All Paper 2 Topics

2.5B explain the importance of cell differentiation in the development of specialised cells

• Cell differentiation- the process whereby a cell becomes specialised in order to perform a specific function
• Differentiated cells are important because they can perform a specialised function in the body

2.6B understand the advantages and disadvantages of using stem cells in medicine

• Advantages (for embryonic stem cells)- they are undifferentiated so can specialise into any cell; easy to extract
• Advantages (for adult stem cells)- no ethical issue; won't be rejected if taken from the patient's body
• Disadvantages (for embryonic stem cells)- ethical issue; may be rejected by patient
• Disadvantages (for adult stem cells)- already specialised so cannot differentiate; difficult to extract

2.14B practical: investigate how enzyme activity can be affected by changes in pH

• Place one drop of iodine solution in each well of a spotting tile
• Take three test tubes and add:
  • 2cm cubed of starch solution to one
  • 2cm cubed of amylase solution to one
  • 2cm cubed of pH 5 buffer solution to one
• Place all three test tubes in a water bath at 30 deg. C and leave for 10 minutes
• Combine the three solutions into one test tube and mix; return it to the water bath and immediately start a stopwatch
• After 30 seconds, transfer a drop of solution to one of the spotting tile wells; the iodine solution should turn blue-black, indicating the presence of starch
• Continue taking samples every 30 seconds until the iodine remains orange and record the time this occurs; this indicates there is no starch, the enzyme reaction has completed

• Repeat the whole experiment using different pH buffer solutions; the reaction will be fastest (the iodine will stop changing colour fastest) at amylase's optimum pH

2.33B practical: investigate the energy content in a food sample

• Add a known volume of water to a boiling tube and measure its temperature
• Take a known mass of dried food and place on the end of a mounted needle
• Set the food on fire and place underneath the boiling tube to heat the water until it won't catch fire any more
• Measure the final temperature of the water and calculate the temperature change

energy content (J) = mass of water (g) × 4.2 (J/g°C) × temperature increase (°C)

2.40B understand the role of diffusion in gas exchange

• Plants get oxygen (for respiration) and carbon dioxide (for photosynthesis) through stomata on the underside of the leaves

2.41B understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

• Respiration- oxygen is taken in; carbon dioxide is released
• Photosynthesis- carbon dioxide is taken in, oxygen is released

2.42B understand how the structure of the leaf is adapted for gas exchange

• Broad- large surface area
• Thin- gases do not have to travel far
• Air spaces inside mesophyll- gases can pass through easily
• Stomata can be opened and closed by guard cells

2.43B describe the role of stomata in gas exchange

• Stomata can be opened or closed in order to take in and release gases as needed

2.44B understand how respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light

• Photosynthesis can only take place during the day (when there is light)
• More carbon dioxide is produced and more oxygen is released in bright light because the plant is photosynthesising more than it is respiring

2.45B practical: investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator

• Hydrogen-carbonate indicator is orange in normal CO2 concentration, yellow in high concentration, and purple in low concentration
• https://www.bbc.com/bitesize/guides/zxtcwmn/revision/3

2.55B understand how water is absorbed by root hair cells

• Water absorbed by root hair cells by osmosis

2.56B understand that transpiration is the evaporation of water from the surface of a plant

2.57B understand how the rate of transpiration is affected by changes in humidity, wind speed, temperature and light intensity

• Rate increased by high wind speed, temperature and light intensity
  • High wind speed means water molecules are blown away from the air close to the leaf, maintaining a high concentration gradient
  • High temperature-molecules have more kinetic energy so leave the stomata faster
  • High light intensity means the cells absorb more water, making them turgid; turgor makes the guard cells open the stomata and water is released
• Rate decreased by high humidity
  • High humidity means a low concentration gradient

2.58B practical: investigate the role of environmental factors in determining therate of transpiration from a leafy shoot

https://www.bbc.com/bitesize/guides/z3w4k7h/revision/5

2.63B understand how vaccination results in the manufacture of memory cells, which enable future antibody production to the pathogen to occur sooner, faster and in greater quantity

• Vaccination involves an injection of a dead or inactive form of a pathogen
• White blood cells still react and destroy the virus while making memory cells; these enable faster production of antibodies should you then be exposed to a live version of that pathogen

2.64B understand how platelets are involved in blood clotting, which prevents blood loss and the entry of micro-organisms

• Exposure to air stimulates the platelets and damaged tissue to make a chemical
• The chemical causes the soluble plasma protein fibrinogen to change into insoluble fibres of another protein, fibrin
• Fibrin forms a network across the wound which traps red blood cells, forming a clot which prevents blood loss and the entry of micro-organisms

2.72B understand how the kidney carries out its roles of excretion and osmoregulation

• Exretion:
  • The renal artery takes oxygenated blood at high pressure to the Bowman's capsule
  • Glomerular filtrate (glucose, water, urea and salts) passes through the Bowman's capsule into the nephron tubules- protein molecules are too large so they stay in the blood
  • Substances are reabsorbed along the way- all the glucose is reabsorbed
  • Some of the water and salts, and all the urea, passes into the collecting duct as urine
  • Urine is transported through the ureter to the bladder, then removed by the urethra
• Osmoregulation:
  • A change in water concentration in the blood is detected by the hypothalmus
    
  • This causes the pituitary gland to change the amount of ADH (anti-diuretic hormone) it secretes- more if the water concentration drops, less if the water concentration rises
  • ADH makes the nephron walls more permeable to water, causing more water to be reabsorbed into the blood
  • This makes urine more concentrated and the body loses less water

2.73B describe the structure of the urinary system, including the kidneys, ureters, bladder and urethra

2.74B describe the structure of a nephron, including the Bowman’s capsule and glomerulus, convoluted tubules, loop of Henle and collecting duct

2.75B describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate

• Blood enters the glomerulus under high pressure; small molecules (water, urea, glucose, salts) are forced out of the blood into the Bowman's capsule

2.76B understand how water is reabsorbed into the blood from the collecting duct

• Duct walls are permeable, how permeable depends on how much ADH has been secreted
• This allows water to be reabsorbed into the capillaries surrounding the duct

2.77B understand why selective reabsorption of glucose occurs at the proximal convoluted tubule

• All glucose is reabsorbed by active transport because it is a useful substance needed in the body, not a waste product

2.95B understand the sources, roles and effects of the following hormones: ADH, FSH and LH

• ADH:
  • Source- pituitary gland
  • Role- controls water content of blood
  • Effect- makes nephron walls more permeable
• FSH:
  • Source- pituitary gland
  • Role- maturing of an egg in the ovary
  • Effect- stimulates egg development and oestrogen secretion in females and testosterone production in males
• LH:
  • Source- pituitary gland
  • Role- stimulation of the ovary to release a mature egg cell
  • Effect- stimulates the release of an egg cell and the release of progesterone

3.10B understand the roles of FSH and LH in the menstrual cycle

• FSH- causes an egg to mature in the ovary; stimulates ovaries to release oestrogen
• LH- causes marure egg to be released from the ovary; stimulates ovaries to release progesterone

3.16B describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

3.17B understand that an RNA molecule is single stranded and contains uracil (U) instead of thymine (T)

3.21B understand the meaning of the term codominance

• Codominance- when two alleles for a trait are equally expressed with neither being recessive or dominant

3.18B describe the stages of protein synthesis including transcription and translation, including the role of mRNA, ribosomes, tRNA, codons and anticodons

https://www.bbc.com/bitesize/guides/z3mbqhv/revision/6

3.35B understand how a change in DNA can affect the phenotype by altering the sequence of amino acids in a protein

• The sequence of amino acids determines the protein in produces
• A change in the sequence can result in a different protein, so a different phenotype

3.36B understand how most genetic mutations have no effect on the phenotype, some have a small effect and rarely do they have a significant effect

• Mutation may have no effect- it could be in a recessive allele or the new sequence could code for the same amino acids

3.37B understand that the incidence of mutations can be increased by exposure to ionising radiation (for example, gamma rays, x-rays and ultraviolet rays) and some chemical mutagens (for example, chemicals in tobacco)

4.3B understand the term biodiversity

• Biodiversity- the amount of variation shown by organisms in an ecosystem

4.4B practical: investigate the distribution of organisms in their habitats and measure biodiversity using quadrats

• Place a quadrat randomly within a sampling area
  • For example, by splitting the sample area ino squares, numbering each square and using a random number generator to choose a square
• Count the populations of all the species within the quadrat and record on a map
• Repeat the process in different sections of the sampling area, using the same size quadrat each time

4.11B describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria (specific names of bacteria are not required)

4.18B understand the effects of deforestation, including leaching, soil erosion, disturbance of evapotranspiration and the carbon cycle, and the balance of atmospheric gases

• Leaching- plants add nutrients to the soil when they die and decompose, so there are less nutrients in the soil if they are removed; soluble nutrients are also washed out of the soil by rain because there are no plant roots protecting the soil (this causes eutrophication)
• Soil erosion- no plant roots protecting the soil so it is washed away in heavy rain
• Disturbance of evapotranspiration- plants absorb water from the soil and lose water from their leaves into the atmosphere which goes on to make clouds. If there are less plants then there are less clouds; less clouds means less rain, which can mean drought.
• Disturbance of the carbon cycle and balance of atmospheric gases- plants convert carbon dioxide into oxygen when they photosynthesise. They use more carbon than they release: this means they help to make sure the levels of CO2 in the atmosphere don't get too high. When forests are cut down this process is lost. The trees are usually burnt,  which releases CO2 into the atmosphere.

5.9B understand the methods used to farm large numbers of fish to provide a source of protein, including:

maintaining water quality; removing waste products- water is pumped through a filter to remove the waste products of the fish

controlling intraspecific and interspecific predation- smaller fish are kept separate from larger fish; enclosing them in tanks keeps out predators

controlling disease- antobiotics are often used, which can cause problems if they have not degraded by the time humans eat them, which increases antibiotic resistance in bacteria

controlling the quality and frequency of feeding- they are fed nutritious food frequently but in small amounts so they do not overeat or begin eating each other

selective breeding- selective breeding can be used to produce fish that grow faster and are less aggressive than wild fish

5.17B describe the process of micropropagation (tissue culture) in which explants are grown in vitro

• Explants are trimmed and surface-sterilised, then placed in a sterile agar solution containing nutrients and plant hormones to encourage shoot growth
• Once shoots have formed, they are transferred to a different solution with a balance of hormones to encourage root growth
• Once roots have grown, they are transferred to a greenhouse and transplanted into compost
  • The atmosphere is kept very moist to reduce water loss in the plants

5.18B understand how micropropagation can be used to produce commercial quantities of genetically identical plants with desirable characteristics

• Micropropagation can produce thousands of genetically identical plants from a single 'parent' plant that has desirable characteristics

5.19B describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep

• An enucleated egg cell (egg cell with its nucleus removed) and a body cell's nuceleus are fused together using an electric current
• The cell develops into an embryo, which is transferred into a surrogate mother
• The baby born is genetically identical to the 'parent' (the one whose cell nucleus was used)

5.20B understand how cloned transgenic animals can be used to produce human proteins

• Transgenic animals can secrete added human proteins in their milk, for example
• These can be cloned to produce multiple transgenic animals

• Worth 70 marks- 38.9% of the overall grade
• Allotted time- 1hr 15mins
• Assesses all content- everything mentioned here and Paper 1 content
• First taking place on 7th June 2019 (UK)