Biology Paper 2

• Selective Breeding


  1. Select parents with desired characteristics

  2. Breed them together

  3. Select offspring with desired characteristics

  4. Repeat for many generations
• Problems with Selective Breeding


  • Inbreeding can cause problems like floppy ears
• Evolution by Natural Selection

  1. Mutations cause changes in DNA

  2. New phenotype/characteristic

  3. Beneficial characteristics more likely to survive and breed

  4. Population has evolved
• Variation


  The differences in a population
• Causes of Variation


  • Genetic
  • Environment
  • Combination of genetics and environment
• Genetic Screening


  When cells from an embryo are taken and tested to see if they have a disorder, so parents can choose to terminate
• Polydactyly


  • Having extra fingers or toes, caused by a dominant allele
• Cystic Fibrosis


  • Disorder of the cell membranes, caused by a recessive allele
• Allele


  Different form of a gene
• Phenotype


  Physical characteristics
• Genotype


  The alleles that an organism has
• Homozygous

  Having two of the same alleles
• Heterozygous

  Having two different alleles
• Dominant


  Always expressed, capital letters
• Recessive

  Only expressed if there are 2 copies of the allele, lower case letters
• DNA and the Genome


  • 46 chromosomes in the nucleus
  • DNA found in chromosomes
  • Genome is the entire genetic material
  • Gene is a small section of DNA that codes for a specific protein
  • DNA is a polymer made of two strands that form a double helix
• Genetic Engineering

  1. Gene cut out and transferred to another organism's genome

  2. New organism will have the desired characteristics
• GM Crops

  • More resistant to disease and insect attacks
  • Able to grow more crops in the same space
• Reaction Time Practical

  1. Hold ruler up with 0 cm mark

  2. Drop without warning and record distance between thumb and index finger

  3. Calculate reaction time

  4. Carry out repeats

  5. Introduce variants like before and after a sugary drink
• Quadrats Practical

  1. Place 1m² quadrat in random grid positions

  2. Count organisms

  3. Calculate number per m²

  4. Multiply by total area to estimate total population
• Homeostasis


  An organism's ability to regulate internal conditions
• What needs to be regulated in homeostasis

  • Blood glucose concentration
  • Internal temperature
  • Water levels
• Nervous System Homeostasis


  1. Stimulus detected by receptor

  2. Sensory neurone

  3. Relay neurone

  4. Synapse

  5. Motor neurone

  6. Effector
• Endocrine System Homeostasis


  System of glands that secrete hormones to control growth, metabolism, etc.
• Type 1 Diabetes


  • Pancreas doesn't produce enough insulin
• Type 2 Diabetes


  • Cells don't absorb glucose properly, often from obesity
• Meiosis

  1. Chromosomes pair up

  2. Cells divide to produce two diploid cells

  3. These divide again to produce four haploid cells (gametes)
• IVF Treatment

  • Difficult and expensive
  • Eggs collected and fertilised in lab
  • Embryo inserted into woman's uterus
  • Success rate is very low
• Menstrual Cycle

  1. FSH causes egg to mature

  2. Estrogen thickens uterus lining and inhibits FSH

  3. LH causes egg to be released
• Reflex Action

  1. Stimulus detected by receptors

  2. Electrical impulse along sensory neurone

  3. Crosses synapse as chemical signal

  4. Reaches motor neurone

  5. Effector carries out response