multicellular organisms

• Stem cells


  Unspecialised cells in animals that can divide to produce more stem cells and have the potential to become different types of cells
• Stem cell specialisation


  1. Stem cell becomes a specific type of cell

  2. Leads to formation of a variety of cells
• Stem cell sources


  • Embryo at very early stage
  • Body throughout life
• Cells


  Make tissues
• Tissues


  Make organs
• Organs


  Make systems
• Nervous system


  • Made up of brain, spinal cord, and nerves
  • Central nervous system is made up of brain and spinal cord
• Cerebrum


  Responsible for personality, logic, memories
• Cerebellum


  Responsible for balance, coordination
• Medulla


  Responsible for breathing, heart rate
• Nerve cell types


  • Sensory
  • Interneurons
  • Motor neurons
• Nerve impulse transmission


  1. Receptors detect stimulus

  2. Sensory neurons pass information to interneurons

  3. Interneurons generate response in motor neurons

  4. Motor neurons send message to effector (muscle or gland)
• Neurotransmitters


  Chemicals that transmit messages across synapses (spaces between neurons)
• Reflex arc


  Pathway involving sensory, interneuron, and motor neurons that produces a rapid, automatic response to a stimulus
• Endocrine glands


  Release hormones into the bloodstream
• Hormones


  Chemical messengers
• Target tissue


  Has cells with complementary receptors for specific hormones
• Blood glucose regulation


  1. Increased blood glucose detected by pancreas

  2. Pancreas releases more insulin, less glucagon

  3. Liver takes up excess glucose and stores as glycogen

  4. Decreased blood glucose detected by pancreas

  5. Pancreas releases less insulin, more glucagon

  6. Liver breaks down glycogen to release glucose into blood
• Diabetes


  Condition caused by inability to regulate blood glucose concentration
• Diploid


  Having two sets of chromosomes
• Gametes


  Sex cells that are haploid
• A diploid cell has 46 chromosomes and a haploid cell has 23 chromosomes
• Where gametes are found

  • Male: Sperm in testes
  • Female: Egg in ovary
• Where gametes are found in plants

  • Male: Pollen in anther
  • Female: Ovule in ovary
• Fertilisation


  Fusion of two haploid gametes to produce a diploid zygote
• Sperm + Egg


  Zygote
• Pollen + Ovule


  Zygote
• Variation


  Differences that exist between members of a species
• Types of variation


  • Discrete: Can split into distinct groups
  • Continuous: Has a range of values from min to max
• Some characteristics are controlled by one gene, others are polygenic
• Inheritance


  Predicted by family trees and monohybrid crosses
• Genetic terms


  • Gene: Unit of chromosome
  • Phenotype: Physical appearance
  • Genotype: Genes present
  • Allele: Different forms of one gene
  • Dominant: Capital letter allele
  • Recessive: Lower case allele
  • Homozygous: Same alleles
  • Heterozygous: Different alleles
• Water absorption in plants

  1. Roots absorb water from soil by osmosis

  2. Water moves into xylem
• Xylem


  • Transports water up from roots
  • Has dead, hollow tubes
  • Contains lignin to withstand pressure
• Leaf structure and function

  • Upper epidermis: Waxy coating
  • Palisade mesophyll: Primary site of photosynthesis
  • Spongy mesophyll: Contains xylem and phloem
  • Lower epidermis: Contains stomata
• Transpiration


  1. Water moving through plant and evaporating through stomata

  2. Rate affected by wind, temperature, humidity, surface area
• Phloem


  • Transports sugars around plant
  • Has living tissue, companion cells, sieve plates
• Red blood cells


  • Biconcave shape
  • No nucleus
  • Contain haemoglobin to transport oxygen
• White blood cell types

  • Phagocytes: Engulf pathogens
  • Lymphocytes: Produce specific antibodies
• Pathway of blood flow

  Vena cava -> Right atrium -> Right ventricle -> Pulmonary artery -> Lungs -> Pulmonary vein -> Left atrium -> Left ventricle -> Aorta -> Body