aqa biology paper 2

• Type 1 diabetes


  The pancreas fails to produce sufficient insulin, causing high blood glucose levels
• Treatment for type 1 diabetes

  Insulin injections
• Type 2 diabetes


  The body cells no longer respond to insulin produced by the pancreas
• Treatments for type 2 diabetes

  Carbohydrate controlled diet and exercise regime
• Body's response to low blood glucose

  1. Pancreas produces glucagon

  2. Glucagon causes glycogen to be converted into glucose

  3. Glucose released into blood
• Condoms


  Barrier method of contraception that protects against STIs
• Hormonal contraceptives


  Can be effective long-term but can have side-effects
• Follicle stimulating hormone (FSH)


  Matures an egg in the ovary
• Hormones that maintain the uterus lining

  • Oestrogen
  • Progesterone
• Role of hormones in fertility drugs and IVF

  FSH and LH stimulate the maturation of several eggs
• Adrenaline


  Produced by the adrenal glands in times of fear or stress, increases heart rate and boosts delivery of oxygen and glucose
• Thyroxine


  From the thyroid gland, stimulates the basal metabolic rate and plays an important role in growth and development
• Meiosis


  The formation of gametes (sex cells) with half the chromosomes of a normal body cell
• Where meiosis happens in humans


  In the testes and ovaries
• Sexual reproduction


  Two parents produce gametes with half the genetic information, which join at fertilisation
• Process of meiosis


  1. Copies of the genetic information are made

  2. The cell divides twice to form four gametes, each with a single set of chromosomes

  3. All gametes are genetically different from each other
• DNA


  A polymer made up of two strands forming a double helix, contained in structures called chromosomes
• Gene


  A small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein
• Genome


  The entire genetic material of an organism
• Studying the genome is important for medicine, searching for disease genes, understanding and treating inherited disorders, and tracing human migration
• Characteristics controlled by single genes

  • Fur colour in mice
  • Red-green colour blindness in humans
• Alleles


  Different forms of a gene
• Dominant allele


  Always expressed, even if only one copy is present
• Recessive allele


  Only expressed if two copies are present (no dominant allele present)
• Homozygous


  If the two alleles present are the same
• Heterozygous


  If the alleles are different
• Polydactyly


  An inherited disorder of having extra fingers or toes, caused by a dominant allele
• Cystic fibrosis


  A disorder of cell membranes caused by a recessive allele
• Sex chromosomes in males and females

  Females have XX, males have XY
• Mutations


  Can lead to new phenotypes suited to environmental changes, resulting in relatively rapid changes in a species
• Evolution


  A change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
• Theory of evolution by natural selection

  All species of living things have evolved from simple life forms that first developed more than three billion years ago
• Process of evolution by natural selection

  1. Individuals in a population show variation due to mutation and sexual reproduction

  2. Organisms compete for survival

  3. Those with features best suited to the environment will survive and breed

  4. Breeding passes on favourable genes to offspring
• Formation of new species

  Two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring
• Selective breeding


  The process by which humans breed plants and animals for particular genetic characteristics
• Process of selective breeding

  1. Choose parents with desired characteristic from a mixed population

  2. Breed them together

  3. From the offspring, breed those with the desired characteristic

  4. Continue over many generations
• Characteristics chosen for selective breeding in plants and animals

  • Plants: Disease resistance, large/unusual flowers

  Animals: More meat/milk production, gentle nature
• Selective breeding can lead to inbreeding where some breeds are particularly prone to disease or inherited defects
• Genetic engineering


  Modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
• Ways plant crops may be genetically modified

  • Resistance to insect attack, disease, or herbicide

  Produce bigger, better fruits