Biology

• Characteristics of Living Organisms:

  • Movement: an action by an organism or part of an organism causing a change of position or place
  • Respiration: the chemical reactions that break down nutrient molecules in living cells to release energy for metabolism
  • Sensitivity: the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses
  • Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both
  • Reproduction: the processes that make more of the same kind of organism
• • Excretion: the removal from organisms of toxic materials, waste products of metabolism and substances in excess of requirements
  • Nutrition: the taking in of materials for energy, growth and development
• Use the mnemonic "MRS. H. GREN" to remember these processes:

  • M ovement
  • R espiration
  • S ensitivity
  • H omeostasis
  • G rowth and development
  • R eproduction
  • E xcretion
  • N utrition
• Concept & Uses of Classification Systems:

  • Species defined as a group of organisms that can reproduce to produce fertile offspring
  • Species classified into groups based on shared features
  • Linnaeus first classified organisms using the binomial system in Latin
  • Binomial system consists of genus (capital letter) and species (lower case letter) names in italics
  • Sequence of classification: Kingdom, Phylum, Class, Order, Family, Genus, Species
• Dichotomous Keys:

  • Used to identify organisms based on a series of questions about their features
  • Dichotomous means 'branching into two'
  • Leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose
  • Follow statements from the beginning to find the name
  • Simple dichotomous keys often come up in the multiple choice paper
• Reflecting Evolutionary Relationships:

  • Classification systems aim to reflect evolutionary relationships between species
  • Traditional biological classification based on shared features
  • Using DNA to classify organisms shows how closely related different species are based on DNA sequences
• DNA sequences of B.armiger and B.hirsutus are almost identical except for the last but one base
• DNA base sequences code for amino acid sequences in proteins
• Similarities in amino acid sequences can be used to determine how closely related organisms are
• The first division of living things in the classification system is to put them into one of five kingdoms: Animals, Plants, Fungi, Protoctists, Prokaryotes
• Main features of all animals:

  • Multicellular
  • Cells contain a nucleus but no cell walls or chloroplasts
  • Feed on organic substances made by other living things
• Main features of all plants:

  • Multicellular
  • Cells contain a nucleus, chloroplasts, and cellulose cell walls
  • Feed by photosynthesis
• All vertebrates have a backbone
• Invertebrates do not possess a backbone
• Arthropods are invertebrates with jointed legs
• Main features of all fungi:

  • Usually multicellular
  • Cells have nuclei and cell walls not made from cellulose
  • Do not photosynthesize but feed by saprophytic or parasitic nutrition
• Main features of all Protoctists:

  • Most are unicellular but some are multicellular
  • All have a nucleus, some may have cell walls and chloroplasts
  • Some photosynthesize and some feed on organic substances made by other living things
• Main features of all Prokaryotes:

  • Often unicellular
  • Cells have cell walls and cytoplasm but no nucleus or mitochondria
• At least some parts of any plant are green due to the presence of chlorophyll
• Ferns reproduce by spores found in the underside of their fronds
• Flowering plants reproduce sexually by means of flowers and seeds
• Monocotyledons and dicotyledons are two groups of flowering plants
• Monocotyledons have flowers with petals in multiples of 3
• Dicotyledons have flowers with petals in multiples of 4 or 5
• Monocotyledons have parallel leaf veins, while dicotyledons have reticulated leaf veins
• Viruses are not considered living things and do not carry out the seven life processes for themselves
• Viruses take over a host cell's metabolic pathways to make multiple copies of themselves
• Virus structure consists of genetic material (RNA or DNA) inside a protein coat
• Main features of animal cells:

  • Multicellular
  • Cells contain a nucleus with a distinct membrane
  • Cells do not have cellulose cell walls
  • Cells do not contain chloroplasts
  • Feed on organic substances made by other living things
  • Store carbohydrates as glycogen
  • Have nervous coordination
  • Able to move from place to place
• Main features of plant cells:

  • Multicellular
  • Cells contain a nucleus with a distinct membrane
  • Cells have cell walls made out of cellulose
  • Cells contain chloroplasts
  • Feed by photosynthesis
  • Store carbohydrates as starch or sucrose
  • Do not have nervous coordination
• Cell structures found in both animal and plant cells
• Bacteria cells:

  • Microscopic single-celled organisms
  • Possess a cell wall made of peptidoglycan
  • Lack a nucleus but contain a circular chromosome of DNA
  • Plasmids may be present
  • Lack mitochondria, chloroplasts, and other membrane-bound organelles
  • Some bacteria have flagellum for movement
• Organelles visible in almost all cells except prokaryotes under higher magnification:

  • Mitochondria
  • Ribosomes
  • Endoplasmic Reticulum
  • Vesicles
• Cells in the body divide to help grow and repair

  • New cells are produced by the division of existing cells
• Specialised cells in animals:

  • Developed certain characteristics to perform particular functions
  • Controlled by genes in the nucleus
  • Cells specialise through differentiation to carry out their functions
• Most incorrect answers in identifying levels of organisation come from not being able to identify a tissue
• Tissues are always made up of only one type of cell
• Magnification formula:

  • Magnification = Image size ÷ Actual size
  • Actual size = Image size / Magnification
  • Image size = Magnification x Actual size
  • Magnification does not have any units and is written as 'x 10' or 'x 5000'
• Converting between units:

  • 1mm = 1000µm
  • 1cm = 10,000µm
  • Convert different units to the same unit before proceeding with calculations
• Example extended magnification question:

  • Actual thickness of the leaf is 2mm
  • Drawing thickness is 50mm
  • Magnification = Image size / Actual size = 50 / 2 = 25
  • Magnification is x 25 (NO UNITS)