher inside the axon than outside because of leaky K+ channels
    Potential difference is -70mV
  2. Depolarisation -
    Stimulus causes Na+ ion to move into axon
    Na+ channels open, more Na+ ions diffuse in
    Positive charge on previously negative environment causes more Na+ ion channels to open further along the axon
    Creates localised current
    Potential difference is +35/+40 mV
  3. Repolarisation -
    Na+ channels close, K+ channels open
    K+ ions diffuse out of axon, more positive charge on outside of membrane
  4. Hyperpolarisation -
    Excessive K+ channels allow extra K+ to diffuse out
    Greater concentration for K+
    Returned to RMP by pump and leaky channels
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12
Q

Synaptic Transmission

A
  1. When action potential reaches the presynaptic membrane, Ca2+ channels open, so Calcium ions flow into the cell
  2. Ca2+ ions cause synaptic vesicles to fuse with cell membrane, releasing neurotransmitter (acetylcholine) by exocytosis
  3. Neurotransmitter diffuses across the synaptic cleft and binds to the neuroreceptors on the postsynaptic membrane
  4. Na+ channels open and sodium diffuses into the postsynaptic neurone
  5. Depolarisation is caused, which may initiate an AP if threshold is reached
  6. Neurotransmitter is broken down by acetylcholinesterase, the breakdown products are absorbed by the presynaptic neurone and used to resynthesise more neurotransmitter- Stops the synapse being permanently on
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13
Q

Muscle Contraction

A
  1. AP reaches neuromuscular junction, releasing neurotransmitter and causing an AP to travel along the sarcolemma to the sarcoplasmic reticulum
  2. Ca2+ channels open and calcium diffuses into the myofibril
  3. Ca2+ ions bind to troponin in actin filaments and activated ATPase
  4. Troponin changes shape and displaces tropomyosin from the myosin binding site so the binding sites are revealed
  5. Myosin head attaches to actin filaments and energy from ATP moves the myosin head though the arc
  6. Actin filaments slide between myosin filaments
  7. When AP has passes Ca2+ dissociate and troponin changes back to its original shape, blocking the bonding sites and the muscle relaxes
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14
Q

Thermoregulation- Too High

A
  1. Change is detected by central thermoreceptors in hypothalamus and peripheral receptors in the skin
  2. Receptor send action potentials to the hypothalamus
  3. Hypothalamus then sends impulses to different effectors to carry out a range of mechanisms
    Vasodilation
    Sweating
    Decreased metabolic rate
    Pilorelaxation
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15
Q

Thermoregulation- Too Low

A
  1. Change is detected by central thermoreceptors in hypothalamus and peripheral receptors in the skin
  2. Receptor send action potentials to the hypothalamus
  3. Hypothalamus then sends impulses to different effectors to carry out a range of mechanisms
    Vasoconstriction
    Decreased sweating
    Increased metabolic rate
    Piloerection
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16
Q

Blood Glucose Regulation - Too high

A
  1. Receptors in islets of langerhans detect change and stimulate insulin release
  2. Insulin travels to target cells in liver and muscle and binds to receptors
  3. Triggers a sequence of enzyme controlled reaction in the cells:
    Protein channels open so more glucose flows into cell
    Glycolysis - Glucose → pyruvate
    Glycogenolysis - Glucose → glycogen
17
Q

Blood Glucose Regulation - Too low

A
  1. Receptors in islets of langerhans detect change and stimulate glucagon release from alpha cells
  2. Glucagon travels in blood to target cells in liver and muscles and binds to receptors on cell membranes
  3. Triggers a sequence of enzyme controlled reactions within the cells:
    Protein channels open so more glucose leaves respiring cells
    Glycogenolysis - glycogen → glucose
    Gluconeogenesis = FA, AA & glycerol → glucose
18
Q

Kidneys - Ultrafiltration

A
  1. Blood enters Bowman’s Capsule in afferent arteriole and passes along glomerulus
  2. High hydrostatic pressure is built up in capillary bed and low HP in the Bowman’s capsule to create a pressure gradient
  3. Small molecules filtered out of blood to form filtrate
  4. Filter is created by fenestrations and squamous epithelial cells in the capillaries, along with the basement membrane and podocytes
19
Q

Kidneys - Selective absorption

A
  1. As filtrate moves along, certain substances are reabsorbed into the cells lining the PCT, then into the blood
  2. Na+ ions are actively transported out of the PCT epithelial cells into the blood
  3. Allows the co-transport of glucose/other molecules with Na+ from the filtrate into the PCT epithelial cells
  4. Facilitated diffusion is used to transport these molecules into the blood
20
Q

Kidneys - Loop of Henle

A
  1. Na+ and Cl- are actively transported out of the impermeable ascending limb into the tissue
  2. The medulla tissue now has a lower water potential value
  3. A WP gradient is established between in the permeable descending limb
  4. Water is reabsorbed by osmosis from the descending limb and collecting duct to the medulla tissue
21
Q

Kidneys - Osmoregulation - fall in WP

A
  1. Osmoreceptors in hypothalamus detect fall in WP as they shrink from loss of water
  2. ADH is secreted from the posterior pituitary gland and passes into kidney
  3. ADH increases permeability of DCT and collecting duct cells to water by increasing the amount of aquaporins in the membrane
  4. More water leaves the DCT into the epithelial cells and re-enters the blood
22
Q

Speciation - Allopatric

A 
Geographical Isolation
Environmental conditions vary between two habitats
Different alleles are advantageous
Natural selection occurs differently
Two populations evolve differently
Can no longer interbreed successfully
23
Q

Speciation - Sympatric

A 
New selection pressure occurs
Populations remain in the same place
Become reproductively isolated
Both evolve because of selection pressure
Can no longer interbreed successfully
24
Q

Predation - Prey-predator relationship

A
  1. Predators eat their prey, therefore reducing prey population size
  2. Fewer prey available means there is more competition between predators
  3. Predator population is reduced as some individuals are unable to obtain enough pay for their survival or to reproduce
  4. With fewer predators left, fewer prey are eaten so prey population grows
  5. With more prey now available as food, the predator population in turn increases
25
Q

Succession

A
  1. A pioneer species colonise an inhospitable environment
  2. Non-living environment becomes less hostile
  3. Greater number and variety of habitats and niches are created
  4. Biodiversity increases
  5. Food webs become more complex
  6. Increased biomass
  7. Climax community is reached
26
Q

In Vivo Gene Cloning

A
  1. Gene is isolated by reverse transcriptase, restriction enzymes or the gene machine
  2. The gene and vector are cut with the same restriction enzyme and the gene is inserted
  3. The bacteria are made to take up the DNA by heat shock
  4. The rDNA bacteria are identified using antibiotic, enzyme or fluorescent markers
27
Q

In Vitro Gene Cloning

A
  1. DNA fragments, primer and DNA (taq) polymerase are heated to 95o so the two strands separate
  2. Mixture is cooled to 55o so the primers join to their complementary bases at the end of the DNA fragment
  3. Primers provide the starting sequences from DNA polymerase to begin copying DNA
  4. Temperature is increased to 72o, the optimum for taq polymerase to work
  5. DNA polymerase begins at the primer on both strands and adds the nucleotides in sequence until it reaches the end of the chain
  6. The process is repeated multiple times to amplify the target section of DNA
28
Q

Genetic Fingerprinting

A
  1. DNA is extracted from tissue and amplified using PCR
  2. The DNA is cut into fragments using the same restriction endonucleases
  3. The fragments are separated according to size by gel electrophoresis
  4. The gel is immersed in alkali to separate the double strands
  5. Multiple different radioactive or fluorescent DNA probes are added to bind to the different fragments
  6. A set of bars is revealed using the markers on the probes
  7. The pattern is unique to each individual, except for identical twins

Biology revision (1 decks)

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