GCSE Biology B3(OCR B721) Understanding Organisms

Year 11 additional science revision

B3A Molecules of Life
  • Identify the mitochondria in an animal cell.
  • Recall that respiration occurs in the mitochondria providing energy for life processes.
  1. Recall that chromosomes in the nucleus:
    • carry coded information in the form of genes
    • are made of a molecule called DNA.
  • Recall that the information in genes is in the form of coded instructions called the genetic code.
  • Understand that the genetic code controls cell activity and consequently some characteristics of the organism.
  • Recall that DNA controls the production of different proteins.
  • Recall that proteins are needed for the growth and repair of cells.
  • Recall that the structure of DNA was first worked out by two scientists called Watson and Crick.(helped by Rosalind Franklin)
  • Explain why liver and muscle cells have large numbers of mitochondria.
  • Describe the structure of DNA as two strands coiled to form a double helix, each strand containing chemicals called bases, of which there are four different types, with cross links between the strands formed by pairs of bases.
  • Describe chromosomes as long, coiled molecules of DNA, divided up into regions called genes.
  1. Know that each gene:
    • contains a different sequence of bases
    • codes for a particular protein.
  • Know that proteins are made in the cytoplasm and understand why a copy of the gene is needed: the gene itself cannot leave the nucleus.
  1. Know that (HL):
    • some structures in cells, such as ribosomes, are too small to be seen with the light microscope
    • ribosomes are in the cytoplasm and are the site of protein synthesis.
  1. Describe how Watson and Crick used data from other scientists to build a model of DNA, to include:
    • X-ray data showing that there were two chains include: wound in a helix,
    • data indicating that the bases occurred in pairs.
  • Know that the four bases of DNA are A, T, C and G (full names will not be required).(HL)
  • Be able to describe the complementary base pairings: A - T and G - C.(HL)
  1. Explain how protein structure is determined by the DNA base code, to include:(HL)
    • the base sequence determines amino acid sequence
    • each amino acid is coded for by a sequence of 3 bases.
  • Explain how the code needed to produce a protein is carried from the DNA to the ribosomes by a molecule called mRNA.(HL)
  • Explain how DNA controls cell function by controlling the production of proteins, some of which are enzymes.(HL)
  1. Explain why new discoveries, such as Watson and Crick's, are not accepted or rewarded immediately, to include(HL)
    • the importance of other scientists repeating or testing the work.
B3B Proteins and mutations
  1. Know some examples of proteins to include:
    • collagen
    • insulin
    • haemoglobin.
  1. Be able to describe enzymes as:
    • proteins
    • molecules that speed up a chemical reaction
    • c) working best at a particular temperature.
  • Know that different cells and different organisms will produce different proteins.
  • Understand that enzymes have active sites that substrate molecules fit into when a reaction takes place.
  • Understand that mutations occur spontaneously but can be made to occur more often by radiation or chemicals.
  • Describe gene mutations as changes to genes.
  • Understand that mutations are often harmful but may be beneficial or have no effect.
  • Be able to describe gene mutations as changes to genes.
  • Be able to recognise that proteins are made of long chains of amino acids.
  • Explain the specificity of enzymes in terms of the enzyme function 'lock and key' mechanism.
  • Explain how each protein has its own number and sequence of amino acids, which results in differently shaped molecules, which have different functions.
  1. Be able to describe some functions of proteins, to include:
    • structural (limited to collagen)
    • hormones (limited to insulin)
    • carrier molecules (limited to haemoglobin)
    • enzymes.
  1. Be able to describe enzymes as:
    • biological catalysts
    • catalysing chemical reactions occurring in living cells: respiration, photosynthesis and protein synthesis
    • having a high specificity for their substrate
  1. Explain how enzyme activity is affected by pH and temperature, to include:(HL)
    • lower collision rates at low temperatures
    • denaturing at extremes of pH and high temperatures
    • denaturing as an irreversible change inhibiting enzyme function
    • denaturing changing the shape of the active site.
  • Describe how changing temperature and pH, away from the optimum, will change the rate of reaction of an enzyme-catalysed reaction.
  1. Calculate and interpret the Q10 value for a reaction of over a 10°C interval, given graphical or numerical data, using the formula:(HL)
    • Q10 = rate at higher temperature / rate at lower temperature
  • Know that gene mutations may lead to the production of different proteins.(HL)
  • Understand that only some of the full set of genes are used in any one cell; some genes are switched off.(HL)
  • Understand that the genes switched on determine the functions of a cell.(HL)
  • Explain how changes to genes alter, or prevent the production of the protein which is normally made.(HL)
B3C Respiration
  • Recognise that the energy provided by respiration is needed for all life processes in plants and in animals.
  • Know and use the word equation for aerobic respiration:
    glucose + oxygen → carbon dioxide + water
  1. Be able to describe examples of life processes that require energy from respiration, to include:
    • muscle contraction
    • protein synthesis
    • control of body temperature in mammals.
  • Explain why breathing and pulse rates increase during exercise.
  • Describe an experiment to measure resting pulse rate and recovery time after exercise.
  • Be able to analyse given data from a pulse rate experiment.
  • Know and use the symbol equation for aerobic respiration:

    C6H12O6 + 6O2 → 6CO2 + 6H2O
  1. Use data from experiments to compare respiration rates, to include:
    • increased oxygen consumption
    • increased carbon dioxide production.
  1. Calculate the respiratory quotient (RQ) using the formula (data provided):
    • RQ = carbon dioxide produced / oxygen used
  • Know that respiration results in the production of ATP and that ATP is used as the energy source for many processes in cells.(HL)
  • Explain how the rate of oxygen consumption can be used as an estimate of metabolic rate because aerobic respiration requires oxygen.(HL)
  • Explain why the rate of respiration is influenced by changes in temperature and pH.(HL)
  • Explain why anaerobic respiration takes place during hard exercise in addition to aerobic respiration.
  • Know that this produces lactic acid which accumulates in muscles causing pain and fatigue.
  1. Know and use the word equation for anaerobic respiration which releases energy:
    • glucose → lactic acid
  • Understand that anaerobic respiration releases much less energy per glucose molecule than aerobic respiration.
  1. Explain fatigue in terms of lactic acid build up (oxygen debt) and how this is removed during recovery, to include:(HL)
    • hard exercise causing lack of oxygen in cells
    • the incomplete breakdown of glucose
    • continued panting replacing oxygen allowing aerobic respiration
    • increased heart rate ensuring that blood carries lactic acid away to the liver.
B3D Cell Division
  • Be able to describe the difference between simple organisms which are unicellular and more complex organisms which are multicellular.
  • Know that most body cells contain chromosomes in matching pairs.
  • Explain why the chromosomes have to be copied to produce new cells for growth.
  1. Know that this type of cell division is also needed for:
    • replacement of worn out cells
    • repair to damaged tissue
    • asexual reproduction
  • Know that gametes have half the number of chromosomes of body cells.
  • Understand that in sexual reproduction to produce a unique individual half the genes come from each parent.
  • Explain why sperm cells are produced in large numbers to increase the chance of fertilisation.
  1. Explain the advantages of being multicellular:
    • allows organism to be larger
    • allows for cell differentiation
    • allows organism to be more complex.
  • Know that in sexual reproduction gametes join in fertilisation.
  1. Explain why becoming multicellular requires the development of specialised organ systems, limited to:(HL)
    • communication between cells
    • supplying the cells with nutrients
    • controlling exchanges with the environment.
  • Know that new cells for growth are produced by mitosis.
  • Explain why these new cells are genetically identical.
  • Know that in mammals, body cells are diploid (two copies of each chromosome).
  • Explain why DNA replication must take place before cells divide.
  1. Be able to describe how, prior to mitosis, DNA replication occurs, to include:(HL)
    • 'unzipping' to form single strands
    • new double strands forming by complementary base pairing.
  1. Be able to describe how in mitosis the chromosomes:(HL)
    • line up along the centre of the cell
    • they then divide
    • the copies move to opposite poles of the cell.
  • Know that gametes are produced by meiosis.
  • Be able to describe gametes as haploid (contain one chromosome from each pair).
  1. Explain why fertilisation results in genetic variation, limited to:
    • gametes combine to form a diploid zygote
    • genes on the chromosomes combine to control the characteristics of the zygote.
  1. Explain how the structure of a sperm cell is adapted to its function, to include:
    • many mitochondria to provide energy
    • an acrosome that releases enzymes to digest the egg membrane.
  1. Explain why, in meiosis, the chromosome number is halved and each cell is genetically different, to include(HL)
    • one chromosome from each pair separate to opposite poles of the cell in the first division
    • chromosomes divide and the copies move to opposite poles of the cell in the second division.
B3E The circulatory system
  1. Be able to describe the functions of components of the blood:
    • red blood cells
    • white blood cells
    • platelets.
  1. Know that the blood moves around the body in:
    • arteries
    • veins
    • capillaries.
  1. Be able to describe the functions of the heart in the pumping of blood, to include:
    • the right side of the heart pumping blood to the lungs
    • the left side of the heart pumping blood to the rest of the body.
  • Know that blood in arteries is under higher pressure than blood in the veins.
  • Explain, in terms of pressure difference, why blood flows from one area to another.
  • Explain how the structure of a red blood cell is adapted to its function: size, shape, contains haemoglobin, lack of nucleus.
  • Describe the function of plasma.
  • Explain how the structure of a red blood cell is adapted to its function in terms of the small size providing a large surface area to volume ratio.(HL)
  • Describe how haemoglobin in red blood cells reacts with oxygen in the lungs to form oxyhaemoglobin and how the reverse of this reaction happens in the tissues(HL)
  1. Describe how the parts of the circulatory system work together to bring about the transport of substances around the body, to include:
    • arteries transporting blood away from the heart
    • veins transporting blood to the heart
    • capillaries exchanging materials with tissues.
  1. Explain how the adaptations of arteries, veins and capillaries relate to their functions, to include:(HL)
    • thick muscular and elastic wall in arteries
    • large lumen and presence of valves in veins
    • permeability of capillaries.
  1. Identify the names and positions of the parts of the heart and describe their functions, to include:
    • left and right ventricles to pump blood
    • left and right atria to receive blood
    • semilunar, tricuspid and bicuspid valves to prevent backflow
    • four main blood vessels of the heart.
  • Explain why the left ventricle has a thicker muscle wall than the right ventricle.
  1. Explain the advantage of the double circulatory system in mammals, to include:(HL)
    • higher pressures
    • therefore greater rate of flow to the tissues.
B4F Growth and development
  1. Describe the functions of parts of a plant cell to include:
    • vacuole, containing cell sap and providing support
    • the cell wall, made of cellulose to provide support.
  • Describe how to make a stained slide of an onion cell.
  • Understand that bacterial cells are smaller and simpler than plant and animal cells.
  • Know that growth can be measured as an increase in height, wet mass or dry mass.
  • Interpret data on a typical growth curve for an individual.
  • Describe the process of growth as cell division followed by cells becoming specialised.
  • Know that the process of cells becoming specialised is called differentiation.
  • Understand that animals grow in the early stages of their lives whereas plants grow continually.
  • Understand that all parts of an animal are involved in growth whereas plants grow at specific parts of the plant.
  • Identify simple differences between bacterial cells and plant and animal cells.
  1. Know that bacterial cells lack:
    • a 'true' nucleus
    • mitochondria
    • chloroplasts
  1. Describe the difference between the arrangement of DNA in a bacterial cell and a plant/animal cell, to include:(HL)
    • presence/absence of a nucleus
    • single circular strand/chromosomes.
  • Know that dry mass is the best measure of growth.
  • Be able to interpret data on increase in mass (including wet and dry mass).
  • Be able to describe the main phases of a typical growth curve.
  1. Be able to explain the advantages and disadvantages of measuring growth by:(HL)
    • length
    • wet mass
    • dry mass.
  • Know that in human growth there are two phases of rapid growth, one just after birth and the other in adolescence.
  • Be able to explain why the growth of parts of an organism may differ from the growth rate of the whole organism.(HL)
  • Know that undifferentiated cells called stem cells can develop into different cells, tissues and organs.
  • Know that stem cells can be obtained from embryonic tissue and could potentially be used to treat medical conditions.
  • Discuss issues arising from stem cell research in animals.
  • Be able to explain the difference between adult and embryonic stem cells.(HL)
  1. Be able to explain why plant growth differs from animal growth, to include:
    • animals tend to grow to a finite size but many plants can grow continuously
    • plant cell division is mainly restricted to areas called meristems
    • cell enlargement is the main method by which plants gain height
    • many plant cells retain the ability to differentiate but most animal cells lose it at an early stage.
B3G New genes for old
  1. Describe the process of selective breeding as involving the:
    • selection of desired characteristics
    • cross breeding
    • selection of suitable offspring over many generations
  • Be able to explain how selective breeding can contribute to improved agricultural yields.
  1. Know that:
    • selected genes can be artificially transferred from one living organism to another
    • this transfer of genes is called genetic engineering or genetic modification
    • the transfer of genes can produce organisms with different characteristics.
  • Identify features of plants and animals that might be selected for in a genetic engineering programme.
  • Recognise that in the future it may be possible to use genetic engineering to change a person's genes and cure certain disorders.
  • Recognise that a selective breeding programme may lead to inbreeding, which can cause health problems within the species.
  1. Be able to explain how a selective breeding programme may reduce the gene pool leading to problems of inbreeding, to include:(HT)
    • accumulation of harmful recessive characteristics
    • reduction in variation
  1. Explain some potential advantages and risks of genetic engineering:
  2. advantage - organisms with desired features are produced rapidly
  3. risks - inserted genes may have unexpected harmful effects.
  1. Describe, in outline only, some examples of genetic engineering:
    • taking the genes from carrots that control beta-carotene production and putting them into rice.
      Humans can then convert the beta-carotene from rice into Vitamin A (solving the problem of parts of the world relying on rice but lacking vitamin A)
    • the production of human insulin by genetically engineered bacteria
    • transferring resistance to herbicides, frost damage or disease to crop plants
  • Be able to discuss the ethical issues involved in genetic modification.
  1. Understand the principles of genetic engineering, to include:(HT)
    • selection of desired characteristics
    • isolation of genes responsible
    • insertion of the genes into other organisms
    • replication of these organisms.
  • Know that changing a person's genes in an attempt to cure disorders is called gene therapy.
  • Know that gene therapy could involve body cells or gametes.(HT)
  • Be able to explain why gene therapy involving gametes is controversial.(HT)
B3H Cloning
  1. Know that:
    • cloning is an example of asexual reproduction
    • cloning produces genetically identical copies (clones).
  • Know that Dolly the sheep was the first mammal cloned from an adult.
  • Be able to recognise that identical twins are naturally occurring clones.
  • Be able to recognise that plants grown from cuttings or tissue culture are clones.
  • Be able to describe how spider plants, potatoes and strawberries reproduce asexually.
  • Be able to describe how to take a cutting.
  • Understand that Dolly the sheep was produced by the process of nuclear transfer and that nuclear transfer involves placing the nucleus of a body cell into an egg cell.
  1. Be able to describe some possible uses of cloning, limited to:
    • mass producing animals with desirable characteristics
    • producing animals that have been genetically engineered to provide human products
    • producing human embryos to supply stem cells for therapy
  • Understand the ethical dilemmas concerning human cloning.
  1. Describe in outline the cloning technique used to produce Dolly, to include:(HL)
    • nucleus removed from an egg cell
    • egg cell nucleus replaced with the nucleus from an udder cell
    • egg cell given an electric shock to make it divide
    • embryo implanted into a surrogate mother sheep
    • embryo grows into a clone of the sheep from which the udder cell came.
  • Describe the benefits and risks of using cloning technology.(HL)
  • Explain the possible implications of using genetically modified animals to supply replacement organs for humans.(HL)
  • Explain why cloning plants is easier than cloning animals: many plant cells retain ability to differentiate unlike animal cells which usually lose this ability at an early stage.(HL)
  1. Describe the advantages and disadvantages associated with the commercial use of cloned plants:
    • advantage - can be sure of the characteristics of the plant since all plants will be genetically identical
    • advantage - it is possible to mass produce plants that may be difficult to grow from seed
    • disadvantage - if plants become susceptible to disease or to change in environmental conditions then all plants will be affected
    • disadvantage - lack of genetic variation.
  1. Describe plant cloning by tissue culture, to include:(HL)
    • selection for characteristics
    • large number of small pieces of tissue
    • aseptic technique
    • use of suitable growth medium and conditions.

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