Unit 3 test

• Food security


  The ability of human populations to access food of sufficient quality and quantity
• The increase in human population and concern for food security leads to a demand for increased food production
• Food production must be sustainable and not degrade the natural resources on which agriculture depends
• Components of food security

  • Quantity
  • Quality
  • Access
• Crop plants


  • Farmers want to achieve the greatest yield from their crops
  • Increased plant productivity and manipulation of genetic diversity will be required in order to maintain a sustainable food supply
• Factors that control plant growth


  • Breeding of higher yielding cultivars
  • Use of fertiliser
  • Protecting crops from pests, diseases and competition
• Crops that breeders seek to develop

  • Have higher nutritional values
  • Are resistance to pests and diseases
  • Show physical characteristics suited to rearing and harvesting
  • Can thrive in particular environmental conditions
• Livestock production


  Less efficient than growing crops because livestock produce less food per unit area than crop plants
• About 90% of energy is lost between trophic levels, so raising animals for meat requires much more energy per unit area than growing crops
• All food production is dependent ultimately upon photosynthesis
• Photosynthesis


  The process by which green plants trap light energy and use it to make carbohydrates
• What happens when light strikes a leaf

  • 12% is reflected
  • 83% is absorbed
  • 5% is transmitted
• Only 4% of absorbed light is used for photosynthesis
• Photosynthetic pigments


  Found within the chloroplasts, they absorb light energy and convert it to chemical energy. Each pigment absorbs a different range of wavelengths of light.
• Principal photosynthetic pigments


  • Chlorophyll a
  • Chlorophyll b
  • Carotenoids
• Carotenoids extend the range of wavelengths absorbed and pass the energy to chlorophyll for photosynthesis
• Absorption spectrum


  Shows the wavelengths of light absorbed by the different photosynthetic pigments in a leaf
• Action spectrum


  Shows how effective the different wavelengths of light are at photosynthesis
• Having multiple photosynthetic pigments increases the range of wavelengths of light that the plant can absorb and so increases photosynthesis
• First stage of photosynthesis

  1. Photosynthetic pigment absorbs light energy

  2. Excited electrons are captured by the electron transport chain, releasing energy to generate ATP by ATP synthase

  3. Energy released is also used for photolysis of water

  4. Photolysis splits water into oxygen and hydrogen ions which are transferred to NADP to form NADPH and is transferred to the Calvin Cycle along with ATP
• Calvin Cycle


  1. Rubisco fixes carbon dioxide by attaching it to ribulose bisphosphate (RuBP) to produce 3-phosphoglycerate (3PG)

  2. 3-phosphoglycerate is phosphorylated by ATP and combined with hydrogen from NADPH to form G3P (glyceraldehyde-3-phosphate)

  3. G3P is used to regenerate RuBP and for the synthesis of glucose
• Uses of glucose produced in the Calvin Cycle

  • Respiratory substrate
  • Synthesised into starch or cellulose
  • Passed to other biosynthetic pathways
• The Calvin Cycle is the temperature-dependent part of photosynthesis
• The DNA of crops and animals has been manipulated by selective breeding for centuries
• Characteristics improved by selective breeding

  • Higher food yields
  • Higher nutritional values
  • Pest and disease resistance
  • Ability to thrive in particular environmental conditions
• The quality of a cultivar can be investigated using plant field trials
• Plant field trials


  • Selection of treatments used to ensure valid comparisons, only one treatment must be trialled at one time
  • Number of replicates - several replicates (minimum of 3) must be used to improve the reliability of results and to take account of variability within the sample
  • Randomisation of treatments - to eliminate bias when measuring treatment effects
• Inbreeding


  Involves 2 closely related relatives reproducing i.e. plants and animals with the best characteristics are selected to be the parents of the next generations
• Inbreeding depression


  An increase in the frequency of individuals who are homozygous for recessive deleterious alleles, these individuals will do less well at surviving to reproduce
• Crossbreeding


  • In animals, individuals from different breeds may produce a new crossbreed population with improved characteristics
  • In plants, F1 hybrids-produced by the crossing of 2 different inbred lines-create a relatively uniform heterozygous crop
• F1 hybrids often have increased vigour and yield - hybrid vigour
• F2 produced from breeding F1 hybrids together shows too much variation
• Test cross


  Carried out to investigate whether the genotype of the crossbreed is heterozygous or homozygous
• Genome sequencing


  A process which allows scientists to determine the precise sequence of DNA nucleotides, as a result of this, organisms with desirable genes can be identified and then used in breeding programmes
• Recombinant DNA technology in plant breeding

  • Insertion of Bt toxin gene into plants for pest resistance
  • Insertion of glyphosate resistance gene for herbicide tolerance
• Pests and diseases reduce productivity of crop plants by damaging them, therefore, reducing the yield
• Pests of crop plants

  • Invertebrates
  • Insects
  • Nematodes
• Causes of plant diseases

  • Fungi
  • Bacteria
  • Viruses
• Methods of controlling weeds, pests and diseases

  • Cultural
  • Chemical
  • Biological
• Cultural control


  • Ploughing - buries weeds so they die and decompose
  • Weeding - removing weeds early in life of the crop plant reduces competition
  • Crop rotation - series of a fleet crops are grown on the same piece of land over time. The current crop cannot have the same pests in the next crop