National 5 Biology Unit 2: Multicellular Organisms

National 5 Biology Unit 2: Multicellular Organisms

• Topic 2.1: Producing New Cells

  • Mitosis is the process of a diploid cell dividing.
  • Chromatids are the two identical copies of a chromosome.
  • The equator is the imaginary line down the middle of the cell.
  • Spindle fibres pull the chromatids apart during mitosis and move them to opposite poles of the cell.
  • Diploid cells have two sets of matching chromosomes.
  • Chromosomes are made of tightly coiled DNA.
  • Stem cells are unspecialized cells that can differentiate into different cell types.
  • Stem cells are important for growth and repair.
  • Stem cells are found in embryos and in the body of adults (e.g., bone marrow).
  • A multicellular organism is made up of more than one cell type.
  • Cells specialize to carry out particular functions.
  • Cells, tissues, organs, and organ systems are used to organize the human body.

• Topic 2.2: Plant Transport Systems

  • Plant organs include roots, stems, and leaves.
  • Key leaf tissues: upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, stomata, guard cells, and veins (containing xylem and phloem).
  • Water transport: root hairs absorb water, moving upward through the xylem to the leaves.
  • Xylem vessels are tube-like structures that transport water and minerals. Lignin strengthens xylem to withstand pressure changes.
  • Transpiration is the process of water moving up the plant and evaporating from the stomata.
  • Factors affecting transpiration rate: wind speed, temperature, surface area, and humidity.
  • Apparatus for measuring transpiration rate: potometer.

• Topic 2.3: Reproduction (animals & plants)

  • Gametes are haploid (single set of chromosomes).
  • Sperm are male gametes, produced in the testes.
  • Eggs are female gametes, produced in the ovaries.
  • Pollen is the male gamete in plants, produced in the anthers.
  • Ovules are the female gamete in plants, produced in the ovary.
  • Fertilization is the fusion of the nuclei of two haploid gametes, producing a diploid zygote.
  • The zygote divides to form an embryo.

• Topic 2.4: Variation and Inheritance

  • Variation is the difference between members of a species.
  • Discrete variation has distinct groups.
  • Continuous variation has a wide range of values.
  • Polygenic inheritance affects traits like height or skin colour
  • Genes are sections of DNA that code for proteins.
  • Alleles are different forms of a gene.
  • Phenotype is an organism's observable characteristics.
  • Genotype is the combination of alleles an organism possesses.
  • Dominant alleles determine the trait even when only one copy is present.
  • Recessive alleles are only expressed when both copies are present.
  • Homozygous means possessing two identical alleles (e.g., BB or bb).
  • Heterozygous means possessing two different alleles (e.g., Bb).
  • Monohybrid crosses using Punnett squares predict offspring genotypes.

• Topic 2.5: Control and Communication

  • The nervous system has three parts: central nervous system, sensory neurons, motor neurons.
  • Receptors detect stimuli and produce electrical signals.
  • Neurons rapidly transmit messages.
  • Synapses are gaps between neurons, passing signals via chemicals (neurotransmitters).
  • Reflexes are automatic responses to stimuli, helping to protect the body.
  • The endocrine system releases hormones into the bloodstream.
  • Hormones regulate specific target tissues.
  • Examples of hormones in blood glucose regulation; insulin, glucagon, glycogen.

• Topic 2.6: Animal Transport Systems

  • The circulatory system transports substances throughout the body, composed of the heart, blood vessels, and blood.
  • Arteries carry blood away from the heart.
  • Veins carry blood towards the heart.
  • Capillaries are thin-walled vessels where exchange between blood and body cells takes place.
  • The heart has four chambers: two atria (receiving chambers) and two ventricles (pumping chambers).
  • Blood is composed of plasma, red blood cells (carrying oxygen), white blood cells (defending against pathogens), and platelets (involved in clotting).
  • Red blood cells have a biconcave shape for maximum surface area and contain haemoglobin to carry oxygen.